JPH08306389A - Lithium battery - Google Patents

Abstract

PURPOSE: To restrict inner short-circuitting by dendrite of lithium in a lithium polymer secondary battery. CONSTITUTION: A thin polymer electrolyte layer 2 is disposed between a positive electrode 1 and a lithium negative electrode 3 to be laminated with them. Roughness of polymer components in electrolyte is eliminated by lamination, so the growth of dendrite can be restricted, thereby a lithium polymer secondary battery of excellent safety without having inner short-circuitting can thus be provided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a lithium battery using a polymer electrolyte.

[0002]

2. Description of the Related Art In a lithium secondary battery using metallic lithium, it is inevitable to avoid safety problems such as internal short circuit due to dendrite deposition of lithium during charging and heat generation / ignition of the battery. The polymer electrolyte suppresses the generation of dendrites due to its solid nature,
It has the potential to realize a highly safe lithium secondary battery. Polymers are also considered to be applied to large lithium batteries because they have advantages such as flexibility in shape and the ability to easily form a large-area sheet.

However, the ionic conductivity of the polymer electrolyte is at most about 10 ⁻⁴ S / cm at room temperature, and the electrolyte solution is placed in the polymer matrix for the purpose of ensuring the same ionic conductivity as the electrolyte solution. The development and research of gel-type polymer electrolytes impregnated with are active.

A gel-like polymer electrolyte is disclosed in, for example, Japanese Patent Laid-Open No.
It is manufactured by the method described in JP-A-109310.
Photocrosslinkable polymer polyethylene glycol diacrylate 10% by weight, photocrosslinkable monomer trimethylolpropane ethoxylated triacrylate 1% by weight, electrolyte solvent 65% by weight propylene carbonate, polyethylene oxide 10% by weight, electrolyte A polymer solution and a monomer are polymerized and cured by applying a mixed solution of 14% by weight of LiCF ₃ SO ₃ which is a salt on a flat plate, and irradiating the plate with an electron beam to obtain a transparent and flexible film-like polymer electrolyte. .

In the above electrolyte, polyethylene glycol diacrylate and trimethylolpropane ethoxylated triacrylate constitute the polymer matrix portion, and the other components correspond to the electrolytic solution, but ionic conduction takes place through the electrolytic solution phase. . The ionic conductivity of this polymer electrolyte is 2 × 10 ⁻³ S / cm at room temperature, which shows a high ionic conductivity comparable to that of an electrolytic solution.

[0006]

However, in the above method for producing a polymer electrolyte, the reaction mixture solution cannot be stirred, so that a non-uniform crosslinking reaction occurs in the electrolyte and the polymer matrix becomes coarse and dense. In the rough portion of the polymer matrix, the electrolytic solution phase occupies the majority, current concentrates, and the mechanical strength is weak. For this reason, when the rough portion of the polymer matrix is in contact with the negative electrode, an electrochemical environment where lithium is likely to be deposited locally is formed, and the deposition of lithium dendrite is induced.

As a result, an internal short circuit occurs due to the lithium dendrite when the battery is charged, which causes heat generation / ignition and a decrease in the number of charge / discharge cycles due to the internal short circuit as in the case of the electrolyte system battery.

As described above, from the viewpoint of ensuring the reliability and safety of the battery, the conventional polymer electrolyte has not yet taken advantage of the solid material, and the deposition / growth of lithium dendrite is suppressed. The development of an electrolyte that can do this has been earnestly desired. The present invention solves such a problem, and an object thereof is to propose a novel lithium polymer secondary battery.

[0009]

In order to achieve the above-mentioned object, in the present invention, a plurality of polymer electrolyte layers are superposed and laminated to eliminate a rough portion of a polymer matrix.

[0010]

[Function] The whole electrolyte is made fine by stacking a plurality of electrolyte layers even if there is a polymer density in one electrolyte layer so that the whole mesh becomes very fine when several meshes are stacked. Then, the density of the polymer disappears. Therefore, when the electrolyte of the present invention is applied to a lithium polymer secondary battery, lithium dendrite does not penetrate the electrolyte layer,
It is possible to solve the problem of internal short circuit which is a conventional problem.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 FIG. 1 is a vertical sectional view of a lithium polymer secondary battery of the present invention. In the figure, 1 is a polymer electrolyte composite positive electrode. This positive electrode was manufactured by the following method. 20% by weight of thermosetting monomer and thermal polymerization initiator 1
A paste-like positive electrode mixture prepared by mixing an active material and a conductive agent is applied to an aluminum foil in a liquid containing 1% by weight and 80% by weight of a non-aqueous electrolyte. By subjecting this to heat treatment at 100 ° C. for 1 hour, the above-mentioned monomer is polymerized and cured, and a positive electrode sheet in which a polymer electrolyte is composited is obtained.

In this case, polyethylene glycol diacrylate is used as the thermosetting monomer, azobisisobutyronitrile is used as the thermal polymerization initiator, and LiPF is used as the non-aqueous electrolyte solution in a 1: 1 equal volume mixed solvent of propylene carbonate and ethylene carbonate. A liquid in which ₆ was dissolved at 1 mol / liter was used. In addition, V ₆ O _{13 + Y} (0 ≦ Y ≦ 0.
16), acetylene black was used as the conductive agent.

Reference numeral 2 is a polymer electrolyte layer in which five electrolytes having a film thickness of 10 μm are laminated. Each of the individual electrolytes is a gel-like polymer electrolyte layer obtained by irradiating a liquid containing an ultraviolet-curable monomer, a photopolymerization initiator, and a nonaqueous electrolytic solution with ultraviolet rays. Polyethylene oxide diacrylate was used as the ultraviolet curable monomer, and benzyl dimethyl ketal (0.1% by weight) was used as the photopolymerization initiator. Here, the weight ratio of the ultraviolet curable monomer to the non-aqueous electrolyte is 2
It is 0:80.

As a stacking method, the operations of synthesizing individual electrolytes separately, stacking them, forming an electrolyte layer on metallic lithium, and curing and forming the next electrolyte layer on this electrolyte are repeated. There is a way. The latter method of directly forming an electrolyte on metallic lithium is excellent in terms of the bondability with the electrode surface, and in this example, the electrolyte layer produced by the latter method was used.

A thin layer of electrolyte was also formed on the positive electrode 1 by ultraviolet curing, and a battery was constructed with the above-mentioned laminated electrolyte and metallic lithium electrode.

In this embodiment, a nonaqueous electrolytic solution prepared by dissolving LiPF ₆ as a solute at 1 mol / liter in a 1: 1 equal volume mixed solvent of propylene carbonate and ethylene carbonate was used as the electrolytic solution.

[Example 2] A lithium-polymer secondary battery was produced in the same manner as in Example 1 except that the weight ratio of the UV-curable monomer to the non-aqueous electrolyte was 40:60.

[Embodiment 3] Two electrolyte layers having a film thickness of 50 μm are provided.
A lithium-polymer secondary battery was produced in the same manner as in (Example 1) except that the sheets were laminated.

Comparative Example The same lithium as in Example 1 except that the electrolyte was a single layer having a thickness of 50 μm.
A polymer secondary battery was produced.

These batteries were charged and discharged at current densities of 0.25 mA / cm ² and 0.5 mA / cm ² in a voltage range of 3.3 to 1.8 V, and their cycle characteristics were evaluated.

[0022]

[Table 1]

Table 1 shows the test results of the prototype battery. In a test with a charge / discharge current density of 0.25 mA / cm ² , 195 cycles in (Example 1), (Example 2)
Showed good cycle characteristics of 210 cycles.
In the case of (Example 3), the characteristics were deteriorated to 80 cycles, but in the case of the electrolyte having a single layer (Comparative example), an internal short circuit occurred at 40 cycles. You can see that In the test in which the charge / discharge current density was 0.5 mA / cm ² , in Example 1, charge / discharge was possible up to 160 cycles. In (Example 2), discharge at this current density was not possible because the ionic conductivity of the electrolyte was low. It is better that the amount of the electrolytic solution in the electrolyte layer is small, but if it is less than 60 wt%, the discharge characteristics are deteriorated. However, since 60 wt% was the best at the low rate discharge, it is preferably 60 wt% or more.

From the above results, it was possible to prevent the internal short circuit due to the dendrite deposition of lithium in the laminated polymer electrolyte and to improve the charge / discharge cycle life of the battery.

In this embodiment, polyethylene oxide diacrylate was used as the thermosetting monomer and the ultraviolet curable monomer, but other monomer such as polyethylene oxide dimethacrylate may be used.

LiPF ₆ was used as the solute of the non-aqueous electrolyte, which was LiCF ₃ SO ₃ , LiClO ₄ , Li.
Other lithium salts such as N (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , and LiBF ₄ may be used.

Although azobisisobutyronitrile was used as the thermal polymerization initiator, other initiators such as benzoyl peroxide and acetyl peroxide may be used.

Benzyl dimethyl ketal was used as the photopolymerization initiator, which was benzoin isopropyl ether, benzophenone, dimethylaminoacetophenone, 4,4'-bis (dimethylamino) benzophenone, 2-chlorothioxanthone, (C ₆ H ₅ ) ₂ IPF ₆ ,
_{(CH 3) 2 N (C} 6 H 5) N 2 PF 6, (C 6 H 5) 3 SPF 6
Other initiators may also be used.

The active material is V ₆ O _{13 + Y} (0≤Y≤
0.16) was used, which was LiCoO ₂ , LiNi
O ₂ , V ₂ O ₅ , LiMnO ₂ , Li _x Mn ₂ O ₄ (0.1 <
Other active materials such as x <0.5) may be used.

Although acetylene black was used as the conductive agent, other carbon such as graphite or a mixture thereof may be used.

Further, metallic lithium was used for the negative electrode for the lithium battery, which is a compound containing lithium, for example, L.
It may be an alloy such as i-Al or C _x Li (lithiated carbon or graphite).

[0032]

As described above, according to the present invention, by using the polymer electrolyte layer laminated on the electrolyte of the lithium battery,
An internal short circuit due to lithium dendrites can be suppressed, and a highly reliable lithium polymer secondary battery can be provided.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a lithium polymer secondary battery of the present invention.

[Explanation of symbols]

 1 Polymer Electrolyte Composite Positive Electrode 2 Laminated Polymer Electrolyte Layer 3 Metal Lithium Negative Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuo Eda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A lithium battery characterized in that a plurality of polymer electrolyte layers are superposed and arranged between a positive electrode and a negative electrode. 2. The lithium battery according to claim 1, wherein the thickness of each layer of the polymer electrolyte is 10 μm or more and 50 μm or less. 3. The lithium battery according to claim 1, wherein a gel electrolyte obtained by impregnating a polymer electrolyte with a non-aqueous electrolyte is used. 4. The amount of non-aqueous electrolyte in the gel electrolyte is 60 wt%.
The lithium battery according to claim 3, which is the above. 5. The lithium battery according to claim 1, wherein the negative electrode is lithium metal. 6. A positive electrode active material comprising V ₆ O _{13 + Y} (0 ≦ Y ≦ 0.1
6. The lithium battery according to claim 1, which uses 6).