JPH0770314B2 - Lithium / manganese dioxide secondary battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a lithium secondary battery that can be repeatedly used by charging, and in particular, a so-called lithium / manganese dioxide secondary battery using a manganese dioxide battery as an anode. It relates to the improvement of batteries.

SUMMARY OF THE INVENTION The present invention is a lithium-manganese dioxide secondary battery in which a lithium-aluminum alloy is used for the cathode and manganese dioxide is used for the anode, and the anode capacity is regulated to be small relative to the cathode capacity. -It aims to realize a lithium-manganese dioxide secondary battery with excellent cycle life characteristics by setting the lithium content in the aluminum alloy to 30 to 45 atom%.

[Conventional technology]

So-called lithium batteries that use lithium as the cathode and organic electrolyte as the electrolyte have long-term reliability because of their high energy density, good leakage resistance, and excellent storage stability. In recent years, it has begun to be used in various applications as a backup power source for electronic timepieces and IC memories that require.

The anode of the lithium battery is generally composed of MnO ₂ , CF _X , Ag ₂ CrO ₄
Etc., and has already been put to practical use as a primary battery. Among them, MnO ₂ is a cheap material and therefore Li / MnO 2
₂ Batteries are known as very good primary batteries in terms of both performance and manufacturing cost.

However, the lithium batteries currently used in this manner are all primary batteries, and so-called lithium secondary batteries, which utilize the characteristics of lithium batteries, have not yet been put into practical use in the field of secondary batteries.

In recent years, with the recent advances in electronic equipment, such as miniaturization, higher performance, and cordlessness, the emergence of a high-performance, inexpensive lithium secondary battery as a power source that can be conveniently and economically used for a long time is strongly desired. In particular, a battery in which lithium is used for the cathode and manganese dioxide is used for the anode is a battery that has received a great deal of attention in terms of its performance and cost.

From such a situation, for example, in JP-A-61-91865,
By using a lithium-aluminum alloy for the cathode, Li
/ MnO ₂ battery is a secondary battery, so-called lithium,
A manganese dioxide secondary battery has been proposed.

However, the lithium-manganese dioxide secondary battery is
The cycle life is not so good, and there are still points to be further improved in practical use.

[Problems to be solved by the invention]

Although the Li / MnO ₂ battery has been made into a secondary battery as described above, the cycle life of the secondary battery is not so good and there is a point to be improved in practical use.

Therefore, the present invention has been made in view of the above conventional circumstances, and an object of the present invention is to provide a practical lithium-manganese dioxide secondary battery having excellent cycle life characteristics.

[Means for solving problems]

In order to achieve the above-mentioned object, the present inventors
As a result of studying the improvement of the cycle life of a manganese dioxide secondary battery, the battery capacity is controlled as the anode and the cycle life is lengthened by limiting the lithium content in the lithium-aluminum alloy used as the cathode material. We have come to the knowledge that it can be done.

The present invention has been completed based on the above findings, using a lithium-aluminum alloy for the cathode and manganese dioxide for the anode, and a lithium-manganese dioxide secondary battery in which the anode capacity is regulated to be small relative to the cathode capacity. The battery is characterized in that the lithium content in the lithium-aluminum alloy forming the cathode is limited to the range of 30 to 45 atom% in the undischarged state.

Here, the content of lithium in the lithium-aluminum alloy used as the cathode material in the present invention is limited to the range of 30 to 45 atomic% is that the discharge, a constant discharge when the cycle of charging is repeated. This is because the cycle life, which indicates the capacity, is in a range in which the cycle life is significantly long. When the content of lithium is 45 atomic% or more, the energy density of the cathode is good, but the reaction of the electrolyte is remarkable and the cycle characteristics are deteriorated. On the other hand, when the content is 30 atomic% or less, the energy density is reduced and the practicality is lost.

Further, in the battery of the present invention, the anode capacity is regulated to be small with respect to the cathode capacity, but this is when the lithium alloy Lithium of the cathode is completely discharged to the limit due to discharge,
This is because the capacity of the secondary battery deteriorates rapidly and the characteristics of the secondary battery deteriorate. Therefore, the anode capacity is made smaller than the anode capacity so that the lithium alloy of the cathode remains at the end of discharge. . That is, the end of the battery capacity is determined by the lithium capacity of the cathode, not by the so-called cathode control, but by the capacity of manganese dioxide, the so-called anode control is determined.

Therefore, in the battery of the present invention, it is preferable that the ratio of the anode capacity to the anode capacity is in the range of 1.3 to 3.7. This is because if the capacity ratio is 1.3 or less, the cycle characteristics deteriorate, and if it is 3.7 or more, a discharge capacity of 10 mAH or more cannot be obtained when considering batteries of the same size.

On the other hand, a non-aqueous organic electrolyte in which a lithium salt is used as an electrolyte and is dissolved in an organic solvent is used as the electrolytic solution.

Here, as the organic solvent, esters, ethers, 3
Substituted-2-oxazolidinones and mixed solvents of two or more of these may be mentioned.

Examples of the esters include alkylene carbonate (ethylene carbonate, propylene carbonate, γ-butyrolactone, etc.) and the like.

The ethers include cyclic ethers, for example, ethers having a 5-membered ring [tetrahydrofuran; substituted (alkyl,
Alkoxy) tetrahydrofuran, for example 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2-
Ethyltetrahydrofuran, 2,2'-dimethyltetrahydrofuran, 2-methoxytetrahydrofuran, 2,5-dimethoxytetrahydrofuran, etc .; dioxolane, etc.], ether having a 6-membered ring [1,4-dioxane, pyran, dihydropyran, tetrahydropyran], Dimethoxyethane and the like can be mentioned.

Examples of 3-substituted-2-oxazolidinones include 3-alkyl-2-oxazolidinone (3-methyl-2-oxazolidinone, 3-ethyl-2-oxazolidinone, etc.), 3-cycloalkyl-2-oxazolidinone (3-cyclohexyl-2). -Oxazolidinone, etc.), 3-aralkyl-2-
Examples thereof include oxazolidinone (3-benzyl-2-oxazolidinone and the like) and 3-aryl-2-oxazolidinone (3-phenyl-2-oxazolidinone and the like).

Among them, propylene carbonate, ether having a 5-membered ring (particularly tetrahydrofuran, 2-methyltetrahydrofuran, 2-ethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-methoxytetrahydrofuran) and 3-methyl-2-oxazolidinone are preferable.

As the electrolyte, lithium perchlorate, lithium borofluoride, lithium phosphofluoride, lithium chloroaluminate, lithium halide, lithium trifluoromethanesulfonate and the like can be used, and lithium perchlorate and lithium borofluoride are preferable.

[Action]

In a lithium-manganese dioxide secondary battery using a lithium-aluminum alloy for the cathode and manganese dioxide for the anode, the battery capacity is regulated so that the anode capacity is less than the cathode capacity, and in the lithium-aluminum alloy constituting the cathode The lithium content of 30 to 45 atoms drastically improves the characteristics of charge / discharge cycle life.

〔Example〕

Hereinafter, the present invention will be described based on specific experimental examples,
Needless to say, the present invention is not limited to these experimental examples.

First, the following Examples 1 to 3 and Comparative Examples 1 and 2 were performed in order to compare the influence of the lithium content of the cathode on the cycle characteristics.

Example 1 A button type battery shown in FIG. 1 was produced according to the procedure as shown below.

First, 88.9 parts by weight of commercially available electrolytic manganese dioxide that was heat-treated at 300 ° C. for about 5 hours, 9.3 parts by weight of graphite,
As a bander, 1.8 parts by weight of polytetrafluoroethylene was added to make an anode mix.
Anode pellets (5) were prepared by pressure molding to a weight of 0.167 g. When the capacity of this anode pellet (5) was measured, a capacity of 37 mAH was obtained.

Next, 0.28 mm thick aluminum was punched out to a diameter of 15.5 mm and spot-welded to the cathode can (2), and the diameter of 15.0 m
A punched lithium foil having a thickness of m and a thickness of 0.32 mm was pressure-bonded to prepare a cathode as a cathode pellet (1). At this time, the content of lithium in the cathode lithium-aluminum alloy is
It was 45 atom%. When the capacity of this cathode pellet (1) was measured, a capacity of 101 mAH was obtained.

The separator (3) is placed on this cathode, the gasket (4) made of plastic is fitted, and the electrolyte (1 mol / mol)
Inject propylene carbonate in which LiClO ₄ was dissolved at a ratio of, and insert the anode pellet (5) prepared earlier, cover the anode can (6), and then seal the opening with an outer diameter of 20
A lithium-manganese dioxide secondary battery with a cathode content of 45 atomic% and a thickness of 1.6 mm was assembled. This battery was designated as sample battery A.

Example 2 In Example 1, in producing the cathode pellet (1), aluminum with a thickness of 0.34 mm and a diameter of 15.5 mm and a thickness of 0.26 m were used.
A lithium foil with m and a diameter of 15.0 mm was used. The lithium content of this cathode pellet was 36 atomic%. Moreover, when the capacity of the cathode was measured, a capacity of 83 mAH was obtained.

Thereafter, in the same manner as in Example 1, a lithium-manganese dioxide secondary battery having an outer diameter of 20 mm and a thickness of 1.6 mm and a cathode lithium content of 36 atom% was assembled. This battery was designated as sample battery B.

Example 3 In Example 1, in producing the cathode pellet (1), aluminum having a thickness of 0.37 mm and a diameter of 15.5 mm and a thickness of 0.23 m were used.
A lithium foil with m and a diameter of 15.0 mm was used. The lithium content of this cathode pellet was 31 atomic%. Moreover, when the capacity of the cathode was measured, a capacity of 73 mAH was obtained.

Thereafter, in the same manner as in Example 1, a lithium-manganese dioxide secondary battery having an outer diameter of 20 mm and a thickness of 1.6 mm and a cathode lithium content of 31 atom% was assembled. This battery was designated as sample battery C.

Comparative Example 1 In Example 1, in producing the cathode pellet (1), aluminum having a thickness of 0.25 mm and a diameter of 15.5 mm and a thickness of 0.35 m
A lithium foil with m and a diameter of 15.0 mm was used. The content of lithium in this cathode pellet was 50 atomic%. Further, when the capacity of the cathode was measured, a capacity of 110 mAH was obtained.

Thereafter, in the same manner as in Example 1, a lithium-manganese dioxide secondary battery having an outer diameter of 20 mm and a thickness of 1.6 mm and a cathode lithium content of 50 atomic% was assembled. This battery was designated as sample battery D.

Comparative Example 2 In manufacturing the cathode pellet (1) in Example 1, a thickness of 0.44 mm, a diameter of 15.5 mm of aluminum and a thickness of 0.16 m were used.
A lithium foil with m and a diameter of 15.0 mm was used. The lithium content of this cathode pellet was 21 atomic%. Moreover, when the capacity of the cathode was measured, a capacity of 51 mAH was obtained.

Thereafter, in the same manner as in Example 1, a lithium-manganese dioxide secondary battery having an outer diameter of 20 mm and a thickness of 1.6 mm and a cathode lithium content of 21 atomic% was assembled. This battery was designated as sample battery E.

Sample battery A to sample battery E assembled as above are discharged by about 33 mAH, and then charged at 2 mA for 10 hours
Discharge was performed for 7 hours at Ω. An experiment of cycle life characteristics was performed by setting this operation as one cycle. The results are shown in FIG. In the figure, A, B, C, D, and E correspond to the respective sample batteries A to E.

From FIG. 2, it can be seen that the lithium content in the lithium-aluminum alloy forming the cathode is 45 atom%, 36 atom% and 31 atom% in the undischarged state of Sample A, Sample Battery B, and Sample Battery C of 30%. It can be seen that the discharge capacity is sufficiently practical even after the cycle has passed. On the other hand, in the lithium-aluminum alloy, the content of lithium in the undischarged state was 50 at%, 21 at%.
It can be seen that the discharge capacity decreased to half of the initial capacity in about 8 to 18 cycles.

Generally, lithium-aluminum alloy has a fast lithium diffusion rate when the lithium content is 7 to 47 atom% in an undischarged state.
A + β phase is formed, but when this alloy is used as the cathode of the battery, as is clear from this experimental example, the lithium content is regulated within the range of 30 to 45 atom% in the undischarged state. The lithium-manganese dioxide secondary battery has excellent cycle life as a secondary battery.

Next, in order to compare the influence by changing the ratio of the cathode capacity and the anode capacity in the case where the lithium content of the cathode was 36 atomic% which had the best cycle characteristics from the above results, the following Example 4 and Comparative example 3 was performed.

Example 4 The same composition as in Example 1, that is, electrolytic manganese dioxide was used.
Heat treated at 300 ° C for about 5 hours, 88.9 parts by weight, 9.3 parts by weight of graphite, and 1.8 parts by weight of polytetrafluoroethylene as a binder were added to form an anode mix. Anode pellets (5) were produced by pressure molding. When the capacity of this anode pellet (5) was measured, a capacity of 41 mAH was obtained.

Next, aluminum with a thickness of 0.27 mm was punched out to a diameter of 14.5 mm and spot-welded to the cathode can (2), and a diameter of 14.0 m
A punched lithium foil having a thickness of m and a thickness of 0.21 mm was pressure-bonded to prepare a cathode as a cathode pellet (1). At this time, the content of lithium in the cathode lithium-aluminum alloy is
It was 36 atomic%. When the capacity of this cathode pellet (1) was measured, a capacity of 58 mAH was obtained. Therefore, the ratio of the cathode capacity to the anode capacity is 1.42.

Thereafter, in the same manner as in Example 1, a lithium-manganese dioxide secondary battery having an outer diameter of 20 mm and a thickness of 1.6 mm was assembled. This battery was designated as sample battery F.

Comparative Example 3 The same composition as in Example 1, that is, electrolytic manganese dioxide was used.
Heat treated at 300 ° C for about 5 hours, 88.9 parts by weight, 9.3 parts by weight of graphite, and 1.8 parts by weight of polytetrafluoroethylene as a binder were added to form an anode mix. Anode pellets (5) were produced by pressure molding. When the capacity of this anode pellet (5) was measured, a capacity of 48 mAH was obtained.

Next, aluminum with a thickness of 0.25 mm was punched out to a diameter of 13.5 mm and spot-welded to the cathode can (2), and a diameter of 13.5 m
A punched lithium foil having a thickness of 0.18 mm and a thickness of 0.18 mm was press-bonded to prepare a cathode as a cathode pellet (1). At this time, the content of lithium in the cathode lithium-aluminum alloy is
It was 36 atomic%. When the capacity of this cathode pellet (1) was measured, a capacity of 46 mAH was obtained. Therefore, the ratio of the cathode capacity to the anode capacity is 0.96.

Thereafter, in the same manner as in Example 1, a lithium-manganese dioxide secondary battery having an outer diameter of 20 mm and a thickness of 1.6 mm was assembled. This battery was used as a sample battery G.

The sample batteries F and G assembled as described above were discharged together with the sample battery B having a lithium content of 36 atomic% as the cathode prepared in Example 2 at about 33 mAH, and then charged at 2 mA for 10 hours and then at 7 kΩ at 7 kΩ. Discharged for an hour. An experiment of cycle life characteristics was performed by setting this operation as one cycle. The results are shown in FIG. In the figure, B,
F and G are each sample battery B, sample battery F, sample battery G
Corresponding to the ratio of cathode capacity to anode capacity,
Is 2.24, the sample battery F is 1.42, and the sample battery G is 0.96.

As shown in FIG. 3, the sample batteries B and F, which have a larger cathode capacity than the anode capacity, showed almost no deterioration in discharge capacity even after repeated charge / discharge cycles. However, the discharge capacity deteriorated remarkably as the charge / discharge cycle was repeated, and was not practical as a secondary battery. That is, it is shown that the characteristics of the secondary battery were deteriorated due to the fact that the lithium in the lithium alloy of the cathode was completely discharged to the limit due to the discharge and the capacity was drastically lowered, and the characteristics as the secondary battery were deteriorated. Therefore, the anode capacity is preferably smaller than the cathode capacity so that the lithium alloy of the cathode remains at the end of the discharge, that is, so-called anode control.

[Effect of the invention]

As is apparent from the above description, in a lithium-manganese dioxide secondary battery using a lithium-aluminum alloy for the cathode and manganese dioxide for the anode, the battery capacity is regulated to a small anode capacity with respect to the cathode capacity, and By setting the lithium content in the lithium-aluminum alloy constituting the cathode to 30 to 45 atomic%, the cycle life of charging / discharging becomes longer and the characteristics are dramatically improved.

Therefore, it is possible to manufacture a highly practical lithium-manganese dioxide secondary battery with great industrial value.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a configuration example of a lithium-manganese dioxide secondary battery. FIG. 2 is a characteristic diagram showing the relationship between the number of cycles and the discharge capacity when the lithium content of the cathode is changed. FIG. 3 is a characteristic diagram showing the relationship between the number of cycles and the discharge capacity when the ratio of the cathode capacity and the anode capacity is changed. 1 …… Cathode pellet 2 …… Cathode can 3 …… Separator 4 …… Gasket 5 …… Anode pellet 6 …… Anode can

Claims (1)

[Claims] 1. A lithium-manganese dioxide secondary battery in which a lithium-aluminum alloy is used for the cathode and manganese dioxide is used for the anode, and the anode capacity is regulated to be small with respect to the cathode capacity. Lithium-aluminum constituting the cathode A lithium-manganese dioxide secondary battery characterized in that the content of lithium in the alloy is 30 to 45 atom%.