CA1149447A

CA1149447A - Nonaqueous cells employing heat-treated mno.sub.2 cathodes

Info

Publication number: CA1149447A
Application number: CA000354021A
Authority: CA
Inventors: Marvin L. Kronenberg
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1979-06-25
Filing date: 1980-06-13
Publication date: 1983-07-05
Also published as: IE49844B1; JPS566383A; BR8003919A; BE883985A; FR2460046B1; IE801312L; GB2054253A; IT1132123B; SE8004657L; ES8102423A1; HK33585A; IN154337B; DK270280A; ES492687A0; AU5956580A; CH642779A5; NO801877L; FR2460046A1; IT8022972A0; NL8003660A

Abstract

12518 NONAQUEOUS CELLS EMPLOYING HEAT-TREATED MnO2 CATHODES ABSTRACT OF THE DISCLOSURE A nonaqueous cell comprising an active metal anode such as lithium, a manganese dioxide-containing cathode which contains less than 1 weight percent water in the manganese dioxide and a liquid organic electrolyte based on 3-methyl-2-oxazolidone in conjunction with a cosolvent and a selected solute. S P E C I F I C A T I O N 1.

Description

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 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~.

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 9.

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and Teflon* The ~econd cell employed the samè type of componentJ
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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 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.

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.

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~t 11 ~ 7 12518 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.

Claims

WHAT IS CLAIMED IS:

1. A nonaqueous cell comprising an active metal anode, a manganese dioxide-containing cathode and a liquid organic electro-lyte comprising 3-methyl-2-oxazolidone in combination with a solute and wherein the manganese dioxide has a water content of less than 1 weight percent based on the weight of the manganese dioxide.

2. The nonaqueous cell of claim 1 wherein the water content is less than 0. 5 weight percent based on the weight of the manganese dioxide.

3. The nonaqueous cell of claim 2 wherein the water content is less than 0.2 weight percent based on the weight of the manganese dioxide.

4. A nonaqueous cell of claim 1 wherein at least one cosolvent is contained in the liquid organic electrolyte.

5. The nonaqueous cell of claim 1 wherein the cathode comprises manganese dioxide, a conductive agent and a binder.

6. The nonaqueous cell of claim 4 wherein the cathode comprises manganese dioxide, a conductive agent and a binder.

7. The nonaqueous cell of claim 5 or 6 wherein the conductive agent is carbon or graphite and the binder is polytetra-fluorethylene or ethylene acrylic acid polymer.

8. The nonaqueous cell of claim 4 wherein said solvent is selected from the group consisting of tetrahydrofuran, dioxolane, dimethoxyethane, dimethyl isoxazole, diethyl carbonate, propylene carbonate, ethylene glycol sulfite, dioxane and dimethyl sulfite.

9. The nonaqueous cell of claim 4 wherein said solute is selected from the group consisting of MCF3SO3, MBF4, MClO4, and MM'F6 wherein M is lithium, sodium or potassium and M' is phosphorus, arsenic or antimony.

16.

10. The nonaqueous cell of claim 1 wherein said active metal anode is selected from the group consisting of lithium, potassium, sodium, calcium, magnesium, aluminum and alloys the reof.

11. The nonaqueous cell of claim 8 wherein said solute is selected from the group consisting of MCF3SO3, MBF4, MC1O4 and MM'F6 wherein M is lithium, sodium or potassium and M' is phosphorus, arsenic or antimony.

12. The nonaqueous cell of claim 11 wherein said active metal anode is selected from the group consisting of lithium, potassium, sodium, calcium, magnesium, aluminum and alloys thereof.

13. The nonaqueous cell of claim 4 wherein the anode is lithium and the electrolyte is LiCF3SO3 dissolved in 3-methyl-2-oxazolidonc, dioxolane, dimethoxyethane and dimethyl isoxazole.

14. The nonaqueous cell of claim 4 wherein the anode is lithium and the electrolyte is LiBF4 dissolved in 3-methyl-2-oxazolidone and dimethoxyethane.

15. The nonaqueous cell of claim 4 wherein the anode is lithium and the electrolyte is LiCF3SO3 dissolved in 3 methyl-2-oxazolidone and dimethoxyethane.

16. The nonaqueous cell of claim 4 wherein the anode is lithium and the electrolyte is LiCF3SO3 dissolved in 3-methyl-2-oxazolidone and propylene carbonate.

17.