U.S. patent application number 10/648801 was filed with the patent office on 2005-03-03 for cathode material and method of manufacturing.
Invention is credited to Bowden, William L., Brandt, Klaus, Chi, Ignacio, Mao, Ou, McGovern, Brian, Sirotina, Rimma A..
Application Number | 20050048366 10/648801 |
Document ID | / |
Family ID | 34216805 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050048366 |
Kind Code |
A1 |
Bowden, William L. ; et
al. |
March 3, 2005 |
Cathode material and method of manufacturing
Abstract
A cathode material for a lithium primary battery can include a
low surface area lithiated manganese dioxide, a mixture of
lithiated manganese dioxide and CF.sub.x, or both. The cathode
materials can provide high capacity and voltage with low
gassing.
Inventors: |
Bowden, William L.; (Nashua,
NH) ; Brandt, Klaus; (Kamenz, DE) ; Chi,
Ignacio; (Mahtomedi, MN) ; Mao, Ou; (Walpole,
MA) ; McGovern, Brian; (Brookfield, CT) ;
Sirotina, Rimma A.; (Ashland, MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Family ID: |
34216805 |
Appl. No.: |
10/648801 |
Filed: |
August 27, 2003 |
Current U.S.
Class: |
429/209 ;
252/182.1; 29/623.1; 429/224; 429/231.1; 429/231.7 |
Current CPC
Class: |
H01M 6/16 20130101; H01M
4/06 20130101; H01M 4/502 20130101; H01M 4/582 20130101; Y10T
29/49108 20150115; H01M 4/364 20130101; H01M 2300/004 20130101 |
Class at
Publication: |
429/209 ;
429/231.1; 252/182.1; 429/231.7; 429/224; 029/623.1 |
International
Class: |
H01M 004/02; H01M
004/58; H01M 004/50; H01M 004/04 |
Claims
What is claimed is:
1. A cathode material comprising an irreversible high capacity
material and a reversible low capacity material.
2. The cathode material of claim 1, wherein the reversible low
capacity material includes a lithiated manganese dioxide.
3. The cathode material of claim 1, wherein the irreversible high
capacity material includes a carbon fluoride.
4. The cathode material of claim 2, wherein the irreversible high
capacity material includes a carbon fluoride.
5. The cathode material of claim 4, wherein the lithiated manganese
dioxide and the carbon fluoride are blended.
6. The cathode material of claim 4, wherein the lithiated manganese
dioxide includes an electrolytic manganese dioxide or a chemical
manganese dioxide.
7. The cathode material of claim 4, wherein the carbon fluoride is
CF.sub.x.
8. The cathode material of claim 4, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 1:99 to 99:1 by weight.
9. The cathode material of claim 4, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 5:95 to 95:5 by weight.
10. The cathode material of claim 4, wherein the lithiated
manganese dioxide and the carbon fluoride are present in a ratio in
the range of 25:75 to 75:25 by weight.
11. The cathode material of claim 4, wherein the lithiated
manganese dioxide and the carbon fluoride are present in a ratio in
the range of 20:80 to 80:20 by weight.
12. The cathode material of claim 2, wherein the lithiated
manganese dioxide includes a low surface area lithiated manganese
dioxide.
13. The cathode material of claim 11, wherein the low surface area
lithiated manganese dioxide has a specific surface area of between
0.50 and 20.0 m 2/g.
14. The cathode material of claim 11, wherein the low surface area
lithiated manganese dioxide has a specific surface area of between
10.0 and 15.0 m.sup.2/g.
15. A cathode material comprising a low surface area lithiated
manganese dioxide.
16. The cathode material of claim 14, wherein the low surface area
lithiated manganese dioxide has a specific surface area of between
0.50 and 20.0 m.sup.2/g.
17. The cathode material of claim 14, wherein the low surface area
lithiated manganese dioxide has a specific surface area of between
10.0 and 15.0 m.sup.2/g.
18. The cathode material of claim 14, wherein the low surface area
lithiated manganese dioxide, when mixed with an electrolyte
including an organic solvent and a lithium salt, produces a gas
pressure of no more than 16 PSI after 100 hours at 70.degree.
C.
19. A primary lithium battery comprising: a cathode including an
irreversible high capacity material and a reversible low capacity
material; an anode including lithium; and a separator between the
cathode and the anode.
20. The battery of claim 18, wherein the reversible low capacity
material includes a lithiated manganese dioxide.
21. The battery of claim 19, wherein the lithiated manganese
dioxide includes an electrolytic manganese dioxide or a chemical
manganese dioxide.
22. The battery of claim 19, wherein the battery delivers a
capacity at least 40% greater than the sum of the expected
capacities of the lithiated manganese dioxide and the irreversible
high capacity material under high drain conditions.
23. The battery of claim 18, wherein the irreversible high capacity
material includes a carbon fluoride.
24. The battery of claim 19, wherein the irreversible high capacity
material includes a carbon fluoride.
25. The battery of claim 23, wherein the lithiated manganese
dioxide and the carbon fluoride are blended.
26. The battery of claim 23, wherein the carbon fluoride is
CF.sub.x.
27. The battery of claim 23, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 1:99 to 99:1 by weight.
28. The battery of claim 23, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 5:95 to 95:5 by weight.
29. The battery of claim 23, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 25:75 to 75:25 by weight.
30. The battery of claim 23, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 20:80 to 80:20 by weight.
31. The battery of claim 23, further comprising an electrolyte
including an organic solvent.
32. The battery of claim 23, wherein the lithiated manganese
dioxide includes a low surface area lithiated manganese
dioxide.
33. The battery of claim 30, wherein the low surface area lithiated
manganese dioxide has a specific surface area between 0.50 and 20.0
m.sup.2/g.
34. The battery of claim 30, wherein the low surface area lithiated
manganese dioxide has a specific surface area between 10.0 and 15.0
m.sup.2/g.
35. The battery of claim 30, wherein the low surface area lithiated
manganese dioxide, when mixed with an electrolyte including an
organic solvent and a lithium salt, produces a gas pressure of no
more than 16 PSI after 100 hours at 70.degree. C.
36. The battery of claim 30, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 1:99 to 99:1 by weight.
37. The battery of claim 30, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 5:95 to 95:5 by weight.
38. The battery of claim 30, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 25:75 to 75:25 by weight.
39. The battery of claim 30, wherein the lithiated manganese
dioxide and the carbon fluoride are present in a ratio in the range
of 20:80 to 80:20 by weight.
40. The battery of claim 30, further comprising an electrolyte
including an organic solvent.
41. A primary lithium battery comprising: a cathode including a low
surface area lithiated manganese dioxide; an anode including
lithium; and a separator between the cathode and the anode.
42. The battery of claim 38, wherein the low surface area lithiated
manganese dioxide has a specific surface area between 0.50 and 20.0
m.sup.2/g.
43. The battery of claim 38, wherein the low surface area lithiated
manganese dioxide has a specific surface area between 10.0 and 15.0
m.sup.2/g.
44. The battery of claim 38, further comprising an electrolyte
including an organic solvent.
45. The battery of claim 38, wherein the low surface area lithiated
manganese dioxide, when mixed with an electrolyte including an
organic solvent and a lithium salt, produces a gas pressure of no
more than 16 PSI after 100 hours at 70.degree. C.
46. A method of manufacturing a cathode active material comprising
combining an irreversible high capacity material and a reversible
low capacity material.
47. The method of claim 43, wherein the reversible low capacity
material includes a lithiated manganese dioxide.
48. The method of claim 43, wherein the irreversible high capacity
material includes a carbon fluoride.
49. The method of claim 44, wherein the irreversible high capacity
material includes a carbon fluoride.
50. A method of manufacturing a primary battery comprising
combining a lithiated manganese dioxide and a carbon fluoride to
form a cathode material.
51. The method of claim 47, wherein the carbon fluoride is
CF.sub.x.
52. The method of claim 47, further comprising forming a cathode
including the cathode material.
53. The method of claim 49, further comprising assembling the
cathode with an anode including lithium in a housing.
54. The method of claim 50, further comprising assembling the
cathode with an electrolyte including an organic solvent in the
housing.
55. The method of claim 47, wherein the lithiated manganese dioxide
includes a low surface area lithiated manganese dioxide.
56. The method of claim 52, wherein the low surface area lithiated
manganese dioxide has a specific surface area between 0.50 and 20.0
m.sup.2/g.
57. The method of claim 52, wherein the low surface area lithiated
manganese dioxide has a specific surface area between 10.0 and 15.0
m.sup.2/g.
58. A method of manufacturing a primary battery comprising forming
a cathode material including a low surface area lithiated manganese
dioxide.
59. The method of claim 55, wherein the low surface area lithiated
manganese dioxide has a specific surface area between 0.50 and 20.0
m.sup.2/g.
60. The method of claim 55, wherein the low surface area lithiated
manganese dioxide has a specific surface area between 10.0 and 15.0
m.sup.2/g.
Description
TECHNICAL FIELD
[0001] This invention relates to cathode materials, and more
particularly to cathode materials for primary lithium
batteries.
BACKGROUND
[0002] Primary lithium batteries are widely used as power sources
in applications where the benefits of high power capability, high
voltage and excellent capacity retention outweigh the cost of the
cell. In particular, lithium batteries can be valuable in
point-and-shoot cameras that use battery power for many functions,
including the range finder, film drive, exposure meter, and
built-in flash. Improved cameras, such as digital cameras, can
require more powerful and smaller batteries than film cameras. To
meet this need for greater power capability in primary lithium
batteries without compromising their stability, a series of
improvements in cathode materials, particularly manganese dioxide
cathode materials, have been developed.
SUMMARY
[0003] In general, a cathode material includes an irreversible high
capacity material and a reversible low capacity material. In
another aspect, a cathode material includes a low surface area
lithiated manganese dioxide. The reversible low capacity material
can include a lithiated manganese dioxide. The irreversible high
capacity material can include a carbon fluoride. The lithiated
manganese dioxide can have a low specific surface area as measured
by the BET method.
[0004] In another aspect, a primary lithium battery includes a
cathode including an irreversible high capacity material and a
reversible low capacity material, an anode including lithium, and a
separator between the cathode and the anode. In another aspect, a
primary lithium battery includes a cathode including a low surface
area lithiated manganese dioxide, an anode including lithium, and a
separator between the cathode and the anode.
[0005] In another aspect, a method of manufacturing a cathode
active material includes combining an irreversible high capacity
material and a reversible low capacity material. In another aspect,
a method of manufacturing a primary battery includes combining a
lithiated manganese dioxide and a carbon fluoride to form a cathode
material. In another aspect, a method of manufacturing a primary
battery includes forming a cathode material including a low surface
area lithiated manganese dioxide.
[0006] The reversible low capacity material can include a lithiated
manganese dioxide. The irreversible high capacity material can
include a carbon fluoride. The lithiated manganese dioxide and the
carbon fluoride can be blended. The lithiated manganese dioxide can
include an electrolytic manganese dioxide or a chemical manganese
dioxide. The carbon fluoride can be CF.sub.x. The lithiated
manganese dioxide and the carbon fluoride can be present in a ratio
in the range of 1:99 to 99:1, in the range of 5:95 to 95:5, in the
range of 25:75 to 75:25, or in the range of 20:80 to 80:20 by
weight. The low surface area lithiated manganese dioxide can have a
specific surface area of between 0.50 and 20.0 m.sup.2/g, or
between 10.0 and 15.0 m.sup.2/g. The low surface area lithiated
manganese dioxide, when mixed with an electrolyte including an
organic solvent and a lithium salt, can produce a gas pressure of
no more than 16 PSI after 100 hours at 70.degree. C.
[0007] The battery can deliver a capacity at least 40% greater than
the sum of the expected capacities of the lithiated manganese
dioxide and the irreversible high capacity material under high
drain conditions. The battery can include an electrolyte including
an organic solvent.
[0008] The method can include forming a cathode including the
cathode material. The method can include assembling the cathode
with an anode including lithium in a housing. The method can
include assembling the cathode with an electrolyte including an
organic solvent in the housing.
[0009] Typical alkaline batteries do not deliver the high power and
energy density necessary to give good service in digital cameras.
Rechargeable batteries can offer the energy density necessary for
good service, but the high cost, poor charge retention, and
complication of battery charging can make a rechargeable battery
unattractive to a consumer. Lithium primary batteries can typically
meet the power demands of a digital camera, but higher capacities,
and therefore longer service lifetimes, are desirable. A lithium
battery that includes a cathode material including a lithiated
manganese dioxide and CF.sub.x can have a greater capacity than a
battery with a cathode material including only lithiated manganese
dioxide, and can provide a higher voltage than a cathode material
including only CF.sub.x.
[0010] When incorporated in a battery with an electrolyte including
an organic solvent, typical lithiated manganese dioxide cathode
materials generate gas. The gas generation can be due to oxidation
of the organic solvents in the electrolyte by high energy surface
sites on the manganese dioxide. Over time, enough gas can be
generated to render the battery nonfunctional, such that the shelf
life of the battery is impractically short. Gas generation can be
prevented and battery shelf life thus extended by predischarging
the cell, which consumes a portion of the cell capacity. A low
surface area lithiated manganese dioxide can generate less gas than
other lithiated manganese dioxide materials when included in a
lithium battery. A battery including a low surface area lithiated
manganese dioxide can have a useful shelf life without the need to
predischarge the battery. A cathode material can include low
surface area lithiated manganese dioxide and CF.sub.x.
[0011] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description and
drawings, and from the claims.
DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a schematic drawing of a battery.
[0013] FIG. 2 is a graph depicting the relationship between gassing
of manganese dioxide materials and BET surface area.
[0014] FIGS. 3A and 3B are graphs depicting volumetric capacity
versus current for various cathode materials.
DETAILED DESCRIPTION
[0015] Referring to FIG. 1, a lithium primary electrochemical cell
10 includes an anode 12 in electrical contact with a negative lead
14, a cathode 16 in electrical contact with a positive lead 18, a
separator 20 and an electrolyte. Anode 12, cathode 16, separator 20
and the electrolyte solution are contained within housing 22. The
electrolyte can be a solution that includes a solvent system and a
salt that is at least partially dissolved in the solvent system.
One end of housing 22 is closed with a cap 24 and an annular
insulating gasket 26 that can provide a gas-tight and fluid-tight
seal. Positive lead 18 connects cathode 16 to cap 24. A safety
valve 28 is disposed in the inner side of cap 24 and is configured
to decrease the pressure within battery 10 when the pressure
exceeds some predetermined value. Electrochemical cell 10 can be,
for example, a cylindrical wound cell, a button or coin cell, a
prismatic cell, a rigid laminar cell or a flexible pouch, envelope
or bag cell.
[0016] Anode 12 can include alkali and alkaline earth metals, such
as lithium, sodium, potassium, calcium, magnesium, or alloys
thereof. The anode can include alloys of alkali or alkaline earth
metals with another metal or other metals, for example, aluminum.
An anode including lithium can include elemental lithium or lithium
alloys, or combinations thereof.
[0017] The electrolyte can be a nonaqueous electrolyte solution
including a solvent and a salt. The salt can be an alkali or
alkaline earth salt such as a lithium salt, a sodium salt, a
potassium salt, a calcium salt, a magnesium salt, or combinations
thererof. Examples of lithium salts include LiPF.sub.6, LiBF.sub.4,
LiAsF.sub.6, LiClO.sub.4, LiI, LiBr, LiAlC.sub.4,
Li(CF.sub.3SO.sub.3), LiN(CF.sub.3SO.sub.2).sub.2, and
LiB(C.sub.6H.sub.4O.sub.2).sub.2. The solvent can be an organic
solvent. Examples of an organic solvent include a carbonate, an
ether, an ester, a nitrile or a phosphate. Examples of a carbonate
include ethylene carbonate, propylene carbonate, diethyl carbonate
or ethylmethyl carbonate. Examples of an ether include diethyl
ether, dimethyl ether, dimethoxyethane or diethoxyethane. Examples
of an ester include methyl propionate, ethyl propionate, methyl
butyrate or gamma-butyrolactone. An example of a nitrile includes
acetonitrile. Examples of a phosphate include triethylphosphate or
trimethylphosphate. The electrolyte can be a polymeric electrolyte.
The concentration of the salt in the electrolyte can range from
about 0.01 molar to about 3 molar, from about 0.5 molar to about
1.5 molar, or, in certain embodiments, about 1 molar.
[0018] Separator 20 can be formed of any of the standard separator
materials used in lithium primary or secondary batteries. For
example, separator 20 can be formed of a polypropylene, a
polyethylene, a polyamide (e.g., a nylon), a polysulfone and/or a
polyvinyl chloride. Separator 20 can have a thickness of from about
12 microns to about 75 microns and more preferably from 25 to about
37 microns.
[0019] Separator 20 can be cut into pieces of a similar size as
anode 12 and cathode 16 and placed therebetween as shown in FIG. 1.
Anode 12, cathode 16 and separator 20 can then be placed within
housing 22 which can be made of a metal such as nickel or nickel
plated steel, stainless steel, or aluminum-clad stainless steel, or
a plastic such as polyvinyl chloride, polypropylene, a polysulfone,
ABS or a polyamide. Housing 22 containing anode 12, cathode 16 and
separator 20 can be filled with the electrolytic solution and
subsequently hermetically sealed with cap 24 and annular insulating
gasket 26.
[0020] Cathode 16 includes a cathode active material that can
undergo alkali ion insertion during discharge of battery 10. The
cathode can also include a binder, for example, a polymeric binder
such as PTFE, PVDF or Viton. The cathode can also include a carbon
source, such as, for example, carbon black, synthetic graphite
including expanded graphite or non-synthetic graphite including
natural graphite, an acetylenic mesophase carbon, coke, graphitized
carbon nanofibers or a polyacetylenic semiconductor.
[0021] A cathode material for a lithium battery can include both an
irreversible high capacity material and a reversible low capacity
material. The reversible low capacity material can include
manganese dioxide. In a reversible discharge process, the
discharged form of the cathode active material is closely related
to the charged form. For example, a lithiated manganese dioxide (a
reversible material) can discharge by insertion of lithium into
ramsdellite domains, forming a lithiated ramsdellite structure. In
contrast, discharge of a heat treated manganese dioxide (i.e., a
non-lithiated manganese dioxide, a non-reversible) involves
insertion of lithium into pyrolusite with decomposition of the
pyrolusite and formation of an unrelated product. The manganese
dioxide can be a lithiated manganese dioxide. Lithiated manganese
dioxide materials and their preparation are described in, for
example, U.S. Pat. Nos. 6,190,800 and 6,403,257, each of which is
incorporated by reference in its entirety. Lithiation of manganese
dioxide can be accomplished by ion exchange in solution with a
lithium salt, for example, lithium hydroxide, or a lithium halide,
such as lithium chloride, lithium bromide, lithium iodide, or a
mixture of lithium hydroxide and lithium chloride. Lithiation of
manganese dioxide can also be accomplished by a mechanochemical
process. A variety of lithium sources, such as lithium carbonate,
lithium chloride, lithium bromide, lithium iodide, or lithium
methoxide can be used in mechanochemical lithiation. Lithiated
manganese dioxide can be heat treated as described in U.S. Pat. No.
4,133,856, which is incorporated by reference in its entirety.
[0022] Different forms of manganese dioxide can be lithiated. For
example, electrolytic manganese dioxide (EMD), such as
lithium-grade or alkaline-grade EMD, chemical manganese dioxide
(CMD), persulfate manganese dioxide (P-CMD) and fibrous manganese
dioxide can be lithiated. It can be preferable to remove sodium
ions from EMD prior to lithiation, as described, for example, in
U.S. Pat. Nos. 5,698,176 and 5,863,675, each of which is
incorporated by reference in its entirety.
[0023] A variety of relatively low energy density, kinetically fast
cathode materials can be used with a higher capacity but
kinetically slow material such as CF.sub.x. Among such materials is
the rechargeable manganese dioxide known as CDMO
(Li.sub.0.3MnO.sub.2). See, for example, Liu, R. et al. Journal of
Materials Science & Technology, 9, 157-160 (1993), and Nohma,
T. et al., Journal of Power Sources, 32, 373-379 (1990). Additional
manganese dioxide materials providing the combination of fast
kinetics with low capacity include the lambda-MnO.sub.2 material
disclosed in U.S. patent application Ser. No. 09/988,298 and
filamentous ramsdellite manganese dioxide known as p-CMD and
disclosed in U.S. Pat. Nos. 5,277,890, 5,348,726, 5,391,365, and
5,482,796, each of which is incorporated by reference in its
entirety. Another material that can be used is the alpha phase
manganese dioxide materials recently described in, for example,
Hill, L. et al., Journal of New Materials for Electrochemical
Systems 5, 129-133, (2002), and Hill, L. et al., Electrochemical
and Solid-State Letters 4, D1-D3, (2001).
[0024] Manganese dioxide materials can be evaluated by powder X-ray
diffraction. Lithium and manganese contents can be determined by
inductively coupled plasma atomic emission spectroscopy. Oxygen
stoichiometry (i.e., x in MnO.sub.x) can be determined by
titrimetry. Specific surface area can be determined from nitrogen
adsorption/desorption isotherms by the BET method.
[0025] In certain circumstances, the nonaqueous electrolyte of a
lithium battery can decompose and release carbon dioxide gas and/or
hydrogen gas, an effect also known as gassing. The decomposition
can be catalyzed by water on the surface of the manganese dioxide.
In some cases, the presence of the generated gas can be sufficient
to rupture the safety vent, which renders the battery useless. In
order to minimize gassing, great care is typically exercised to
eliminate water from the electrolyte and other components. Water
can become adsorbed on the surface of particles in the cathode
during manufacture of the cell. Even when prepared in a dry room,
the cathode can contain up to 600 ppm of surface water before the
battery is sealed. Under such conditions, lithium manganese dioxide
cells can undergo gassing and rupture the safety vent within about
ten days after they are filled with electrolyte. In order to
prevent gassing, lithium manganese dioxide cells can be
predischarged as described in U.S. Pat. No. 4,328,288, which is
incorporated by reference in its entirety. The predischarge process
can convert the surface water to lithium oxide and hydrogen gas,
thereby deactivating the catalytic surface of the manganese
dioxide. The predischarge can also sacrifice about 5% of the cell
capacity and increase the time required for manufacturing.
[0026] Moisture associated with manganese dioxide materials can be
evaluated with a Mitsubishi CA100 moisture analyzer equipped with a
VA21 modified moisture vaporizer. The temperature controller on the
vaporizer, such as a Model 0689-0010 controller from Barnant Co.,
can allow multiple steps of temperature ramping and soaking.
Surface moisture can be measured at 110.degree. C. Structural water
(also called lattice water) can be measured as the moisture evolved
above 110.degree. C. To measure structural water, samples can be
pre-dried under argon flow in the moisture analyzer at 110.degree.
C. for about two hours. Moisture analysis can also be carried out
with a Computrac 3000 from Arizona Instruments.
[0027] Gas formation by a manganese dioxide material can be
evaluated either in-cell, for instance by incorporating the
material in a 2/3A cell, or out-of-cell. Gas formation can be
measured by a constant volume test using an air-tight stainless
steel fixture with a pressure transducer, or in a constant pressure
test using a heat-sealed aluminized foil bag. For out-of-cell
testing, manganese dioxide materials can be examined alone or in
combination with other cathode materials such as graphite and
binders. Finished cells can also be examined by the thermal cycling
leakage test, in which a cell is subjected to a repeating
temperature program in an oven. The oven spends seven hours at
-40.degree. C., then warms to 70.degree. C. in one hour, is held
for fifteen hours at 70.degree. C., and then returns to -40.degree.
C. in one hour. The mass of the cell is recorded at intervals to
determine the quantity of gas that leaks out. For 2/3A cells, mass
loss of less than 6 mg after 5 days of thermal cycling and less
than 10 mg after 10 days is considered passing.
[0028] Typical manganese dioxide materials used in lithium
manganese dioxide cells have a high specific surface area as
measured by the BET method. The technical literature on lithium
manganese dioxide batteries teaches that high surface area
manganese dioxide is necessary for good high power performance. In
particular, high specific surface area manganese dioxide used in
lithium manganese dioxide cells can have a specific surface area in
the range of 40 to 80 m.sup.2/g. In contrast, manganese dioxide
used in alkaline batteries typically has a specific surface area in
the range of 25 to 35 m.sup.2/g. See, for example, N. Iltchev et
al., J. Power Sources (1991) 35, 175; J. Power Sources (1989) 25,
167; J. Power Sources (1989) 25, 177; Progress in Batteries and
Solar Cells (1991) 10, 232; and U.S. Pat. No. 5,156,933, each of
which is incorporated by reference in its entirety.
[0029] A low surface area lithiated manganese dioxide has a
specific surface area less than 40.0 m.sup.2/g, such as between
0.50 and 35.0 m.sup.2/g, between 0.50 and 20 m.sup.2/g, or between
10.0 and 15.0 m.sup.2/g. Cathode materials for lithium batteries
can include a low surface area lithiated manganese dioxide. Low
surface area lithiated manganese dioxide can be prepared by
lithiation of a low surface area manganese dioxide, such as
alkaline grade manganese dioxide. In particular, the specific
surface area of the low surface area lithiated manganese dioxide
can be less than 40.0 m.sup.2/g, such as between 0.50 and 35.0
m.sup.2/g, between 0.50 and 20.0 m.sup.2/g, or between 10.0 and
15.0 m.sup.2/g. Surprisingly, gas generation from cathode materials
including low surface area lithiated manganese dioxide can be
diminished compared to conventional lithiated manganese dioxide
cathode materials without loss of good high power performance.
Lithium primary cells including low surface area lithiated
manganese dioxide can be manufactured without a need for
predischarge.
[0030] The irreversible high capacity material can include a carbon
fluoride. Carbon fluoride, which includes carbon monofluoride,
polycarbon monofluoride, graphite fluoride or CF.sub.x, is a solid,
structural, non-stoichiometric fluorocarbon of empirical formula
(CF.sub.x).sub.n where 0<x<1.25. One example of a CF.sub.x
material is grade 1000 CF.sub.x from Advance Research Chemicals
(Catoosa, Okla.). A chlorine containing CF.sub.xCl.sub.y where
x=0.9-1.0 and y=0.01-0.05 is also available from Advance Research
Chemicals. When the carbon fluoride is CF.sub.x, the cathode can
have a higher weight capacity and volumetric capacity than heat
treated EMD. The average voltage of the carbon fluoride can be
lower than that of a heat treated EMD cathode material.
[0031] The cathode material can provide both high energy density
and high discharge voltage. For example, a cathode material can
include both manganese dioxide and a carbon fluoride, such as
CF.sub.x. The manganese dioxide can be, for example, EMD, or
preferably a lithiated manganese dioxide or low surface area
lithiated manganese dioxide. In certain circumstances, the cathode
material can show a synergistic interaction between the materials
at high discharge rates, allowing superior performance compared to
other cathode formulations as measured by volumetric capacity and
energy density. In particular, the irreversible material can have a
higher open circuit voltage than the reversible material, and the
reversible material can have a higher rate capability than the
irreversible material. A high discharge rate is one such that the
measured coulombic capacity of the battery is less than that
calculated from the capacities of the active materials in the
battery. See, for instance, Selim and Bro, (J. Electrochemical
Society 1971), which is incorporated by reference in its entirety.
In other words, the high rate capacity of a cathode including, for
example, a lithiated manganese dioxide and CF.sub.x, can be greater
than the sum of the capacities of each material when measured
separately. The proportion of lithiated manganese dioxide and
CF.sub.x in the cathode material can vary. The weight ratio of
lithiated manganese dioxide to CF.sub.x can be between 99:1 and
1:99, for example, 99:1, 95:5, 80:20, 75:25, 60:40, 50:50, 40:60,
25:75, 20:80, 5:95, or 1:99. A cathode material including more
lithiated manganese dioxide than CF.sub.x can be preferable for
heavy duty use, e.g. with nearly continuous discharge. A cathode
material including more CF.sub.x than lithiated manganese dioxide
can be preferable for light duty use, e.g. with long delays between
pulses.
[0032] Both CF.sub.x and heat treated EMD discharge by irreversible
processes. During discharge, a phase change occurs and the
discharged material cannot be easily recharged. In contrast,
lithiated manganese dioxide can have an initially reversible
reduction process. The synergistic benefit of the lithiated
manganese dioxide-CF.sub.x mixture can be due to the high voltage
CF.sub.x material acting to recharge the lithiated manganese
dioxide, thus allowing more complete utilization of both the
CF.sub.x capacity and the fast discharge properties of the
lithiated manganese dioxide. This internal recharge process can
take place both during discharge and voltage recovery portions of
the discharge, and can occur as follows:
[0033] During Discharge:
Li.sub.0.1MnO.sub.2+Li.fwdarw.Li.sub.1.1MnO.sub.2
CF+Li.fwdarw.LiF+C
[0034] Internal Recharge:
CF+Li.sub.1.1MnO.sub.2.fwdarw.C+LiF+Li.sub.0.1MnO.sub.2
[0035] Cells can be discharged to determine cell performance, for
example by the SPECS method as described in U.S. Pat. No.
6,440,181, which is incorporated by reference in its entirety.
Power capability of the cathodes can be determined by use of a
signature test. Generally, in a signature test, a cell is
discharged to a given condition at a high current, then the load is
removed and the cell allowed to equilibrate. A reduced load is then
applied until the given condition is again reached. The process is
repeated until discharge is complete. In the continuous signature
test (CST), the cathode is discharged at a high drain (2 C) until a
cutoff voltage of 1.8 V is reached. The load is removed for 1 hour.
The cell is then discharged at half the previous rate (1 C) until
the cutoff voltage is again reached. The procedure is repeated
until the current has reached a very low value (C/512).
[0036] The intermittent signature test (IST) is more complex. The
cell is discharged at the same rate for a given period of time
unless the cutoff voltage is reached. The cell is then allowed to
recover for 15 minutes and then placed on the same high load
regime. When the cell reaches the cutoff voltage it then moves to
the next lower current. For example the cells were discharged for
15 seconds at the 2 C rate then allowed to recover for 15 minutes
before a second discharge. As in the CST, the final current is very
low. The capacity/rate relationship can be a convenient way to
present results from signature tests (see R. Selim and P. Bro J.
Electrochem. Soc. 1971).
EXAMPLE 1
[0037] EMD samples were either lithium-grade EMD from Delta (South
Africa) or alkaline grade EMD from Kerr-McGee (Oklahoma City,
Okla.). Heat-treated EMD (HEMD) was prepared according to U.S. Pat.
No. 4,133,856. Samples of lithiated manganese dioxide were prepared
separately from each type of EMD. Specific surface area of the
manganese dioxide samples was measured by the BET method. The
lattice moisture of the manganese dioxide samples was determined as
water released above 110.degree. C. using a Mitsubishi CA100
moisture analyzer.
[0038] Out-of-cell gassing of manganese dioxide was measured by
combining a 4.55 g sample of manganese dioxide with 5 cc of
electrolyte in a closed 10 cc stainless steel vessel fitted with a
pressure transducer. The electrolyte was 10% ethylene carbonate,
20% propylene carbonate, 70% dimethoxyethane with 0.5 M lithium
trifluoromethanesulfonate. The vessel was maintained at 70.degree.
C. and the gas pressure in the vessel was recorded for 100 hours.
Table 1 presents a summary of lattice water, BET surface area, and
gassing test results. Lithiation with lithium halides can reduce
the BET surface area of manganese dioxide. The effect is more
pronounced with LiCl than LiBr as can been seen in Table 1. The
gassing results are presented graphically in FIG. 2.
[0039] Gassing of cathode materials was also tested in cells.
During a foil bag test, a 2/3A cell including a low surface area
lithiated manganese dioxide generated half as much as gas as a cell
containing a typical lithiated manganese dioxide did in the same
amount of time. A 2/3A cell including low surface area lithiated
manganese dioxide can outperform a cell containing typical
lithiated manganese dioxide on the thermal cycling leakage test.
For example, a 2/3A cell including low surface area lithiated
manganese dioxide lost about 5 mg of weight to gassing over 10 days
whereas a cell containing typical lithiated manganese dioxide lost
about 20 mg in the same time.
1TABLE 1 Gas pressure BET surface Initial lattice at 100 h Sample
Description area (m.sup.2/g) moisture (ppm) (PSI) Lithiated high
power EMD 11.7 -- 11.0 Lithiated EMD (LiCl) 12.3 -- 12.0 High power
EMD 12.6 4,100 9.9 (.beta.-converted) Lithiated EMD (LiBr) 22.4
5,300 15.85 High power EMD 24.0 17,500 23.0 (no .beta.-conversion)
.beta.-converted EMD 30.8 5,300 22.5 Lithiated EMD 33.1 4,200 19.8
EMD (no .beta.-conversion) 58.7 15,000 39.1
EXAMPLE 2
[0040] Lithium cells containing a cathode mixture of 60% active
material, 30% graphite conductive diluent and 10%
poly(tetrafluoroethylene) binder were prepared. The cathode active
materials tested were CF.sub.x, heat treated EMD, lithiated
manganese dioxide (LiMD), a 50:50 mixture (by weight) of CF.sub.x
and heat treated EMD, or a 50:50 mixture (by weight) of CF.sub.x
and lithiated manganese dioxide. The CF.sub.x was ARC-1000 CF.sub.x
from Advance Research Chemicals (Katoosa, Okla.). The heat treated
EMD (HEMD) was from Kerr-McGee Chemical Co. (Oklahoma City, Okla.).
The lithiated manganese dioxide (LiMD) was prepared according to
U.S. Pat. No. 6,190,800. The cells were 2430-size cells prepared
with electrolyte (10% ethylene carbonate, 20% propylene carbonate,
70% dimethoxyethane with 0.5 M lithium trifluoromethanesulfonate).
Cells were subjected to the continuous and intermittent signature
tests. Cells including a mixture of CF.sub.x and lithiated
manganese dioxide had a higher volumetric capacity at a high
current discharge than cells including other cathode active
materials as measured by both the IST (FIG. 3A) and CST (FIG.
3B).
[0041] The mixture of lithiated manganese dioxide and CF.sub.x can
have a higher capacity than the other materials tested. Table 2
shows that, under continuous discharge, the capacity of cells
including manganese dioxide-CF.sub.x mixtures is greater than would
be expected based on the capacities of each material alone. The
synergy is more pronounced at higher rates of discharge.
2TABLE 2 Wh Wh at Predicted at Predicted In- 130 Wh at Increased
260 Wh at creased Cathode mA/g 130 mA/g capacity mA/g 260 mA/g
capacity HEMD 1.24 -- -- 0.39 -- -- LiMD 1.71 -- -- 0.52 -- --
CF.sub.x 1.77 -- -- 1.10 -- -- CF.sub.x-HEMD 2.03 1.51 34% 1.28
0.75 71% CF.sub.x-LiMD 2.55 1.74 47% 1.69 0.81 109%
[0042] Table 3 demonstrates that manganese dioxide-CF.sub.x
mixtures show greater than expected capacity under intermittent
discharge conditions as well.
3TABLE 3 Wh Wh at Predicted at Predicted In- 130 Wh at Increased
260 Wh at creased Cathode mA/g 130 mA/g capacity mA/g 260 mA/g
capacity HEMD 1.43 -- -- 0.83 -- -- LiMD 1.83 -- -- 1.65 -- --
CF.sub.x 1.96 -- -- 1.27 -- -- CF.sub.x-HEMD 2.32 1.69 37% 1.6 1.05
52% CF.sub.x-LiMD 2.68 1.89 42% 1.85 1.46 57%
EXAMPLE 3
[0043] The performance of the materials was measured by using a
simulated digital camera test. This test repeats complex series of
pulses that simulate the various battery-powered operational
functions performed by a digital camera. A battery including
CF.sub.x as the only cathode active material did not support a
single cycle of digital camera functions. When HEMD material
prepared according to U.S. Pat. No. 4,133,856 was the cathode
material, the battery delivered 205 cycles. A battery including
LiMD cathode material (prepared according to U.S. Pat. No.
6,190,800) delivered 291 cycles. A cathode with a mixture of LiMD
and CF.sub.x (90:10 LiMD:CF.sub.x by weight) delivered 379 cycles,
and a cathode including 80:20 LiMD:CF.sub.x by weight delivered 441
cycles.
[0044] A number of embodiments have been described. Nevertheless,
it will be understood that various modifications may be made.
Accordingly, other embodiments are within the scope of the
following claims.
* * * * *