U.S. patent application number 13/919818 was filed with the patent office on 2013-12-26 for multi-shell structures and fabrication methods for battery active materials with expansion properties.
This patent application is currently assigned to Sila Nanotechnologies Inc.. The applicant listed for this patent is Sila Nanotechnologies Inc.. Invention is credited to Eugene Michael Berdichevsky, Eerik Torm Hantsoo, Alexander Thomas Jacobs, Addison Newcomb Shelton, Gleb Nikolayevich Yushin, Bogdan Zdyrko.
Application Number | 20130344391 13/919818 |
Document ID | / |
Family ID | 49769298 |
Filed Date | 2013-12-26 |
United States Patent
Application |
20130344391 |
Kind Code |
A1 |
Yushin; Gleb Nikolayevich ;
et al. |
December 26, 2013 |
MULTI-SHELL STRUCTURES AND FABRICATION METHODS FOR BATTERY ACTIVE
MATERIALS WITH EXPANSION PROPERTIES
Abstract
Battery electrode compositions are provided comprising
core-shell composites. Each of the composites may comprise, for
example, an active material, a collapsible core, and a shell. The
active material may be provided to store and release metal ions
during battery operation, whereby the storing and releasing of the
metal ions causes a substantial change in volume of the active
material. The collapsible core may be disposed in combination with
the active material to accommodate the changes in volume. The shell
may at least partially encase the active material and the core, the
shell being formed from a material that is substantially permeable
to the metal ions stored and released by the active material.
Inventors: |
Yushin; Gleb Nikolayevich;
(Atlanta, GA) ; Zdyrko; Bogdan; (Clemson, SC)
; Jacobs; Alexander Thomas; (Atlanta, GA) ;
Hantsoo; Eerik Torm; (Atlanta, GA) ; Shelton; Addison
Newcomb; (Atlanta, GA) ; Berdichevsky; Eugene
Michael; (Atlanta, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sila Nanotechnologies Inc. |
Atlanta |
GA |
US |
|
|
Assignee: |
Sila Nanotechnologies Inc.
Atlanta
GA
|
Family ID: |
49769298 |
Appl. No.: |
13/919818 |
Filed: |
June 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61661336 |
Jun 18, 2012 |
|
|
|
Current U.S.
Class: |
429/231.8 ;
429/218.1 |
Current CPC
Class: |
H01M 4/587 20130101;
Y02E 60/10 20130101; H01M 10/052 20130101; H01M 4/583 20130101;
H01M 4/366 20130101; H01M 4/386 20130101 |
Class at
Publication: |
429/231.8 ;
429/218.1 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 4/583 20060101 H01M004/583 |
Claims
1. A battery electrode composition comprising core-shell
composites, each of the composites comprising: an active material
provided to store and release metal ions during battery operation,
whereby the storing and releasing of the metal ions causes a
substantial change in volume of the active material; a collapsible
core disposed in combination with the active material to
accommodate the changes in volume; and a shell at least partially
encasing the active material and the core, the shell being formed
from a material that is substantially permeable to the metal ions
stored and released by the active material.
2. The battery electrode composition of claim 1, wherein the
collapsible core is formed from a porous material that absorbs the
changes in volume via a plurality of open or closed pores.
3. The battery electrode composition of claim 2, wherein the porous
material of the core comprises a porous and electrically-conductive
carbon material.
4. The battery electrode composition of claim 2, wherein the active
material at least partially encases the porous material of the
core.
5. The battery electrode composition of claim 2, wherein the active
material is interspersed with the porous material of the core.
6. The battery electrode composition of claim 2, wherein the porous
material comprises a porous substrate formed of one or more curved
linear or planar backbones.
7. The battery electrode composition of claim 6, wherein the porous
material further comprises a porous filler interspersed with the
porous substrate.
8. The battery electrode composition of claim 1, wherein the
collapsible core comprises a central void that is encased by the
active material.
9. The battery electrode composition of claim 8, wherein the
central void directly contacts the active material.
10. The battery electrode composition of claim 1, wherein the shell
comprises a protective coating at least partially encasing the
active material and the core to prevent oxidation of the active
material.
11. The battery electrode composition of claim 1, wherein the shell
comprises a porous coating at least partially encasing the active
material and the core, the porous coating having a plurality of
open or closed pores to further accommodate changes in volume.
12. The battery electrode composition of claim 11, wherein at least
some of the pores in the porous coating are closed pores filled
with a first functional filler material.
13. The battery electrode composition of claim 12, wherein at least
some other pores in the porous coating are closed pores filled with
a second functional filler material.
14. The battery electrode composition of claim 11, wherein at least
some of the pores in the porous coating are open pores
interpenetrating the porous coating and filled by a functional
filler material.
15. The battery electrode composition of claim 1, wherein the shell
is a composite material comprising an inner layer and an outer
layer.
16. The battery electrode composition of claim 15, wherein the
inner layer is one of a protective coating layer or a porous
coating layer, and wherein the outer layer is the other of the
protective coating layer or the porous coating layer.
17. The battery electrode composition of claim 16, wherein the
inner layer is the protective coating layer and the outer layer is
the porous coating layer, and wherein the composite material
further comprises an additional coating layer at least partially
encasing the other layers and formed from a material that is (i)
substantially electrically conductive and (ii) substantially
impermeable to electrolyte solvent molecules.
18. The battery electrode composition of claim 1, wherein the
active material comprises discrete particles disposed around or
interspersed with the collapsible core.
19. The battery electrode composition of claim 18, wherein the
particles are coated with a protective coating to prevent oxidation
of the active material.
20. The battery electrode composition of claim 1, wherein the
active material is conformally coated onto the collapsible core.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.119
[0001] The present application for patent claims priority to
Provisional Application No. 61/661,336 entitled "Multi Shell
Structures Designed for Battery Active Materials with Expansion
Properties" filed on Jun. 18, 2012, which is expressly incorporated
by reference herein.
BACKGROUND
[0002] 1. Field
[0003] The present disclosure relates generally to energy storage
devices, and more particularly to metal-ion battery technology and
the like.
[0004] 2. Background
[0005] Owing in part to their relatively high energy densities,
light weight, and potential for long lifetimes, advanced metal-ion
batteries such as lithium-ion (Li-ion) batteries are desirable for
a wide range of consumer electronics. However, despite their
increasing commercial prevalence, further development of these
batteries is needed, particularly for potential applications in
low- or zero-emission hybrid-electrical or fully-electrical
vehicles, consumer electronics, energy-efficient cargo ships and
locomotives, aerospace applications, and power grids.
[0006] Accordingly, there remains a need for improved batteries,
components, and other related materials and manufacturing
processes.
SUMMARY
[0007] Embodiments disclosed herein address the above stated needs
by providing improved battery components, improved batteries made
therefrom, and methods of making and using the same.
[0008] According to various embodiments, various battery electrode
compositions are provided comprising core-shell composites. Each of
the composites may comprise, for example, an active material, a
collapsible core, and a shell. The active material may be provided
to store and release metal ions during battery operation, whereby
the storing and releasing of the metal ions causes a substantial
change in volume of the active material. The collapsible core may
be disposed in combination with the active material to accommodate
the changes in volume. The shell may at least partially encase the
active material and the core, the shell being formed from a
material that is substantially permeable to the metal ions stored
and released by the active material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The accompanying drawings are presented to aid in the
description of embodiments of the invention and are provided solely
for illustration of the embodiments and not limitation thereof.
[0010] FIG. 1 illustrates an example battery electrode composition
comprising core-shell composites according to certain example
embodiments.
[0011] FIG. 2 illustrates an alternative example core-shell
composite design according to other example embodiments.
[0012] FIG. 3 illustrates a particular example core-shell composite
design utilizing a curved linear backbone according to other
example embodiments.
[0013] FIG. 4 illustrates a particular example core-shell composite
design utilizing a curved planar backbone according to other
example embodiments.
[0014] FIGS. 5-6 illustrate two example core-shell composite
designs utilizing a porous substrate in combination with a porous
filler according to other example embodiments.
[0015] FIG. 7 illustrates a particular example core-shell composite
design having a central void according to other example
embodiments.
[0016] FIG. 8 illustrates a particular example core-shell composite
design having a larger central void according to other example
embodiments.
[0017] FIG. 9 illustrates a particular example core-shell composite
design where the shell includes a protective coating according to
certain example embodiments.
[0018] FIG. 10 illustrates a particular example core-shell
composite design where the shell includes a porous coating
according to certain example embodiments.
[0019] FIGS. 11-14 are cutaway views of a portion of different
example porous coatings for use as a shell in various
embodiments.
[0020] FIGS. 15-17 illustrate three particular example core-shell
composite designs where the shell is a composite material according
to various embodiments.
[0021] FIGS. 18-21 illustrate four example core-shell composite
designs utilizing discrete particles of the active material
according to various embodiments.
[0022] FIG. 22 illustrates a still further example core-shell
composite design having an irregular shape according to other
embodiments.
[0023] FIG. 23 illustrates an electrode composition formed from
agglomerated core-shell composites according to certain
embodiments.
[0024] FIGS. 24-25 illustrate still further example composite
designs according to other embodiments.
[0025] FIGS. 26A-26E provide experimental images showing various
phases of formation for a particular example embodiment.
[0026] FIG. 27 provides electrochemical performance data of an
example anode composite containing high surface area silicon
nanoparticles.
[0027] FIG. 28 illustrates an example battery (e.g., Li-ion) in
which the components, materials, methods, and other techniques
described herein, or combinations thereof, may be applied according
to various embodiments.
DETAILED DESCRIPTION
[0028] Aspects of the present invention are disclosed in the
following description and related drawings directed to specific
embodiments of the invention. The term "embodiments of the
invention" does not require that all embodiments of the invention
include the discussed feature, advantage, process, or mode of
operation, and alternate embodiments may be devised without
departing from the scope of the invention. Additionally, well-known
elements of the invention may not be described in detail or may be
omitted so as not to obscure other, more relevant details.
[0029] The present disclosure provides for the use and formation of
active core-shell composites designed to accommodate volume changes
experienced by certain active materials during battery operation,
in which the insertion and extraction of metal ions may cause the
active material to significantly expand and contract. According to
various embodiments described in more detail below, a "collapsible"
core is provided in combination with the active material and one or
more shell layers that may be variously deployed for different
purposes. The collapsible core inside the composite structure
provides space for expansion of the active material during
insertion of the ions (e.g. metal ions, such as Li ions) during the
battery operation. The shell may be variously constructed of
different layers to provide, for example, protection of the surface
of the active material from undesirable reactions with air or with
a binder solvent used in electrode formation, to provide further
volume accommodations for expansion/contraction of the active
material, to provide an outer (rigid) structure relatively
permeable to the metal ions but, in some cases, relatively
impermeable to electrolyte solvent(s) in order to have a smaller
electrode surface area in direct contact with the electrolyte, and
to provide other advantages described in more detail below.
Reduction in the electrode/electrolyte interfacial area allows for
fewer undesirable reactions during battery operation. For example,
in cases where the core-shell composite particles are used in an
anode of a metal-ion battery with an organic solvent-based
electrolyte operating in a potential range, when the electrolyte
undergoes a reduction process with the solid electrolyte interphase
(SEI) formation, preventing electrolyte solvent transport into the
core by making a shell largely impermeable to the solvent reduces
the total SEI content and irreversible electrolyte and metal ion
consumption. Furthermore, by reducing or largely preventing the
core-shell composite particles from changing their outer
dimensions, a significantly more stable SEI layer can be
established. Composites of this type have been shown to exhibit
high gravimetric capacity (e.g., in excess of about 400 mAh/g for
anodes and in excess of about 200 mAh/g for cathodes) while
providing enhanced structural and electrochemical stability.
[0030] FIG. 1 illustrates an example battery electrode composition
comprising core-shell composites according to certain example
embodiments. As shown, each of the composites 100 includes an
active material 102, a collapsible core 104, and a shell 106. The
active material 102 is provided to store and release metal ions
during battery operation. As discussed above, for certain active
materials of interest (e.g., silicon), the storing and releasing of
these metal ions (e.g., Li ions in a Li-ion battery) causes a
substantial change in volume of the active material, which, in
conventional designs, may lead to irreversible mechanical damage,
and ultimately a loss of contact between the individual electrode
particles or the electrode and underlying current collector.
Moreover, it may lead to continuous growth of the SEI around such
volume-changing particles. The SEI growth, in turn, consumes metal
ions and reduces cell capacity. In the design shown here, however,
the collapsible core 104 is disposed in combination with the active
material 102 to accommodate such changes in volume by allowing the
active material 102 to expand inward into the collapsible core 104
itself, rather than expanding outward. The shell 106 at least
partially encases both the active material 102 and the core 104.
The shell 106 may be formed from various layers but in general
includes a material that is substantially permeable to the metal
ions stored and released by the active material, so as not to
impede battery operation.
[0031] In some embodiments, the collapsible core 104 may be formed
from a porous material that absorbs the changes in volume via a
plurality of open or closed pores. In general, the porosity may be
between about 20% and about 99.999% void space by volume, or more
preferably, between about 50% and about 95% void space. In the
design of FIG. 1, the pores may be kept small enough to keep the
active material 102 from depositing inside the core 104 during
synthesis, and instead deposit on the outside of the core 104 as
shown. In some embodiments, the porous material of the core 104 may
also be electrically-conductive to enhance electrical conductivity
of the active material 102 during battery operation. An example
porous material is a carbon sphere made from carbonized polymer
precursors which is then activated (e.g., by exposure to an oxygen
containing environment such as CO.sub.2 gas or H.sub.2O vapors at
elevated temperatures of around 500-1100.degree. C.) to remove
about 50% to about 95% of the material in, preferably, sub-3 nm
pores. The porous material may also advantageously be
electrochemically inert in the battery, such as a porous polymer
having no reduction-oxidation reactions in the potential range
where ions are inserted or extracted from the electrode, though
materials such as carbon (generally not inert if used as an anode
in a Li-ion cell, for example) may also be advantageous.
[0032] Various methods may be utilized to produce core-shell
composites such as the one shown in FIG. 1. For example, one method
for the production of a silicon-based active material with a
central carbon-based collapsible core and carbon-based shell
includes the following steps: (a) synthesize mono dispersed polymer
particles (e.g., using a polyDVB monomer); (b) oxidize the
particles (e.g., at approximately 250.degree. C., for around 8
hours); (c) carbonize the particles to form solid carbon spheres
(e.g., at around 900.degree. C. and 10 torr, for around 1 hour);
(d) activate the carbon spheres to remove most of the mass and
leave a highly porous (e.g., greater than about 90% pores) core
structure behind (e.g., at around 1015.degree. C., for around 12
hours), having pores that are generally small (e.g., less than
around 3 nm); (e) deposit the silicon (in this example) active
material onto the porous cores via thermal decomposition from
silane (SiH.sub.4) (e.g., at approximately 525.degree. C. in Ar at
1 torr, for around 1 hour); and (f) deposit a shell, such as a
protective carbon coating (discussed in more detail below) via
thermal decomposition from a carbon precursor (e.g., at
approximately 900.degree. C. in C.sub.2H.sub.4 at 10 torr, for
about 5 hours). It may be beneficial to mix the particles between
steps to reduce agglomeration during deposition.
[0033] In the design of FIG. 1, the active material 102 is shown as
at least partially encasing the porous material of the core 104.
With a highly porous, but solid core, deposition of the active
material 102 as a coating around the core 104 is relatively
straightforward and the impact of any defects that may be
introduced during fabrication is relatively minimal. However, in
other embodiments, the relationship between the active material 102
and the core 104 may be modified to achieve other advantages for a
given application.
[0034] FIG. 2 illustrates an alternative example core-shell
composite design according to other example embodiments. In this
design, the composite 200 is formed such that the active material
102 is interspersed with the porous material of the core 104. Here,
the porous material should be ionically conductive and electrically
conductive. The advantage of this design is that smaller stresses
are induced in the shell 106 because much of the stress caused
during the expansion of the active material 102 is dissipated by
the core 104. As a result, the outer shell 106 can be made thinner
but nonetheless remain functional (and largely defect-free) during
battery operation. In addition, higher interfacial area between the
active material 102 and the core 104 helps to retain good ionic and
electrical transport within the core-shell composite during battery
operation.
[0035] In such designs, the porous material of the collapsible core
104 may be provided not only as an amorphous structure but also
include a porous substrate formed of one or more curved linear or
planar backbones, for examples.
[0036] FIG. 3 illustrates a particular example core-shell composite
design utilizing a curved linear backbone according to other
example embodiments. In this design, the composite 300 is formed
from a collection of curved linear backbones 304 serving as the
collapsible core and providing a substrate for the active material
102. The curved linear backbones 304 may comprise, for example,
porous carbon strands with large pores, the surface of which can be
coated with the active material 102. The curved nature of the
linear backbones 304 also introduces an element of porosity into
the design. It may be advantageous for this backbone to be
electrically conductive and ionically conductive. In some designs,
the linear building blocks of the linear backbone 304 can be
composed of linked nanoparticles. Advantages of the linear backbone
304 include its open structure, which makes it easy for this
structure to be coated uniformly by an active material using, for
example, vapor deposition or electroless deposition methods. This
is because the diffusion of the precursor for the active material
within the open framework structure of the curved linear backbone
is fast. In addition, after this deposition, the active material
coated linear backbone can remain sufficiently flexible and robust
and thus withstand mixing, calendaring, and various handling
procedures without failure.
[0037] FIG. 4 illustrates a particular example core-shell composite
design utilizing a curved planar backbone according to other
example embodiments. In this design, the composite 400 is formed
from a collection of curved planar backbones 404 serving as the
collapsible core and providing a substrate for the active material
102. The curved planar backbones 404 may comprise, for example,
carbon (nano) flakes such as exfoliated graphite or multi-layered
graphene, the surface of which can be coated with the active
material 102. The curved nature of the planar backbones 304 also
introduces an element of porosity into the design. One advantage of
the planar backbone is its optimal use of the pore space available
to accommodate the volume changes in active material. In addition,
the curved planar morphology may provide high structural integrity
to both the core and the overall core-shell composite. Further, the
curved planar morphology makes it easy to deposit a conformal shell
106 encasing the composite particles.
[0038] In each of these designs, the different substrates may be
combined with a porous filler material to further enhance the
overall porosity of the collapsible core. The porous filler
material may be similar to that discussed above in conjunction with
the design of FIG. 1, leading to a composite or hybrid design.
[0039] FIGS. 5-6 illustrate two example core-shell composite
designs utilizing a porous substrate in combination with a porous
filler according to other example embodiments. The first example
composite 500 in FIG. 5 is similar to the design of FIG. 3 in which
the porous substrate includes a collection of curved linear
backbones 304. Here, the composite 500 further includes a porous
filler 508 interspersed with the curved linear backbones 304
deployed as the porous substrate. The second example composite 600
in FIG. 6 is similar to the design of FIG. 4 in which the porous
substrate includes a collection of curved planar backbones 404.
Here, the composite 600 further includes a porous filler 608
interspersed with the curved planar backbones 404 deployed as the
porous substrate. The material used for the filler 508, 608 should
ideally be electrically and ionically conductive. In some designs,
it may also be advantageous to have a strong, electrically and
ionically conductive interface between both the active material 102
and the filler 508, 608, as well as between the shell 106 and the
filler 508, 608. In this case, the battery operation would be more
reliable and higher power performance would be achieved. In order
to reduce the interfacial resistance between the active material
102 and the filler 508, 608, the active material 102 can be coated
with a thin interfacial layer. Conductive carbon is an example of
such a layer, which may improve, for example, electrical
conductivity of this interface in some designs.
[0040] Returning to FIG. 1, in some designs, the collapsible core
104 may be formed in such a way so as to form a substantial void in
the center of each composite that provides additional accommodation
for changes in volume of the active material 102.
[0041] FIG. 7 illustrates a particular example core-shell composite
design having a central void according to other example
embodiments. As shown, the composite 700 is formed such that the
collapsible core 104 includes a central void 710 that is encased
(at least indirectly) by the active material 102. One way in which
the central void 710 may be formed, for example, is by polymerizing
two different monomers, such as polystyrene and polyDVB. First, a
solid polymer core may be created from polystyrene, followed by a
polymer shell created from polyDVB. A subsequent carbonization
process may be used to remove the polystyrene core (with little or
no residual material) while creating a carbon residual from the
polyDVB to form a shell with a hollow center. This structure may
then be left as is (as a solid) or activated to remove additional
material until a desired thickness is reached.
[0042] In some applications, it may be advantageous for the
thickness of any substantive material of the collapsible core 104
to be made relatively thin in relation to the central void 710. For
example, it may be made no thicker than is needed to stay intact
during further processing. Alternatively, the substantive material
of the collapsible core 104 may be removed altogether or nearly
altogether such that the central void 710 directly contacts the
active material 102 at one or more points.
[0043] FIG. 8 illustrates a particular example core-shell composite
design having a larger central void according to other example
embodiments. In this design, the composite 800 is formed such that
the collapsible core 104 includes a larger central void 810 that is
encased (at least indirectly) by the active material 102 and formed
large enough within the collapsible core 104 so as to contact the
active material 102 at one or more points.
[0044] Returning again to FIG. 1, the shell 106 may be formed in a
variety of ways and include a variety of layers each specially
designed to provide corresponding functionality. For example, the
shell 106 may include a protective coating at least partially
encasing the active material 102 and the core 104 to prevent
oxidation of the active material 102. The shell 106 may also
include a porous coating at least partially encasing the active
material 102 and the core 104 to further accommodate changes in
volume, within or among the composites.
[0045] FIG. 9 illustrates a particular example core-shell composite
design where the shell includes a protective coating according to
certain example embodiments. Here, the composite 900 includes an
active material 102, a collapsible core 104, and a protective
coating 906, serving as the shell 106 in the more generic design of
FIG. 1. As shown, the protective coating 906 at least partially
encases the active material 102 and the core 104. It will be
appreciated that the active material 102 and the core 104 are shown
for illustration purposes as in the more generic design of FIG. 1,
but may be implemented according to any of the various embodiments
disclosed herein.
[0046] The protective coating 906 may be provided, for example, to
prevent oxidation of the active material 102. In some applications,
it may be particularly important to avoid oxidation of the surface
of the active material 102 after its synthesis. One such
application is in cases where a thin (e.g., 1-2 nm) surface layer
comprises a substantial amount (e.g., more than about 10%) of the
total volume of active material. For example, small nanoparticles
of silicon with a diameter of 3 nm have nearly 90% of their volume
within a 1 nm surface layer. Therefore exposure of the 3 nm silicon
particles to air and the resulting formation of a native oxide
would result in a nearly complete oxidation. Deposition and use of
the protective coating 906 on the surface of freshly synthesized
active material before any exposure to air or other oxidizing media
reduces or prevents such an oxidation.
[0047] An example method for depositing a carbon-based protective
coating without exposure of a synthesized silicon-based active
material to air is as follows. The carbon layer can be deposited by
chemical vapor deposition of carbon from one of various hydrocarbon
precursors, such as acetylene and propylene, to name a few. In one
embodiment, the deposition may be conducted in the same reactor
where silicon deposition or formation is performed. In another
embodiment, the chamber where silicon is deposited may be
subsequently filled with an inert gas (such as argon or helium) and
sealed with valves. To minimize leaks in the system, a positive
(above atmospheric) pressure may be applied. The sealed chamber may
then be transferred into a carbon deposition tool. The chamber may
be connected to the gas lines of the carbon deposition tool, while
remaining sealed. Prior to opening the valve connecting the
silicon-containing chamber and the carbon-deposition tool gas
lines, the line to the carbon precursor may be evacuated and filled
with either an inert gas or a hydrocarbon gas in such a way so as
to minimize the content of water or oxygen molecules within the
system that are to be exposed to silicon during the carbon
deposition process. In another embodiment, the particles can be
transferred internally between silicon and carbon deposition zones
using gravity or other powder transfer means.
[0048] It may be advantageous to have the total number of oxygen
atoms in the system be at least twenty times smaller than the total
number of silicon atoms in the silicon nanopowder or silicon
nanostructures contained within the chamber and to be protected
from oxidation by the carbon layer. In one example, the
silicon-containing chamber filled with an inert gas may be heated
to an elevated temperature of between about 500-900.degree. C.
After the desired temperature is reached, the carbon precursor gas
(vapor) may be introduced into the system, depositing a carbon
layer onto the silicon surface. In some embodiments, it may be
advantageous to perform carbon deposition in sub-atmospheric
pressures (for example, at about 0.01-300 torr) in order to form a
more crystalline, conformal layer with better protective
properties. After the deposition of the protective carbon, the
chamber can be cooled down to below 300.degree. C., or preferably
below 60.degree. C., prior to exposure to air. For this carbon
layer to serve as an effective protective barrier against
oxidation, the thickness of the conformal carbon layer should meet
or exceed approximately 1 nm.
[0049] FIG. 10 illustrates a particular example core-shell
composite design where the shell includes a porous coating
according to certain example embodiments. Here, the composite 1000
includes an active material 102, a collapsible core 104, and a
protective coating 1006, serving as the shell 106 in the more
generic design of FIG. 1. As shown, the protective coating 1006 at
least partially encases the active material 102 and the core 104.
Here, the porous coating 1006 is formed with a plurality of open or
closed pores to further accommodate changes in volume. It will
again be appreciated that the active material 102 and the core 104
are shown for illustration purposes as in the more generic design
of FIG. 1, but may be implemented according to any of the various
embodiments disclosed herein.
[0050] In some embodiments, the porous coating 1006 may be composed
of a porous electrically-conductive carbon. An example process for
the formation of a porous carbon layer includes formation of a
polymer coating layer and its subsequent carbonization at elevated
temperatures (e.g., between about 500-1000.degree. C., but below
the thermal stability of the active material or the active
material's reactivity with the carbon layer). This results in the
formation of a carbon containing pores. Additional pores within the
carbon can be formed as desired upon activation under certain
conditions, with the oxidation rate of the active material being
significantly lower than the oxidation (activation) rate of porous
carbon. In other embodiments, the porous coating 1006 may comprise
a polymer-carbon mixture. In still other embodiments, the porous
coating 1006 may comprise a polymer electrolyte. Polyethylene oxide
(PEO) infiltrated with a Li-ion salt solution is an example of a
polymer electrolyte. If a polymer electrolyte does not have mixed
(both electronic and ionic) conductivities (as in the case of PEO)
but only a significant ionic conductivity, the porous shell may
further comprise an electrically conductive component, such as
carbon, in order to inject electrons or holes into the active
material during battery operation.
[0051] As noted above, according to various embodiments, the pores
of the porous coating 1006 may be open or closed. In either case,
the various pores may further include different functional fillers,
used alone or in combination, as discussed in more detail
below.
[0052] FIGS. 11-14 are cutaway views of a portion of different
example porous coatings for use as a shell in various embodiments.
FIG. 11 illustrates an example design 1100 of the porous coating
1006 shown in FIG. 10 in which a plurality of closed pores 1112 are
present, at least some of the pores 1112 being filled with a first
functional filler material 1114. FIG. 12 illustrates an example
design 1200 of the porous coating 1006 shown in FIG. 10 in which a
plurality of closed pores 1112 are again present, and at least some
of the pores 1112 are again filled with the first functional filler
material 1114. However, in this design, at least some other pores
1112 are filled with a second functional filler material 1216,
creating a composite material of different functional fillers. FIG.
13 illustrates an example design 1300 of the porous coating 1006
shown in FIG. 10 in which a plurality of open pores 1318 are
present and interpenetrating the porous coating 1006. In some
designs, the open pores 1318 may be formed in combination with the
closed pores 1112, as shown. FIG. 14 is an example design 1400 of
the porous coating 1006 shown in FIG. 10 in which a plurality of
open pores 1318 and closed pores 1112 are present and filled with a
given functional filler material 1420.
[0053] In some applications, particularly in those where formation
of some fraction of small cracks is likely, it is advantageous that
at least a fraction of the pores within the porous coating be
filled with functional fillers such as electrolyte additives, which
are capable of sealing the micro-cracks formed within such a layer
during metal-ion insertion into the active particle core and the
resulting volume changes. One example of such an additive is a
vinylene carbonate (VC) optionally mixed with a metal-ion (such as
Li-ion) containing salt. Another example of such an additive is an
initiator for radical polymerization, capable of inducing
polymerization of the electrolyte solvent(s). Conventional use of
these additives (such as VC) has been limited to Li-ion battery
electrolytes, without any such infiltration or incorporation within
a porous layer around the active particles. This approach improves
stability of the composite electrodes without significantly
sacrificing other advantageous properties of the bulk electrolyte.
In addition, it allows one to use different additives within porous
layers on the surfaces of anodes and cathodes.
[0054] In some designs, the shell may be a composite material
comprising at least an inner layer and an outer layer, with
potentially one or more other layers as well. The shell may
accordingly be made by combining different coatings of the types
described above and the different layers may be provided for
different functions. For example, one component of the shell may
provide better structural strength, and another one better ionic
conductivity. In another example, one component can provide better
ionic conductivity, and another one better electrical conductivity.
In some applications, it may be advantageous to have these
components interpenetrate each other. In this case, the composite
shell may provide both high ionic and electrical conductivity if
one component is more electrically conductive and another one more
ionically conductive.
[0055] FIGS. 15-17 illustrate three particular example core-shell
composite designs where the shell is a composite material according
to various embodiments. FIG. 15 illustrates an example composite
1500 in which the inner layer of the shell is a protective coating
layer 906 of the type described in conjunction with FIG. 9, and the
outer layer is a porous coating layer 1006 of the type described in
conjunction with FIG. 10. Conversely, FIG. 16 illustrates an
example composite 1600 in which the inner layer of the shell is a
porous coating layer 1006 of the type described in conjunction with
FIG. 10, and the outer layer is a protective coating layer 906 of
the type described in conjunction with FIG. 9. The outer protective
coating layer 906 in FIG. 16 may offer other useful
functionalities. For example, it may prevent electrolyte solvent
transport into the porous component of the shell and the core,
which reduces the sites of undesirable reactions between
electrolyte and the composite core-shell electrode particles.
Formation of an SEI on a core-shell anode operating in the
potential range of 0-1.2V vs. Li/Li+ in Li-ion batteries is an
example of such reactions. This outer coating layer 906 (if made
impermeable to electrolyte solvent) reduces the total SEI content
and irreversible electrolyte and metal ion consumption.
Alternatively, the outer coating layer 906 in FIG. 16 may offer
improved electrical conductivity, which may enhance capacity
utilization and power characteristics of the electrodes based on
the described core-shell particles. Further, the outer coating
layer 906 in FIG. 16 may provide structural integrity to the
core-shell particles with a volume-changing active material.
[0056] FIG. 17 illustrates an example composite 1700 that further
includes an additional coating layer 1722 at least partially
encasing the other layers. The additional coating layer 1722 may be
formed, for example, from a material that is (i) substantially
electrically conductive and (ii) substantially impermeable to
electrolyte solvent molecules. In each illustration, it will again
be appreciated that the active material 102 and the core 104 are
shown for illustration purposes as in the more generic design of
FIG. 1, but may be implemented according to any of the various
embodiments disclosed herein.
[0057] In some applications, it may be advantageous to provide a
solid carbon layer between porous carbon and silicon. This solid
layer may be deposited in order to prevent the oxidation of the
silicon surface, as discussed above. In other applications where
high surface area pores are open to the electrolyte and thus
available for electrolyte decomposition, it may be advantageous to
deposit a solid carbon layer onto the outer surface of the porous
carbon layer. This deposition seals the pores and reduces the total
surface area of the material exposed to electrolyte. As a result,
this deposition reduces undesirable side reactions, such as
electrolyte decomposition. In still other applications, both
approaches may be used to create a three-layered structure.
[0058] In addition or alternatively, an additional coating layer
may be provided to impart further mechanical stability. Thus, the
outermost shell layer can comprise ion permeable materials other
than carbon, such as metal oxides. In some applications, where
minimal volume changes of the composites is particularly important,
it is advantageous for at least the outermost shell layer to
experience significantly smaller volume changes (e.g., twice as
small, or preferably three or more times as small) than the core
active material during battery operation.
[0059] A rigid outer shell of this type can be made of carbon or
ceramic coating(s) or both, for example. In one configuration, such
a shell can be made of conductive carbon. The coating can be
deposited by decomposition of carbon containing gases, such as
hydrocarbons (the process is often called chemical vapor
deposition) according to the following reaction:
2C.sub.xH.sub.y=2xC+yH.sub.2, where C.sub.xH.sub.y is the
hydrocarbon precursor gas. The carbon deposition temperature may be
in the range of about 500-1000.degree. C. After deposition, the
core-shell structure can be annealed at temperatures of about
700-1100.degree. C., but preferably about 800-1000.degree. C. to
induce additional structural ordering within the carbon, to desorb
undesirable impurities, and to strengthen the bonding between core
and shell.
[0060] An alternative method of depositing carbon on the surface of
the active material includes catalyst-assisted carbonization of
organic precursors (e.g., polysaccharide or sucrose carbonization
in the presence of sulfuric acid). Yet another method of producing
the carbon coating includes hydrothermal carbonization of the
organic precursors on the surface of the active material at
elevated temperatures (e.g., about 300-500.degree. C.) and elevated
pressures (e.g., about 1.01-70 atm). Yet another method of
producing the carbon outer coating includes formation of the
polymer around the active material and subsequent carbonization at
elevated temperatures. In addition to a polymer coating, the active
material can be initially coated with small carbon particles or
multi- or single-graphene layers. Carbonization may be used to
transform the polymer-carbon composite outer shell into a
conductive carbon-carbon composite shell.
[0061] In addition to pure carbon, a metal-ion permeable shell in
this and other described structures may be composed of or contain
metal oxides, metal phosphates, metal halides or metal nitrides,
including, but not limited to, the following metals: lithium (Li),
aluminum (Al), cobalt (Co), boron (B), zirconium (Zr), titanium
(Ti), chromium (Cr), tantalum (Ta), niobium (Nb), zinc (Zn),
vanadium (V), iron (Fe), magnesium (Mg), manganese (Mn), copper
(Cu), nickel (Ni), and others. They main requirements include, but
are not limited to, high ionic conductivity in combination with
good structural and chemical stability during electrode operation
in the selected battery chemistry.
[0062] Deposition of such coatings can be performed using a variety
of oxide coating deposition techniques, including physical vapor
deposition, chemical vapor deposition, magnetron sputtering, atomic
layer deposition, microwave-assisted deposition, wet chemistry,
precipitation, solvothermal deposition, hydrothermal deposition,
and others in combination with an optional annealing at elevated
temperatures (e.g., greater than about 200.degree. C.). For
example, metal oxide precursors in the form of a water-soluble salt
may be added to the suspension (in water) of the composites to be
coated. The addition of a base (e.g., sodium hydroxide or amine)
causes formation of a metal (Me) hydroxide. Active material
particles suspended in the mixture may then act as nucleation sites
for Me-hydroxide precipitation. Once coated with a shell of
Me-hydroxide, they can be annealed in order to convert the
hydroxide shell into a corresponding oxide layer that is then
well-adhered to their surface.
[0063] Accordingly, throughout the various embodiments discussed
herein, it will be appreciated that the shell may serve several
purposes. First, it may create a mechanically rigid surface that
prevents the active material from expanding outwards. Because the
core may be highly porous and "soft," and the active material must
expand, the active material expands inward, towards the core rather
than outwards. Without the shell, the active material might expand
inwards and outwards, which would cause the outer surface of the
structure to change. Second, the shell may also be made ionically
conductive for metal ions or the like to move to the active
material. It may also be electrically conductive so that the
composites making up the electrode will make better electrical
contact with each other. Third, it may advantageously have good
properties for forming SEI in the electrolyte used. Although the
example shell material discussed most prominently above is carbon
or carbon-based, certain oxides and ceramics may also be used to
form shells with advantageous properties. Metals may also be used
if channels for ionic conductivity are formed without compromising
the mechanical integrity.
[0064] Returning again to FIG. 1, the active material 102 may be
provided in various forms according to different embodiments, both
for better matching a given implantation of the other composite
components as well as for other reasons. In the design of FIG. 1,
the active material 102 is shown in a generally amorphous or
nanocrystalline (grain size below 1 micron, preferably below 500
nm) form as conformally coated onto the collapsible core 104. This
amorphous or nanocrystalline form is similarly shown in FIG. 2
where the active material 102 is interspersed with the porous
material of the core 104, in FIG. 3 where the active material 102
is conformally coated onto the curved linear backbones 304, in FIG.
4 where the active material 102 is conformally coated onto the
curved linear backbones 404, and so on. In each of these designs,
however, the active material 102 may be provided in an alternative
form for different applications.
[0065] FIGS. 18-21 illustrate four example core-shell composite
designs utilizing discrete particles of the active material
according to various embodiments. FIG. 18 illustrates a composite
1800 that is similar to the design of FIG. 1 but with discrete
particles 1802 disposed around the collapsible core 104. These
particles may optionally (but preferably) be electrically connected
to each other and to the shell 106. These electrical connections
provide more uniform insertion and extraction of ions from the
active material 102. These electrical connections may be direct
(particle-to-particle) or via the collapsible core 104 (when
produced from an electrically conductive material) or via an
electrically conductive shell 106 (when the shell is electrically
conductive). FIG. 19 illustrates a composite 1900 that is similar
to the design of FIG. 2 but with discrete particles 1802
interspersed with the collapsible core 104. FIGS. 20-21 illustrate
respective composites 2000 and 2100 that are similar to the designs
of FIGS. 3-4, respectively, but with discrete particles 1802
interspersed with their respective cores on their different
backbone substrates 304, 404.
[0066] In any case, the individual particles 1802 may be further
coated with a protective coating to prevent oxidation of the active
material. When the discrete particles 1802 are interspersed with
the core 104, they should be electrically connected to each other
and to the shell 106. These electrical connections are needed for
the reversible electrochemical reduction and oxidation processes
(which take place during normal battery operation) to proceed. As
in the discussion above, these electrical connections may be direct
(particle-to-particle) or via the collapsible core 104 (when
produced from an electrically conductive material) or via
electrically conductive links (such as electrically conductive
particles of various shapes maintaining a direct contact between
the discrete active particles 1802). In the latter two instances,
there is no requirement for direct contact between the discrete
active particles 1802.
[0067] It will be appreciated that these examples are merely
provided as exemplary and not an exhaustive list of discrete
particle design for the active material. The other designs
disclosed herein for different arrangements of cores and shells may
likewise be implemented using discrete active particles.
[0068] In some embodiments, the active material may be a silicon or
silicon-rich material, as in a few of the examples above. In other
embodiments, however, the disclosed techniques may be applied to a
variety of higher capacity anode materials including not only
silicon, but also other anode materials that experience significant
volume changes (e.g., greater than about 7%) during insertion or
extraction of their respective metal ions. Examples of such
materials include: (i) heavily (and "ultra-heavily") doped silicon;
(ii) group IV elements; (iii) binary silicon alloys (or mixtures)
with metals; (iv) ternary silicon alloys (or mixtures) with metals;
and (v) other metals and metal alloys that form alloys with metal
ions such as lithium.
[0069] Heavily and ultra-heavily doped silicon include silicon
doped with a high content of Group II elements, such as boron (B),
aluminum (Al), gallium (Ga), indium (In), or thallium (Tl), or a
high content of Group V elements, such as nitrogen (N), phosphorus
(P), arsenic (As), antimony (Sb), or bismuth (Bi). By "heavily
doped" and "ultra-heavily doped," it will be understood that the
content of doping atoms is typically in the range of 3,000 parts
per million (ppm) to 700,000 ppm, or approximately 0.3% to 70% of
the total composition.
[0070] Group IV elements used to form higher capacity anode
materials may include Ge, Sn, Pb, and their alloys, mixtures, or
composites, with the general formula of
Si.sub.a--Ge.sub.b--Sn.sub.c--Pb.sub.d--C.sub.e-D.sub.f, where a,
b, c, d, e, and f may be zero or non-zero, and where D is a dopant
selected from Group III or Group V of the periodic table.
[0071] For binary silicon alloys (or mixtures) with metals, the
silicon content may be in the range of approximately 20% to 99.7%.
Examples of such as alloys (or mixtures) include, but are not
limited to: Mg--Si, Ca--Si, Sc--Si, Ti--Si, V--Si, Cr--Si, Mn--Si,
Fe--Si, Co--Si, Ni--Si, Cu--Si, Zn--Si, Sr--Si, Y--Si, Zr, --Si,
Nb--Si, Mo--Si, Tc--Si, Ru--Si, Rh--Si, Pd--Si, Ag--Si, Cd--Si,
Ba--Si, Hf--Si, Ta--Si, and W--Si. Such binary alloys may be doped
(or heavily doped) with Group III and Group V elements.
Alternatively, other Group IV elements may be used instead of
silicon to form similar alloys or mixtures with metals. A
combination of various Group IV elements may also be used to form
such alloys or mixtures with metals.
[0072] For ternary silicon alloys (or mixtures) with metals, the
silicon content may also be in the range of approximately 20% to
99.7%. Such ternary alloys may be doped (or heavily doped) with
Group III and Group V elements. Other Group IV elements may also be
used instead of silicon to form such alloys or mixtures with
metals. Alternatively, other Group IV elements may be used instead
of silicon to form similar alloys or mixtures with metals. A
combination of various Group IV elements may also used to form such
alloys or mixtures with metals.
[0073] Examples of other metals and metal alloys that form alloys
with lithium include, but are not limited to, Mg, Al, Ga, In, Ag,
Zn, Cd, etc., as well as various combinations formed from these
metals, their oxides, etc.
[0074] The disclosed techniques may also be applied to several high
capacity cathode active materials, which experience significant
(e.g., greater than about 7%) volume changes during insertion and
extraction of metal ions (such as Li ions, for example) during the
operation of a metal-ion cell (such as a Li-ion cell).
[0075] Examples of high capacity cathode materials include, but are
not limited to, conversion-type cathodes, such as metal fluorides,
metal oxy-fluorides, various other metal halides and oxy-halides
(such as metal chlorides, metal bromides, metal iodides) and
others. Examples of metal fluorides based on a single metal
include, but are not limited to, FeF.sub.2 (having a specific
capacity of 571 mAh/g in Li-ion battery applications), FeF.sub.3
(having a specific capacity of 712 mAh/g in Li-ion battery
applications), MnF.sub.3 (having a specific capacity of 719 mAh/g
in Li-ion battery applications), CuF.sub.2 (having a specific
capacity of 528 mAh/g in Li-ion battery applications), and
NiF.sub.2 (having a specific capacity of 554 mAh/g in Li-ion
battery applications). It will be appreciated that metal halides
may include two or more different metals. For example, Fe and Mn or
Ni and Co or Ni and Mn and Co. The metal halides mentioned above
may also contain lithium (particularly in the case of Li-ion
batteries) or other metals for the corresponding metal-ion
batteries. Finally, metal halide active materials may comprise both
metal atoms in a metallic form and in the form of a metal halide.
For example, the metal halide-based active materials may comprise a
mixture of a pure metal (such as Fe) and a lithium halide (such as
LiF) in case of a Li-ion battery (or another metal halide in case
of a metal-ion battery, such as sodium halide (such as NaF) in case
of a Na-ion battery or magnesium halide (MgF.sub.2) in case of a
Mg-ion battery). The pure metal in this example should ideally form
an electrically connected array of metal species. For example,
electrically connected metal nanoparticles (such Fe nanoparticles)
or electrically connected curved metal nanowires or metal dendritic
particles or metal nanosheets. Alternatively, the metal-1 component
of the active (metal-1/metal-2 halide) mixture can form a curved
linear or curved planar backbone onto which the metal-2 halide is
deposited.
[0076] The disclosed techniques may also be applied to several high
capacity anode and cathode active materials that experience
significant volume changes when used in battery chemistries other
than metal-ion batteries.
[0077] FIG. 22 illustrates a still further example core-shell
composite design having an irregular shape according to other
embodiments. As shown, the composite 2200 is compositionally
equivalent to the design of FIG. 1 and includes an active material
102, a collapsible core 104, and a shell 106. It is, however,
irregularly shaped to demonstrate that the generally spherical
shape of various composites illustrated in other figures is not
required and that other, even irregular shapes are
contemplated.
[0078] FIG. 23 illustrates an electrode composition formed from
agglomerated core-shell composites according to certain
embodiments. As shown, each composite of the agglomeration 2300
includes active material particles 1802, a collapsible core 104,
and a porous shell 1006, similar to various design aspects
discussed above. In this design, the porous material for the
collapsible core 104 and the porous shell 1006 are selected to be
the same. Accordingly, as demonstrated in the figure, a design
incorporating such elements effectively blurs the distinction
between core and shell, leading to a structure that is equivalent
to an agglomeration of composites formed without shells per se
(i.e., in that the core of one composite acts as a shell for
another composite in the agglomeration by providing an equivalent
accommodation for volume changes). Such a design is contemplated
herein as well.
[0079] FIGS. 24-25 illustrate still further example composite
designs according to other embodiments. FIG. 24 illustrates a
design 2400 including an example porous active material powder
structure 2402 encased in a shell 2406 but in which volume changes
are accommodated by the porous nature of the active material itself
rather than a collapsible core. FIG. 25 illustrates a design 2500
including a similar example porous active material powder structure
2402 but with a shell 2506 disposed as a conformal coating.
[0080] In general, it is noted that composite particles of the type
discussed herein can be synthesized from about 50 nm to about 50
.mu.m in size. The core and shells can be designed to vary in
thickness or diameter from about 1 nm to about 20 .mu.m. Electrode
designs with a relatively uniform size distribution of the
composites may be beneficial, as properties remain consistent from
particle to particle. However, it may be advantageous for other
embodiments to create structures of two, three, or more uniform
diameters and mix them together to allow for high packing density
when electrodes are fabricated. Because these composites change
very little if at all in size during cycling on the outer surface,
the particle-to-particle connection can stay intact with strong or
weak binders.
[0081] Composite size is driven by a multitude of factors. In
particular, additive CVD processes tend to bind adjacent particles
together, forming large agglomerates. This is true especially in
bulk powder processing. Agglomeration of adjacent composites can be
mitigated during bulk powder processing in all synthesis processes
by any combination of tumble agitation of the entire powder volume,
entrainment of the composites in a fluid flow, dropping composites
to maintain separation between them, vibratory agitation, milling,
electrostatic charging, or other means. Composite particle size can
also be controlled by reducing it after synthesis using milling
techniques.
[0082] FIGS. 26A-26E provide experimental images showing various
phases of formation for a particular example embodiment, including
(a) polymerized core precursor particles (oxidized polyDVB) (FIG.
26A), (b) carbonized core particles (FIG. 26B), (c) activated core
particles (FIG. 26C), (d) silicon deposited on activated carbon
core particles (FIG. 26D), and (e) a carbon shell deposited on
silicon on activated carbon core particles (FIG. 26E). It will be
appreciated that the example design shown here is for illustration
purposes only, and is not intended to represent the only or the
best implementation.
[0083] FIG. 27 provides electrochemical performance data of an
example anode composite containing high surface area silicon
nanoparticles. Discharge capacity is shown as a function of cycle
number and the presence or absence of a protective carbon layer
deposited on the fresh silicon surface without its exposure to air.
The positive impact of the protective layer on the reversible
capacity is evident. Without the protective coating over 60% of the
silicon atoms became oxidized, which resulted in a significant
reduction of the capacity utilization.
[0084] FIG. 28 illustrates an example battery (e.g., Li-ion) in
which the components, materials, methods, and other techniques
described herein, or combinations thereof, may be applied according
to various embodiments. A cylindrical battery is shown here for
illustration purposes, but other types of arrangements, including
prismatic or pouch (laminate-type) batteries, may also be used as
desired. The example battery 2801 includes a negative anode 2802, a
positive cathode 2803, a separator 2804 interposed between the
anode 2802 and the cathode 2803, an electrolyte (not shown)
impregnating the separator 2804, a battery case 2805, and a sealing
member 2806 sealing the battery case 2805.
[0085] The forgoing description is provided to enable any person
skilled in the art to make or use embodiments of the present
invention. It will be appreciated, however, that the present
invention is not limited to the particular formulations, process
steps, and materials disclosed herein, as various modifications to
these embodiments will be readily apparent to those skilled in the
art. That is, the generic principles defined herein may be applied
to other embodiments without departing from the spirit or scope of
the invention.
* * * * *