JP3144833B2 - Non-aqueous solvent secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous solvent secondary battery using a carbonaceous material as a negative electrode carrier, and more particularly to an improved negative electrode.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. As this type of secondary battery, those using lithium or a lithium alloy as a negative electrode active material, and using oxides such as molybdenum, vanadium, titanium, and niobium, sulfides, and selenides as a positive electrode active material are known. I have.

Recently, studies have been actively conducted on spinel-type LiMn ₂ O ₄ having improved and improved cycle characteristics of a manganese oxide having a high energy density and other lithium manganese oxides.

On the other hand, for the positive electrode, an electrode active material utilizing intercalation or doping of a layered compound having a different reaction form from these manganese oxides has attracted attention. Since these electrode active materials do not cause complicated chemical reactions during charge and discharge reactions, they are expected to have extremely excellent charge / discharge cycle characteristics. Among them, a carbonaceous material is used as a negative electrode carrier, and Li is used as a positive electrode active material.
Battery systems using CoO ₂ / LiNiO ₂ , TiS ₂ , and MoS ₂ have been proposed.

In a battery system in which these oxides, sulfides, and selenides are used as a positive electrode active material and lithium is used as a negative electrode active material, the dissolution / precipitation reaction of lithium as the negative electrode active material is repeated by repeating the cycle. Eventually, a problem arises in that needle-like lithium dendrite deposits are formed on the lithium metal. Therefore, in the battery system, the battery structure gradually collapses with each repetition of charge / discharge in the positive electrode active material, lithium dendrite is generated on the negative electrode side, and the solvent is decomposed by the lithium deposited on the negative electrode to cause a solvent decomposition reaction. Life is specified, 500
It has been very difficult to manufacture a battery having a life of more than a cycle and a long-term reliability.

Further, in order to reduce lithium dendrite generated at the negative electrode during charging, studies are being made on using an alloy of lithium with a metal such as aluminum, lead, or silicon as the negative electrode active material. However, even in this case, when charge and discharge are repeated, powdering of the alloy occurs, and the battery life is not significantly increased. In order to avoid such a problem, a secondary battery in which a negative electrode is formed by supporting lithium or an alkali metal mainly composed of lithium on a carbonaceous material obtained by firing various organic compounds has been attempted. By using such a negative electrode, precipitation of lithium dendrite is prevented and cycle characteristics are improved, and safety is also improved because metal lithium is not used.

However, when a carbonaceous material is used as the negative electrode active material, when a metal chalcogen compound such as TiS ₂ or MoS ₂ is used as the positive electrode active material, the electromotive force is small (from 1.0 to 1.0).
1.2V). Therefore, as the positive electrode active material, LiCoO ₂ , LiNiO ₂ , which exhibits an average operating voltage of about 3.5 V,
LiCo _x Ni _(1-x) O _{2 and the} like have been studied.

[0008] These positive and negative electrode active material materials are usually
When used as a battery electrode, a conductive agent is used in such a manner that the reaction of the active material can proceed effectively, and a binder is used in such a manner as to maintain the shape of the electrode. For example, in a cylindrical battery, a strip-shaped electrode in which a positive electrode, a separator, and a negative electrode are formed in a spiral shape is used. In this case, the strip-shaped electrode is formed on a substrate made of stainless steel, nickel, titanium, copper, aluminum, or the like or an alloy of these metals, by applying a slurry made of a mixture of an active material, a conductive agent, a binder, and water or an organic solvent. It is made by coating, drying and rolling. It is desirable that the slurry used at this time be uniformly dispersed without any lumps.

[0009]

However, a battery using a carbonaceous material as a negative electrode carrier has a short charge-discharge cycle life and cannot provide a sufficient capacity retention rate. That is, when conventionally used polytetrafluoroethylene is used as a binder for a battery electrode, as the charge / discharge cycle progresses, lithium reacts with polytetrafluoroethylene, which is a binder, to form polytetrafluoroethylene. Decomposes and greatly reduces the binding ability of the negative electrode body. As a result, the conductivity between the current collector and the negative electrode carrier is impaired, and the internal resistance of the battery is greatly increased. There were also problems such as falling off of the negative electrode carrier and internal short circuit due to a decrease in binding ability. In addition, those using a conventionally used terpolymer of ethylene-propylene-cyclic diene, which is a binder, take a binding form that covers the negative electrode carrier, so that the internal resistance of the battery is significantly increased. And sufficient characteristics could not be obtained.

The present invention has been made to solve such problems, and an object thereof is to provide a nonaqueous solvent secondary battery having high charge / discharge efficiency and excellent charge / discharge cycle life.

[0011]

That is, a non-aqueous solvent secondary battery according to the present invention comprises a negative electrode made of lithium or a carbonaceous material carrying lithium-based alkali metal, a separator, and a lithium-containing composite oxide. In a non-aqueous solvent secondary battery including a power generating element obtained by integrally laminating a positive electrode body having a positive electrode active material in this order, carboxymethyl cellulose or a salt thereof and fluorine as a binder for the negative electrode body It is characterized by using rubber.

The lithium-containing composite oxide used in the present invention is generally synthesized by the following method. That is, lithium and one or more transition metal carbonates, nitrates, sulfates, hydroxides, etc. selected from Co, Ni, Fe or Mn are used as starting materials and mixed at a stoichiometric ratio. And fired. In addition, carbonate is preferable as a starting material. The firing temperature varies somewhat depending on the starting materials, but is usually in the temperature range of 600 to 1,000 ° C, preferably in the range of 600 to 800 ° C.

As the carbonaceous material as the negative electrode carrier, a carbonaceous material obtained by firing an organic compound is preferably used in order to improve battery characteristics. The organic compound serving as a raw material of the carbonaceous material is not particularly limited as long as it is a commonly used one, and a phenol resin, particularly a novolak resin, and polyacrylonitrile can be used. The carbonaceous material includes hydrogen /
The atomic ratio of carbon is less than 0.15, the spacing (d ₀₀₂ ) of the (002) plane by X-ray wide angle diffraction is 3.37 ° or more, and the crystallite size (Lc) in the c-axis direction is 150 °.
An organic compound fired body having the following crystal characteristics is particularly preferred.

A feature of the present invention is that carboxymethylcellulose or a salt thereof (hereinafter, referred to as CMC) and fluororubber are used as a binder for the negative electrode.

The CMC is not particularly limited, and carboxymethylcellulose, its sodium salt, potassium salt, ammonium salt and a mixture thereof can be used. Degree 100-2,000, average molecular weight 25,000-40
000 is preferred, and ammonium salts are particularly preferred.

There is no particular limitation on the fluororubber, and a copolymer of ethylene tetrafluoride and ethylene difluoride,
Copolymers of ethylene tetrafluoride and propylene hexafluoride, poly (trifluorochloroethylene) are used, and commercially available products can be used. Among them, copolymers of ethylene tetrafluoride and ethylene difluoride are used. preferable.

The amount of the negative electrode carrier in the negative electrode body is preferably 90% by weight or more of the whole, and the amount of the binder is 0.5 to 10% by weight.
5.0% by weight is preferred. Of which CMC amount is 0.5
-3.0 wt% is preferable, and 1.0-1.5 wt% is more preferable. The amount of fluoro rubber is 1.0% by weight or more,
It is preferably less than 5.0% by weight, more preferably 2.0 to 3.0% by weight. If the amount of the binder exceeds 5.0% by weight, the internal resistance of the negative electrode increases, and the heavy load discharging capability of the battery is unpreferably reduced. On the other hand, if the amount of CMC exceeds 3.0% by weight, the thickening effect becomes large, and it is not preferable because it is difficult to form a slurry as described later. ,
It is not preferable because it causes an increase in the internal resistance of the battery.

As the electrolyte of the non-aqueous electrolyte used in the non-aqueous solvent secondary battery of the present invention, LiPF ₆ , LiClO 2
₄ , lithium salts such as LiBF ₄ and LiCF ₃ SO ₃ . Examples of the solvent for the electrolyte include propylene carbonate, ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,2-dimethoxyethane, and the like. These solvents can be used alone or in a mixture of two or more, and particularly from the viewpoint of extending the charge / discharge cycle life,
A mixed solvent of propylene carbonate and 1,2-dimethoxyethane, a mixed solvent of ethylene carbonate and 2-methyltetrahydrofuran, a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane, and a mixed solvent of propylene carbonate and ethylene carbonate desirable.

[0019]

The nonaqueous solvent secondary battery of the present invention uses a carbonaceous material for the negative electrode carrier, a lithium-containing composite oxide as the positive electrode active material, and CMC and fluororubber as binders for the negative electrode body. By using the compound, it is possible to prevent the reaction between the lithium and the binder and the decomposition of the binder due to the progress of the charge / discharge cycle. As a result, it is possible to prevent the negative electrode carrier from dropping off and an internal short circuit caused by this.

According to the present invention, it is possible to obtain an excellent non-aqueous solvent secondary battery having an improved capacity retention ratio, an improved charge / discharge cycle life, and a stable battery performance.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings by way of examples and comparative examples. The present invention is not limited by the embodiments.

Example Commercially available lithium carbonate and cobalt carbonate were weighed so that the molar ratio of Li to Co became Li / Co = 1.10, and thoroughly mixed using a mortar. This mixture was placed in an alumina crucible and heat-treated at 800 ° C. for 6 hours in an electric furnace. After the obtained fired product was cooled, it was pulverized again, and similarly heated at 800 ° C. for 6 hours. Thereafter, the resultant was sufficiently washed with distilled water to wash away unreacted alkali components. The product was identified as LiCoO ₂ by powder X-ray method. 90% by weight of this product, 7% by weight of acetylene black as a conductive agent, and 3% by weight of a terpolymer of ethylene-propylene-cyclic diene as a binder are kneaded in hexane to form a slurry-like positive electrode mixture. Was prepared. This positive electrode mixture was applied on a stainless steel substrate having a thickness of 10 μm, air-dried, and then pressurized to a constant thickness, followed by producing a plate-like positive electrode having a 0.26 mm thick positive electrode mixture layer.

On the other hand, the carbonaceous material as the negative electrode carrier is obtained by firing a novolak resin at 950 ° C. in a nitrogen atmosphere.
Further, it was obtained by heating to 2,000 ° C. to carbonize and pulverizing it into a powder having an average particle size of 10 μm.

CMC and fluorine rubber were used as a binder for the negative electrode. That is, CMC used had a degree of etherification of 1, an average degree of polymerization of 1,000, and an average molecular weight of 50,000, and was neutralized into an ammonium salt type. The fluororubber used was a copolymer of ethylene tetrafluoride and ethylene difluoride. The CMC was previously dissolved in distilled water, and the fluororubber was dispersed and mixed in an ester solvent. The slurry was dispersed such that the ratio of the total of the carbonaceous material and the binder was 96: 4 by weight, and the ratio of CMC and fluororubber in the binder was 1: 2 by weight. A negative electrode mixture was produced.

This negative electrode mixture was coated on a stainless steel substrate having a thickness of 10 μm and dried to produce a negative electrode on a plate having a negative electrode mixture layer having a thickness of 0.2 mm.

Using the positive and negative electrodes thus obtained, a non-aqueous solvent secondary battery of AA size as shown in FIG. 1 was assembled. That is, the non-aqueous solvent secondary battery 1
Has a bottomed cylindrical stainless steel container 3 in which an insulator 2 is disposed at the bottom and also serves as a negative electrode terminal. In this container 3,
The electrode group 4 is housed. The electrode group 4 includes a negative electrode 5,
The belt-like material in which the separator 6 and the positive electrode 7 are laminated in this order is wound in a spiral shape so that the negative electrode 5 is located outside. The separator 6 is formed from a porous polypropylene film impregnated with an electrolytic solution. Each electrolytic solution was composed of propylene carbonate and 1,2-
Mixed solvent with dimethoxyethane (volume ratio 50:50)
And lithium hexafluorophosphate (LiPF ₆ ) as electrolyte
Is contained at 0.5 molar concentration.

An insulating plate 8 having an open center is arranged above the electrode group 4 in the container 3. The container 3
An insulating sealing body 9 is air-tightly fixed to the container 3 at the upper opening of the container 3. In the central opening of the insulating plate 8,
The positive electrode terminal 10 is fitted. This positive terminal 10 is
The positive electrode 7 is connected to the positive electrode 7 via a positive electrode lead 11. The negative electrode 5 is connected to the container 3 as a negative terminal via a negative lead (not shown).

Comparative Example 1 A non-aqueous solvent secondary battery was assembled in the same manner as in Example except that polytetrafluoroethylene was used as a binder for the negative electrode.

Comparative Example 2 A non-aqueous solvent secondary battery having the same structure as that of the example except that a terpolymer of ethylene-propylene-cyclic diene was used as a binder for the negative electrode was assembled.

With respect to the three types of nonaqueous solvent secondary batteries of the embodiment and Comparative Examples 1 and 2 assembled in this manner, from 4.3 V to 3.0 V at a constant temperature of 20 ° C. and a constant current of 100 mA.
The charge / discharge evaluation in the voltage range up to was performed. Figure 2 shows the result.
Shown in 2A is a discharge capacity retention rate curve of the battery of the example according to the present invention, B is a battery of Comparative Example 1, and C is a discharge capacity retention rate curve of the battery of Comparative Example 2.

As is apparent from FIG. 2, the non-aqueous solvent secondary battery of the example shows a higher capacity retention ratio even after repeated charge / discharge cycles than the battery of the comparative example, and has excellent performance. are doing. Furthermore, when the surface state of the negative electrode was observed by disassembling the battery after the evaluation, the electrode of the battery of Comparative Example 1 was in a state where the carbon material was easily dropped from the substrate,
This is probably because lithium and the binder reacted to decompose the binder. In the battery of Comparative Example 2, considerable lithium was deposited on the electrode surface.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a non-aqueous solvent secondary battery of an example.

FIG. 2 is a characteristic diagram showing a change in a discharge capacity retention ratio with respect to the number of charge / discharge cycles in non-aqueous solvent secondary batteries of Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-aqueous solvent secondary battery 2 Insulator 3 Stainless steel container 4 Electrode group 5 Negative electrode 6 Separator 7 Positive electrode 8 Insulating plate 9 Insulating sealing plate 10 Positive terminal 11 Positive electrode lead A 〃 〃 C Comparative Example 2 〃 〃

Continuation of front page (72) Inventor Yoji Ishihara 3-4-1-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (56) References JP-A-57-96471 (JP, A) JP-A-2- 33868 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/62 H01M 10/40

Claims (1)

(57) [Claims] 1. An anode body made of a carbonaceous material carrying lithium or an alkali metal mainly composed of lithium, a separator, and a cathode body made of a lithium-containing composite oxide as a cathode active material are integrally formed in this order. A non-aqueous solvent secondary battery comprising a power generating element laminated on a non-aqueous solvent secondary battery, wherein carboxymethyl cellulose or a salt thereof and fluororubber are used as a binder for the negative electrode body.