JPH11121032A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a high energy density non-aqueous electrolyte secondary battery excellent in low-temperature characteristics, long-term stability, and recycling characteristics. SOLUTION: A non-aqueous material comprising a negative electrode and a positive electrode containing graphite as at least one component thereof as a negative electrode material capable of inserting and extracting lithium, a negative electrode current collector, a positive electrode current collector, a solute and an organic solvent. A non-aqueous electrolyte secondary battery comprising an electrolyte and a separator, wherein a mixed solvent containing ethylene sulfite and vinylene carbonate is used as the organic solvent. A material for a portion of the positive electrode current collector and a positive electrode side outer can that is in contact with the nonaqueous electrolyte is a valve metal or an alloy thereof, wherein the secondary battery is a nonaqueous electrolyte secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high energy density non-aqueous electrolyte secondary battery having excellent low-temperature characteristics, long-term stability, and cycle characteristics.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries having a high energy density have attracted attention as electric appliances become lighter and smaller. In addition, with the expansion of the application field of the lithium secondary battery, improvement in battery characteristics is also demanded. Non-aqueous organic solvents such as carbonates or esters such as ethylene carbonate, propylene carbonate, diethyl carbonate, and γ-butyrolactone have been used as the solvent for the electrolyte solution of such a lithium secondary battery.

[0003] Among them, propylene carbonate is a solvent having a high dielectric constant, dissolves a lithium salt-based solute (electrolyte) well, and has a high electric conductivity even at a low temperature. It is. However, when highly crystalline graphite or graphitized carbon is used for the negative electrode material, if an electrolytic solution containing a large amount of the propylene carbonate is used, propylene carbonate is decomposed on the carbon material surface, and a problem such as gas generation occurs. Therefore, ethylene carbonate is used instead. Since ethylene carbonate has a higher freezing point of 36.4 ° C. than propylene carbonate, ethylene carbonate is not used alone, but is used by mixing with a low-viscosity solvent.

Various solvents have been studied as solvents used as low-viscosity solvents. However, low-viscosity solvents generally have a low boiling point in many cases. If only a small amount is added, there is a problem in terms of electric conductivity and viscosity at low temperature. Under such circumstances, a mixed solvent of ethylene carbonate and diethyl carbonate or the like is used as an electrolyte for a lithium secondary battery. However, batteries using these electrolytes also have problems in low-temperature characteristics and the like.

[0005] In order to solve the above problems, it has been proposed to use a sulfite compound as a solvent (for example, JP-A-6-302336, JP-A-7-302).
122295, JP-A-8-96851, JP-A-9-
No. 120837). According to these, it has been reported that an electrolytic solution using a sulfite compound has high electric conductivity and low viscosity, and thus has good low-temperature characteristics and the like of a battery. However, when the sulfite compound was used as a solvent for the electrolytic solution, the charge / discharge efficiency, particularly the initial charge / discharge efficiency, was not sufficient.

[0006]

According to the present invention, when ethylene sulfite having excellent low-temperature characteristics is used as one component of a mixed solvent of an electrolytic solution, a film derived from ethylene sulfite formed on the electrode surface can be further stabilized. It is intended to provide a high-energy-density non-aqueous electrolyte secondary battery having excellent low-temperature characteristics, long-term stability, and cycle characteristics.

[0007]

SUMMARY OF THE INVENTION The present invention provides a non-aqueous electrolyte comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, a negative electrode current collector, a positive electrode current collector, a solute and an organic solvent. Liquid, a non-aqueous electrolyte secondary battery comprising a separator and an outer can, wherein the organic solvent comprises ethylene sulfite and vinylene carbonate, wherein the non-aqueous electrolyte secondary battery is provided. is there.

[0008]

It is considered that a stable composite film is formed on the negative electrode by using the electrolytic solution containing ethylene sulfite and vinylene carbonate, and the decomposition of the electrolytic solution on the negative electrode can be minimized. In addition, since the surface of the valve metal is covered with an oxide film, it is possible to prevent the oxidative decomposition reaction of ethylene sulfite at a portion in contact with the electrolytic solution of the positive electrode current collector or the positive electrode outer can.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention comprises a negative electrode and a positive electrode capable of inserting and extracting lithium, a negative electrode current collector and a positive electrode current collector, a solute and an organic solvent. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte solution comprising: a separator and an outer can, comprising ethylene sulfite and vinylene carbonate as the organic solvent.

Non-aqueous electrolyte : The non-aqueous electrolyte is composed of a solute and
Contains a mixed solvent of ethylene sulfite and vinylene carbonate. The vinylene carbonate content in the mixed solvent of the non-aqueous electrolyte is 0.01 to 10 vol%, and the ethylene sulfite content is 0.05 to 99.99 vol.
%, Preferably in the range of 0.05 to 50 vol%.

In the above-mentioned mixed solvent, as a third solvent component other than the vinylene carbonate and ethylene sulfite, cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. , Γ-butyrolactone, cyclic esters such as γ-valerolactone, chain esters such as methyl acetate and methyl propionate, cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and tetrahydropyran, dimethoxyethane, dimethoxymethane and the like. It is possible to use a mixture of a chain ether, a sulfur-containing organic solvent such as sulfolane, diethyl sulfone and the like. These solvents may be used as a mixture of two or more kinds.

As a solute, LiClO_Four, LiP
F₆, LiBF_FourAn inorganic lithium salt or L selected from
iCF_ThreeSO_Three, LiN (CF_ThreeSO_Two)_Two , LiN
(CF_ThreeCF_TwoSO_Two)_Two, LiN (CF_ThreeSO_Two)
(C_FourF₉SO_Two), LiC (CF _ThreeSO_Two)_ThreeIncluding
Fluoroorganic lithium salts can be used. these
Two or more solutes may be used as a mixture. Dissolution in electrolyte
The molar concentration of the lithium salt is 0.5 to 2.0 mol / l
It is desirable to be a title. 0.5 mol / l or less
Below or at 2.0 mol / L or more, the
Air conductivity is low and battery performance deteriorates.
No.

Negative electrode: As a negative electrode material constituting a battery,
Organic pyrolysis products under various thermal decomposition conditions, carbonaceous materials such as artificial graphite and natural graphite that can occlude and release lithium, metal oxide materials that can occlude and release lithium such as tin oxide and silicon oxide, Lithium metal and various lithium alloys can be used. These negative electrode materials may be used as a mixture of two or more. When a graphite-based carbonaceous material is used as a negative electrode material, artificial graphite and natural graphite produced by high-temperature heat treatment of easily-graphitizable pitch obtained from various raw materials, or these graphites are subjected to various surface treatments. These materials are mainly used, and these graphite materials have a d value (interlayer distance) of 0.3 (lattice plane) of the lattice plane (002 plane) obtained by X-ray diffraction.
35-0.34 nm, more preferably 0.335-0.
Those having a thickness of 337 nm are preferred. As the shape of the negative electrode, a sheet electrode applied to a current collector after mixing with a binder and a conductive agent, if necessary, and a pellet electrode subjected to press molding can be used.

Negative electrode current collector: As the material of the negative electrode current collector, metals such as copper, nickel, and stainless steel are used, and among these, copper foil is preferable in terms of easy processing into a thin film and cost. Separator: As a separator constituting a battery, a porous sheet or a nonwoven fabric made of a polyolefin such as polyethylene or polypropylene can be used.

Positive electrode: As a positive electrode material constituting a battery,
Materials that can occlude and release lithium, such as lithium transition metal composite oxide materials such as lithium cobalt oxide and lithium nickel oxide, can be used. As the shape of the positive electrode, a sheet electrode applied to a current collector after mixing with a binder and a conductive agent as necessary, and a pellet electrode subjected to press molding can be used. Positive electrode current collector: The material of the positive electrode current collector is preferably a valve metal such as aluminum, titanium, and tantalum, or an alloy thereof, because the oxidation decomposition reaction of ethylene sulfite can be prevented and cycle characteristics can be improved. Among these valve metals, aluminum or its alloy is particularly preferable in terms of energy density because of its light weight.

Outer can: Stainless steel is preferably used as the outer can material of the battery, but it is preferable from the above-mentioned reason that the portion electrically connected to the positive electrode and in contact with the electrolyte is a valve metal such as aluminum. As a method of protecting with valve metal, there is a method of protecting with plating or foil. Further, aluminum or an aluminum alloy may be used as the outer can material. The outer can referred to here includes a lead wire housed inside the battery, a safety valve that operates when the internal pressure inside the battery rises, and the like.

Battery: The shape of the battery can be a cylinder type in which a sheet electrode and a separator are formed in a spiral shape, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, and a coin type in which a pellet electrode and a separator are laminated. is there. FIG. 1 shows a sectional view of a coin-type non-aqueous electrolyte battery.
In the figure, 1 is a positive electrode, 2 is a negative electrode, 3 is a positive electrode can, 4 is a sealing plate,
5 is a separator, 6 is an aluminum foil, 7 is a gasket, 8 is a positive electrode current collector, and 9 is a negative electrode current collector. Non-aqueous electrolyte is generally impregnated in the separator

[0018]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. (Examples 1 to 3 and Comparative Examples 1 to 3) Carbon black (6 parts by weight) and polyvinylidene fluoride (9 parts by weight) were added to LiCoO ₂ (85 parts by weight) as a positive electrode active material and mixed. A slurry obtained by dispersing with 2-pyrrolidone and forming a slurry was uniformly applied on a 20 μm-thick aluminum foil serving as a positive electrode current collector, dried, and punched into a predetermined shape to obtain a positive electrode.

As the negative electrode active material, artificial graphite powder KS-44 (trade name, manufactured by Timcal Co., Ltd., trade name) (94 parts by weight) having a lattice plane (002) d value of 0.336 nm in X-ray diffraction was used. (6 parts by weight) and mix with N
A slurry prepared by dispersing in -methyl-2-pyrrolidone was uniformly applied on a 18 μm-thick copper foil as a negative electrode current collector, dried, and punched into a predetermined shape to obtain a negative electrode.

As for the electrolyte, lithium hexafluorophosphate (Li) which has been sufficiently dried in a dry argon atmosphere is used.
PF ₆ ) as a solute and ethylene sulfite (E
S), vinylene carbonate (VC), ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a mixed solution having the composition shown in Table 1 were prepared by dissolving LiPF ₆ at a ratio of 1 mol / liter. Prepared.

Using these positive electrode, negative electrode, and electrolyte, a coin-type nonaqueous electrolyte battery as shown in FIG. 1 was prepared in a dry argon atmosphere. In the following, referring to FIG. 1, the positive electrode 1 and the negative electrode 2 are accommodated in a stainless steel positive electrode can 3 and a sealing plate 4, respectively, and a separator 5 made of a polypropylene microporous film impregnated with each electrolytic solution is formed. In this case, the inside of the positive electrode can 3 is previously made of aluminum foil 6 so that the material of the liquid contact portion on the positive electrode side is made of valve metal.
Covered with and used. Subsequently, the positive electrode can 3 and the sealing plate 4 were caulked and sealed via the gasket 7 to complete a coin-type battery.

These batteries were heated at 25 ° C. for 0.5 m
At a constant current of A, the charge end voltage is 4.2 V and the discharge end voltage is 2.
A charge / discharge test was performed at 5V. Table 1 shows the charge and discharge efficiencies at the first and tenth cycles of these batteries.
Here, charge / discharge efficiency (%) = (discharge capacity) / (charge capacity)
It is.

[0023]

[Table 1] Note) ES: Ethylene sulfite EC: Ethylene carbonate PC: Propylene carbonate VC: Vinylene carbonate

From Table 1, it can be seen that by using vinylene carbonate in combination with the electrolyte containing ethylene sulfite, the charge and discharge efficiency, especially the initial charge and discharge efficiency, can be improved. This is considered to be because the use of the electrolyte containing ethylene sulfite and vinylene carbonate forms a fairly stable composite film on the negative electrode and minimizes the decomposition of the electrolyte on the negative electrode.

[0025]

EFFECTS OF THE INVENTION Ethylene sulphite and vinylene carbonate are selected as organic solvents for the electrolyte of the non-aqueous electrolyte secondary battery, and the material of the positive electrode current collector and the part in contact with the electrolyte of the outer can of the positive electrode side By selecting a valve metal or its alloy, decomposition of the electrolyte on the negative electrode can be minimized, high capacity can be obtained, and a battery with excellent cycle characteristics and low-temperature characteristics can be produced. This can contribute to miniaturization and high performance of the liquid secondary battery.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of a coin-type battery.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 positive electrode 2 negative electrode 3 positive electrode can 4 sealing plate 5 separator 6 aluminum foil 7 gasket 8 positive electrode current collector 9 negative electrode current collector

──────────────────────────────────────────────────続 き Continuing on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 4/66 H01M 4/66 A (72) Inventor Mark Deshamp. Tsukuba Research Laboratories

Claims (10)

[Claims] 1. A negative electrode and a positive electrode capable of inserting and extracting lithium, a negative electrode current collector, a positive electrode current collector, a nonaqueous electrolytic solution including a solute and an organic solvent, a separator and an outer can. A non-aqueous electrolyte secondary battery comprising: a non-aqueous electrolyte secondary battery, wherein the organic solvent includes ethylene sulfite and vinylene carbonate. 2. The non-aqueous liquid electrolyte according to claim 1, wherein a material of a portion of the positive electrode current collector and the positive electrode side outer can that is in contact with the electrolyte is a valve metal or an alloy thereof. Next battery. 3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the valve metal and its alloy are aluminum and an aluminum alloy. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode capable of inserting and extracting lithium is made of a carbonaceous material or a metal oxide material. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode capable of inserting and extracting lithium is made of lithium metal or a lithium alloy. 6. The negative electrode capable of inserting and extracting lithium is made of a carbon material having a lattice plane (002 plane) having a d value of 0.335 to 0.34 nm in X-ray diffraction. Item 2. The non-aqueous electrolyte secondary battery according to Item 1. 7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode capable of inserting and extracting lithium is made of a lithium transition metal composite oxide material. 8. The method according to claim 1, wherein the solute is LiClO ₄ , LiPF ₆ , L
Inorganic lithium salt selected from iBF ₄ or LiCF ₃
SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃
CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is an organic lithium salt selected from SO ₂ ) and LiC (CF ₃ SO ₂ ) ₃ . 9. The content of vinylene carbonate in the organic solvent is 0.01 vol% to 10 vol%, and the content of ethylene sulfite is 0.05 vol% to 99 vol.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the content is 99 vol%. 10. The solute concentration in the non-aqueous electrolyte solution is 0.5
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amount is 2.0 to 2.0 mol / liter.