U.S. patent application number 16/533907 was filed with the patent office on 2019-12-26 for anode active material with a buffering zone.
This patent application is currently assigned to STOREDOT LTD.. The applicant listed for this patent is STOREDOT LTD.. Invention is credited to Daniel Aronov, Doron BURSHTAIN, Nir Kedem, Eran Sella.
Application Number | 20190393562 16/533907 |
Document ID | / |
Family ID | 60000040 |
Filed Date | 2019-12-26 |
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United States Patent
Application |
20190393562 |
Kind Code |
A1 |
BURSHTAIN; Doron ; et
al. |
December 26, 2019 |
ANODE ACTIVE MATERIAL WITH A BUFFERING ZONE
Abstract
Improved anodes and cells are provided, which enable fast
charging rates with enhanced safety due to much reduced probability
of metallization of lithium on the anode, preventing dendrite
growth and related risks of fire or explosion. Anodes and/or
electrolytes have buffering zones for partly reducing and gradually
introducing lithium ions into the anode for lithiation, to prevent
lithium ion accumulation at the anode electrolyte interface and
consequent metallization and dendrite growth. Various anode active
materials and combinations, modifications through nanoparticles and
a range of coatings which implement the improved anodes are
provided.
Inventors: |
BURSHTAIN; Doron; (Herzliya,
IL) ; Kedem; Nir; (Haifa, IL) ; Sella;
Eran; (Tel-Aviv, IL) ; Aronov; Daniel;
(Netanya, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STOREDOT LTD. |
Herzeliya |
|
IL |
|
|
Assignee: |
STOREDOT LTD.
Herzeliya
IL
|
Family ID: |
60000040 |
Appl. No.: |
16/533907 |
Filed: |
August 7, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15480888 |
Apr 6, 2017 |
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16533907 |
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15414655 |
Jan 25, 2017 |
10454101 |
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15480888 |
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15447889 |
Mar 2, 2017 |
10096859 |
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15414655 |
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15447784 |
Mar 2, 2017 |
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15447889 |
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62319341 |
Apr 7, 2016 |
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62337416 |
May 17, 2016 |
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62371874 |
Aug 8, 2016 |
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62401214 |
Sep 29, 2016 |
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62401635 |
Sep 29, 2016 |
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62421290 |
Nov 13, 2016 |
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62426625 |
Nov 28, 2016 |
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62427856 |
Nov 30, 2016 |
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62435783 |
Dec 18, 2016 |
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62441458 |
Jan 2, 2017 |
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62481752 |
Apr 5, 2017 |
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62482227 |
Apr 6, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 5/24 20130101; H01M
4/387 20130101; H01M 4/364 20130101; C09D 179/02 20130101; H01M
4/366 20130101; H01M 10/0525 20130101; H01M 4/386 20130101; H01M
10/4235 20130101; H01M 2004/027 20130101 |
International
Class: |
H01M 10/42 20060101
H01M010/42; H01M 10/0525 20060101 H01M010/0525; H01M 4/36 20060101
H01M004/36; H01M 4/38 20060101 H01M004/38; C09D 179/02 20060101
C09D179/02; C09D 5/24 20060101 C09D005/24 |
Claims
1. An anode comprising anode active material particles, wherein the
anode active material particles have, at a surface thereof, a
buffering zone configured to receive lithium ions from an interface
of the anode active material particles with an electrolyte, partly
mask a positive charge of the received lithium ions, and enable the
partly masked lithium ions to move into an inner zone of the anode
active material particles for lithiation therein, wherein the
interface of the anode active material particles with the
electrolyte comprises an ionic liquid additive comprising anions
and cations, wherein the anions are larger than lithium ions, and
wherein a size and concentration of the anions in the buffering
zone provides a mobility gradient of lithium ions in the buffering
zone.
2. An anode according to claim 1, wherein the anode active material
particles comprise metalloid cores and composite coatings, wherein
the metalloid cores comprise at least one of Si, Ge and Sn and are
between 20-500 nm in diameter.
3. The anode of claim 1, wherein the buffering zone contains anions
providing electron donating groups and cations providing
non-electron donating groups, wherein the anions are more mobile
than the cations in the buffering zone.
4. The anode according to claim 1, wherein the anode active
material particles have a coating comprising bonding molecules
which bind to the anions and/or cations in the ionic liquid.
5. The anode of claim 1, wherein the buffering zone is further
configured to provide a mobility gradient for anions in the
buffering zone.
6. A lithium ion cell comprising the anode of claim 1.
7. A method of configuring an anode, comprising providing anode
active material particles, at a surface thereof, with a buffering
zone configured to receive lithium ions from an interface of the
anode active material particles with an electrolyte, partially mask
a positive charge of the received lithium ions, and enable the
partially masked lithium ions to move into an inner zone of the
anode active material particles for lithiation therein, comprising
wherein the interface of the anode active material particles with
the electrolyte comprises an ionic liquid additive comprising
anions and cations, wherein the anions are larger than lithium
ions, and wherein a size and concentration of the anions in the
buffering zone provides a mobility gradient of lithium ions in the
buffering zone.
8. The method according to claim 7, comprising providing the anode
active material particles with metalloid cores and composite
coatings, wherein the metalloid cores comprise at least one of Si,
Ge and Sn and are between 20-500 nm in diameter.
9. The method according to claim 7, wherein the buffering zone
contains anions providing electron donating groups and cations
providing non-electron donating groups, wherein the anions are more
mobile than the cations in the buffering zone.
10. The method according to claim 7, comprising providing the anode
active material particles with a coating having bonding molecules
which bind to the anions and/or cations in the ionic liquid.
11. The method according to claim 7, comprising configuring the
buffering zone to provide a mobility gradient for anions in the
buffering zone.
12. The method according to claim 7, comprising charging the anode
in a lithium ion cell.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/480,888, filed Apr. 6, 2017, which is a
continuation-in-part of U.S. patent application Ser. No.
15/414,655, filed Jan. 25, 2017 and a continuation-in-part of U.S.
patent application Ser. No. 15/447,889, filed Mar. 2, 2017 and a
continuation-in-part of U.S. patent application Ser. No.
15/447,784, filed Mar. 2, 2017; U.S. patent application Ser. No.
15/480,888 further claims the benefit of U.S. Provisional Patent
Application Nos. 62/319,341, filed Apr. 7, 2016, 62/337,416, filed
May 17, 2016, 62/371,874, filed Aug. 8, 2016, 62/401,214, filed
Sep. 29, 2016, 62/401,635, filed Sep. 29, 2016, 62/421,290, filed
Nov. 13, 2016, 62/426,625, filed Nov. 28, 2016, 62/427,856, filed
Nov. 30, 2016, 62/435,783, filed Dec. 18, 2016, 62/441,458, filed
Jan. 2, 2017, 62/481,752, filed Apr. 5, 2017 and 62/482,227, filed
Apr. 6, 2017, all of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
1. Technical Field
[0002] The present invention relates to the field of energy storage
devices, and more particularly, to fast charging lithium ion
batteries.
2. Discussion of Related Art
[0003] A major barrier in battery technology concerns safety
requirements, particularly when batteries are overheated or
overcharged, resulting in thermal runaway, cell breakdown and
possibly fire or explosion. Additionally, a short circuit or a
design defect may also bring about battery failure resulting in
fire and safety risks. Lithium ion batteries in particular, while
having operational advantages, are potentially flammable due to
their high reactivity, particular when in contact with
humidity.
SUMMARY OF THE INVENTION
[0004] The following is a simplified summary providing an initial
understanding of the invention. The summary does not necessarily
identify key elements nor limit the scope of the invention, but
merely serves as an introduction to the following description.
[0005] One aspect of the present invention provides an anode
comprising anode active material particles, wherein the anode
active material particles have, at a surface thereof, a buffering
zone configured to receive lithium ions from an interface of the
anode active material particles with an electrolyte, partly mask a
positive charge of the received lithium ions, and enable the partly
masked lithium ions to move into an inner zone of the anode active
material particles for lithiation therein, wherein the buffering
zone comprises a plurality of electron donating groups interspaced
between non-electron donating groups at a ratio of at least
1:2.
[0006] These, additional, and/or other aspects and/or advantages of
the present invention are set forth in the detailed description
which follows; possibly inferable from the detailed description;
and/or learnable by practice of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] For a better understanding of embodiments of the invention
and to show how the same may be carried into effect, reference will
now be made, purely by way of example, to the accompanying drawings
in which like numerals designate corresponding elements or sections
throughout.
[0008] In the accompanying drawings:
[0009] FIG. 1A is a high level schematic illustration of various
anode configurations, according to some embodiments of the
invention.
[0010] FIG. 1B is a high level schematic illustration of various
anode components in a preparation process, and various anode
configurations in the lithium ion cell, according to some
embodiments of the invention.
[0011] FIG. 2A is a high-level schematic illustration of a
metallization process in prior art lithium ion batteries, according
to the prior art.
[0012] FIG. 2B is a high level schematic illustration of several
processes which affect composite anode material particles during
battery operation, according to some embodiments of the
invention.
[0013] FIGS. 2C and 2D are high level schematic illustrations of
configurations of anode material particles, according to some
embodiments of the invention.
[0014] FIGS. 2E-2G schematically illustrate buffering zones
configured to provide a mobility gradient of anions and/or electron
donating groups, according to some embodiments of the
invention.
[0015] FIGS. 3A-3D are high level schematic illustrations of
modified anode active material particles, according to some
embodiments of the invention.
[0016] FIGS. 4A-4F are high level schematic illustrations of
coatings in composite anode particles, according to some
embodiments of the invention.
[0017] FIG. 4G-4J are high level schematic illustrations of in-situ
polymerization of conductive polymers, according to some
embodiments of the invention.
[0018] FIGS. 5A and 5B are high level schematic illustrations of
lithium polymer coatings applied to anode active material
particles, according to some embodiments of the invention.
[0019] FIG. 5C is a high level schematic illustration of a
hydrophobic polymer coating applied to pre-lithiated anode active
material particles, according to some embodiments of the
invention.
[0020] FIG. 6 is a high level schematic illustration of composite
coating comprising interconnected organic and inorganic compounds,
according to some embodiments of the invention.
[0021] FIG. 7A is a high level schematic illustration of a
core-shell particle with a composite shell in composite anode
material and its advantages, according to some embodiments of the
invention--with respect to prior art illustrated schematically in
FIG. 7B.
[0022] FIG. 7C is a high level schematic illustration of composite
anode material particles with graphite shells, according to some
embodiments of the invention.
[0023] FIG. 7D is a high level schematic illustration of composite
anode material particles with porous graphite shells, according to
some embodiments of the invention.
[0024] FIG. 8A is a high level schematic illustration of a
core-shell particle, according to some embodiments of the
invention.
[0025] FIGS. 8B and 8C are high level schematic illustrations of
composite anode material comprising a plurality of core-shell
particles, according to some embodiments of the invention.
[0026] FIG. 8D is a high level schematic illustration of a
core-shell particle, according to some embodiments of the
invention.
[0027] FIG. 8E is a high level schematic illustration of composite
anode material comprising a plurality of core-shell particles,
according to some embodiments of the invention.
[0028] FIG. 8F is a high level schematic illustration of composite
anode material, according to some embodiments of the invention.
[0029] FIG. 9A-9C are high level schematic illustrations of cell
configurations, according to some embodiments of the invention,
compared with prior art configurations illustrated in FIG. 9D.
[0030] FIGS. 10A-10C and 11A-11C are high level schematic
illustrations of electrolyte-based buffering zones which may be
used in place or in addition to anode-based buffering zones,
according to some embodiments of the invention.
[0031] FIG. 11D is a high level schematic illustration of
non-limiting examples for bonding molecules, according to some
embodiments of the invention.
[0032] FIG. 12 is a high level flowchart illustrating a method,
according to some embodiments of the invention.
[0033] FIGS. 13A-13C are examples for charging/discharging cycles
of anodes with respect to lithium (half cells), according to some
embodiments of the invention.
[0034] FIGS. 14A-14F are examples for performance of anodes made of
modified anode active material particles, according to some
embodiments of the invention.
[0035] FIGS. 14G-14K are examples for modified anode active
material particles, according to some embodiments of the
invention.
[0036] FIG. 15 presents an example for formation of LTB (lithium
tetraborate) in modified anode material particles, according to
some embodiments of the invention.
[0037] FIG. 16A is an example for the surface of an anode produced
with in situ polyaniline polymerization disclosed herein, compared
to FIG. 16B showing an example of a cracked anode surface prepared
under similar conditions without polyaniline.
[0038] FIGS. 17A and 17B are examples for improved performance of
Sn:Si anodes produced with in situ polyaniline polymerization,
according to some embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] In the following description, various aspects of the present
invention are described. For purposes of explanation, specific
configurations and details are set forth in order to provide a
thorough understanding of the present invention. However, it will
also be apparent to one skilled in the art that the present
invention may be practiced without the specific details presented
herein. Furthermore, well known features may have been omitted or
simplified in order not to obscure the present invention. With
specific reference to the drawings, it is stressed that the
particulars shown are by way of example and for purposes of
illustrative discussion of the present invention only, and are
presented in the cause of providing what is believed to be the most
useful and readily understood description of the principles and
conceptual aspects of the invention. In this regard, no attempt is
made to show structural details of the invention in more detail
than is necessary for a fundamental understanding of the invention,
the description taken with the drawings making apparent to those
skilled in the art how the several forms of the invention may be
embodied in practice.
[0040] Before at least one embodiment of the invention is explained
in detail, it is to be understood that the invention is not limited
in its application to the details of construction and the
arrangement of the components set forth in the following
description or illustrated in the drawings. The invention is
applicable to other embodiments that may be practiced or carried
out in various ways as well as to combinations of the disclosed
embodiments. Also, it is to be understood that the phraseology and
terminology.
[0041] Improved anodes and cells are provided, which enable fast
charging rates with enhanced safety due to much reduced probability
of metallization of lithium on the anode, preventing dendrite
growth and related risks of fire or explosion. Anodes and/or
electrolytes have buffering zones for partly reducing and gradually
introducing lithium ions into the anode for lithiation, to prevent
lithium ion accumulation at the anode electrolyte interface and
consequent metallization and dendrite growth. Various anode active
materials and combinations, modifications through nanoparticles and
a range of coatings which implement the improved anodes are
provided.
[0042] FIG. 1A is a high level schematic illustration of various
anode configurations, according to some embodiments of the
invention. FIG. 1A illustrates schematically, in a non-limiting
manner, a surface of anode 100, which may comprise anode active
material particles 110 (e.g., particles of metalloids such as
silicon, germanium and/or tin, and/or possibly particles of
aluminum, lead and/or zinc, and see below for more details and
possibilities; anode active material particles 110 may also
possibly comprise composite particles 115 disclosed below in more
detail) at different sizes (e.g., in the order of magnitude of 100
nm, and/or possibly in the order of magnitude of 10 nm or
1.mu.)--for receiving lithiated lithium during charging and
releasing lithium ions during discharging. Anodes 100 may further
comprise binder(s) and additive(s) 102 as well as optionally
coatings 130 (e.g., conductive polymers, lithium polymers, etc.,
see below). Active material particles 110 may be pre-coated by one
or more coatings 120 (e.g., by conductive polymers, lithium
polymers, etc.), have borate and/or phosphate salt(s) 128 bond to
their surface (possibly forming e.g., B.sub.2O.sub.3,
P.sub.2O.sub.5 etc., see below), bonding molecules 180 (illustrated
schematically) which may interact with electrolyte 85 (and/or ionic
liquid additives thereto, see below) and/or various nanoparticles
112 (e.g., B.sub.4C, WC, VC, TiN see below), may be attached
thereto in anode preparation processes 105 such as ball milling
(see, e.g., U.S. Pat. No. 9,406,927, which is incorporated herein
by reference in its entirety), slurry formation, spreading of the
slurry and drying the spread slurry. For example, anode preparation
processes 105 may comprise mixing additive(s) 102 such as e.g.,
binder(s) (e.g., polyvinylidene fluoride, PVDF, styrene butadiene
rubber, SBR, or any other binder), plasticizer(s) and/or conductive
filler(s) with a solvent such as water or organic solvent(s) (in
which the anode materials have limited solubility) to make an anode
slurry which is then dried, consolidated and is positioned in
contact with a current collector (e.g., a metal, such as aluminum
or copper). Details for some of these possible configurations are
disclosed below.
[0043] It is explicitly noted that in certain embodiments, cathodes
may be prepared according to disclosed embodiments, and the use of
the term anode is not limiting the scope of the invention. Any
mention of the term anode may be replaced in some embodiments with
the terms electrode and/or cathode, and corresponding cell elements
may be provided in certain embodiments. For example, in cells 150
configured to provide both fast charging and fast discharging, one
or both electrodes 100, 87 may be prepared according to embodiments
of the disclosed invention.
[0044] Certain embodiments comprise composite anode material
particles 115 which may be configured as core shell particles, as
disclosed below. The different configurations are illustrated
schematically in different regions of the anode surface, yet
embodiments may comprise any combinations of these configurations
as well as any extent of anode surface with any of the disclosed
configurations. Anode(s) 100 may then be integrated in cells 150
which may be part of lithium ion batteries, together with
corresponding cathode(s) 87, electrolyte 85 and separator 86, as
well as other battery components (e.g., current collectors,
electrolyte additives--see below, battery pouch, contacts, and so
forth).
[0045] Anode material particles 110, 110A, 115, anodes 100 and
cells 150 may be configured according to the disclosed principles
to enable high charging and/or discharging rates (C-rate), ranging
from 3-10 C-rate, 10-100 C-rate or even above 100C, e.g., 5C, 10C,
15C, 30C or more. It is noted that the term C-rate is a measure of
charging and/or discharging of cell/battery capacity, e.g., with 1C
denoting charging and/or discharging the cell in an hour, and XC
(e.g., 5C, 10C, 50C etc.) denoting charging and/or discharging the
cell in 1/X of an hour--with respect to a given capacity of the
cell.
[0046] FIG. 1B is a high level schematic illustration of various
anode components in a preparation process 105, and various anode
configurations in lithium ion cell 150, according to some
embodiments of the invention. FIG. 1B illustrates schematically, in
a non-limiting manner, a surface of anode 100, which may comprise
anode active material particles 110 (e.g., shell-core particles 115
with cores 110 being particles of metalloids such as silicon,
germanium and/or tin, and/or of aluminum, or cores made of other
materials, listed below) at different sizes (e.g., in the order of
magnitude of 100 nm, and/or possible in the order of magnitude of
10 nm or 1 .mu.m), binder(s) 102 (for binding particles 110 and/or
115 in the anode material to each other and to the current
collector, not shown) and additive(s) 102 as well as optionally
coating(s) 130A and/or conductive fiber(s) 130 (e.g., conductive
polymers, lithium polymers, carbon fibers etc. and see details
below). Active material particles 110 may be pre-coated 120 (in one
or more layers 120, e.g., by conductive polymers, lithium polymers,
etc., B.sub.2O.sub.3, P.sub.2O.sub.5, etc., see details below)
and/or various nanoparticles (e.g., B.sub.4C, WC etc., see details
below) 112, may be attached thereto in preparation processes 105
such as ball milling (see, e.g., U.S. Pat. No. 9,406,927, which is
incorporated herein by reference in its entirety), slurry
formation, spreading of the slurry and drying the spread slurry.
Details for some of these possible configurations are disclosed in
the patent documents which were listed herein. The different
configurations are illustrated schematically in different regions
of the anode surface, yet embodiments may comprise any combinations
of these configurations as well as any extent of anode surface with
any of the disclosed configurations.
[0047] In the illustrated configurations, conductive fibers 130 are
shown to extend throughout anode 100, interconnect cores 110 and
interconnected among themselves. Electronic conductivity may be
enhanced by any of the following: binder and additives 102,
coatings 130A, conductive fibers 130, nanoparticles 112 and
pre-coatings 120, which may be in contact with an electronic
conductive material (e.g., fibers) 130. Lithium ion cell 150
comprises anode 100 (in any of its configurations disclosed herein)
comprising anode material with composite anode material such as
core-shell particles 115, electrolyte 85 and at least cathode 87
delivering lithium ions during charging through cell separator 86
to anode 100. Lithium ions (Li.sup.+) are lithiated (to
Li.sup..about.01, indicating substantially non-charged lithium, in
lithiation state) when penetrating the anode material, e.g., into
anode active material cores 110 of core-shell particles 115. Any of
the configurations of composite anode material and core-shell
particles 115 presented below may be used in anode 100, as
particles 115 are illustrated in a generic, non-limiting way. In
core-shell particle configurations 115, the shell may be at least
partly be provided by coating(s) 120, and may be configured to
provide a gap 140 for anode active material 110 to expand 101 upon
lithiation. In some embodiments, gap 140 may be implemented by an
elastic or plastic filling material and/or by the flexibility of
coating(s) 120 which may extend as anode active material cores 110
expands (101) and thereby effectively provide room for expansion
101, indicated in FIG. 1B schematically, in a non-limiting manner
as gap 140. Examples for both types of gaps 140 are provided below,
and may be combined, e.g., by providing small gap 140 and enabling
further place for expansion by the coating flexibility.
[0048] Examples for electrolyte 85 may comprise liquid electrolytes
such as ethylene carbonate, diethyl carbonate, propylene carbonate,
fluoroethylene carbonate (FEC), EMC (ethyl methyl carbonate), DMC
(dimethyl carbonate), VC (vinylene carbonate) and combinations
thereof and/or solid electrolytes such as polymeric electrolytes
such as polyethylene oxide, fluorine-containing polymers and
copolymers (e.g., polytetrafluoroethylene), and combinations
thereof. Electrolyte 85 may comprise lithium electrolyte salt(s)
such as LiPF.sub.6, LiBF.sub.4, lithium bis(oxalato)borate,
LiN(CF.sub.3SO.sub.2).sub.2, LiN(C.sub.2F.sub.5SO.sub.2).sub.2,
LiAsF.sub.6, LiC(CF.sub.3SO.sub.2).sub.3, LiClO.sub.4, LiTFSI,
LiB(C.sub.2O.sub.4).sub.2, LiBF.sub.2(C.sub.2O.sub.4),
tris(trimethylsilyl)phosphite (TMSP) and combinations thereof.
Ionic liquid(s) may be added to electrolyte 85 as disclosed
below.
[0049] In certain embodiments, cathode(s) 87 may comprise materials
based on layered, spinel and/or olivine frameworks, and comprise
various compositions, such as LCO formulations (based on
LiCoO.sub.2), NMC formulations (based on lithium
nickel-manganese-cobalt), NCA formulations (based on lithium nickel
cobalt aluminum oxides), LMO formulations (based on
LiMn.sub.2O.sub.4), LMN formulations (based on lithium
manganese-nickel oxides) LFP formulations (based on LiFePO.sub.4),
lithium rich cathodes, and/or combinations thereof. Separator(s) 86
may comprise various materials, such as polyethylene (PE),
polypropylene (PP) or other appropriate materials. Possible
compositions of anode(s) 100 are disclosed below in detail.
Buffering Zone
[0050] FIG. 2A is a high-level schematic illustration of a
metallization process in lithium ion batteries according to the
prior art. Typical lithium ion batteries use graphite anode
material 95 which receives lithium ions 91 (from an electrolyte 85)
in an intercalation process between graphite layers. The maximal
capacity of the graphite is limited to approximately one lithium
ion for every ca. six carbon atoms and is influenced by the
solid-electrolyte interface (SEI) formed between anode material 95
and electrolyte 85, typically on the intercalation basal planes
(e.g., layers in the graphite material between which the lithium
ions intercalate). Such lithium ion batteries typically have low
charging and discharging rates due to limiting charge transfer
rates and limiting lithium ions diffusion rate into the graphite
anode. As shown schematically in illustration 90A in FIG. 2A, under
low charging rates, the intercalation rate is higher than the
lithium ion accumulation rate, resulting in proper intercalation 96
of lithium ions Li.sup.+ into graphite anode material 95 as
L.sup..about.01, denoting approximately neutral lithium atoms which
receive electrons e.sup.- from the graphite and are intercalated in
anode material 95. The intercalation rate is limited by the
Li.sup.+ supply rate. As the charging rate increases (schematic
illustrations 90B, 90C, 90D represent increasing charging rate with
respect to illustration 90A), the rate of incoming lithium ions
increases, and lithium ions accumulate on the surface (of anode
material 95 or particles thereof, at the solid-electrolyte
interface) as illustrated in 90B, with an accumulation rate that
exceeds the intercalation rate of the lithium ions. As a result,
reduction 97 of the lithium ions is carried out on the interface in
addition to the intercalated lithium ions, as illustrated in 90C,
which shows schematically the increasing flow of electrons to the
interface without lithium ion intercalation in anode material 95.
Finally, as lithium ion accumulation and reduction at the interface
increase (as illustrated in 90D), lithium metallization at the
interface and dendrite growth 99 commence and damage the cell.
Additional considerations include volume changes of the graphite
electrode material, influences of anode additives, characteristics
of the SEI and details of the charging and discharging cycles.
[0051] Embodiments of the present invention provide electrode and
cell configurations which enable fast charging rates with enhanced
safety due to much reduced probability of metallization of lithium
on the anode, preventing dendrite growth and related risks of fire
or explosion. Anode material particles have buffering zones for
partly reducing and gradually introducing lithium ions into the
anode for lithiation, to prevent lithium ion accumulation at the
anode electrolyte interface and consequent metallization and
dendrite growth. The electrolyte in the cell may be chosen to
further reduce the accumulation rate of lithium ions at the
interface, and the cell may be designed to have lithiation in the
anode material as the rate limiting factor, thereby avoiding
lithium ion accumulation at the anode material particles'
surface.
[0052] FIG. 2B is a high level schematic illustration of several
process which affect composite anode material particles 115 during
battery operation, according to some embodiments of the invention.
In many of the disclosed embodiments, the inventors allow for
expansion and contraction 101 of anode material particles 110
during charging and discharging of the battery (respectively), in
order to be able to utilize materials having high capacity for
absorbing lithium (such as Si, Ge, Sn, Al, Pb, Zn, their alloys and
mixtures, as well as other materials) for energy storage. It is
noted that many of the disclosed embodiments are likewise
applicable to graphite anode material and/or modified graphite
anode material, with respect to the lithiation process being
lithium ion intercalation in the graphite.
[0053] Moreover, in many of the disclosed embodiments, the
inventors succeed in maintaining required electronic (e.sup.-) and
ionic (Li.sup.+) conductivity, schematically denoted 106 and 103,
respectively, which enable fast charging and/or fast discharging
the battery, while maintaining the mechanical stability of anode
material particles 110 and composite anode particles 115, e.g.,
through the use of a range of coatings 120 and added nanoparticles,
as disclosed herein. The notation Li.sup..delta.+ indicates
partially reduced lithium ions, as an intermediate stage between
lithium ions Li.sup.+ and lithium L.sup..about.01 in lithiated
anode material. The partial reduction of Li.sup..delta.+ may result
from adjacent negative charges which partially reduce the positive
charge of Li.sup.+. Various anode material configurations which
enable partial reduction of the lithium ions and resulting
advantages are described below in detail. Examples for mechanical
stability of anode material particles 110 include reduction or lack
of cracking of particles 110, e.g., after a certain number (e.g.,
50, 100, 500 etc.) of charge/discharge cycles, possibly at fast
charge/discharge rate (e.g., 5C, 10C, 50C, etc.).
[0054] FIGS. 2C and 2D are high level schematic illustrations of
configurations of anode material particles 110, according to some
embodiments of the invention. The illustrated configurations may
likewise be applicable to composite anode material particles 115.
The illustrated configurations may be implemented in corresponding
cells 150 of energy storage devices (e.g., lithium ion batteries)
to provide safe cells having high charging and/or discharging
rates, e.g., 5C, 10C, 15C or more.
[0055] Anode material particles 110 may be designed to handle the
ion accumulation at the interface between the anode active material
and electrolyte 85 at high charging rates by regulating lithium ion
accumulation as well as by regulating the reduction mechanism of
the lithium ion at the interface to reduce the probability of
on-surface metallization and dendrite growth. Such designs may
increase safety by reducing the probability of surface lithium
metallization. Without intending to be bound by theory, anode
material particles 110 may implement, by various active material
surface modifications, a lowering of the surface energy, and a
buffering in the interface for the reduction mechanism of Li.sup.+
to Li.sup.0. These mechanisms reduce the lithium ion accumulation
at the interface and the reduction of the lithium ions at the
interface which were illustrated schematically in FIG. 2A and which
lead to surface metallization and dendrite growth.
[0056] FIG. 2C schematically illustrates at least one buffering
zone 110B (e.g., at least a partial coating 120 or at least part of
coating 120) on the surface of anode material particle 110--which
separates electrolyte 85 from an internal anode material particle
region 110C, according to some embodiments of the invention.
Buffering zone(s) 110B may be configured to accumulate lithium
atoms with partial charge (denoted by Li.sup..delta.+), an
accumulation which dramatically reduces the probability of surface
lithium metallization. Buffering zone(s) 110B may be further
configured to enable faster and smoother transition of the lithium
ions Li.sup.+ via the partly charge state Li.sup..delta.+ to the
lithiated state Li.sup..about.01 in the active material in zone(s)
110C. In disclosed anode configurations, buffering zone(s) 110B may
be configured to absorb the fast diffusion of incoming lithium ions
at high charging rates and thus prevent surface accumulation,
metallization and dendrite growth of lithium. The dimensions and
parameters of buffering zone(s) 110B may be configured to buffer an
expected amount of lithium ions that is derived from parameters and
operation conditions of the battery.
[0057] For example, materials in buffering zone(s) 110B may be
selected to provide electrons (e.sup.-, illustrated schematically
by the black dots) at sufficient proximity to the lithium ions to
reduce their +1 charge to partial charge .delta.+ without creating
chemical bonds between material of buffering zone(s) 110B and
lithium ions Li.sup..delta.+--in order to enable their further
movement into anode material 110 and being lithiated therein and
prevent reduction and metallization of them in buffering zone(s)
110B. Examples for materials in buffering zone(s) 110B are ionic
conductors which are medium electronic conductors, such as
inorganic borates, phosphates or polyphosphates and organic
polymers such as polypyrrole and polyaniline--the particle size of
which and thickness of buffering zone(s) 110B may be determined
according to specified performance requirements. More examples for
material that may constitute buffering zone(s) 110B are presented
below as various coatings 120, which may at least partly be
configured to generate buffering zone(s) 110B. For example, various
conductive polymers, possibly lithiated polymers and/or lithiated
conductive polymers, may be used as coatings 120.
[0058] FIG. 2D schematically illustrates at least one buffering
zone 110B on the surface of anode material particle 110 as support
for a SEI 122, according to some embodiments of the invention. In
certain embodiments, at least one of buffering zone(s) 110B may be
configured to provide a flexible skeleton for the formation of SEI
122 (which is typically brittle), to improve the stability of SEI
122 during mechanical expansion and contraction 101 (SEI
deformation illustrated schematically by arrows 101A, and see FIG.
2B) of anode material particle 110. The flexibility of buffering
zone(s) 110B, possibly achieved by flexible materials such as
inorganic structures and/or organic polymers disclosed below as
coating(s) 120 may be configured to prevent damage to SEI 122
undergoing mechanical deformations 101A due to expansion and
contraction 101 of anode material particle 110 in its operation.
For example, at least some of the anions in buffering zone(s) 110B
may be immobile or at least less mobile than the respective cations
in buffering zone(s) 110B in order to provide a higher electron
concentration that provides the partial charge Li.sup..delta.+ to
lithium ions entering buffering zone(s) 110B.
[0059] FIGS. 2E-2G schematically illustrate buffering zones 110B
configured to provide a mobility gradient 125 of anions and/or
electron donating groups 126, according to some embodiments of the
invention. In certain embodiments, buffering zone(s) 110B may be
configured to provide a mobility gradient 125 (indicated
schematically by the tapered arrow) of anions and/or electron
donating groups 126 (illustrated schematically as providing
negative charges) which in turn provides a charge gradient that
reduces lithium ions 91 entering buffering zones 110B from
electrolyte 85 in a gradual manner (indicated schematically by
Li.sup..delta.+ expressing the partial screening of the positive
charge of Li.sup.+ in buffering zones 110B) until they reach
lithiation in anode material particle 110. Gradient 125 may be
configured to enable modification of the interface between anode
material particle 110 and electrolyte 85 (the area where two
immiscible phase surfaces are coming in contact with each other)
into an interphase region having a gradual change of parameters
which gradually reduces the activation energy of the reduction
reaction of the lithium ions, and further prevents metallization of
lithium and dendrite growth. Coating(s) 120 disclosed below may be
configured to facilitate and support the interphase region and
thereby regulate lithium ion flow into and out from anode material
particle 110, especially during fast charging and/or discharging at
rates of several C-rate, several tens of C-rate and possible even a
few hundred C-rate.
[0060] Buffering zone(s) 110B may be configured to form a barrier
which reduces the speed of lithium ions 91 and locally increases
the resistance of buffering zone(s) 110B to lithium ions 91 to
prevent or attenuate reduction of lithium ions 91 (see r'.sub.A in
FIG. 9A below). Coating(s) 120 disclosed below may be configured to
provide the required local resistance.
[0061] As illustrated schematically in FIG. 2F, buffering zone 110B
may be configured to provide negative electric charge at predefined
density to replace a solvation shell 91A of Li.sup.+ 91 in
electrolyte 85 by an equivalent environment 91B within solid
buffering zone 110B, which may e.g., comprise coating 120 such as a
polymer coating, possibly a conductive polymer coating. For
example, coating 120 may comprise electron donating groups 126
(e.g., atoms such as N or O, having a lone pair of electrons,
aromatic groups and/or conjugated systems as disclosed below etc.)
at specified densities, which form environment 91B which partly
screens the positive charge of Li.sup.+ passing through buffering
zone 110B (denoted schematically as Li.sup..delta.+). In contrast
to prior art SEI's, which impede the entering of lithium ions into
the anode material particles by the required removal of solvation
shell 91A upon entering the SEI from the electrolyte,
advantageously disclosed buffering zone(s) 110B and coating(s) 120,
by providing equivalent environment 91B increase ionic conductivity
103 and enable high charging rates with reduced or avoided risk for
lithium metallization due the prior art SEI impediments. In certain
embodiments, buffering zone(s) 110B and coating(s) 120 may be
configured to provide environment 91B that provides enough negative
charge to incoming lithium ions to make de-solvation (of the
lithium ions from the electrolyte) not the rate limiting step in
the lithiation (charging) process. Without being bound by theory,
by relieving the rate limitation of the de-solvation process,
buffering zone 110B may prevent prior art metallization of lithium
on the anode particles' surface (see e.g., FIG. 2A, in which
de-solvation may be considered the rate limiting step in the prior
art).
[0062] FIG. 2G illustrates in a high level schematic fashion a
possible spatial arrangement of electron donating groups 126 and
non-electron donating groups 123 (e.g., groups which do not have
free or conjugated electrons) in buffering zone 110B. Only a few
groups and a two dimensional structure are presented for
illustration purposes, clearly real buffering zone(s) 110B comprise
a large number of interconnected groups in a three dimensional
structure. The distance between electron donating groups 126
(indicated schematically as D) may be selected (with respect to the
statistical properties of coating 120 and other polymer parameters)
to increase ionic conductivity 103 and provide environment 91B to a
sufficient extent that provides required fast charging and safety
parameters. For example, electron donating groups 126 may be
separated by 2-5 non-electron donating groups 123 (e.g., D=2-5
non-electron donating groups 123) in the structure of buffering
zone 110B. The composition and structure of buffering zone 110B may
be configured to enhance ionic conductivity 103 while maintain
electronic conductivity at a level which does not cause
metallization of the lithium ions in buffering zone 110B and
encourages lithiation of lithium in anode material 110. For
example, buffering zone 110B may be configured to have ionic
conductivity 103 in the order of magnitude of 0.01-10 S/cm or any
subrange thereof. Gradient 125 in buffering zone 110B may be formed
by configuration of coating(s) 120 which provide solid environment
91B which is equivalent to solvation shell 91B in electrolyte 85,
partly mask the positive charge of the lithium ions moving
therethrough (to Li.sup..delta.+) and maintain high ionic
conductivity 103 to deliver the lithium ions to lithiation in anode
material 110.
Anode Material
[0063] In the following, various material combination embodiments
for the active anode material are presented. It is emphasized that
elements from different embodiments may be combined to form
additional embodiments, and that any of the anode active material
embodiments may be combined with various coating embodiments and
anode embodiments disclosed herein.
Silicon Active Material
[0064] In some embodiments, anode active material particles 110 may
comprise any of Si (silicon), B (boron) and W (tungsten) and/or
combinations thereof as mixtures and/or alloys. In some
embodiments, anode active material particles 110 may comprise Si at
4-35 weight % of the total weight of the anode material, e.g.,
anode active material particles 110 may comprise 4-35 weight % Si
and/or 4-35% of anode active material particles 110 may comprise
Si, and/or anode 100 may comprise any combination thereof. In
certain embodiments, B and/or W may be included in anode active
material particles 110 as dopant(s) and/or as attached particles or
nanoparticles.
[0065] In some embodiments, anode active material particles 110 may
comprise B at 2-20 weight % of the total weight of the anode
material. In some embodiments, anode active material particles 110
may comprise W at 5-20 weight % of the total weight of the anode
material. In some embodiments, anode active material particles 110
may comprise C (carbon) at 5-60 weight % of the total weight of the
anode material, e.g., as any of spherical carbon particles, CNTs
(carbon nanotubes) and graphene particles. In certain embodiments,
anode active material particles 110 may comprise CNTs at 0.05-0.5
weight % of the total weight of the anode material. CNTs may be
used as part of modified anode active material particles 110A, as
part of composite anode particles 115 and/or in anode 100, as
disclosed herein.
[0066] In certain embodiments, Si may be used at 2-25 weight % of
the total weight of the anode material and B may be used at 5-18
weight % of the total weight of the anode material and/or W may be
used at 7-13 weight % of the total weight of the anode material.
Conductive materials may be added to the anode material, e.g., at
0.01-15 weight % of the total weight of the anode material.
[0067] In certain embodiments, Si may be used at 5-47 weight % of
the total weight of the anode material and B may be used at 3-25
weight % of the total weight of the anode material and/or W may be
used at 6-25 weight % of the total weight of the anode material.
Conductive materials may be added to the anode material, e.g., at
0.01-15 weight % of the total weight of the anode material.
[0068] In certain embodiments, Si may be used at 4-35 weight % of
the total weight of the anode material and B may be used at
2.5-25.6 weight % of the total weight of the anode material and/or
WC may be used at 7-14 weight % of the total weight of the anode
material. Possibly, conductive materials such as carbon may be
added to the anode material, e.g., at 5-60 weight % of the total
weight of the anode material.
[0069] The weight % disclosed herein may be with respect to the
total material of any of anode active material particles 110,
modified anode active material particles 110A (see below, e.g., B
may be at least partly used as B.sub.4C, W may be at least partly
used as WC), composite anode particles 115 (e.g., the total weight
including coating 120), and/or all anode material of anode 100.
Components of any of the disclosed embodiments may be combined in
various embodiments.
[0070] Binders 102 may be added at 0.1-15 weight % of the total
weight of the anode material of anode 100.
Germanium Active Material
[0071] In some embodiments, anode active material particles 110 may
comprise any of Ge (germanium), B and W and/or combinations thereof
as mixtures and/or alloys. In some embodiments, anode active
material particles 110 may comprise Ge at 5-80 weight % of the
total weight of the anode material, e.g., anode active material
particles 110 may comprise 5-80 weight % Ge and/or 5-80% of anode
active material particles 110 may comprise Ge, and/or anode 100 may
comprise any combination thereof. In certain embodiments, B and/or
W may be included in anode active material particles 110 as
dopant(s) and/or as attached particles or nanoparticles.
[0072] In some embodiments, anode active material particles 110 may
comprise B at 2-20 weight % of the total weight of the anode
material. In some embodiments, anode active material particles 110
may comprise W at 5-20 weight % of the total weight of the anode
material. In some embodiments, anode active material particles 110
may comprise C (carbon) at 0.5-5, or possibly up to 10 weight % of
the total weight of the anode material, e.g., as any of spherical
carbon particles, CNTs (carbon nanotubes) and graphene particles.
In certain embodiments, anode active material particles 110 may
comprise CNTs at 0.05-0.5 weight % of the total weight of the anode
material. CNTs may be used as part of modified anode active
material particles 110A, as part of composite anode particles 115
and/or in anode 100, as disclosed herein.
[0073] In some embodiments, Si may be used to at least partly
complement Ge, e.g., at weight ratios of at least 4:1 (Ge:Si). In
certain embodiments, other anode active materials disclosed herein
may be used to complement Ge, e.g., Sn, Al or other materials. For
example, Sn may be used to replace Ge at least partly in the
compositions disclosed above. In case Sn, Ge and Si are used for
anode material, Si may be used at weight ratios of at least 4:1
(Sn+Ge):Si.
[0074] In certain embodiments, Ge may be used at 60-75 weight % of
the total weight of the anode material and B may be used at 3-6
weight % of the total weight of the anode material and/or W may be
used at 7-11 weight % of the total weight of the anode material.
Conductive materials may be added to the anode material, e.g., at
0.01-5 weight % of the total weight of the anode material.
[0075] The weight % disclosed herein may be with respect to the
total material of any of anode active material particles 110,
modified anode active material particles 110A (see below, e.g., B
may be at least partly used as B.sub.4C, W may be at least partly
used as WC), composite anode particles 115 (e.g., the total weight
including coating 120), and/or all anode material of anode 100.
Components of any of the disclosed embodiments may be combined in
various embodiments.
[0076] Binders 102 may be added at 0.1-15 weight % of the total
weight of the anode material of anode 100.
Tin Active Material
[0077] In some embodiments, anode active material particles 110 may
comprise any of Sn (tin), Sn and Si, Sn and B, Sn and W and/or
combinations thereof as mixtures and/or alloys. For example, Sn may
be used at 5-80 weight % of the total weight of the anode material,
e.g., anode active material particles 110 may comprise 5-80 weight
% Sn and/or 5-80% of anode active material particles 110 may
comprise Sn, and/or anode 100 may comprise any combination thereof.
Si and/or B may be used for the rest of the anode material in any
of the above combinations. In certain embodiments, B and/or W may
be included in anode active material particles 110 as dopant(s)
and/or as attached particles or nanoparticles.
[0078] In some embodiments, B may be used at 2-20 weight % of the
total weight of the anode material. In some embodiments, W may be
used at 5-20 weight % of the total weight of the anode material. In
certain embodiments, carbon may be used at 0.5-5 weight % of the
total weight of the anode material, e.g., in B.sub.4C and/or WC
nanoparticles 112 and/or as conductive material 130.
[0079] In some embodiments, Si may be used to at least partly
complement Sn, e.g., at weight ratios of at least 4:1 (Sn:Si). In
certain embodiments, other anode active materials disclosed herein
may be used to complement Sn, e.g., Ge, Al or other materials. For
example, Ge may be used to replace Sn at least partly in the
compositions disclosed above. In case Sn, Ge and Si are used for
anode material, Si may be used at weight ratios of at least 4:1
(Sn+Ge):Si.
[0080] In certain embodiments, Sn may be used at 60-75 weight % of
the total weight of the anode material and B may be used at 3-6
weight % of the total weight of the anode material and/or W may be
used at 7-11 weight % of the total weight of the anode material.
Conductive materials may be added to the anode material, e.g., at
0.01-5 weight % of the total weight of the anode material.
[0081] In certain embodiments, Sn may be used at 6.5-94 weight % of
the total weight of the anode material and B may be used at 1.5-15
weight % of the total weight of the anode material and/or W may be
used at 6-25 weight % of the total weight of the anode
material.
[0082] The weight % disclosed herein may be with respect to the
total material of any of anode active material particles 110,
modified anode active material particles 110A (see below, e.g., B
may be at least partly used as B.sub.4C, W may be at least partly
used as WC,) and/or composite anode particles 115 (e.g., the total
weight including coating 120). Components of any of the disclosed
embodiments may be combined in various embodiments.
[0083] Non-limiting examples for preparation procedures of
tin-containing anode active material particles 110 include ball
milling of a specified ratio of Sn and Si (as non-limiting
examples, any of 1:1, 1:2, 4:1 or intermediate ratios) at a
specified milling speed (as non-limiting examples, any of 200, 300,
400 rpm, or intermediate speeds) for between 6 and 12 hours. In
certain embodiments, additional milling was performed after adding
1-20% w/w graphite. The additional milling process was performed at
a same or different specified milling speed (as non-limiting
examples, any of 200, 300, 400 rpm, or intermediate speeds) for
between 6 and 12 hours.
Aluminum Active Material
[0084] In some embodiments, anode active material particles 110 may
comprise treated aluminum particles, from which a native surface
oxide may be removed and a lithium-containing surface layer may be
applied.
[0085] Formation of anode 100 from anode active material particles
110 comprising aluminum particles may be carried out by
consolidating treated aluminum particles 110 with one or more
additives, while preventing the formation of an oxidation layer on
particles 110. The additives may comprise, e.g., binders and
additives 102 such as particulate conductive filler(s),
plasticizer(s), and/or other binder(s); and possibly pre-coating(s)
120, nanoparticles 112 and/or coating(s) 130.
[0086] In certain embodiments, the applied lithium-containing
surface layer may be applied as pre-coating 120, e.g., using
lithium polymer(s) such as lithium polyphosphate, lithium
poly(acrylic acid), lithium carboxyl methyl cellulose and/or
lithium alginate (see below). In certain embodiments,
lithium-containing surface pre-coating 120 may comprise
lithium-aluminum compound(s) having the formula Li.sub.xAl.sub.y,
e.g., Li.sub.9Al.sub.4.
[0087] In certain embodiments, B.sub.2O.sub.3 may be applied as
either pre-coating 120 and/or nanoparticles 112 onto the treated
aluminum particles, from which the native oxide has been removed,
in addition or in place of the lithium-containing surface
layer.
[0088] In certain embodiments, Zn, Cd and/or Pb may be added to any
one of the disclosed embodiments to further increase the lithium
capacity of anode active material particles 110.
Nanoparticles and Modifications
[0089] FIGS. 3A-3D are high level schematic illustrations of
modified anode active material particles 110A, according to some
embodiments of the invention. Anode active material particles 110
may be modified by attachment or embedment of smaller nanoparticles
112, as illustrated schematically in FIGS. 3A-3D. Embodiments
comprise single modified anode active material particles 110A
(FIGS. 3A, 3C) or aggregates thereof (FIGS. 3B, 3D) which may be
used together or separately to prepare anode 100. Coatings 120 may
be applied on modified anode active material particles 110A and/or
aggregates thereof to form composite particles 115 (FIGS. 3C, 3D
respectively), which may be used together or separately to prepare
anode 100. The optional embedding of nanoparticles 112 in anode
active material particles 110 may form an interface layer 114
having alloy-like characteristics, shown schematically in FIG.
3A.
[0090] In some embodiments, anode active material particles 110 may
have a particle size at a range of 30-500 nm, and further comprise
nanoparticles 112 (e.g., B.sub.4C, boron carbide, and/or WC,
tungsten carbide, nanoparticles) at a range of 10-50 nm on a
surface of anode active material particles 110 to yield modified
anode active material particles 110A. Nanoparticles 112 may be
configured to reinforce anode active material particles 110, e.g.,
with respect to mechanical forces of expansion and contraction 101
upon lithiation and de-lithiation of lithium ions (respectively),
providing increased mechanical stability during repeated
fast-charging/discharging cycles. Alternatively or complementarily,
nanoparticles 112 may be configured to regulate (e.g., reduce) the
surface energy of modified anode active material particles 110A to
improve lithium ion conductivity 103, e.g., via providing better
contact with electrolyte 85; to improve the dispersion of modified
anode active material particles 110A throughout the anode slurry
and the spreading thereof throughout anode 100; and/or to enhance
the consolidation of modified anode active material particles 110A
with conductive filler 102 on the current collector.
[0091] In certain embodiments, nanoparticles 112 may comprise,
additionally or in place of B.sub.4C and/or WC, VC (vanadium
carbide), TiN (titanium nitride) and/or equivalent compounds.
Nanoparticles 112 may have various effects such as partial
reduction of lithium ions which may structurally stabilize modified
anode active material particles 110A during lithiation and
de-lithiation, improve the electrochemical behavior of modified
anode active material particles 110A with respect to partial
reduction of Li.sup.+ to Li.sup..delta.+ and prevention of
metallization.
[0092] In certain embodiments, anode active material particles 110
may comprise any of Sn, Pb, Ge, Si, their alloys and mixtures
thereof, having a particle size in a range of 30-500 nm and
B.sub.4C nanoparticles 112 having a particle size range of 10-50
nm, embedded (114) on the surface of anode active material
particles 110. The particle size of anode active material particles
110 may be in any of the ranges 30-50 nm, 50-100 nm, 30-100 nm,
50-200 nm, 100-500 nm or in sub-ranges thereof. Anode active
material particles 110 may comprise an oxide layer or parts
thereof. Alternatively or complementarily, the oxide layer, parts
thereof, and/or the thickness of the oxide layer may be modified
during preparation, e.g., by oxidation, heat, reduction and/or
combinations thereof, as described herein in various embodiments.
Full or partial de-oxidation may be applied in any of the
embodiments of anode active material particles 110, e.g., in which
Si, Ge, Sn, Al, Pb or other elements are used as the anode active
material.
[0093] In certain embodiments, the particle size of nanoparticles
112 (e.g., the B.sub.4C nanoparticles) may be at least one order of
magnitude smaller than the particle size of anode active material
(e.g., metalloid) particles 110. In certain embodiments, the amount
of nanoparticles 112 (e.g., B.sub.4C nanoparticles) may be in the
range of 5 to 25 weight percent of anode active material particles
110. Interface layer 114 may comprise a transition metal oxide
layer on the surface of active material particles 110, which has
e.g., a thickness of 1-10 nm.
[0094] In certain embodiments, anode active material particles 110
may have an average diameter of e.g., 100 nm, 200 nm, 250 nm, 300
nm, 400 nm or 500 nm and some, most or all of anode active material
particles 110 may comprise nanoparticles 112, attached thereto
and/or embedded therein (depending e.g., on the energy involved in
preparation processes 105). Nanoparticles 112 may at least partly
cover and/or be embedded in anode active material particles 110,
with respect to at least a part of the surface area of anode active
material particles 110. For example, ball milling may yield a
powder of anode active material particles 110 with nanoparticles
112 (illustrated schematically in FIG. 3A) and/or of aggregated
anode active material particles 110 (illustrated schematically in
FIG. 3B)--to form modified anode active material particles
110A.
[0095] In certain embodiments, at least some of B.sub.4C
nanoparticles 112 may interact with metal oxides on the surface of
anode active material particles 110 to form Li.sub.2B.sub.4O.sub.7
(lithium tetra-borate salt) and/or related materials as interface
layer 114 (see e.g., FIG. 3A) and/or as at least part of
nanoparticles 112, to further reduce the surface potential of
modified anode active material particles 110A and possibly leave
the surface thereof partly charged (implementing e.g., buffering
zone 110B in FIGS. 2C, 2E). Partly charged modified anode active
material particles 110A may then partly reduce lithium ions during
charging (Li.sup.+.fwdarw.Li.sup..delta.+) and enhance the battery
safety by preventing lithium metallization on the surface of
modified anode active material particles 110A, as explained
herein.
[0096] In certain embodiments, any of coatings 120 disclosed herein
may be applied onto modified anode active material particles 110A
and/or their aggregates to form composite particles 115, for
example coatings 120 may comprise amorphous carbon, graphene and/or
graphite, covering at least partly (or fully) modified anode active
material particles 110A. For example, coatings 120 may comprise a
layer. In certain embodiments, coatings 120 may comprise lithium
polymer(s) chemically bonded to the surface of modified anode
active material particles 110A.
[0097] Without being bound by theory, the inventors have found out
that nanoparticles 112 and processes 105 for their attachment to
anode active material particles 110 may be optimized to achieve any
of the following effects, improving the operation of anodes 100 in
lithium ion batteries and especially in fast charging lithium ion
batteries. Nanoparticles 112 and processes 105 may be selected
and/or configured to increase the mechanical stability of anode
active material particles 110 by providing an external and/or
internal backbone to modified anode material particles 110A,
especially during expansion and contraction 101 thereof upon
lithiation and de-lithiation, respectively. The SEI that may be
formed on the surfaces of particles 110 may be more stable and less
brittle due to the presence of nanoparticles 112. Nanoparticles 112
may be selected from hard materials (such as B.sub.4C, WC, VC, TiN)
and may moderate expansion and contraction 101, prevent cracking,
reduce the amount of agglomeration during multiple charging and
discharging cycles and/or prevent oxidation as described below.
[0098] Nanoparticles 112 and processes 105 may be selected and/or
configured to provide any of the following effects. During
expansion and contraction 101, nanoparticles 112 may be pushed
further into modified anode material particles 110A, to provide
internal mechanical stabilization. Positioned mainly on the surface
of modified anode material particles 110A, nanoparticles 112 may be
selected to lower the surface potential of modified anode material
particles 110A and reduce the rate modified anode material
particles 110A merge and agglomerate. Reduction of surface
potential may also provide better contact with electrolyte 85,
improving ionic conductivity of the lithium ions into and out of
modified anode material particles 110A. Moreover, reducing
agglomeration also increases the surface area of modified anode
material particles 110A which is available to lithium ions
movements into and out of modified anode material particles 110A,
and thereby increases the ionic conductivity and speed of charging
and discharging.
[0099] In certain embodiments, nanoparticles 112 attached onto
anode active material particles 110 may form at least a partial
shell structure which allows expansion and contraction 101 of
modified anode material particles 110A, as illustrated below
concerning composite anode material particles 115.
[0100] In certain embodiments, nanoparticles 112 and processes 105
may be selected and/or configured to reduce or remove oxides of the
anode active material which may be present and/or may evolve in
anode 100, by forming instead compounds such as
Li.sub.2B.sub.4O.sub.7 (lithium tetra-borate salt, e.g., via a
reaction such as
4Li+7MeO+2B.sub.4C.fwdarw.2Li.sub.2B.sub.4O.sub.7+C+7Me, reaction
not balanced with respect to C and O, with Me denoting active
material such as Si, Ge, Sn etc. and carbon originating from
additives) or equivalent compounds selected from e.g., WC, VC, TiN,
which have higher affinity to oxygen than the anode active
material. Preventing oxidation not only increases the available
active material surface area for lithiation but also helps prevent
metallization of lithium on the surface of modified active material
particles 110A.
[0101] In certain embodiments, coatings 120, such as illustrated
e.g., in FIGS. 3C, 3D, may further enhance electronic and/or ionic
conductivity. For example, thin films (e.g., 1-50 nm, or 2-10 nm
thick) of carbon (e.g., amorphous carbon, graphite, graphene, etc.)
and/or transition metal oxide(s) (e.g., Al.sub.2O.sub.3,
B.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, MnO etc.) may be added to
modified anode material particles 110A and/or their aggregates to
form composite active material particles 115, as disclosed in
additional examples below. Any of coatings 120 disclosed below may
be applied onto modified anode material particles 110A comprising
nanoparticles 112.
[0102] In certain embodiments, coating(s) 120 may be configured to
provide gaps 140 for expansion and contraction 101 and/or may be
flexible to allow for expansion and contraction 101, as disclosed
below (see e.g., FIGS. 8A, 8D).
[0103] In certain embodiments, coating(s) 120 may be configured to
support and stabilize a SEI (as illustrated schematically, e.g. in
FIG. 2D), preventing cracks therein and preventing particles from
merging into one another, thereby maintaining a large active
material surface area.
[0104] In certain embodiments, nanoparticles 112 and processes 105
may be selected and/or configured to reduce potential decomposition
of electrolyte solvent by carbon coating(s) 120, through the close
proximity of nanoparticles 112 and coating 120, which decreases its
surface potential and the carbon's reactivity towards the
electrolyte solvent.
[0105] Coating(s) 120 of transition metal oxide(s) (e.g.,
Al.sub.2O.sub.3, B.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, MnO etc.)
may further enhance mechanical stability of modified active
material particles 110A, and may be combined with other coating(s)
120 disclosed below to form composite active material particles
115. Transition metal oxide coating(s) 120 may be further
configured to provide buffering zone 110B and prevent lithium
metallization as described above, and possibly increase ionic
conductivity of composite active material particles 115.
[0106] In certain embodiments, nanoparticles 112 and processes 105
may be selected and/or configured to prevent prior art
disadvantages of using transition metal oxide coating(s) 120, by
stabilizing the SEI and preventing crack formation. Combining
nanoparticles 112 and transition metal oxide coating(s) 120 may
provide an improved mechanical skeleton for composite active
material particles 115 (e.g., a stable shell structure, as shown
below) which provides sufficient mechanical support and maintains
anode performance at high C rates, e.g., 2C, 5C, 10C or possibly
tens or even a few hundred C.
[0107] In certain embodiments, nanoparticles 112 may complement
and/or replace doping of anode active material particles 110 with B
and/or W and may achieve similar or complementary effects with
respect to reduction of the surface potential and reactivity toward
the electrolyte.
[0108] FIGS. 14A-14F presented below are examples for performance
of anodes 100 made of modified anode active material particles
110A, according to some embodiments of the invention.
Coatings
[0109] In the following, various material combination embodiments
for coatings are presented. For example, various conductive
polymers, possibly lithiated polymers and/or lithiated conductive
polymers, may be used as coatings 120. It is emphasized that
elements from different embodiments may be combined to form
additional embodiments, and that any of the coatings embodiments
may be combined with various anode active material embodiments and
anode embodiments disclosed herein. Some of the disclosed coatings
may be applied as coatings 120 and/or as coatings 130, depending on
the exact details of the applied processes.
[0110] FIGS. 4A-4F are high level schematic illustrations of
coatings 120 in composite anode particles 115, according to some
embodiments of the invention. Coatings 120 are illustrated in three
different forms in the figures, namely as spherical coating 120
(e.g., in FIGS. 4A, 4C, 4E), as wriggly lines indicating coating
120 (e.g., in FIGS. 4B, 4C, 4E, 4F), and as a thicker line
indicating a surface layer coating 120 (e.g., in FIGS. 4D, as well
as 3C, 3D). These illustrations are used to illustrate coating(s)
schematically, and in certain embodiments may represent equivalent
and/or complementary coatings 120. Any of coatings 120 disclosed
below may be understood and partial or full coating of different
thickness. Coating 120 may comprise multiple coating layers 120A,
120B, which are not limited to the illustrated two layered
coatings. Any of disclosed coatings 120 may be applied to one or
more coating layers, each of which may be partial or full coating
with respect to the surface of anode active material particles
110.
[0111] It is emphasized that any of disclosed coatings 120 may be
applied to either or both anode active material particles 110 and
modified anode active material particles 110A (the latter
illustrated explicitly in FIG. 4F). Moreover, in case of very
partial coatings 120 (sparse coatings 120) coated particles may be
understood as modified anode active material particles 110A rather
than as composite anode particles 115, as indicated e.g., in FIGS.
4B, 4F.
[0112] In some embodiments, coating(s) 120 may build one or more
shell(s) 120 with respect to cores of anode active material
particles 110 and/or modified anode active material particles 110A.
In this respect, composite anode particles 115 may form core-shell
particles 115, with coating 120 providing at least part of the
shell structure and the anode material providing at least part of
the core structure.
Conductive Coatings
[0113] FIG. 4G-4J are high level schematic illustrations of in-situ
polymerization of conductive polymers, according to some
embodiments of the invention.
[0114] Conductive coatings 120, as well as conductive polymer
coatings and/or matrix 130 may be used to improve anode
conductivity, as well as to improve structural and mechanical
properties of anode 100. Disclosed coatings 120, 130, such as
coatings with conductive polymers, may be applied to any of the
disclosed anode active materials, such as any of Si, Sn and Ge,
their mixtures (in various ratios), combinations and alloys, as
well as other anode active materials disclosed herein. Non-limiting
examples are Si:Sn anode active materials mixed at ratios of at
1:1, 2:1, or other ratios, as well as mixtures thereof with Ge.
[0115] FIG. 4G is a high level schematic illustration of in-situ
polymerization of conductive polymers, according to some
embodiments of the invention. A slurry 107 may comprise monomers
127 (or possibly at least partly oligomers), active material
particles 110 and possibly additives 102 and be used (105) to form
anode 100. The conductive polymers resulting from the
polymerization of monomers 127 may form particle coatings 120
and/or matrix 130 in which particles 110 are embedded. In certain
embodiments, linker(s) 119 may be added to bind at least some of
anode material particles 110 to the conductive polymer.
[0116] FIG. 4I is a high level schematic illustration of additional
benefits of using monomers 127 (or possibly oligomers) in slurry
107 according to some embodiments of the invention, with respect to
an approach, illustrated in FIG. 4H, in which polymers 98A are used
in slurry 98. In the latter approach (FIG. 4H) dispersion of anode
material particles 110 and additives 102 is non-uniform and
requires using a surfactant to achieve more even dispersion.
Surprisingly, the inventors have found out that using monomers 127
(or possibly oligomers) in slurry 107 contributes to dispersion of
anode material particles 110 and/or additives 102 (illustrated
schematically in FIG. 4I) and results in a more uniform
distribution thereof in polymerized matrix 130. The dispersion of
anode material particles 110 was observed visually as transparent
slurry when using monomers 127 with respect to using polymer 98A in
slurry 98 which resulted in turbid slurry due to agglomeration of
anode material particles 110.
[0117] FIG. 4J is a high level schematic illustration of binding
anode material particles 110 by linker molecules 119, according to
some embodiments of the invention. Linker molecules 119 provide at
least partial chemical attachment of anode material particles 110
to matrix 130, which may be stronger and more stable than physical
attachment achieved in the milling process. The resulting
stabilization may contribute to higher level of uniformity of anode
100 and its better mechanical handling of expansion and contraction
stresses (101) during lithiation and de-lithiation.
[0118] In certain embodiments, polymer coatings may be polymerized
in situ, in anode 100, in the presence of anode active material--to
create coating 120 and/or matrix 130 of the conductive polymer
surrounding active material particles 110. Polymerization may be
configured to yield coatings 120 and/or coatings 130 (coatings 130
may function as matrix 130 and/or as anode coatings, as explained
below), and may be configured to provide multiple contributions to
the structure of anode 100, such as holding together active
material particles 110, 110A and/or 115, complementing or possibly
replacing binder(s) 102--e.g., to improve cycle life; and/or
increasing anode conductivity as conductive additive 102 and/or
130, as polyaniline in the emeraldine form has high electrical
conductivity--e.g., to improve the rate capability at high
currents. In certain embodiments, other conductive polymers may be
used in addition or in place of polyaniline.
[0119] Certain embodiments comprise a method of forming anode
material for Li-ion batteries comprising adding an acidic solution
to anode active material particles 110; adding aniline; stirring
the acidic solution (e.g., for at least one hour); and adding a
basic solution (e.g., NaOH, KOH, LiOH or any other base) to the
stirred acidic solution until a specified basic pH (in embodiments,
a pH of about 9) is achieved--to form polyaniline as coating 120
and/or as matrix 130. The method may further comprise separating
polyaniline matrix 130 (including anode active material particles
110) from the solution and drying it to form anode 100.
[0120] In certain embodiments, aniline derivatives may be used, for
example, some or all of the added aniline monomers may be
substituted by one or more sulfonic functional groups. The sulfonic
functional groups may be selected to improve the adhesion between
the polyaniline and the active material by chemically binding the
active material. In some embodiments the aniline may be replaced,
partly or completely, by monomers of other conducting polymers.
[0121] In some embodiments, the acidic solution may be a strong
acid such as HCl, HNO.sub.3, H.sub.3PO.sub.4 and other phosphate or
polyphosphate acids and/or equivalent acids. Phosphate and
polyphosphate acids, being slightly bulky, may increase capacity
and electric conductivity. In certain embodiments, phosphate and/or
polyphosphate acids may be used as polymer dopants.
[0122] In certain embodiments, NH.sub.4S.sub.2O.sub.8 (or possibly
equivalent salts or peroxides) may be added to the acidic solution
with the aniline monomers, to promote polymerization.
[0123] In certain embodiments, polymerization may be performed,
alternatively or complementarily, by oxidative polymerization,
polycondensation, electrochemical polymerization or any other
polymerization.
[0124] In certain embodiments, linkers 119 may be used to bind the
polyaniline to anode active material particles 110, as illustrated
schematically in FIG. 4G. FIG. 4G schematically illustrates a
linker 119 binding a polymer as coating 120 and/or 130 to anode
active material particle(s) 110, according to some embodiments of
the invention. In some embodiments, linker molecules 119 may be
added after the polymerization is completed, e.g., after conductive
polymer (e.g., polyaniline) matrix 130 is separated and dried.
Linkers 119 may have carboxylic groups which chemically bind to the
oxides of active material particles 110 and to conductive polymer
matrix 130, e.g., to the lone electron pair on a nitrogen of the
aniline monomers in polyaniline. Linker molecules 119 may also have
sulfonate groups, or other groups, which may also bind to the
active material oxides. Due to the chemical binding, linkers 119
may increase conductivity and stability and provide flexibility to
the electrode matrix, e.g., stability when the expansion of the
active material occurs during cycling. Linker molecules 119 may
comprise 5-sulfoisophthalic acid or its derivatives, succinic acid
or other dicarboxylic acids. In some embodiments, dried slurry 107
may be mixed with linker molecules 119 in the presence of a solvent
(e.g., water).
[0125] Anodes 100 may be formed of various active materials, e.g.,
Si, Si:Sn at various ratios, e.g., 1:1 and 2:1 ratios, possibly
mixed with Ge, and for various ratios of aniline to active
material. Certain embodiments comprise addition of MoS.sub.2, e.g.,
as additives 102, to increase the capacity of anode 100 (possibly
due to an increase in ionic conductivity). Certain embodiments
comprise addition of carbon nanotubes (CNTs), e.g., as additives
102, to improve the electronic and ionic conductivity. Certain
embodiments comprise pre-lithiation by replacing NaOH in the
procedure with LiOH in order to add Li ions to anode 100. Certain
embodiments comprise adding 5-sulfoisophthalic acid and/or adding
sulfonic functional group(s) on the aniline to improve the adhesion
between the polyaniline and the active material.
[0126] Advantageously, methods and anodes are provided in which
matrix 130 of a conductive polymer surrounding the active material
is created--independently as coating 130 and/or in relation to
anode material coatings 120. The polymerization process may be
performed in-situ, in the presence of the active material.
Advantageously, matrix 130 may be configured to both hold together
active material particles 110, 110A and/or 115, which may cooperate
with and/or replace binder 102, and also act as a conductive
additive to the electrode, such as anode 100. The binding quality
of the polymer helps hold the electrode together while cycling thus
improving cycle life. The conductivity improves the rate capability
even at high currents. Polyaniline may be in emeraldine form which
contributes to the high electrical conductivity.
[0127] Advantageously, provided matrices 130 were found to overcome
cracking and adhesion problems in prior art examples, with
polyaniline reducing the amount of cracking drastically--as
illustrated in FIG. 16A with respect to prior art FIG. 16B (see
images below).
Lithium Polymers and Prelithiation
[0128] In certain embodiments, coating 120 may comprise
lithium-containing polymer(s) bonded to the surface of anode active
material particles 110 (and/or modified anode active material
particles 110A). In certain embodiments, anode active material
particles 110 may be pre-lithiated by introducing lithium ions into
anode active material particles 110 and coating them by hydrophobic
polymer layer 120 which conducts electrons and ions, and enables
applying anode preparation processes 105 in spite of the high
reactivity of the lithium ions. Anode 100 may then be prepared from
a slurry comprising the coated anode material particles 110,
coating 120 preventing the lithium ions from chemically reacting
with water molecules in the slurry. Any of the disclosed anode
active material particles 110 may be coated as disclosed below,
e.g., Si, SnSi, Ge and Ge with B.sub.4C anode materials disclosed
herein.
[0129] FIGS. 5A and 5B are high level schematic illustrations of
lithium polymer coatings 120 applied to anode active material
particles 110, according to some embodiments of the invention. FIG.
5C is a high level schematic illustration of hydrophobic polymer
coating 120 applied to pre-lithiated anode active material
particles 110, according to some embodiments of the invention.
Lithium Polymers
[0130] In certain embodiments, the lithium-containing polymer may
comprise negatively charged group(s) bonded to the surface of anode
active material particles 110 and lithium groups on the polymer
having a partial positive charge. For example, as illustrated
schematically in FIGS. 5A and 5B with anode active material as
metalloid (such as Si, Ge, Sn, combinations and/or alloys thereof,
and in certain embodiments also Pb, Al, Zn, combinations and/or
alloys thereof), an interfacial reaction may chemically bind
lithium polymer 120 to the surface of anode active material
particles 110. The interfacial reaction may be carried out e.g., in
dry conditions inside a ball miller using lithium polymer with many
lithium salt sites, alternatively or complementarily, using
physical vapor deposition or equivalent processes.
[0131] For example, the lithium-containing polymer may comprise any
of lithium polyphosphate (Li.sub.(n)PP or LiPP), lithium
poly-acrylic acid (Li.sub.(n)PAA or LiPAA), lithium carboxyl methyl
cellulose (Li.sub.(n)CMC or LiCMC), lithium alginate (Li.sub.(n)Alg
or LiAlg) and combinations thereof, with (n) denoting multiple
attached Li.
[0132] In some embodiments, a positively charged lithium (Li.sup.+)
of the lithium polymer salt may be used to bind the polymer to the
active material, reacting on the alloy material surface to bind the
negatively charged anion of the polymer, leaving a partly charged
entity (denoted Li.sup..delta.+ to express partial screening of the
positive charge of Li.sup.+ by anions and/or electron donating
groups; and see also FIG. 2C as embodiment of buffering zone 110B;
and FIGS. 2E-2G disclosing gradient 125 with polymer anions and/or
electron donating groups which provide negative charge 126)
chemically bound to the surface, coating anode active material
particles 110. As illustrated schematically in FIG. 2C, an ionic
nature of the SEI/polymer interface may decrease the surface energy
by leaving the interfacial lithium ions with positive or partly
positive charge to form gradient 125 (e.g., an intermediate stage
between ionic and covalent bond and/or an intermediate stabilized
species in between fully charged (Li.sup.+) and neutral (Li.sup.0)
states of lithium). Gradient 125 may reduce or prevent lithium
metallization and dendrites formation, especially during fast
charge where the anode surface is likely to face under-potential
(see e.g., FIGS. 13A-C and the related explanations).
[0133] In certain embodiments, lithium polymer coating 120 may have
a direct chemical and/or partial chemical bonding to the active
material. In certain embodiments, Li-polymer coating 120 bonded to
the surface of anode active material particles 110 may be
configured to serve as a backbone for the SEI growth which provides
flexibility and stability to the fragile SEI 122, as illustrated
schematically in FIG. 2D. Moreover, coating 120 (and its
preparation process 105) may be configured to leave some of the
lithium ions sites on the polymer without binding to the surface,
to enable fast ionic transport between electrolyte 85 and anode
active material particles 110. Polymeric coating 120 may further be
able to support an increased material load and thickening of anode
100 (e.g., due to SEI formation of SEI 122), possibly even up to 3
mg/cm.sup.2 or above, without losing performance.
[0134] In some embodiments, a physical evidence for the
effectiveness of lithium polymeric coating 120 for surface
protection of anode active material particles 110 was seen while
monitoring the viscosity stability of the active material in the
electrode slurry (e.g., water-based slurry for example) during
anode preparation process 105. For example, without polymeric
coating the slurry's viscosity was stable for approximately 1 hour.
However, after coating anode active material particles 110 with
Li-polymer coating 120, the slurry did not change its viscosity
even a week after the preparation.
[0135] In certain embodiments, illustrated schematically e.g., in
FIGS. 4C and 4D, lithium-containing polymer(s) coating 120A may be
further coated with a layer 120B of carbon and/or transition metal
oxide, e.g., a thin layer thereof. Alternatively or
complementarily, in certain embodiments, layer(s) 120A of carbon
and/or transition metal oxide may be further coated by
lithium-containing polymer(s) coating 120A. In some embodiments,
coating 120 may comprise lithium-containing polymers with
additional coating elements, e.g., any of carbon, transition metal
oxide and/or borate or phosphate salts, as disclosed below.
Direct Pre-Lithiation
[0136] Pre-lithiated anodes 100 and methods of pre-lithiating
anodes 100 are provided, in which anode active material particles
110 are coated by hydrophobic polymer layer 120 which is electron
and ion conductive. Hydrophobic polymer layer 120 is configured to
prevent the lithium ions from chemically reacting with water
molecules in the slurry and/or humidity, to provide pre-lithiated
anodes 100 which improve the operation of lithium ion cells 150 by
preventing accumulation of lithium ions (from cathode 87) in anode
100. Anode active material particles 110 may further comprise
alloyed boron carbide nanoparticles 112 or lithium tetraborate, and
may possibly be coated by a graphene-like layer 120B to reduce
reactivity toward electrolyte 85. Coating 120 of anode material
particles 110 by hydrophobic polymer coating 120 may be carried out
mechanically, e.g., by dry ball milling.
[0137] Certain embodiments comprise coating lithium-doped anode
active material particles 110 comprising e.g., any of Si, Ge, Sn,
Al, Pb, Zn, Cd, and mixtures and alloys thereof, with coating 120
comprising hydrophobic polymer layer(s) bonded thereto.
[0138] In certain embodiments, hydrophobic polymer layer(s) coating
120A may be further coated with a layer 120B of carbon and/or
transition metal oxide, e.g., a thin layer thereof (e.g., a 1-10 nm
carbon layer). The hydrophobic polymer(s) may be bonded to the
lithium ions in anode active material particles 110 and at least
partly protect them from contacting water in the anode slurry
and/or water vapor in the air. In certain embodiments the
hydrophobic polymer(s) contains conjugated aromatic groups and is
electron-conducting and/or ion-conducting.
[0139] FIG. 5C is a high level schematic illustration of
hydrophobic polymer coating 120C applied to pre-lithiated anode
active material particles 110, according to some embodiments of the
invention.
[0140] Pre-lithiated anode material particles 110 which contain
lithium ions Li.sup.+, e.g., as Si.sub.xLi.sub.y, Al.sub.zLi.sub.n,
etc., may be coated by hydrophobic polymer layer 120C configured to
prevent the lithium ions from chemically reacting with water
molecules surrounding anode material particles 110 and/or with
humidity, and to conduct electrons (e) and ions, e.g., Li.sup.+. It
is noted that coated anode material particles 115 (or 110A) may
also be used in dry environment, low humidity environment and/or in
non-aqueous slurry. It is also noted that the degree of
pre-lithiation of anode material particles 110 may vary, e.g., be
full or partial pre-lithiation.
[0141] Attaching hydrophobic polymer 120C onto anode material
particles 110 may be carried out by providing an appropriate amount
of energy which forms multiple bonds therebetween, e.g., multiple
relatively weak bonds which together maintain polymer 120 attached
to anode material particles 110. For example the bonds may be oxide
bonds between polymer molecules and the anode material, possibly
involving lithium ions (Li.sup.+) of the pre-lithiated anode
material and/or lithium ions (Li.sup.+) attached to the polymer.
Hydrophobic polymer layer 120C may comprise lithium ions which are
bonded to hydrophobic polymer 120. For example, for a case in which
the monomers are bonded to lithium ions, the anode material may
favor the lithium ions in the polymer salt, which lithiate the
surface leaving the lithium ions partly charged on the anode
material particles' surface, and hence chemically bond the anionic
part of the polymer directly to the metalloid surface of anode
material particles 110.
[0142] Attaching of polymer 120 onto anode material 110 may be
carried out by solid phase interfacial reaction due to favorable
Li.sup.+ to metalloid/metal oxide interaction. For example, dry
ball milling may be used for the attaching, configured to provide
sufficient energy for creating the bonds, while being carried out
at energy that maintains anode material particles 110 and the
polymer's monomer intact (e.g., not reduced in size and maintaining
the molecular structure, respectively). The inventors note that
solid phase reactions may in certain embodiments be implemented for
the attaching of polymers to provide coatings 120.
[0143] In certain embodiments, the attaching may be carried out
thermally, e.g., by providing the required energy thermally.
[0144] Advantageously, as illustrated in FIG. 5C by coated anode
material particles 115, the attaching provides polymer 120 as a
stable backbone for the SEI (Solid-Electrolyte Interface) formation
in the operating cell with disclosed anodes, enabling fast ionic
transport, flexibility and SEI stability during many cycles in the
operating cell (as illustrated schematically in FIGS. 2C-2G). The
inventors expect that coated anode material particles 115 have a
TEM (transmission electron microscopy) image indicating a uniform
coating of anode material particles 110 by polymer 120.
[0145] Anode active material particles 110 may comprise metalloids
such as silicon, germanium, tin, lead, zinc and cadmium. In certain
embodiments, anode material particles 110 may comprise any of
silicon, germanium, tin as well as oxides and/or alloys thereof. In
certain embodiments, anode active material particles 110 may
comprise any of various metal oxides.
[0146] Hydrophobic polymer layer 120C may be prepared from
hydrophobic polymers comprising e.g., conjugated aromatic groups,
such as polypyrroles, polyanilines and other hydrophobic, electron
and ion conducting polymers and/or polymers comprising electron and
ion conducting substituents. It is emphasized that hydrophobic
polymer layer 120C may be free of lithium, particularly when anode
material particles 110 are fully pre-lithiated.
[0147] Advantageously, coating anode material particles 110 by
hydrophobic polymer layer 120 enables pre-lithiating anode material
in spite of the high reactivity of lithium ions to water in
slurries used to manufacture the anode. The hydrophobic protection
enables production of anodes under less strict dryness conditions
than those required when handling lithium directly, and thereby
simplifies the production process of pre-lithiated anodes while
providing the benefits as cell anodes which include higher
performance and longer operation efficiency.
[0148] In certain embodiments, pre-lithiation may be applied to any
of anode material particles 110 disclosed herein. For example,
pre-lithiation may be applied to anode active material particles
110 in the range of 30-50 nm, 30-100 nm, 50-200 nm, 100-500 nm
and/or 500-1000 nm (pre-lithiation may enable and/or require using
particles in the larger range) and be at least partially covered
(e.g., coated, doped) with B.sub.4C (boron carbide) nanoparticles
112 of smaller scale (e.g., one order of magnitude smaller than the
metalloid particle), for example, 10-50 nm, as described above.
B.sub.4C nanoparticles 112 may be at least partially embedded on
the surface of anode material particles 110, as illustrated
schematically in FIG. 5B. Polymer coating 120 may be applied on
anode material particles 110 and cover B.sub.4C nanoparticles 112
as well. B.sub.4C nanoparticles 112 may be alloyed to anode
material particles 110 (illustrated schematically by region 114
where B.sub.4C nanoparticle 112 contacts anode material particle
110), thereby further lowering the surface energy of particles 115
and preventing metallization and/or enhancing polymer binding by
keeping the lithium ions on the surface partly positive.
[0149] Certain embodiments comprise multi-layered coated anode
material particles 115 having an additional graphene-like coating
120B (see e.g., FIG. 4E, made of e.g., amorphous carbon, graphite,
graphene etc.) may be applied on top of polymer 120, e.g., by
mechanical grinding of graphite to form a multi-layered
graphene-like coating on top of polymer 120. Graphene-like coating
120B may be applied on top of polymer layer 120 (optionally when
applied to anode material particles 110A with embedded B.sub.4C
nanoparticles 112) to further reduce the surface potential of
particles 115 and make them less reactive to electrolyte 85,
thereby reducing the probability for catalytic reaction with the
electrolyte and increasing the lifetime of cell 150 and energy
storage devices (such as batteries) produced therefrom.
Borates and/or Phosphates
[0150] In certain embodiments, coating 120 may comprise any of
boron oxide(s), phosphorus oxide(s), borate(s), phosphate(s) and
combinations thereof. For example, coating 120 may have a thickness
between 2-200 nm, and be applied onto anode active material
particles 110 (and/or modified anode active material particles
110A) having a diameter in the range between 20-500 nm (thicker
coatings 120 generally apply to larger particles 110). For example,
coating 120 may comprise borate salt crystals and/or phosphate
salt(s) applied onto anode active material particles 110 made of
any of Si, Sn, Ge, Pb, Al, mixtures thereof, and alloys
thereof.
[0151] In certain embodiments, boron and/or phosphorous containing
coating 120A may comprise borate and/or phosphate salt(s) 128
disclosed below. In certain embodiments, boron and/or phosphorous
containing coating 120A may be further coated with a layer 120B of
carbon and/or transition metal oxide, e.g., a thin layer thereof.
In certain embodiments, any of the disclosed borate/phosphate
coatings may be combined with any of the disclosed polymer
coatings, as illustrated schematically in FIG. 6 below.
[0152] In certain embodiments, borate and/or phosphate salt(s) 128
may comprise borate salts such as lithium bis(oxalato)borate
(LiBOB, LiB(C.sub.2O.sub.4).sub.2), lithium bis(malonato)borate
(LiBMB), lithium bis(trifluoromethanesulfonylimide) (LiTFSI).
lithium difluoro(oxalato)borate (LiFOB,
LiBF.sub.2(C.sub.2O.sub.4)), lithium tetraborate (LiB.sub.4O.sub.7)
or any other compound which may lead to formation of borate oxides
(B.sub.2O.sub.3) (or related salts) on anode active material
particles 110, including in certain embodiments B.sub.4C
nanoparticles 102.
[0153] In certain embodiments, borate and/or phosphate salt(s) 102A
may comprise phosphate salts such as lithium phosphate
(LiPO.sub.4), lithium pyrophosphate (LiP.sub.2O.sub.7), lithium
tripolyphosphate (LiP.sub.3O.sub.10) or any other compound which
may lead to formation of phosphate oxides (P.sub.2O.sub.5) (or
related salts) on anode active material particles 110.
[0154] The diameter of anode active material particles 110 may be
e.g., between 20-500 nm, for example having an average particle
size of 50 nm, 100 nm, 200 nm, 250 nm, 300 nm, 400 nm or more. The
thickness of layer 120 of borate and/or phosphate salt(s) 102A
and/or of borate oxides (B.sub.2O.sub.3, and/or related salts)
and/or phosphate oxides (P.sub.2O.sub.5, and/or related salts)
formed therefrom of the surface of anode active material particles
110 may be between 2-200 nm, e.g., having an average particle size
of 2 nm, 5 nm, 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, which may be
uniform or non-uniform with respect to anode active material
particles 110 in anode 100 and not necessarily corresponding to the
size of anode active material particles 110 which carry layer 120.
Layer 120 of borate and/or phosphate salt(s) 102A and/or of borate
oxides (B.sub.2O.sub.3, and/or related salts) and/or phosphate
oxides (P.sub.2O.sub.5, and/or related salts) formed therefrom of
the surface of anode active material particles 110 may be
continuous or discontinuous (e.g., small B.sub.2O.sub.3 and/or
P.sub.2O.sub.5 crystals in the latter case) and may be coated by
additional coating(s) 120B--see e.g., FIG. 4C, with coating 120A
possible indicating layer 120 of borate and/or phosphate salt(s)
102A and/or of borate oxides (B.sub.2O.sub.3, and/or related salts)
and/or phosphate oxides (P.sub.2O.sub.5, and/or related salts).
[0155] In certain embodiments, borate and/or phosphate salt(s) 102A
and/or of borate oxides (B.sub.2O.sub.3, and/or related salts)
and/or phosphate oxides (P.sub.2O.sub.5, and/or related salts) may
be used to form modified anode active material particles 110A and
configured to reduce or prevent aggregation of modified anode
active material particles 110A, possibly utilizing similar
mechanical effects as B.sub.4C nanoparticles 112 described
above.
[0156] Without being bound by theory, understood as part of
modified anode active material particles 110A, borate and/or
phosphate salt(s) 102A and processes 105 may be selected and/or
configured to provide any of the following effects. During
expansion and contraction 101, formed borate oxides
(B.sub.2O.sub.3, and/or related salts), LTB (lithium tetraborate)
and/or phosphate oxides (P.sub.2O.sub.5, and/or related salts) may
be pushed further into modified anode material particles 110A, to
provide internal mechanical stabilization. Positioned mainly on the
surface of modified anode material particles 110A, borate and/or
phosphate salt(s) 102A may be selected to lower the surface
potential of modified anode material particles 110A and reduce the
rate modified anode material particles 110A merge and agglomerate.
Reduction of surface potential may also provide better contact with
electrolyte 85, improving ionic conductivity of the lithium ions
into and out of modified anode material particles 110A. Moreover,
reducing agglomeration also increases the surface area of modified
anode material particles 110A which is available to lithium ions
movements into and out of modified anode material particles 110A,
and thereby increases the ionic conductivity and speed of charging
and discharging.
[0157] In certain embodiments, borate and/or phosphate salt(s) 102A
attached onto anode active material particles 110 may form at least
a partial shell structure which allows expansion and contraction
101 of modified anode material particles 110A, as illustrated below
concerning composite anode material particles 115.
[0158] In certain embodiments, borate and/or phosphate salt(s) 102A
and processes 105 may be selected and/or configured to reduce or
remove oxides of the anode active material which may be present
and/or may evolve in anode 100 by forming compounds such as
Li.sub.2B.sub.4O.sub.7 (lithium tetra-borate salt, e.g., via the
reaction 4Li.sup.+
7MeO+2B.sub.2O.sub.3.fwdarw.2Li.sub.2B.sub.4O.sub.7+C+7Me (not
balanced with respect to C and O, carbon originating from
additives), with Me denoting active material such as Si, Ge, Sn, Al
etc.), which have higher affinity to oxygen than the anode active
material. Preventing oxidation not only increases the available
active material surface area for lithiation but also helps prevent
metallization of lithium on the surface of modified active material
particles 110A (see above).
[0159] In certain embodiments, coatings 120, such as illustrated
e.g., in FIGS. 3C and 3D, may further enhance electronic and/or
ionic conductivity. For example, thin films (e.g., 1-50 nm, or 2-10
nm thick) of carbon (e.g., amorphous carbon, graphite, graphene,
etc.) and/or transition metal oxide(s) (e.g., Al.sub.2O.sub.3,
B.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, MnO etc.) may be added to
modified anode material particles 110A and/or their aggregates to
form composite active material particles 115, as disclosed in
additional examples below. Any of coatings 120 disclosed below may
be applied onto modified anode material particles 110A comprising
borate and/or phosphate salt(s) 102A.
[0160] In certain embodiments, coating(s) 120 may be configured to
provide gaps 140 for expansion and contraction 101 and/or be
flexible to allow for expansion and contraction 101, as disclosed
below (see e.g., FIGS. 8A, 8D).
[0161] In certain embodiments, coating(s) 120 may be configured to
support and stabilize a SEI (as illustrated schematically, e.g. in
FIG. 2D), preventing cracks therein and preventing particles from
merging into one another, thereby maintaining a large active
material surface area.
[0162] In certain embodiments, borate and/or phosphate salt(s) 102A
and processes 105 may be selected and/or configured to reduce
potential decomposition of electrolyte solvent by carbon coating(s)
120, through the close proximity of borate and/or phosphate salt(s)
102A and coating 120, which decreases its surface potential and the
carbon's reactivity towards the electrolyte solvent.
[0163] Coating(s) 120 of transition metal oxide(s) (e.g.,
Al.sub.2O.sub.3, B.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, MnO etc.)
may further enhance mechanical stability of modified active
material particles 110A, and may be combined with other coating(s)
120 disclosed below to form composite active material particles
115. Transition metal oxide coating(s) 120 may be further
configured to provide buffering zone 110B and prevent lithium
metallization as described above, and possibly increase ionic
conductivity of composite active material particles 115.
[0164] In certain embodiments, borate and/or phosphate salt(s) 102A
and processes 105 may be selected and/or configured to prevent
prior art disadvantages of using transition metal oxide coating(s)
120, by stabilizing the SEI and preventing crack formation.
Combining borate and/or phosphate salt(s) 102A and transition metal
oxide coating(s) 120 may provide an improved mechanical skeleton
for composite active material particles 115 (e.g., a stable shell
structure, as shown below) which provides sufficient mechanical
support and maintains anode performance at high C rates, e.g., 2C,
5C, 10C or possibly tens or even a few hundred C.
[0165] In certain embodiments, borate and/or phosphate salt(s) 102A
may complement and/or replace doping of anode active material
particles 110 with B and may achieve similar or complementary
effects with respect to reduction of the surface potential and
reactivity toward the electrolyte.
[0166] Some embodiments may include ball milling, under protective
atmosphere, anode active material particles 110 with nanoparticles
102A comprising B.sub.2O.sub.3 and/or P.sub.2O.sub.5. For example,
ball milling of oxo-borate salt with active material nanoparticles
(e.g. Li.sub.2B.sub.4O.sub.7 and Ge). In some embodiments, the ball
milled active material nanoparticles include tin, silicon,
germanium, lead and/or their alloys). The ball milling may enforce
surface reaction and coating of the anode material with
P.sub.2O.sub.5 and/or B.sub.2O.sub.3 layer 120 (102A)--to yield a
powder of modified anode material particles 110A and/or aggregate
thereof which are coated with B.sub.2O.sub.3 and/or P.sub.2O.sub.5.
Modified anode material particles 110A may be between 20-500 nm
(average diameter), and may be further milled in the presence of
carbon (e.g., graphite, graphene and the like) to form carbon
coating 120B and/or may be further milled in the presence of
transition metal oxide (e.g., Al.sub.2O.sub.3, TiO.sub.2,
ZrO.sub.2, MnO and the like) to form an oxide coating 120B of the
surface of modified anode material particles 110A coated with
B.sub.2O.sub.3 and/or P.sub.2O.sub.5 as layer 120A. Anode 100 may
be formed therefrom by processes 105 discussed above.
Composite Organic-Inorganic Coatings
[0167] FIG. 6 is a high level schematic illustration of composite
coating 120 comprising interconnected organic and inorganic
compounds, according to some embodiments of the invention. In the
illustrated non-limiting example, coating 120 may comprise a
combination of lithium borates (e.g., Li.sub.2B.sub.4O.sub.7) which
anchor (180A) coating layer 120 to anode active material 110, and
polymer molecules (180B) having electron rich groups (e.g.,
conjugated bonds, acidic groups, etc.) which provide, together with
lithium borates interconnecting the polymer molecules, ionic
conductivity paths 103 through coating layer 120 and have an ionic
conductivity which is much larger than electronic conductivity
(e.g., by one or few orders of magnitude). It is noted that lithium
borates and lithium phosphates 128 may in some embodiments be used
similarly to Li.sub.2B.sub.4O.sub.7, which is provided in FIG. 6 as
a non-limiting example.
[0168] Either or both the lithium borate molecules (and/or borate
and/or phosphate salts 128) and the polymer molecules may have
electron rich groups and may be pre-lithiated. Surface molecules
layer 120 may comprise multiple polymer layers interconnected by
lithium borates. Surface molecules layer 120 may effectively
protect anode active material 110 from reacting and decomposing the
solvent of electrolyte 85. Surface molecules layer 120 may bond
cations and/or anions of ionic liquid additive (see below) at its
top layer 180C. In certain embodiments, coating layer 120 may
comprise bonding molecules 180 (see below) comprising the lithium
borates and/or the polymer molecules configured to bind electrolyte
compound to provide electrolyte-buffering zone(s) during charging
and discharging of cell 150, as described below in more detail. The
lithium borates may be replaced by other inorganic compounds, such
as lithium phosphates disclosed above such as any of lithium
borates and/or phosphates 128 disclosed herein. The polymer
molecules may comprise any of the polymers disclosed above, in
operative configuration.
Composite Particles
[0169] FIG. 7A is a high level schematic illustration of core-shell
particle 115 with composite shell 120 in composite anode material
and its advantages, according to some embodiments of the
invention--with respect to prior art 80 illustrated schematically
in FIG. 7B. Core-shell particle 115 may be implemented as composite
anode material particles 115 disclosed herein, with anode material
particles 110 and/or 110A as cores and coating(s) 120 as
shells.
[0170] As prior art brittle coating 83 of anode active material
particles 81 cracks upon expansion of lithiated particles 81A due
to the mechanical strain, active material particles 81 lose
coatings 83A after the first charging cycles. In contrast,
core-shell particle 115 with composite shells 120 made of brittle
component 120A embedded in a flexible component 120B--maintain
cracked brittle coating 120A (cracking may occur during or after at
least one charging and discharging cycle) at the vicinity of
lithiated cores 110 (lithiation indicated schematically by
Li.sup..about.01) within flexible component 120B of shell 120.
Moreover, brittle component 120A is retained at the vicinity of
cores 110 during further cycles by flexible component 120B, and may
at least partially adhere to cores 110.
[0171] Finally, brittle component 120A may be selected to be a good
ionic conductor and thereby function as ionic conductive material
142 (illustrated in FIG. 8D below) to provide ion paths or gates
among core-shell particle 115 in anode 100, while flexible
component 120B may be selected to be a good electronic conductor
and thereby function as electronic conductive material 144
(illustrated in FIG. 8D below), as schematically required in FIG.
2B. For example, lithium titanate oxide (LTO) may be used as ionic
conductive brittle component 120A and polyaniline may be used as
electronic conducting flexible component 120B, forming conducting
elastic shell 120 with high electronic and ionic conductivity
encapsulating anode active material particles 110 to form
core-shell particles 115 as composite anode material. Flexible
component 120B may be re-enforced with conductive fibers 130, at
least some of which contact cores 110, as explained below.
[0172] In some embodiments, ionic conductive material 142 (FIG. 8D
below) may be at least partly embodied in brittle component 120A
embedded in a flexible component 120B (FIG. 7A). For example,
metalloid nanoparticles (as cores 110, or possibly cores made of
other materials, listed above) may be coated by a TiO.sub.2
precursor to form an amorphous TiO.sub.2 and/or possibly be
calcined or annealed to form TiO.sub.2 coating on the metalloid
nanoparticles, such as cores 110. The TiO.sub.2 may then undergo
lithiation with a lithium salt, followed by a second annealing (or
calcination), e.g., in air or in an inert atmosphere, to form the
lithium titanate oxide (LTO) coating 120A, which has fast anodic
kinetics. The particles may be coated again by elastic and
electronic conducting shell 120B which may comprise a layered
material and/or an organic polymer. When used as an electrode
material in lithium ion batteries, metalloid cores 110 expand,
breaking up LTO layer 120A, fragments 120A of which becoming
embedded in elastic shell 120B. As metalloid particle cores 110
expand, their surface presses up against LTO fragments 120A
embedded in elastic shell 120B to form an ionic conducting bridge
(as ionic conductive material 142) to encapsulated metalloid
particle cores 110, while elastic shell 120B maintains the
electronic connection (as electronic conductive material 144) to
cores 110. Advantageously, the suggested procedure results in
composite anode material with core-shell particles 115 that provide
good ionic and electronic conductivity and is mechanically robust
with respect to expansion and contraction 101 caused by lithiation
and de-lithiation processes. It is noted that cores 110 may be
metalloid and/or be made of other materials, listed above.
[0173] In a specific, non-limiting example, metalloid nanoparticles
(as cores 110) were dispersed in ethanol solution. A metalorganic
titanium precursor, e.g., titanium isopropoxide, was added as a
precursor for TiO.sub.2. The particles were coated in solution,
using ammonium hydroxide as a catalyst. The product was calcined in
air at 700.degree. C. to form the TiO.sub.2 coating. The particles
were again dispersed in ethanol and LiOH.2H.sub.2O was added. The
ethanol was evaporated and the particles were calcined again in air
at 700.degree. C. to form LTO-covered metalloid particles (having
cores 110 and brittle component 120A). The particles were dispersed
in a mixture of acidic water and ethanol along with aniline, and
then an ammonium persulfate acidic solution was added. After
polyaniline was formed a base was added until reaching pH of about
9. Particles 115 (having cores 110, brittle component 120A and the
polyaniline as flexible component 120B) were then dried and used to
prepare a slurry which was coated on a current collector and used
as an anode (see process 105 in FIG. 1B). Alternatively or
complementarily, polypyrrole-based flexible component 120B may be
prepared, using pyrrole monomers instead or in addition to the
aniline monomers, and adjusting the polymerization conditions.
Elements from procedures for preparing conductive coatings may be
incorporated in these embodiments as well.
[0174] In certain embodiments, with metalloid nanoparticles
comprising Sn or any other material which may oxidize in the
process disclosed above, formation of TiO.sub.2 may be carried out
at room temperature by dispersing the nanoparticles (e.g., Si--Sn
nanoparticles) in deionized water (DI) and adding them to a mixture
of boric acid and (NH.sub.4).sub.2TiF.sub.6, which after stirring
and cleaning in DI, may be followed by lithiation and optionally
annealing in argon atmosphere to avoid oxidation.
[0175] FIG. 7C is a high level schematic illustration of composite
anode material particles 115 with graphite shell 120, according to
some embodiments of the invention. Composite anode material
particles 115 may be prepared by milling 105A of anode material
particles 110 with graphite particles 120 to form graphite layer,
or shell 120 over anode material particles 110. An oxide layer 111
may cover at least part of the surface of anode material particles
110, and/or oxide layer 111 may be at least partly removed, as
taught in U.S. Pat. No. 9,406,927, which is incorporated herein by
reference in its entirety. In a non-limiting example, Ge anode
material particles 110 may be milled with 1-10% (of the overall
weight) graphite particles 120, in a non-limiting example with 2-3%
graphite particles 120 to yield graphite layer 120 1-5 nm thick
over Ge anode material particles 110. Advantageously, graphite
layer 120 may provide several benefits such as reduction of
agglomeration of composite anode material particles 115 and
reduction or prevention of contact between the electrolyte solvent
and the anode material.
[0176] FIG. 7D is a high level schematic illustration of composite
anode material particles 115 with porous graphite shell 120,
according to some embodiments of the invention. Graphite particles
121A may be milled (105B) with carbohydrate particles 121B such as
sugar crystals to yield graphite-sugar particles 121C (as a
non-limiting example for graphite-carbohydrate particles).
Non-limiting examples may comprise mixing (105B) graphite 121A and
sucrose 121B at 1:1 weight ratio, or between 3:7 and 8:2 weight
ratios (respectively).
[0177] Graphite-sugar particles 121C may then be milled (105A) with
anode material particles 110 to form graphite-sugar layer 121C over
anode material particles 110, having native oxide layer 111 over at
least part of the surface of anode material particles 110. Then, a
carbonization step 105C is carried out to form porous graphite
shell 120 and yield de-oxidized anode material particles with
composite porous carbon-graphite coating 115. It is emphasized that
illustrated process 105B, 105A, 105C may be carried out in dry
environment, avoiding agglomeration of composite anode material
particles 115.
[0178] Carbonization step 105C may be carried out at
600-900.degree. C. in neutral atmosphere (e.g., Ar, N, CO.sub.2,
and their mixtures) and be fine-tuned to carry out simultaneously
at least partial reduction of native oxide layer 111 and
evaporation of water and gasses from graphite-sugar layer 121C to
make graphite coating (or shell) 120 porous. For example,
carbonization step 105C may be configured for any of the following
reactions to take place. First, carbonization of the carbohydrate
component of graphite-sugar layer 121C occurs, namely
C.sub.m(H.sub.2O).sub.n.fwdarw.mC+nH.sub.2O (e.g., for sucrose,
C.sub.12H.sub.22O.sub.11.fwdarw.12C+11H.sub.2O), releasing water
vapor and leaving behind carbon and pores in graphite shell 120.
Second, multiple reduction reactions remove at least part of the
anode material native oxide, due to its interactions with carbon
and CO released by the carbonization of the carbohydrates and
interactions of the water vapor with carbon (for example, in the
non-limiting case of Ge with GeO.sub.2, GeO.sub.2+2C.fwdarw.Ge+2CO,
GeO.sub.2+2CO.fwdarw.Ge+2CO.sub.2,
GeO.sub.2+2H.sub.2.fwdarw.Ge+2H.sub.2O, with H.sub.2 formed by
C+2H.sub.2O.fwdarw.CO.sub.2+2H.sub.2 and so forth). Carbonization
step 105C may be configured to remove at least part of native oxide
layer 111, provide a predefined level of porosity in graphite shell
120 and strengthen the binding of graphite shell 120 to anode
material particle 110 by the multitude of reduction and other
reactions occurring in carbonization step 105C.
[0179] Advantageously, de-oxidized anode material particles with
porous graphite coating 115 provide multiple advantages, both in
anode operation aspects and with respect to anode preparation
processes 105.
[0180] In anode 100, porous graphite shell 120 may enhance ionic
conductivity, as lithium (e.g., Li.sup.+ and/or Li.sup..delta.+)
may diffuse at least partly through the formed pores, while
maintaining electronic conductivity through the graphite. Removal,
or partial removal, of native oxide layer 111 may further improve
ionic and electronic conductivity. Moreover, porous graphite shell
120 may be configured to stabilize anode material particles 110 and
possibly reduce their expansion 101 due to the mechanical stability
of porous graphite shell 120 and/or due to the stronger binding
between anode material particles 110 and porous graphite shell 120
which is formed during carbonization step 105C. Reduction of anode
material expansion increases the mechanical stability of anode 100
and its cycle lifetime. Moreover, porous graphite shell 120 may be
configured to regulate the formation of SEI in an advantageous way
such as on the surface of porous graphite shell 120 and away from
reactive anode material particles 110, thereby possibly reducing
lithium consumption in the SEI, providing some flexibility to the
formed SEI, and maintaining good ionic and/or electronic
conductivity of composite particles 115. In certain embodiments,
additional coatings such as polymer coatings and/or lithiated
coatings disclosed herein may be applied on top of porous graphite
shell 120 to further enhance any of these advantages and/or provide
buffering zone(s) 110B. In certain embodiments, porous graphite
shell 120 may be configured to provide at least part of buffering
zone(s) 110B.
[0181] With respect to anode preparation process 105, porous
graphite shell 120 may be configured to prevent aggregation of
composite particles 115, in the milling processes and particularly
when processed in water-based slurries, due to lower surface energy
thereof. Advantageously, composite particles 115 with porous
graphite shell 120 also exhibit less aggregation in organic
solvents, such as NMP (N-Methyl-2-pyrrolidone). Dry processes 105B,
105A, 105C provide fine powder composite particles 115, which is
beneficial for anode preparation process 105.
[0182] In any of the disclosed embodiments, electronic conductive
material and/or fibers 130 may extend to the surface of anode 100.
Electronic conductive material 130 may comprise electronic
conductive fibers and/or non-fibrous electronic conductive
material.
[0183] Cores 110 may comprise any of anode active material
particles 110, 110A disclosed above. Cores 110 may comprise
alloy-type materials such as any of single elements Sn, Si, Ge, Pb,
P, Sb, Bi, Al, Ga, Zn, Ag, Mg, As, In, Cd and Au, and/or mixtures
and/or alloys of these elements. In some embodiments, cores 110 may
comprise any of the above materials, mixed with a carbon
matrix.
[0184] Various pre-coatings 120 and coatings 130 may be applied to
core-shell particles 115 and/or anode 100, e.g., at least partially
filling gaps 140, coating shells 120 and/or coating regions of
anode 100. Example for various pre-coatings 120 and coatings 130
are disclosed above and may be implemented in this context.
Carbon-based material may be configured to form coatings 120 around
cores 110 and/or cores 110 may be embedded in carbon matrix forming
a composite structure. For example, carbon coatings may be applied
in a thickness range of 5 nm to 5 .mu.m, in a concentration range
of 5% to 95% of anode 100, and possibly be made of soft carbon,
hard carbon and/or graphitic carbon. In certain embodiments,
pre-coatings 120 and/or coatings materials 130 may be configured to
provide at least part of the shell material of shells 120.
[0185] Conductive fibers 130 may comprise carbon-based material,
such as specifically designed fibers e.g., carbon fibers and/or
carbon nanotubes, and/or carbon-based coating material which is
modified into conductive fibers 130 during preparation of anode
100. For example, conductive fibers 130 may comprise any of
nanofibers structures CNT (carbon nanotubes), carbon fibers and/or
graphene nano-sheets/plates structures at an amount in a range of
0.0001%-15% with respect to the total anode material, possibly
embedded, at least initially, in the carbon-based coating.
[0186] In certain embodiments, anode 100 may comprise weight ranges
of 50-95% active material, at least partly as core-shell particles
115, 1-40% of conductive fibers 130 (e.g., as conductive agent
material, possibly including coating material) and 1-40% of binder
material.
[0187] Advantageously, disclosed core-shell particles 115 and the
composite anode material enable use of metalloid (e.g., Si, Ge, Sn,
mixtures and/or alloys thereof) particles (or cores made of other
materials, listed above) as anode material, in spite of their lower
electronic conductivity and larger mechanical expansion upon
lithiation with respect to graphite as anode material, and thereby
enable taking advantage of their remarkably high capacity. In
particular, disclosed core-shell particles 115 and composite anode
material may be especially advantageous for fast charging lithium
ion cells, to accommodate the mechanical stresses and maintain high
electronic and ionic conductivities to metalloid cores 110 (or
cores made of other materials, listed above).
Conductive Fibers and Core-Shell Particles
[0188] In various embodiments, the anode material of anode 100 may
comprise composite anode material particles 115 which may be
configured as core shell particles, e.g., with anode material
particles 110 and/or 110A as cores and coating(s) 120 or parts
thereof as shells. Active material particles 110, possibly
pre-coated 120 (in one or more layers 120, e.g., by conductive
polymers, lithium polymers, etc., B.sub.2O.sub.3, P.sub.2O.sub.5,
etc.) and possibly with various nanoparticles (e.g., B.sub.4C, WC
etc.) 112 attached thereto, may provide at least part of cores 110
of core-shell particle 115, while shell 120 may be at least partly
be provided by coating(s) 120, and may be configured to provide a
gap 140 for anode active material 110 to expand 101 upon
lithiation. In some embodiments, gap 140 may be implemented by an
elastic or plastic filling material and/or by the flexibility of
coating(s) 120 which may extend as anode active material cores 110
expand (101) and thereby effectively provide room for expansion 101
(see e.g., high-level schematic illustration in FIG. 8D).
[0189] FIG. 8A is a high level schematic illustration of core-shell
particle 115, according to some embodiments of the invention.
Core-shell particle 115 comprises at least one core 110 and shell
120 which may be in direct contact and/or may be connected by
electronic conductive material 130 such as conductive fibers 130
(in non-limiting examples). One or more cores 110 are configured to
receive and release lithium ions (Li.sup.+) in the charging and
discharging process, respectively, and shell 120 is configured to
allow for, or accommodate core expansion 101 upon lithiation in
core 110 (see also FIG. 2B). Core(s) 110 may be separated from
shell(s) 120 by gap(s) 140 which may be voids, gaseous or at least
partly filled with compressible material such as a polymer material
or other mechanically compliant material. In some embodiments,
core(s) 110 may be in direct contact with respective shell(s) 120,
in some of the lithiation states of core(s) 110 and/or in some of
core-shell particle 115 in anode 100. Shell 120 is further
configured to enable and/or facilitate movement of lithium ions
(indicated schematically in a non-limiting manner by arrow 103) to
core(s) 110, e.g., have high ionic conductivity, while conductive
fibers 130 are configured to conduct electrons (indicated
schematically in a non-limiting manner by arrow 106) from core(s)
110 to shell 120, e.g., have high electronic conductivity. It is
noted that arrows 103, 106 denote lithium ion and electron movement
during charging of the respective lithium cell. Electronic
conductive material 130 (such as conductive fibers 130) may be
configured to form a network throughout anode material 100
(non-limiting examples for networks are illustrated in FIGS. 1B,
8A, 8C and 8F) and possibly interconnect cores 110 of many
core-shell particles 115 to provide conduction pathways between
particles 115 and enhance the electronic conductivity of anode
100.
[0190] In certain embodiments, shell 120 may be made of an ionic
conductive material having a high ionic conductivity only, without
electron conductivity, e.g., from an insulating material, while the
electronic conductivity is provided by electronic conductive
material 130 (such as conductive fibers 130, e.g., carbon fibers or
carbon nanotubes). Such configurations may vastly improve upon
prior art technology which would have required shell material and
structure to possess high conductivity for both electrons and ions.
The disclosed ability to provide the electronic conductivity by
electronic conductive material 130 opens up a large variety of
ionic conductors, including insulators, to be used as shell
material for shells 120. Thus, in certain embodiments, shells 120
are made of ionic conductors which are electronic insulators.
[0191] FIGS. 8B and 8C are high level schematic illustrations of
composite anode material 100 comprising a plurality of core-shell
particles 115, according to some embodiments of the invention. As
illustrated schematically in FIG. 8B, particles 115 and/or cores
110 may be interconnected by conductive fibers 130, which may
extend beyond shells 120. As illustrated schematically in FIG. 8C,
conductive fibers 130 may extend over a plurality of core-shell
particles 115, interconnecting their cores 110 along long distances
of multiple particles 115.
[0192] For example, cores 110 may be made of SnSi, shells 120 may
be made of carbon and conductive fibers 130 may comprise carbon
nanotubes, e.g., having diameters between 10-20 nm, and/or possibly
up to diameters in the order of magnitude of 100 nm and lengths
between 3 .mu.m and 100 .mu.m, and/or possibly down to lengths in
the order of magnitude of 100 nm. For example, conductive fibers
130 may be grown in a chemical vapor deposition (CVD) process,
e.g., using cores 110 as seeds. Cores 110 may comprise any of anode
active material particles 110 and/or any of anode active material
particles 110A disclosed above. Multiple types and/or sizes of
core-shell particles 115 may be used in preparing anode 100.
[0193] FIG. 8D is a high level schematic illustration of a
core-shell particle 115, according to some embodiments of the
invention. In certain embodiments, core(s) 110 and shell 120 of
core-shell particle 115 may be connected by ionic conductive
material 142 (ionic conductivity indicated schematically by arrow
103), by electronic conductive material 144 (electronic
conductivity indicated schematically by arrow 106, e.g., conductive
fibers 130), with mechanical elements or material (and/or gaps(s))
140 between core(s) 110 and shell 120 being empty or having
compliant material which allows for and/or accommodates mechanical
expansion of core(s) 110 (indicated schematically by arrow 101)
upon lithiation into core(s) 110. It is noted that arrows 103, 106
denote lithium ion and electron movement during charging of the
respective lithium cell.
[0194] FIG. 8E is a high level schematic illustration of composite
anode material 100 comprising a plurality of core-shell particles
115, according to some embodiments of the invention. As illustrated
schematically in FIG. 8E, at least some of shells 120 may comprise
multiple cores 110 which are interconnected by conductive fibers
130 and together form one or more layers of anode 100. Core-shell
particles 115 may extend to regions of anode 100 having assemblies
of interconnected cores 110 (interconnected by conductive fibers
130).
[0195] FIG. 8F is a high level schematic illustration of composite
anode material 100, according to some embodiments of the invention.
Composite anode material 100 may comprise extended shell 120,
possibly even single shell 120 per anode layer, having a large
plurality of cores 110, interconnected among themselves and with
shell 120 by conductive fibers 130.
[0196] Referring back to FIG. 7A it is noted that, in certain
embodiments, shells 120 may comprise composite material, such as a
brittle, ionic conductive component 120A embedded in a flexible,
electronic conductive component 120B, selected to accommodate
swelling and contraction (101) of core 110 upon lithiation and
de-lithiation, respectively. For example, the shell material may be
coated onto cores 110 prior to lithiation and expand with core
lithiation (at least during over or a few formation cycles, after
which shell 120 may remain expanded). Referring back to FIG. 7D it
is noted that, in certain embodiments, shells 120 may comprise
porous graphite 120.
Preparation Processes
[0197] Examples for preparation stages 105 of the anode material
may comprise milling and/or mixing processes. In non-limiting
examples, selected anode material(s) may be milled e.g., in a
high-energy ball-miller under protective atmosphere or
non-protective atmosphere to predefined average particle sizes,
e.g., by milling the anode material(s) with graphite powder and
using hardened alumina media agitated at e.g., at least at 650 RPM
(revolutions per minute), possibly at 1000-1500 RPM, e.g., 1100
RPM, 1200 RPM, 1300 RPM, 1500 RPM etc. for at least 45 hours,
possibly for 48 hours, 55 hours, 60 hours or more.
[0198] Various additives such as B, W, nanoparticles 112 etc. may
be introduced into the ball milling process at specified stages
thereof (for example, as WC or B.sub.4C nanoparticles), to reach
required particle sizes and aggregation levels, as disclosed
herein. Various alloys may be formed in the milling process, such
as any combinations of Si, C, B and W alloys.
[0199] Specific non-limiting examples for anode compositions may
comprise e.g., (in weight percentage from the total weight of the
anode): (i) 48% C, 30% Si, 5.5% B, 8.3% binder and 8.2% conductive
additives
(C.sub.0.48Si.sub.0.30B.sub.0.055Binder.sub.0.083ConductiveAditive.sub.0.-
082), with the as-milled C/Si/B alloy (active material particles)
comprising 57% C, 36% Si and 7% B weight percent of the total
weight of the alloy (C.sub.0.57Si.sub.0.36B.sub.0.07); (ii) 41.3%
C, 30.1% Si, 11.6% W, 8.4% binder and 8.6% conductive additives
(C.sub.0.413Si.sub.0.301W.sub.0.116Binder.sub.0.084ConductiveAditive.sub.-
0.086) with the as-milled C/Si/W alloy (active material particles)
comprising 50% C, 36% Si and 14% W in weight percentage of the
total weight of the alloy (C.sub.0.50Si.sub.0.36W.sub.0.14); (iii)
42% C, 30% Si, 5.0% B, 10.0% W, 10% binder and 3% conductive
additives
(C.sub.0.42Si.sub.0.3B.sub.0.05W.sub.0.1Binder.sub.0.1ConductiveAditive.s-
ub.0.03 with the as-milled C/Si/B/W alloy (active material
particles) comprising 48.3% C, 34.5% Si, 5.7% B and 10.5% W in
weight percentage of the total weight of the alloy
(C.sub.0.483Si.sub.0.345B.sub.0.057W.sub.0.105); (iv) 57% C, 30%
Si, 10% binder and 3% conductive additives
(C.sub.0.57Si.sub.0.3Binder.sub.0.1ConductiveAditive.sub.0.03) with
the as-milled C/Si alloy (active material particles) comprising 66%
C and 34% Si in weight percentage of the total weight of the alloy
(C.sub.0.66Si.sub.0.34); (v) 69% Ge, 3% C, 10% W, 5% B, 10% binder
and 3% conductive additives
(Ge.sub.0.69C.sub.0.03W.sub.0.10B.sub.0.050Binder.sub.0.1ConductiveAditiv-
e.sub.0.03) with the as-milled Ge/C/W/B alloy (active material
particles) comprising 79% Ge, 3% C, 12% W and 6% B weight percent
of the total weight of the alloy
(Ge.sub.0.79C.sub.0.03W.sub.0.12B.sub.0.06).
[0200] In certain embodiments, oxide layers (e.g., GeO.sub.2,
SiO.sub.2, Al.sub.2O.sub.3, SnO.sub.2) on anode material particles
110 may be removed during preparation processes 105 and possibly
followed by application of protective coating(s), disclosed e.g.,
above, which prevent oxidation and maintain electronic and ionic
conductivity. For example, removal of oxide layers (de-oxidation)
may be carried out by heating particle mixture(s) in a vacuum
atmosphere, e.g., before or after ball milling steps. In a
non-limiting example, de-oxidation may be carried out in a vacuum
atmosphere of 10.sup.-3-10.sup.-6 mbar for 60-100 hours (removing
formed gases such as CO) at a temperature of 150-350.degree. C.
Specific temperatures may be selected according to oxide bond
strengths, e.g., for Ge a temperature of 200.degree. C. may be
adequate to remove oxides without removing Ge; for Al a temperature
between 400-600.degree. C. may be adequate and for Sn to a
temperature between 600-900.degree. C. may be adequate remove
oxides. Borates and/or phosphates 128 may be introduced in the
de-oxidation stage to form B.sub.2O.sub.3/P.sub.2O.sub.5 oxide
layer(s) or nanocrystals to yield modified anode active material
particles 110A as disclosed above.
[0201] In certain embodiments, binder or additives 102, as well as
possibly coatings 130, 120 may be selected to de-oxidize and/or
contribute to de-oxidation of anode material particles 110. In
certain embodiments, alumina may be removed from Al anode material
particles 110 chemically, e.g., by immersing the aluminum particles
in a dilute solution (for example, 0.05M to 2M) of H.sub.2SO.sub.4
solution to form aluminum sulfate
(Al.sub.2O.sub.3+3H.sub.2SO.sub.4--.fwdarw.Al.sub.2(SO.sub.4).sub.3(aq)+3-
H.sub.2O), which can then be used to bond various molecules or
polymers as disclosed above, e.g., aqueous aluminum sulfate may be
aggressively stirred with a lithium polymer to form coating
120.
[0202] Examples for preparation stages 105 of coating(s) 120 may
comprise preparing lithium polymers by mixing 5 gr of PAA
(polyacrylic acid) solution (25% wt) with LiOH solution and with
415 mg of LiOH powder (lithium hydroxide anhydrous), dissolved by
adding 3.74 ml DI (distillated water) and stirring until clear
solution is reached and/or until complete chemical reaction is
achieved (e.g., overnight). In certain embodiments, the pH of the
resulting solution may be very basic, e.g., around 13. The Li-PAA
solution may then be transferred into evaporation glass according
to the solution volume, evaporated in Rotavapor evaporation glass
which is then dried in an oven, e.g., overnight at 120.degree. C.
The prepared Li-polymer may be placed in the ball miller together
with the anode material particles, which may possibly be coated
with B.sub.4C (e.g., any of particles 110, 110A, 115) and milled
together. A non-limiting example for a ball milling method may
include, milling 5% w/w lithium polymer powder with germanium (or
with germanium doped with B.sub.4C, and/or with Si, Sn, Al alloys
and mixtures thereof, possibly doped with B and/or W) for 6 h at
200 rpm. Details of the milling process may be configured to cause
the positively charged lithium of the lithium polymer salt to favor
the alloy anode material and to react the alloy anode material
surface to bind the negatively charged anion of the polymer to the
surface of particles 110, 110A, 115, leaving a partly charged
entity chemically bound to coating 120.
Cell Configurations
[0203] Complementarily or alternatively, electronical properties of
cell 150 may be configured to optimize the dynamic charge/discharge
and further reduce lithium ion accumulation at the interface. FIG.
9A-9C are high level schematic illustrations of cell configurations
150, according to some embodiments of the invention, compared with
prior art configurations 90 illustrated in FIG. 9D. In prior art
designs 90, the resistance of cell elements to the movement of
lithium ions is denoted R.sub.E for the resistance of electrolyte
85, R.sub.S for the resistance of a cell separator 86, and R.sub.A
for the resistance of anode material 95, and generally these
resistances are reduced to accommodate fast charging. According to
embodiments of the invention, cell configurations 150, as
illustrated e.g., in FIG. 9A, may comprise increasing a resistance
r.sub.E of a selected electrolyte 160 (and/or optionally a
resistance r.sub.S of a selected separator 152) to reduce the rate
at which lithium ions reach anode material particles 110 (here and
in the following, referring optionally to modified anode material
particles 110A and/or to composite anode material particles 115).
The increase may be selected to maintain resistance r.sub.E of
electrolyte 160 significantly lower than the resistance of anode
100 in order not to reduce the overall rate of lithium ion movement
from cathode 87 to anode 100, as the main limiting factor may be
the lithiation rate of the lithium ions in anode material particles
110. For example, the inventors have surprisingly found that
electrolytes 160 with higher resistance r.sub.E>R.sub.E may be
used in cells 150 to improve cell performance at high charging
rates. Moreover, as explained above, buffering zones 110B, 110C in
anode material particles 110 (shown schematically) may be
configured to regulate lithium ion lithiation process to be
gradual, e.g., by designing anode 100 to have an initial resistance
r.sub.A and resistances r''.sub.A, r'.sub.A of buffering zones
110B, 110C, respectively, which control lithium ion movements into
anode material particles 110 (e.g., into the lithiation zone)
according to the lithiation capacity of the anode material, to
prevent lithium accumulation and metallization at the SEI. Clearly,
resistance r.sub.E of electrolyte 160 may be selected to diminish
lithium ion accumulation at anode 100 to prevent metallization but
not too large, in order to still enable fast charging of anode 100
in cell 150. See also FIGS. 2A-2D above depicting ways to optimize
the resistances in cell 150, in which buffering zone(s) 110B, 110C
may correspond to buffering zone(s) 110B and/or coatings 120
illustrated therein.
[0204] As illustrated schematically in FIGS. 9B and 9C, lithium ion
cell 150 may comprise modified anode 100 and modified electrolyte
160 comprising up to 20%, up to 5%, and/or ca. 1% ionic liquid
additive(s) which may form a mobile SEI (e.g., in place of (static)
SEI 122, in addition to SEI 122 or in an interaction with SEI 122,
see FIG. 2D) on anode material particles 110, e.g., during
charging, as illustrated in FIG. 9B and disclosed above. The ionic
liquid additive(s) may comprise nitrogen-based ionic liquid(s) and
may be selected to have a melting temperature below 10.degree. C.,
below 0.degree. C. or below -4.degree. C., in certain embodiments
(see examples below).
[0205] Layer 120 may be part of anode material particles 110 or
coated thereupon (see examples for bonding molecules 180 as part of
coating 120, below), and bind at least a part of the ionic liquid
additive(s) to hold at least stationary portion 165A of the ionic
liquid additive(s) at the anode surface (FIG. 9C, leaving a mobile
portion 165B of the ionic liquid additive(s) in electrolyte 160) to
support the SEI, prevent decomposition of electrolyte 160 and
prevent lithium metallization on anode 100. Layer 120 of bonding
molecules 180 and/or layer 165A of bonded ionic liquid additive may
also provide some negative electric charge that partly reduces the
lithium ions, leaving them with a partial charge .delta..sup.+ and
preventing full reduction and metallization of lithium on the anode
surface, providing, supporting and/or complementing gradient 125
and/or the partial charge in buffering zone 110B (see FIGS. 2C,
2E-2G). Layer 120 of bonding molecules 180 and/or layer 165A of
bonded ionic liquid additive may be configured to support an
electric charge gradient 125 extending into electrolyte 160.
Bonding Molecules for Electrolyte-Based Buffering Zones
[0206] FIGS. 10A-10C and 11A-11C are high level schematic
illustrations of electrolyte-based buffering zone(s) 165 which may
be used in place or in addition to anode-based buffering zone(s)
110B disclosed above, according to some embodiments of the
invention. Coating 120 may be configured to support and stabilize
disclosed electrolyte-based buffering zones 165 during charging
and/or discharging of cells 150, and further enhance battery safety
by preventing metallization, preventing interaction between
electrolyte solvents and the anode material, and possibly improving
the operation of the lithium ion batteries by increasing the
reversibility of lithiation and/or increasing the coulombic
efficiency of cells 150. The following disclosure relates to anode
active material particles 110 in a non-limiting manner, and may be
equally applied in some embodiments to modified anode active
material particles 110A and/or to composite anode active material
particles 115 as described above.
[0207] In certain embodiments, electrolyte 85 may be replaced or
modified into an electrolyte 160 which comprises one or more ionic
liquid additive 163 having at least one type of cation 162 and at
least one kind of anion 161. For example, ionic liquid additive(s)
163 may comprise nitrogen-based ionic liquids and their
combinations: 1-butyl-1-methylpyrrolidinium as cation 162 and
bis(trifluoromethanesulfonyl)imide as anion 161;
1-butyl-6-methylimidazolium as cation 162 and
bis(trifluoromethanesulfonyl)imide as anion 161;
1-butyl-6-methylimidazolium as cation 162 and
bis(fluorosulfonyl)imide as anion 161;
N,N-Diethyl-N-methyl-N-propylammonium as cation 162 and
bis(fluorosulfonyl)imide as anion 161; and
N-propyl-N-methylpiperidinium as cation 162 and
bis(trifluoromethanesulfonyl)imide as anion 161. Certain
embodiments comprise nitrogen-based ionic liquids which are derived
from these combinations, e.g., having various substituents. In
certain embodiments, ionic liquid additive(s) 163 may be configured
for use at room temperature, have a negligible vapor pressure, a
wide electrochemical potential window (e.g., up to 5.0 V in
nitrogen-based ionic liquids), and structural stability across a
large temperature range (e.g., down to any of 20.degree. C.,
10.degree. C., 0.degree. C. or lower, and up to one or several
hundred .degree. C.). Ionic liquid additive(s) 163 may contribute
to formation of at least one electrolyte-buffering zone 165 in
electrolyte 160, at the interface of electrolyte 160 and anode
material 110 and/or coating 120, which further prevents contact
between the solvent(s) of the electrolyte and reactive anode
material 110, while maintaining required lithium ion conductivity
between electrolyte 160 and anode material 110. In certain
embodiments, coating 120 may comprise bonding molecules 180 which
bind at least some of cations 162 and/or anions 161 of ionic liquid
additive(s) 163 to stabilize electrolyte-buffering zone(s) 165
during charging and discharging of cell 150. Non-limiting examples
for bonding molecules 180 are provided below.
[0208] In certain embodiments, coating layer 120 may comprise
bonding molecules 180 in a structure as illustrated in FIG. 6,
configured to bind at least some of cations 162 and/or anions 161
of ionic liquid additive(s) 163 to stabilize electrolyte-buffering
zone(s) 165 during charging and discharging of cell 150.
[0209] FIG. 10A schematically illustrates at least one
electrolyte-buffering zone 165 in an electrolyte 160, according to
some embodiments of the invention. Electrolyte-buffering zone(s)
165 is illustrated schematically as an accumulation of anions 161
and cations 162, which provides additional separation between
electrolyte 160 and anode active material particles 110 and may be
configured to further regulate lithium ion movement between
electrolyte 160 and anode active material particles 110. For
example, anions 161 and/or cations 162 may be relatively large,
e.g., larger than lithium ions 91 and/or significantly larger than
lithium ions 91 to establish a gradient in physical and/or chemical
characteristics in region 165 and possibly provide an interphase
transition between electrolyte 160 and anode active material
particles 110 that enhances the stabilization of transition region
and prevents lithium ion accumulation and/or metallization and
dendrite growth. Anions 161 may be selected to provide negative
electric charge in the region of lithium ions 91 moving towards
anode active material particles 110, which somewhat, yet not fully,
reduces the positive charge of lithium ions 91 to 6+(e.g., by
physical proximity and not by a chemical bond).
[0210] In certain embodiments, electrolyte 160 may comprise an
ionic liquid additive 163 added to prior art electrolyte 85 (e.g.,
at 20%, 10%, 5% or any other volume part of electrolyte 160), which
is selected to at least partially provide anions 161 and/or cations
162 to build electrolyte-buffering zone(s) 165. For example, ionic
liquid additive 163 may comprise acidic groups which are selected
to be anionic in the environment of lithium ions 91. Anions 161
and/or cations 162 may be relatively large to form a barrier which
reduces the approaching speed of lithium ions 91 and locally
increases the resistance of buffering zone(s) 165 to lithium ions
91 to prevent or attenuate accumulation of lithium ions 91 at the
surface of anode active material particles 110 (see e.g., r.sub.A
in FIG. 9A) and/or achieve any of the effects disclosed below.
[0211] FIG. 10B schematically illustrates at least one
electrolyte-buffering zone 165 (MSEI) in an electrolyte 160, which
is configured to provide a mobility and charge gradient 125
(indicated schematically by the tapered arrows) having surrounding
electric charge 126 (illustrated schematically as a non-specific
symbol), according to some embodiments of the invention. Mobility
and charge gradient 125 reduces and slows lithium ions 91 entering
zone 165 in a gradual manner (indicated schematically by
Li.sup..delta.+, with the partial charge of the lithium ions
changing gradually within zone 165) until they reach lithiation in
the anode active material. Gradient 125 enables modification of the
interface (the area where the two immiscible phase surfaces of
anode and electrolyte come into contact with each other) into an
interphase region 165 having a gradual change of parameters which
gradually reduces the activation energy of the reduction reaction
of the lithium ions, and further prevents metallization of lithium
and dendrite growth. MSEI zone 165 helps smoothen the lithium ion
transport into the active material for full reduction and
intercalation (to Li.sup..about.01). The resulting ionic liquid
layer 165 reduces the probability of both lithium metallization and
de-composition of the organic solvent (electrolyte 85) at the
metalloid-lithium surface. Once the electrical field stops (e.g.,
at the end or interruption of the charging), ionic liquid 163 may
slowly diffuse to form homogenous electrolyte 160. It is explicitly
noted, however, that ionic liquid additive 163 may be used in cells
having metalloid-based and/or graphite-based anodes (either option
possibly coated and/or pre-coated).
[0212] FIG. 10C schematically illustrates at least one
electrolyte-buffering zone 165 (MSEI) in an electrolyte 160,
according to some embodiments of the invention.
Electrolyte-buffering zone(s) 165 may be configured to fill in
possible cracks 124 appearing in composite anode material particles
115, e.g., due to cracking of any of coating 120, anode buffering
zone 110B, or SEI layer 122 (see FIGS. 2B-2F) upon expansion and
contraction 101 of anode material particles 110.
[0213] Filling cracks 124 may prevent renewed contact between the
anode active material and/or metal lithium and electrolyte 85 due
to exposure of the anode active material (e.g., when coating 120 is
cracked) or due to the increase in the surface area available for
such contact due to cracks 124. Electrolyte-buffering zone(s) 165
thus prevent further electrolyte decomposition, prevent further SEI
growth and thickening, and block possible sites for lithium
metallization from solvents of electrolyte 85. Ionic liquid
additive 163 may be configured to fill in such cracks 124
(illustrated schematically in FIG. 10C) once an electric field is
applied, or possibly also after the electric field is applied, to
reduce the extent of, or prevent, cracks 124 from enhancing
electrolyte decomposition and lithium metallization. Ionic liquid
additive 163 may be configured to fill in cracks or uncoated
surface areas as explained above, including possible exposed
surfaces in the coating resulting from expansion and contraction
101 during cell cycles. Bonding molecules 180 of any of the
disclosed types may be incorporated in coating(s) 120 and/or in
coating(s) 130 and be configured to be present in cracks 124 to
bond with cations 162 and/or anions 161 of ionic liquid additive
163 and achieve the crack filling and anode active material
protection described above.
[0214] FIG. 11A is a high level schematic illustration of bonding
molecules 180 forming a surface molecules layer 120C at least as
part of coating 120 on anode 100 and/or on anode active material
particles 110, according to some embodiments of the invention. It
is emphasized that FIG. 11A is highly schematic and represents
principles for selecting bonding molecules 180, according to some
embodiments of the invention. Actual bonding molecules 180 may be
selected according to requirements, e.g., from bonding molecules
180 represented by any one of formulas I-VII (detailed below),
under any of their embodiments. The surface molecules layer may be
part of coating 120 and/or associate or bonded thereto.
[0215] Surface molecules layer 120C may be configured to prevent
contact of electrolyte solvent (of electrolyte 85) with anode
active material 110, e.g., through steric hindrance by molecules
180. Non-limiting examples are embodiments represented e.g., by
formulas II, IV and V, among others, such as the non-limiting
examples lithium 3,5-dicarboxybenzenesulfonate, lithium
2,6-di-tert-butylbenzene-1,4-disulfonate,
3,3'-((1,2-dithiane-4,5-diyl)bis(oxy))bis(N-hydroxypropanamide),
3,3'-((4-mercapto-1,2-phenylene)bis(oxy))bis(N-hydroxypropanamide),
etc.
[0216] Molecules 180 may be selected and attached onto anode active
material 110 in a way that forms a mechanical and/or electrostatic
barrier towards electrolyte solvent and prevents it from reaching
and interacting with anode active material 110. Bonding molecules
180 may be selected to have electron rich groups that provide
mobile electric charge on the surface of molecules layer 120C.
Non-limiting examples are embodiments represented e.g., by formulas
II, and IV-VII, having conjugated double bonds, acidic groups and
benzene groups, among others, such as the non-limiting examples
lithium 4-methylbenzenesulfonate, lithium
3,5-dicarboxybenzenesulfonate, lithium
2,6-dimethylbenzene-1,4-disulfonate,
3,3'-((1,2-dithiane-4,5-diyl)bis(oxy))bis(N-hydroxypropanamide),
3,3'-((4-mercapto-1,2-phenylene)bis(oxy))bis(N hydroxypropanamide),
lithium aniline sulfonate, poly(lithium-4-styrenesulfonate)
etc.
[0217] For example, bonding molecules 180 may be selected to have a
width W (anchored in anode 100 and/or anode active material
particles 110) of up to three benzene rings and a length L
(protruding into electrolyte 160) of up to four benzene rings, as
exemplified in a non-limiting manner in embodiments represented
e.g., by formulas II and VII having bicyclic or tricyclic
structures, e.g., anthracene-based structures and/or in embodiments
represented e.g., by formulas IV and V.
[0218] In some embodiments, bonding molecules 180 may comprise an
anode material anchoring part 180A, configured to bind to or be
associated with anode active material 110, e.g., via lithium,
thiols, or other functional groups in bonding molecules 180. In
some embodiments, anode material anchoring part 180A may be
pre-lithiated exemplified in a non-limiting manner in embodiments
represented by any of formulas I-VII which include lithium, such as
the non-limiting examples illustrated in FIG. 11D. FIG. 11D is a
high level schematic illustration of non-limiting examples for
bonding molecules 180, according to some embodiments of the
invention.
[0219] In some embodiments, bonding molecules 180 may comprise an
ionic conductive part 180B having an ionic conductivity which is
much higher than its electronic conductivity, e.g., by one, two,
three or more orders of magnitude. Ionic conductive part 180B may
extend through most or all of length L of bonding molecules 180 and
provide a conductivity path 103 (illustrated schematically) for
lithium ions 91 moving back and forth between electrolyte 160 and
anode 110 during charging and discharging cycles. Conductivity
paths 103 may be provided e.g., by conjugated double bonds, acidic
groups, benzene rings, carbon-fluorine bonds, charged functional
groups etc. which are disclosed above. For example, the charge
distribution on bonding molecules 180 may be selected to be mobile
and support lithium ion movement across molecules layer 120C,
possibly reducing the charge of the lithium ion to Li.sup..delta.+
as explained above, to prevent metallization on the surface of
anode 110. Partial charge reduction may be carried out by electron
rich groups such as aromatic groups and acidic groups disclosed
above.
[0220] In some embodiments, bonding molecules 180 may comprise a
top, ionic liquid binding part 180C configured to bind cations 162
and/or anions 161 of ionic liquid additive 163 in electrolyte 160.
For example, embodiments represented by any of formulas I-VII which
involve charged and/or polar functional groups may provide top,
ionic liquid binding part 180C, e.g., lithium
3,5-dicarboxybenzenesulfonate, lithium sulfate, lithium phosphate,
lithium phosphate monobasic, lithium trifluoromethanesulfonate,
lithium
1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonate,
lithium 2,6-dimethylbenzene-1,4-disulfonate, lithium
2,6-di-tert-butylbenzene-1,4-disulfonate,
3,3'-((1,2-dithiane-4,5-diyl)bis(oxy))bis(N-hydroxypropanamide),
3,3'-((4-mercapto-1,2-phenylene)bis(oxy))bis(N-hydroxypropanamide),
lithium aniline sulfonate (the sulfonate may be in any of para,
meta and ortho positions) as well as
poly(lithium-4-styrenesulfonate), as some non-limiting examples.
Ionic liquid binding part 180C may be further configured to
stabilize electrolyte-buffering zone(s) 165 as described above.
[0221] FIGS. 11B and 11C are high level schematic illustrations of
an immobilized/mobilized SEI (I/MSEI) during charging and
discharging, according to some embodiments of the invention. In
certain embodiments, surface functionalization of the anode active
material may enhance the functionality of MSEI 165, e.g., by
increasing the affinity of ionic liquid additive 163 to the active
material--electrolyte interface, and protecting the interface
further more from direct interaction with the organic solvent (of
electrolyte 85). Surface functionalization may be applied by anode
coatings 130 and/or by anode material particle pre-coatings 120
and/or by additional modifications of the surface of anode 100
(e.g., of anode material particles 110) and/or of the active
material on the anode surface. For example, chemically bonded layer
120C of bonding molecules 180 (possibly as part of coating 120)
such as large volume salt(s) on the active material surface may be
used to keep some of ionic liquid 163 on the surface and reduce the
probability of the organic solvent de-composition prior to the MSEI
re-arrangement at the interface. FIGS. 11B and 11C schematically
illustrate this effect by the retainment of at least some of
cations 162 bonded to the surface even when cell 150 is not
charged. FIGS. 11B and 11C schematically illustrate anode material
particles 110 during charging and discharging (or no charging) with
ionic liquid additive 163 building MSEI 165 in the charging state,
which may comprise an immobilized section 165A and a mobile section
165B, the former remaining in the discharging state, bonded or
associated with anode surface while the latter return into
electrolyte 160 in the discharging state. Coating 120 may comprise
layer 120C in which bonding molecules 180 are associated with anode
material particle coating 120 and/or attached to anode 100,
possibly as coating 130. Cations 162C and possibly anions 161C
which stay bonded to bonding molecules 180 (immobilized section
165A of ionic liquid additive 163) are denoted differently from
cations 162B and anions 161B which stay in electrolyte 160 (mobile
section 165B of ionic liquid additive 163), to illustrate that a
part (or possibly all) of electrolyte additive 163 is immobilized
onto layer 120C of anode material particle 110 during operation of
cell 150. Immobilized layer 165A at the interface may have a better
affinity to ionic liquid 163 and less affinity toward organic
solvent of electrolyte 85, and therefore keep the organic solvent
away from the interface and reduce the probability for its
de-composition.
[0222] In some embodiments, the bonding of ions of ionic liquid
additive(s) 163 may involve bonding cations 162 or possibly anions
161 by bonding molecules 180 as the layer closest to the surface of
anode active material particles 110. The bonding may be carried out
during one or more first charging and discharging cycles of cell
150. In certain embodiments, the bonding of cations 162 and/or
anions 161 may be carried out, at least partially, on active
material particles 110 themselves, even before the first charging
cycle. The bonding of ionic liquid additive 163 to bonding layer
120C of coating 120 may be electrostatic and/or salt-like (ionic).
In certain embodiments, the bonding may be at least partly
covalent. The bonding may involve any number of ionic layers,
typically a few layers, possibly providing a salt layer which
isolates the organic solvent used for electrolyte 85 at least from
active material 110 of anode 100.
[0223] Bonding molecules 180 may be ionic or have electron rich
groups such as sodium aniline sulfonate. Bonding molecules 180 may
comprise lithium cations and/or possibly magnesium cations, the
latter possibly when the anode material is graphite. In case of
aluminum as anode material, bonding molecules 180 may comprise
lithium cations and/or aluminum cations. The lithium in the
following examples may thus be replaced in some embodiments by
magnesium and/or aluminum. In case of graphite anodes, a wide range
of activation techniques which yield oxidized graphite may be used
to enhance chemical bonding of molecules 180 (e.g., using halides
or alkoxides).
[0224] Non-limiting examples for bonding molecules 180 comprise
lithium alkylsulfonate, poly(lithium alkylsulfonate), lithium
sulfate, lithium phosphate, lithium phosphate monobasic,
alkylhydroxamate salts and their acidic forms (e.g., lithium
sulfonic acid, LiHSO.sub.4, instead of lithium sulfonate,
Li.sub.2SO.sub.4). The chemical bonding of molecules 180 to anode
100 (e.g., to anode material particles 110) may be carried out, for
example, in the anode slurry solution and/or in dry ball milling
with anode material particles (in process 105). The bonding
mechanism may comprise, e.g., reaction(s) of the lithium sulfonates
and/or salts with metal oxides, releasing the oxide and creating a
direct chemical bond to the anode material (e.g., Si, Ge, Sn, Al,
mixture and alloys thereof) surface of anode material particles
110, where the lithium cation remain partly charged
(Li.sup..delta.+) in the anode material. For example, using a large
volume salt with an additional anion group as bonding molecules 180
may create a salt surface 120C on anode active material particles
110, which can both protect the interface and co-operate with ionic
liquid additive 163 in electrolyte 160. Layer 120C may bind a
stationary portion of ionic liquid additive 163 on the surface of
anode active material particles 110 while the rest of ionic liquid
additive 163 is mobilized in electrolyte 160, providing a hybrid
ionic liquid additive which is partly bonded and partly free in
electrolyte 160. Stationary portion 165A may increase the
re-ordering rate of ionic liquid additive 163 on the surface during
charging, help repel organic electrolyte 85 from the interface and
hence reduce the probability for the de-composition of the organic
solvent. Non-limiting examples for bonding molecules 180 include
large anionic salts or their acids which may be selected to
sterically repel the smaller organic carbonates solvents (of
electrolyte 85) from the active material surface. Layer 120C and
stationary portion 165A of ionic liquid additive 163 on surface of
anode active material particles 110 may be highly effective during
the initial charging, and enable or support the building of a
stable SEI during the formation cycle(s) which protects the surface
of anode active material particles 110 and of anode 100 during
later operation, and prevent decomposition of electrolyte on anode
100 as well as lithium metallization thereupon.
[0225] The resulting SEI may be modified toward enhanced stability
and be possibly provided with self-healing mechanisms through layer
120C and stationary portion 165A of ionic liquid additive 163.
[0226] Non-limiting examples for bonding molecules 180 include any
of the following, illustrated below: lithium
4-methylbenzenesulfonate, lithium 3,5-dicarboxybenzenesulfonate,
lithium sulfate, lithium phosphate, lithium phosphate monobasic,
lithium trifluoromethanesulfonate, lithium
4-dodecylbenzenesulfonate, lithium propane-1-sulfonate, lithium
1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-heptadecafluorooctane-1-sulfonate,
lithium 2,6-dimethylbenzene-1,4-disulfonate, lithium
2,6-di-tert-butylbenzene-1,4-disulfonate,
3,3'4(1,2-dithiane-4,5-diyl)bis(oxy))bis(N-hydroxypropanamide),
3,3'-((4-mercapto-1,2-phenylene)bis(oxy))bis(N hydroxypropanamide),
lithium aniline sulfonate (the sulfonate may be in any of para,
meta and ortho positions) as well as
poly(lithium-4-styrenesulfonate) applied in coating the anode
material particles as disclosed herein. It is noted that in cases
of coatings that contain lithium (e.g., metallic lithium), ionic
liquid additive(s) 163 may be selected to be non-reactive toward
it.
[0227] For example, various coatings of the anode active material
may be used to bond or enhance bonding of molecules 180 to anode
material 110, as disclosed above. The size(s) of molecules 180 may
be selected to provide good lithium ion conductivity therethrough.
In certain embodiments, molecules 180 may be selected (e.g., some
of the disclosed salts) to form channels configured to enable fast
lithium ion movement therethrough.
[0228] In a more generalized sense, bonding molecules 180 may be
selected from any of the following sets of molecules, according to
Formulas I-IV.
[0229] In some embodiments, surface layer 120C may comprise bonding
molecules 180 represented by the structure of formula I:
##STR00001##
wherein: each Z is independently selected from aryl,
heterocycloalkyl, crown etheryl, cyclamyl, cyclenyl,
1,4,7-Triazacyclononanyl, hexacyclenyl, cryptandyl, naphtalenyl,
anthracenyl, phenantrenyl, tetracenyl, chrysenyl, triphenylenyl
pyrenyl and pentacenyl; R.sup.1 is
[C(L.sup.1).sub.2].sub.q.sup.1-R.sup.101; each L.sup.1 is
independently selected from H, F and R.sup.101; R.sup.2, R.sup.3,
R.sup.4, R.sup.5, R.sup.6 and R.sup.101 are each independently
selected from CO.sub.2H, CO.sub.2M.sup.1, CO.sub.2R, SO.sub.3H,
SO.sub.3M.sup.1, PO.sub.3H.sub.2, PO.sub.3M.sup.1.sub.2,
PO.sub.3M.sup.1H, PO.sub.4H.sub.2, PO.sub.4M.sup.1.sub.2,
PO.sub.4M.sup.1H, PO.sub.4M.sup.2, C(O)NHOH, NH.sub.2, NHR,
N(R).sub.2, NO.sub.2, COOR, CHO, CH.sub.2OH, OH, OR, SH, SR,
C(O)N(R).sub.2, C(O)NHR, C(O)NH.sub.2, halide, tosylate, mesylate,
SO.sub.2NHR, triflate, isocyanate, cyanate, thiocyanate,
isothiocyanate, R, cyano, CF.sub.3, and Si(OR).sub.3; each R is
independently selected from methyl, ethyl, isopropyl, n-propyl,
alkyl, haloalkyl, cycloalkyl, heterocycloalkyl, aryl, and benzyl;
each M.sup.1 is independently Li, Na, K, Rb or Cs; each M.sup.2 is
independently Be, Mg, Ca, Sr or Ba; T.sup.1 and T.sup.2 are each
independently absent, or selected from H, CO.sub.2H,
CO.sub.2M.sup.1, CO.sub.2R, SO.sub.3H, SO.sub.3M.sup.1,
PO.sub.3H.sub.2, PO.sub.3M.sup.1.sub.2, PO.sub.3M.sup.1H,
PO.sub.4H.sub.2, PO.sub.4M.sup.1.sub.2, PO.sub.4M.sup.1H,
PO.sub.4M.sup.2, C(O)NHOH, NH.sub.2, NHR, N(R).sub.2, NO.sub.2,
COOR, CHO, CH.sub.2OH, OH, OR, SH, SR, C(O)N(R).sub.2, C(O)NHR,
C(O)NH.sub.2, halide, tosylate, mesylate, SO.sub.2NHR, triflate,
isocyanate, cyanate, thiocyanate, isothiocyanate, R, cyano,
CF.sub.3, and Si(OR).sub.3; m.sup.1, m.sup.2, m.sup.3, m.sup.4,
m.sup.5, and m.sup.6 are each independently an integer between 0-6;
n.sup.1 is an integer between 1-10; q.sup.1 is an integer between
0-10; and Z is connected to any of R.sup.1-R.sup.6, T.sup.1-T.sup.2
or to any neighboring repeating unit in any possible substitution
position and via one or more atoms.
[0230] In some embodiments, surface layer 120C may comprise bonding
molecules 180 represented by the structure of formula II:
##STR00002##
wherein: R.sup.7 is [C(L.sup.2).sub.2].sub.q.sup.2-R.sup.102; each
L.sup.2 is independently selected from H, F and R.sup.102; R.sup.8,
R.sup.9, R.sup.10, R.sup.11, R.sup.12 and R.sup.102 are each
independently selected from CO.sub.2H, CO.sub.2M.sup.1, CO.sub.2R,
SO.sub.3H, SO.sub.3M.sup.1, PO.sub.3H.sub.2, PO.sub.3M.sup.1.sub.2,
PO.sub.3M.sup.1H, PO.sub.4H.sub.2, PO.sub.4M.sup.1.sub.2,
PO.sub.4M.sup.1H, PO.sub.4M.sup.2, C(O)NHOH, NH.sub.2, NHR,
N(R).sub.2, NO.sub.2, COOR, CHO, CH.sub.2OH, OH, OR, SH, SR,
C(O)N(R).sub.2, C(O)NHR, C(O)NH.sub.2, halide, tosylate, mesylate,
SO.sub.2NHR, triflate, isocyanate, cyanate, thiocyanate,
isothiocyanate, R, cyano and Si(OR).sub.3; each R is independently
selected from methyl, ethyl, isopropyl, n-propyl, alkyl, haloalkyl,
cycloalkyl, heterocycloalkyl, aryl, and benzyl; each M.sup.1 is
independently Li, Na, K, Rb or Cs; each M.sup.2 is independently
Be, Mg, Ca, Sr or Ba; m.sup.7, m.sup.8, m.sup.9, m.sup.10, m.sup.11
and m.sup.12 are each independently an integer between 0-6; and
q.sup.2 is an integer between 0-10.
[0231] In some embodiments, surface layer 120C may comprise bonding
molecules 180 represented by the structure formula III:
(L.sup.3).sub.3C--R.sup.103 (III)
wherein: R.sup.103 is [C(L.sup.4).sub.2].sub.q.sup.3-R.sup.105;
each L.sup.3 is independently selected from H, F and R.sup.104;
each L.sup.4 is independently selected from H, F and R.sup.106;
R.sup.104, R.sup.105, and R.sup.106 are each independently selected
from CO.sub.2H, CO.sub.2M.sup.1, CO.sub.2R, SO.sub.3H,
SO.sub.3M.sup.1, PO.sub.3H.sub.2, PO.sub.3M.sup.1.sub.2,
PO.sub.3M.sup.1H, PO.sub.4H.sub.2, PO.sub.4M.sup.1.sub.2,
PO.sub.4M.sup.1H, PO.sub.4M.sup.2, C(O)NHOH, NH.sub.2, NHR,
N(R).sub.2, NO.sub.2, COOR, CHO, CH.sub.2OH, OH, OR, SH, SR,
C(O)N(R).sub.2, C(O)NHR, C(O)NH.sub.2, halide, tosylate, mesylate,
SO.sub.2NHR, triflate, isocyanate, cyanate, thiocyanate,
isothiocyanate, R, cyano, CF.sub.3 and Si(OR).sub.3; each R is
independently selected from methyl, ethyl, isopropyl, n-propyl,
alkyl, haloalkyl, cycloalkyl, heterocycloalkyl, aryl, or benzyl;
each M.sup.1 is independently Li, Na, K, Rb or Cs; each M.sup.2 is
independently Be, Mg, Ca, Sr or Ba; and q.sup.3 is an integer
between 0-10.
[0232] In some embodiments, surface layer 120C may comprise bonding
molecules 180 represented by the structure of formula IV:
##STR00003##
wherein: X.sup.1 and X.sup.2 are each independently selected from
S, O and CH.sub.2; R.sup.13 and R.sup.14 are each independently
selected from CO.sub.2H, CO.sub.2M.sup.1, CO.sub.2R, SO.sub.3H,
SO.sub.3M.sup.1, PO.sub.3H.sub.2, PO.sub.3M.sup.1.sub.2,
PO.sub.3M.sup.1H, PO.sub.4H.sub.2, PO.sub.4M.sup.1.sub.2,
PO.sub.4M.sup.1H, PO.sub.4M.sup.2, C(O)NHOH, NH.sub.2, NHR,
N(R).sub.2, NO.sub.2, COOR, CHO, CH.sub.2OH, OH, OR, SH, SR,
C(O)N(R).sub.2, C(O)NHR, C(O)NH.sub.2, halide, tosylate, mesylate,
SO.sub.2NHR, triflate, isocyanate, cyanate, thiocyanate,
isothiocyanate, R, cyano, CF.sub.3 and Si(OR).sub.3; each M.sup.1
is independently Li, Na, K, Rb or Cs; each M.sup.2 is independently
Be, Mg, Ca, Sr or Ba; each R is independently selected from methyl,
ethyl, isopropyl, n-propyl, alkyl, haloalkyl, cycloalkyl,
heterocycloalkyl, aryl, or benzyl; and n.sup.2, n.sup.3, n.sup.4
and n.sup.5 are each independently an integer between 0-10.
[0233] In some embodiments, surface layer 120C may comprise bonding
molecules 180 represented by the structure of formula V:
##STR00004##
wherein: X.sup.3 and X.sup.4 are each independently selected from
S, O and CH.sub.2; R.sup.15 and R.sup.16 are each independently
selected from CO.sub.2H, CO.sub.2M.sup.1, CO.sub.2R, SO.sub.3H,
SO.sub.3M.sup.1, PO.sub.3H.sub.2, PO.sub.3M.sup.1.sub.2,
PO.sub.3M.sup.1H, PO.sub.4H.sub.2, PO.sub.4M.sup.1.sub.2,
PO.sub.4M.sup.1H, PO.sub.4M.sup.2, C(O)NHOH, NH.sub.2, NHR,
N(R).sub.2, NO.sub.2, COOR, CHO, CH.sub.2OH, OH, OR, SH, SR,
C(O)N(R).sub.2, C(O)NHR, C(O)NH.sub.2, halide, tosylate, mesylate,
SO.sub.2NHR, triflate, isocyanate, cyanate, thiocyanate,
isothiocyanate, R, cyano, CF.sub.3 and Si(OR).sub.3; each M.sup.1
is independently Li, Na, K, Rb or Cs; each M.sup.2 is independently
Be, Mg, Ca, Sr or Ba; each R is independently selected from methyl,
ethyl, isopropyl, n-propyl, alkyl, haloalkyl, cycloalkyl,
heterocycloalkyl, aryl, or benzyl; and n.sup.6, and n.sup.7 are
each independently an integer between 0-10.
[0234] In some embodiments, surface layer 120C may comprise bonding
molecules 180 represented by the structure of formula VI:
##STR00005##
wherein: each R.sup.17 is independently selected from CO.sub.2H,
CO.sub.2M.sup.1, CO.sub.2R, SO.sub.3H, SO.sub.3M.sup.1,
PO.sub.3H.sub.2, PO.sub.3M.sup.1.sub.2, PO.sub.3M.sup.1H,
PO.sub.4H.sub.2, PO.sub.4M.sup.1.sub.2, PO.sub.4M.sup.1H,
PO.sub.4M.sup.2, C(O)NHOH, NH.sub.2, NHR, N(R).sub.2, NO.sub.2,
COOR, CHO, CH.sub.2OH, OH, OR, SH, SR, C(O)N(R).sub.2, C(O)NHR,
C(O)NH.sub.2, halide, tosylate, mesylate, SO.sub.2NHR, triflate,
isocyanate, cyanate, thiocyanate, isothiocyanate, R, cyano,
CF.sub.3 and Si(OR).sub.3; T.sup.3 and T.sup.4 are each
independently selected from H, CO.sub.2H, CO.sub.2M.sup.1,
CO.sub.2R, SO.sub.3H, SO.sub.3M.sup.1, PO.sub.3H.sub.2,
PO.sub.3M.sup.1.sub.2, PO.sub.3M.sup.1H, PO.sub.4H.sub.2,
PO.sub.4M.sup.1.sub.2, PO.sub.4M.sup.1H, PO.sub.4M.sup.2, C(O)NHOH,
NH.sub.2, NHR, N(R).sub.2, NO.sub.2, COOR, CHO, CH.sub.2OH, OH, OR,
SH, SR, C(O)N(R).sub.2, C(O)NHR, C(O)NH.sub.2, halide, tosylate,
mesylate, SO.sub.2NHR, triflate, isocyanate, cyanate, thiocyanate,
isothiocyanate, R, cyano, CF.sub.3 and Si(OR).sub.3; each M.sup.1
is independently Li, Na, K, Rb or Cs; each M.sup.2 is independently
Be, Mg, Ca, Sr or Ba; each R is independently selected from methyl,
ethyl, isopropyl, n-propyl, alkyl, haloalkyl, cycloalkyl,
heterocycloalkyl, aryl, or benzyl; and n.sup.8 is an integer
between 2-10000.
[0235] It is explicitly noted that bonding molecules 180 may be
combined with any of the disclosed anode materials and/or with any
of the disclosed coatings, and possibly provide at least one
coating layer 120, possibly in connection with any of the disclosed
polymers (e.g., the lithium polymers).
Methods
[0236] FIG. 12 is a high level flowchart illustrating a method 200,
according to some embodiments of the invention. The method stages
may be carried out with respect to the anode and cell
configurations described above, which may optionally be configured
to implement method 200. Method 200 may comprise stages for
producing, preparing and/or using cells and anodes, such as any of
the following stages, irrespective of their order.
[0237] Method 200 comprises increasing cell capacity and enabling
fast charging by using as anode active material any of Si, Ge, Sn,
Al, alloys and mixtures thereof (stage 202) and/or configuring the
anode to buffer the interface reaction, zone the electrode to
graduate Li.sup.+ ion lithiation and/or provide graduated
resistance of the anode to the Li.sup.+ ions (stage 205). Any of
these configuration options may be provided separately or in
combination, and be implemented by any of the active materials,
modifications and coatings provided above. For example, method 200
may comprise creating the buffering zone(s) using any of
nanoparticles, borate/phosphate salt(s), pre-lithiation and
coatings disclosed above (stage 210). In certain embodiments,
method 200 may further comprise configuring the buffering zone to
contain anions which are more mobile than associate cations in the
buffering zone and possibly further comprising configuring the
buffering zone to provide a mobility gradient for anions in the
buffering zone
[0238] In certain embodiments, method 200 comprises configuring the
anode material particles to provide flexible support for a brittle
SEI (stage 212), e.g., by attaching flexible polymer coating(s) to
the surface thereof. The buffering zone may be configured to
comprise a polymer configured to support, mechanically, a solid
electrolyte interphase at the interface during expansion and
contraction of the solid electrolyte interphase.
[0239] Method 200 may comprise removing a native oxide layer from
the active material particles (stage 214), e.g., removing any of
GeO.sub.2, SiO.sub.2, Al.sub.2O.sub.3, SnO.sub.2 at least
partially, and protecting the exposed surface of the active
material particles, e.g., by disclosed coatings.
[0240] Method 200 may comprise attaching nanoparticles and/or
borate/phosphate salt(s) to active material particles (stage 220)
to stabilize particle structure, prevent or reduce agglomeration,
improve lithium conductivity and/or prevent lithium metallization
as disclosed above.
[0241] Method 200 may comprise lithiating the buffering zone, for
example by pre-lithiating the active material particles and coating
the pre-lithiated particles by conductive hydrophobic polymer(s)
attached thereto (stage 230) and/or by attaching lithium polymer(s)
to the active material particles (stage 240).
[0242] Method 200 may comprise coating the active material
particles with bonding molecules (possibly lithiated) selected to
bind ionic liquid additive in the electrolyte to the surface of the
particles (stage 250). For example, in certain embodiments, method
200 may comprise forming a surface layer on the anode to bond
(e.g., electrostatically and/or ionically) at least some of ionic
liquid additive(s) in the electrolyte, e.g., by coating the anode
active material by various bonding molecules as disclosed above
and/or partly or fully pre-coating and/or coating the active
material using corresponding polymers. Method 200 may comprise
carrying out the bonding of the ionic liquid to the bonding
molecules during at least a first charging cycle of the cell,
possibly during several first charging and discharging cycles. In
certain embodiments, the bonding of cations and/or anions may be
carried out, at least partially, on the active material itself,
even before the first charging cycle. The bonding of the ionic
liquid to the bonding layer may be electrostatic and/or salt-like
(ionic). In certain embodiments, the bonding may be at least partly
covalent.
[0243] Method 200 may comprise stabilizing the SEI of the cell
through the bonded portion of the ionic liquid additive(s) to the
surface layer and possibly configuring the bonding molecules to
prevent contact of electrolyte solvent with anode active material,
e.g., through steric hindrance. Method 200 may further comprise
configuring the bonding molecules to have electron rich groups that
provide mobile electric charge on the surface of molecules layer,
e.g., to provide an ionic conductivity path through the surface
molecules layer.
[0244] Method 200 may comprise pre-lithiating the anode active
material through an anode material anchoring part of the bonding
molecules. Method 200 may comprise using anchored and
interconnected conductive polymer molecules as the surface layer.
Alternatively or complementarily, method 200 may comprise using a
thick surface layer that protrudes significantly into the
electrolyte.
[0245] Any of the examples for the bonding molecules may be at
least partially implemented using coating and attaching stages 220,
230, 240, and the bonding molecules may be bonded to or associated
to any of the disclosed polymers. The bonded layer of ionic liquid
may replace, support or cooperate with any of the buffering zone(s)
on the surface of the anode active material particles, provided by
stages 205, 210, 212.
[0246] Method 200 may comprise carrying out any of the attaching(s)
(e.g., any of stages 220, 230, 240, 250) in a dry ball milling
process or other low energy production processes (stage 260).
[0247] Method 200 may comprise configuring the active material
particles as composite core-shell particles (stage 270). For
example, method 200 may comprise configuring the cores to receive
and release lithium ions and the shells to allow for core expansion
and contraction while maintaining ionic conductivity to the cores
(stage 272), for example using active material particles, possibly
modified, as cores, and coatings, possibly combining brittle and
flexible elements, as shells (stage 275), as disclosed herein.
[0248] Method 200 may comprise connecting multiple cores and/or
cores with shells by electronic conductive fibers (stage 280),
e.g., by carbon fibers and/or nanotubes. Method 200 may further
comprise forming electric interconnections among multiple
core-shell structures. Method 200 may comprise connecting the cores
of the core-shell particles to the respective shells by electronic
conductive material. In certain embodiments, method 200 may
comprise making the shells of the core-shell particles from ionic
conducting material which is an electronic insulating material and
maintaining electronic conductivity among the cores through the
electronic conductive material. In certain embodiments, method 200
may comprise forming anode active material to have cores surrounded
by and connected to shells, possibly designing the shells to be
ionic conducting and the connections to be electronic conducting
and configuring the shells to provide space for expansion of the
corresponding cores upon lithiation in the cores.
[0249] Method 200 may further comprise interconnecting multiple
cores per shell. Method 200 may further comprise interconnecting
the cores of the core-shell particles throughout the composite
anode material by conductive fibers possibly preparing an anode
with conductive fibers that reach its surface. Method 200 may
comprise configuring the electronic conductive material (e.g.,
conductive fibers) to form a network throughout the anode material
to provide electron paths between the core-shell particles and to
enhance the electronic conductivity of the anode.
[0250] In certain embodiments, method 200 may comprise connecting
the cores and the respective shells by electronic conducting
material(s), ionic conducting material(s), and possibly mechanical
element(s) that enable core expansion upon lithiation. In some
embodiments, method 200 may comprise forming the shells from
brittle, ionic conductive material embedded in flexible electronic
conductive material. For example, the flexible electronic
conductive material may comprise conductive polymers disclosed
above and the brittle ionic conductive material may comprise SEI
fragments which result from cracked SEI upon expansion and
contraction of the anode material particles and/or any
modifications of the anode material particles such as B.sub.4C, WC,
B.sub.2O.sub.3, P.sub.2O.sub.5 nanoparticles or nanocrystals etc.
which may become embedded upon expansion and contraction of the
anode material particles in any of the coatings disclosed
above.
[0251] Method 200 may comprise preparing the anode from active
material particles slurry and additives and preparing corresponding
lithium ion cells and batteries from the anode(s), cathode(s),
electrolyte(s), separator(s) and corresponding enclosure, contacts
and current collectors, control circuits and other cell and battery
elements (stage 290). In certain embodiments, method 200 may
comprise any of the processing stages of processes 105 disclosed
above.
[0252] In certain embodiments, method 200 may comprise forming an
alloy from silicon powder, carbon, and a boron-containing compound
to form an active material, and adding the active material to a
matrix to form the anode material, wherein the weight percentage of
the silicon is between about 4 to about 35 weight % of the total
weight of the anode material and the weight percentage of the boron
is between about 2 to about 20 weight % of the total weight of the
anode material. The active material may comprise carbon at a weight
percentage of between about 5 to about 60 weight % of the total
weight of the anode material. The active material may comprise
tungsten at a weight percentage of between about 5 to about 20
weight % of the total weight of the anode material. The active
material may further comprise carbon nanotubes (CNTs) at a weight
percentage of between about 0.05 to about 0.5 weight % of the total
weight of the anode material. The weight percentage of the silicon
may be between about 5 to about 25 weight % of the total weight of
the anode material and the weight percentage of the boron between
about 5 to about 18 weight % of the total weight of the anode
material. The active material may comprise tungsten at a weight
percentage of between about 7 to about 13 weight % of the total
weight of the anode material. The active material may comprise one
or more conductive materials, wherein the weight percentage of the
conductive materials may be between about 0.01 to about 15 weight %
of the total weight of the anode material. The active material may
be milled to a particle size of about 20 to 100 nm.
[0253] In certain embodiments, method 200 may comprise forming an
alloy from germanium powder, carbon, and a boron-containing
compound to form an active material, and adding the active material
to a matrix to form the anode material, wherein the weight
percentage of the germanium is between about 5 to about 80 weight %
of the total weight of the anode material and the weight percentage
of the boron is between about 2 to about 20 weight % of the total
weight of the anode material. The active material may comprise
carbon at a weight percentage of between about 0.5 to about 5
weight % of the total weight of the anode material. The active
material may comprise tungsten at a weight percentage of between
about 5 to about 20 weight % of the total weight of the anode
material. The active material may comprise silicon and a weight
ratio of germanium to silicon in the active material is at least 4
to 1. The weight percentage of the germanium may be between about
60 to about 75 weight % of the total weight of the anode material
and the weight percentage of the boron is between about 3 to about
6 weight % of the total weight of the anode material.
[0254] In certain embodiments, method 200 may comprise forming an
alloy from tin powder, carbon, and a boron-containing compound to
form an active material, and adding the active material to a matrix
to form the anode material, wherein the weight percentage of the
tin is between about 5 to about 80 weight % of the total weight of
the anode material and the weight percentage of the boron is
between about 2 to about 20 weight % of the total weight of the
anode material. The active material may comprise carbon at a weight
percentage of between about 0.5 to about 5 weight % of the total
weight of the anode material. The active material further comprises
tungsten at a weight percentage of between about 5 to about 20
weight % of the total weight of the anode material. The active
material may further comprise silicon, and method 200 may comprise
adding the silicon to provide a weight ratio between the tin and
the silicon is at least 4 to 1. The active material may further
comprise germanium.
[0255] In certain embodiments, method 200 may comprise forming an
alloy from aluminum powder, carbon, possibly boron and/or tungsten
containing compounds, and possibly any of Si, Ge, Sn, their alloys
and/or mixtures. Method 200 may comprise at least partially
removing (and/or thinning) a native alumina (oxide) layer from
aluminum particles to form aluminum particles having no more than a
1-5 nm thick alumina layer and coating the (at least partially
exposed and/or having thinned alumina layer thereupon) aluminum
particles with lithium based polymer to replace the oxide surface
layer at least partially. Method 200 may comprise removing the
alumina layer at least partially through de-oxidation of aluminum
particles by mixing aluminum particles with carbon particles to
form a mixture and deoxidizing the aluminum particles in the
mixture by heating the mixture in a vacuum atmosphere in a range of
10.sup.-3 to 10.sup.-6 mbar for 60-100 hours at a temperature in a
range of 600 to 750.degree. C. to form aluminum particles at least
partially exposed and/or having an alumina layer in a thickness of
no more than 5 nm. Method 200 may further comprise coating the
de-oxidized aluminum particles with lithium based polymer, e.g., by
ball milling the deoxidized aluminum particles with the lithium
polymer in an inert atmosphere and/or possibly applying lithium
polymers as disclosed above. In certain embodiments, method 200 may
comprise removing at least part of the alumina layer from aluminum
particles chemically, e.g., by immersing the aluminum particles in
a dilute solution of H.sub.2SO.sub.4 to yield the reaction
Al.sub.2O.sub.3+3H.sub.2SO.sub.4.sup.-.fwdarw.Al.sub.2(SO.sub.4).sub.3(aq-
)+3H.sub.2O, and aggressively stirring the solution with lithium
polymer.
[0256] In certain embodiments, method 200 may comprise mixing anode
material particles (e.g., any of Ge, Sn, Si or any other anode
material disclosed herein, their alloys and combinations) with
carbon particles to form a mixture, deoxidizing the anode material
particles in the mixture by heating the mixture in a vacuum
atmosphere in a range of 10.sup.-3 to 10.sup.-6 mbar for 60-100
hours at a temperature in a range of 150 to 350.degree. C. to form
a deoxidized mixture, adding a binder material to the deoxidized
mixture and consolidating the deoxidized mixture and binder
material to form the anode. The mixing may comprise milling the
anode material particles and carbon particles in a ball mill,
possibly adding B.sub.4C particles to the anode material particles
and carbon particles prior to mixing and/or adding WC particles to
the deoxidized mixture. Method 200 may further comprise adding
conductive additives to the deoxidized mixture. The mixture may be
held in a stainless steel container during deoxidation of the metal
particles and evolved CO may be removed from the container during
deoxidation of the anode material particles.
[0257] In certain embodiments, method 200 may comprise preparing
lithium polymers and attaching them to the anode material particles
(stage 240) as disclosed above (e.g., mixing LiOH with respective
polymers and then with respective anode material), adjusting the
process conditions to bind the polymer at least partly by the
lithium to the anode material, achieving thereby also
pre-lithiation (stage 230).
[0258] In certain embodiments, method 200 may comprise
pre-lithiating the anode by introducing and/or preparing anode
material particles to contain lithium (possibly through a prior
process of pre-lithiation, possibly through attaching lithium
polymers 240, direct lithium doping, milling processes, etc.) and
then coating the anode material particles, which contain lithium
ions, by a hydrophobic polymer layer (stage 230), and preparing the
anode from a slurry comprising the coated anode material particles,
wherein the coating and the hydrophobic polymer layer are
configured to prevent the lithium ions from chemically reacting
with water molecules in the slurry, and wherein the hydrophobic
polymer layer is configured to conduct electrons and ions. In
certain embodiments, the coating may be carried out mechanically,
e.g., by ball milling configured to maintain a structure of the
anode material particles and a composition of the hydrophobic
polymer. In certain embodiments, the coating may be carried out
chemically in a suspension. The hydrophobic polymer layer may
comprise conjugated aromatic compounds and/or lithium ions which
are bonded to the hydrophobic polymer.
[0259] In certain embodiments, method 200 may comprise attaching
borate and/or phosphate salts (stage 220) by ball milling, under
protective atmosphere, the anode material particles with
nanoparticles comprising B.sub.2O.sub.3 or other borate oxides or
salts and/or P.sub.2O.sub.5 or other phosphate oxides or salts, and
mixing the milled modified anode material particles with conductive
additives and binder to form the anode.
Experimental Data
[0260] In the following, experimental data, graphs and images are
provided to exemplify some non-limiting embodiments. FIGS. 13A-13C
indicate the fun