CH642779A5 - NON - AQUEOUS BATTERIES HAVING HEAT TREATED MANGANESE BIOXIDE CATHODES. - Google Patents

Description

The present invention relates to a non-aqueous cell comprising a highly active metal anode, a cathode containing manganese dioxide, which contains less than about 1% water based on the weight of manganese dioxide, and a liquid organic electrolyte. based on 3-methyl-2-oxazolidone, together with a cosolvent and a determined dissolved body.

The production of high-energy batteries requires the compatibility of an electrolyte, endowed with advantageous electrochemical properties, with highly reactive anode materials such as lithium, sodium, etc., and the efficient use of high density cathode materials d energy, such as manganese dioxide. The use of aqueous electrolytes is ruled out in such systems, since the anode materials are sufficiently active to react chemically with water. It was therefore necessary, in order to achieve the high energy density which can be obtained by the use of these very reactive anodes and of these high energy density cathodes, to direct research towards electrolyte systems. non-aqueous and more particularly non-aqueous organic electrolytic compositions.

The expression nonaqueous organic electrolyte is used in the prior art to designate an electrolyte which is formed of a dissolved body, for example a salt or a complex salt of the elements of group IA, group II-A or group III -A of the periodic table-5 that, in solution in a suitably chosen non-aqueous organic solvent. Typical solvents include propylene carbonate, ethylene carbonate or γ-butyrolactone. The expression periodic table used in this memo designates the periodic table of the elements which appears on the third cover page of the work entitled "Handbook of Chemistry and Physics", 48th edition, Chemical Rubber Co., Cleveland, Ohio , 1967-1968.

A multitude of dissolved bodies are known to be recommended for use, but the choice of a suitable solvent has been particularly difficult, since many of the solvents which are used to prepare electrolytes which are sufficiently conductive to allow efficient migration of ions into the solution are reactive with the high activity anodes mentioned above. Most researchers in this field, wishing to find suitable solvents, have concentrated their efforts on aliphatic and aromatic compounds containing nitrogen and oxygen, with some attention being paid to organic compounds containing sulfur, phosphorus and arsenic. The results of this research were not entirely satisfactory, since many of the solvents tested could still not be effectively used with cathode materials of high energy density such as manganese dioxide (Mn02) , and were sufficiently corrosive to lithium anodes to prevent effective performance for any length of time.

Although manganese dioxide has been mentioned as a cathode suitable for use in batteries, this compound contains an unacceptable amount of water, both of the absorbed type and of the adsorptively bound type, which is sufficient to cause a corrosion of the anode (lithium) accompanied by evolution of hydrogen. This type of corrosion which gives off gas is a serious problem in closed cells, especially button cells of the miniaturized type. To keep electronic devices powered by batteries as compact as possible, electronic assemblies are usually designed so as to present cavities which receive the miniature batteries as a source of energy. The cavities are usually made in such a way that a battery can be adapted to it correctly, thereby establishing electronic contact with corresponding terminals provided in the device. An important problem which can be encountered in the use of devices of this type powered by batteries 45 lies in the fact that, if the evolution of gas causes the expansion of the battery, the latter can become trapped in the cavity. This may result in damage to the device. Likewise, if there is a leakage of electrolyte from the battery, this leakage can cause deterioration of the device. Therefore, it is important that the physi-50 ques dimensions of the battery housing remain constant during discharge and that no leakage of electrolyte from the battery can enter the powered device.

U.S. Patent No. 4,133,856 describes a process for producing an MnO2 electrode (cathode) for 55 nonaqueous cells, in which the MnOz dioxide is initially heated in the range of 350 to 430 ° C. so as to substantially eliminate the absorbed water and the fixed water, then, after transformation into an electrode with a conductive agent and a binder, the electrode is further heated in a range of 200 to 350 ° C. before being incorporated 60 to a pile. U.S. Patent No. 1,199,426 also describes the heat treatment of MnOz in air at a temperature of 250-450 ° C to substantially remove its water of constitution.

U.S. Patents Nos. 3871916, 3951685 and ss 3996069 describe a non-aqueous cell containing an electrolyte based on 3-methyl-2-oxazolidone together with a solid cathode selected from the group comprising (CFx) n, CuO , FeS2, Co304, V2Os, Pb304, In2S3 and CoS2.

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While the theoretical energy, i.e. the electrical energy virtually supplied by a chosen anode-cathode couple, is relatively easy to calculate, it is necessary to choose a nonaqueous electrolyte for a couple which allows the real energy produced by a battery of batteries approach theoretical energy. The common problem is that it is virtually impossible to predict how a nonaqueous electrolyte will behave, or even if it is able to operate with a specified torque. Therefore, a battery should be considered as a unit made up of three parts: a cathode, an anode and an electrolyte, and it should be noted that the parts of a battery are not predictably interchangeable with the parts of another stack to form an efficient and functional third stack.

One of the aims of the present invention is to find a non-aqueous cell containing, among other components, an electrolyte based on 3-methyl-2-oxazolidone and a cathode containing manganese dioxide in which the water content is lower. at 1% by weight based on the weight of manganese dioxide.

Another object of the present invention is to find a non-aqueous manganese dioxide battery comprising a lithium anode.

Another object of the present invention is to provide a non-aqueous lithium / MnO2 cell containing a liquid organic electrolyte essentially formed from 3-methyl-2-oxazolidone in association with at least one cosolvent and a dissolved body.

The invention provides a new non-aqueous battery with high energy density, comprising a very active metal anode, a cathode containing manganese dioxide and a liquid organic electrolyte composed of 3-methyl-2-oxazolidone in combination with a dissolved conductive substance, in the presence or absence of at least one cosolvent with a viscosity lower than that of 3-methyl-2-oxazolidone and in which the manganese dioxide has a water content of less than 1% by weight on the basis of the weight of Mn02 *. Preferably, the water content must be less than 0.5% by weight and in particular less than about 0.2% by weight.

The water normally contained in electrolytic and chemical type manganese dioxide can be substantially removed by various treatments. For example, manganese dioxide can be heated in air or in an inert atmosphere at a temperature of 350 ° C for about 8 h or at a lower temperature for a longer period. Care should be taken to avoid heating the manganese dioxide above its decomposition temperature, which is about 400 ° C in the air. In atmospheres containing oxygen, higher temperatures can be used. According to the present invention, the manganese dioxide must be heated for a sufficient period to ensure that its water content is reduced below about 1% by weight, preferably below about 0.5 and in particular below about 0.2% by weight, based on the weight of manganese dioxide. An amount of water greater than about 1% by weight would react with the anode of a very active metal such as lithium and cause its corrosion, which would lead to the evolution of hydrogen. As noted above, this could cause physical deformation of the battery and / or electrolyte leakage from the battery during storage or discharge.

In order to effectively remove the undesirable water from MnO2 or from the mixture of MnO2 with a suitable conductive agent and binder, up to the level necessary for the practice of the present invention, it is believed that an appreciable amount of both absorbed and bound water. After the water removal treatment has been completed, it is essential to provide protection to prevent the manganese dioxide from absorbing water into the atmosphere. This could be achieved by handling the treated manganese dioxide in an enclosure protected from moisture or in a similar device. Alternatively, the treated manganese dioxide or the manganese dioxide combined with a conductive agent and a suitable binder could be heat treated.

to remove water that may have been absorbed into the atmosphere.

Preferably, the manganese dioxide should be heat treated to reduce its water content to less than about 1% by weight, then it may be mixed with a conductive agent such as graphite, carbon, etc., and a binder such as Teflon (registered trademark of polytetrafluoroethylene), a polymer of ethylene and acrylic acid, etc., to produce a solid cathode electrode. If necessary, a small amount of the electrolyte can be incorporated into the manganese dioxide mixture.

Another possible advantage of practically complete removal of water from the manganese dioxide is that, if small amounts of water are present in the battery electrolyte, the manganese dioxide then absorbs most of the electrolyte water and thereby prevents or substantially delays the reaction of water with the anode, for example lithium. In this case, manganese dioxide behaves as an agent for extracting the impurities formed by water in organic solvents.

The electrolyte intended to be used in accordance with the invention is an electrolyte based on 3-methyl-2-oxazolidone. 3-methyl-2-oxazolidone (3Me20x), liquid organic matter of formula:

CH2 - CH2 - O - CO -> 1 - CH3 is an excellent non-aqueous solvent because of its high dielectric constant, its chemical inertness towards the components of the battery, its wide range in the liquid state and its low toxicity.

However, it has been found that, when metal salts are dissolved in the liquid 3Me20x in order to improve the conductivity of the latter, the viscosity of the solution may be too high for it to be able to be used effectively as an electrolyte for certain applications in nonaqueous batteries other than those which require very low current consumption. Consequently, in certain applications in accordance with the invention, the addition of a cosolvent of low viscosity would be desirable if the compound 3Me20x were to be used as electrolyte for nonaqueous batteries capable of operating at a high degree of energy density. In particular, to obtain a high degree of energy density in accordance with the invention, it is essential to use a thermally treated MnO2 cathode at the same time as a very active metal anode. Thus, the invention is focused on a new battery with high energy density comprising a very active metal anode such as lithium, a heat-treated MnO2 cathode and an electrolyte formed from 3Me2ox in association with a dissolved conductive body. , in the presence or absence of at least one cosolvent of low viscosity.

Low viscosity cosolvents which may be used in the present invention include tetrahydrofuran (THF), dioxolane (DIOX), dimethoxyethane (DME), propylene carbonate (PC), dimethylisoxazole (DMI), carbonate diethyl (DEC), ethylene glycol sulfite (EGS), dioxane, dimethyl sulfite (DMS), etc. Dimethoxyethane (DME), dioxolane (DIOX) and propylene carbonate (PC) are popular co-solvents because of their compatibility with metallic salts dissolved in the liquid 3Me20x compound and their chemical inertness towards the components of the battery. In particular, the total amount of low viscosity cosolvent that is added could be between approximately 20 and approximately 80% based on the total volume of solvent, that is to say excluding the dissolved body, in order to lower the viscosity to a level favorable for its use in a battery with great consumption.

Dissolved conductive bodies (metal salts) which can be used in accordance with the invention with the liquid 3Me20x can be chosen from the group of compounds of formulas MCF3SO3, MBF4, MCIO4 and MM'F <5 where M denotes lithium, sodium or potassium and M 'is phosphorus, arsenic or antimony. The addition of the dissolved body is necessary to improve the conductivity of the 3Me20x compound so that it can be used as an electrolyte in non-aqueous batteries. Thus, the particu5 salt

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The link you choose must be compatible and non-reactive with the 3Me20x compound and the battery electrodes. The amount of dissolved body which must be in solution in the liquid 3Me20x compound must be sufficient to provide good conductivity, for example at least about 10 ~ 4 fi-'cm-1. Generally, a molar amount of at least about 0.5 mol should be sufficient for most battery applications.

Highly active metal anodes which can be advantageously used in the present invention include lithium (Li), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), aluminum (Al) anodes and their alloys. Among these active metals, preference is given to lithium not only because it is a malleable and ductile metal, but also because it can be easily incorporated into a battery, and because it has the highest energy to weight ratio in the group of suitable anode metals.

Other details on the high energy density cell of the invention, comprising an electrolyte based on 3Me20x, a solid cathode based on MnO2 having less than 1% by weight of water and a very active metal anode , are given in the following examples.

Example 1:

Thermogravimetric analyzes have been performed on various samples of commercial manganese dioxide. Some of the samples were analyzed as obtained, others were heat treated at 350 ° C for 8 h, still others were heat treated at 350 ° C for 8 h, then mixed with carbon and Teflon to produce cathode mixtures. The results obtained in the thermogravimetric analyzes are reproduced in Table I. These results clearly demonstrate that types of commercial manganese dioxide contain large amounts of water. Furthermore, the results show that even after the manganese dioxide has been heat treated as indicated above, it absorbs water from the atmosphere even after only a short time.

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Example 2:

Flat batteries of two different types have been produced using a nickel metal support having a shallow depression in which the contents of the battery have been placed and on which a nickel metallic cap has been placed to close the battery. The contents of each sample cell consisted of a 2.54 cm diameter lithium disk formed of 5 very thin sheets of lithium with a total thickness of 2.54 mm, approximately 4 ml of an electrolyte comprising approximately 40% volume of dioxolane, approximately 30% by volume of dimethoxyethane (DME), approximately 30% by volume of 3Me20x, plus approximately 0.1% of dimethylisoxazole (DMI) and containing 1M LÌCF3SO3, a separator (0.254 mm thick) made of porous non-woven polypropylene 2.54 cm in diameter absorbing part of the electrolyte, and 2 g of cathode mixture compressed 20 so as to form a cathode having an apparent interfacial area of 5 cm 2. In the first cell, the cathode mixture consisted of Tekkosha electrolytic MnO2 heat treated at 350 ° C for 20 h, carbon black and Teflon. The second pile contained the same type of components as the first, except the absence of treatment of Mn02 Tekkosha. Each cell was discharged at the terminals of a resistance of 1200 fl to a cut-off voltage of 1 V and the cathodic yields were calculated at the same time as the overall energy densities, assuming a reaction of the electrons of the layer L. The results obtained are re-produced in Table II.

Example 3:

Ten miniature button cells are produced using a 60 lithium anode, an electrolyte formed of approximately 40% by volume of dioxolane, approximately 30% by volume of DMER, approximately 30% by volume of 3Me20x plus approximately 0, 1% of DMI and containing 1M LÌCF3SO3, and a cathode comprising 80% by weight of MnO, unheated or heat-treated, 1.5% by weight of carbon black 65, 13.5% by weight of graphite and 5, 0% by weight of a binder of the ethylene / acrylic acid type. The heat treated manganese dioxide is heated at a temperature of 350 ° C for 18 h under an atmosphere of argon. Each stack (11.48 mm in diameter;

Table I

Loss,% by weight, at different temperatures as indicated by thermogravimetric analysis

Description of the sample

Total loss,% by weight, at the indicated temperature (cumulative values)

100 ° C

200 ° C

250 ° C

300 ° C

350 ° C

400 ° C

* Mn02 Tekkosha, as received

1.0

2.1

2.7

3.5

4.4

5.1

Tekkosha as above, but dried at 350 ° C for 8 h;

exposed to the ambient atmosphere for 5 min during

sample transfer

0.2

0.3

0.3

0.3

0.4

0.6

** Cathodic mixture taken directly from an enclosure

anhydrous; exposure to the ambient atmosphere for 5 min

when transferring the sample

0.3

0.4

0.5

0.7

1.1

-

Cathodic mixture exposed to the ambient atmosphere

0.3

0.5

0.5

-

-

-

Same cathodic mixture as above, but exposed to at

ambient atmosphere for another 5 hrs ****

0.6

0.8

0.8

0.9

1.1

1.9

*** Mn02 Sedema

1.4

2.1

2.4

2.6

2.9

3.7

* MnOz Tekkosha oxide is a commercial electrolytic manganese dioxide.

** Cathodic mixture = MnOz Tekkosha heat treated + carbon black + graphite + Teflon.

*** Mn02 Sedema: commercial chemical manganese dioxide.

**** Ambient humidity 35-50%.

Table II

Cathode

Yield *, L-layer electrons (%)

Cathodic energy density (Wh / cm3)

Mn02 heat treated Mn02 unheated

81.0 48.2

4.46 2.16

* Coulombien.

4.12 mm high) contains 0.3045 g of the cathode mixture containing untreated manganese dioxide or 0.3036 g of the cathode mixture containing heat treated manganese dioxide, 0.037 g of lithium, a polypropylene separator and 140 | of electrolyte. Each cell is continuously discharged in a basic resistance of 6200 Q. and it is drawn across a 250 Cl resistance for 2 s once a week. When a cut-off voltage of 1 V has been reached, the capacity of the cell and the Coulomb efficiency of the cathode for each cell are determined; the results are reproduced in table III.

Table III

Battery number

Capacity

Yield

Mn02

of the cathode stack

(mAh)

(%, The)

1

heat treated

37.6

50.0

2

heat treated

30.2

40.3

3

heat treated

39.2

52.2

4

heat treated

46.0

61.4

5

heat treated

41.4

55.3

6

unheated

6.1

8.2

7

unheated

26.4

35.5

8

unheated

34.2

45.7

9

unheated

10.9

14.5

10

unheated

4.9

6.6

Example 4:

Two cells similar to those of Example 2 are produced, with the difference that 1.5 ml of the electrolyte is used and that, in the first cell, the cathode mixture (porosity 33%) is formed by 80% in weight of MnOa Tekkosha, 10% by weight of carbon black and 10% of Teflon and that, in the second cell, the cathode mixture (porosity 45%) is the same, with the difference that the manganese dioxide consists of electrolytic Mn02 produced by Union Carbide Corporation. The manganese dioxide in each stack is heat treated, then incorporated into cathode pellets which are dried at 120 ° C under vacuum. The nominal interfacial area for each electrode is 2 cm2. The cells are continuously discharged across a 3000 Cl resistor and the Coulomb operating efficiency of the cathode up to a cut-off voltage of 2.0 V is found, by calculation, to be 88% for the stack containing Mn02 Tekkosha and 99% for the other stack.

Example 5:

Several stacks of 11.56 mm in diameter and 4.19 mm in height are produced using 0.36 g of cathode mixture containing 86% by weight of MnO2 Tekkosha, 8.5% by weight of carbon black, 2.5 % by weight of graphite and 3.0% by weight of Teflon; a lithium anode of 0.03 g and 140 dj.1 of the electrolyte used in Example 3. The manganese dioxide, before the formation of the cathode mixture, is treated by heating at 350 ° C for 8 h. Then, the molded cathode mixture pellets are exposed to various levels of humidity for varying lengths of time, then collected in various stacks. The measures of possible expansion and leaks, when they exist, after storage for various periods, are indicated in Table IV. The dilation measurement is the difference, in mil642,779

limiters of the height of the cell compared to its initial height, due to corrosion of the anode and / or to the evolution of gas in the cell. A leak exists whenever the presence of electrolyte can be visually observed at the battery seal. The batteries are then discharged across a 15,000 Q resistor until the voltage has dropped to 2.4 V. The average capacity in milliampere-hours delivered by the batteries in each test group is also reproduced in Table IV.

The results shown in Table IV demonstrate that the cells in which the heat treated manganese dioxide cathodes were exposed to significant degrees of humidity begin to show signs of expansion after 24 h. Some reduction in expansion over time may be caused by the escape of a small amount of gas at the interface between the lid, the gasket and the container, when a leak occurs.

Example 6:

Six cells similar to the first test cell of Example 4 are produced, with the difference that three of them (samples 1 to 3) contain an electrolyte formed of LiBF4 1M in a mixture at 2: 3 (% by volume) of 3Me20x and DME and that the other three batteries (samples 4 to 6) contain an electrolyte formed of LÌCF3SO3 1M in a 2: 3 mixture (% by volume) of 3Me20x and DME. The batteries are continuously discharged across a 3000 fì resistor and, at different times, they are drawn across a 250 fi resistor for 2 s.

The voltages observed and the Coulomb efficiency of the cathode, calculated up to a cut-off voltage of 2.0 V, are reproduced in Table V.

Table V

Battery number

Number of days

Coulomb cathode efficiency (%)

1

3

6

8

Read voltages * (V)

1

2.92

2.87

2.68

2.11

89

(2.31)

(2.31)

(2.00)

(1.45)

2

2.83

2.83

2.64

2.07

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)

(2.15)

(L91)

(1.58)

5

2.88

2.82

2.64

1.92

88

(2.01)

(2.06)

(1.87)

(1.32)

6

2.89

2.85

2.68

2.08

88

(2.03)

(2.05)

(1.81)

(1.37)

* The voltages read placed in parentheses are the pulsed voltages and the other voltage values constitute the readings of DC voltages observed after the period indicated.

It goes without saying that the present invention has been described for explanatory purposes, but in no way limiting, and that numerous modifications can be made thereto without departing from its scope.

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(Finally patent table)

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Table IV

Group number

Humidity (%)

Duration of cathode exposure in Mn02

Average expansion (mm) after storage during ld

7 d

1 month

2 months

3 months ,

Leaks *

mAh

1

<1

2 hrs

0

-0.025

0

0/100

65

2

3 +

2 hrs

+0.076

+0.254

+0.051

+0.025

+0.051

0/45

61

3

2.7

2h

-0.018

-0.025

+0.05

0

-0.025

5/16

72

4

14

30 mins

+0.254

+0.152

+0.102

+0.102

+0.076

15/20

66

5

14

2 hrs

+0.356

+0.305

+0.229

+0.203

+0.178

6/20

62

6

15

25 mins

+0.305

+0.152

+0.076

-

+0.076

-

-

7

19

50 mins

+0.470

+0.572

+0.406

+ 0.356

+0.330

27/46

29

8

26

30 mins

+0.279

+0.152

+0.102

+0.102

+0.076

6/20

68

9

26

2 hrs

+0.432

+0.38

+0.254

+0.279

+0.254

6/19

58

10

27

40 mins

+0.533

+0.533

+0.38

+0.254

+0.279

27/47

36

11

69

20-30 mins

+0.584

+0.559

+0.457

+0.406

+0.38

7/19

41

12

72

45 mins

+0.533

+0.610

+0.432

+0.356

+0.102

37/50

31

* The first number represents the number of batteries for which the presence of electrolyte has been observed and the second number is the total number of batteries in the group.

R

Claims (3)

642,779 1. Non-aqueous cell, characterized in that it comprises an active metal anode, a cathode containing manganese dioxide and a liquid organic electrolyte comprising 3-methyl- 2. Non-aqueous cell according to claim 1, characterized in that the water content is less than 0.5% by weight and preferably less than 0.2% by weight based on the weight of manganese dioxide. 3. Non-aqueous cell according to claim 1, characterized in that the liquid organic electrolyte contains at least one co-solvent. 4. Non-aqueous cell according to one of claims 1 or 3, characterized in that the cathode is formed of manganese dioxide, a conductive agent and a binder. 5. Non-aqueous cell according to claim 4, characterized in that the conductive agent is carbon or graphite and the binder is polytetrafluoroethylene or a polymer of ethylene and acrylic acid. 6. Nonaqueous cell according to claim 3, characterized in that the solvent is chosen from tetrahydrofuran, dioxolane, dimethoxyethane, dimethylisoxazole, diethyl carbonate, propylene carbonate, ethylene glycol sulfite, dioxane and dimethyl sulfite. 7. Non-aqueous cell according to one of claims 3 or 6, characterized in that the dissolved body is chosen from compounds of formulas MCF3S03, MBF4, MC104 and MM'F6 where M represents lithium, sodium or potassium and I am phosphorus, arsenic or antimony. 8. A non-aqueous cell according to one of claims 1 or 7, characterized in that the active metal anode is chosen from lithium, potassium, sodium, calcium, magnesium, aluminum and their alloys. 9. Non-aqueous cell according to claim 3, characterized in that the anode is made of lithium and the electrolyte is LiCF3S03 dissolved in 3-methyl-2-oxazolidone, dioxolane, dimethoxyethane and dimethylisoxazole or in 3- methyl-2-oxazolidone and dimethoxyethane or in 3-methyl-2-oxazolidone and propylene carbonate. 10. Non-aqueous cell according to claim 3, characterized in that the anode is lithium and the electrolyte is LiBF4 dissolved in the 2-oxazolidone in combination with a dissolved body and manganese dioxide has a water content of less than 1% by weight, based on its own weight. 2 3-methyl-2-oxazolidone and dimethoxyethane.