JPH0574485A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolyte secondary battery in which a diole compound within the range in which a practical and good battery characteristic can be maintained is contained in a nonaqueous electrolyte containing cyclic carbonic ester. CONSTITUTION:In a nonaqueous electrolyte secondary battery which uses composite metal oxides composed mainly of Li and Co as positive electrode active material, a carbonaceous material as negative electrode active material, and a nonaqueous electrode wherein at least cyclic carbonic ester is contained by not less than 10wt.% in an electrolyte solvent, a diole compound contained in the nonaqueous electrolyte is selected between 25ppm and l,500ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a cycle property, a storage property,
The present invention relates to a novel secondary battery with excellent safety.

[0002]

2. Description of the Related Art In recent years, various non-aqueous secondary batteries have been proposed as small and lightweight secondary batteries replacing conventional acid-lead batteries and nickel / cadmium batteries. Among them, for example, JP-A-62-90,863, JP-A-63-121,
A new secondary battery system using a composite metal oxide containing Li and Co as a main component in the positive electrode and a carbonaceous material in the negative electrode is disclosed in JP-A No. 260 and JP-A-3-49,155. Has been done. Conventionally proposed as such a non-aqueous secondary battery is metal L as a negative electrode active material.
i or Li alloy was used. Although a secondary battery using such a metallic Li as a negative electrode is satisfactory from the viewpoint of small size and light weight, it has a problem in performance such as cycleability and storage characteristics due to dendrite precipitation, and also a separator due to dendrite precipitation. Life problem of causing internal short circuit due to breakthrough of metal, and further metal L
There were major obstacles to practical use, such as safety problems based on the active chemical reactivity of i. On the other hand, the new battery system using the carbonaceous material as the negative electrode active material has excellent cycleability and storage characteristics without causing such dendrite precipitation, and has an active chemical reaction such as metallic Li. Since it does not have the property, it has a feature that the safety is very excellent.

In particular, when a positive electrode active material is combined with a composite metal oxide containing Li and Co as a main component, it is expected that a battery having a high voltage and a high capacity can be obtained.

[0004]

By the way, such L
In the case of a battery using a composite metal oxide containing i, Co as a main component as a positive electrode active material and a carbonaceous material as a negative electrode active material,
Cyclic carbonic acid esters such as propylene carbonate and ethylene carbonate are used as an electrolytic solution solvent showing good performance.

However, such cyclic carbonic acid ester usually contains a considerable amount of a diol compound as an impurity. These glycols have an adverse effect on battery characteristics, particularly storage characteristics and cycleability. Furthermore, in extreme cases, phenomena such as gas generation, internal pressure increase, and battery blister occur, which is a safety issue. It is true that it is preferable that the amount of impurities such as diol compounds is as small as possible,
Since the boiling point is close to that of the cyclic carbonic acid ester, it is difficult to reduce the concentration to a low concentration, and there is a possibility that the cost may increase.

In particular, in the battery system of the present invention in which a Li, Co composite oxide is used as the positive electrode active material and a carbonaceous material is used as the negative electrode active material, the allowable mixing range of diols is clarified, and an efficient removal method thereof is found. This is an important problem to be solved when putting this battery system into practical use.

[0007]

Means and Actions for Solving the Problems The present inventors have
As a result of extensive studies on the influence of the diols in the battery system, it was found that a battery having excellent characteristics can be obtained by setting the concentration of the diols in the non-aqueous electrolyte to a specific concentration range.

The non-aqueous electrolyte secondary battery of the present invention has been completed on the basis of the above findings, and uses a composite metal oxide containing Li and Co as main components as a positive electrode active material and a carbonaceous material as a negative electrode active material. In a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte solution containing at least 10% by weight or more of cyclic carbonate as a substance, the diol compound contained in the non-aqueous electrolyte solution is 25 ppm to 1, It is characterized by being 500 ppm.

The composite metal oxide containing Li and Co as the main components in the present invention is a compound having a layered structure and capable of electrochemically intercalating and deintercalating Li ions, and at least Co Is contained in the metal component in an amount of 50% by weight or more. Although not particularly limited, an example of such a composite metal oxide is shown in, for example, JP-A-55-1.
36,131, LiCoO ₂ , and the general formula Li disclosed in JP-A-62-90,863.
_x Co _y N _z O ₂ (wherein N represents at least one selected from the group consisting of Al, In and Sn, and x, y and z are each 0.05 ≦ x ≦ 1.10 and 0.85 ≦ y. ≤1.00,
It represents a number of 0.001 ≦ z ≦ 0.10. ), And Li _x Ni _y C disclosed in JP-A-3-49,155.
o _(1-y) O ₂ (where 0 <x ≦ 1, 0 ≦ y <0.50)
Etc.

In order to obtain such a compound, L hydroxide such as lithium hydroxide, lithium oxide, lithium carbonate and lithium nitrate is used.
It can be easily obtained by a firing reaction between the i compound and a cobalt compound such as cobalt oxide, cobalt hydroxide, cobalt carbonate, or cobalt nitrate, and if necessary, another metal compound.

Each of these composite oxides has, as a positive electrode active material, excellent characteristics such as high voltage and high capacity, which are not found in other active materials. In particular, the above general formula Li _x Co _y
N _z O ₂ (where N represents at least one selected from the group consisting of Al, In and Sn, and x, y and z are each 0.05
≤ x ≤ 1.10, 0.85 ≤ y ≤ 1.00, 0.001
Represents a number ≦ z ≦ 0.10. ) Is a complex oxide which is particularly preferably used in the present invention because it has excellent characteristics such as cycle characteristics.

The carbonaceous material referred to in the present invention is not particularly limited.
-35,881 high surface area carbon material, JP-A-58-209,864 JP-A No. 61-111,907 JP Examples include calcined carbides of condensed polycyclic hydrocarbon compounds. Above all, the BET specific surface area A (m ² / g) disclosed in JP-A-62-90,863 is 0.1.
Crystal thickness Lc in X-ray diffraction in the range of <A <100
The value of (Å) and true density ρ (g / cm ³ ) are the following conditions 1.7.
The carbonaceous material in the range of 0 <ρ <2.18 and 10 <Lc <120ρ-189 has a high capacity and excellent cycle characteristics, and is particularly preferably used in the present invention.

The cyclic carbonic acid ester used as the solvent for the electrolytic solution of the present invention exhibits excellent characteristics in the battery of the positive and negative active material combinations of the present invention as described above. Carbonate, ethylene carbonate, vinylene carbonate, etc. are mentioned as an example. In the present invention, the cyclic carbonic acid ester may be used alone, or two or more kinds of cyclic carbonic acid ester may be mixed and used. Further, the cyclic carbonic acid ester and a solvent other than the cyclic carbonic acid ester may be mixed, but in this case, the cyclic carbonic acid ester in the electrolytic solution solvent must be 10% by weight or more. If the amount is less than 10% by weight, the excellent properties of the above cyclic carbonic acid ester are impaired, which is not preferable. As the solvent other than the cyclic carbonic acid ester used here, for example, ethers, ketones, lactones, nitriles, amines,
Amides, sulfur compounds, chlorinated hydrocarbons, esters, linear carbonates, nitro compounds, phosphoric acid ester-based compounds, sulfolane-based compounds and the like can be used. Among them, ethers, ketones, Nitriles, chlorinated hydrocarbons, linear carbonates, and sulfolane compounds are preferable.

Typical examples of these are tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1 , 2-
Dichloroethane, γ-butyrolactone, dimethoxyethane, methyl formate, dimethyl carbonate, diethyl carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, triethyl phosphate and mixed solvents thereof, etc. However, the present invention is not limited to these.

In the present invention, the diols contained in the non-aqueous electrolyte solvent are ethylene glycol, 1,2
-Propanediol, 1,3-propanediol and the like are given as examples, and the amount contained in the electrolytic solution is 25
It must be in the range of ppm to 1,500 ppm.

Preferably 25 ppm to 1,000 pp
m, more preferably 25 ppm to 75 ppm.

When it exceeds 1,500 ppm, the battery characteristics such as storage characteristics and cycleability are deteriorated, and in some cases, the phenomenon of blistering of the battery due to gas generation occurs, which is not preferable. In order to reduce the amount to less than 25 ppm, there is no choice but to use a technique such as an extremely sophisticated precision distillation that causes a cost increase, and if the amount is less than 25 ppm, the effect of improving the characteristics is not seen, which is not preferable.

Various means are conceivable as an efficient method for controlling the content of the diols within the range limited by the present invention. The method of rectifying the cyclic carbonic acid ester to be used is also one of the effective means. For that purpose, the setting conditions such as the reflux ratio, the rectification temperature and the degree of pressure reduction are important.

Other methods include treatment with an adsorbent such as silica gel, activated carbon, activated alumina, and special molecular sieves. This method is a simple and efficient method and is mentioned as a practical method. It is particularly important that the diol compound tends to increase over time due to the action of the cyclic carbonic acid ester and water, and it is preferable to perform the treatment immediately before use as much as possible.

The separator is not particularly limited, and examples thereof include woven cloth, non-woven cloth, glass woven cloth, and synthetic resin microporous film. When a thin film or a large area electrode is used, for example, JP-A-58-59072 is used. The synthetic resin microporous membrane disclosed in, particularly, the polyolefin microporous membrane is preferable in terms of thickness, strength and membrane resistance.

The electrolyte of the non-aqueous electrolyte is not particularly limited, but as an example, LiClO ₄ , LiBF ₄ , L
iAsF ₆ , CF ₃ SO ₃ Li, LiPF ₆ , LiI,
LiAlCl ₄ , NaClO ₄ , NaBF ₄ , NaI,
(N-Bu) ₄ N ⁺ ClO ₄ , (n-Bu) ₄ N ⁺ BF ₄
, KPF _{6 and the} like.

Further, if necessary, a battery is constructed by using components such as a current collector, a terminal and an insulating plate. Further, the structure of the battery is not particularly limited, but a positive electrode, a negative electrode, and further, if necessary, a paper-type battery having a single layer or a multi-layer separator, a laminated battery, or a positive electrode, a negative electrode, and further required. For example, a form of a cylindrical battery or the like in which a separator is wound in a roll shape can be mentioned.

[0023]

The present invention will be described in more detail with reference to the following examples.

Example 1 Li, C having a composition of Li _1.03 Co _0.92 Sn _0.02 O ₂
o 100 parts by weight of complex oxide, 2.5 parts by weight of graphite and 2.5 parts by weight of acetylene black were mixed, and then 2 parts by weight of fluororubber was mixed with 60 parts by weight of a mixed solvent of ethyl acetate / ethyl cellosolve 1: 1 (weight ratio). The liquid dissolved in the parts was mixed to obtain a slurry coating liquid.

The coating solution was applied to both sides of an Al foil having a width of 600 mm and a thickness of 15 μm by using a coating machine having a doctor blade coater head. Coating thickness after double-sided coating is 290μ
Met.

100 parts by weight of crushed needle coke and 5 parts by weight of fluororubber were dissolved in 90 parts by weight of a 1: 1 (weight ratio) mixed solvent of ethyl acetate / ethyl cellosolve to obtain a slurry coating solution. It was

A coating machine having a doctor blade coater head was used to apply the above coating solution to both sides of a Cu foil having a width of 600 mm and a thickness of 10 μm. Coating thickness after coating on both sides is 350μ
Met.

After pressing the above-mentioned two kinds of coated products with a calendar roll, both were slit to a width of 41 mm using a slitter. The Li _1.03 Co _0.92 Sn _0.02 O ₂ coated product was used as the positive electrode, the needle coke coated product was used as the negative electrode, and a polyethylene microporous membrane (hypore 4030) was used as the separator.
U Asahi Kasei Co., Ltd.) with a winding machine, outer diameter 14.9 mm
Was wound into a coil. This winding coil has an outer diameter of 16 mm
After put into the battery can, of propylene carbonate / ethylene carbonate / .gamma.-butyrolactone 1: 1: 2 mixture solvent (cyclic carbonate content of 50 wt%) (by weight) LiBF ₄ those dissolved in 1M concentration Was impregnated as an electrolytic solution and then sealed, to fabricate a prototype A-sized battery can having a height of 50 mm shown in FIG.

The propylene carbonate and ethylene carbonate used here were both treated with silica gel, and the diol compound in the electrolytic solution immediately before impregnation was 75 ppm of ethylene glycol, 65 ppm of 1,2-propanediol, and 1 ppm of 1,2-propanediol. , 3-propanediol 25p
pm, and the total content of diol compounds is 165 pp
It was m. The content of the diol compound was measured by a gas chromatograph (GC-14A, manufactured by Shimadzu Corporation). The column used was a PEG20M capillary column.

When this battery was charged, normal battery performance was exhibited without the phenomenon of blistering of the battery can. The results are shown in Table 1.
Shown in.

Examples 2 to 4 and Comparative Examples 1 to 2 Except that the treatment of the electrolytic solution solvent was carried out under the operating conditions shown in Table 1, the same operation was carried out, and an A size battery was experimentally produced and evaluated.

The results are also shown in Table 1.

[0033]

[Table 1]

[0034]

As is clear from the above description, Li, C
In a secondary battery using a non-aqueous electrolyte solution containing a composite oxide as a positive electrode active material, a carbonaceous material as a negative electrode active material, and an electrolyte solution solvent containing at least 10% by weight or more of cyclic carbonate, By adjusting the content of the diol compound contained in the composition to 25 ppm to 1,500 ppm, battery characteristics such as self-discharge can be improved.

[Brief description of drawings]

FIG. 1 is a half cutaway view of a battery according to the present invention.

[Explanation of symbols]

 1 positive electrode 2 separator 3 negative electrode 4 insulating plate 5 negative electrode lead 6 positive electrode lead 7 gasket

Claims (1)

[Claims] 1. A composite metal oxide containing Li and Co as a main component is used as a positive electrode active material, a carbonaceous material is used as a negative electrode active material, and at least 10% by weight of cyclic carbonic acid ester is contained in an electrolytic solution solvent.
A non-aqueous electrolyte secondary battery using the above non-aqueous electrolyte solution, wherein the diol compound contained in the non-aqueous electrolyte is 25 ppm to 1,500 ppm.