JPH04370661A - Secondary battery with nonaqueous solvent - Google Patents

Abstract

PURPOSE:To accomplish a secondary battery with nonaqueous solvent, which excels in the charge/discharge cycle life and has a high rate of capacity maintenance. CONSTITUTION:A negative electrode 5 is formed from a carbonaceous material bearing Li or alkali metal containing Li as major component. and the power generating element of a non-aqueous solvent secondary battery 1 is constructed by laminating this negative electrode 5, a separator 6, and a positive electrode 7 using Li-containing composite oxide as pos. electrode active substance in the sequence as named fast in consolidation. This secondary battery uses polyacrylic acid or its salt and acrylonitrile butadiene rubber as a binder for the negative electrode 5.

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 thereof.

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 LiMn2 O4 and other lithium manganese oxides, which have improved cycle characteristics of manganese oxides having high energy density, have been actively studied.

[0004] In a battery system in which lithium manganese oxide, sulfide or selenide is used as a positive electrode active material and lithium is used as a negative electrode active material, the dissolution/precipitation reaction of lithium, which is the negative electrode active material, occurs through repeated cycles. The problem is repeated and eventually forms needle-like lithium dendrite precipitates on the lithium metal. Therefore, in battery systems, as the crystal structure of the positive electrode active material gradually progresses with each repeated charge and discharge, the formation of lithium dendrites on the negative electrode side and the decomposition reaction of the solvent caused by the lithium precipitated on the negative electrode cause the battery to collapse. The lifespan is regulated, and it has been extremely difficult to manufacture batteries with a lifespan of 500 cycles or more and long-term reliability.

[0005] In order to avoid such problems, attempts have been made to create 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. By using such a negative electrode, the precipitation of lithium dendrites is prevented and cycle characteristics are improved, and since metallic lithium is not used, safety is also improved.

On the other hand, for positive electrodes, 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 Li is used as a positive electrode active material.
CoO2 /LiNiO2, TiS2, MoS2
A battery system using this has 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, LiNiO exhibiting an average operating voltage of about
2, LiCox Ni(1-x)O2, etc. have been studied.

[0008]

[Problems to be Solved by the Invention] However, batteries using a carbonaceous material as a negative electrode carrier have a short charge/discharge cycle life, and therefore, it has not been possible to ensure sufficient capacity and a sufficient number of recycles. In other words, when polytetrafluoroethylene, which has traditionally been used as a binder for battery electrodes, is used, as the charge/discharge cycle progresses, lithium and the binder polytetrafluoroethylene react to form polytetrafluoroethylene. decomposes, significantly reducing 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 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.

[0009]Also, a binder using a ternary copolymer of ethylene-propylene-cyclic diene has been proposed, but since it takes the form of a binder that covers the negative electrode carrier,
This significantly increases the internal resistance of the battery, making it impossible to obtain sufficient characteristics when discharging large currents.

[0010] The present invention was made to improve these problems, and aims to provide a nonaqueous solvent secondary battery that has high charge/discharge efficiency, excellent charge/discharge cycle life, and high capacity retention rate. It is something.

[0011]

[Means for Solving the Problems] That is, the non-aqueous solvent secondary battery of the present invention comprises a negative electrode body made of a carbonaceous material supporting lithium or an alkali metal mainly composed of lithium, a separator, and a lithium-containing composite oxide. In a non-aqueous solvent secondary battery equipped with a power generation element formed by integrally laminating in this order a positive electrode body having a positive electrode active material, polyacrylic acid or its salt and It is characterized by using acrylonitrile-butadiene rubber.

The lithium-containing composite oxide used in the present invention is generally synthesized by the following method. That is, lithium and carbonate, nitrate, sulfate, hydroxide, etc. of one or more transition metals selected from Co, Ni, Fe, or Mn are used as starting materials, and these are mixed in a stoichiometric ratio. It is obtained by baking. Note that carbonate is preferred as the starting material. 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.

[0013] 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 novolac resins, polyacrylonitrile, and the like can be used. In addition, this carbonaceous material includes hydrogen/
The atomic ratio of carbon is less than 0.15, and the interplanar spacing (d002) of the (002) plane by X-ray wide-angle diffraction method is 3.37 Å.
above, and the crystallite size (Lc) in the c-axis direction is 150
A fired organic compound having crystal properties of Å or less is particularly preferred.

The characteristic feature of the present invention is that polyacrylic acid or its salt (hereinafter referred to as PAA) is used as a binder for the negative electrode.
) and acrylonitrile-butadiene rubber (hereinafter referred to as NBR).

The PAA used in the present invention is not particularly limited, and polyacrylic acid, its sodium salt, potassium salt, ammonium salt, and mixtures thereof can be used. Although common commercially available products can be used, a 10-30% by weight aqueous solution in salt form is particularly preferred.

[0016] NBR is not particularly limited,
Polymerization rate 60-95%, acrylonitrile unit content 6
Those with a content of 0% or less are preferable, and among them, carboxy-modified ones are particularly preferable. General commercially available products can be used, and it is preferable to use them in latex form.

[0017] The amount of the negative electrode carrier in the negative electrode body is preferably 90% by weight or more of the total weight, and the amount of the binder is 0.5 to 0.5% by weight.
5.0% by weight is preferred. Of these, the amount of PAA is 0.5
-3.0 weight% is preferable, and 1.0-1.5 weight% is more preferable. The amount of NBR is 1.0% by weight or more, 5.0% by weight
Less than % by weight is preferred, and 2.0-3.0% by weight is more preferred. If the amount of the binder exceeds 5.0% by weight, it is not preferable because the internal resistance of the negative electrode increases and the heavy load discharge capacity of the battery is significantly reduced. Also, the amount of PAA is 3.0
If it exceeds 5% by weight, it is not preferable because the thickening effect becomes large and it becomes difficult to form a slurry, which will be described later.
If it is 0% by weight or more, the binding effect becomes large and causes an increase in the internal resistance of the battery, which is not preferable.

[0018] As the electrolyte of the non-aqueous electrolyte used in the non-aqueous solvent secondary battery of the present invention, LiPF6, LiClO
4, LiBF4, LiCF3SO3, and other lithium salts. Examples of the solvent for the electrolytic solution include propylene carbonate, ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, and 1,2-dimethoxyethane. These solvents can be used singly or in a mixture of two or more, and from the viewpoint of prolonging the charge/discharge cycle life, mixed solvents of propylene carbonate and 1,2-dimethoxyethane, ethylene carbonate and 2-methyltetrahydrofuran are particularly preferred. A mixed solvent of ethylene carbonate and 1,2-dimethoxyethane, a mixed solvent of propylene carbonate and ethylene carbonate are desirable.

[0019]

Effects of the Invention The non-aqueous 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 PAA and NBR as the binder for the negative electrode body. By using it, it is possible to prevent the reaction between lithium and the binder as the charge/discharge cycle progresses and the resulting decomposition of the binder. As a result, even if charge/discharge cycles are repeated, the conductivity between the current collector and the negative electrode carrier is not impaired, and the resulting drop-off of the negative electrode carrier and internal short circuit can be prevented.

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

[0021]

EXAMPLES The present invention will now be explained in detail by way of examples and comparative examples with reference to the drawings. Note that the present invention is not limited to the examples.

Example Commercially available lithium carbonate and cobalt carbonate were weighed so that the molar ratio of Li and Co was 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 cooling the obtained baked product, it was ground again and similarly heat-treated at 800° C. for 6 hours. Thereafter, it was thoroughly washed with distilled water to wash away unreacted alkaline components. The product was confirmed to be LiCoO2 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 an ethylene-propylene-cyclic diene terpolymer as a binder are kneaded in hexane to form a positive electrode mixture in the form of a slurry. was prepared. After applying this positive electrode mixture onto a 10 μm thick stainless steel substrate and air-drying it,
The mixture was pressurized to a constant thickness, and then a plate-shaped positive electrode 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 heated to 2,000°C to carbonize it and pulverized to obtain a powder with an average particle size of 10 μm.

PAA and NBR were used as the binder for the negative electrode. In other words, PAA is made by neutralizing with ammonia to make ammonium salt, and NBR is made by neutralizing acrylonitrile with 3
The content of 0 to 40% by weight was used. PAA is dissolved in distilled water in advance, NBR is dispersed in water, and the ratio of the total of the above carbonaceous material and binder is 96% by weight.
:4, and in the binder, PAA and NBR were dispersed in a carbonaceous material so that the ratio by weight was 1:2 to produce a slurry-like negative electrode mixture.

This negative electrode mixture was coated on a stainless steel substrate with a thickness of 10 μm and dried to produce a negative electrode on a plate having a negative electrode mixture layer with 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 is
It has a bottomed cylindrical stainless steel container 3 with an insulator 2 disposed at the bottom and serving also as a negative electrode terminal. This container 3 houses an electrode group 4. This electrode group 4 has a structure in which a band-like material in which a negative electrode 5, a separator 6, and a 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 was made by adding lithium hexafluorophosphate (LiPF6) as an electrolyte to a mixed solvent of propylene carbonate and 1,2-dimethoxyethane (volume ratio 50:50).
．． Contains 5 molar concentrations.

An insulating plate 8 with an open center is arranged above the electrode group 4 in the container 3. Said container 3
An insulating sealing body 9 is hermetically caulked and fixed to the container 3 at the upper opening of the container 3 . In the central opening of this insulating plate 8,
The positive electrode terminal 10 is fitted. This positive electrode terminal 10 is
It 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 an ethylene-propylene-cyclic diene ternary copolymer was used as the negative electrode binder.

Regarding the three types of non-aqueous solvent secondary batteries of Example, Comparative Examples 1 and 2 assembled in this way, voltage from 4.3 V to 3.0 V at a constant temperature of 20° C. and a constant current of 100 mA.
Charging and discharging evaluation was performed in the voltage range up to V. The results are shown in FIG. In FIG. 2, A is a discharge capacity retention rate curve of a battery of an example according to the present invention, B is a battery of Comparative Example 1, and C is a discharge capacity retention rate curve of a battery of Comparative Example 2.

As is clear from FIG. 2, the nonaqueous solvent secondary battery of the example exhibits a higher capacity retention rate even after repeated charge/discharge cycles than the battery of the comparative example, and has excellent performance. are doing. Furthermore, 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 in a state where the carbon material easily fell off from the substrate.
This is considered to be because the lithium and the binder reacted and the binder decomposed. Furthermore, in the battery of Comparative Example 2, a considerable amount of lithium was deposited on the electrode surface.

[Brief explanation of 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 changes in discharge capacity retention rate with respect to the number of charge/discharge cycles in non-aqueous solvent secondary batteries of Examples and Comparative Examples.

[Explanation 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 board 9 Insulating sealing board 10 Positive terminal 11 Positive electrode lead

Claims (1)

[Claims] [Claim 1] A negative electrode body made of a carbonaceous material supporting lithium or an alkali metal mainly composed of lithium, a separator, and a positive electrode body having a lithium-containing composite oxide as a positive electrode active material are integrated in this order. A non-aqueous solvent secondary battery comprising a power generation element laminated with polyacrylic acid or a salt thereof and acrylonitrile-butadiene rubber as a binder for the negative electrode body. battery.