U.S. patent application number 10/957539 was filed with the patent office on 2005-09-08 for novel composite cathodes, eletrochemical cells comprising novel composite cathodes, and processes for fabricating same.
Invention is credited to Mukherjee, Shyama P., Skotheim, Terje A..
Application Number | 20050196672 10/957539 |
Document ID | / |
Family ID | 21786328 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050196672 |
Kind Code |
A1 |
Mukherjee, Shyama P. ; et
al. |
September 8, 2005 |
Novel composite cathodes, eletrochemical cells comprising novel
composite cathodes, and processes for fabricating same
Abstract
The present invention pertains to composite cathodes suitable
for use in an electrochemical cell, said cathodes comprising: (a)
an electroactive sulfur-containing cathode material, wherein said
electroactive sulfur-containing cathode material, in its oxidized
state, comprises a polysulfide moiety of the formula --S.sub.m--,
wherein m is an integer equal to or greater than 3; and, (b) an
electroactive transition metal chalcogenide composition, which
encapsulates said electroactive sulfur-containing cathode material,
and which retards the transport of anionic reduction products of
said electroactive sulfur-containing cathode material, said
electroactive transition metal chalcogenide composition comprising
an electroactive transition metal chalcogenide having the formula
M.sub.j Y.sub.k (OR).sub.l wherein: M is a transition metal; Y is
the same or different at each occurrence and is oxygen, sulfur, or
selenium; R is an organic group and is the same or different at
each occurrence; j is an integer ranging from 1 to 12; k is a
number ranging from 0 to 72; and l is a number ranging from 0 to
72; with the proviso that k and l cannot both be 0. The present
invention also pertains to methods of making such composite
cathodes, cells comprising such composite cathodes, and methods of
making such cells.
Inventors: |
Mukherjee, Shyama P.;
(Tucson, AZ) ; Skotheim, Terje A.; (Tucson,
AZ) |
Correspondence
Address: |
Fish & Neave LLP
1251 Avenue of the Americas
New York
NY
10020
US
|
Family ID: |
21786328 |
Appl. No.: |
10/957539 |
Filed: |
October 1, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10957539 |
Oct 1, 2004 |
|
|
|
09795915 |
Feb 27, 2001 |
|
|
|
09795915 |
Feb 27, 2001 |
|
|
|
09293498 |
Apr 15, 1999 |
|
|
|
6238821 |
|
|
|
|
09293498 |
Apr 15, 1999 |
|
|
|
08859996 |
May 21, 1997 |
|
|
|
5919587 |
|
|
|
|
60018115 |
May 22, 1996 |
|
|
|
Current U.S.
Class: |
429/218.1 ;
252/182.1; 429/213; 429/231.5; 429/303; 429/307; 429/313; 429/314;
429/317; 429/326; 429/330; 429/337; 429/338; 429/341 |
Current CPC
Class: |
H01M 2010/4292 20130101;
Y02E 60/10 20130101; H01M 4/587 20130101; H01M 6/166 20130101; H01M
4/405 20130101; H01B 1/12 20130101; H01M 4/622 20130101; H01M
2004/021 20130101; H01M 4/36 20130101; H01M 4/1397 20130101; H01M
10/0587 20130101; H01M 4/62 20130101; H01M 4/04 20130101; H01M
4/131 20130101; H01M 4/48 20130101; H01M 10/052 20130101; H01M 4/13
20130101; H01M 4/581 20130101; H01M 4/60 20130101; H01M 10/05
20130101; Y10S 977/948 20130101; H01M 10/0569 20130101; H01M
2300/0085 20130101; H01M 4/485 20130101; H01M 10/054 20130101; H01M
4/137 20130101; H01M 4/40 20130101; H01M 4/602 20130101; H01M 6/40
20130101; H01M 4/362 20130101; H01M 2004/028 20130101; H01M 4/364
20130101; H01M 4/139 20130101; H01M 4/366 20130101; H01M 4/38
20130101; H01M 4/5815 20130101; H01M 10/0525 20130101; H01M
2300/0082 20130101; H01M 4/5825 20130101; H01M 2300/0025 20130101;
H01M 4/0404 20130101; H01M 4/136 20130101 |
Class at
Publication: |
429/218.1 ;
429/213; 252/182.1; 429/231.5; 429/303; 429/317; 429/314; 429/313;
429/307; 429/338; 429/337; 429/341; 429/326; 429/330 |
International
Class: |
H01M 004/58; H01M
004/60; H01M 004/48; H01M 010/40 |
Claims
1-51. (canceled)
52. A rechargeable battery cell comprising: a) an anode comprising
a metal or an ion of a metal; b) a cathode comprising a mixture of:
(i) an electrochemically active material comprising sulfur in the
form of at least one of elemental sulfur, a sulfide of the metal,
or a polysulfide of the metal, and (ii) an electronically
conductive material; and c) a liquid electrolyte comprising a
solvent for at least some discharge products of the positive
electrode; wherein the battery cell attains a utilization of 50-75%
over 2-10 cycles.
53. A rechargeable battery cell comprising: d) an anode comprising
a metal or an ion of a metal; e) a cathode comprising a mixture of:
(i) an electrochemically active material comprising sulfur in the
form of at least one of elemental sulfur, a sulfide of the metal,
or a polysulfide of the metal, and (ii) an electronically
conductive material; and f) a liquid electrolyte comprising a
solvent for at least some discharge products of the positive
electrode; wherein the battery cell attains a utilization of 10-75%
over 200 cycles.
54. A rechargeable battery cell comprising: a) an anode comprising
a metal or an ion of a metal; b) a cathode comprising a mixture of:
(i) an electrochemically active material comprising sulfur in the
form of at least one of elemental sulfur, a sulfide of the metal,
or a polysulfide of the metal, and (ii) an electronically
conductive material; and c) a liquid electrolyte comprising a
solvent for at least some discharge products of the positive
electrode; wherein the battery cell attains a utilization of 38-75%
over 2-50 cycles.
55. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by an
initial capacity of at least 1172 mAh/g and has a utilization of at
least 69.97%.
56. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 1103 mAh/g and has a utilization of at least
65.85% after 20 cycles.
57. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 850 mAh/g and has a utilization of at least
50.57% at the second cycle.
58. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and. (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 850 mAh/g and has a utilization of at least
50.57% at the second cycle.
59. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 1387.5 mAh/g and has a utilization of at
least) 82.84% at the 12th cycle.
60. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 1300 mAh/g and has a utilization of at least
77.61% at the 18th cycle.
61. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 850 mAh/g and has a utilization of at least
50.57% at the second cycle.
62. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 750 mAh/g and has a utilization of at least
44.78% over 23 cycles.
63. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 1000 mAh/g and has a utilization of at least
44.78% over the 7th through 22nd cycles.
64. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 600 mAh/g and has a utilization of at least
35.82% over 61 cycles.
65. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 525 mAh/g and has a utilization of at least
31.34% over 65 cycles.
66. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 860 mAh/g and has a utilization of at least
51.3% over 10 cycles.
67. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by
first cycle capacity of 1265 mAh/g and has a utilization of
75.54%.
68. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of 1103 mAh/g and has a utilization of 65.85% at the 2
cycle
69. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of at least 956 mAh/g and has a utilization of at least
57.07% after 30 cycles.
70. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by an
initial capacity of around 1382 mAh/g and has a utilization of
about 82.5%.
71. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of 738 mAh/g and has a utilization of 44.06% after 81
cycles.
72. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by an
initial capacity of 1270 mAh/g and has a utilization of 75.8%.
73. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of 380 to 450 mAh/g and has a utilization of 22.7 to 26.9%
after 76 cycles.
74. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of 900 mAh/g and has a utilization of 53.7% after 4
cycles.
75. A rechargeable battery cell comprising: a) a negative electrode
including a metal or an ion of the metal; b) a positive electrode
comprising a mixture of: (i) an electrochemically active material
comprising sulfur in the form of at least one of elemental sulfur,
a sulfide of the metal, or a polysulfide of the metal, and (ii) an
electronically conductive material; and c) a liquid electrolyte
including a solvent for at least some discharge products of the
positive electrode; wherein the battery cell is characterized by a
capacity of 880 mAh/g and has a utilization of 52.5% after 2
cycles. (i) an electrochemically active material comprising sulfur
in the form of at least one of elemental sulfur, a sulfide of the
metal, or a polysulfide of the metal, and (ii) an electronically
conductive material; and d) a liquid electrolyte comprising a
solvent for at least some discharge products of said cathode,
wherein the battery cell attains a utilization of 38-75% over 2-50
cycles.
76. The rechargeable battery cell of claim 52, wherein the anode
comprises one or more materials selected from the group consisting
of lithium metal, lithium-aluminum alloys, lithium-tin alloys,
lithium-intercalated carbons, lithium-intercalated graphites,
calcium metal, aluminum metal, sodium metal, and sodium alloys.
77. The rechargeable battery cell of claim 52, wherein the cathode
comprises one or more electronically conductive materials selected
from the group consisting of conductive carbons, graphites, metal
flakes, metal powders, and conductive polymers.
78. The rechargeable battery cell of claim 52, wherein the cathode
further comprises one or more of the materials selected from the
group consisting of binder, electrolytes and conductive
additives.
79. The rechargeable battery cell of claim 52, wherein said cathode
is disposed on a positive current collector.
80. The rechargeable battery of claim 53 wherein the positive
electrode has a back boundry and a front boundry and the negative
electrode has a front boundry, the electrolyte being between the
front boundry of the positive electrode and the front boundry of
the negative electrode, the distance between the back boundry of
the positive electrode and the front boundry of the negative
electrode being about 125 micrometers or less.
81. The rechargeable battery of claim 53 wherein the positive
electrode has a back boundry and a front boundry and the negative
electrode has a front boundry, the electrolyte being between the
front boundry of the positive electrode and the front boundry of
the negative electrode, the distance between the back boundry of
the positive electrode and the front boundry of the negative
electrode being about 75 micrometers or less.
82. The rechargeable battery of claim 53 wherein the positive
electrode has a back boundry and a front boundry and the negative
electrode has a front boundry, the electrolyte being between the
front boundry of the positive electrode and the front boundry of
the negative electrode, the distance between the back boundry of
the positive electrode and the front boundry of the negative
electrode being about 50 micrometers or less.
83. The rechargeable battery of claim 53 wherein the positive
electrode has a back boundry and a front boundry and the negative
electrode has a front boundry, the electrolyte being between the
front boundry of the positive electrode and the front boundry of
the negative electrode, the distance between the back boundry of
the positive electrode and the front boundry of the negative
electrode being about 150 micrometers or less.
84. The rechargeable battery of claim 53 wherein the positive
electrode has a back boundry and a front boundry and the negative
electrode has a front boundry, the electrolyte being between the
front boundry of the positive electrode and the front boundry of
the negative electrode, the distance between the back boundry of
the positive electrode and the front boundry of the negative
electrode being selected from one of the group consisting of: about
50 micrometers or less, up to about 75 micrometers or less, up to
about 125 micrometers or less, and about 150 micrometers or
less.
85. A rechargeable battery cell comprising: a) an anode comprising
a metal or an ion of a metal; b) a cathode comprising a mixture of:
(i) an electrochemically active material comprising sulfur in the
form of at least one of elemental sulfur, a sulfide of the metal,
or a polysulfide of the metal, and (ii) an electronically
conductive material; and c) a liquid electrolyte comprising a
solvent for at least some discharge products of the positive
electrode; wherein the battery cell attains a utilization of 10-75%
over 200 cycles and wherein the cell discharges at an average
current density of at least about 0.5 mA/cm.sup.2.
Description
RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 08/859,996 filed 21 May 1997, now U.S. Pat.
No. ______, which claims priority to U.S. provisional patent
application Ser. No. 60/018,115 filed 22 May 1996, the contents of
both of which are incorporated herein by reference in their
entirety.
TECHNICAL FIELD
[0002] The present invention pertains generally to the field of
cathodes and rechargeable electric current producing cells. More
particularly, the present invention pertains to composite cathodes
which comprise (a) an electroactive sulfur-containing cathode
material, wherein said electroactive sulfur-containing cathode
material, in its oxidized state, comprises a polysulfide moiety of
the formula --S.sub.m--, wherein m is an integer equal to or
greater than 3; and, (b) an electroactive transition metal
chalcogenide composition, which encapsulates said electroactive
sulfur-containing cathode material, and which retards the transport
of anionic reduction products of said electroactive
sulfur-containing cathode material. The present invention also
pertains to methods of making such composite cathodes, cells
comprising such composite cathodes, and methods of making such
cells.
BACKGROUND
[0003] Throughout this application, various publications, patents,
and published patent applications are referred to by an identifying
citation. The disclosures of the publications, patents, and
published patent specifications referenced in this application are
hereby incorporated by reference into the present disclosure to
more fully describe the state of the art to which this invention
pertains.
[0004] As the evolution of batteries continues, and particularly as
lithium batteries become more widely accepted for a variety of
uses, the need for safe, long lasting high energy batteries becomes
more important. There has been considerable interest in recent
years in developing high energy density cathode-active materials
and alkali-metals as anode materials for high energy primary and
secondary batteries. Several types of cathode materials for the
manufacture of thin film lithium and sodium batteries are known in
the art. The most widely investigated group are metallic or
inorganic materials which include transition metal chalcogenides,
such as titanium disulfide with alkali-metals as the anode as
described in U.S. Pat. No. 4,009,052. Also among the cathode active
chalcogenides, U.S. Pat. No. 4,049,879 lists transition metal
phosphorous chalcogenides, and U.S. Pat. No. 3,992,222 describes
cells using mixtures of FeS.sub.2 and various metal sulfides as the
electroactive cathode materials. U.S. Pat. No. 3,639,174 describes
primary and secondary voltaic cells utilizing lithium aluminum
alloy anodes and a reversible cathode depolarizer such as cupric
sulfide, cuprous oxide, cupric carbonate, and the like that have
low solubility in the electrolyte. U.S. Pat. No. 4,576,697
describes electroactive cathode materials in alkali-metal
non-aqueous secondary batteries comprised of carbon-containing
intercalatable layered or lamellar transition metal chalcogenides
having the general formula M.sub.nX.sub.2C, wherein M is a
transition metal selected from the group consisting of Ti, V, Cr,
Fe, Zr, and Ta; X is sulfur; and n is 1-2. High energy density
solid state cells comprising cathodes using selected ionically and
electronically conductive transition metal chalcogenides in
combination with other non-conductive electroactive cathode
materials are described in U.S. Pat. No. 4,258,109.
[0005] Another type of cathode materials disclosed for use in
lithium and sodium batteries are organic materials such as
conductive polymers. A further type of organic type cathode
materials are those comprised of elemental sulfur, organo-sulfur
and carbon-sulfur compositions where high energy density is
achieved from the reversible electrochemistry of the sulfur moiety
with the alkali metal. U.S. Pat. No. 4,143,214 to Chang et al.
describes cells having cathodes containing C.sub.vS wherein v is a
numerical value from about 4 to about 50. U.S. Pat. No. 4,152,491
to Chang et al. relates to electric current producing cells where
the cathode-active materials include one or more polymer compounds
having a plurality of carbon monosulfide units. The carbon
monosulfide unit is generally described as (CS).sub.w, wherein w is
an integer of at least 5, and may be at least 50, and is preferably
at least 100.
[0006] U.S. Pat. No. 4,664,991 to Perichaud et al. describes an
organo-sulfur material containing a one-dimensional electric
conducting polymer and at least one polysulfurated chain forming a
charge-transfer complex with the polymer. Perichaud et al. use a
material which has two components. One is the conducting or
conductive polymer, which is selected from a group consisting of
polyacetylenes, polyparaphenylenes, polythiophenes, polypyrroles,
polyanilines and their substituted derivatives. The other is a
polysulfurated chain which is in a charge transfer relation to the
conducting polymer. The polysulfurated chain is formed by high
temperature heating of sulfur with the conductive polymer to form
appended chains of . . . --S--S--S--S-- . . . of indeterminate
length.
[0007] In a related approach, a PCT application (PCT/FR84/00202) of
Armand et al. describes derivatives of polyacetylene-co-polysulfurs
comprising units of Z.sub.q(CS.sub.r).sub.n wherein Z is hydrogen,
alkali-metal, or transition metal, q has values ranging from 0 to
values equal to the valence of the metal ion used, values for r
range from greater than 0 to less than or equal to 1, and n is
unspecified. These derivatives are made from the reduction of
polytetrafluoroethylene or polytrifluorochloroethyl- ene with
alkali-metals in the presence of sulfur, or by the sulfuration of
polyacetylene with vapors of sulfur monochloride at 220.degree.
C..
[0008] U.S. Pat. No. 5,441,831 relates to an electric current
producing cell which comprises a cathode containing one or more
carbon-sulfur compounds of the formula (CS.sub.x).sub.n, in which x
takes values from 1.2 to 2.3 and n is equal to or greater than
2.
[0009] U.S. Pat. Nos. 4,833,048 and 4,917,974 to De Jonghe et al.
describe a class of cathode materials made of organo-sulfur
compounds of the formula (R(S).sub.y).sub.n where y=1 to 6; n=2 to
20, and R is one or more different aliphatic or aromatic organic
moieties having one to twenty carbon atoms. One or more oxygen,
sulfur, nitrogen or fluorine atoms associated with the chain can
also be included when R is an aliphatic chain. The aliphatic chain
may be linear or branched, saturated or unsaturated. The aliphatic
chain or the aromatic rings may have substituent groups. The
preferred form of the cathode material is a simple dimer or
(RS).sub.2. When the organic moiety R is a straight or a branched
aliphatic chain, such moieties as alkyl, alkenyl, alkynyl,
alkoxyalkyl, alkylthioalkyl, or aminoalkyl groups and their
fluorine derivatives may be included. When the organic moiety
comprises an aromatic group, the group may comprise an aryl,
arylalkyl or alkylaryl group, including fluorine substituted
derivatives, and the ring may also contain one or more nitrogen,
sulfur, or oxygen heteroatoms as well.
[0010] In the cell developed by De Jonghe et al. the main cathode
reaction during discharge of the battery is the breaking and
reforming of disulfide bonds. The breaking of a disulfide bond is
associated with the formation of an RS.sup.-M.sup.+ ionic complex.
The organo-sulfur materials investigated by De Jonghe et al.
undergo polymerization (dimerization) and de-polymerization
(disulfide cleavage) upon the formation and breaking of the
disulfide bonds. The depolymerization which occurs during the
discharging of the cell results in lower molecular weight polymeric
and monomeric species, namely soluble anionic organic sulfides,
which can dissolve into the electrolyte and cause self-discharge as
well as reduced capacity, thereby severely reducing the utility of
the organo-sulfur material as cathode-active material and
eventually leading to complete cell failure. The result is an
unsatisfactory cycle life having a maximum of about 200 deep
discharge-charge cycles, more typically less than 100 cycles as
described in J. Electrochem. Soc., Vol. 138, pp. 1891-1895
(1991).
[0011] A significant drawback with cells containing cathodes
comprising elemental sulfur, organosulfur and carbon-sulfur
materials relates to the dissolution and excessive out-diffusion of
soluble sulfides, polysulfides, organo-sulfides, carbon-sulfides
and/or carbon-polysulfides, hereinafter referred to as anionic
reduction products, from the cathode into the rest of the cell.
This process leads to several problems: high self-discharge rates,
loss of cathode capacity, corrosion of current collectors and
electrical leads leading to loss of electrical contact to active
cell components, fouling of the anode surface giving rise to
malfunction of the anode, and clogging of the pores in the cell
membrane separator which leads to loss of ion transport and large
increases in internal resistance in the cell.
[0012] Composite cathodes containing an electroactive transition
metal chalcogenide have been described, typically as a random
agglomeration or distribution of the electroactive materials,
polymers, conductive fillers, and other solid materials in the
cathode layer. In an exception to these homogeneous composite
cathodes, U.S. Pat. Nos. 4,576,883, 4,720,910, and 4,808,496
disclose composite cathodes comprising spheres of an electroactive
transition metal chalcogenide, such as vanadium pentoxide,
encapsulated as a core material in a polymeric shell containing a
polymer, an inorganic salt, such as a lithium salt, and optionally,
a conductive carbon. These spheres are prepared by an emulsifying
or a spray drying process. However, no mention is made in these
references of encapsulation by transition metal chalcogenides, of
any retarding of the transport of reduced species, of any use with
elemental sulfur or sulfur-containing electroactive organic
materials, or of any shape of the combined materials other than
spheres.
[0013] U.S. Pat. No. 3,791,867 to Broadhead et al. describes cells
containing cathodes consisting of elemental sulfur as the
electroactive material present in a layered structure of a
transition metal chalcogenide. This patent is directed at
preventing the solubilization and transport of the elemental sulfur
electroactive material by the electrolyte solvent. It has no
mention of the formation of soluble reduced species of the
electroactive material, such as soluble sulfides, or of the
retarding or control by any means of the transport of these soluble
reduced species into the electrolyte layer and other parts of the
cell. The transition metal chalcogenides in this patent are limited
to sulfides and selenides and do not include transition metal
oxides. They are present either as a totally separate layer from
the sulfur layer or pressed together with sulfur, in powder form,
to provide the composite cathode. There is no mention of any
organo-sulfur materials, carbon-sulfur materials, or polymeric
binders in the composite cathode. Also there is no mention of
improved capacity and battery cycle stability and life by the use
of an electroactive transition metal chalcogenide with the
elemental sulfur electroactive material.
[0014] U.S. Pat. No. 5,324,599 to Oyama et al. discloses composite
cathodes containing disulfide organo-sulfur or polyorgano-disulfide
materials, as disclosed in U.S. Pat. No. 4,833,048, by a
combination with or a chemical derivative with a conductive
polymer. The conductive polymers are described as capable of having
a porous fibril structure and holding disulfide compounds in their
pores. Japanese patent publication number Kokai 08-203530 to
Tonomura describes the optional addition of electroactive metal
oxide, such as vanadium oxide, to a composite cathode containing
disulfide organo-sulfur materials and polyaniline as the conductive
polymer. Japanese patent publication number Kokai 08-124570
describes a layered cathode with alternative layers of organo
disulfide compound, electroactive metal oxide and conductive
polymer with layers of mainly conductive polymers.
[0015] In a similar approach to overcome the dissolution problem
with polyorgano-disulfide materials by a combination or a chemical
derivative with a conductive, electroactive material, U.S. Pat. No.
5,516,598 to Visco et al. discloses composite cathodes comprising
metal-organosulfur charge transfer materials with one or more
metal-sulfur bonds, wherein the oxidation state of the metal is
changed in charging and discharging the positive electrode or
cathode. The metal ion provides high electrical conductivity to the
material, although it significantly lowers the cathode energy
density and capacity per unit weight of the polyorgano-disulfide
material. This reduced energy density is a disadvantage of
derivatives of organo-sulfur materials when utilized to overcome
the dissolution problem. The polyorganosulfide material is
incorporated in the cathode as a metallic-organosulfur derivative
material, similar to the conductive polymer-organosulfur derivative
of U.S. Pat. No. 5,324,599, and presumably the residual chemical
bonding of the metal to sulfur within the polymeric material
prevents the formation of highly soluble sulfide or thiolate anion
species. However, there is no mention in these references of
retarding of the transport of actual soluble reduced sulfide or
thiolate anion species formed during charging or discharging of the
cathode. Also, there is no mention in these references of the
utility of transition metal chalcogenides, including oxides, in
solving the dissolution problem with polyorganodisulfide materials.
Instead, the transition metal chalcogenides are mentioned as
specifically restricted to their known art of electroactive cathode
insertion materials with lithium ions, with no utility with
polyorgano-disulfide materials, and with significantly less
electrical conductivity than the charge-transfer materials
described in these references.
[0016] Despite the various approaches proposed for the fabrication
of high energy density rechargeable cells containing elemental
sulfur, organo-sulfur and carbon-sulfur cathode materials, or
derivatives and combinations thereof, there remains a need for
materials and cell designs that retard the out diffusion of anionic
reduction products, from the cathode compartments into other
components in these cells, improve the utilization of electroactive
cathode materials and the cell efficiencies, and provide
rechargeable cells with high capacities over many cycles.
[0017] It is therefore an object of the present invention to
provide composite cathodes containing high loadings of
electroactive sulfur-containing cathode material that exhibit a
high utilization of the available electrochemical energy and retain
this energy capacity without significant loss over many
charge-discharge cycles.
[0018] It is another object of the present invention to provide
composite cathodes, composite cathode materials, and composite
cathode designs, for use in rechargeable cells which allow for
highly selective transport of alkali-metal ions into and out of the
sulfur-containing cathodes while retarding the out-diffusion of
anionic reduction products from the cathodes into the cells.
[0019] It is a further object of this invention to provide
convenient methods for fabricating such composite cathodes.
[0020] It is yet a further objective of this invention to provide
energy storing rechargeable battery cells which incorporate such
composite cathodes, and which exhibit much improved self-discharge
characteristics, long shelf life, improved capacity, and high
manufacturing reliability.
SUMMARY OF THE INVENTION
[0021] One aspect of the present invention pertains to a composite
cathode for use in an electrochemical cell, said cathode
comprising:
[0022] (a) an electroactive sulfur-containing cathode material,
wherein said electroactive sulfur-containing cathode material, in
its oxidized state, comprises a polysulfide moiety of the formula
--S.sub.m--, wherein m is an integer equal to or greater than 3;
and,
[0023] (b) an electroactive transition metal chalcogenide
composition, which encapsulates said electroactive
sulfur-containing cathode material, and which retards the transport
of anionic reduction products of said electroactive
sulfur-containing cathode material, said electroactive transition
metal chalcogenide composition comprising an electroactive
transition metal chalcogenide having the formula M.sub.j
Y.sub.k(OR).sub.l wherein: M is a transition metal; Y is the same
or different at each occurrence and is oxygen, sulfur, or selenium;
R is an organic group and is the same or different at each
occurrence; j is an integer ranging from 1 to 12; k is a number
ranging from 0 to 72; and l is a number ranging from 0 to 72; with
the proviso that k and l cannot both be 0. In one embodiment, j is
an integer ranging from 1 to 6; k is a number ranging from 0 to 13;
and, l is a number ranging from 0 to 18.
[0024] In one embodiment, the transition metal of said
electroactive transition metal chalcogenide is selected from the
group consisting of: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo,
Ru, Rh, Pd, Hf, Ta, W, Re, Os, and Ir.
[0025] In one embodiment, the electroactive transition metal
chalcogenide is selected from the group consisting of: TiS.sub.2,
Cr.sub.2S.sub.3, MoS.sub.2, MoSe.sub.2, MnS.sub.2, NbS.sub.2,
VS.sub.2, V.sub.2S.sub.5, WS.sub.2, and V.sub.2O.sub.3S.sub.3.
[0026] In one embodiment, Y is oxygen. In one embodiment, the
electroactive transition metal chalcogenide is selected from the
group consisting of: MoO.sub.2, MnO.sub.2, NbO.sub.5,
V.sub.2O.sub.5, WO.sub.3, MoO.sub.3, Ta.sub.2O.sub.5,
V.sub.2O.sub.4.5(OCH(CH.sub.3).sub.2).sub.0.5- , and
V.sub.2O.sub.4.5.
[0027] In one embodiment, wherein l is greater than 0, said organic
group is selected from the group consisting of: alkyl, aryl,
arylalkyl, alkanone, alkanol, and alkoxy groups, each containing 1
to 18 carbons. In one embodiment, wherein l is greater than 0, said
organic group is selected from the group consisting of: methyl,
ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl, pentyl,
isopentyl, hexyl, octyl, ethylhexyl, isooctyl, dodecyl, cyclohexyl,
decahydronaphthyl, phenyl, methylphenyl, ethylphenyl, hexylphenyl,
dodecylphenyl, isopropylphenyl, benzyl, phenylethyl, naphthyl,
acetyl, and acetoacetylonate.
[0028] In one embodiment, M is selected from the group consisting
of V, Nb, Cr, Mo, Mn, W, and Ta; Y is oxygen; R is selected from
the group consisting of: ethyl, isopropyl, butyl, acetyl, and
acetylacetonate; j is a number ranging from 1 to less than 7; k is
a number ranging from l to less than 14; and, l is equal to or less
than about 1.5.
[0029] In one embodiment, the transition metal of said
electroactive transition metal chalcogenide is V. In one
embodiment, the transition metal of said electroactive transition
metal chalcogenide is V and Y is oxygen. In one embodiment, the
electroactive transition metal chalcogenide is a vanadium oxide. In
one embodiment, the electroactive transition metal chalcogenide
composition comprises an aerogel comprising a vanadium oxide or a
xerogel comprising a vanadium oxide. In one embodiment, the
electroactive transition metal chalcogenide is V.sub.2O.sub.5. In
one embodiment, the electroactive transition metal chalcogenide is
a vanadium alkoxide. In one embodiment, the electroactive
transition metal chalcogenide is a vanadium oxide isopropoxide.
[0030] In one embodiment, the electroactive transition metal
chalcogenide is present in said composite cathode in the amount of
from 2 to 70 weight %. In one embodiment, the electroactive
transition metal chalcogenide is present in said composite cathode
in the amount of from 5 to 50 weight %. In one embodiment, the
electroactive transition metal chalcogenide is present in said
composite cathode in the amount of from 5 to 40 weight %.
[0031] In one embodiment, the electroactive transition metal
chalcogenide composition comprises an aerogel or a xerogel
comprising an electroactive transition metal chalcogenide. In one
embodiment, the electroactive transition metal chalcogenide
composition encapsulates said electroactive sulfur-containing
cathode material by impregnation of said electroactive
sulfur-containing cathode material into said electroactive
transition metal chalcogenide composition. In one embodiment, the
electroactive transition metal chalcogenide composition is present
as an interface layer on the outer surface of said electroactive
sulfur-containing cathode material. In one embodiment, the
composite cathode comprises: (a) a first coating on an electrically
conductive substrate, said first coating comprising said
electroactive sulfur-containing cathode material; and, (b) a second
coating over said first coating, said second coating comprising
said electroactive transition metal chalcogenide composition. In
one embodiment, the second coating comprises greater than 2.5
g/m.sup.2 of said electroactive transition metal chalcogenide.
[0032] In one embodiment, the sulfur-containing material comprises
elemental sulfur.
[0033] In one embodiment, the sulfur-containing material comprises
a carbon-sulfur polymer material. In one embodiment, the
sulfur-containing material is a carbon-sulfur polymer material,
wherein m of the polysulfide moiety, --S.sub.m--, of said
carbon-sulfur polymer material is an integer equal to or greater
than 6. In one embodiment, the polymer backbone chain of said
carbon-sulfur polymer material comprises conjugated segments. In
one embodiment, the polysulfide moiety, --S.sub.m--, is covalently
bonded by one or both of its terminal sulfur atoms on a side group
to the polymer backbone chain of said carbon-sulfur polymer
material. In one embodiment, the polysulfide moiety, --S.sub.m--,
is incorporated into the polymer backbone chain of said
carbon-sulfur polymer material by covalent bonding of said
polysulfide moiety's terminal sulfur atoms.
[0034] In one embodiment, the carbon-sulfur polymer material
comprises greater than 75 weight percent of sulfur.
[0035] In one embodiment, the composite cathode further comprises
one or more of the materials selected from the group consisting of:
binders, electrolytes, and conductive additives. In one embodiment,
the composite cathode further comprises one or more binders
selected from the group consisting of: polytetrafluoroethylenes,
polyvinylidene fluorides, ethylene propylene diene (EPDM) rubbers,
polyethylene oxides, UV curable acrylates, UV curable
methacrylates, and UV curable divinyl ethers. In one embodiment,
the composite cathode further comprises one or more conductive
additives selected from the group consisting of: conductive
carbons, graphites, metal flakes, metal powders, and conductive
polymers.
[0036] Another aspect of the present invention pertains to methods
for preparing a composite cathode, as described herein, for use in
an electrochemical cell.
[0037] In one embodiment, said methods comprise the steps of:
[0038] (a) dissolving or dispersing the electroactive transition
metal chalcogenide in a liquid medium;
[0039] (b) adding to the composition resulting from step (a) the
electroactive sulfur-containing cathode material;
[0040] (c) mixing the composition resulting from step (b) to
dissolve or disperse said electroactive sulfur-containing cathode
material, thereby forming a composition having a desired
consistency and particle size distribution;
[0041] (d) casting the composition resulting from step (c) onto a
suitable substrate or placing the composition resulting from step
(c) into a mold;
[0042] (e) removing some or all of the liquid from the composition
resulting from step (d) to provide a solid or gel-like composite
cathode structure in the shape or form desired; and
[0043] (f) optionally heating the composite cathode structure of
step (e) to a temperature of 100.degree. C. or greater.
[0044] In one embodiment, said methods comprise the steps of:
[0045] (a) dissolving or dispersing the electroactive transition
metal chalcogenide in a liquid medium;
[0046] (b) adding to the composition resulting from step (a) the
electroactive sulfur-containing cathode material;
[0047] (c) mixing the composition resulting from step (b) to
dissolve or disperse said electroactive sulfur-containing cathode
material, thereby forming a composition having a desired
consistency and particle size distribution;
[0048] (d) contacting the composition resulting from step (c) with
a gelling agent, thereby forming a sol-gel having a desired
viscosity;
[0049] (e) casting the composition resulting from step (d) onto a
suitable substrate or placing the composition resulting from step
(d) into a mold;
[0050] (f) removing some or all of the liquid from the composition
resulting from step (e) to provide a solid or gel-like composite
cathode structure in the shape or form desired; and
[0051] (g) optionally heating the composite cathode structure of
step (f) to a temperature of 100.degree. C. or greater.
[0052] In one embodiment, said methods comprise the steps of:
[0053] (a) dissolving the electroactive transition metal
chalcogenide (e.g., electroactive transition metal alkoxide or
electroactive transition metal chalcogenide precursor) in a liquid
medium;
[0054] (b) contacting the composition resulting from step (a) with
a gelling agent, thereby forming a sol-gel having a desired
viscosity;
[0055] (c) adding to the composition resulting from step (b) the
electroactive sulfur-containing cathode material;
[0056] (d) mixing the composition resulting from step (c) to
dissolve or disperse said electroactive sulfur containing cathode
material, thereby forming a composition having a desired
consistency and particle size distribution;
[0057] (e) casting the composition resulting from step (d) onto a
suitable substrate or placing the composition resulting from step
(d) into a mold;
[0058] (f) removing some or all of the liquid from the composition
resulting from step (e) to provide a solid or gel-like composite
cathode structure in the shape or form desired; and
[0059] (g) optionally heating the composite cathode structure of
step (f) to a temperature of 100.degree. C. or greater.
[0060] In one embodiment, said methods comprise the steps of:
[0061] (a) coating a current collector substrate with a composition
comprising the electroactive sulfur-containing cathode material and
drying or curing said composition to form a solid or gel-type
electroactive cathode layer on said current collector
substrate;
[0062] (b) dissolving or dispersing the electroactive transition
metal chalcogenide in a liquid medium; and
[0063] (c) coating said electroactive cathode layer with the
composition resulting from step (b) and drying or curing said
composition to form a solid layer of said electroactive transition
metal chalcogenide composition which covers the outer surface of
said electroactive cathode layer.
[0064] In one embodiment, said methods comprise the steps of:
[0065] (a) coating a current collector substrate with a composition
comprising the electroactive sulfur-containing cathode material and
drying or curing said composition to form a solid or gel-type
electroactive cathode layer on said current collector
substrate;
[0066] (b) dissolving or dispersing the electroactive transition
metal chalcogenide in a liquid medium;
[0067] (c) contacting the composition resulting from step (b) with
a gelling agent, thereby forming a sol-gel having a desired
viscosity; and
[0068] (d) coating said electroactive cathode layer with the
composition resulting from step (c) and drying or curing said
composition to form a solid layer of said electroactive transition
metal chalcogenide composition which covers the outer surface of
said electroactive cathode layer.
[0069] Another aspect of the present invention pertains to electric
current producing cells comprising (a) an anode; (b) a composite
cathode, as described herein; and (c) an electrolyte between said
anode and said composite cathode.
[0070] In one embodiment, the cell has an increase of specific
capacity of greater than 150 mAh per gram of said electroactive
transition metal chalcogenide, with respect to the specific
capacity of said electroactive sulfur-containing cathode material.
In one embodiment, the cell has an increase of specific capacity of
greater than 200 mAh per gram of said electroactive transition
metal chalcogenide, with respect to the specific capacity of said
electroactive sulfur-containing cathode material. In one
embodiment, the cell has an increase of specific capacity of
greater than 300 mAh per gram of said electroactive transition
metal chalcogenide, with respect to the specific capacity of said
electroactive sulfur-containing cathode material. In one
embodiment, the anode comprises one or more materials selected from
the group consisting of: lithium metal, lithium-aluminum alloys,
lithium-tin alloys, lithium intercalated carbons, lithium
intercalated graphites, calcium metal, aluminum metal, sodium
metal, and sodium alloys. In one embodiment, the electrolyte
comprises one or more materials selected from the group consisting
of: liquid electrolytes, gel polymer electrolytes, and solid
polymer electrolytes. In one embodiment, the electrolyte comprises:
(a) one or more solid polymer electrolytes selected from the group
consisting of: polyethers, polyethylene oxides, polyimides,
polyphosphazenes, polyacrylonitriles, polysiloxanes, polyether
grafted polysiloxanes; derivatives of the foregoing; copolymers of
the foregoing; crosslinked and network structures of the foregoing;
blends of the foregoing; and (b) one or more ionic electrolyte
salts. In one embodiment, the electrolyte comprises: (a) one or
more materials selected from the group consisting of: polyethylene
oxides, polypropylene oxides, polyacrylonitriles, polysiloxanes,
polyimides, polyethers, sulfonated polyimides, perfluorinated
membranes (Nafion.TM. resins), divinyl polyethylene glycols,
polyethylene glycol-bis-(methyl acrylates), polyethylene
glycol-bis(methyl methacrylates); derivatives of the foregoing;
copolymers of the foregoing; crosslinked and network structures of
the foregoing; blends of the foregoing; (b) one or more gel forming
agents selected from the group consisting of: ethylene carbonate,
propylene carbonate, N-methyl acetamide, acetonitrile, sulfolane,
polyethylene glycols, 1,3-dioxolanes, glymes, siloxanes, and
ethylene oxide grafted siloxanes; blends of the foregoing; and (c)
one or more ionic electrolyte salts. In one embodiment, the
gel-forming agent is a material of the following formula: 1
[0071] wherein o is an integer equal to or greater than 1; p is an
integer equal to or greater than 0 and less than about 30, and, the
ratio t/s is equal to or greater than 0. In one embodiment, the
electrolyte comprises: (a) one or more electrolyte solvents
selected from the group consisting of: ethylene carbonate,
propylene carbonate, N-methyl acetamide, acetonitrile, sulfolane,
polyethylene glycols, 1,3-dioxolanes, glymes, siloxanes, and
ethylene oxide grafted siloxanes; blends of the foregoing; and (b)
one or more ionic electrolyte salts. In one embodiment, the
electrolyte comprises one or more ionic electrolyte salts selected
from the group consisting of: MClO.sub.4, MAsF.sub.6,
MSO.sub.3CF.sub.3, MSO.sub.3CH.sub.3, MBF.sub.4, MB(Ph).sub.4,
MPF.sub.6, MC(SO.sub.2CF.sub.3).sub.3, MN(SO.sub.2CF.sub.3).sub.2,
2
[0072] where M is Li or Na.
[0073] Another aspect of the present invention pertains to methods
of forming an electric current producing cells comprising the steps
of: (a) providing an anode; (b) providing a composite cathode, as
described herein; and (c) enclosing an electrolyte between said
anode and said composite cathode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0074] FIG. 1 shows a composite cathode on a current collector
incorporating a cathode configuration wherein the electroactive
sulfur-containing cathode material is encapsulated with a thin
coating of the electroactive transition metal chalcogenide
composition. These "core-shell" electroactive cathode materials are
bound together in a composite cathode optionally using a binder
containing a conductive additive and/or an electrolyte.
[0075] FIG. 2 shows a composite cathode configuration on a current
collector wherein the electroactive transition metal chalcogenide
composition remains as an interface layer at the boundaries of the
electroactive sulfur-containing cathode particles.
[0076] FIG. 3 shows a cathode design on a current collector wherein
a coating of the electroactive sulfur-containing cathode material
is coated or impregnated with a layer of the electroactive
transition metal chalcogenide composition.
[0077] FIG. 4 shows a cathode design on a current collector wherein
the electroactive transition metal chalcogenide composition is an
aerogel or xerogel and forms a highly porous, fibrous, and
ultrafine sponge-like network into which the electroactive
sulfur-containing cathode materials are embedded or encapsulated.
The matrix of the transition metal chalcogenide composition may
optionally contain binders, electrolytes, and conductive
additives.
[0078] FIG. 5 shows cyclic voltammograms of a composite cathode of
the present invention as described in Example 5: (a) initial scan,
and (b) second scan.
[0079] FIG. 6 shows discharge curves for a battery cell comprised
of the composite cathode material described in Examples 3 and 6, a
lithium anode, and an electrolyte of tetraethyleneglycol dimethyl
ether (TEGDME) and lithium triflate at 25.degree. C.
[0080] FIG. 7 shows charge-discharge curves for a battery cell
containing a composite cathode described in Example 6.
[0081] FIG. 8 shows the ultraviolet (UV)-visible absorption spectra
of the liquid electrolytes removed from battery cells after
cycling: (a) electrolyte from a battery cell comprising a sulfur
and carbon cathode without an electroactive transition metal
chalcogenide composition, and (b) the electrolyte from a similar
battery cell containing a composite cathode of the present
invention comprising the same sulfur and carbon materials and an
electroactive V.sub.2O.sub.5 material. Curve (c) shows the spectrum
of the electrolyte before cycling.
[0082] FIG. 9 is a plot of capacity versus cycle number for a
rechargeable battery cell described in Example 10.
[0083] FIG. 10 is a plot of the specific capacity versus cycle
number for rechargeable batteries with (.circle-solid.) and without
(.box-solid.) a surface barrier coating comprising a transition
metal chalcogenide composition described in Example 16.
DETAILED DESCRIPTION OF THE INVENTION
[0084] One aspect of the present invention pertains to novel high
energy density composite cathodes comprised of:
[0085] (a) an electroactive sulfur-containing cathode material
comprising one or more materials selected from the group consisting
of elemental sulfur, organo-sulfur and carbon-sulfur compositions,
and derivatives and combinations thereof; and
[0086] (b) an electroactive transition metal chalcogenide
composition comprising one or more electroactive transition metal
chalcogenides.
[0087] In one embodiment, the present invention pertains to a
composite cathode for use in an electrochemical cell, said cathode
comprising:
[0088] (a) an electroactive sulfur-containing cathode material,
wherein said electroactive sulfur-containing cathode material, in
its oxidized state, comprises a polysulfide moiety of the formula
--S.sub.m--, wherein m is an integer equal to or greater than 3, as
described herein; and,
[0089] (b) an electroactive transition metal chalcogenide
composition, which encapsulates said electroactive
sulfur-containing cathode material, and which retards the transport
of anionic reduction products of said electroactive
sulfur-containing cathode material.
[0090] The electroactive transition metal chalcogenide facilitates
the transport of alkali-metal and/or alkaline-earth metal cations
reversibly from an electrolyte to the electroactive
sulfur-containing cathode material, and also efficiently retards
the transport of anionic reduction products from the composite
cathode to the electrolyte or other layers or parts of the cell
(e.g., retards the transport of anionic reduction products of said
sulfur-containing material to the outside of said composite
cathode). Thus, the transition metal chalcogenide composition
effectively encapsulates or embeds the electroactive
sulfur-containing cathode material and/or effectively entraps any
soluble sulfide species generated during charging and discharging
of the cell. The composite cathodes of the present invention thus
provide high energy density and low out-diffusion of anionic
reduction products.
[0091] The composite cathodes of the present invention are
particularly preferred for use in electrolytic cells, rechargeable
batteries, fuel cells, and the like that comprise organic type
electroactive sulfur-containing cathode components and require high
energy storage capacity, long shelf life, and a low rate of
self-discharge.
[0092] Electroactive Transition Metal Chalcogenides
[0093] The composite cathodes of the present invention comprise an
electroactive transition metal chalcogenide composition comprising
one or more electroactive transition metal chalcogenides of the
formula M.sub.jY.sub.k(OR).sub.l, wherein:
[0094] M is a transition metal;
[0095] Y is the same or different at each occurrence and is oxygen,
sulfur or selenium;
[0096] R is an organic group and is the same or different at each
occurrence;
[0097] j is an integer ranging from 1 to about 12;
[0098] k is a number ranging from 0 to about 72; and
[0099] l is a number ranging from 0 to about 72;
[0100] with the proviso that k and l cannot both be 0;
[0101] wherein said electroactive transition metal chalcogenide
composition effectively encapsulates or embeds the electroactive
sulfur-containing cathode material.
[0102] In one embodiment, the electroactive transition metal
chalcogenide composition consists essentially of an electroactive
transition metal chalcogenide. In one embodiment, the electroactive
transition metal chalcogenide composition further comprises
additives such as binders, fillers, and/or electrolytes, as
described herein.
[0103] The electroactive transition metal chalcogenide facilitates
the transport of alkali-metal ions and/or alkaline-earth metal ions
reversibly from an electrolyte in an electrolytic cell to the
electroactive sulfur-containing cathode material, and also retards
the transport of anionic reduction products from the composite
cathode to the electrolyte or other layers or parts of the cell.
Thus, useful electroactive transition metal chalcogenides are those
that allow for either alkali-metal or alkaline-earth metal ion
insertion and transport, but which retard or hinder the transport
of anionic reduction products.
[0104] As used herein, the term "electroactive" material is a
material which takes part in the electrochemical reaction of charge
or discharge. As used herein, the term "electroactive transition
metal chalcogenide" is an electroactive material having a
reversible lithium insertion ability, wherein the transition metal
is at least one selected from the group consisting of Ti, V, Cr,
Mn, Fe, Nb, Mo, Ta, W, Co, Ni, Cu, Y, Zr, Ru, Rh, Pd, Hf, Re, Os,
and Ir, and the chalcogenide is at least one selected from the
group consisting of O, S, and Se.
[0105] Examples of preferred electroactive transition metal
chalcogenides for use in the composite cathodes of the present
invention are those of empirical formula M.sub.jY.sub.k(OR).sub.l
wherein:
[0106] M is a transition metal;
[0107] Y is the same or different at each occurrence and is
selected from the group consisting of oxygen, sulfur, and
selenium;
[0108] R is an organic group and is the same or different at each
occurrence and is selected from the group of alkyl, aryl,
arylalkyl, alkylaryl, alkanone, alkanol, and alkoxy groups each
containing 1 to about 18 carbons;
[0109] j is an integer ranging from 1 to about 12;
[0110] k is a number ranging from 0 to about 72; and
[0111] l is a number ranging from 0 to about 72;
[0112] with the proviso that k and l cannot both be 0.
[0113] More examples of preferred electroactive transition metal
chalcogenides are those wherein:
[0114] M is selected from the group consisting of Ti, V, Cr, Mn,
Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, and
Ir;
[0115] Y is the same or different at each occurrence and is
selected from the group consisting of oxygen and sulfur;
[0116] R is the same or different at each occurrence and is
selected from the group consisting of methyl, ethyl, propyl,
isopropyl, butyl, isobutyl, tertiary butyl, pentyl, isopentyl,
hexyl, octyl, ethylhexyl, isooctyl, dodecyl, cyclohexyl,
decahydronaphthyl, phenyl, methylphenyl, ethylphenyl, hexylphenyl,
dodecylphenyl, isopropylphenyl, benzyl, phenylethyl, naphthyl,
acetyl, and acetoacetylonate
(--CH.sub.2--CO--CH.sub.2--CO--CH.sub.3);
[0117] j is an integer ranging from 1 to about 6;
[0118] k is a number ranging from 0 to about 13; and
[0119] l is a number ranging from 0 to about 18;
[0120] with the proviso that k and l cannot both be 0.
[0121] Still more examples of preferred electroactive transition
metal chalcogenides are those wherein:
[0122] M is selected from the group consisting of V, Nb, Cr, Mo,
Mn, W, and Ta;
[0123] Y is oxygen;
[0124] R is selected from the group consisting of ethyl, isopropyl,
butyl, acetyl, and acetylacetonate;
[0125] j is equal to or greater than 1 and less than 7;
[0126] k is equal to or greater than 1 and less than 14; and,
[0127] l is equal to or less than about 1.5.
[0128] Still more examples of useful electroactive transition metal
chalcogenides in the practice of this invention are
Cr.sub.2O.sub.3, CrO.sub.3, Cr.sub.3O.sub.8, CrS.sub.2,
Cr.sub.2S.sub.3, CoO.sub.2, CoS.sub.2, Co.sub.6S.sub.5,
Co.sub.4S.sub.3, CuO, Cu.sub.2O, CuSe, CuS, Ti.sub.2O.sub.3,
TiO.sub.2, TiS.sub.2, TiS.sub.3, V.sub.2O.sub.3, VO.sub.2,
V.sub.2O.sub.4, V.sub.2O.sub.5, V.sub.3O.sub.8, V.sub.6O.sub.13,
V.sub.2O.sub.4.5, V.sub.2O.sub.3S.sub.3,
V.sub.2O.sub.4.5(OCH(CH.sub.3).sub.2).sub.0.5, V.sub.2S.sub.3,
VSe.sub.2, MnS.sub.2, MnO, Mn.sub.2O.sub.3, MnO.sub.2, MnS,
Fe.sub.3O.sub.4, Fe.sub.2O.sub.3, FeSe, FeS, FeS.sub.2, NiO.sub.2,
NiSe, NiS.sub.2, NiS, Y.sub.2O.sub.3, Y.sub.2S.sub.3, NbS.sub.2,
NbO, NbO.sub.2, Nb.sub.2O.sub.5, NbSe.sub.2, NbSe.sub.3, MoO.sub.2,
MoO.sub.3, MoSe.sub.2, MoS.sub.2, MoS.sub.3, Rh.sub.2O.sub.3,
RhO.sub.2, PdO, PdS, HfO.sub.2, Ta.sub.2O.sub.5, TaS.sub.2,
WO.sub.2.9, WO.sub.3, WSe.sub.2, WS.sub.2, ReO.sub.2,
Re.sub.2O.sub.7, ReS.sub.2, Re.sub.2S.sub.7, OSO.sub.4, and
OsO.sub.2. Also useful are carbon-containing transition metal
chalcogenides as described in U.S. Pat. No. 4,576,697.
[0129] Especially preferred are electroactive transition metal
chalcogenides selected from the group consisting of: TiS.sub.2,
Cr.sub.2S.sub.3, MoS.sub.2, MoSe.sub.2, MoO.sub.2, MnO.sub.2,
MnS.sub.2, Nb.sub.2O.sub.5, NbS.sub.2, VS.sub.2, V.sub.2O.sub.5,
V.sub.2S.sub.5, WO.sub.3, WS.sub.2, MoO.sub.3, Ta.sub.2O.sub.5,
V.sub.2O.sub.4.5(OCH(CH.s- ub.3).sub.2).sub.0.5, V.sub.2O.sub.4.5,
and V.sub.2O.sub.3S.sub.3.
[0130] Particularly preferred are electroactive V.sub.2O.sub.5 and
vanadium oxides of other stoichiometry, including vanadium
oxysulfides.
[0131] Both electrically conductive and electrically non-conductive
electroactive transition metal chalcogenides are useful in the
practice of this invention. Preferred electroactive transition
metal chalcogenides are those that are electrically conductive in
addition to being ionically conductive. Some transition metal
chalcogenides are inherently electrically conductive while others
become electrically conductive upon insertion of alkali-metal or
alkaline-earth metal cations. Both types are particularly useful.
Without wishing to be bound to any particular theory, it is
believed that good electrical conductivity in a transition metal
chalcogenide in the composite cathodes of the present invention can
provide for a more even distribution of electric fields within the
composite cathode thereby providing a more even distribution of
charge storage in the electroactive sulfur-containing cathode
material in the composite cathode, improving charge and discharge
characteristics, and improving overall capacity and utilization of
the electroactive cathode materials. Additionally, transition metal
chalcogenides which are electrically conductive can eliminate or
reduce the need for incorporating non-electroactive conductive
additives in the composite cathodes of the present invention.
Especially preferred are electroactive transition metal
chalcogenide compositions having electrical conductivities between
about 10.sup.-5 S/cm and 10.sup.+3 S/cm (S=Siemens).
[0132] Preferred electroactive transition metal chalcogenides for
use in the practice of the present also insert (or intercalate) and
transport alkali-metal cations within the voltage range from about
+0.1 to about +6 volts versus lithium. Especially preferred are
electroactive transition metal chalcogenides which insert and
transport alkali-metal cations within the voltage range of about
+1.0 to +4.5 volts versus lithium. Particularly preferred are
electroactive transition metal chalcogenides that are electroactive
at voltages equal to and greater than the onset reduction voltage
of the employed electroactive sulfur-containing cathode material in
the composite cathode of the present invention, and also insert and
transport alkali metal cations within a voltage range up to +4.5
volts versus lithium.
[0133] Also preferred in the practice of this invention are
electroactive transition metal chalcogenides that independently or
in combination with the electroactive sulfur-containing cathode
composition provide energy storage capacity to the composite
cathode. Preferred are compositions with additional specific energy
storage capacities of greater than about 150 mAh/g. Especially
preferred are compositions with additional storage capacities of
greater than 200 mAh/g and particularly preferred are those with
additional storage capacities of greater than about 300 mAh/g.
[0134] Especially preferred are electroactive transition metal
chalcogenides, such as vanadium oxides, which may be processed by
sol-gel techniques (such as those described below), and aerogel and
xerogel processing methods, as known in the art. Without wishing to
be bound to any particular theory, it is believed that composite
cathodes fabricated by a sol-gel type process additionally provide
enhanced adhesion to metallic current-collecting substrates and
have good self-adhesion properties so as to minimize the need for
adding binders to the composite cathode. It is further believed
that the nanoscale porosity provided in the gels provides
nanostructured electroactive transition metal chalcogenide
materials that act like porous catalytic surfaces within the
composite cathode. These active nanoscale structures effectively
encapsulate, bind or entrap, the electroactive sulfur-containing
cathode materials, as well as effectively bind or complex the
anionic reduction products produced during discharge of the cells,
thereby retarding their diffusion out of the cathode structures
into the cells. In support of this, the experimental results on the
zeta potential of vanadium oxide sol indicate that the sol is
cationic in nature. Thus, it is expected that, in the cell in the
presence of liquid electrolyte, the corresponding gel particles
formed from an electroactive transition metal chalcogenide sol
(e.g., vanadium oxide sol) can prevent or retard the anionic
reduction products from being transported outside of the composite
cathode layer. Further, since the electroactive transition-metal
chalcogenide facilitates reversible metal-ion transport, these
porous catalytic surfaces may facilitate the redox reactions of the
electroactive sulfur-containing cathode materials on their surfaces
thereby enhancing both capacity and cycleability of the
electroactive materials. This is especially true when the
electroactive transition metal chalcogenide composition is
inherently electrically conductive in addition to being ionically
conductive. Hence, it is believed that the transition metal
chalcogenide in the composite cathodes of the present invention is
highly multifunctional in terms of its performance.
[0135] Electroactive Sulfur-Containing Cathode Materials
[0136] The nature of the electroactive sulfur-containing cathode
materials useful in the practice of this invention can vary widely.
The electroactive properties of elemental sulfur and of
sulfur-containing organic materials are well known in the art, and
include the reversible formation of lithiated or lithium ion
sulfides during the discharge or cathode reduction cycle of the
battery cell.
[0137] Examples of electroactive sulfur-containing cathode
materials are carbon-sulfur compositions of general formula
C.sub.vS, wherein v is a numerical value within the range of about
4 to about 50 as described in U.S. Pat. No. 4,143,214. Other
examples of electroactive sulfur-containing cathode materials are
those which contain one or more polymer compounds having a
plurality of carbon monosulfide units that may generally be written
as (CS).sub.w, wherein w is an integer of at least 5, as described
in U.S. Pat. No. 4,152,491.
[0138] Further examples include those containing one or more
carbon-sulfur compounds of formulae (CS.sub.x).sub.n,
(CS.sub.2).sub.n, and (C.sub.2S.sub.z).sub.n. Compositions of
general formula I,
--(CS.sub.x).sub.n-- I
[0139] wherein x takes values from 1.2 to 2.3 and n is an integer
equal to or greater than 2, are described in U.S. Pat. No.
5,441,831. Additional examples are those of general formula I
wherein x ranges from greater than 2.3 to about 50, and n is equal
to or greater than 2, as described in U.S. Pat. No. 5,601,947 and
U.S. patent application Ser. No. 08/729,713. These materials may
optionally incorporate large fractions of elemental sulfur or
polysulfur components, which on electrochemical reduction in an
electrolytic cell, provide exceptionally high storage capacity per
unit weight of material. Other examples of sulfur-containing
compositions in the practice of this invention are materials of
formula (CS.sub.2).sub.n made from carbon disulfide as described by
J. J. Colman and W. C. Trogler in J. Amer. Chem. Soc. 1995, 117,
11270-11277. These various carbon-sulfur materials, when used as
cathode materials in battery cells, may be optionally mixed with
conductive components, electrolytes, and binders to improve
electrochemical recycleability and capacity of the electroactive
sulfur-containing cathode material.
[0140] Materials of formula I can be prepared by the reduction of
carbon disulfide with alkali-metals, such as sodium or lithium, in
an appropriate solvent such as dimethyl sulfoxide, dimethyl
formamide (D)MF), N-methyl pyrrolidinone, hexamethyl phosphoramide,
and the like, incorporating long reaction times before work-up, as
described in the aforementioned U.S. Pat. No. 5,601,947 and U.S.
patent application Ser. No. 08/729,713. Reaction times greater than
about 41 hours provide electroactive carbon-sulfur cathode
materials with elemental compositions containing between about 86
wt % and 98 wt % sulfur. Preferred compositions are those that have
elemental compositions containing between about 90 wt % and 98 wt %
sulfur. Although the detailed structures of the materials made by
this method have not been completely determined, available
structural information suggests that materials of this general
formula are comprised of one or more of the structural units of
formulae II-V, 3
[0141] wherein m is the same or different at each occurrence and is
greater than 2, u is the same or different at each occurrence and
is equal to or greater than 1, and the relative amounts of a, b, c,
and d comprising said carbon-sulfur polymer or polycarbon sulfide
(PCS) material can vary widely and depend on the method of
synthesis. Preferred PCS compositions with high electrochemical
capacity are those containing substantial amounts of polysulfide
species --(S.sub.m)-- incorporated in and attached to the polymer
backbone. Especially preferred compositions are those wherein m is
on the average equal to or greater than 6. A key feature of these
compositions is that the polymer backbone structure contains
conjugated segments which may facilitate electron trans port during
electrochemical oxidation and reduction of the polysulfur side
groups.
[0142] Additional examples of electroactive carbon-sulfur cathode
materials are compositions of general formula VI,
--(C.sub.2S.sub.z).sub.n-- VI
[0143] wherein z ranges from greater than 1 to about 100, and n is
equal to or greater than 2, as described in U.S. Pat. No. 5,529,860
and U.S. patent application Ser. No. 08/602,323. The material may
also comprise large fractions of elemental sulfur and polysulfur
components, which on electrochemical reduction in an electrolytic
cell, provide exceptionally high storage capacity per unit weight
of material. These carbon-sulfur materials when used as cathode
materials in battery cells, may be optionally mixed with conductive
components, polymeric binders and electrolytes to further improve
electrochemical recycleability and capacity of said electroactive
cathode material.
[0144] Materials of formula VI can be prepared, as described in the
aforementioned U.S. Pat. No. 5,529,860 and U.S. patent application
Ser. No. 08/602,323, by the reaction of acetylene with a metal
amide, such as sodium amide or sodium diisopropylamide, and
elemental sulfur in a suitable solvent, such as liquid ammonia.
Although the detailed structure of such materials has not been
completely determined, available structural information suggests
that these compositions are comprised of one or more of the
structural units of formulae IV-V, VII-IX; 4
[0145] wherein m is the same or different at each occurrence and is
greater than 2; and the relative amounts of c, d, e, f, and g, in
said materials can vary widely and will depend on the method of
synthesis. Preferred compositions are those wherein m is equal to
or greater than 3, and especially preferred compositions are those
wherein m is on the average equal to or greater than 6. These
materials typically have elemental compositions containing between
about 50 wt % and 98 wt % sulfur. Preferred compositions are those
that have elemental compositions containing between about 80 wt %
and 98 wt % sulfur.
[0146] Additional examples of electroactive sulfur-containing
cathode materials are organo-sulfur substances containing
one-dimensional electron conducting polymers and at least one
polysulfurated chain forming a complex with said polymer, as
described in U.S. Pat. No. 4,664,991. Other examples of
electroactive sulfur-containing cathode materials are those
comprising organo-sulfur compounds of the formula
(R(S).sub.y).sub.n, where y=1 to 6; n=2 to 20, and R is one or more
different aliphatic or aromatic organic moieties having one to
twenty carbon atoms as described in U.S. Pat. Nos. 4,833,048 and
4,917,974. Still other examples of electroactive sulfur-containing
cathode materials are organo-sulfur polymers with the general
formula (R(S).sub.y).sub.n, as described in U.S. Pat. No.
5,162,175. Yet more examples of organo-sulfur cathode materials are
those comprising a combination of a compound having a disulfide
group and a conductive polymer, or an organo-disulfide derivative
of a conductive polymer, as described in U.S. Pat. No.5,324,599.
Additional examples of organo-sulfur materials are the
organo-sulfur derivatives of metal ions as described in U.S. Pat.
No. 5,516,598.
[0147] Thus, in a preferred embodiment, composite cathodes of the
present invention comprise (a) an electroactive sulfur-containing
material, wherein said electroactive sulfur-containing material, in
its oxidized state, comprises a polysulfide moiety of the formula
--S.sub.m--, wherein m is an integer equal to or greater than 3;
and, (b) an electroactive transition metal chalcogenide
composition, as described herein.
[0148] In one embodiment, the electroactive sulfur-containing
material comprises elemental sulfur. In one embodiment, the
electroactive sulfur-containing material comprises a carbon-sulfur
polymer. In one embodiment, the electroactive sulfur-containing
material comprises a carbon-sulfur polymer and m is an integer
equal to or greater than 6. In one embodiment, the electroactive
sulfur containing material comprises a carbon-sulfur polymer, and
the polymer backbone chain of said carbon-sulfur polymer comprises
conjugated segments. In one embodiment, the electroactive
sulfur-containing material comprises a carbon-sulfur polymer, and
the polysulfide moiety, --S.sub.m--, is covalently bonded by one or
both of its terminal sulfur atoms on a side group to the polymer
backbone chain of said carbon-sulfur polymer material. In one
embodiment, the electroactive sulfur-containing material comprises
a carbon-sulfur polymer, and the polysulfide moiety, --S.sub.m--,
is incorporated into the polymer backbone chain of said
carbon-sulfur polymer by covalent bonding of said polysulfide
moiety's terminal sulfur atoms. In one embodiment, the
electroactive sulfur-containing material comprises a carbon-sulfur
polymer comprising more than 75% sulfur by weight.
[0149] Quite surprisingly, it, was discovered that when elemental
sulfur is used as the electroactive sulfur-containing material in
the composite cathodes of the present invention, the sulfur is
rendered more highly electrochemically active providing very high
reversible capacity. Low self discharge and high cycle life are
provided by the effective encapsulation or entrapping of the
elemental sulfur and retarding of sulfide out-diffusion by the
transition metal chalcogenide compositions.
[0150] Composite Cathodes
[0151] One aspect of the present invention pertains to a composite
cathode for use in an electrochemical cell, said cathode
comprising:
[0152] (a) an electroactive sulfur-containing cathode material,
wherein said electroactive sulfur-containing cathode material, in
its oxidized state, comprises a polysulfide moiety of the formula
--S.sub.m--, wherein m is an integer equal to or greater than 3, as
described herein; and,
[0153] (b) an electroactive transition metal chalcogenide
composition, which encapsulates said electroactive
sulfur-containing cathode material, and which retards the transport
of anionic reduction products of said electroactive
sulfur-containing cathode material, said electroactive transition
metal chalcogenide composition comprising an electroactive
transition metal chalcogenide having the formula:
M.sub.jY.sub.k(OR).sub.l
[0154] wherein
[0155] M is a transition metal;
[0156] Y is the same or different at each occurrence and is oxygen,
sulfur, or selenium;
[0157] R is an organic group and is the same or different at each
occurrence;
[0158] j is an integer ranging from 1 to 12;
[0159] k is a number ranging from 0 to 72; and
[0160] l is a number ranging from 0 to 72;
[0161] with the proviso that k and l cannot both be 0; as described
herein.
[0162] The present invention also pertains to the design and
configuration of composite cathodes of the present invention. The
relative configuration of the electroactive sulfur-containing
cathode material and the electroactive transition metal
chalcogenide composition in the composite cathode is critical. In
all cases, in order to retard out-diffusion of anionic reduction
products from the cathode compartment in the cell, the
sulfur-containing cathode material must be effectively separated
from the electrolyte or other layers or parts of the cell by a
layer of an electroactive transition metal chalcogenide
composition. Surprisingly, it has been discovered that this layer
can be dense or porous.
[0163] One design incorporates a fabricated cathode comprising a
mixture of the electroactive sulfur-containing cathode material,
the electroactive transition metal chalcogenide, and optionally
binders, electrolytes, and conductive additives, which is deposited
onto a current collector.
[0164] Another design is one where a coating of the electroactive
sulfur-containing cathode material is encapsulated or impregnated
by a thin coherent film coating of the cation transporting, anionic
reduction product transport-retarding, transition metal
chalcogenide composition.
[0165] Yet another design of said composite cathode of the present
invention incorporates a cathode comprised of particulate
electroactive sulfer-containing cathode materials individually
coated with an encapsulating layer of the cation transporting,
anionic reduction product transport-retarding, transition metal
chalcogenide composition.
[0166] In one embodiment of the present invention, the cathode is
comprised of particulate sulfur-containing cathode materials,
generally less than 10 .mu.m (microns) in diameter, individually
coated with an encapsulating layer of an alkali-metal
cation-transporting, yet anionic reduction product
transport-retarding electroactive transition metal chalcogenide
composition. A cathode fabricated from such a "core-shell"
configuration of materials is illustrated in FIG. 1. Here, the
prismatic cathode structure 1 in contact with a current collector 2
is comprised of compacted powders of the composite cathode. Each
composite cathode particle is comprised of a core 3 of the
electroactive sulfur-containing cathode material with an outer
shell 4 of a retarding barrier layer comprising an electroactive
transition metal chalcogenide. Optionally, said composite cathode
may contain fillers 5 comprising various types of binders,
electrolytes and conductive materials that are well known to those
skilled in the art.
[0167] Another embodiment of the present invention is shown in FIG.
2, which illustrates a prismatic composite cathode structure 1 in
contact with a current collector 2 and comprising electroactive
sulfur-containing cathode particles 6 as a dispersed phase in a
matrix consisting of an electroactive transition metal chalcogenide
phase 7 that optionally contains a binder, an electrolyte, and a
conductive filler. The electroactive transition metal chalcogenide
phase facilitates the highly selective and reversible transport of
alkali-metal cations from the electroactive cathode materials in
the composite cathode to the electrolyte and also retards the
transport of anionic reduction products from the composite cathode
to the electrolyte or other layers or parts of the cell.
[0168] Yet another embodiment of the present invention incorporates
a cathode comprising a coating of the electroactive
sulfur-containing cathode material, binders, electrolytes,
conductive additives on a current collector. This resulting cathode
is encapsulated, or otherwise effectively separated from the
electrolyte layer, by a coherent film coating or impregnation
comprising one or more electroactive transition metal
chalcogenides. Such a cathode is illustrated in FIG. 3. Here, the
prismatic sulfur containing cathode structure 8 in contact with the
current collector 2 is effectively encapsulated with a layer of the
electroactive transition metal chalcogenide composition 9. Either
or both of the electroactive sulfur-containing cathode material and
the electroactive transition metal chalcogenide material may
optionally contain binders, electrolytes, and conductive fillers.
Of course, if such a composite cathode is to be used in combination
with a solid electrolyte, one need only employ an effective layer
of the transition metal chalcogenide between the solid electrolyte
and the cathode structure rather than coating the entire cathode
structure.
[0169] Still another embodiment of the present invention is shown
in FIG. 4, which illustrates a prismatic composite cathode
structure 1 in contact with a current collector 2 and comprising a
highly porous, fibrous, and ultrafine sponge-like structure or
network of an aerogel or xerogel of an electroactive transition
metal chalcogenide composition 10 into which the electroactive
sulfur-containing cathode materials 11 are embedded or
encapsulated. The fibrous nature of such aerogel and xerogel
materials is described, for example, by Chaput et al., J.
Non-Cryst. Solids 1995, 118, 11-18, and references therein. Again,
the electroactive transition metal chalcogenide matrix optionally
contains a binder, an electrolyte, and/or a conductive
additive.
[0170] For the composite cathode structures which employ a
composite cathode bound to a current collector, such as those
illustrated FIGS. 1, 2, and 4, preferred electroactive transition
metal chalcogenides are those which yield composite cathodes having
good adhesion to the metal current collector. The use of such
materials can greatly facilitate the collection of current from the
composite cathode and improve the integrity of the cathode
structure.
[0171] In one embodiment of the present invention, the composite
cathode is a particulate, porous electroactive transition metal
chalcogenide composition, optionally containing non-electroactive
metal oxides, such as silica, alumina, and silicates, that is
further impregnated with a soluble electroactive sulfur-containing
cathode material. This is especially beneficial in increasing the
energy density and capacity above that achieved with the
electroactive sulfur-containing cathode material (e.g.,
electroactive organo-sulfur and carbon-sulfur cathode materials)
only.
[0172] The relative amounts of electroactive transition metal
chalcogenide and electroactive sulfur-containing cathode material
in the composite cathode can vary widely so long as sufficient
electroactive transition metal chalcogenide is present to
effectively retard anionic reduction products from out-diff using
into the surrounding medium or layer while effectively maintaining
or improving the capacity and cell efficiencies. Typically, the
amount of electroactive transition metal chalcogenide used in the
complete composite cathode will vary from 2 wt % to about 70 wt %.
When used in a separate layer of the composite cathode, such as in
FIG. 3, the amount of electroactive transition metal chalcogenide
in the separate layer only will vary from about 5 wt % to 100 wt %.
Preferred composite cathodes are those that contain between about 5
wt % and 50 wt % electroactive transition metal chalcogenide
compounds, and most preferred composite cathodes contain between
about 5 wt % and 40 wt % electroactive transition metal
chalcogenide compounds.
[0173] The composite cathodes of the present invention may further
comprise a non-electroactive metal oxide to further improve the
fabrication as well as the electrical and electrochemical
properties of the resulting cathode. Examples of such
non-electroactive metal oxides are silica, alumina, and silicates.
Preferably, such metal oxides are porous in nature, and have a high
surface area of greater than 20 m.sup.2/g. Typically, the
non-electroactive metal oxide material is incorporated or mixed
with the transition metal chalcogenide during fabrication of the
composite cathode.
[0174] The composite cathodes of the present invention may further
comprise one or more materials selected from the group of binders,
electrolytes, and conductive additives, usually to improve or
simplify their fabrication as well as improve their electrical and
electrochemical characteristics. Similarly, such materials may be
used as a matrix for the electroactive sulfur-containing cathode
material, the electroactive transition metal chalcogenide, or
both.
[0175] The choice of binder material may vary widely so long as it
is inert with respect to the composite cathode materials. Useful
binders are those materials, usually polymeric, that allow for ease
of processing of battery electrode composites and are generally
known to those skilled in the art of electrode fabrication.
Examples of useful binders are organic polymers such as
polytetrafluoroethylene (s.RTM.), polyvinylidine fluorides
(PVF.sub.2 or PVDF), ethylene-propylene-diene (EPDM) rubbers,
polyethylene oxides (PEO), UV curable acrylates, UV curable
methacrylates, and UV curable divinylethers, and the like.
[0176] Useful conductive additives are those known to one skilled
in the art of electrode fabrication and are such that they provide
electrical connectivity to the majority of the electroactive
materials in the composite cathode. Examples of useful conductive
fillers include conductive carbons (e.g., carbon black), graphites,
metal flakes, metal powders, electrically conductive polymers, and
the like.
[0177] Examples of useful electrolytes include any liquid, solid,
or solid-like materials capable of storing and transporting ions,
so long as the electrolyte material is chemically inert with
respect to the composite cathode material and the electrolyte
material facilitates the transportation of ions.
[0178] In those cases where binder and conductive filler are
desired, the amounts of binder and conductive filler can vary
widely and the amounts present will depend on the desired
performance. Typically, when binders and conductive fillers are
used, the amount of binder will vary greatly, but will generally be
less than about 15 wt % of the composite cathode. Preferred amounts
are less than 10 wt %. The amount of conductive filler used will
also vary greatly and will typically be less than 15 wt % of the
composite cathode. Preferred amounts of conductive additives are
generally less than 12 wt %.
[0179] Particularly preferred composite cathodes are those
comprising an electroactive sulfur-containing material (e.g., a
carbon-sulfur polymer or elemental sulfur);. V.sub.2O.sub.5;
conductive carbon; and a PEO binder.
[0180] Methods of Making Composite Cathodes
[0181] One aspect of the present invention pertains to methods for
fabricating composite cathodes.
[0182] One method relates to the fabrication of composite cathodes
by the physical mixture of the electroactive sulfur-containing
cathode material, the electroactive transition metal chalcogenide,
and optionally binders, electrolytes, and conductive fillers either
as dry solids, or as a slurry in a solvent or mixtures of solvents.
The resulting mixture is then fabricated into a cathode structure
of desired,dimensions, for example, by casting, coating,
dip-coating, extrusion, calendering, and other means known in the
art.
[0183] Thus, in one embodiment, the present invention pertains to
methods for preparing the composite cathodes of the present
invention, said methods comprising the steps of:
[0184] (a) dissolving or dispersing an electroactive transition
metal chalcogenide in a liquid medium;
[0185] (b) adding to the composition resulting from step (a) an
electroactive sulfur-containing cathode material;
[0186] (c) mixing the composition resulting from step (b) to
dissolve or disperse said electroactive sulfur-containing cathode
material, thereby forming a composition having a desired
consistency and particle size distribution;
[0187] (d) casting the composition resulting from step (c) onto a
suitable substrate or placing the composition resulting from, step
(c) into a mold;
[0188] (e) removing some or all of the liquid from the composition
resulting from step (d) to provide a solid or gel-like composite
cathode structure in the shape or form desired; and
[0189] (f) optionally heating the composite cathode structure of
step (e) to a temperature of 100.degree. C. or greater.
[0190] Examples of liquid media suitable for use in the methods of
the present invention include aqueous liquid, non-aqueous liquids,
and mixtures thereof. Especially preferred liquids are non-aqueous
liquids such as methanol, ethanol, isopropanol, propanol, butanol,
tetrahydrofuran, dimethoxyethane, acetone, toluene, xylene,
acetonitrile, and cyclohexane. Most preferred liquids are those
selected from the group consisting of acetone, acetonitrile, and
dimethoxyethane.
[0191] Another method relates to the fabrication of a composite
cathode by a sol-gel method wherein the electroactive
sulfur-containing cathode material, and optionally binders and
conductive fillers, are suspended or dispersed in a medium
containing a sol (solution) of the desired electroactive transition
metal chalcogenide composition; the resulting composition is first
converted into a sol-gel (e.g., a gel-like material having a
sol-gel structure or a continuous network-like structure) by the
addition of a gelling agent, and the resulting sol-gel further
fabricated into a composite cathode.
[0192] The electroactive transition metal chalcogenide sols are
dispersions of colloidal particles in the liquid. Dispersions of
colloidal particles of the electroactive transition metal
chalcogenides can be prepared by a variety of methods known in the
art, including, for example, the methods described in U.S. Pat. No.
4,203,769. From the sol, a sol-gel or gel-like material is formed
which has an interconnected, rigid network, typically having
submicron-sized pores. This network (e.g., oxide network) is the
result of an inorganic polymerization reaction. Typically the
precursor for forming the sol-gel is a molecular derivative, such
as an transition metal alkoxide or a transition metal
acetylacetonate.
[0193] Thus, in one embodiment, the present invention pertains to
methods for preparing the composite cathodes of the present
invention, said methods comprising the steps of:
[0194] (a) dissolving or dispersing an electroactive transition
metal chalcogenide in a liquid medium;
[0195] (b) adding to the composition resulting from step (a) an
electroactive sulfur-containing cathode material;
[0196] (c) mixing the composition resulting from step (b) to
dissolve or disperse said electroactive sulfur-containing cathode
material, thereby forming a composition having a desired
consistency and particle size distribution;
[0197] (d) contacting the composition resulting from step (c) with
a gelling agent, thereby forming a sol-gel having a desired
viscosity;
[0198] (e) casting the composition resulting from step (d) onto a
suitable substrate or placing the composition resulting from step
(d) into a mold;
[0199] (f) removing some or all of the liquid from the composition
resulting from step (e) to provide a solid or gel-like composite
cathode structure in the shape or form desired; and
[0200] (g) optionally heating the composite cathode structure of
step (f) to a temperature of 100.degree. C. or greater.
[0201] In another embodiment, the present invention pertains to
methods for preparing the composite cathodes of the present
invention, said methods comprising the steps of:
[0202] (a) dissolving an electroactive transition metal
chalcogenide (e.g., electroactive transition metal alkoxide or
electroactive transition metal chalcogenide precursor) in a liquid
medium;
[0203] (b) contacting the composition resulting from step (a) with
a gelling agent, thereby forming a sol-gel having a desired
viscosity;
[0204] (c) adding to the composition resulting from step (b) an
electroactive sulfur-containing cathode material;
[0205] (d) mixing the composition resulting from step (c) to
dissolve or disperse said electroactive sulfur-containing cathode
material, thereby forming a composition having a desired
consistency and particle size distribution;
[0206] (e) casting the composition resulting from step (d) onto a
suitable substrate or placing the composition resulting from step
(d) into a mold;
[0207] (f) removing some or all of the liquid from the composition
resulting from step (e) to provide a solid or gel-like composite
cathode structure in the shape or form desired; and
[0208] (g) optionally heating the composite cathode structure of
step (f) to a temperature of 100.degree. C. or greater.
[0209] Gelling agents that can effectively cause the electroactive
transition metal chalcogenide to form a sol-gel (e.g., a gel-like
or network structure) include both chemical and physical agents.
Useful chemical gelling agents are those that convert the
electroactive transition metal chalcogenide to a form with lower
solubility in the liquid medium used. Typical effective chemical
agents are water, and lower alcohols such as methanol, ethanol,
isopropanol, ethylene glycol, and the like. Other useful chemical
gelling agents are non-solvents for the electroactive transition
metal chalcogenide, acids, and polymeric binders. With the addition
of small amounts of non-solvent, the electroactive transition metal
chalcogenide will gradually precipitate giving rise to powders or
gel-like structures. Useful physical gelling agents are heating,
cooling, light, x-rays, and electron beams. Thus, the application
of heat may cause decomposition of alkoxy groups or other
functional groups in a electroactive transition metal compound
leading to a new composition with a networked structure giving rise
to a gel. Likewise, the application of light, x-rays, or electron
beams may cause decomposition or crosslinking of the alkyl groups
or other functional groups, giving rise to a gel or precipitated
slurry of the composite cathode.
[0210] This sol-gel method can be used to provide composite
cathodes in at least two different configurations. One relates to a
configuration in which particulate electroactive sulfur-containing
cathode material is encapsulated with a layer of the electroactive
transition metal chalcogenide composition. The other relates to a
configuration in which the electroactive sulfur-containing cathode
material is embedded in a continuous network or continuous phase of
the electroactive transition metal chalcogenide composition. The
transition metal chalcogenide phase can be viewed as an interfacial
boundary layer around the particulate electroactive
sulfur-containing cathode material. This boundary layer has a high
concentration of interconnecting nanoscale porosity.
[0211] In another embodiment, the present invention pertains to
methods for preparing the composite cathodes of the present
invention, said methods comprising the steps of:
[0212] (a) coating a current collector substrate with a composition
comprising an electroactive sulfur-containing cathode material and
drying or curing said composition to form a solid or gel-type
electroactive cathode layer on said current collector
substrate;
[0213] (b) dissolving or dispersing an electroactive transition
metal chalcogenide in a liquid medium;
[0214] (c) coating said electroactive cathode layer with the
composition resulting from step (b) and drying or curing said
composition to form a solid layer of said electroactive transition
metal chalcogenide composition which covers the outer surface of
said electroactive cathode layer.
[0215] In another embodiment, the present invention pertains to
methods for preparing the composite cathodes of the present
invention, said methods comprising the steps of:
[0216] (a) coating a current collector substrate with a composition
comprising an electroactive sulfur-containing cathode material and
drying or curing said composition to form a solid or gel-type
electroactive cathode layer on said current collector
substrate;
[0217] (b) dissolving or dispersing an electroactive transition
metal chalcogenide in a liquid medium;
[0218] (c) contacting the composition resulting from step (b) with
a gelling agent, thereby forming a sol-gel having a desired
viscosity;
[0219] (d) coating said electroactive cathode layer with the
composition resulting from step (c) and drying or curing said
composition to form a solid layer of said electroactive transition
metal chalcogenide composition which covers the outer surface of
said electroactive cathode layer.
[0220] Examples of electroactive transition metal chalcogenides and
electroactive sulfur-containing cathode materials for use in the
above methods are described in detail above.
[0221] The temperature at which various components in the above
processes are dissolved or dispersed is not critical and any
temperature can be used so long as the desired solution or
dispersion of the components in the liquid medium is obtained. For
the fabrication of some composite cathodes it may be desirable to
use higher temperatures so as to effect dissolution of one or more
components during the process. A lower temperature may then be
desired so as to effectively cause one or more components to
separate out in a gel or precipitate form. Useful temperatures can
be routinely determined experimentally by one skilled in the art.
Preferred temperatures are those at which the transition metal
chalcogenide initially dissolves or forms a colloidal solution in
the liquid medium. Especially preferred temperatures are those
which further provide for an economical process. Most preferred
temperatures are those which further are close to room temperature
or slightly above.
[0222] Optionally, binders, electrolytes, and conductive fillers
may be added to the compositions at one or more of the various
steps in the methods described above, usually at steps which
involve dissolving, dispersing, or mixing. Such additives often
facilitate or improve adhesion, cohesion, current collection, and
ion transport.
[0223] Mixing of the various compositions in the methods described
above can be accomplished by a variety of methods so long as the
desired dispersion of the materials is obtained. Suitable methods
of mixing include mechanical agitation, grinding, ultrasonication,
ball-milling, sand milling, impingement milling, and the like.
[0224] Removal of some or all of the liquid from the various
compositions in the methods described above can be accomplished by
a variety of conventional means, so long as the resulting product
has a desired porosity and/or pore size distribution, surface area,
shape, chemical composition, adhesion to the current collector or
other substrate, and the like. Useful methods for removal of liquid
employ forced hot air convection, heat, infrared radiation, flowing
gases, vacuum, reduced pressure, extraction, and the like.
Preferred methods for removal of liquid include forced hot air
convection, vacuum evaporation, reduced pressure, infrared heating,
and flowing gas. Most preferred methods involve a combination of
these preferred techniques.
[0225] It is well known in the art of battery electrode fabrication
that, by casting a slurry of electrode components and removing the
solvent, thin films and coatings with the desired thickness can be
made. One of skill in the art will appreciate that, by flash
evaporation of the solvent from a slurry of the electroactive
transition metal chalcogenide and the electroactive
sulfur-containing cathode material, one can produce finely divided
powders with varying particle sizes. Powdered composite cathode
materials prepared by the processes of the present invention can be
hot or cold pressed, slurry coated or extruded onto current
collecting materials by techniques known to those skilled in the
art of battery electrode fabrication.
[0226] Examples of preferred composite cathodes prepared using the
processes of the present invention include thin film structures up
to about 25 .mu.m in thickness, coatings on current collectors up
to about 100 .mu.m in thickness, and powdered composite
structures.
[0227] Composite cathodes with the configuration shown in FIG. 3
can also be fabricated by vacuum evaporation of the electroactive
transition metal chalcogenide composition on top of the
electroactive sulfur-containing cathode material. Films and
membranes of transition metal chalcogenide compounds such as
V.sub.2O.sub.5 and MnO.sub.2 can be deposited in vacuum using
several techniques, including sputtering and electron-beam
evaporation (e-beam) using target materials of the same. Both
sputtering and e-beam may be done as reactive evaporation with a
partial oxygen pressure in order to achieve the proper
stoichiometry. Plasma spraying may also be applicable. Vacuum
evaporation fabrication of composite cathodes of the present
invention is preferred when said composite cathode material is used
in an all solid-state cell fabricated using vacuum web coating
technologies for most or all of the layers in the cell.
[0228] Rechargeable Battery Cells and Methods of Making Same
[0229] One aspect of the present invention pertains to a
rechargeable, electric current producing cell which comprises:
[0230] (a) an anode,
[0231] (b) a composite cathode of the present invention, and
[0232] (c) an electrolyte that is stable in the presence of the
anode and cathode.
[0233] Another aspect of the present invention pertains to methods
of forming a rechargeable, electric current producing cell, said
method comprising the steps of:
[0234] (a) providing an anode;
[0235] (b) providing a composite cathode of the present invention;
and,
[0236] (c) enclosing an electrolyte between said anode and said
composite cathode.
[0237] The anode material may be comprised of one or more metals or
metal alloys or a mixture of one or more metals and one or more
alloys, wherein said metals are selected from the Group IA and IIA
metals in the Periodic Table. Anodes comprising lithium and sodium
are useful for the anode of the battery of the invention. The anode
may also be alkali-metal intercalated carbon, such as LiC.sub.x
where x is equal to or greater than 2. Also useful as anode
materials of the present invention are alkali-metal intercalated
conductive polymers, such as lithium, sodium or potassium doped
polyacetylenes, polyphenylenes, polyquinolines, and the like.
Examples of suitable anodes include lithium metal, lithium-aluminum
alloys, lithium-tin alloys, lithium-carbon, lithium-graphite,
calcium metal, aluminum, sodium, sodium alloys, and the like.
[0238] Preferred anodes are those selected from the group of
lithium metal and lithium-aluminum and lithium-tin alloys.
[0239] The electrolytes used in battery cells function as a medium
for storage and transport of ions, and in the special case of solid
electrolytes these materials additionally function as separator
materials between the anodes and cathodes. Any liquid, solid, or
solid-like material capable of storing and transporting ions may be
used, so long as the material is chemically inert with respect to
the anode and the cathode and the material facilitates the
transportation of ions between the anode and the cathode.
[0240] Examples of useful electrolytes are solid electrolyte
separators comprised of polyethers, PEO, polyimides,
polyphosphazenes, polyacrylonitriles (PAN), polysiloxanes,
polyether grafted polysiloxanes, derivatives of the foregoing,
copolymers of the foregoing, crosslinked and network structures of
the foregoing, blends of the foregoing, and the like to which is
added an appropriate electrolyte salt.
[0241] Examples of useful gel-polymer electrolytes are those
prepared from polymer matrices derived from polyethylene oxides,
polypropylene oxides, polyacrylonitriles, polysiloxanes,
polyimides, polyethers, sulfonated polyimides, perfluorinated
membranes (Nafion.TM. resins), divinyl polyethylene glycols,
polyethylene glycol-bis methyl acrylates), polyethylene
glycol-bis(methyl methacrylates), derivatives of the foregoing,
copolymers of the foregoing, crosslinked and network structures of
the foregoing, blends of the foregoing, and the like.
[0242] Examples of useful solvents or plasticizing agents as gel
forming agents for electrolytes include ethylene carbonate (EC),
propylene carbonate (PC), N-methyl acetamide, acetonitrile,
sulfolane, tetraethyleneglycol dimethyl ether (TEGDME),
1,2-dimethoxyethane, polyethylene glycols, 1,3-dioxolanes, glymes,
siloxanes, and ethylene oxide grafted siloxanes, and blends
thereof. Particularly preferred solvents and plasticizing agents
are those derived from graft copolymers of ethylene oxide and
oligomers of poly(dimethyl siloxane) of general formula X, as
described in U.S. Pat. No. 5,362,493, 5
[0243] wherein o is an integer equal to or greater than 1; p is an
integer equal to or greater than 0 and less than about 30; and, the
ratio t/s is equal to or greater than 0. Values for o, p, s, and t
can vary widely and depend on the desired properties for said
liquid or plasticizing agent. Preferred agents of this type are
those wherein o ranges from about 1 to 5, p ranges from about 1 to
20, and the ratio t/s is equal to or greater than 0.5. An
especially preferred composition of formula X is that in which o is
equal to 3, p is equal to 7, and the ratio of t to s is 1.
[0244] These liquid or plasticizing agents themselves, and blends
thereof, are useful solvents to form liquid electrolytes which
provide other effective electrolyte systems for the cells of the
present invention. For example, glymes or sulfolane with lithium
salts, such as LiAsF.sub.6, are useful liquid electrolytes.
1,3-Dioxolane and TEGDME are especially useful as a blend of
solvents for liquid electrolytes. Likewise, compositions of TEGDME
or of formula X together with LiSO.sub.3CF.sub.3 are especially
useful as liquid electrolytes.
[0245] Examples of ionic electrolyte salts for electrolytes include
MClO.sub.4, MAsF.sub.6, MSO.sub.3CF.sub.3, MSO.sub.3CH.sub.3,
MBF.sub.4, MB(Ph).sub.4, MPF.sub.6, MC(SO.sub.2CF.sub.3).sub.3,
MN(SO.sub.2CF.sub.3).sub.2, 6
[0246] and the like, where M is Li or Na. Other electrolytes useful
in the practice of this invention are disclosed in U.S. Pat. No.
5,538,812.
EXAMPLES
[0247] Several embodiments of the present invention are described
in the following examples, which are offered by way of illustration
and not by way of limitation.
Example 1
[0248] This example describes the fabrication of a composite
cathode of the present invention. Vanadium oxide isopropoxide (25
mL, Alpha AESAR Co.) was placed in a dry flask and 500 mL of
acetone (having 0.5% water) was added drop wise to the alkoxide
liquid with constant stirring. The amount of acetone added was
based on getting a final concentration of vanadium pentoxide
(V.sub.2O.sub.5) in the sol (solution) of 4 g/100 mL. After mixing
the vanadium oxide isopropoxide with acetone, a mixture of
water-acetone (1 to 10 by volume) was added drop wise; the total
molar ratio of water to vanadium alkoxide was 0.5, including the
water present in the acetone. The color of the sol was yellow to
orange. The molar ratio of water to alkoxide can be varied in the
range 0.5 to 3.0, depending on the subsequent slurry and coating
procedure desired.
[0249] A slurry of a electroactive sulfur-containing cathode
material was made with the sol prepared above. A requisite amount
of sulfur was taken in a mortar and a proportionate amount of sol
was added to the agate mortar. The mixture was gently ground for 15
minutes. Dry carbon powder (Shawinigan 50AB black, hereafter
designated as SAB) was then added and the mixture was ground again
for 15 minutes with an additional amount of acetone being added.
The composition of the slurry as expressed in terms of sulfur,
vanadium pentoxide and carbon black was as follows: sulfur 80 wt %,
V.sub.2O.sub.5 15 wt % and carbon 5 wt %. This slurry was deposited
on nickel foil using a doctor blade in a hood under ambient
atmosphere. The coating was dried under an IR lamp overnight in
ambient atmosphere. The coating after IR drying was further dried
in a vacuum oven at 50.degree. C. for one hour yielding the
composite cathode on the current collector.
Example 2
[0250] In this example, a sulfur-containing composite cathode of
the present invention with the configuration shown in FIG. 3 was
fabricated on a nickel foil current collector substrate. The
composition of the electroactive sulfur-containing cathode layer
was as follows: 44 wt % sulfuir, 26 wt % carbon (SAB), and 30 wt %
of a UV curable binder comprising 25 wt % polyethylene glycol
dimethacrylate, 25 wt % polyethylene glycol divinylether, and 50 wt
% polyethylene glycol dimethyl ether. After UV curing of the
cathode layer, the sulfur-containing cathode layer was coated with
the V.sub.2O.sub.5 sol prepared in Example 1 using a dipping
technique. Two dippings were made. Subsequently, the coated
composite cathode was dried in a vacuum oven at 60.degree. C. for
an hour.
[0251] It was noted that the sulfur-containing cathode layer
obtained by casting of the slurry was porous. It was found that the
sol mix impregnated through the pores in the sulfur-containing
cathode layer and formed a thin V.sub.2O.sub.5 gel layer at the
pore boundaries as well as over the entire structure. It is
anticipated that because of the low viscosity of the V.sub.2O.sub.5
sol, impregnation into the finer pores is also likely.
Example 3
[0252] Vanadium oxide isopropoxide (12.53 mL, Alpha AESAR Chemical
Co.) was dissolved in anhydrous ethylene glycol dimethyl ether
(DME) resulting in a slightly yellow solution. Subsequently 4.0 mL
of a solution of 0.4644 g of water in 5 mL DME was added dropwise
over 30 minutes at 20.degree. C. with stirring under dry argon. The
resulting yellow-brown, slightly translucent sol was stirred for
2.5 hour and stored under positive argon pressure. The
concentration of vanadium oxide in the as synthesized sol was 4.4
g/100 mL. To this sol was added powdered sulfur and conductive
carbon with mixing to make a slurry. Prior to use, the sulfur and
carbon were dried in an oven at 60.degree. C. and 180.degree. C.,
respectively and subsequently stored in a dry room.
[0253] The slurry was processed using a ball milling technique. The
jars and beakers used for the slurry making were dried in an oven
at 110.degree. C. for several hours and were stored in a dry room.
The powdered sulfur was first mixed with the vanadium sol in a ball
mill for 1 hour. Then, the carbon black (SAB) was added and the
milling process continued. After 1 hour an additional amount of DME
solvent was added to reduce the solid content to about 12 g/100 mL
and the milling resumed for another 3 hours. This slurry was then
cast onto a nickel foil by the doctor blade technique in a hood
under ambient conditions. The wet coating was left overnight in a
hood to air dry. The coating was then heat treated in an oven at
110.degree. C. for 1 hour and then subsequently in a vacuum oven at
60.degree. C. for 1 hour. The composition of the dry composite
cathode was 75 wt % sulfur, 15 wt % V.sub.2O.sub.5 and 10 wt %
C.
Example 4
[0254] A slurry similar to that described in Example 3 was made
using a vanadium sol with acetone as solvent instead of DME. The
molar ratio of water to alkoxide was 0.5. The procedure used to
make the slurry was similar to that described in Example 3 with
acetone as the solvent and a milling time of 15 hours. The
conditions of deposition of the coating, drying and heat treatment
were the same as that described in Example 3. The composition of
the dried composite cathode was 80 wt % sulfur, 15 wt %
V.sub.2O.sub.5, and 5 wt % conductive carbon. The cast composite
cathode layer was 25 .mu.m thick after drying.
Example 5
[0255] This example describes the fabrication and performance of
flooded battery cells comprising the composite cathodes of the
present invention. A working electrode with a composite cathode
made by the procedure described in Example 1, prepared by dipping a
Pt disk (0.015 cm) into the slurry of the carbon, sulfur, and
vanadium pentoxide composite followed by drying under an IR-lamp,
was immersed into an undivided electrochemical cell with lithium
wire and lithium foil as reference and counter electrodes,
respectively. The cell was filled with a 1 M solution of lithium
triflate in electrolyte grade TEGDME.
[0256] Cyclic voltammograms of the electrode recorded at a scan
rate of 1 mV/s at 25.degree. C. are shown in FIG. 5. Three
quasi-reversible reduction-oxidation peaks corresponding to
formation of .delta.-V.sub.2O.sub.5 and two steps of sulfur
reduction confirm the composite nature of the material. Continuous
cycling between 1.5 and 4.4 V results in decrease of both
sulfur-related peaks. However, the electrode retains its integrity,
indicating improved adhesion to the Pt surface. Parallel increase
of the vanadium oxide peaks allows one to assume that some
interconversion of material takes place, probably with formation of
the .omega.-phase of vanadium pentoxide or a mixed vanadium
oxo-sulfide. Such interconversion resulting in the increase of the
apparent cathode potential should be suitable for improved battery
performance.
Example 6
[0257] A working electrode, prepared by dipping a large area Pt
current collector (2 cm.sup.2) into the final slurry before coating
of the carbon-sulfur-vanadium pentoxide composite of Example 3,
followed by drying under an IR-lamp, was immersed into a
3-compartment electrochemical cell separated by glass filter
membranes. The cell was filled with a 1 M solution of lithium
triflate in electrolyte grade TEGDME. Lithium wire and lithium foil
were used as reference and counter electrodes, respectively.
[0258] The working electrode was galvanostatically
charged/discharged at a current density of 0.1 mA/cm.sup.2.
Discharge curves at 25.degree. C. are shown in FIG. 6. A
significant increase in the electrode mid-potential can be seen at
the second discharge compared to the first one. Additional
charge/discharge curves are shown in FIG. 7 which indicate the
appearance of increased capacity with cycle number.
[0259] After 5 complete charge/discharge cycles, a small amount of
the electrolyte solution from the working electrode compartment was
removed for analysis. The UV-visible absorption spectrum of the
solution is shown as curve (b) in FIG. 8. No significant absorption
peaks in the 320-380 nm region were observed, indicating the
absence of sulfide and polysulfide species in the electrolyte. For
comparison, a control sulfur-containing electrode was prepared to
compare the out-diffusion behavior of this cathode without the
transition metal chalcogenide layer. The control cathode was made
by dipping a Pt current collector (2 cm.sup.2) into a slurry
containing 50% of elemental sulfur, 30% of carbon black (SAB), and
20% of UV-curable binder. A electrochemical cell with the UV-cured
electrode was assembled and tested as described above. A UV
absorption spectrum of the electrolyte solution, taken after the
first discharge, is shown in curve (a) of FIG. 8. A very strong
absorption peak at about 350 nm owing to dissolved sulfides and
polysulfides is easily observed. Curve (c) of FIG. 8 shows the
absorption spectrum of the electrolyte solution of both the control
and the vanadium pentoxide electrodes of the example before the
first discharge cycle, showing the absence of any appreciable
amounts of sulfides and polysulfides.
Example 7
[0260] This example describes the construction and performance of a
button cell constructed from the composite cathode made in Example
1. The button cell was fabricated by the conventional method. The
electroactive material (sulfur) in the composite cathode layer was
1.36 mg/cm.sup.2. TEGDME electrolyte with lithium triflate salt was
used as a liquid electrolyte. The separator used was CELGARD.TM.
2500 (Hoechst Celanese Corporation), and the anode was lithium
metal. The cell was tested under the following conditions: current
density 0.1 mA/cm.sup.2, cycling voltage 2.75 V to 1.85 V. The cell
capacity was initially around 504 mAh/g, but subsequently increased
to 956 mAh/g and remained stable without fade after 30 cycles.
Example 8
[0261] A button cell similar to that described in Example 7 was
constructed using the composite cathode fabricated in Example 2.
The cell testing conditions were as follows: current density 0.1
mA/cm.sup.2, cycling voltage 2.75 V to 1.85, 10 hours time limited.
The initial cell capacity was around 1382 mAh/g. After 81 cycles
the capacity was 738 mAh/g.
Example 9
[0262] A button cell was fabricated using the composite cathode of
Example 3 using the conventional button cell configuration. A
liquid electrolyte having TEGDME with lithium triflate salt was
used as electrolyte. Celgard.TM. 2500 was used as a separator. The
composite cathode provided the cell performance shown in Table
1.
1TABLE 1 Thickness (.mu.m) Capacity (mAh/g) Capacity (mAh/g)
Capacity (mAh/g) Coating at 0.1 mA/cm.sup.2 at 0.2 mA/cm.sup.2 at
0.3 mA/cm.sup.2 weight (g) (at cycle no.) (at cycle no.) (at cycle
no.) 45 .mu.m 900 mAh/g 450 to 380 mAh/g 520 mAh/g 2 mg/cm.sup.2
(4) (76) (46) 50 .mu.m 1270 mAh/g 600 mAh/g No data. 1.2
mg/cm.sup.2 (1) (5) 25 .mu.m 880 mAh/g 700 mAh/g No data 2
mg/cm.sup.2 (2) (8)
Example 10
[0263] Button cells similar to those fabricated in Example 9 were
fabricated using the composite cathode of Example 4. The thickness
of the cathode layer was 25 .mu.M and the amount of sulfur as
electroactive material was 1.0 mg/cm.sup.2. Evaluation of the cell
performance gave the results shown in FIG. 9. The initial capacity
at 0.1 mA/cm.sup.2 was 1172 mAh/g, and the capacity after 20 cycles
was 1103 mAh/g.
Example 11
[0264] This example describes the fabrication of a composite
cathode containing conductive carbon and a polymeric binder.
Elemental sulfur was ground in an IKA grinder for 5 seconds. Into a
dry ceramic ball mill jar containing 35 pieces of ceramic cylinders
was added 8.7 g of the ground sulfur, 1.5 g of dry V.sub.2O.sub.5
aerogel powder prepared by supercritical extraction of the solvent
from a vanadium acetylacetonate sol, 3.0 g of dry conductive carbon
(SAB), and 72 g of a 2.5 wt % solution of polyethylene oxide binder
in acetonitrile. The jar was sealed and put onto the ball mill at a
high speed of revolution for 22 hours. The milling was stopped and
a sample of the slurry was withdrawn for analysis. The mean
particle size was 6.4 .mu.m, and the slurry exhibited a viscosity
of 1142 cp 10 s.sup.-1 and 58 cp at 740 s.sup.-1 as determined by a
Rheometrics model DSR200. This slurry was then used to cast hand
drawn coatings onto both sides of a 17.5 .mu.m thick nickel foil
substrate with a wet thickness of 325 .mu.m on each side. The
coatings were dried under ambient conditions overnight, then
further dried under vacuum at 60.degree. C. for one hour. The
resulting dry coating thickness was 75 .mu.m on each side, and the
weight of the electroactive cathode material was 1.09 mg/cm.sup.2.
The apparent density of the composite cathode was 0.496
g/cm.sup.3.
Example 12
[0265] This example describes the fabrication and performance of AA
sized cells constructed using the composite cathode made in Example
11. On top of one side of the composite cathode structure
fabricated in Example 11 was placed a piece of Celgard 2500
separator and on top of this was placed a piece of lithium foil
(Cyprus, 50 .mu.m thick). This set of sandwiched battery electrodes
was then rolled up into a "jelly roll" configuration and placed
into a AA battery sized metal container. The container was filled
with the electrolyte comprising 1 M lithium triflate in TEGDME, and
the lid was sealed onto the container after making the appropriate
internal connections. The battery cell was then discharged and
charged for 400 cycles. The first discharge cycle exhibited a total
capacity of 726 mAH and a specific capacity for the electroactive
cathode material of 1232 mAh/g. By the third cycle, the total
capacity of the cell was fairly steady between 387-396 mAh, and the
specific capacity was 650-670 mAh/g.
Example 13
[0266] This example describes the fabrication of a composite
cathode containing a carbon-sulfur polymer of general formula VI,
where z was 4.8. The procedure of Examples 11 and 12 were followed
except that a carbon-sulfur polymer of formula VI, where z was 4.8,
was substituted in equal amounts for the ground sulfur. The
resulting dry coating thickness was 44 .mu.m on each side, and the
weight of the electroactive cathode material was 0.77
mg/cm.sup.2.
[0267] The first discharge cycle exhibited a total capacity of 495
mAh and a specific capacity for the electroactive cathode material
of 1269 mAh/g. By the fifth cycle, the total capacity of the cell
was fairly steady between 165-218 mAh, and the specific capacity
was 417-559 n/g.
Example 14
[0268] The following procedures was used to prepare transition
metal chalcogenides impregnated with soluble electroactive
sulfur-containing cathode species.
[0269] To 500 mL of toluene was added 72 g of sulfur and 48 g of
vanadium oxide aerogel powder. The mixture was refluxed at
110.degree. C. for 3 hours with constant stirring. The product was
filtered and washed with acetone and dried in vacuum at 90.degree.
C. for 4 hours. The sulfur content of the impregnated product was
57.3 wt %.
[0270] By varying the relative amount of sulfur compared to the
aerogel, the sulfur content of impregnated aerogel could be varied
from 50 wt % to 82 wto/o. Elemental analysis has shown the final
impregnated product contains small amounts of carbon. An elemental
analysis of sulfur-impregnated vanadia aerogel with 76.81 wt %
sulfur content showed 18.49 wt % vanadium, 0.54 wt % carbon, and
4.16 wt % oxygen (calculated by difference).
Example 15
[0271] This example describes the fabrication of composite cathodes
containing sulfur impregnated aerogel powder prepared as described
in Example 14 with an overall content of electroactive material of
55 wt % sulfur and 45 wt/o vanadium oxide. The sulfur-impregnated
aerogel was ground in an agate mortar to break agglomerates and
produce a fine powder. To a ball mill jar containing ceramic
cylinders was added 45 g of elemental sulfur, 22.5 g of the
sulfur-impregnated (55 wt % sulfur) vanadia aerogel, 13.5 g of
carbon (SAB) and 90 g of a 1 wt % solution of polyethylene oxide
dissolved in a mixed solvent of methyl acetate and n-propanol
(90:10 wt ratio). The solid content of the slurry was 11 wt %. The
mixture was ball milled for 22 hours. The slurry was cast hand
drawn onto both sides of a 18 .mu.m thick conductive carbon coated
aluminum foil (Rexam Graphics, South Hadley, Mass.) as a current
collector. The coatings were dried under ambient conditions
overnight, and then under vacuum at 60.degree. C. for one hour. The
resulting dry cathode coating had a thickness in the range of 60 to
70 .mu.m on each side of the current collector, with a density of
electroactive cathode material in the range of 2.1 mg/cm.sup.2 to
2.7 mg/cm.sup.2. The volumetric density of the electroactive
materials was 293 to 389 mg/cm.sup.3.
[0272] Wound AA size cells were fabricated from these cathodes with
a 4 mil (0.1 mm) lithium anode and a TONEN.TM. (Tonen Chemical
Corporation) polyolefin separator. The cells were filled with a
liquid electrolyte (50% 1,3-dioxolane, 20% diglyme, 10% sulfolane
and 20% dimethoxyethane (DME) by volume). The cells were cycled at
a rate of charge and discharge of 0.32 mA/cm.sup.2 and 0.5
mA/cm.sup.2 respectively. Cell performance data showed that these
cathodes had good capacity and stability. They showed a low rate of
capacity loss with cycling with values ranging from 0.003 to 1.7
mAh/cycle for the first 50 cycles. In some cells the capacity
actually increased up to the 25th cycle at rates ranging from 0.32
to 1.32 mAb/cycle.
Example 16
[0273] This example describes the cathode design and process
whereby a coating of sulfur-containing electroactive cathode
material is coated with a layer of electroactive transition metal
chalcogenide. Cathodes prepared from a slurry coating on a
conductive carbon coated aluminum foil (Rexam Graphics, South
Hadley, Mass.) as a current collector with a composition of 53 wt %
sulfur, 16 wt % carbon (SAB), 26 wt % V.sub.2O.sub.5 and 5 wt %
PEO, were coated with a barrier layer of vanadia sol. The coating
layer was prepared by dissolving 2 wt % vanadium oxide
tri-isopropoxide and 0.75 wto/o polyethylene oxide (molecular
weight 5,000,000) in a 90:10 methylacetate/n-propanol solvent blend
and hand coating this solution using the doctor blade technique on
top of the dried cathode. The coating layer thickness was
approximately 10 .mu.m and the amount of vanadia xerogel in the
layer was in the range of 0.25 to 0.4 mg/cm.sup.2. An identical
cathode without a barrier coating was used as a control. Wound AA
cells were constructed from the above cathodes using a 3 mil (0.075
mm) lithium anode and a TONEN.TM. separator. A liquid electrolyte
consisting of 50% 1,3-dioxolane, 20% diglyme, 10% sulfolane and 20%
dimethoxyethane (DME) (by volume) was used. FIG. 10 shows data for
typical AA wound cells with the vanadia xerogel coated cathode
(.circle-solid.) and an uncoated control cathode (.box-solid.)
cycled at a charge and discharge rate of 0.57 mA/cm.sup.2. It is
evident from this data that the vanadia xerogel coating layer has a
significant positive effect on the specific capacity of the cathode
and on the reduction of capacity fading with cycling.
Example 17
[0274] In a second approach to that described in example 16,
amorphous submicron vanadia aerogel powders were dispersed in a PEO
polymer matrix in a 70:30 ratio by weight. A 4 wt % solids
dispersion of this mixture in acetonitrile was applied to the
surface of a control cathode sheet similar to that of Example 16 by
either a dipping or doctor blade technique. The thickness of the
coating layer was in the range of 5 to 7 .mu.m. Cycling data from
these cells showed a similar increase in the specific capacities
and in the reduction of capacity fading with cycling, compared to
the control with no vanadia aerogel overcoating, as shown in
Example 16.
[0275] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made without departing from the spirit and scope thereof.
* * * * *