U.S. patent application number 15/686788 was filed with the patent office on 2018-06-14 for high-rate-charging cathodes with in-battery polymerization of conducting polymers.
The applicant listed for this patent is Storedot Ltd.. Invention is credited to Daniel ARONOV, Libi BRAKHA, Doron BURSHTAIN, Carmit OPHIR.
Application Number | 20180166679 15/686788 |
Document ID | / |
Family ID | 60407764 |
Filed Date | 2018-06-14 |
United States Patent
Application |
20180166679 |
Kind Code |
A1 |
OPHIR; Carmit ; et
al. |
June 14, 2018 |
HIGH-RATE-CHARGING CATHODES WITH IN-BATTERY POLYMERIZATION OF
CONDUCTING POLYMERS
Abstract
Cathodes for a fast charging lithium ion battery, processes for
manufacturing thereof and corresponding batteries are provided.
Cathode formulations comprise cathode material having an
olivine-based structure, binder material, and monomer material
selected to polymerize into a conductive polymer upon partial
delithiation of the cathode material during at least a first
charging cycle of a cell having a cathode made of the cathode
formulation. When the cathode is used in a battery, polymerization
is induced in-situ (in-cell) during first charging cycle(s) of the
battery to provide a polymer matrix which is evenly dispersed
throughout the cathode.
Inventors: |
OPHIR; Carmit; (Holon,
IL) ; BRAKHA; Libi; (Tel Aviv, IL) ;
BURSHTAIN; Doron; (Herzliya, IL) ; ARONOV;
Daniel; (Netanya, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Storedot Ltd. |
Herzeliya |
|
IL |
|
|
Family ID: |
60407764 |
Appl. No.: |
15/686788 |
Filed: |
August 25, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15434083 |
Feb 16, 2017 |
9831488 |
|
|
15686788 |
|
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|
|
62432588 |
Dec 11, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/1397 20130101;
C08G 2261/3221 20130101; C08G 61/124 20130101; C08G 2261/1424
20130101; H01M 4/583 20130101; H01M 2004/028 20130101; H01M 10/049
20130101; H01M 10/052 20130101; H01M 4/5825 20130101; H01M 4/623
20130101; C08G 61/126 20130101; C08G 73/0266 20130101; C08G
2261/3223 20130101; Y02E 60/10 20130101; H01M 10/0525 20130101;
H01M 4/608 20130101; H01M 4/624 20130101; H01M 4/0445 20130101;
C08G 2261/228 20130101; C08G 2261/18 20130101; H01M 4/136 20130101;
H01M 10/44 20130101; H01M 4/622 20130101 |
International
Class: |
H01M 4/04 20060101
H01M004/04; H01M 4/58 20100101 H01M004/58; H01M 4/136 20100101
H01M004/136; C08G 61/12 20060101 C08G061/12; H01M 4/583 20100101
H01M004/583; H01M 4/60 20060101 H01M004/60; H01M 10/44 20060101
H01M010/44; H01M 10/0525 20100101 H01M010/0525; H01M 4/62 20060101
H01M004/62 |
Claims
1. A cathode, prepared from a cathode formulation comprising:
cathode material having an olivine-based structure, binder
material, and monomer material selected to polymerize into a
conductive polymer upon partial delithiation of the cathode
material during at least a first charging cycle of a cell having
the cathode, wherein: the monomer material is in monomer form in
the cathode in its pristine form prior to the first charging cycle
of the cell, the partial delithiation is carried out
electrochemically during the first charging cycle of the cell, and
following the first charging cycle of the cell, the monomer
material is at least partly polymerized.
2. The cathode of claim 1, wherein the cathode material comprises
LFP (LiFePO.sub.4).
3. The cathode of claim 1, wherein the cathode material is
A.sub.zMXO.sub.4 wherein A is Li, alone or partially replaced by at
most 10% of Na and/or K; 0.ltoreq.z.ltoreq.1, M is at least 50% of
Fe(II) or Mn(II) or mixture thereof; and XO.sub.4 is PO.sub.4,
alone or partially replaced by at most 10 mol % of at least one
group selected from SO.sub.4 and SiO.sub.4.
4. The cathode of claim 1, wherein the cathode material further
comprises a carbon coating.
5. The cathode of claim 1, wherein the monomer material comprises
monomers of at least one of pyrrole, aniline, thiophene, phenyl
mercaptan, furan, phenol, ethylenedioxythiophene and
styrenesulfonate.
6. The cathode of claim 5, wherein at least one ring in the
monomers is substituted with one or more straight, branched or
bridged alkyl, alkenyl, oxa-alkyl, oxa-alkenyl, aza-alkyl,
aza-alkenyl, thia-alkyl, thia-alkenyl, sila-alkyl, sila-alkenyl,
aryl, aryl-alkyl, alkyl-aryl, alkenyl-aryl, dialkylamino or
dialkylazo group, comprising 1-30 carbon atoms.
7. The cathode of claim 1, wherein the monomer material comprises a
combination of monomers and oligomers.
8. The cathode claim 1, wherein the binder material comprises at
least one of: carboxymethyl cellulose (CMC), polyvinylidene
difluoride (PVDF), polyacrylic acid (PAA), polyethylene oxide
(PEO), polyvinyl alcohol (PVA) and alginate.
9. The cathode of claim 1, comprising 80-90% of the cathode
material, 1-10% of the binder material and 1-10% of the monomer
material.
10. The cathode of claim 1, comprising 90-98% of the cathode
material, 1-5% of the binder material and 1-5% of the monomer
material.
11. A cell comprising the cathode of claim 1.
12. A cell comprising: an anode, electrolyte, a separator, and a
cathode comprising: cathode material having an olivine-based
structure, binder material, and a conductive polymer formed during
at least a first charging cycle of the cell from monomer material
selected to polymerize into the conductive polymer upon partial
delithiation of the cathode material, wherein: the monomer material
is in monomer form in the cathode in its pristine form prior to the
first charging cycle of the cell, the partial delithiation is
carried out electrochemically during the first charging cycle of
the cell, and following the first charging cycle of the cell, the
monomer material is at least partly polymerized.
13. The cell of claim 12, having a charging curve, in at least a
first charging thereof, which comprises a local peak at a specified
potential which corresponds to a polymerization reaction of the
monomer material in presence of the partially delithiated cathode
material.
14. A method comprising configuring a cathode made of cathode
material having an olivine-based structure for in-situ
polymerization, by adding to the cathode material monomer material
selected to polymerize into a conductive polymer upon partial
delithiation of the cathode material during at least a first
charging cycle of a cell with the cathode, wherein the monomer
material is in monomer form in the cathode in its pristine form
prior to the first charging cycle of the cell, the partial
delithiation is carried out electrochemically during the first
charging cycle of the cell, and following the first charging cycle
of the cell, the monomer material is at least partly
polymerized.
15. The method of claim 14, further comprising polymerizing the
monomer material during the at least first charging cycle of the
cell.
16. The method of claim 14, wherein the monomer material comprises
monomers and oligomers, and the method further comprises
polymerizing the monomers and the oligomers during the at least
first charging cycle of the cell.
17. The method of claim 14, further comprising operating the cell
at a charging and/or discharging rate of at least 5 C.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/434,083, filed Feb. 16, 2017, which claims the benefit of
U.S. Provisional Patent Application No. 62/432,588, filed Dec. 11,
2016, both of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Technical Field
[0002] The present invention relates to the field of batteries, and
more particularly, to cathodes for fast charge lithium ion
batteries.
2. Discussion of Related Art
[0003] Rechargeable lithium batteries are extensively used for
portable electronic devices as well as hybrid electronic vehicles.
The cell capacity and rate capability as well as safety,
environmental compatibility, life cycle, and cost are among the
commercial considerations in preparing and using various types of
batteries. The olivine LiFePO.sub.4 (LFP) cathode material is known
to be low-cost, safe, environmentally benign, and further, provides
beneficial cyclability and large capacity at high rates of charge
and discharge. It is noted that the LFP particles used are of
nano-scale and/or are coated with carbon; due to poor kinetic
response of electronic and Li.sup.+-ion transfer under rapid-rate
conditions.
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 a cathode
formulation comprising cathode material having an olivine-based
structure, binder material, and monomer material selected to
polymerize into a conductive polymer upon partial delithiation of
the cathode material during at least a first charging cycle of a
cell having a cathode made of the cathode formulation.
[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. 1 is a high level schematic illustration of cathode
formulations, cathodes and cells, according to some embodiments of
the invention.
[0010] FIGS. 2A-2C illustrate examples for a prior art charging
curve (FIG. 2A), a first cycle of a charging curve of the pristine
cell with the pristine cathode having pyrrole monomers as monomer
material (FIG. 2B), and a potential curve of the pristine cathode
having pyrrole monomers as monomer material which is surface
polymerized outside cell, as comparison (FIG. 2C), according to
some embodiments of the invention.
[0011] FIG. 3 is an illustration of an experimental comparison of
cells with disclosed cathodes, with prior art cells having cathodes
that lack the monomers, according to some embodiments of the
invention.
[0012] FIG. 4 is an illustration of an experimental comparison of
cathodes having pyrrole as monomer material versus cathodes having
aniline as monomer material, according to some embodiments of the
invention.
[0013] FIGS. 5A-5J are high resolution scanning electron microscope
(HRSEM) images comparing prior art cathodes with pristine and
operative cathodes respectively, according to some embodiments of
the invention.
[0014] FIG. 6 is a high level schematic illustration of a method,
according to some embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] 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.
[0016] 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 employed herein is for the purpose of description and
should not be regarded as limiting.
[0017] It is noted that the disclosed general formulas relate to
the stoichiometry of the material, which may vary by a few percent
from the stoichiometry due to substitution or other defects present
in the structure.
[0018] Cathodes for a fast charging lithium ion battery, processes
for manufacturing thereof and corresponding batteries are provided.
Cathode formulations comprise cathode material having an
olivine-based structure, binder material, and monomer material
selected to polymerize into a conductive polymer upon partial
delithiation of the cathode material during at least a first
charging cycle of a cell having a cathode made of the cathode
formulation. When the cathode is used in a battery, polymerization
is induced in-situ (in-cell) during first charging cycle(s) of the
battery to provide a polymer matrix which is evenly dispersed
throughout the cathode. The disclosed cathodes may be used in any
energy storage device.
[0019] FIG. 1 is a high level schematic illustration of cathode
formulations 100, cathodes 110, 115 and cells 120, 125, according
to some embodiments of the invention.
[0020] Cathode formulations 100 comprise cathode material 90 having
an olivine-based structure (and optional additives, see below),
binder material 98, and monomer material 95 selected to polymerize
into a conductive polymer upon partial delithiation of cathode
material 90 during at least a first charging cycle of cell 120, 125
having cathode 110, 115 made of cathode formulation 100. Pristine
cathode 110 and pristine cell 120 denote for example cathodes and
cells prior to their first charging cycle, while cathode 115 and
operating cell 125 denote for example cathodes and cells after
their first charging cycle has been carried out. Dried cathode
slurries made of cathode formulations 100 are likewise part of the
present disclosure. It is noted that similar configurations may be
applied to other electrodes and are shown here for cathodes as a
non-limiting example.
[0021] Cathode formulations 100 may comprise cathode material 90
consisting of A.sub.zMXO.sub.4, wherein A is Li, alone or partially
replaced by at most 10% of Na and/or K; 0.ltoreq.z.ltoreq.1; M is
at least 50% of Fe(II) or Mn(II) or mixture thereof; and XO.sub.4
is PO.sub.4, alone or partially replaced by at most 10 mol % of at
least one group selected from SO.sub.4 and SiO.sub.4. For example,
cathode material 90 may include LFP (LiFePO.sub.4) cathode
material. Cathode material 90 may further comprise additives such
as conductive materials, e.g., carbon black and/or carbon
nano-tubes. Cathode formulations 100 may comprise a carbon
coating.
[0022] In certain embodiments M may be selected from Fe(II), Mn(II)
and mixtures thereof, alone or partially replaced by at most 50% of
one or more other metals selected from Ni and Co and/or by at most
15% of one or more aliovalent or isovalent metals other than Ni or
Co, and/or by at most 5% as atoms of Fe(III).
[0023] In certain embodiments, M may be selected from Fe(II),
Mn(II) and mixtures thereof, alone or partially replaced by at most
50% of one or more other metals chosen from Ni and Co and/or by at
most 15% as atoms of one or more aliovalent or isovalent metals
selected from Mg, Mo, Nb, Ti, Al, Ta, Ge, La, Y, Yb, Cu, Sm, Ce,
Hf, Cr, Zr, Bi, Zn, Ca, B and W and/or by at most 5% as atoms of
Fe(III).
[0024] In certain embodiments, cathode material 90 may comprise a
compound corresponding to the general formula
Li.sub.zFe.sub.yMn.sub.1-yPO.sub.4 which has an olivine structure,
wherein z and y are each independently between 0 and 1 (e.g., A may
be Li, M may be Fe.sub.yMn.sub.1-y, X may be P,
0.ltoreq.z.ltoreq.1, 0.ltoreq.y.ltoreq.1, independently).
[0025] Cathode formulations 100 may comprise monomer material 95
consisting of monomers of any of pyrrole, aniline, thiophene,
phenyl mercaptan, furan, and phenol. In certain embodiments,
monomer material 95 may comprise oligomers, at least as part of
monomer material 95. In certain embodiments, monomer material 95
may comprise ethylenedioxythiophene and styrenesulfonate which may
polymerize to conductive polymer PEDOT-PSS
(Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) upon
partial delithiation of cathode material 90 during at least a first
charging cycle of cell 120, 125. In certain embodiments, monomer
material 95 may comprise combinations of monomers and/or oligomers.
In certain embodiments, the rings in any of the monomer embodiments
may be substituted with one or more straight, branched or bridged
alkyl, alkenyl, oxa-alkyl, oxa-alkenyl, aza-alkyl, aza-alkenyl,
thia-alkyl, thia-alkenyl, sila-alkyl, sila-alkenyl, aryl,
aryl-alkyl, alkyl-aryl, alkenyl-aryl, dialkylamino and dialkylazo
compounds comprising about 1-30 carbon atoms.
[0026] Cathode formulations 100 may comprise binder material 98
such as carboxymethyl cellulose (CMC), polyvinylidene difluoride
(PVDF), polyacrylic acid (PAA), polyethylene oxide (PEO), polyvinyl
alcohol (PVA) and/or alginate as non-limiting examples.
[0027] Some embodiments comprise cathode formulations 100 having
80-90% of cathode material 90, 1-10% of binder material 98 and
1-10% of monomer material 95. Some embodiments comprise cathode
formulations 100 having 90-98% of cathode material 90, 1-5% of
binder material 98 and 1-5% of monomer material 95. In certain
embodiments, cathode formulations 100 may comprise more than 90% of
cathode material 90. In certain embodiments, cathode formulations
100 may comprise more than 10% of binder material 98. In certain
embodiments, cathode formulations 100 may comprise more than 10% of
monomer material 95. Some embodiments comprise any sub-range of
weight % combinations within the disclosed ranges.
[0028] Cells 120, 125 may comprise cathodes 110, 115 prepared from
cathode formulations 100, as well as an anode, electrolyte and a
separator (illustrated collective and schematically by a member 80
in the cell). Pristine cathode 110 is prepared from cathode
formulations 100, e.g., by spreading and drying, with cathode
material 90 having an olivine-based structure, binder material 98,
and monomer material 95, while cathode 115 has a conductive polymer
formed during at least a first charging cycle of cell 120, 125 from
monomer material 95. Without being bound by theory, it is suggested
that the polymerization of monomer material 95 into the conductive
polymer is carried out upon partial delithiation of cathode
material 90 during the first cycle(s) of charging and discharging
cell 120, 125. As the polymerization probably occurs during first
charging cycle(s), it is referred to herein as in-situ, or in-cell
polymerization, in contrast to prior art cathodes which are
polymerized before being incorporated in operating cell 125.
[0029] Without being bound by theory, an indication to the
occurrence of the polymerization process during the charging
process is illustrated schematically by peak 113 in FIG. 1 and is
further illustrated in examples provided in FIGS. 2A-2C. FIGS.
2A-2C illustrate examples for a prior art charging curve 85 (FIG.
2A), a first cycle of a charging curve 130 of pristine cell 120
with pristine cathode 110 having pyrrole monomers as monomer
material 95 (FIG. 2B) and a potential curve 130A of pristine
cathode 110 having pyrrole monomers as monomer material 95 which is
surface electro-polymerized outside cell 120 (FIG. 2C), as
comparison, according to some embodiments of the invention. While
in prior art charging 85 the measured cathode potential is
monotonous after the initial rise, charging curve 130 shows a clear
local peak 113 in the potential at around 3.465V which is
understood as corresponding to the polymerization of monomer
material 95 in cathode 110 in cell 120 during actual charging, once
sufficient partial delithiated cathode material has formed during
the charging, as indicated by the potential value. This
understanding was corroborated by identifying a peak 113A at a
similar potential value under surface polymerization of another
cathode 110 outside cell 120. The inventors suggest that, without
being bound by theory, local peak 113 in charging curve 130
indicates the specified potential which corresponds to a
polymerization reaction of monomer material 95 in presence of the
partially delithiated cathode material (e.g., by oxidation). It is
noted that peak 113 is reduced and/or vanishes in later cycles,
probably due to the completion of the polymerization. In different
experiments, local peal 113 was found between 3.455V-3.465V. It is
noted that cathodes 115 may be made operable by polymerization of
monomer material 95 during the first cycle(s) even if local peal
113 is not visible on the charging curve, possibly due to cycling
conditions and cathode composition. The presence of peak 113 is
merely understood as a non-limiting indicator of the polymerization
process, and not as a required condition thereto.
[0030] FIG. 3 is an illustration of an experimental comparison of
cells 125 with disclosed cathode 115 with prior art cells having
cathodes that lack the monomers, according to some embodiments of
the invention. The cell capacity and cyclability are exemplified at
charging/discharging rates of 0.1 C, 1 C, 5 C, 10 C and 15 C,
illustrating the superior capacity of cells 125, particularly at
high charging rates such as 15C in which cells 125 achieved more
than threefold the capacity of prior art cells (indicated by
.DELTA. in the figure).
[0031] FIG. 4 is an illustration of an experimental comparison of
cathodes 115 having pyrrole as monomer material 95 versus cathodes
115 having aniline as monomer material 95, according to some
embodiments of the invention. In both cases, monomer material 95
was added as 5% (weight %) of the cathode slurry and both cases
show high capacities in all charging rates, and particularly at
high charging rates such as 5 C, 10 C, 15 C and possibly higher
charging rates.
[0032] FIGS. 5A-5J are high resolution scanning electron microscope
(HRSEM) images comparing prior art cathodes 86A, 86B with pristine
and operative cathodes 110, 115, respectively, according to some
embodiments of the invention. FIGS. 5A and 5C show surface HRSEM
images of pristine prior art cathodes 86A (LFP) and 86B (LFP with
polypyrrole, polymerized prior to the first cycle, added
polymerized into the cathode slurry), respectively, and FIG. 5B is
a surface HRSEM image of pristine cathode 110 (in the illustrated
non-limiting example, LFP with pyrrole monomer material 95). FIGS.
5D and 5F show cross section HRSEM images of pristine prior art
cathodes 86A and 86B, respectively, and FIG. 5E is a cross section
HRSEM image of pristine cathode 110. FIGS. 5G and 5I show surface
HRSEM images of operative cathode 115 and prior art cathode 86B,
respectively. FIGS. 5H and 5J show cross section HRSEM of operative
cathode 115 and prior art cathode 86B, respectively.
Advantageously, the inventors have found out that the disclosed
in-cell polymerization of monomer material 95 yields thick and
uniform polymerization of polypyrrole through the whole cross
section of electrode 115 (FIG. 5H), in stark contrast to prior art
electrode 86B (FIG. 5J).
[0033] FIG. 6 is a high level schematic illustration of a method
200, according to some embodiments of the invention. The method
stages may be carried out with respect to cathode formulations 100,
cathodes 110, 115 and cells 120, 125 described above, which may
optionally be configured to implement method 200. Method 200 may
comprise stages for producing, preparing and/or using device
cathode formulations 100, cathodes 110, 115 and cells 120, 125
described above, such as any of the following stages, irrespective
of their order.
[0034] Method 200 may comprise configuring an olivine-based cathode
for in-situ (in-cell) polymerization (stage 210), e.g., by
selecting monomers which polymerize into a conducting polymer in
presence of partially delithiated olivine-based cathode material
(stage 215), adding the monomers to the cathode material (stage
220) configuring the cathode to undergo the polymerization during
the first charging cycle(s) (stage 225), e.g., polymerizing the
monomers during the first charging cycle(s) (stage 230) and
producing the operative cathode in-situ by the polymerization
(stage 240).
[0035] In certain embodiments, in cathode material 90 consisting of
A.sub.zMXO.sub.4, wherein A is Li, alone or partially replaced by
at most 10% of Na and/or K; 0.ltoreq.z.ltoreq.1, M may be selected
from Fe(II), Mn(II) and mixtures thereof, alone or partially
replaced by at most 50% of one or more other metals selected from
Ni and Co and/or by at most 15% of one or more aliovalent or
isovalent metals other than Ni or Co, and/or by at most 5% as atoms
of Fe(III) and XO.sub.4 is PO.sub.4, alone or partially replaced by
at most 10 mol % of at least one group selected from SO.sub.4 and
SiO.sub.4.
[0036] In certain embodiments, M may be selected from Fe(II),
Mn(II) and mixtures thereof, alone or partially replaced by at most
50% of one or more other metals chosen from Ni and Co and/or by at
most 15% as atoms of one or more aliovalent or isovalent metals
selected from Mg, Mo, Nb, Ti, Al, Ta, Ge, La, Y, Yb, Cu, Sm, Ce,
Hf, Cr, Zr, Bi, Zn, Ca, B and W and/or by at most 5% as atoms of
Fe(III).
[0037] In certain embodiments, cathode material 90 may comprise a
compound corresponding to the general formula
Li.sub.zFe.sub.yMn.sub.1-yPO.sub.4 which has an olivine structure,
wherein z and y are each independently between 0 and 1 (e.g., A may
be Li, M may be Fe.sub.yMn.sub.1-y, X may be P,
0.ltoreq.z.ltoreq.1, 0.ltoreq.y.ltoreq.1, independently).
[0038] In certain embodiments, cathode material 90 may comprise a
compound corresponding to the general formula Li.sub.zFePO.sub.4
which has an olivine structure, wherein 0.ltoreq.z.ltoreq.1 (e.g.,
with M as Fe).
[0039] In certain embodiments, cathode material 90 may be a
partially delithiated polymerization initiator with the formula
C-A.sub.zMXO.sub.4, having on at least a portion of a surface
thereof, a film of carbon (e.g., deposited by pyrolysis, as an
additive to cathode material 90, coated on the surface, etc.). The
film of carbon may be uniform, adherent and non-powdery. The film
of carbon may be up to 15% of a weight of the polymerization
initiator, or between 0.5%-5% of a weight of the polymerization
initiator.
[0040] According to some embodiments, when the cathode is used in a
battery comprising a current collector, a first charging cycle of
the cathode causes polymerization initiator molecules (e.g., the
partially delithiated A.sub.zMXO.sub.4) to induce polymerization of
monomer material 95 incorporated in cathode 110, thereby providing
a polymer matrix between cathode material 90 and the current
collector (not shown) to which cathode 110 is attached. According
to some embodiments, the polymerization process which occurs within
the cathode may provide a polymer that is evenly dispersed
throughout the cathode.
[0041] Introduction of electrochemically-active conducting polymers
such as polypyrrole (PPy) and polyaniline (PAni) into LFP/C-LFP
composite cathodes is known to enhance both the capacity and rate
capability. The conductive polymers appear to provide good
electronic contact between active particles themselves and with the
current collector, and acts as a host material for Li.sup.+
insertion/extraction. It has also been shown that the Li.sup.+
diffusivity is greatly enhanced probably due to electrostatic
attraction between the anions of the conducting polymer and
Li.sup.+ which can help Li.sup.+ pull out of LFP particles.
However, in the prior art, solutions concerning the incorporation
of the conductive polymer are insufficiently effective or are
industrially inapplicable. For example, prior art methods for
preparing such composite cathodes include: (i) oxidative
polymerization of the monomer in solution containing suspended
oxide powders, wherein the prepared PPy-LFP particles are mixed
with a binder and carbon to prepare the cathode; (ii) conventional
fabrication by mixing the formerly synthesized polymer with oxide
and the inactive additives (carbon and binder). The polymer can be
synthesized chemically or electrochemically using the monomer as-is
or following chemical modification for covalently attaching a redox
couple, such as ferrocene; (iii) in-situ electrodeposition onto
designated current collector (e.g., stainless-steel mesh) from
suspension containing oxide particles and a monomer in an organic
solvent (e.g., acetonitrile) via cyclic voltammetry--the resulted
cathode may be used as-is without any additional binder or
additives; (iv) in-battery electro-polymerization--an LFP cathode
is closed in a coin-cell in the presence of a monomer dissolved in
an electrolyte and the polymer is polymerized by either a single
step of charging to induce de-lithiation of the cathode or by
initial charge to induce de-lithiation followed by the addition of
a monomer solution after which an additional galvanostatic step is
performed to complete the polymerization, wherein the partially
delithiated lithium metal phosphate acts as a polymerization
initiator.
[0042] Advantageously, while prior art polymerization is carried
out prior to the preparation of the cathode or prior to the
insertion of the cathode into the cell, and typically from compound
in the electrolyte or in a solution, disclosed cathodes 110 are
prepared from slurries which include monomer material 95 and
polymerization is carried out in cell 120, 125 without need for
polymerization of monomer material 95 during the preparation of
cathode 110, before introducing cathode 100 into cell 120. The
disclosed invention thus provides significant process advantages as
well as superior cathodes and cells, as explained above.
[0043] In the above description, an embodiment is an example or
implementation of the invention. The various appearances of "one
embodiment", "an embodiment", "certain embodiments" or "some
embodiments" do not necessarily all refer to the same embodiments.
Although various features of the invention may be described in the
context of a single embodiment, the features may also be provided
separately or in any suitable combination. Conversely, although the
invention may be described herein in the context of separate
embodiments for clarity, the invention may also be implemented in a
single embodiment. Certain embodiments of the invention may include
features from different embodiments disclosed above, and certain
embodiments may incorporate elements from other embodiments
disclosed above. The disclosure of elements of the invention in the
context of a specific embodiment is not to be taken as limiting
their use in the specific embodiment alone. Furthermore, it is to
be understood that the invention can be carried out or practiced in
various ways and that the invention can be implemented in certain
embodiments other than the ones outlined in the description
above.
[0044] The invention is not limited to those diagrams or to the
corresponding descriptions. For example, flow need not move through
each illustrated box or state, or in exactly the same order as
illustrated and described. Meanings of technical and scientific
terms used herein are to be commonly understood as by one of
ordinary skill in the art to which the invention belongs, unless
otherwise defined. While the invention has been described with
respect to a limited number of embodiments, these should not be
construed as limitations on the scope of the invention, but rather
as exemplifications of some of the preferred embodiments. Other
possible variations, modifications, and applications are also
within the scope of the invention. Accordingly, the scope of the
invention should not be limited by what has thus far been
described, but by the appended claims and their legal
equivalents.
* * * * *