JP2001266940A - Non-aqueous electrolytic solution for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control generation of HF by decomposition of a lithium salt containing fluorine, and improve a charging/discharging cycle characteristic of a secondary battery with electrolyte. SOLUTION: This is a non-aqueous electrolytic solution for a secondary battery which can be used for a secondary battery comprising a negative electrode made of carbonaceous materials in which dope and de-doping of Li is possible and a positive electrode made of metallic oxide materials or the like in which dope and de-doping of Li is possible, and this contains hexamethylene tetramine in a non-aqueous electrolytic solution for a secondary battery containing a lithium compound as a non-aqueous solvent and an electrolyte. This non-aqueous electrolytic solution enables to solve problems that Mn containing lithium oxide in the positive electrode causes blisters of battery and reduction of discharging characteristics by problems of elution of Mn by HF, and controls decomposition of the electrolytic solution and prevents blisters of battery by elevation of an inner pressure of the battery by the formation of carbon dioxide gas and olefin gas, and enhances a charging/discharging characteristics of the electrolytic solution in the lithium secondary battery containing the non-aqueous solvent, and improves the charging/discharging cycle characteristics, and in addition, enables to use a non-aqueous solvent which was assumed difficult to use in the secondary battery with the negative electrode of carbonaceous materials because the decomposition occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a technique for improving a non-aqueous electrolyte for a secondary battery.

[0002]

2. Description of the Related Art In recent years, camera-integrated video tape recorders have been developed.
As a new portable power source such as a VTR, a mobile phone, a laptop computer, etc., in particular, lithium which is lighter, has a higher capacity and a higher energy density than conventional nickel-cadmium (Ni-Cd) secondary batteries or lead secondary batteries. Secondary batteries are attracting attention. An example of a configuration example of a lithium secondary battery uses a carbon material capable of doping and dedoping Li for a negative electrode, using lithium as a negative electrode active material, and doping and dedoping Li for a positive electrode. Using a metal oxide that can be doped, for example, a Mn-containing lithium oxide such as LiMn ₂ O ₄ ,
An electrolyte using a non-aqueous solvent and a lithium compound as an electrolyte is used as the electrolyte.

Conventionally, a lithium compound, for example, a fluorine-containing inorganic or organic lithium compound such as LiPF ₆ has been used as an electrolyte of a nonaqueous electrolyte of a lithium secondary battery. Examples of the non-aqueous solvent include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (MEC), diethyl carbonate (DEC), γ-butyrolactone (GBL),
Ethyl acetate (EA), methyl propionate (MPR),
1,2-Dimethoxyethane (DME), 2-methyltetrahydrofuran (2-MeTHF) and the like are used.

However, lithium, which is a negative electrode active material in a lithium secondary battery, is highly reactive and reacts with the above-mentioned electrolyte, and the reaction product adheres to the electrode surface as a film, and the film is formed. Greatly affect the battery characteristics. In addition, carbonates in a non-aqueous solvent react with lithium to form a film of a carbonate having ion conductivity, so that adverse effects on battery characteristics, such as an increase in battery internal resistance, are small. Since it becomes a protective film on the surface of the negative electrode and improves the storage characteristics and the like of the battery, it has conventionally been the main component of the nonaqueous electrolyte for a lithium secondary battery of a negative electrode made of a carbon material. Some of them have disadvantages such as relatively high melting point and high viscosity, and linear carbonates such as dimethyl carbonate (DMC) and diethyl carbonate (DEC) are: The dielectric constant is low, the conductivity of the electrolyte when used as an electrolyte solvent is low, and there is a problem that sufficient fast charging characteristics or low-temperature discharging characteristics required for a high-output secondary battery cannot be obtained. Furthermore, carbonates are decomposed by HF released by the decomposition of the fluorine-containing inorganic or organic lithium compound in the electrolyte to generate carbon dioxide gas and olefin gas, so that the internal pressure rises and the battery swells and the cycle capacity deteriorates. There was a problem. Further, in the case of the Mn-containing lithium oxide in the positive electrode, there is a problem that Mn is eluted by the HF, thereby causing swelling of the battery and lowering of discharge characteristics.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique capable of solving the drawbacks of the prior art. The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for producing Li
And a negative electrode made of a carbon material or the like which can be
i can be used for a secondary battery having a positive electrode made of a metal oxide material or the like which can be doped and dedoped, and can be used for a secondary battery containing a non-aqueous solvent and a lithium compound as an electrolyte. In water electrolyte, hexamethylenetetramine represented by the following formula 1

(Equation 1) The present invention relates to a non-aqueous electrolyte for a secondary battery, characterized by comprising: Also, as a preferred embodiment thereof,
The concentration of the hexamethylenetetramine in the nonaqueous electrolyte for a secondary battery is 0.001 to 5% by weight;
The present invention also relates to a non-aqueous electrolyte for a secondary battery, wherein the lithium compound of the electrolyte is a lithium compound containing fluorine.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

According to the present invention, various non-aqueous solvents can be used regardless of carbonates. Examples of the non-aqueous solvent used in the present invention include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (MEC), diethyl carbonate (DEC), and γ-butyrolactone (GBL). ), Ethyl acetate (EA), methyl propionate (MPR), ethyl propionate (EPR), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE),
-Various solvents such as methyltetrahydrofuran (2-MeTHF), tetrahydrofuran (THF), sulfolane (SL), and methylsulfolane (MeSL) which have been conventionally used in nonaqueous electrolytes for secondary batteries can be used. These may be used in combination of two or more.

In the non-aqueous electrolyte for a secondary battery according to the present invention,
Uses a lithium compound as an electrolyte. to this
Therefore, this electrolyte is particularly useful as an electrolyte for lithium secondary batteries.
Will be useful. As such a lithium compound, fluorine is used.
-Containing lithium compounds such as LiAsF₆, Li
PF₆, LiBF₄, LiCF₃SO₃, LiN (CF
₃SO₂)₂, LiC (CF₃SO₂)₃Use
For example, LiClO₄Etc.
Also used in secondary batteries
can do. Secondary of lithium compound as electrolyte
The concentration in the non-aqueous electrolyte for a battery is set at 0.1 from the viewpoint of conductivity.
1 to 3.0 mol / l, preferably 0.3 to 2.
It is good to be 0 mol / liter.

The concentration of the above hexamethylenetetramine in the non-aqueous electrolyte is 0.001 to 5% by weight, preferably 0.1 to 5% by weight.
The content is desirably from 0.01 to 0.5% by weight. 0.001
When the amount is less than 5% by weight, the effect of improving the charge / discharge characteristics and the like is not sufficient. On the other hand, when the amount exceeds 5% by weight, the effect is saturated and the battery capacity tends to decrease.

The non-aqueous electrolyte for a secondary battery of the present invention is dissolved by adding a lithium compound as an electrolyte into the non-aqueous solvent while stirring the non-aqueous solvent, and adding and dissolving the above hexamethylenetetramine. It can be manufactured by the following.

The non-aqueous electrolyte for a secondary battery of the present invention can be applied to various secondary batteries using a lithium compound as an electrolyte.
In particular, it is effective for various secondary batteries using a fluorine-containing inorganic or organic lithium compound as an electrolyte. The present invention can be preferably applied to a secondary battery having a negative electrode made of a carbon material capable of doping and dedoping Li. That is, the present invention is effective for a secondary battery having a negative electrode made of a carbon material that causes Li to be inserted during charging and released during discharging. Li above
Can be carried out, for example, with lithium metal, lithium alloy or lithium ion. Here, as the lithium alloy, a lithium-aluminum alloy can be exemplified. Examples of the carbon material constituting the negative electrode include pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.),
Graphites, organic polymer compound fired bodies (phenol resins, furan resins, etc. fired at an appropriate temperature and carbonized), carbon fibers, activated carbon and the like can be mentioned. The carbon material may be graphitized.

On the other hand, the positive electrode is made of various chargeable / dischargeable materials.
For example, LiCoO₂, Li
NiO₂, LiMn₂O₄, LiMnO₂Li such as_x
MO ₂(Where M is one or more transition metals and x is
Normally 0.05 ≦ x ≦
1.20), lithium and one or more transitions
Complex oxide with metal transfer, FeS₂, TiS₂, V₂O
₅, MoO₃, MoS ₂Chalcogenai of transition elements such as
Or polymers such as polyacetylene and polypyrrole
Etc. can be used, but above all, from the above purpose,
The present invention relates to a metal acid capable of doping and dedoping Li.
Effective when formed from a nitride material, etc.
₂O₄, LiMnO₂Lithium containing fluorine such as
It is effective for compounds.

The shape of the secondary battery using the non-aqueous electrolyte for a secondary battery of the present invention is not particularly limited.
Various shapes such as a button type, a cylindrical type, a square type, and a coin type can be used.

[0015]

The present invention will be further described below with reference to examples.

Embodiment 1 FIG. LiPF ₆ was added to each solvent of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (MEC).
mol / l of a solution dissolved in a concentration of 0.5% by weight of hexamethylenetetramine and sealed in a 50 ml stainless steel pressure vessel.
The HF concentration after keeping at 100C for 100 hours was measured by alkali titration.

Comparative Example 1 The same electrolytic solution was tested under the same conditions as described above except that hexamethylenetetramine was not added in Example 1.

Embodiment 2 FIG. The non-aqueous electrolyte secondary battery used in this example has a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, a button-type battery container, a positive electrode current collector, a negative electrode current collector, and a gasket. Wherein the positive electrode is LiMn
A molded product obtained by press-molding a mixture containing ₂ O ₄ as a positive electrode active material into a pellet is used, and a graphite-based MCM is used as a negative electrode.
A molded product obtained by pressure-forming a mixture containing B as a negative electrode active material carrier into a pellet was used. The non-aqueous electrolyte contains an electrolyte composed of LiPF ₆ at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 2: 3). A solution containing 0.5% by weight of hexamethylenetetramine was used. Further, a separator made of a nonwoven fabric made of polypropylene is used for the separator, the positive electrode-side current collector is made of stainless steel, while the negative electrode-side current collector is made of nickel expanded metal, and the battery container is made of stainless steel. The positive electrode can and the negative electrode can were made of steel, and were fixed with a polypropylene gasket. The charge / discharge cycle characteristics of the battery fabricated as described above were examined. The charging was performed by the constant current method, the upper limit voltage was set to 4.2 V, the current density at constant current was set to 0.5 C, and the discharge was set to 0.5 C at the current density, and the final voltage was 2.7 V. And
Normal charging and discharging were performed at 25 ° C. for 100 cycles. 100
Evaluation was made based on a comparison of battery capacity in each cycle.

Embodiment 3 FIG. The solvent of the non-aqueous electrolyte in Example 2 was ethylene carbonate (EC) and dimethyl carbonate (DMC)
And a mixed solvent (volume ratio 1: 1).
A button-type battery was manufactured in the same manner as in Example 2 except that CoO ₂ was used and the addition amount of hexamethylenetetramine was 0.1% by weight, and charge and discharge were performed under the same conditions as in Example 2. The cycle characteristics were examined.

Comparative Example 2 A button-type battery was prepared in the same manner as in Example 2 except that hexamethylenetetramine was not added in Example 2, and the charge / discharge cycle characteristics were examined under the same conditions as in Example 2.

Comparative Example 3 A button-type battery was produced in the same manner as in Example 3 except that hexamethylenetetramine was not added in Example 3, and the charge / discharge cycle characteristics were examined under the same conditions as in Example 2.

The above results are shown in Table 1 and FIG.

[0023]

[Table 1]

As shown in Table 1, the electrolyte solution (Example 1) to which hexamethylenetetramine of the present invention was added was 85%.
100 ° C., after 100 hours, compared with the electrolyte solution (Comparative Example 1) to which the hexamethylenetetramine was not added,
It can be seen that there is an effect of suppressing an increase in HF.

As shown in FIG. 1, the electrolyte solution (Examples 2 and 3) to which hexamethylenetetramine of the present invention was added was 1
At a discharge capacity of 00 cycles, the battery capacity cycle deterioration was not observed as compared with the electrolyte solution to which hexamethylenetetramine was not added (Comparative Examples 2 and 3), indicating that the battery was effective.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the invention. Needless to say, For example,
In the above embodiment, the shape of the battery is described as a button type, but the shape is not limited to this, and similar effects can be obtained even with other square, cylindrical, coin type, etc. .

[0027]

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows. That is, according to the present invention, in a non-aqueous electrolyte for a secondary battery, by adding hexamethylenetetramine, generation of HF due to decomposition of a fluorine-containing lithium salt is suppressed, and a secondary battery using the electrolyte is used. Can be improved in charge-discharge cycle characteristics. Further, the Mn-containing lithium oxide in the positive electrode was changed to M
It is possible to solve the problem that n is eluted to cause swelling of the battery and deterioration of discharge characteristics. Further, the decomposition of the electrolyte is suppressed to prevent the battery from swelling due to an increase in the internal pressure of the battery due to the generation of carbon dioxide gas and olefin gas, and to charge and discharge the electrolyte in a lithium secondary battery containing a non-aqueous solvent. The characteristics can be improved, the charge / discharge cycle characteristics can be improved, and further, in a secondary battery of a negative electrode made of a carbon material, a non-aqueous solvent that is decomposed and is considered difficult to use can be used. You can do so.

[Brief description of the drawings]

FIG. 1 is a graph illustrating the operation and effect of the present invention.

[Explanation of symbols]

 1 ... Example 2 2 ... Example 3 3 ... Comparative Example 2 4 ... Comparative Example 4

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takahiro Hexagon 3-11-1 Mizutani Higashi, Fujimi-shi, Saitama Toyama Pharmaceutical Co., Ltd. Shiki Plant (72) Inventor Tetsuo Kojima 3-11 Mizutani-Higashi, Fujimi-shi, Saitama -1 Inside the Shiki Plant of Toyama Pharmaceutical Co., Ltd. (72) Inventor Sadao Ueda 3-1-1-1 Mizutani Higashi, Fujimi City, Saitama Prefecture Inside the Shiki Plant of Toyama Pharmaceutical Co., Ltd. (72) Inventor Minoru Nakano Mizutani, Fujimi City, Saitama Prefecture 3-11-1 Higashi F-term (reference) in the Shiki Plant of Toyama Pharmaceutical Co., Ltd. 5H029 AJ02 AJ05 AJ07 AK03 AK05 AK16 AK18 AL06 AL07 AL08 AL12 AM01 AM02 AM03 AM04 AM05 AM07 DJ09 EJ07 EJ12 HJ10

Claims (3)

[Claims] 1. A negative electrode comprising a carbon material or the like capable of doping and undoping Li and a positive electrode comprising a metal oxide material or the like capable of doping and undoping Li. In a non-aqueous electrolyte for a secondary battery containing a non-aqueous solvent and a lithium compound as an electrolyte, the following formula 1
Hexamethylenetetramine represented by Formula 1 A non-aqueous electrolyte for a secondary battery, comprising: 2. The non-aqueous electrolyte for a secondary battery according to claim 1, wherein the concentration of hexamethylenetetramine in the non-aqueous electrolyte for a secondary battery is 0.001 to 5% by weight. . 3. The non-aqueous electrolyte for a secondary battery according to claim 1, wherein the lithium compound of the electrolyte is a lithium compound containing fluorine.