U.S. patent application number 11/932889 was filed with the patent office on 2009-09-10 for conductive polymeric compositions for lithium batteries.
This patent application is currently assigned to Arizona Board of Regents for and on behalf of Arizona State University. Invention is credited to Charles Austen Angell, Wu Xu.
Application Number | 20090226817 11/932889 |
Document ID | / |
Family ID | 26906914 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090226817 |
Kind Code |
A1 |
Angell; Charles Austen ; et
al. |
September 10, 2009 |
CONDUCTIVE POLYMERIC COMPOSITIONS FOR LITHIUM BATTERIES
Abstract
Novel chain polymers comprising weakly basic anionic moieties
chemically bound into a polyether backbone at controllable anionic
separations are presented. Preferred polymers comprise orthoborate
anions capped with dibasic acid residues, preferably oxalato or
malonato acid residues. The conductivity of these polymers is found
to be high relative to that of most conventional salt-in-polymer
electrolytes. The conductivity at high temperatures and wide
electrochemical window make these materials especially suitable as
electrolytes for rechargeable lithium batteries.
Inventors: |
Angell; Charles Austen;
(Mesa, AZ) ; Xu; Wu; (Broadview Heights,
OH) |
Correspondence
Address: |
FISH & RICHARDSON, PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Arizona Board of Regents for and on
behalf of Arizona State University
|
Family ID: |
26906914 |
Appl. No.: |
11/932889 |
Filed: |
October 31, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10311643 |
Sep 3, 2003 |
7504473 |
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PCT/US01/41009 |
Jun 16, 2001 |
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11932889 |
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60212231 |
Jun 16, 2000 |
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60290864 |
May 14, 2001 |
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Current U.S.
Class: |
429/309 ;
29/623.1 |
Current CPC
Class: |
H01M 10/052 20130101;
C08G 65/328 20130101; C08G 65/32 20130101; C08G 79/08 20130101;
H01M 10/0565 20130101; C08G 79/10 20130101; Y02E 60/10 20130101;
H01M 2300/0082 20130101; Y10T 29/49108 20150115; H01M 2300/0085
20130101 |
Class at
Publication: |
429/309 ;
29/623.1 |
International
Class: |
H01M 6/18 20060101
H01M006/18 |
Goverment Interests
[0002] Financial assistance for this project was provided by the
U.S. Government through the National Science Foundation under Grant
No. CHE-9808678 and the Department of Energy under Grant Nos.
DEFG0393ER14378-003 and DEFG0395ER45541. Therefore, the United
States Government may own certain rights to this invention.
Claims
1-40. (canceled)
41. A method of making an electrochemical cell, comprising:
assembling an anode and a cathode in a case; and disposing an
electrolyte between the anode and the cathode to form the
electrolytic cell, wherein the electrolyte provides an electrical
conduction path through the electrochemical cell, and wherein the
electrolyte comprises a plurality of polyanionic polymer chains
forming a solid polymer having a negatively charged surface, each
polyanionic polymer chain having a formula:
M.sub.b.sup.+k[AL].sub.p.sup.-q wherein: AL is a repeat unit in the
chain wherein AL includes the formula: ##STR00002## wherein X is a
Group III element; O is oxygen, Y includes a formula
OC(CR.sup.1.sub.2).sub.aCO, SO.sub.2, aryl, phenyl, and
R.sup.1-substituted phenyl, wherein a ranges from 0 to 5, R.sup.1
is selected from the group consisting of alkyl 1,3
tetra(trifluoromethyl)ethylene dialato, halo 1,3 tetra
(trifluoromethyl)ethylene dialato, and
silane-co-tetraethleneglycalato, L comprises n spacer groups z, z
is selected from the group consisting of alkyl, R.sup.2-substituted
alkyl, alkoxy and R.sup.2-substituted alkoxy, wherein R.sup.2 is
selected from the group consisting of hydrogen, halo, alkyl,
alkoxy, phenyl, and substituted phenyl, wherein n ranges from about
1 to 30, and p is the number of repeating units in the polymer, q
is charge on the anion, M.sup.+ is a cation, b is the repeat number
of compounds with a positive charge, k is the charge on the
compound with a positive charge, and bk equals qp.
42. The method of claim 41, wherein p is a number from 1 to 3.
43. The method of claim 41, wherein the M.sup.+k is selected from
the group consisting of hydrogen, Group I metals, Group II metals,
NR.sup.3.sub.4 and PR.sup.3.sub.4, and wherein R.sup.3 is selected
from the group consisting of hydrogen, alkyl, and halo, and wherein
k ranges from 1 to 3.
44. The method of claim 41, wherein the repeating spacer groups
include a polysiloxane having the formula
Si[(CR.sup.4.sub.3).sub.2]--O(CR.sup.4.sub.2CR.sup.4.sub.2O)].sub.w,
wherein w ranges from about 2 to 50, and wherein R.sup.4 is
selected from the group consisting of hydrogen and alkyl.
45. The method of claim 41, wherein A comprises a borate anion
having two oxygens bound to a dibasic acid residue and two oxygens
bound to polymeric chain groups L, wherein spacer group z is
[(CR.sup.2.sub.2).sub.x(CR.sup.2.sub.2O)], and wherein x ranges
from 0 to 50.
46. The method of claim 41, wherein the polyanionic polymer chain
is selected from the group consisting of poly[lithium oxalato
oligo(ethylene glycolato)n orthoborate], poly [lithium oxalate
oligo(propylene glycolato)n orthoborate], poly [lithium malonato
oligo(ethyleneglycolato)n orthoborate], and poly [lithium malonato
oligo(propylene glycolato)n orthoborate], and wherein n is 3,5, 9
or 14.
47. The method of claim 41, wherein the solid polymer further has
chemical bonds between polymer chains.
48. The method of claim 41, wherein the polyanionic polymer chain
includes a plasticizer.
49. A method of making an electrochemical cell, comprising:
assembling an anode and a cathode in a case; and disposing an
electrolyte between the anode and the cathode to form the
electrolytic cell, wherein the electrolyte provides an electrical
conduction path through the electrochemical cell, and wherein the
electrolyte comprises a plurality of polyanionic polymer chains
forming a solid polymer having a negatively charged surface, each
polyanionic polymer chain having a formula:
M.sub.b.sup.+k[AL].sub.p.sup.-q wherein: AL is a repeat unit in the
chain, wherein A is an anionic group including a Group III element,
L is a polymeric chain group chemically linked to A, the polymeric
chain having repeating polyether spacer groups, the spacer groups
providing distance between each anionic group, p is the number of
repeating units in the polymer, q is charge on the anion, M.sup.+
is a cation, b is the repeat number of compounds with a positive
charge, k is the charge on the compound with a positive charge, and
bk equals pq.
50. The method of claim 49, wherein AL of the polyanionic polymer
chain includes the formula: ##STR00003## wherein X is a Group III
element; O is oxygen, Y includes a formula OC(CR.sub.2).sub.aCO,
SO.sub.2, aryl, phenyl, and R-substituted phenyl, wherein a ranges
from 0 to 5, R is selected from the group consisting of alkyl 1,3
tetra(trifluoromethyl)ethylene dialato, halo 1,3
tetra(trifluoromethyl)ethylene dialato, and
silane-co-tetraethyleneglycalato, L comprises n spacer groups z, z
is selected from the group consisting of alkyl, R-substituted
alkyl, alkoxy and R-substituted alkoxy, wherein R is selected from
the group consisting of hydrogen, halo, alkyl, alkoxy, phenyl and
substituted phenyl, wherein n ranges from about 1 to 30, and p is a
number from 1 to 3.
51. The method of claim 49, wherein M.sup.+k is selected from the
group consisting of hydrogen, Group I metals, Group II metals,
NR.sup.3.sub.4 and PR.sup.3.sub.4, and wherein R.sup.3 is selected
from the group consisting of hydrogen, alkyl, and halo, and wherein
k ranges from 1 to 3.
52. The method of claim 49, wherein the repeating spacer groups
include a polysiloxane having the formula
Si[(CR.sup.4.sub.3).sub.2]--O(CR.sup.4.sub.2CR.sup.4.sub.2O)].sub.w,
wherein w ranges from about 2 to 50, and wherein R.sup.4 is
selected from the group consisting of hydrogen and alkyl.
53. The method of claim 49, wherein A comprises a borate anion
having two oxygens bound to a dibasic acid residue and two oxygens
bound to polymeric chain groups L, and wherein
[(CR.sup.2.sub.2).sub.x(CR.sup.2.sub.2O)], and wherein x ranges
from about 0 to 50.
54. The method of claim 49, wherein polyanionic polymer chain is
selected from the group consisting of poly[lithium oxalate
oligo(ethylene glycolato)n orthoborate], poly [lithium oxalate
oligo(propylene glycolato)n orthoborate], poly [lithium malonato
oligo(ethyleneglycolato)n orthoborate], and poly [lithium malonato
oligo(propylene glycolato)n orthoborate], and wherein n is 3,5, 9
or 14.
55. The method of claim 49, wherein the solid polymer further has
chemical bonds between the polymeric chains.
56. The method of claim 49, wherein the polyanionic polymer chain
includes a plasticizer.
57. An electrochemical cell, comprising: an anode; a cathode; and a
means for providing an electrical conduction path between the anode
and the cathode, wherein the conduction path comprises a plurality
of polyanionic polymer chains forming a solid polymer having a
negatively charged surface, each polyanionic polymer chain having a
formula: M.sub.b.sup.+k[AL].sub.p.sup.-q wherein: AL is a repeat
unit in the chain, wherein A is an anionic group including a Group
III element, L is a polymeric chain group chemically linked to A,
the polymeric chain having repeating polyether spacer groups, the
spacer groups providing distance between each anionic group, p is
the number of repeating units in the polymer, q is charge on the
anion, M.sup.+ is a cation, b is the repeat number of compounds
with a positive charge, k is the charge on the compound with a
positive charge, and bk equals pq.
Description
[0001] This application is a continuation application of U.S.
patent application Ser. No. 10/311,643 entitled "Conductive
Polymeric Compositions For Lithium Batteries" and filed on Dec. 12,
2002 and published as U.S. Publication No. US 2004-0054126 (A1) on
Mar. 18, 2004 which claims priority to PCT Application No.
PCT/US01/41009 entitled "Conductive Polymeric Compositions for
Lithium Batteries" and filed on Jun. 16, 2001 and published as PCT
Publication No. 01/96446 on Dec. 20, 2001 which claims priority to
the following two provisional applications: U.S. Provisional Patent
Application No. 60/212,231 filed on Jun. 16, 2000 and entitled
"High Conductivity Polyanionic Electrolytes for Batteries and other
Electrolytic Devices" and U.S. Provisional Patent Application No.
60/290,864 filed May 14, 2001. This application incorporates by
reference the entire disclosures of the above applications as part
of the specification of this application.
INTRODUCTION
[0003] 1. Technical Field
[0004] The present invention relates to novel highly conductive
polyanionic polymers suitable for use in solid polymeric
electrolytes in lithium batteries, especially secondary lithium
batteries.
[0005] 2. Background
[0006] Lithium batteries supply energy to a growing number of
portable electrochemical devices and are a promising energy source
for larger applications such as electric automobiles. Accordingly,
lithium batteries are the subject of intense research and the
effort to improve performance continues.
[0007] A major area of interest has been in the field of
electrolytes for lithium cells where high conductivity and
transport number for lithium ion has been the goal. Electrolytes
are generally prepared by dissolving a highly-conductive salt in a
polymer, usually an ether polymer, to make solid polymeric
electrolytes (SPE). Examples of the "salt-in-polymer" approach
include the electrolytes disclosed in U.S. Pat. No. 5,849,432, U.S.
Pat. No. 5,824,433 U.S. Pat. No. 5,660,947, and U.S. Pat. No.
6,235,433.
[0008] A "polymer-in-salt" approach has also been attempted. In
this approach, chain polymers are added as a dilute component to
impart solidity to molten alkali metal salt mixtures of high
conductivity (1). Unfortunately, it has been difficult to find
simple salts of lithium that are stable and liquid at room
temperature. Examples of the polymer-in-salt approach include U.S.
Pat. No. 5,962,169, U.S. Pat. No. 5,855,809, U.S. Pat. No.
5,786,110, U.S. Pat. No. 5,506,073 and U.S. Pat. No. 5,484,670.
[0009] Investigations of weakly coordinating anion groups continue
to spur the development of new polymeric materials suitable for
inclusion into SPE. Fujinami et al. in U.S. Pat. No. 6,210,838,
disclose a Lewis acid, the weakly coordinating boroxine ring in a
polymeric ether chain. Good conductivities are achieved by adding a
salt to the polymer. Although the polymer appears to have good
mechanical properties, the reported conductivity is too low for
commercial applications. Strauss et al. in U.S. Pat. No. 6,221,941
disclose weakly coordinating polyfluoroalkoxide anions for
applications in electrochemical devices. A highly conductive salt,
bis(oxalato)borate, has recently been discovered (German patent No.
DE 19829030) and its potential as a SPE is being studied. (6).
[0010] The need for conductive polymers continues to spur the
development of new materials. Polymeric films which contain weakly
coordinating anionic groups are promising candidates as SPE, as
they would have good decoupling characteristics and thus high
transport number for cations. Batteries and other ionic devices
could be made much smaller and lighter by exploiting these films.
(2).
[0011] Despite continuing discoveries of highly conductive
electrolytic salts, and advances in polymerizing these salts, solid
polymer electrolytes for lithium batteries are still needed.
Especially sought are weakly coordinating anionic materials that
can be fabricated into films with high conductivity.
RELEVANT LITERATURE
[0012] 1. C. A. Angell, K. Xu, S. S. Zhang and M. Videa,
"Variations on the Salt-Polymer Electrolyte Theme for Flexible
Solid Electrolytes", Solid State Ionics, 86-88, 17-28 (1996).
[0013] 2. C. A. Angell, C. Liu and G. Sanchey, "Rubbery Solid
Electrolytes with Dominant Catronic Transport and High Ambient
Conductivity", Nature, 362, 137-139, Mar. 11, 1993. [0014] 3. J. R.
MacCallum and C. A. Vincent (Eds.), Polymer Electrolytes Reviews,
Vol. 1, Elsevier, London, 1987. [0015] 4. H. Ohno, "Molten Salt
Type Polymer Electrolytes", Electrochimica, 46, 1407-1411 (2001).
[0016] 5. S. S. Zhang, Z. Chang, K. Xu and C. A. Angell, `Molecular
and Anionic Polymer System with Micro-Decoupled Conductivities",
Electrochimica Acta, 45, 12-29 (2000). [0017] 6. W. Xu, and C. A.
Angell, Electrochem. and Solid State Lett., 4, E1 (2001).
SUMMARY OF THE INVENTION
[0018] It has been discovered that certain anionic groups may be
readily bound into chain polymers to make conductive solid
polymers. The novel polymers comprise repeat units of weakly
coordinating anions in a polyether backbone at separations
determined by the number and nature of repeating spacer groups in
the polymer chains. The repeating spacer groups also determine the
physical characteristics of the polymer including glass transition
temperature and mechanical properties such as flexibility, shear
strength and solubility.
[0019] A method for preparing the subject polymers is provided. In
the method the anionic component of certain electrolytic salts
comprising a Group III element, preferably orthoborate is modified
by chelation with a capping group to make weakly coordinating
anionic moieties when incorporated into the polymeric chains. This
property makes them suitable for use as solid polymeric
electrolytes (SPE) in lithium batteries.
[0020] In an important aspect of the invention, certain
modifications of the polyanionic polymers, plasticization and
cross-linking, e.g., are provided to enhance the conductivity and
optimize certain physical properties of the polymers. The modified
polymers may be formed into films, coatings and extruded into solid
forms for use in electrochemical devices and especially in lithium
batteries and rechargeable Lithium batteries.
BRIEF DESCRIPTION OF THE FIGURES
[0021] FIG. 1 illustrates temperature dependence of ionic
conductivities of PEG-spaced polyMOBs, P(LiOEG.sub.nB), where the
length of spacer EG.sub.n is 3 to 23.
[0022] FIG. 2 illustrates temperature dependence of ionic
conductivities of PPG-spaced polyMOBs, P(LiOPG.sub.nB), where the
length of spacer PG.sub.n is 7 to 17.
[0023] FIG. 3 illustrates temperature dependence of ionic
conductivities of PEG-spaced polyMMBs, P(LiMEG.sub.nB), where the
length of spacer EG.sub.n is 5 and 14.
[0024] FIG. 4 illustrates temperature dependence of ionic
conductivities of LiBH.sub.4 crosslinked PEG-spaced polyMOBs,
BCLEG.sub.nB, where the length of spacer EG.sub.n is 5 to 14.
[0025] FIG. 5A illustrates temperature dependence of ionic
conductivity of EC-PC (1:1) plasticized P(LiOEG.sub.3B) with
different EC-PC content.
[0026] FIG. 5B illustrates temperature dependence of ionic
conductivity of EC-PC (1:1) plasticized P(LiOEG.sub.5B) with
different EC-PC content.
[0027] FIG. 5C illustrates temperature dependence of ionic
conductivity of EC-PC (1:1) plasticized P(LiOEG.sub.9B) with
different EC-PC content.
[0028] FIG. 5D illustrates temperature dependence of ionic
conductivity of EC-PC (1:1) plasticized P(LiOEG.sub.14B) with
different EC-PC content.
[0029] FIG. 6 illustrates temperature dependence of ionic
conductivity of plasticized P(LiOEG.sub.5B) by different EC-PC
compositions.
[0030] FIG. 7 illustrates the room temperature conductivity of
P(LiOEG.sub.3B) plasticized by different solvents and solvent
mixtures with the variation of Lithium concentrations. Comparison
is also made with the conductivity of simple LiBOB solutions in PC.
Remembering that our conductivity is entirely due to Li.sup.+
cations, these results are seen as highly promising.
[0031] FIG. 8A illustrates temperature dependence of ionic
conductivity of EC-PC (1:1 by wt) plasticized
LiBH.sub.4-crosslinked P(LiOEG.sub.5B) with different content of
plasticizer.
[0032] FIG. 8B illustrates temperature dependence of ionic
conductivity of EC-PC (1:1 by wt) plasticized
LiBH.sub.4-crosslinked P(LiOEG.sub.9B) with different content of
plasticizer.
[0033] FIG. 8C illustrates temperature dependence of ionic
conductivity of EC-PC (1:1 by wt) plasticized
LiBH.sub.4-crosslinked P(LiOEG.sub.14B) with different content of
plasticizer.
[0034] FIG. 9 illustrates temperature dependence of ionic
conductivities of two gel electrolytes with composition of 20.92
PPMA-8.09 P(LiOEG3B)-35.45 EC-35.44 PC (Example 8), and 21.05
PMMA-7.91 BCLEG5B-35.53 EC-35.52 PC (Example 9), respectively.
[0035] FIG. 10A illustrates lithium deposition-stripping process
and electrochemical oxidation of 80% EC-PC plasticized
P(LiOEG.sub.3B) on stainless steel electrode, at a scan rate of 1
mVs.sup.-1 at room temperature. SS area=1.963.times.10.sup.-3
cm.sup.2.
[0036] FIG. 10B illustrates lithium deposition-stripping process
and electrochemical oxidation of 80% EC-PC plasticized
P(LiOEG.sub.3B) on nickel electrode, at a scan rate of 1 mVs.sup.-1
at room temperature. Ni area=1.963.times.1010.sup.-3 cm.sup.2.
[0037] FIG. 10C illustrates lithium deposition-stripping process
and electrochemical oxidation of 80% EC-PC plasticized
P(LiOEG.sub.3B) on aluminum electrode, at a scan rate of 1
mVs.sup.-1 at room temperature. A1 area=1.963.times.10.sup.-3
cm.sup.2.
[0038] FIG. 10D illustrates lithium deposition-stripping process
and electrochemical oxidation of 80% EC-PC plasticized
P(LiOEG.sub.3B) on copper electrode, at a scan rate of 1 mVs.sup.-1
at room temperature. Cu area=1.963.times.1010.sup.-3 cm.sup.2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] It has been discovered that certain anionic groups may be
readily bound into chain polymers to make conductive solid
polymers. The novel polymers and their formulations are provided
wherein the polymeric compositions comprise repeat units of weakly
coordinating anions positioned between polymer chains comprising
repeating spacer groups.
[0040] The weakly coordinating anions will, for the most part, be
tetra-coordinated members of the Group III elements, preferably
tetra-coordinated boron and most preferably orthoborate,
substituted with appropriate chelating groups for providing the
desired weakly coordinating characteristics of the resulting
anionic moiety. The chelating groups bind two oxygen members of the
orthoborate anion, thus leaving two oxygens free for binding into
the polymeric chains. Preferred chelating groups are dibasic acid
residues, most preferably oxalato, malonato or succinato. Certain
other preferred chelating groups
1,2,tetra(trifluoromethyl)ethylenedialato, aryl phenyl and
R-substituted phenyl wherein R is alkyl or halo, SO.sub.2 and
silane-co-tetraethylene glycalato[DMSI]. The chelating group may be
a bi-dentate group or may be two monodentate groups.
[0041] To space the repeating anions in the polymer chain, the
repeating spacer groups are chosen to have a length and structure
required to achieve the desired separation. Most generally, the
spacer groups are polyethers, which may be the same or different in
each occurrence. Certain preferred polyethers are poly(ethylene
glycol), (hereinafter termed PEG), or poly(propylene glycol),
(hereinafter termed PPG), of different molecular weights. Certain
other spacer groups are siloxanes.
[0042] Certain physical characteristics are also determined by
choice of repeating spacer groups in the polymer. Glass transition
temperature and mechanical properties such as flexibility, shear
strength and solubility are affected by the nature of the repeating
spacer groups. At room temperature, for example, the PEG-spaced
polymers are almost glassy for short spacer units, e.g. when
tri(ethylene glycol) (n=3) is used in the polymerization. They are
almost rubbery (very slowly flowing at high temperatures, but
rubbery for short time stresses) when PEG200 (n.apprxeq.5) is used
in the polymerization, and soft or sticky rubbery when PEG400
(n.apprxeq.9) and PEG600 (n.apprxeq.14) are used in the
polymerization. The polymer from PEG1000 (n.apprxeq.23) is partly
crystallized (the polyether segment) at room temperature. The three
PPG-spaced polymers are all highly viscous liquids. The polymers
are soluble in various polar solvents, like acetonitrile, acetone
and even chloroform. Slow hydrolysis and alcoholysis of the
polymers take place on prolonged exposure to water or alcohols.
However, the reaction products are benign.
[0043] The choice of spacer group also determines the conductivity
of the polyanionic polymers. FIG. 1 and FIG. 2 show the temperature
dependence of ionic conductivity of PEG and PPG spaced polyanionic
electrolytes measured during steady cooling, before (B) and after
(A) chloroform treatment to remove LiBOB. The conductivities of
these polymeric forms are strongly dependent on the length of the
PEG or PPG spacer between the anionic groups, which can be
characterized by the number of ethyleneoxy or propyleneoxy units, n
value. The actual separation of anions depends on chain
conformations. For equal n value, PPG-spaced polymers are
distinctly less conducting than PEG-spaced polymers.
[0044] A method for preparing the subject polymers is provided. In
the method, the anionic component of certain electrolytic salts
comprising a Group III element, preferably orthoborate is modified
by chelation with a capping group to make weakly coordinating
anionic groups. The anionic groups are then reacted with the
polymer chains, preferably polyalkylene oxides comprising a
terminal reactive group, preferably hydroxyl, under condensations
whereby a condensation reaction occurs between the capped anionic
group and the reactive group. The weakly coordinating polyanionic
polymer and a small molecule result.
[0045] In the preferred method, an oxalato-capped orthoboric acid
anion, B(C.sub.2O.sub.4)(OH).sub.2.sup.-, is provided. A
poly(alkylene glycol) is also provided. The capped orthoboric acid
and the polyalkylene glycol are allowed to react to form a
mono-oxalato orthoborate (a polyMOB'' having the formula
P(LiOEG.sub.nB) or P(LiOPG.sub.nB), where EG represents ethylene
glycol, PG represents propylene glycol and n represents the number
of the spacer repeat units) eliminating water in a condensation
polymerization process to provide the polymeric polyanion of
whatever cation was used to charge-compensate the anion. Preferably
the cation is monovalent and is lithium or sodium. In other
instances, a malonato-capped orthoboric acid anion,
B(CR.sub.2C.sub.2O.sub.4)(OH).sub.2.sup.- wherein R is hydrogen or
halo, preferably fluoro, is provided. In yet other instances the
anion comprises a succinic acid residue of the formula
B((CR.sub.2)bC.sub.2O4)(OH).sub.2.sup.-. In certain preferred
instances the anion comprises
1,2-tetra(trifluoromethyl)ethylenedialato(2-)O,O'
[OC(CF.sub.3).sub.2]. This anion is disclosed in Xu, W. and Angell,
C. A, Electrochim. And Solid-State Letters, 3 (8)366-368 (2000)
which is hereby incorporated by reference. In certain other
instances, the capping group is silane-co-tetraethylene glycalato
[DMSI].
[0046] The method may be illustrated by the following equations for
the preparation of the lithium borate polymer of PEG:.
LiOH+HOOCCOOH+B(OH).sub.3.fwdarw.LiB(C.sub.2O.sub.4)(OH).sub.2+2H.sub.2O
(1)
mLiB(C.sub.2O.sub.4)(OH).sub.2+mHO(CH.sub.2CH.sub.2O).sub.nH.fwdarw.H{O[-
Li(C.sub.2O.sub.4)B(OCH.sub.2CH.sub.2).sub.n}.sub.mOH+2mH.sub.2O
(2)
Certain by-products of these reactions may be separated from the
desired polyanionic polymer by treatment with a suitable solvent
such as acetonitrile or chloroform in which the by-products are
poorly soluble. The glass transition temperatures, for example,
before and after chloroform extraction are given in Table 1.
TABLE-US-00001 TABLE 1 DTA data for P(LiOEG.sub.nB).sub.S and
P(LiOPG.sub.nB).sub.S before and after chloroform treatment to
remove dissolved LiBOB Before CHCl.sub.3 treatment After CHCl.sub.3
treatment T.sub.g T.sub.c T.sub.l T.sub.g T.sub.c T.sub.l Spacer n
value (.degree. C.) (.degree. C.) (.degree. C.) (.degree. C.)
(.degree. C.) (.degree. C.) PEG 3 a a a -0.9 -- -- 5 -22.9 -- --
-20.1 -- -- 9 -41.8 -- -- -44.3 -- -- 14 -51.5 -15.4 6.6 -53.3
-15.4 23.1 23 -54.5 -2.3 20.6 -63.1 -47.2 39.7 PPG 7 -43.3 -- --
-47.0 -- -- 13 -56.9 -- -- -56.0 -- -- 17 -63.4 -- -- -61.0 -- --
a: Not measured.
It may be seen that most of the polymers exhibit glass transitions
in only the studied temperature range between -150 and 100.degree.
C. The glass transition temperature (T.sub.g) decreases with
increasing the spacer length for both types of spacers. Although it
is not intended that the invention be bound by explanation of this
behavior, it is thought that the effect of increasing spacer length
is because the shorter spacer polymer has higher lithium ion
concentration, raising the cohesive energy via transient
crosslinking. Thus at ambient temperature the segmental mobility,
and hence the Li.sup.+ mobility increases with increasing the
spacer length.
[0047] It may also be seen from Table 1 that the glass transition
temperature has decreased after chloroform treatment in nearly
every case. Apparently this is because the LiBOB content has been
reduced and the number of transient crosslinking sites has
decreased. However, the liquidus temperature for n.apprxeq.14 and
n.apprxeq.23 PEG spaced polymers increases relative to mat before
chloroform treatment. Clearly, therefore, the LiBOB is dissolved
preferentially in the polyether chains domains and this has the
usual melting point lowering effect. When the salt is removed the
melting point goes up again.
[0048] The polyanionic polymers of the present invention have one
of the formulae:
M.sub.b.sup.+k[AL].sub.p.sup.-q
wherein
[0049] AL is a repeat unit in the chain wherein: [0050] A is an
anionic group comprising a Group III element.
[0051] The anionic groups are preferably orthoborate and are capped
with a chemical group that modifies their anionic bonding strength.
In certain preferred embodiments wherein the anionic group is an
orthoborate, the capping groups bind pairwise to two oxygens of the
orthoborate leaving two oxygens free to bind into the chain polymer
units. The capping groups may be a divalent chelate group that
binds both oxygens on the Lewis base or may be more than one group,
each binding one oxygen.
[0052] The capping groups are preferably dibasic acids, most
preferably oxalato or malonato groups. In certain preferred
instances the capping group is
1,2-tetra(trifluoromethyl)ethylenedialato(2-)O,O'[OC(CF.sub.3).s-
ub.2]. In certain other instances, the capping group is
silane-co-tetraethylene glycalato [DMSI].
Certain other preferred capping groups are SO2, aryl, phenyl and
substituted phenyl [0053] L is a polymeric chain group chemically
linked to A. [0054] and wherein L comprises a determined number
[0055] of spacer groups and has the formula:
[0055] L=(Z).sub.n [0056] wherein [0057] Z is a spacer group; and
[0058] n is the number of each said spacer groups [0059] and
wherein Z is the same or different in each occurrence; and [0060] Z
is preferably chosen from the group comprising alkyl, R-substituted
alkyl, alkoxy and R-substituted alkoxy wherein R is selected from
the group comprising hydrogen, halo, alkyl, alkoxy, phenyl and
substituted phenyl. In other instances, Z is a polysiloxane having
the formula Si[(CR.sub.3).sub.2]--O(CR.sub.2CR.sub.2O).sub.n
wherein n is independently 2 to about 50, preferably 2 to about 20,
and R is hydrogen or alkyl. [0061] Z most preferably is a polyether
having the formula [(O(CR.sub.2).sub.aCR.sub.2].sub.n wherein n is
from 2 to about 100, most preferably 2 to about 20, a is zero to
about 20 and R is hydrogen, halo, alkyl or R-substituted alkyl
wherein R is halo, alkyl or phenyl. [0062] p is a number from about
1 to about 100.
[0063] In these preferred embodiments the ether groups may be the
same or different in each occurrence.
[0064] p is the number of repeat units in the polymer.
[0065] k is one to 3, most preferably one.
[0066] q is one to 3
[0067] bq equals bk.
[0068] In certain preferred embodiments of the present invention,
the repeat group in the polyanionic polymer has one of the
formulae:
##STR00001##
[0069] wherein X is a Group III element; [0070] O are oxygen;
[0071] Y is a capping group. [0072] The counterion M.sup.+k is a
cation or a canonic group selected from the comprising hydrogen,
Group I metals, Group II metals, NR.sub.4 and PR.sub.4 wherein R is
hydrogen, alkyl, or halo, and k is one to three. In certain
instances wherein the polyanionic polymer is used as an electrolyte
in a lithium battery, the counterion is most favorably lithium. In
those embodiments wherein the polyanionic polymer is incorporated
into an ion exchange system, the cation is preferably a Group I
metal or Group II metal, most preferably sodium, potassium, and
calcium. It will be appreciated that a molar ratio of a cation to
an anion in the polymer of the present invention depends on the
valence of the cation and the valence on the anion as well as the
number of anionic groups in the polymer. If the total charge on the
polymer is k, the ration is reflected in the value of p and k. For
example, if both the cation and the anion are monovalent, then k
and p are 1, and there will be a 1:1 molar ratio between the cation
and the anionic group. Whereas if the cation is divalent and the
anion is monovalent, then k is 2 and p is 1, and there will be a
1:2 molar ratio between the cation and the anionic group of the
present invention. Preferably, k is an integer from 1 to 3, more
preferably 1 to 2, still more preferably k is 1 or 2, and most
preferably 1. Preferably p is 1 or 2 and most preferably 1.
[0073] The weak charge on the anionic compound acts as a coulombic
trap for M.sup.+p and as a result, M.sup.+p is easily decoupled
from the anionic polymer. This decoupling property imparts high
cationic conductivity to the polymer and makes the polymers useful
as solid polymeric electrolytes in lithium batteries. In certain
instances wherein the polyanionic polymer is incorporated into a
lithium battery, the counterion is lithium. In those embodiments
wherein the polyanionic polymer comprises an ion exchange system,
the cation is preferably a Group I metal or Group II metal, most
preferably sodium, potassium, calcium.
[0074] Preferred methods for preparing the present polymers
comprises providing a precursor anionic group wherein the anionic
group comprises a Group III element tetragonally coordinated with
oxygen and wherein two of the oxygens are capped with an electron
withdrawing group. Also provided is a polymeric group comprising
repeating spacer groups and having a reactive group. The anionic
group and the polymeric group are combined to form the polyanionic
polymer and a small molecule. In preferred embodiments wherein the
anionic group comprises a tetra-coordinated oxide of a Group III
element wherein two oxygens are capped and two oxygens are
coordinated to hydrogen or a cation, the reactive group condenses
with the uncapped oxygen and a small molecule such as water or a
hydroxide is formed.
[0075] The present invention further relates to solid polymeric
electrolytes incorporating such polymers and to rechargeable
batteries and other electrochemical devices which utilize solid
polymeric electrolytes.
[0076] Certain modifications can be made to the present conductive
polymers to enhance their mechanical properties so they can be more
readily formed into films or otherwise fabricated into components
suitable for use in secondary lithium batteries. Certain properties
of the present polymers indicate their suitability for such
purposes. They are soluble in certain solvents and plasticizers,
which is a prerequisite for film formation. They may be
cross-linked to form polyanionic composites, and these cross-linked
composites are likewise soluble or swollen in plasticizers. The
polymeric chains in the present polymers may be chosen to be
reactive with other polymers so that they may be mixed with, bonded
to, or otherwise incorporated into suitable non-ionic chain
polymers, ionic chain polymers comprising other ionic groups,
polymer networks or block-co-polymers. These modifications have
been illustrated in the following examples. Certain similar
modifications will be apparent to one skilled in the polymer
arts.
[0077] In an important aspect of the present invention, the
polyanionic chain polymers are cross-linked to form a polyanionic
polymeric network. Any suitable cross-linking agent may be used,
but most preferably the string polymers are chemically crosslinked
with lithium boron hydride. Cross-linked polymers exhibit greater
mechanical strength than the simple polymer chains.
[0078] In yet a further important aspect of the present invention,
the polyanionic chain polymers are dissolved in solvents,
preferably polar solvents, for example tetrahydrofuran (THF),
acetonitrile and acetone. This advantageous property of the
polyanionic polymers of the present invention makes them suitable
for fabrication into films and coatings.
[0079] In a related aspect of the present invention, the
polyanionic chain polymers incorporating weakly coordination
anionic groups may be affixed to a solid surface and incorporated
into an ion-exchange system. The spacer groups may be chosen to
provide a tethering group for bonding to a surface such as an ion
exchange resin bead or a porous membrane.
[0080] In yet another aspect of the present invention, a method is
given for increasing the conductivity of the polyanionic polymers
wherein certain plasticizers are added to the polymers. Although it
is not intended that the present invention be bound by a
description of the mechanism of the plasticization effect, it is
proposed that the local mobility of the polymeric chain is
increased by the plasticizers and as a result the conductivity is
increased.
[0081] In an advantageous embodiment of the invention, the anionic
chain polymers and the cross-linked network polymers comprise
certain plasticizers that enhance the conductivity of the polymer.
The plasticized polymers and cross-linked polymers can be formed
into conductive films by methods known in the art. Preferred
plasticizers are carbonate and non-carbonate plasticizers. Suitable
carbonate plasticizers are, for example, ethylene carbonate (EC),
propylene carbonate (PC), butylene carbonate (BC),
dimethylcarbonate (DMC) and diethyl carbonate (DEC). Suitable
non-carbonate plasticizers are 1,2-dimethoxyethane (DME) and
1,2-diethoxyethane (DEE), dimethylsulfoxide (DMSO), dimethylsulfone
(DMS), ethylmethylsulfone (EMS), .gamma.-butyrolactone (BL).
Preferred plasticizers comprise mixtures of carbonate plasticizer,
preferably mixtures of ethylene carbonate and propylene carbonate
(EC-PC), ethylene carbonate and dimethyl carbonate (EC-DMC), and
propylene carbonate and dimethylxyethane (PC-DME).
[0082] The above-mentioned polyanionic polymers and cross-linked
polymers and those embodiments wherein the polymers are dissolved
in solvents or comprise plasticizers can be employed advantageously
as solid polymeric electrolytes in most any type of electrochemical
device. Most specifically the polyanionic polymers of the present
invention are suitable SPE for electrochemical devices comprising
lithium and in particular, lithium rechargeable batteries. The
polyanionic polymers can be incorporated in electrochemical cells
and lithium batteries, especially rechargeable lithium
batteries.
[0083] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following description, and accompanying drawings.
Example 1
[0084] This example illustrates the preparation of a Lewis
base-containing polyanionic polymer wherein the Lewis base
comprises a tetrakis-coordinated boron structure wherein two
ligands are connected with an oxalyl groups and the other two
ligands are oxygen linked to the polymeric chain containing
repeating spacer units of ethylene glycol. This polymer is
generally called polyMOB (wherein "MOB" is for mono-oxalato borate)
and has the formula poly[lithium mono-oxalato oligo(ethylene
glycol).sub.n borate] which termed P(LiOEG.sub.nB) wherein n is 3
to 23.
[0085] The route to the polyanion polymers is to first form the
oxalato-capped orthoboric acid B(C.sub.2O.sub.4)(OH).sub.2.sup.-
and then to react this compound with poly(ethylene glycol), PEG, of
different molecular weight, eliminating water in a condensation
polymerization process to provide the polyanion of whatever cation
was used to charge-compensate the anion.
[0086] In practice, equal molar quantities of lithium hydroxide
monohydrate, oxalic acid dihydrate and boric acid were reacted and
all the water was removed by boiling. The solid oxalatoboric acid
residue was then refluxed with PEG, chosen from tri(ethylene
glycol), PEG200, PEG400, PEG600 and PEG1000, in benzene in a
distillation flask equipped with a water separator. The reaction
continued until no more water was released. This procedure yielded
a rubbery polymer with some fine white particles inside the
polymer. The polymer is insoluble in benzene. The supernatant
solvent (benzene) was decanted and the residue was washed with
fresh benzene once and then evaporated on a rotary evaporator under
reduced pressure to obtain a dry gel-like residue. This mass was
refluxed with anhydrous acetonitrile to yield a clear solution with
white precipitates. The precipitates were filtered off and the
solvent in the filtrate was evaporated thoroughly. Then the
residual rubbery solid was dissolved in anhydrous chloroform to
yield a clear solution with small amount of a white precipitate.
After filtration, the filtrate was evaporated down and the polymer
was dried in a vacuum oven at 90.degree. C. for 48 hours. The
products were rubbery, soft or sticky rubbery, or crystal solid,
depending on the PEG used. The ionic conductivities of the
PEG-spaced polyMOBs are shown in FIG. 1.
Example 2
[0087] This example illustrates the preparation of a Lewis
base-containing polyanionic polymer wherein the Lewis base
comprises a tetrakis-coordinated boron structure wherein two
ligands are connected with an oxalyl groups and the other two
ligands are oxygen linked to the polymeric chain containing
repeating spacer units of propylene glycol. This polymer is
generally called polyMOB (wherein "MOB" is for mono-oxalato borate)
and has the formula poly[lithium mono-oxalato oligo(propylene
glycol).sub.n borate] which termed P(LiOPG.sub.nB) wherein n is 7,
13 and 17.
[0088] The white product of lithium hydroxide monohydrate, oxalic
acid dihydrate and boric acid was refluxed with PPG, chosen from
PPG425, PPG725 and PPG1000, in benzene as described in Example 1.
The polymers were viscous liquid. The ionic conductivities of the
PPG-spaced polyMOBs are shown in FIG. 2.
Example 3
[0089] This example illustrates the preparation of a Lewis
base-containing polyanionic polymer wherein the Lewis base
comprises a tetrakis-coordinated boron structure wherein two
ligands are connected with an oxalyl groups and the other two
ligands are oxygen bound to dimethyl siloxane-co-tetraethylene
glycol. This polymer is generally called polyMOB (wherein "MOB" is
for mono-oxalato borate) and has the formula poly[lithium
mono-oxalato oligo(dimethyl siloxane-co-tetraethylene
glycolato).sub.n borate] herein abbreviated as
P[LiO(DMSiEG.sub.4).sub.nB] wherein n is around 12.
[0090] To a flame dried 500 ml three-neck flask equipped with
condenser, thermometer and dropping funnel was added 23.9 g (0.123
mole) tetraethylene glycol. The flask was heated to 100.degree. C.
and 18.0 g (0.123 mole) bis(dimethylamino)dimethyl silane was added
dropwise under vigorous stirring. After the addition the reaction
was continued at the same temperature while a lot of gas
(dimethylamine) was bubbling out of the solution. When the gas
evolution nearly ceased (about 2 hours), 250 ml benzene was added
to the reaction flask and followed by adding the product from the
reaction of lithium hydroxide monohydrate, oxalic acid dihydrate
and boric acid. The azeotropic distillation process was begun and
the reaction was treated following the procedures described in
Example 1. The polymer was sticky rubbery solid.
Example 4
[0091] This example illustrates the preparation of a Lewis
base-containing polyanionic polymer wherein the Lewis base
comprises a tetrakis-coordinated boron structure wherein two
ligands are connected with an malonyl groups and the other two
ligands are oxygen linked to the polymeric chain containing
repeating spacer units of ethylene glycol. This polymer is
generally called polyMMB (wherein "MMB" is for mono-malonato
borate) and has the formula poly[lithium mono-malonato
oligo(ethylene glycol).sub.n borate] which termed P(LiMEG.sub.nB)
wherein n is 5 to 23.
[0092] The white product from the reaction of lithium hydroxide
monohydrate, malonic acid dihydrate and boric acid after
evaporating all water was refluxed with PEG, chosen from PEG200,
PEG400, PEG600 and PEGIOOO, in benzene as described in Example 1.
The polymers were rubbery solid. The ionic conductivities of the
PEG-spaced polyMMBs are shown in FIG. 3.
Example 5
[0093] This example illustrates the preparation of a crosslinked
polyanionic polymer from the Lewis base-containing polymers of
Example 1. Lithium borohydride (LiBH.sub.4) was used as the
crosslinker.
[0094] Polymers from Example 1 (wherein the length of spacer groups
was 5 to 14) was dissolved in anhydrous THF and cooled in
acetone-dry ice bath. Certain amount of LiBH.sub.4; in THF solution
was dropwise added into the above solution with vigorous stirring.
After addition, the solution was stirred at room temperature
overnight. The solvent was then evaporated at reduced pressure and
the residual polymer was dried in a vacuum oven at ca. 70.degree.
C. for 48 hours. The product was stiff rubber and soft rubber
depending on the length of the spacer. The temperature dependence
of ionic conductivity of these crosslinked polyanionic electrolytes
are shown in FIG. 4.
Example 6
[0095] This example illustrates the plasticization of a polyanionic
polymer prepared in Example 1, in non-aqueous solvents. The
non-aqueous solvent is chosen from carbonate, non-carbonate
plasticizers or their mixtures. Suitable carbonate plasticizers
are, for example, ethylene carbonate (EC), propylene carbonate
(PC), butylene carbonate (BC), dimethyl carbonate (DMC) and diethyl
carbonate (DEC). Suitable non-carbonate plasticizers are
1,2-dimethoxyethane (DME), 1,2-diethoxyethane PEE),
dimethylsulfoxide (DMSO), dimethyl sulfone (DMS),
ethylmethylsulfone (EMS), .gamma.-butyrolactone (BL). Preferred
plasticizer mixtures are EC-PC, EC-DMC, EC-DMC-DEC, and PC-DME.
[0096] The polyanionic polymer from Example 1 wherein the length of
the spacer EG.sub.n was 3 to 14 was mixed well with different
amount of plasticizers or plasticizer mixtures. The conductivities
of the plasticized electrolytes are given in FIGS. 5A to 5D, 6 and
7.
Example 7
[0097] This example illustrates the plasticization of a crosslinked
polyanionic polymer prepared in Example 5. The plasticizing effect
was measured by using EC-PC(1:1, o/w) as the plasticizer.
[0098] The crosslinked polyanionic polymer from Example 5 wherein
the length of the spacer EG.sub.n was 5 to 14 was mixed well with
different amount of EC-PC (1:1, o/w). The conductivities of the
plasticized electrolytes are given in FIGS. 8A, 8B and 8C.
Example 8
[0099] This example illustrates the preparation of a gel
electrolyte containing a Lewis base-containing polyanionic polymer
prepared in Example 1 as a polymeric lithium salt.
[0100] In a dry glove box, the polyanionic polymer from Example 1
wherein the length of the EG.sub.n spacer was 3 was dissolved in a
certain amount of EC-PC (1:1, o/w) mixture in a vial. A quantity
poy(methyl methacrylate), PMMA, with high molecular weight of
996,000 was added. The vial was sealed and heated to around
140.degree. C. with occasionally shaking till the mixture was well
done. The hot viscous mass was pressed in between two stainless
steel plates covered with Teflon films. After cooling, the
self-standing membrane was pealed off. The conductivity of the gel
electrolyte is given in FIG. 9.
Example 9
[0101] This example illustrates the preparation of a gel
electrolyte containing a crosslinked polyanionic polymer prepared
in Example 5 as a polymeric lithium salt.
[0102] The gel electrolyte was prepared by dissolving PMMA and the
crosslinked polyanionic polymer from Example 5 wherein the length
of the EGn spacer was 3 in EC-PC (1:1, o/w) mixture in a vial, as
described in Example 8. The conductivity of the gel electrolyte is
given in FIG. 9.
Example 10
[0103] This example illustrates the electrochemical properties of a
plasticized polyanionic polymer prepared in Example 6. The cyclic
voltammograms were measured at room temperature on an EG&G
potentiostat/galvanostat model 273, with a three-electrode dip-cell
with platinum, stainless steel, nickel, aluminum or copper wire as
working electrode and lithium metal as counter and reference
electrodes. The scan rate was 1 mVs.sup.-1. The cyclic voltammetric
results are given in FIGS. 10A to 10D.
Example 111
[0104] This example illustrates the electrochemical properties of a
plasticized crosslinked polyanionic polymer prepared in Example 5.
The cyclic voltammograms may be measured as described in Example
10.
Example 12
[0105] This example illustrates the battery performance of an
electrolytic solution containing a polyanionic polymer in EC/PC
(1:1, o/w) mixture from Example 6, wherein the polyanionic polymer
has the spacer length of 3 from Example 1. Prototype lithium
rechargeable batteries were assembled by pressing into appropriate
cases a sequence of a lithium metal disk anode, a glass fiber film
soaked saturatedly with an electrolytic solution of a polyanionic
polymer (wherein the length of the polyanionic polymer spacer from
Example 1 was 3) in EC/PC (1:1, o/w) mixture from Example 6, and a
composite cathode membrane. The latter was a blend of
LiCr.sub.0.015Mn.sub.1.985O.sub.4 as the active intercalation
material, carbon black as an electronic conductor and PVdF as a
polymer binder, in a weight ratio of 82:10:8. The batteries were
assembled in a VAC dry box filled with purified argon. Preliminary
investigation into the battery characteristics and performance was
performed by examining their galvanostatic charge-discharge cyclic
curves.
[0106] Those skilled in the art will appreciate that numerous
changes and modifications may be made to the preferred embodiments
of the invention and that such changes and modifications may be
made without departing from the spirit of the invention. It is
therefore intended mat the appended claims cover all such
equivalent variations as fall within the true spirit and scope of
the invention.
* * * * *