JP2002343364A - Nonaqueous electrolyte solution secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte solution secondary battery with low inner resistance and excellent self discharge characteristics. SOLUTION: The nonaqueous electrolyte solution secondary battery composed of a positive and a negative electrodes which can absorb and desorb lithium ion, and nonaqueous electrolyte solution generating hydrogen fluoride by reacting with water, is also provided with hydrogen fluoride decomposing agent. That is to say, hydrogen fluoride generated by the existence of water is converted into innoxious silicon tetrafluoride through reaction shown in formula (2) below. 3SiO2 +12HF→3SiF4 ↑+6H2 O...(2). The silicon tetrafluoride generated here is a gas at normal temperature, and is accumulated in the battery, but does not affect battery performance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery which is hardly affected by moisture inside the battery.

[0002]

2. Description of the Related Art With the miniaturization of personal computers, video cameras, mobile phones, and the like, in the fields of information-related equipment and communication equipment, a lithium secondary battery is used as a power source for these equipment because of its high energy density. And other non-aqueous electrolyte secondary batteries have been put to practical use and have come into widespread use. On the other hand, in the field of automobiles, the development of electric vehicles is urgent due to environmental problems and resource problems, and lithium secondary batteries are being studied as power sources for electric vehicles.

As a lithium secondary battery, a layered rock salt structure of LiCoO ₂ ,
Positive electrode active materials such as LiNiO ₂ , LiMn ₂ O _{4 having} a spinel structure, and a lithium transition metal composite oxide in which a part thereof is replaced with another element are well known. Among these,
At present, batteries using a LiCoO ₂ -based lithium transition metal composite oxide as a positive electrode active material occupy the mainstream because they are easy to synthesize and obtain the highest operating voltage.

[0004] Incidentally, in order to achieve a working voltage of the 4V class, it is necessary to use a non-aqueous electrolyte as an electrolyte. In the non-aqueous electrolyte, a fluorine compound such as LiPF ₆ which is a halogen compound is often used as an electrolyte.However, some water is inevitably mixed in the electrolyte which should be non-aqueous,
Or if moisture is adsorbed on other battery materials,
The reaction shown in the following formula (1) occurs, and hydrogen fluoride HF
Generates halogen acids such as

[0005] 2LiPF ₆ + 12H ₂ O → 12HF + 2LiP (OH) ₆ (1) The generated hydrogen fluoride deteriorates the materials constituting the battery such as the current collector and the positive electrode active material, and further deteriorates the battery performance. There's a problem. As a result of the deterioration of the constituent materials, the internal resistance of the battery deteriorates. In addition, when the aluminum positive electrode current collector is dissolved, the dissolved metal ions precipitate from the negative electrode, which leads to deterioration of self-discharge characteristics.

Although the water inside the battery often mixes from the electrode active material, the water in the electrolyte cannot be neglected. As a solution, there is a method of strictly drying and managing each component of the lithium secondary battery in a dry room or the like to suppress the amount of water mixed in the battery.
Nevertheless, the amount of water mixed in the initial stage of production may reach several thousand ppm in the electrolytic solution, and the constituent materials of the battery are deteriorated by the generated hydrogen fluoride.

To solve this problem, Japanese Patent Laid-Open No.
No. 2,838,671 discloses that a non-aqueous electrolyte containing LiPF ₆ or the like as an electrolyte is treated with Mg _X Al _Y O _Z (X
+ Y = 1, Z> 0) is disclosed. Mg _X Al _Y O _Z
The compound represented by can adsorb HF and can suppress the adverse effect on the battery material.

It is also conceivable to control the manufacturing process more strictly.

[0009]

However, even in the battery described in Japanese Patent Application Laid-Open No. H11-283671, there were cases where the effect of hydrogen fluoride could not be sufficiently suppressed. In addition, a large dry atmosphere was required to limit the amount of water for each component, which contributed to an increase in cost.

Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having low internal resistance and excellent self-discharge characteristics.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, hydrogen fluoride generated by mixing of water into the inside of the battery is reacted with SiO ₂ to remove it. , And found that it can be rendered harmless, and made the following invention.

That is, the non-aqueous electrolyte secondary battery of the present invention comprises a non-aqueous electrolyte having a positive electrode and a negative electrode capable of absorbing and desorbing lithium ions, and a non-aqueous electrolyte which generates hydrogen fluoride when reacted with water. An electrolyte secondary battery further comprising Si
It has a hydrogen fluoride decomposer composed of O ₂ .

That is, hydrogen fluoride generated by the presence of water is converted into harmless silicon tetrafluoride by a reaction represented by the following formula (2).

3SiO ₂ + 12HF → 3SiF ₄ ↑ + 6H ₂ O (2) The SiF ₄ generated here is a gas at normal temperature and accumulates in the battery but does not adversely affect the battery performance.

Although water is produced by this reaction, the amount of water is reduced by half as is apparent from comparison with the equation (1), and hydrogen fluoride is produced by reacting again with the electrolyte. Even if it does, the amount is reduced by half, and by repeating the reaction of the formulas (1) and (2), both hydrogen fluoride and moisture can be finally reduced to negligible levels.

Preferably, the hydrogen fluoride decomposing agent is dispersed in the positive electrode and / or the negative electrode and / or the non-aqueous electrolyte. By dispersing the hydrogen fluoride decomposer,
This is because the generated hydrogen fluoride can be quickly removed.

Further, the negative electrode has a negative electrode active material composed of a carbon material, and the hydrogen fluoride decomposing agent is dispersed inside the negative electrode together with the negative electrode active material. The content is preferably 6% by mass or less based on the sum with the substance. Although the present hydrofluoric acid decomposing agent does not contribute to the battery reaction, by setting its content within this range, a sufficient hydrogen fluoride decomposing effect can be obtained in a state where adverse effects on battery performance are minimized. .

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous electrolyte secondary battery of the present invention
It has a hydrogen fluoride decomposer inside. The hydrogen fluoride decomposing agent contains SiO ₂ as a main component. The shape of the hydrogen fluoride decomposer is not particularly limited, but is preferably a fine powder. This is because the reaction area with hydrogen fluoride can be increased and the influence on the battery reaction can be suppressed. Further, the particle diameter is preferably smaller than the particle diameter of the active material or the like.

The site in the battery to which the hydrogen fluoride decomposing agent is added is not particularly limited as long as hydrogen fluoride generated by the reaction between the electrolytic solution and water moves therethrough.
It is preferably dispersed in the positive electrode and / or the negative electrode and / or the non-aqueous electrolyte. By widely dispersing in the battery, the generated hydrogen fluoride can be quickly decomposed. Further, by dispersing, the influence on the battery reaction can be suppressed.

The hydrogen fluoride decomposing agent uses a carbon material as the negative electrode active material and is dispersed inside the negative electrode together with the negative electrode active material. , 6% by mass or less. By setting the content of the hydrogen fluoride decomposing agent in this range, a sufficient hydrogen fluoride decomposing effect can be obtained without adversely affecting the battery performance. Further, the content is preferably 2 to 6% by mass based on the sum of the hydrogen fluoride decomposing agent and the pole active material.

The non-aqueous electrolyte secondary battery of the present invention can have a known battery structure such as a coin battery, a button battery, a cylindrical battery, and a square battery. In any case, the positive electrode and the negative electrode are overlapped or wound with a separator interposed therebetween to form an electrode body, and the positive electrode terminal and the negative electrode terminal communicate with the positive electrode terminal and the negative electrode terminal. After the connection is made using a current collecting lead or the like, the electrode body is inserted into a battery case together with the non-aqueous electrolyte, and the battery case is sealed to complete a lithium battery.

The positive electrode is prepared by mixing a conductive material and a binder with a positive electrode active material capable of inserting and extracting lithium ions, adding an appropriate solvent as necessary, and forming a paste-like positive electrode mixture into aluminum. Apply to the surface of the current collector made of metal foil, etc.
It is formed by drying and then increasing the active material density by pressing.

As the positive electrode active material, a known positive electrode active material such as a lithium transition metal composite oxide can be used. The lithium transition metal composite oxide is a preferable material for the present positive electrode active material because of its low electric resistance, excellent lithium ion diffusion performance, high charge / discharge efficiency and good charge / discharge cycle characteristics. For example, lithium cobalt oxide,
Lithium nickel oxide, lithium manganese oxide,
These are materials to which transition metals such as Li, Al, and Cr are added or substituted. When these lithium-metal composite oxides are used as the positive electrode active material, they can be used not only alone but also in a mixture of plural kinds.

The conductive material is for ensuring the electrical conductivity of the positive electrode, and may be a mixture of one or more powdered carbon materials such as carbon black, acetylene black, and graphite. it can. The binding agent plays a role of binding the active material particles and the conductive material particles, and may be a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene. . As a solvent for dispersing these active material, conductive material and binder, N-
An organic solvent such as methyl-2-pyrrolidone can be used.

The material of the negative electrode is not particularly limited as long as it can use a negative electrode active material that occludes lithium ions at the time of charging and releases it at the time of discharging. Can be. For example, a carbon material such as lithium metal, graphite, or amorphous carbon is used. Among them, it is particularly preferable to use a carbon material. Since the specific surface area can be made relatively large, and the lithium insertion and extraction speed is high, the charge / discharge characteristics at a large current and the output / regeneration density are good. In particular,
In consideration of the balance between the output and the regenerative density, it is preferable to use a carbon material having a relatively large voltage change due to charging and discharging. Above all, it is preferable to use one made of natural graphite or artificial graphite having high crystallinity. By using such a highly crystalline carbon material, it is possible to improve the lithium ion transfer efficiency of the negative electrode.

When a carbon material is used as the negative electrode active material as described above, the negative electrode mixture obtained by mixing the conductive material and the binder as described for the positive electrode, if necessary, is used as a current collector. It is preferable to use one that is applied to the body.

The non-aqueous electrolyte is obtained by dissolving an electrolyte in an organic solvent.

The organic solvent is not particularly limited as long as it is an organic solvent usually used for a non-aqueous electrolyte of a lithium secondary battery. Examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, and nitriles. , Lactones, oxolane compounds and the like can be used. In particular,
Propylene carbonate, ethylene carbonate, 1,
Suitable are 2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran and the like and a mixed solvent thereof. For example, a mixed organic solvent of a main solvent having a high dielectric constant such as ethylene carbonate and propylene carbonate and a low-viscosity sub-solvent such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate is preferable. Further, dimethoxyethane, tetrahydrofuran, butyl lactone, or the like may be used as a secondary solvent.

The type of the electrolyte is not particularly limited, but may be selected from LiPF ₆ , LiBF ₄ and LiAsF _6.
Inorganic salts, derivatives of inorganic salts selected from, LiSO ₃ C
F ₃ , LiC (SO ₃ CF ₃ ) ₂ , LiN (SO ₃ C
_{F 3) 2, LiN (SO} 2 C 2 F 5) 2 and LiN (SO ₂
It is preferably at least one kind of an organic salt selected from CF ₃ ) (SO ₂ C ₄ F ₉ ) and a derivative of the organic salt. These electrolytes react with moisture to produce hydrogen fluoride.

By using these electrolytes, the battery performance can be further improved, and the battery performance can be maintained even higher in a temperature range other than room temperature. The concentration of the electrolyte is not particularly limited, either, and it is preferable to appropriately select the electrolyte and the organic solvent in consideration of the type of the organic solvent.

The separator serves to electrically insulate the positive electrode and the negative electrode and retain the electrolyte. For example, a porous synthetic resin film, particularly a porous film of a polyolefin polymer (polyethylene, polypropylene) may be used. Note that the separator is preferably larger than the positive electrode and the negative electrode in order to ensure insulation between the positive electrode and the negative electrode.

The case is not particularly limited.
It can be made of a known material and form.

The gasket ensures electrical insulation between the case and both the positive and negative terminal portions and the hermeticity of the case. For example, it can be composed of a polymer such as polypropylene which is chemically and electrically stable with respect to the electrolytic solution.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The non-aqueous electrolyte secondary battery of the present invention will be described below based on the lithium secondary battery of the embodiment.

<Lithium Secondary Battery of Embodiment 1> The lithium secondary battery of this embodiment uses a lithium nickel composite oxide represented by a composition formula of LiNiO ₂ as a positive electrode active material.
This is a lithium secondary battery using carbon black as a negative electrode active material, and contains 2% by mass of silica powder as a hydrogen fluoride decomposer with respect to the sum of the negative electrode active material and the hydrogen fluoride decomposer.

The positive electrode of the lithium secondary battery of this embodiment was prepared by mixing 85 parts by mass of the above-mentioned LiNiO ₂ , 10 parts by mass of acetylene black as a conductive material, and 5 parts by mass of polyvinylidene fluoride as a binder. By adding and kneading N-methyl-2-pyrrolidone, a paste-like positive electrode mixture is obtained, and this positive electrode mixture is applied to both sides of a 15 μm-thick Al foil positive electrode current collector, dried, and pressed. After that, a sheet-shaped positive electrode was produced.

The negative electrode contains 90 parts by mass of carbon black,
8 parts by mass of polyvinylidene fluoride as a binder, and 2 parts by mass of silica (average particle diameter: 0.6 μm, spherical silica (trade name: Admafile silica, manufactured by Admatechs Co., Ltd.)) as a hydrogen fluoride decomposer And an appropriate amount of N-methyl-
By adding and kneading 2-pyrrolidone, a paste-like negative electrode mixture was obtained, and this negative electrode mixture was applied to both surfaces of a 10-μm-thick negative electrode current collector made of Cu foil, dried, and subjected to a pressing step.
A sheet negative electrode was produced.

Each of the positive electrode and the negative electrode is cut into a predetermined size, and the cut positive electrode and negative electrode are separated by a thickness of 2 mm therebetween.
5μm polyethylene separator sandwiched and wound,
A roll-shaped electrode body was formed. A current collecting lead was attached to this electrode body, inserted into a 18650 type battery case, and then a non-aqueous electrolyte was injected into the battery case. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1 M in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3: 7 was used. Finally, the battery case was sealed to complete the lithium secondary battery of the present example. In addition, the positive electrode contained 2000 ppm of water and the negative electrode contained 500 ppm of water by mass ratio.

Thereafter, as conditioning, 4.1.
Charge / discharge was performed between V and 3 V at 1 C for 5 cycles.

<Lithium Secondary Batteries of Examples 2 to 5> In the lithium secondary batteries of the present example, 4% by mass of silica powder was added to the sum of the negative electrode active material and the hydrogen fluoride decomposing agent.
(Example 2) Except for containing 6% by mass (Example 3), 8% by mass (Example 4), and 10% by mass (Example 5), the same configuration as the lithium secondary battery of Example 1, It is a manufacturing method.

<Lithium Secondary Battery of Comparative Example 1> The lithium secondary battery of this comparative example has the same configuration and manufacturing method as the lithium secondary battery of Example 1 except that silica powder was not added. .

<Measurement of Internal Resistance> With respect to the lithium secondary batteries of Examples and Comparative Examples, the internal resistance at the initial stage and after the endurance was measured. The internal resistance was measured by measuring the value of the terminal voltage of the battery when the value of the current applied to the battery was changed at 25 ° C., and derived from the slope of a line connecting each current value and the voltage value.

The initial internal resistance was the same as that of the battery after conditioning, and the internal resistance after durability was 3.0 V.
After charging / discharging for 500 cycles between 2 and 4.1 V under the condition of 2 C, the measurement was performed.

<Results> FIG. 1 shows the relationship between the amount of silica added and the internal resistance (relative value when the comparative example is set to 1). FIG. FIG. 2 shows the relationship between the initial internal resistance of the lithium secondary battery (1) and the relative value (1).

As is apparent from FIG. 1, the addition of silica up to Example 3 (6% by mass) caused little increase in the internal resistance due to the addition of silica, and almost no decrease in battery performance was observed. . As is clear from FIG. 2, it was clarified that the increase in the internal resistance after the durability was suppressed with the addition of silica, and the effect of the suppression was sufficient at 2% by mass (Example 1) or more. Was. It is considered that this is because hydrogen fluoride can be decomposed by incorporating silica as a hydrogen fluoride decomposing agent into the battery, and the deterioration of the constituent materials of the battery is suppressed.

Therefore, from the viewpoint of the effect of suppressing the internal resistance, the addition of 6% by mass or less of silica is preferable, and the addition of 2 to 6% by mass is more preferable.

<Measurement of Self-Discharge Amount> The self-discharge amount after endurance of the lithium secondary battery of Example 3 and the lithium secondary battery of Comparative Example was measured. Further, the initial self-discharge amount of the lithium secondary battery of Example 3 was also measured.
The conditions of the lithium secondary battery at the initial stage and after the endurance were the same as those in the internal resistance measurement test described above.

The amount of self-discharge was measured after charging to 3.75 V, followed by 5, 10, 15, 20, 2,
After being left for 5 days, each voltage was measured, and the difference from the initial voltage value (voltage drop amount) was defined as the amount of self-discharge.

<Results> The results are shown in FIG. 3, the self-discharge amount of the lithium secondary battery of Example 3 was smaller than that of the lithium secondary battery of Comparative Example. This is thought to be because hydrogen fluoride can be decomposed by incorporating silica as a hydrogen fluoride decomposing agent into the battery, and dissolution of the positive electrode active material and the positive electrode current collector and deposition on the negative electrode are suppressed. Can be

[0050]

As described above, in the nonaqueous electrolyte secondary battery of the present invention, the adverse effect of moisture in the electrolyte or the like can be suppressed, and the life of the battery can be extended. Also,
There is no need to perform strict management to reduce the amount of water in the battery, so that the manufacturing process can be shortened and the effect of cost reduction is great.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of added silica and the value of the initial internal resistance in the lithium secondary batteries of Examples and Comparative Examples.

FIG. 2 is a graph showing the relationship between the amount of added silica and the rate of increase in internal resistance after endurance from the value of initial internal resistance in the lithium secondary batteries of Examples and Comparative Examples.

FIG. 3 is a graph showing self-discharge characteristics of Example 3 and Comparative Example.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (3)

[Claims] 1. A positive electrode and a negative electrode of lithium ion capable of absorbing and desorbing, a non-aqueous electrolyte secondary battery having a non-aqueous electrolytic solution to generate hydrogen fluoride to react with water, further SiO ₂ A non-aqueous electrolyte secondary battery comprising a hydrogen fluoride decomposer comprising: 2. The hydrogen fluoride decomposer is dispersed in a positive electrode and / or a negative electrode and / or a non-aqueous electrolyte.
3. The non-aqueous electrolyte secondary battery according to 1. 3. The negative electrode has a negative electrode active material made of a carbon material. The hydrogen fluoride decomposing agent is dispersed inside the negative electrode together with the negative electrode active material, and the hydrogen fluoride decomposing agent and the negative electrode active material are dispersed. 3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the content is 6% by mass or less based on the sum with the substance.