JPH04342966A - Secondary battery with non-aqueous solvent - Google Patents

Abstract

PURPOSE:To equip a secondary battery with excellent charge/discharge cyclic life and a high rate of capacity retention by using carboxymethylcellulose and styrene butadiene rubber as a bonding agent for a negative electrode body. CONSTITUTION:A negative electrode body 5 consisting of a carbonaceous substance as a sintered body of an organic compound and Li or a Li-based alkali metal which is borne by this carbonaceous substance, a separator 6, and a positive electrode body 7 whose active substance is Li-containing composite oxide are put one over another consolidatedly in the sequence as named, and thus a non-aqueous solvent secondary battery 1 is constructed. Carboxymethyle cellulose and styrene butadiene rubber are used as a bonding agent for the negative electrode body 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a negative electrode body for a non-aqueous solvent secondary battery using a carbon material as a negative electrode carrier.

0002

BACKGROUND OF THE INVENTION In recent years, with the development of electronic devices, there has been a demand for the development of secondary batteries that are small, lightweight, have high energy density, and can be repeatedly charged and discharged. This type of secondary battery is known to use lithium or lithium alloy as the negative electrode active material and oxides, sulfides, selenides, etc. of molybdenum, vanadium, titanium, niobium, etc. as the positive electrode active material. There is. Recently, spinel-type LiMn2O4, which has improved cycle characteristics of manganese oxide having a high energy density, and other lithium manganese oxides have been actively studied.

[0003] In these battery systems in which lithium manganese oxide is used as a positive electrode active material and lithium is used as a negative electrode active material, by repeating the cycle, the dissolution and precipitation reactions of lithium, which is the negative electrode active material, are repeated, and eventually the lithium substrate A problem arises with the formation of acicular lithium dendrite precipitates on top. Therefore, in battery systems,
Battery life is determined by the gradual collapse of the crystal structure in the positive electrode active material, the formation of dendrites on the negative electrode side, and the decomposition reaction of the solvent, and the production of batteries with a lifespan of 500 cycles or more and long-term reliability is essential. It was extremely difficult.

[0004] In order to avoid such problems, attempts have been made to create a secondary battery in which the negative electrode is made of a carbonaceous material obtained by firing various organic compounds and supports lithium or an alkali metal mainly composed of lithium. By using such a negative electrode, precipitation of lithium dendrites is prevented, cycle characteristics are improved, and safety is also improved because metallic lithium is not used.

On the other hand, electrode active materials that utilize the intercalation or doping phenomenon of layered compounds, which have a different reaction form from these manganese oxides, are attracting attention. Since these electrode active materials do not cause complex chemical reactions during charging and discharging 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 LiCoO2 is used as a positive electrode active material.
Battery systems using /LiNiO2, TiS2, and MoS2 have been proposed. However, when a carbonaceous material is used as the negative electrode active material and a metal chalcogen compound such as TiS2 or MoS2 is used as the positive electrode active material, the electromotive force is small (1.0
~1.2V). Therefore, as a positive electrode active material, 3.5V
LiCoO2, LiNiO2 exhibiting an average operating voltage of about
, LiCoxNi(1-x)O2, etc. have been studied.

[0006]

[Problems to be Solved by the Invention] However, batteries using carbonaceous materials as negative electrode carriers have a short charge/discharge cycle life and have not been able to obtain a sufficient capacity retention rate. That is, although polytetrafluoroethylene was used as a binder here, as the charge/discharge cycle progresses, lithium and the binder polytetrafluoroethylene react and decompose, significantly reducing the binding ability of the negative electrode body. lower. As a result, the conductivity between the current collector and the negative electrode carrier was impaired, and the internal resistance of the battery was significantly increased. Further, there were 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 terpolymer of ethylene-propylene-cyclic diene as a binder have a binding form that covers the negative electrode carrier, which greatly increases the internal resistance of the battery and provides sufficient characteristics. I couldn't do it.

[0007] The present invention has been made in order to improve these problems, and aims to provide a non-aqueous solvent secondary battery that has an excellent charge/discharge cycle life and a high capacity retention rate.

[0008]

[Means for Solving the Problems] The non-aqueous solvent secondary battery of the present invention has a negative electrode comprising a carbonaceous material which is a fired product of an organic compound and lithium or an alkali metal mainly composed of lithium supported on the carbonaceous material. In a non-aqueous solvent secondary battery comprising a power generation element formed by integrally laminating in this order a separator, a separator, and a positive electrode body having a lithium-containing composite oxide as a positive electrode active material, the negative electrode body It is characterized by using a mixed solvent of carboxymethyl cellulose and styrene-butadiene rubber as a binder.

The lithium-containing composite oxide used in the present invention is generally synthesized by the following method. That is, using lithium and carbon salts, nitrates, sulfates, hydroxides, etc. of one or more transition metals selected from Co, Ni, Fe, or Mn as starting materials, these are mixed in stoichiometric ratios. Obtained by mixing and baking. Note that carbonates are preferred as starting materials. The firing temperature varies somewhat depending on the starting materials, but is usually in the range of 600 to 1,000°C, preferably in the range of 600 to 800°C.

[0010] The carbonaceous material serving as the negative electrode carrier is preferably a carbonaceous material obtained by firing an organic compound in order to improve battery characteristics. The organic compound serving as a raw material for this carbonaceous material is not particularly limited as long as it is commonly used, and phenol resins, particularly novolak resins, polyacrylonitrile, and the like can be used. Moreover, as this carbonaceous material, patent application No.
Particularly preferred are those having the characteristics of an organic compound fired product as shown in No. 283086.

Carboxymethylcellulose (hereinafter referred to as CMC) used as a binder in the present invention is not particularly limited, and commercially available products can generally be used. 100-2,000
, those having an average molecular weight of 25,000 to 400,000 and using an ammonium salt as a neutralizing agent are particularly preferred. In addition, there are no particular limitations on styrene-butadiene rubber (hereinafter referred to as SBR), and general products can be used, but in particular, modified SBR latex with a polymerization rate of 60 to 95% and bound styrene of 20 to 50% should be used. is preferred.

[0012] The amount of the negative electrode carrier in the negative electrode body is 90% by weight or more of the total weight, and the amount of the binder is 0.5 to 5% by weight. Among these, the amount of CMC is 0.5 to 3% by weight, preferably 1 to 1.5% by weight, and the amount of SBR is 1 to 5% by weight, preferably 2 to 3% by weight. If the amount of the binder exceeds 5%, the internal resistance of the negative electrode will increase and the heavy load discharge capacity of the battery will be significantly reduced, which is not preferable. Also, the amount of CMC is 3
If the SBR amount exceeds 5%, the thickening effect becomes large and it becomes difficult to form a slurry as described later, which is undesirable. If the SBR amount exceeds 5%, the binding effect becomes large and causes an increase in the internal resistance of the battery, so it is not preferable. do not have.

[0013] As the electrolyte of the non-aqueous electrolyte used in the non-aqueous solvent secondary battery of the present invention, LiPF6, LiClO4
, LiBF4, LiCF3SO3, and other lithium salts. Solvents for the electrolyte include propylene carbonate (PC), ethylene carbonate (EC),
Tetrahydrofuran, 2-methyltetrahydrofuran,
γ-Butyrolactone, 1,2-dimethoxyethane (DM
E) is mentioned. These solvents can be used alone or in a mixture of two or more, and in particular, from the viewpoint of extending the charge/discharge cycle life, propylene carbonate and 1,
A mixed solvent of 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 are desirable.

[0014]

[Function] In the secondary battery of the present invention, by using CMC and SBR as the binder in the negative electrode body, there is no reaction between lithium and the binder, and as a result, even after repeated charge/discharge cycles, the current collector remains There is no increase in internal resistance of the battery caused by loss of electrical conductivity with the negative electrode carrier, and there is no possibility of the negative electrode carrier falling off due to a decrease in binding ability, and internal short circuits. Therefore,
A non-aqueous solvent secondary battery with improved charge/discharge cycle life and stable battery performance can be obtained.

[0015]

EXAMPLES The present invention will now be explained in detail by way of examples and comparative examples with reference to the drawings. Example Commercially available lithium carbonate and cobalt carbonate were weighed so that the molar ratio of Li to Co was Li/Co=1.10, and thoroughly mixed in a mortar. This mixture was placed in an alumina crucible and heat-treated at 800° C. for 6 hours in an electric furnace. The obtained baked product was cooled, then crushed again, and similarly heat-treated at 800° C. for 6 hours. Thereafter, it was thoroughly washed with distilled water to wash away unreacted alkali components. This product was confirmed to be LiCoO2 by powder X-ray method. 90% by weight of this product, acetylene black 7 as a conductive material
A positive electrode mixture in the form of a slurry was prepared by kneading 3% by weight of a terpolymer of ethylene-propylene-cyclic diene as a binder in hexane.
After coating and air-drying on a μm stainless steel substrate, pressure was applied to give a constant thickness, and a positive electrode on a plate having a positive electrode mixture layer with a thickness of 0.26 mm was manufactured.

On the other hand, the carbonaceous material serving as the negative electrode carrier is prepared by baking a novolak resin at 950°C in a nitrogen atmosphere.
Further, it was manufactured by heating to 2,000°C to carbonize it, and pulverized to obtain a powder with an average diameter of 10 μm. CMC and SBR used as binders were each dissolved in distilled water, and the weight ratio of the above-mentioned carbonaceous material and binder was 96:
4 (also, the ratio of CMC and SBR was 1:2 by weight) to produce a slurry-like negative electrode mixture. This negative electrode mixture was applied onto a stainless steel substrate with a thickness of 10 μm.
After drying, a plate-shaped negative electrode having a negative electrode mixture layer with a thickness of 0.2 mm was manufactured. Using the positive and negative electrodes thus obtained, an AA-sized non-aqueous solvent secondary battery as shown in FIG. 1 was assembled.

That is, the non-aqueous solvent secondary battery 1 has a bottomed cylindrical stainless steel container 3 with an insulator 2 disposed at the bottom and also serving as a negative electrode terminal. This container 3 houses an electrode group 4. This electrode group 4 includes a negative electrode 5, a separator 6
It has a structure in which a band-like material in which the positive electrode 7 and the positive electrode 7 are laminated in this order is spirally wound so that the negative electrode 5 is located on the outside. The separator 6 is formed from a polypropylene porous film impregnated with an electrolytic solution. Each electrolytic solution contains 0.5 molar concentration of lithium hexafluorophosphate (LiPF6) as an electrolyte in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane (volume ratio 50:50). An insulating plate 8 with an opening at the center is disposed above the electrode group 4 in the container 3. An insulating sealing body 9 is hermetically caulked to the container 3 at the upper opening of the container 3. Fixed. A positive electrode terminal 10 is fitted into the central opening of the insulating plate 8 . This positive terminal 10
is connected to the above-mentioned positive electrode 7 via a positive electrode lead 11. Note that the negative electrode 5 is connected to the container 3, which is a negative electrode terminal, via a negative electrode 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 the binder for the negative electrode.

Comparative Example 2 A non-aqueous solvent secondary battery was assembled in the same manner as in Example except that a terpolymer of ethylene-propylene-cyclic diene was used as the binder for the negative electrode. The three types of non-aqueous solvent secondary batteries of Example, Comparative Examples 1 and 2 assembled in this manner were tested at a constant temperature of 20° C. and a constant current of 100 mA.
Charging and discharging evaluation was performed in the voltage range from 3V to 3.0V. The results are shown in FIG. In the figure, A is the battery of this example, and B is the battery of this example.
is the discharge capacity retention rate curve of the battery of Comparative Example 1, and C is the discharge capacity retention rate curve of the battery of Comparative Example 2. As is clear from FIG. 2, the nonaqueous solvent secondary battery of this example exhibits a higher capacity retention rate even after repeated charge/discharge cycles than the batteries of Comparative Examples 1 and 2, and has excellent performance. I understand. In addition, when the battery that had been evaluated was disassembled and the surface condition of the negative electrode was observed, the electrode of the battery of Comparative Example 1 was crumbled, which was thought to be due to the reaction and decomposition of the lithium and the binder. is,
In the battery of Comparative Example 2, a considerable amount of lithium was deposited on the electrode surface.

[0020]

Effects of the Invention As described in detail above, the non-aqueous solvent secondary battery of the present invention uses a carbonaceous material for the negative electrode support, a lithium-containing composite oxide as the positive electrode active material, and By using CMC and SBR as adhesives, it is possible to eliminate the reaction and decomposition of lithium and the binder during charge/discharge cycles, and it also improves the falling off of the negative electrode carrier and internal short circuits that occur due to the causes described above. be able to. Therefore, it is possible to obtain an excellent non-aqueous solvent secondary battery with improved capacity retention and long life.

[Brief explanation of the drawing]

FIG. 1 is a half-mounted sectional view of a non-aqueous solvent secondary battery that is an example of the present invention.

FIG. 2: Example battery A of the present invention, comparative example 1 battery B,
2 is a characteristic diagram of the number of charge/discharge cycles and the discharge capacity retention rate of Comparative Example 2 Battery C. FIG.

[Explanation of symbols]

1...Nonaqueous solvent secondary battery 4...Electrode group 5...Negative electrode

Claims (1)

[Claims] 1. A negative electrode body comprising a carbonaceous material which is a fired body of an organic compound and lithium or an alkali metal mainly composed of lithium supported on the carbonaceous material, and a separator;
In a non-aqueous solvent secondary battery comprising a power generation element formed by integrally laminating in this order a positive electrode body having a lithium-containing composite oxide as a positive electrode active material, as a binder for the negative electrode body,
A non-aqueous solvent secondary battery characterized by using carboxymethyl cellulose and styrene-butadiene rubber.