JPH0821431B2 - Organic electrolyte secondary battery - Google Patents

Description

The present invention relates to a chargeable / dischargeable organic electrolyte secondary battery expected to be used as a power source for various small electronic devices.

[Outline of Invention]

The present invention uses LiMn ₂ O ₄ as an anode material for an organic electrolyte secondary battery that uses a lithium-containing material as a cathode material, so that the battery capacity is less deteriorated with charge / discharge cycles, and the organic electrolyte has excellent cycle life characteristics. It aims to provide a secondary battery.

[Conventional technology]

A so-called organic electrolyte battery using lithium as a cathode material and an organic electrolyte as an electrolyte has a low self-discharge, a high voltage, and an extremely excellent storability.
As a battery with long-term reliability of 10 years, it is widely used as an electronic timepiece and various memory backup power supplies.

However, these currently used organic electrolyte batteries are temporary batteries, and their lifespan ends with a single use, leaving a point to be improved in terms of economic efficiency.

In recent years, with the dramatic progress of various electronic devices,
There is a strong demand for the advent of a rechargeable organic electrolyte secondary battery as a power source that can be used conveniently and economically for a long time, and many studies have been conducted.

Generally, as a cathode material of an organic electrolyte secondary battery, metallic lithium, a lithium alloy (for example, Li-Al alloy), a conductive polymer doped with lithium ions (for example, polyacetylene, polypyrrole, etc.), and lithium ions in a crystal are used. A mixed intercalation compound or the like is used, and an organic electrolytic solution is used as the electrolytic solution.

On the other hand, various materials have been researched and proposed as an anode active material.
As described in the publication, TiS ₂ , MoS ₂ , NbSe ₂ , V ₂ O _{5 and the} like can be mentioned.

The discharge reaction of the battery using these materials proceeds by intercalation of the lithium ions of the cathode between the layers of these materials that are the anode active material, and in the case of charging on the contrary, lithium ions from the layers of the materials are Deintercalate to the cathode. That is, charging and discharging can be repeated by repeating the reaction in which lithium ions of the cathode enter and leave the layers of the anode active material. For example, when TiS ₂ is used as the anode active material, the charge and discharge reactions are expressed by the following equations.

The conventional anode material is charged and discharged by the above-described reaction, but has a drawback that the discharge capacity is gradually reduced when the charge and discharge reaction is repeated as a secondary battery. This is because the lithium ions that have entered the anode active material due to discharge gradually become less likely to come out, and less of them return to the cathode side due to the charging reaction. That is, the Li _X TiS ₂ remains in the form in the anode, and the amount of lithium ions involved in the next discharge reaction is reduced. Therefore, even if the battery is charged, the discharge capacity is reduced, and the secondary battery has poor cycle life characteristics.

[Problems to be solved by the invention]

As described above, in the material used as the anode active material of the conventional secondary battery, the charging reaction does not proceed as expected, the discharge capacity decreases as the charging and discharging are repeated, and the cycle life characteristics are not excellent. The secondary battery cannot be used for a long period of time.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and uses a material with less deterioration of deintercalation of lithium ions found in conventional anode active materials, and is associated with charge / discharge cycles. It is an object of the present invention to provide an organic electrolyte secondary battery that has little deterioration in discharge capacity and has excellent cycle life characteristics.

[Means for solving problems]

The present inventor, as a result of various studies to find a material having less deterioration of deintercalation of lithium ions as an anode active material in order to achieve the above-mentioned object, as a result,
We have come to the finding that LiMn ₂ O ₄ having a spinel structure shows extremely good results. The present invention has been completed based on such findings, and a cathode containing lithium and LiMn ₂ O ₄
And an organic electrolyte solution.

LiMn ₂ O ₄ used as the positive electrode active material of the organic electrolyte secondary battery of the present invention is lithium carbonate (Li ₂ Co ₃ ) and manganese dioxide (MnO ₂ ) heated to 400 ° C. in a nitrogen atmosphere to react with each other. Alternatively, it can be easily obtained by heating lithium iodide (LiI) and manganese dioxide (MnO ₂ ) at 300 ° C. in a nitrogen atmosphere to cause a reaction.

On the other hand, as the substance containing lithium used as the cathode material, metallic lithium, lithium alloy (for example,
LiAl, LiPb, LiSn, LiBi, LiCd, etc.), conductive polymer doped with lithium ions (eg, polyacetylene, polypyrrole, etc.), intercalation compounds with lithium ions mixed in (eg, TiS ₂ , MoS ₂ etc.) A material containing lithium between layers) can be used.

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

Here, as the organic solvent, 1,2-dimethoxyethane,
A single solvent such as 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane or a mixed solvent of two or more thereof can be used.

As the electrolyte, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C
One or a mixture of two or more of ₆ H ₅ ) ₄ can be used.

[Action]

By using LiMn ₂ O ₄ as the anode active material of the organic electrolyte secondary battery, it became possible to satisfactorily deintercalate the lithium ions of the cathode material that moved to the anode by the discharge reaction in the reaction by charging. .

〔Example〕

Hereinafter, the present invention will be described based on specific experimental examples, but it goes without saying that the present invention is not limited to these experimental examples.

Comparative Example First, TiS ₂ or MoS ₂ was used as the anode active material.
The cycle characteristics of Li / TiS ₂ or Li / MoS ₂ organic electrolyte secondary batteries were investigated. The results are shown in FIG. According to Fig. 1, in the organic electrolyte secondary battery using TiS ₂ or MoS ₂ as the anode active material, the discharge capacity of the battery suddenly decreased after only about 10 charge / discharge cycles, and the organic electrolyte secondary battery The secondary battery has only about half the discharge capacity it had initially. After that, it was found that the discharge capacity decreased as the charge / discharge cycle was repeated.

Example 1 A button type battery shown in FIG. 2 was produced according to the procedure shown below.

After 87 g of commercially available electrolytic manganese dioxide and 26 g of lithium carbonate were thoroughly mixed in a mortar, the mixture was heat-treated on an alumina board in nitrogen gas at 400 ° C. for 10 hours. After cooling, the obtained product was subjected to X-ray analysis to obtain an X-ray diffraction chart as shown in FIG. When this was compared with the substance represented by the chemical formula LiMn ₂ O ₄ on the ASTM card, it completely agreed with the X-ray diffraction chart of LiMn ₂ O ₄ . Therefore, the substance produced by the above operation is LiMn
₂ O ₄ .

Next, 9.3 parts by weight of graphite was added to 88.9 parts by weight of LiMn ₂ O ₄ obtained as described above, 1.8 parts by weight of polytetrafluoroethylene was further added as a binder, and a diameter of 15.5 mm was obtained at a pressure of 3 ton / cm ^2. Pellets with a thickness of 0.3 mm and a thickness of 0.3 mm were molded. This was further vacuum dried at 300 ° C. for 5 hours to obtain an anode pellet (5).

On the other hand, 0.3 mm thick aluminum foil was punched out to a diameter of 15.5 mm, spot-welded to the cathode can (2), and 0.3 m thick on top of it.
A m-thick lithium foil punched into a diameter of 15 mm was pressure-bonded to prepare a cathode as a cathode pellet (1).

Next, a non-woven fabric of propylene was stacked on the cathode as a separator (3), propylene carbonate in which 1 mol / LiClO ₄ was dissolved was added as a solution, and a gasket (4) made of plastic was fitted and already prepared. After stacking the anode pellets (5) on the separator (3) and covering the anode can (6), the opening is sealed by caulking to seal the organic electrolyte secondary with an outer diameter of 20,0 mm and a thickness of 1.6 mm. A battery was made. This battery was designated as sample battery A.

Example 2 Commercially available electrolytic manganese dioxide (50 g), lithium iodide (39 g) and graphite (5.2 g) were thoroughly mixed in a mortar, and the mixture was pressure-formed into pellets at a pressure of 3 ton / cm ² and then placed on an alumina board. Then, heat treatment was performed at 300 ° C. for 6 hours in nitrogen gas. After cooling, it was washed with ethylene glycol dimethyl ether (DME). The product thus obtained was subjected to X-ray analysis to obtain an X-ray diffraction chart as shown in FIG. When this was compared with the substance represented by the chemical formula LiMn ₂ O ₄ on the ASTM card, it almost agreed with the X-ray diffraction chart shown by LiMn ₂ O ₄ . Therefore, the substance produced by the above operation is LiMn ₂ O ₄ . In addition, in FIG. 4, a peak of Li ₂ MnO ₃ was also observed, though it was a slight peak of graphite.

Next, using the LiMn ₂ O ₄ obtained as described above, a sample battery B was prepared by the same procedure as in Example 1.

When the sample batteries A and B prepared as described above were subjected to a discharge test through a resistance of 1 kΩ, the electrode wire shown in FIG. 5 was obtained.

The capacity obtained by this discharge was in very good agreement with the capacity obtained by the following reaction formula.

Li ⁺ + LiMn ₂ O ₄ − → 2LiMn ₂ O ₄ Subsequently, the discharged sample batteries A and B were charged at a current of 2 mA with the upper limit voltage set to 3.1 V. The result is shown in FIG. It can be seen from FIG. 6 that the charging voltage is extremely flat, which is considered to mean that the deintercalation of lithium ions in the charging reaction represented by the following equation proceeded extremely smoothly.

2LiMn ₂ O ₄ − → LiMn ₂ O ₄ + Li ⁺ The charge and discharge cycle characteristics of the sample battery were examined by repeating charge and discharge using the sample battery A and the sample battery B exhibiting the charge and discharge characteristics as described above. , 7th
As shown in the figure, no deterioration of discharge capacity due to charge / discharge cycles was observed, and it was found that a secondary battery was obtained.

〔The invention's effect〕

As is clear from the above description, by using LiMn ₂ O ₄ as the anode active material of the organic electrolyte secondary battery, it is possible to favorably deintercalate the lithium ions that have moved the anode by the discharge reaction in the reaction by charging. It is possible to significantly improve the cycle life characteristics of charge and discharge of the organic electrolyte secondary battery.

Therefore, it is possible to provide an organic electrolyte secondary battery that has little deterioration in battery capacity due to charge / discharge cycles and has excellent cycle life characteristics.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing charge / discharge cycle characteristics of an organic electrolyte secondary battery using TiS ₂ and MoS ₂ as an anode agent. FIG. 2 is a schematic cross-sectional view showing a structural example of an organic electrolyte secondary battery. FIG. 3 is a characteristic diagram showing X-ray diffraction results of LiMn ₂ O ₄ synthesized from electrolytic manganese dioxide and lithium carbonate, and FIG. 4 is a characteristic diagram showing LiMn ₂ O ₄ synthesized from electrolytic manganese dioxide and lithium iodide. It is a characteristic view which shows a X-ray-diffraction result. FIG. 5 is a characteristic diagram showing discharge characteristics of the organic electrolyte secondary battery to which the present invention is applied. FIG. 6 is a characteristic diagram showing the charging characteristics of the organic electrolyte secondary battery to which the present invention is applied. FIG. 7 is a characteristic diagram showing charge / discharge cycle characteristics of the organic electrolyte secondary battery to which the present invention is applied. 1 …… Cathode pellet 2 …… Cathode can 3 …… Separator 4 …… Gasket 5 …… Anode pellet 6 …… Anode can

Claims (1)

[Claims] 1. An organic electrolyte secondary battery comprising a cathode containing lithium, an anode containing LiMn ₂ O ₄ as an anode active material, and an organic electrolyte solution.