Note: Descriptions are shown in the official language in which they were submitted.
125 1 8
F~ELD OF THE INVENTION
The invention relates to a nonaqueous cell utilizing a
highly active metal anode, a manganese dioxide-containing cathode
which contains less than about I percent water based on the weight
of tbe manganese dioxide and a liquid organic electrolyte based on
3-methyl-2-oxazolidone in conjunction with a cosolvent and a
~elected solute.
BACKGROUND OF THE INVENTION
The development of high energy battery systems require~
10 the compatibility of an electrolyte posse~ing desirable electrochen~-
ical properties with highly reactive anode materials, such as lithium,
sodium, and the like and the efficient use of high energy density
cathode material~, such as manganese dioxide. The use of aqueou~
electrolytes is precluded in the~e sy~tems since the anode materials
are sufficiently active to react with water chemically. It has there
fore been necessary, in order to realize the high energy denQity
obtainable thro~gh use of these highly reactive anode~ and high
energy density cathodes, to turn to the investigation of nonaqueous
electrolyte 6ystems and more particularly to nonaqueou~ organic
20 electrolyte systems.
The term "nonaqueous organic electrolyte" in the prior
art refers to an electrolyte which is composed of a ~olute, for example,
a salt or complex salt of Group ~-A, Group II-A or Group III-A elements
of the Periodic Table, dis-~olved in an appropriate nonaqueous organic
solvent. Conventional solvents include propylene carbonate, ethylenc
carbonate or y-~utyrolactone. The term "Periodic Table" as used
herein refers to the Periodic Table of the Elements as set forth on
the inside back cover of the E~andboo~c of Chemist~y and Physics,
48th Edition, the Chemical Rubber Co., Cleveland, Ohio, 1967_196~.
2.
~2518
9~47
,
A multitude of solutes is known and reco~s~nended for
use but the selection of a suitable solvent has been particularly
troublesome since many of those ~olvent~ which are u~ed to prepare
electrolytes sufficiently conductive to permit effective ion migration
through the solution are reactive with the highly active anodes men-
tioned above. Most inve~tigators in this area, in search of suitable
Jolvents, have concentrated on aliphatic and aromatic nitrogen-
and oxygen-containing compoundJ with 30me attention given to
organic sulfur-, phosphorus- and arsenic-containing compound~.
The results of this search have not been entirely satisfactory since
10 many of the ~olvents investigated still could not be used effectively
with high energy density cathode materials. such as manganese
dioxide (MnO2),and were sufficiently corrosive to lithium anodes
to prevent efficient performance over any length of time.
Although manganese dioxide has been mentioned as a
possible cathode for cell applications, manganese dioxide inherently
contains an unacceptable amount of water, both of the absorbed and
bound (adsorbed) types, which is sufficient to cause anode (lithium)
corrosion along with its a~sociated hydrogen evolution. This type
of corrosion that cauJes gas evolution is a serious problem in sealed
21) cells, particularly in miniature type button cells. ~n order to main-
tain overall battery-powered electronic devices as compact as pos-
sible, the electronic devices are usually designed with cavities to
accommodate the miniature cells as their power source. The cavitie~
are usually made ~o that a cell can be snugly po~itioned therein thu~
making electronic contact with appropriate tenninals within the device.
A major potential problem in the u~e of cell-powered devices of this
nature is that if the gas evolution cau~es the cell to bulge then the cell
12518
9'~'7
could become wedged within the cavity. Thi~ could result in damage
to the device. Also, if electrolyte leaks from the cell it could cause
damage to the device. Thus it is important that the physical dimen-
sions of the cell's housing remain constant during discharge and that
the cell will not leak any electrolyte into the device being powered.
U. S. Patent 4, 133, 856 disclose9 a process for producing a
MnO2 electrode (cathode) for nonaqueous cells whereby the MnO2 i~
initially heated within a range of 350to 430C 80 as to Jub~tantially
remove both the absorbed and bound water and then, after being
- 10 formed into an electrode with a conductive agent and bonder, it iJ
further heated in a range of 200 to 350C prior to its assembly into
a cell. British Patent 1, 199, 426 also discloses the heat treatment
of MnO2 in air at 250 to 450C to substantially remove its water
component .
U. S. Patents 3, 871, 916; 3, 951, 685, and 3, 996, 069
disclose a nonaqueous cell employing a 3-methyl-2-oxazolidone-
based electrolyte in conjunction w~th a solid cathode selected from
the group consisting of (CFx)n, CuO, FeS2, Co304, V205, Pb304,
In2S3, and CoS2.
While the theoretical energy, i. e., the electrical energy
potentially available from a selected anode-cathode couple, i~ rela-
tively easy to calculate~ there i~ a need to choo~e a nona~3ueou~
electrolyte for a couple that permits the actual energy produced by
an assembled battery to approach the theoretical energy. The problem
usually encountered i~ that it is practically impossible to predict
in advance how well, if at all, a nonaqueous electrolyte will function
with a ~elected couple. ThuJ a cell must be considered as a unit
having three parts: a cathode, an anode, and an electrolyte, and
it i~ to be understood that the part~ o~ one cell are not predictably
interchangeable with part~ of a~other cell to produce an efficient
and workable cell.
.lLl`~i9~7 12518
It i~ an object of the pre~ent invention to provide a
nonaqueous cell employing among other components a 3-methyl-
2-oxazolidonen-based electrolyte and a mangane~e dioxide-containing
cathode wherein the water content i9 1e98 than 1 weight percent
ba~ed on the weight of the manganese dioxide.
It i9 another object of the present invention to provide
a rnanganese dioxide nonaqueou~ cell employing a lithium anode.
It is another object of the present invention to provide
a lithium/MnO2 nonagueous cell employing a liquid organic elec-
10 trolyte consisting essentially of 3-methyl-2-oxazolidone in combin-
ation with at least one cosolvent and a solute.
SUMMA~Y OF THE INVENTION
The invention provides a novel high energy density
nonaque OU9 cell comprising a highly active metal anode, a manganese
dioxide-containing cathode and a liquid organic electrolyte comprising
3-methyl-2-oxazolidone in combination with a conductive ~olute with
or without at least one cosolvent having a viscosity lower than that
of 3-methyl-Z-oxazolidone and wherein the manganese dioxide has
a water content of less than ~ weight percent based on the weight of
20 the manganese dioxide. Preferably the water content should be lower
than 0. 5 weight percent and most preferably below about 0. 2 weight
pe rcent.
The water inherently contained in both elec-trolytic and
chemical types of manganese dioxide can be substantially removed by
various treatment~. For example, the manganese dioxide can be
heated in air or an inert atmosphere at a temperature of 350DC for
about 8 hours or at a lower temperature for a longer period of time.
Care should be tal~en to avoid heating the manganese dioxide above
its decomposition temperature which i9 about 400-C in air. In oxygen
30 atmo 8 phere 9, higher temperatures may be employed. In accordance
l 2 5 1 8
with this invention the manganese dioxide shou1d be heated for a
sufficient period of time to insure that the water content is reduced
below about 1 weight percent, preferably below about 0. 5 and most
preferably below about 0. 2 weight percent based on the weight of
the manganese dioxide. An amount of water above about 1 weight
percent would react with the highly active metal anode, ~uch as
lithium, and cause it to corrode thereby resulting in hydrogen
evolution. AY stated above thi~ could result in physical distortion
of the cell and/or electrolyte leakage from the cell during storage
or discharge.
To effectively remove the undesirable water from MnO2,
or MnO2 mixed with a conductive agent and a suitable binder, to
the level necessary to practice this invention, it is believed neces-
sary that both the absorbed and bound water be substantially removed.
After the water removal treatment has been completed, it is essential
that the manganese dioxide be shielded to prevent absorption of water
from the atmosphere. This could be accomplished by handling the
treated manganese dioxide in a dry box or the like. Alternatively,
the treated mangane~e dioxide or the manganese dioxide combined
with a conductive agent and a suitable binder could be heat treated
to remove water that could have been absorbed from the atmosphere.
Preferably, the rnanganese dioxide should be heat treated
to remove its water content to below about 1 weight percent and then
it can be mixed with a conductive agent ~uch as graphite, carbon or
the like and a binder such as Teflon (trademark for polytetrafluoro-
ethylene), ethylene acrylic acidpolymerorthelike to produce a solid
cathode electrode. If desired, a small amount of the electrolyte can
be incorporated into the mangane3e dioxide mix.
An added pos~ible benefit in the removal of substantially
all the water from manganese dioxide is that if small amounts of water
6.
9 ~7 1 2~l8
are present in the cell'~ electrolyte then the manganese dioxide
will absorb the main portion of that water from the electrolyte and
thereby prevent or substantially delay the reaction of the water with
the anode such as lithium. In this situation, the manganese dioxide
will act as an extracting agent for the water impurities in the
o rganic solvent s .
The electrolyte for use in thi~ invention i8 a 3-methyl- -
2-oxazolidone-based electrolyte. ~i~uid organic 3-methyl-
2-oxazolidone material, (3Me20x)
I I
10 ca~2 - C ~2 - O - co - h - CH3,
is an excellent nonaqueous ~olvent because of its high dielectric
constant, chemical inertness to battery components, wide liquid
range and low toxicity.
However, it ha~ been found that when metal salts are
diqsolved in liquid 3Me2C)x for the purpose of improving the con-
ductivity of 3Me20x, the viscosity of the solution may be too high
for its efficient use as an electrolyte for some nonaqueous cell
applications other than those requiring very low current drains.
Thus, in some applications in accordance with this invention,
Z0 the addition of a low viscosity co~olvent would be desirable if
3Me20x iY to be used as an electrolyte for nonaqueous cells which
can operate or perform at a high energy density level. Specifically,
in order to obtain a high energy density level in accordance with
this invention, it is essential to use a heat-treated MnO2cathode
along with a highly active metal anode. Thus thi~ invention is
directed to a novel high energy density cell having a highly acti~re
metal anode, such as lithium, a heat-treated MnO2 cathode, and
an electrolyte compri~ing 3Me20x in combination with a conductive
solute with or without at least one low viscosity co~olvent.
9~7 2518
The low viscosity cosolvents if used in this invention
include tetrahydrofuran (THF), dioxolane (DIOX), dimethoxyethane
(DME), propylene carbonate (PC), dimethyl isoxazole (DMI), diethyl
carbonate (DEC), ethylene glycol sulfite (EGS), dioxane, dimethyl
sulfite (DMS) or the like. Dimethoxyethane (DME), dioxolane (DIOX)
and propylene carbonate (PC3 are preferred cosolvents because of
their compatibility with metal salts dissolved in liquid 3Me20x
ar~d their chemical inertness to cell components. Specifically, the
total amount of the low viscosity cosolvent added could be between
about 20~o and about 80% based on total solvent volume, i. e. exclu-
sive of solute. so as to lower the viscosity to a level ~uitable for
use in a high drain cell.
Conductive solutes (metal salt~) for use in this invention
with the !i~}uid 3Me20x may be selected from the group MCF3S03,
MBF4, MC104, and MM'F6 wherein M is lithium, sodium or potas-
sium, and M' is phosphorus, arsenic or antimony. The addition
of the solute is necessary to improve conductivity of 3Me20x so
that said 3Me20x can be used a~ the electrolyte in nonaqueous cell
applications. Thus the particular salt selected has to be compatible
and nonreactive with 3Me20x and the electrodes of the cell. The
amount of solute to be dissolved in the liquid 3MeZOx should be
sufficient to provide good conductivity. e.g., at least about 10 4
ohm cm . Generally an amount of at least about 0. 5 molar
would be suf~icient for most cell applications.
~3ighly active me.al anodes suitable for this inver.tion
include lithium (Li), potassium (K), sodium (Na), calciunl (Ca),
magnesium (Mg), aluminum (Al~, and their alloy~. Of these active
metal~, lithium would be preferred because in addition to being a
ductile, ~oft metal that can easily be assembled in a cell, it pos-
esse~ the highest energy-to-weight ratio of the group of suitable
anode metal~.
12518
The pre~ent invention of a high energy density cell with
a 3-Me20~c-based electrolyte, a solid MnOz-containing cathode
having le~ than 1 weight percent water and a highly active metal
anode will be further illustrated in the following examples.
EXAMPLE I
Thermogravimetric a~laly~e~ (TGA) were made of variouJ
Jample~ of commercial manganese dioxide. Some of the sample~
were analyzed as obtained, other samples were heat ireated at 350-C
for 8 hours, and other sampleJ were heat treated at 350C for 8 hours
and then blended with carbon a~nd Teflon*to produce cathode mixe~.
The data obtained from the thcrmogravimetric analyses are shown
in Table I. The data clearly show that commercial type~ of manganeJe
dioxide contain large amountJ of water. In addition, the data ~how
that even after the manganese dioxide had been heat treated as
specified above, it will ab~orb water from the atmo~phere even after
only a small period of time.
EXAMPLE II
Each of two flat-type cells was constructed utilizing a
nickel metal baJe having therein a shallow depression into which
the cell contento were placed and over which a nickel metal cap was
placed to close the cell. The content~ of each ~ample cell consisted
of a 1. 0 inch diameter lithium disc consisting of five sheets of lithium
foil having a total thickness of 0. IQ inch, about 4 ml of an electrolyte
con~isting of about 40 vol.~ dioxoLane, about 30 vol.% dimethoxy-
ethane ~DME~, about 30 vol. % 3Me20x pl~ls about 0. 1% dimethyli~ox-
azole ~DMI) a~ld containing I M LiCF3S03, a l. 0 inch diameter porous
nonwo~en polypropylene separator ~0. 01 inch thick) which absorbet
some of the electrolyte and two grams of cathode mix compressed
to form a cathode having an apparent interfacial area of S sq~3are
centimeters. In the first ceLI the cathode mix con~isted of Tekkosha
clectrolytic M~0z heat treated at 350'C for 20 hours, carbon black,
* Trademark n~ or polyte~rafltloroet}ly1ene
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12518
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1251 8
and Teflon* The ~econd cell employed the samè type of componentJ
a~ in the first cell except that the Tekko~ha MnO2 was untreated.
Each cell wa~ di~charged acros~ a 1200-ohm load to a l-volt cutoff
and the cathode efficiencieJ assuming a l-electron reaction were
calculated along with the overall energy densities. The data obtained
are ~hown in Table Il.
TABLE II
Efficiencv* Cathode Energy
Cathode l_electron Density ~WhJin3)
Heat Treated MnO2 81. 0~0 72. 8
Unheated MnO248. 2% 35. z
I
* Coulombic
EXAMPLE III
Ten miniature button cells were constructed using a
lithium anode, an electrolyte consi~ting of about 40 vol. ~yO dioxolane,
about 30 vol. % DME, about 30 vol. % 3Me20x plu8 about 0. 1% DMI
and containing I M LiCF3S03, and a cathode containing 80 wt.~o
unheated or heat-treated MnO2, 1. 5 wt. % carbon black, 13. 5 wt. %
graphite, and 5. 0 wt.% ethylene acrylic acid binder. The heat-
tre?Led MnO2 was heated at a temperature of 350-C for 18 hour~
under an argon atmosphere. Each cell (0.452 inch diameter; 0.166
inch height) contained Q. 3045 gram of the untreated MnO2-containing
cathode mix, or 0, 3036 gram of the heat-treated MnO2-containing
cathode mix, 0.037 gram of lithium, a polypropylene separator,
and 140 ~1 of the electrolyte. Each cell was placed on a continuouc
6~00-ohm background load and was pul~ed on a 250-ohm load for
2 secondo once a week. Upon reaching a cutoff voltage of 1 volt,
the cell capaci~y and cathode coulombic efficiency for each cell were
calculated and are shown in Table lII.
* Tra~rarlc rame ~or polytetrafluoroetlylene
1251 8
TAB LE r~I
Cell Cell Capacity Cathode Efficiency
Sample MnO2 (mAh) (%. le)
Heat Trcated37. 6 50. 0
2 Heat Treated30. 2 40. 3
3 Heat Treated39. 2 52. 2
4 Heat Treated46. 0 61.4
Heat Treated41. 4 55. 3
6 Not Heated6. l 8. 2
7 Not HeatedZ6.4 35. 5
8 Not heated34. 2 45. 7
9 Not Heated10. 9 14. 5
Not ~eated4. 9 6. 6
EXAMPLE IV
. .
Two cells were constructed similar to cells in E~cample II
e~ccept that l. 5 ml of the electrolyte wa~ used and in the fir~t cell the
cathode rnix (33% porosity) consi~ted of 80 wt. ~0 Tekkosha MnO2, l0
wt.qo carbon black and 10% Teflon* and in the second cell the cathode
mix (45% porosity) was the same except that the MnOz was electrolytic
MnO2 made by Union Carbide Corporation. The MnOz in each cell
was heat treated and then blende~d into cathode pellet~ which were
dried at 120-C in ~acuum. The nominal interfacial electrode area
for each electrode wa~ 2 square centimeters. The cell~ were continu-
ously discharged across a 3000-oh$n load and the cathode coulombic
cfficiency of utilization to a 2. 0-volt cutoff wa~ calculated to be 88%
for the Tekkosha MnO2-contain;ng cell and 99~o for the other cell.
EXAMPLE ~
Se:lreral 0. 455 inch diameter, 0. 165 inch high cells were
constructed using 0. 36 gram of cathode mix containing 86 wt. go
Tekkosha MnO2, 8. ~ wt. % carbon black, 2. 5 wt. 9'o graphite, and
3. 0 wt. 'Yo Te~lon~ 0. 03 gram lithium anode; and 140 ~ ~ of the electrolyte
* Tradç~rk na~e f~r polytetraf1~ 0ethyl~ne
12.
7 1 5 1 8
used in Example III. The MnO2, prior to forming the cathode mix,
was heat treated at 350C for 8 hours. Thereafter the molded
cathode mix pellets were exposed to various levels of hu~nidity
for various lengths of time and then assembled into cells. The
bulge measurements, if any, and the leakage, if any, after storage
for various period~ of time are shown in Table IV. The bulge
measurement is the deviation in mils of the height of the cell from
the original height of the cell due to anode corro~ion andlor gas
evolution within the cell. Leakage i8 any electrolyte visually
lO observable at the seal area of the cell. The cells were then dis-
charged across a 15, 000-ohm load until the voltage dropped to Z.4
volts. The average milliampere hour~ capacity delivered by the
cells in each sample group is also shown in Table IV.
The data shown in Table IV demonstrate that the cells
in which the heat-treated MnO2 cathode~ have been exposed to sub-
~tantial levels of humidity begin to show bulging within 24 hours.
Some decrea~e in bulge with time may be due to some of the gas
escaping through the cover/ga~ketlcontainer interface when leakage
occurs.
EXAMPLE VI
Six cell~ were constructed similar to the first cell
~ample in Example IV except that three cells (samples 1-3) employed
an electrolyte of I M LiBF4 in a Z:3 volume % ratio of 3Me20x-DME;
ant the second three cell~ (~amples 4-6) employed an electrolyte
of 1 M LiCF3S03 in a 2:3 volume % ratio of 3Me20x-DME. The
cells were continuously disc:harged across a 3ûO0-ohrn load and at
different time periods the cells were pulsed across a 250-ohm
load for 2 second~. The voltages observed and the cathode coulombic
efficiency calculated to a 2. 0-volt cutoff are shown in Table V.
9~7 12518
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TABLE V
~s Cathode Coulombic
Sample 1 3 Efficiency (%)
*Voltage Readin~s (Volts)
1 2.92 2.87 2.68 2.11 89
(2.3}) (2.31) (2.00) (1.45)
2 2.83 2.83 2.64 ~.07 87
(1.96) (2.03) (1.70) (1.31)
3 2.87 2.83 2.59 2.28 88
(1.72) (1.86) (1.33) (1.14)
4 2 89 2.85 2 69 2.28 88
(2 12) (2.1S) (1 91) (1.58)
2.88 2.82 2.64 1.92 88
(2.01) (2.06) (1.8~) (1.32)
6 2 89 2.85 2.68 2.08 88
(2 03) (2.05) (1.81) (1.37)
* Voltage values in parenthesis (~ are the pulse voltages
and the other voltage values are the continuous voltage
readingsobserved after th~ time period shown.
While the present invention ha~ been described with
reference to many particular details thereof, it is not intended that
these details should be construed as limiting the scope of the invention.
