JP2000353545A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with high charge and discharge efficiency, a superior cycle characteristic, and a high energy density by minimizing decomposition of an electrolyte in a nonaqueous electrolyte secondary battery using a graphite base negative electrode. SOLUTION: In this nonaqueous electrolyte secondary battery composed of at the least a negative electrode containing graphite as a negative electrode material capable of occluding and releasing lithium, a positive electrode, and a nonaqueous electrolyte comprising lithium salt dissolved in a nonaqueous solvent, the nonaqueous solvent is a mixed nonaqueous solvent containing cyclic carbonate and chain carbonate, and contains cyclic sulfone having a carbon- carbon double bond inside a ring of 0.1 vol.% or more and less than 5 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to improvement of a non-aqueous electrolyte secondary battery using an electrolyte containing a sulfone having a specific structure. The battery of the present invention has high charge / discharge efficiency and excellent cycle characteristics, so that the nonaqueous electrolyte secondary battery can be reduced in size,
It can contribute to higher performance.

[0002]

2. Description of the Related Art With the recent reduction in the weight and size of electric products, development of lithium secondary batteries having a high energy density has been promoted. In addition, with the expansion of the application field of the lithium secondary battery, improvement in battery characteristics is also demanded. Secondary batteries using lithium metal as a negative electrode have been actively studied for a long time as batteries capable of achieving high capacity.However, lithium metal grows in a dendrite shape by repeated charge and discharge, and eventually becomes a positive electrode. As a result, the occurrence of a short circuit inside the battery is the biggest technical problem that prevents practical use. Therefore, a non-aqueous electrolyte secondary battery using a carbonaceous material capable of occluding and releasing lithium ions such as coke, artificial graphite, and natural graphite for the negative electrode has been proposed. In such a non-aqueous electrolyte secondary battery,
Since lithium does not exist in a metallic state, formation of dendrites is suppressed, and battery life and safety can be improved.

In particular, graphite-based carbon materials such as artificial graphite and natural graphite are expected as materials capable of improving the energy density per unit volume. However, non-aqueous electrolyte secondary batteries, which are made of various graphite materials alone or mixed with other anode materials capable of inserting and extracting lithium, are used as a lithium primary battery. When an electrolytic solution containing propylene carbonate as a main solvent is used, the decomposition reaction of the solvent proceeds sharply on the graphite electrode surface, making it impossible to smoothly insert and extract lithium into and from the graphite electrode. On the other hand, since ethylene carbonate is less decomposed, ethylene carbonate is frequently used as a main solvent in the electrolyte of a non-aqueous electrolyte secondary battery using a graphite-based negative electrode. However, even when ethylene carbonate is used as the main solvent, there are problems such as a decrease in charge / discharge efficiency and a decrease in cycle characteristics because the electrolyte is decomposed on the electrode surface during the charge / discharge process. Therefore, there is a need to provide a non-aqueous electrolyte secondary battery that does not cause these problems even when a graphite-based negative electrode is used.

[0004] Since the performance of graphite-based negative electrodes greatly differs depending on the type of the electrolyte, it is necessary to optimize the composition of the electrolyte. Various electrolytes have been studied in the past. Some batteries using a non-aqueous solvent containing a cyclic sulfone such as sulfolane as an electrolyte have been proposed. For example, JP-A-8-78052 discloses that a mixed nonaqueous solvent containing ethylene carbonate and chain carbonate contains sulfolane or 3-methylsulfolane as a nonaqueous solvent for a nonaqueous electrolyte secondary battery using graphite as a negative electrode. It is proposed that the content is 5 to 65
% By volume is preferred. Also, JP-A-8-32
No. 1312 discloses ethylene carbonate as an electrolytic solution,
One or more high dielectric constant solvents selected from propylene carbonate and butylene carbonate, or 1,2-
It has been proposed that butadiene sulfone, 3-methylsulfolene, and other additives be contained in a mixed solvent with dimethoxyethane in an amount of 1 to 20% by volume as an additive.

[0005]

However, the electrolyte disclosed in the above publication containing a large amount of cyclic sulfone such as sulfolane has a problem that the electric conductivity tends to be low and sufficient battery characteristics cannot be exhibited. . In addition, since ethylene carbonate is solid at room temperature, when used in a mixed solvent with 1,2-dimethoxyethane, the withstand voltage characteristic of 1,2-dimethoxyethane increases when the operating potential of the secondary battery increases. Sometimes it is not enough. The present invention
It solves these problems of the prior art, and minimizes the decomposition of the electrolyte in a non-aqueous electrolyte secondary battery using a graphite-based negative electrode, has high charge and discharge efficiency, and has excellent cycle characteristics. An object is to provide a non-aqueous electrolyte secondary battery with high energy density.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above circumstances, and have found that a cyclic carbonate and a chain carbonate are contained as an electrolyte of a non-aqueous electrolyte secondary battery using a graphite-based negative electrode. It has been found that the use of an electrolytic solution containing a lithium salt and a predetermined amount of a cyclic sulfone having a specific structure in a mixed nonaqueous solvent can improve charge / discharge efficiency and cycle characteristics, and have completed the present invention. Was.

That is, the gist of the present invention is to store and store lithium.
In a non-aqueous electrolyte secondary battery at least comprising a negative electrode containing graphite as a negative electrode material capable of being released, a positive electrode and an electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent,
The non-aqueous solvent is a mixed non-aqueous solvent containing a cyclic carbonate and a chain carbonate, and the non-aqueous solvent has a carbon-carbon double bond in the ring of 0.1% by volume or more and less than 5% by volume. And a non-aqueous electrolyte secondary battery.

The non-aqueous solvent used in the secondary battery of the present invention is a mixed non-aqueous solvent containing a cyclic carbonate and a chain carbonate, and it is preferable that 70% by volume or more of the non-aqueous solvent is a carbonate. In particular, the mixed non-aqueous solvent has a cyclic carbonate selected from the group consisting of alkylene carbonates having 2 to 4 carbon atoms of an alkylene group and a chain selected from the group consisting of dialkyl carbonates having 1 to 4 carbon atoms of an alkyl group. Carbonate and 20 each
It is preferable that these carbonates contain at least 70% by volume of the mixed nonaqueous solvent.

Further, the negative electrode material used in the secondary battery of the present invention may be a negative electrode material made of graphite only, or non-graphite carbon, lithium, lithium alloy, and metal oxide capable of inserting and extracting lithium. It is preferable that the negative electrode material is a mixture of at least one member selected from the group consisting of graphite and graphite. In particular, when the negative electrode material has a lattice plane (002 plane) d value of 0.335 to 0.34 nm in X-ray diffraction and a crystallite size (Lc) of 30 nm or more, preferably 50 nm or more, particularly 100 nm or more. It is preferable to include a carbon material. Further, the secondary battery of the present invention is more preferably applied to a battery having a charge potential of 4.0 V or more at the positive electrode during charging.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The secondary battery of the present invention comprises a negative electrode containing graphite as a negative electrode material capable of inserting and extracting lithium, a positive electrode, and an electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent. Be composed. In the present invention, the non-aqueous solvent of the electrolytic solution is a mixed non-aqueous solvent containing a cyclic carbonate and a chain carbonate, and the non-aqueous solvent contains carbon in an amount of 0.1% by volume or more and less than 5% by volume. -It is characterized by containing a cyclic sulfone having a carbon double bond.

The cyclic carbonate used in the present invention is not particularly limited, but is preferably an alkylene carbonate, and more preferably an alkylene group having 2 to 4 carbon atoms. Specific examples of such an alkylene carbonate include ethylene carbonate, propylene carbonate, and butylene carbonate. Among them, ethylene carbonate and propylene carbonate are preferable. These alkylene groups may have a substituent within a range that does not unduly inhibit the intended effect of the present invention.

The chain carbonate used in the present invention is not particularly limited, but is preferably a dialkyl carbonate, and more preferably an alkyl group having 1 to 4 carbon atoms. Specific examples of such dialkyl carbonate include, for example, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and the like.
Among them, dimethyl carbonate, diethyl carbonate,
Ethyl methyl carbonate is preferred. The alkyl group of these dialkyl carbonates may have a substituent within a range that does not unduly inhibit the intended effect of the present invention.

The combination of the cyclic carbonate and the chain carbonate is not particularly limited. Preferred combinations are
A mixed nonaqueous solvent containing a cyclic carbonate selected from the group consisting of alkylene carbonates having 2 to 4 carbon atoms in an alkylene group and a chain carbonate selected from the group consisting of dialkyl carbonates having 1 to 4 carbon atoms in the alkyl group It is. A more preferred combination is a mixed non-aqueous solvent containing at least one selected from ethylene carbonate and / or propylene carbonate as the cyclic carbonate and at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate as the chain carbonate. The proportions of the cyclic carbonate and the chain carbonate in the mixed non-aqueous solvent are each preferably at least 20% by volume, and more preferably at least 25% by volume. Further, the total amount of the cyclic carbonate and the chain carbonate in the mixed non-aqueous solvent is preferably 70% by volume or more, more preferably 80% by volume or more, and particularly preferably 90% by volume or more.

The mixed non-aqueous solvent may contain a solvent other than carbonate. As solvents other than carbonates, for example, cyclic esters such as γ-butyrolactone and γ-valerolactone, chain esters such as methyl acetate and methyl propionate, cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and tetrahydropyran, dimethoxy Chain ethers such as ethane and dimethoxymethane; These solvents may be used in combination of two or more kinds. These solvents can be contained in the mixed non-aqueous solvent in an amount that does not impair the properties of the carbonate-based solvent. Specifically, the amount of the solvent other than carbonate is preferably 30% by volume or less of the mixed non-aqueous solvent, more preferably 20% by volume or less, and particularly preferably 10% by volume or less. It should be noted that the volume% in this specification is all measured at room temperature, that is, at 25 ° C. However, when the solid is at 25 ° C., it is heated to its melting point and measured in a molten state.

The electrolyte used in the present invention contains carbon-
It contains a cyclic sulfone having a carbon double bond. The type of the cyclic sulfone used in the present invention is not particularly limited as long as the compound has a sulfone structure in a part of the cyclic structure and has a carbon-carbon double bond in the ring. Specific examples of the cyclic sulfone having a carbon-carbon double bond in the ring used in the present invention include 3-sulfolene, 2-sulfolene, and 3-sulfolene.
-Methyl-3-sulfolene, 3-ethyl-3-sulfolene, 3-methyl-2-sulfolene, 3-ethyl-2-sulfolene, and the like. Among them, 3-sulfolene and 3-methyl-3-sulfolene are preferable. These may be used as a mixture of two or more. The content of the cyclic sulfone having a carbon-carbon double bond in the ring in the electrolytic solution used in the present invention is 0.1% by volume or more and less than 5% by volume, preferably 0.5 to 5% by volume in the mixed non-aqueous solvent. 4.5
% By volume.

In the electrolytic solution used in the present invention, a lithium salt is used as a solute. The type of the lithium salt that can be used is not particularly limited as long as it can be used as a solute of the electrolytic solution. For example, LiClO ₄ , LiPF ₆ , LiB
An inorganic lithium salt selected from F ₄ , 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 SO ₂ ),
Fluorine-containing organic lithium salts such as LiC (CF ₃ SO ₂ ) ₃ can be used. Among them, LiPF ₆ , LiBF ₄
It is preferable to use These lithium salts may be used as a mixture of two or more kinds. The molar concentration of the lithium salt in the solute in the electrolyte is desirably 0.5 to 2 mol / liter. Less than 0.5 mol / l or 2 mol /
If it exceeds 1 liter, the electric conductivity of the electrolytic solution tends to decrease, and the performance of the battery tends to decrease.

The negative electrode constituting the non-aqueous electrolyte secondary battery of the present invention contains graphite as a component thereof. The physical properties of graphite are not particularly limited as long as it can absorb and release lithium. Preferred are artificial graphite and purified natural graphite produced by high-temperature heat treatment of graphitic pitch obtained from various raw materials, or materials obtained by subjecting these graphites to various surface treatments including pitch. These graphite materials have a lattice plane (002) determined by X-ray diffraction by the Gakushin method.
The d value (interlayer distance) of the (surface) is preferably from 0.335 to 0.34 nm, more preferably from 0.335 to 0.337 nm. The ash content of these graphite materials is preferably 1% by weight or less, more preferably 0.5% by weight or less, and particularly preferably 0.1% by weight or less. The crystallite size (Lc) determined by X-ray diffraction according to the Gakushin method is preferably 30 nm or more.
It is more preferably at least 100 nm, particularly preferably at least 100 nm.

Further, graphite materials obtained by a laser diffraction / scattering method
The median diameter of the material is preferably 1 to 100 μm.
More preferably 3 to 50 μm or less, and 5 to 4 μm.
0 μm is more preferable, and it is 7 to 30 μm.
Is particularly preferred. The BET specific surface area of the graphite material is 0.
5 to 25.0m^Two/ G, preferably 0.7 to 2
0.0m^Two/ G, more preferably 1.0 to 1
5.0m^Two/ G, more preferably 1.5 to 1
0.0m^Two/ G is particularly preferred. Argo
Raman spectrum analysis using ion laser light
And 1580-1620cm^-1Peak P in the range
_A(Peak intensity I_A) And 1350-1370 cm ^-1of
Range peak P_B(Peak intensity I_B) Intensity ratio R = I_B
/ I_A Is from 0 to 1.4, preferably from 0 to 1.2, particularly preferably
Or 0-0.5, 1580-1620cm^-1of
The peak half width of the range is 26cm^-1Below, especially 25cm
^-1It is preferred that:

A negative electrode material capable of occluding and releasing lithium can be further mixed with these graphite materials and used. As the negative electrode material capable of inserting and extracting lithium other than graphite, non-graphitic carbon materials such as non-graphitizable carbon or low-temperature fired carbon, metal oxide materials such as tin oxide and silicon oxide, lithium metal and various other materials A lithium alloy can be exemplified.
These negative electrode materials may be used as a mixture of two or more.
The method for producing a negative electrode using these negative electrode materials is not particularly limited. For example, a negative electrode can be manufactured by adding a binder, a thickener, a conductive material, a solvent, and the like to a negative electrode material as needed to form a slurry, applying the slurry to a current collector substrate, and drying. Alternatively, the negative electrode material can be roll-formed as it is to form a sheet electrode, or can be formed into a pellet electrode by compression molding.

The binder used in the production of the electrode is not particularly limited as long as it is a material that is stable with respect to the solvent and the electrolyte used in the production of the electrode. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene / butadiene rubber, isoprene rubber, and butadiene rubber. As a thickener,
Examples include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. Examples of the conductive material include metal materials such as copper and nickel, and carbon materials such as graphite and carbon black. The material of the negative electrode current collector is copper,
Metals such as nickel and stainless steel are used, and among these, copper foil is preferred from the viewpoint of easy processing into a thin film and cost.

As the material of the positive electrode constituting the battery of the present invention, a material capable of occluding and releasing lithium such as a lithium transition metal composite oxide material such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide is used. Can be used. In the present invention, LiCo
Lithium transition metal composite oxides such as O ₂ , LiNiO ₂ , and LiMn ₂ O ₄ , which have a positive electrode potential of 4.0 V or more during charging, are preferable. The method for manufacturing the positive electrode is not particularly limited, and the positive electrode can be manufactured according to the above-described method for manufacturing the negative electrode. As for the shape, a binder, a conductive material, a solvent, and the like are added to the positive electrode material as necessary and mixed, and then applied to a current collector substrate to form a sheet electrode, or a pellet electrode formed by press molding. It can be. As a material of the current collector for the positive electrode, a metal such as aluminum, titanium, and tantalum or an alloy thereof is used. Among these, aluminum or its alloy is desirable in terms of energy density because it is lightweight.

The material and shape of the separator used in the battery of the present invention are not particularly limited. However, it is preferable to select from materials that are stable with respect to the electrolyte and have excellent liquid retention properties, and it is preferable to use a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene as a raw material. The method for producing the battery of the present invention having at least the negative electrode, the positive electrode, and the nonaqueous electrolyte is not particularly limited, and can be appropriately selected from commonly employed methods. The shape of the battery is not particularly limited, and 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 stacked are used. It is possible.

[0023]

EXAMPLES The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples unless it exceeds the gist. (Example 1) As for an electrolytic solution, lithium hexafluorophosphate (Li) was sufficiently dried under a dry argon atmosphere.
Using PF ₆ ) as a solute, 3-sulfolene was dissolved at a rate of 3% by volume in 97% by volume of a mixture of propylene carbonate and diethyl carbonate (1: 1 by volume), and LiPF ₆ was further dissolved at a rate of 1 mol / L. Prepared by dissolution.

D of lattice plane (002 plane) in X-ray diffraction
Value is 0.336 nm, crystallite size (Lc) is 100 n
m (264 nm), ash content: 0.04% by weight, median diameter by laser diffraction / scattering method: 17 μm, BET specific surface area: 8.9 m ² / g, Raman spectrum analysis using argon ion laser light: 1580 to 16
Intensity ratio R = I _B / I _A of the peak P _A in the range of 20 cm ^-1 (peak intensity I _A) and the peak P _B in the range of 1350 ^-1 (peak intensity I _B) is 0.15,158
The half width of the peak in the range of ⁰ to 1620 cm ^-1 is 22.2.
A styrene-butadiene rubber (SBR) dispersed in distilled water was added to 94 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by Timcal Co., Ltd.) having a cm ^-1 of 6 parts by weight in a solid content to obtain a disperser. The slurry was uniformly mixed on a 18 μm-thick copper foil as a current collector, dried, and punched into a disk having a diameter of 12.5 mm to produce an electrode. A coin-type half cell having a lithium foil as a counter electrode via a separator impregnated with the liquid was produced.

Comparative Example 1 A mixture of propylene carbonate and diethyl carbonate (1: 1 by volume) was mixed with Li
A coin-type half cell was produced in the same manner as in Example 1, except that an electrolyte prepared by dissolving PF ₆ at a rate of 1 mol / liter was used. Next, with respect to the coin-type half cells of Example 1 and Comparative Example 1 produced as described above, at 25 ° C., a discharge end voltage of 0 V at a constant current of 0.2 mA, and a charge end voltage of 1 at a constant current of 0.4 mA. A charge / discharge test was performed at 0.5 V. The undoping capacity (the undoping capacity of lithium from the working electrode) in the first cycle of Example 1 was 2
The efficiency at the first cycle (dedoping capacity / doping capacity) was 69%. On the other hand, in Comparative Example 1, the solvent was decomposed and did not operate as a battery. Here, the capacity indicates a capacity per weight of graphite used as a working electrode.

Example 2 LiCoO as a positive electrode active material
₂ 85 parts by weight of carbon black and 6 parts by weight of polyvinylidene fluoride KF-1000 (trade name, manufactured by Kureha Chemical Co., Ltd.) 9
Parts by weight and mixed with each other, and dispersed with N-methyl-2-pyrrolidone to form a slurry.
It was uniformly coated on a 0-μm aluminum foil, dried, and then punched into a 12.5 mm diameter disk to form a positive electrode.

As a negative electrode active material, a lattice in X-ray diffraction
D value of plane (002 plane) is 0.336 nm, crystallite size
(Lc) is 100 nm or more (264 nm) and ash content is
0.04% by weight, median by laser diffraction / scattering method
Diameter 17μm, BET specific surface area 8.9m^Two/ G, a
Raman spectrum analysis using Lugon ion laser light
At 1580-1620cm^-1Peak P in the range_A
(Peak intensity I_A) And 1350-1370 cm^-1Range of
Surrounding peak P_B(Peak intensity I_B) Intensity ratio R = I _B/
I_AIs 0.15, 1580-1620cm^-1Range of pi
The half width of the peak is 22.2cm^-1Is artificial graphite powder KS
-44 (Timcal Co., trade name) 95 parts by weight of polyfu
5 parts by weight of vinylidene difluoride, and N-methyl-2-pi
Slurry dispersed with loridone
Apply evenly on 18μm thick copper foil and dry
Then, it is punched out into a disk shape with a diameter of 12.5 mm to form a negative electrode.
Was.

As for the electrolytic solution, lithium hexafluorophosphate (Li) was sufficiently dried in a dry argon atmosphere.
PF ₆ ) was used as a solute, and 3-sulfolene was dissolved at a ratio of 2% by volume in 98% by volume of a mixture of ethylene carbonate and diethyl carbonate (1: 1 by volume).
It was prepared by dissolving iPF ₆ at a rate of 1 mol / liter. Using these positive electrode, negative electrode, and electrolyte, the positive electrode is housed in a stainless steel can body whose inner surface also serving as the positive electrode conductor is coated with aluminum, and a polyethylene separator impregnated with the electrolyte is placed on the positive electrode. The negative electrode was placed. The can body and the sealing plate also serving as the negative electrode conductor were caulked and sealed via an insulating gasket to produce a coin-type battery.

Example 3 Ethylene carbonate and die
98% by volume of a mixture of chill carbonate (1: 1 by volume)
3-methyl-3-sulfolene in 2% by volume
And then LiPF ₆Dissolved at a rate of 1 mol / liter
Same as Example 2 except that the electrolyte solution prepared in
To produce a coin-type battery. (Comparative Example 2) Ethylene
A mixture of carbonate and diethyl carbonate (1: 1
Capacity ratio), LiPF₆At a rate of 1 mol / l
Example 2 except that the electrolyte solution prepared by disassembly was used.
Similarly, a coin-type battery was produced.

Example 4 3-Sulfolene was dissolved at a ratio of 2% by volume in 98% by volume of a mixture of propylene carbonate and diethyl carbonate (1: 1 by volume).
A coin-type battery was produced in the same manner as in Example 2, except that an electrolytic solution prepared by dissolving iPF ₆ at a rate of 1 mol / liter was used. Example 5 3-methyl-3-sulfolene was dissolved in 98% by volume of a mixture of propylene carbonate and diethyl carbonate (1: 1 by volume) at a ratio of 2% by volume, and L
A coin-type battery was produced in the same manner as in Example 2, except that an electrolytic solution prepared by dissolving iPF ₆ at a rate of 1 mol / liter was used.

Comparative Example 3 A mixture of propylene carbonate and diethyl carbonate (1: 1 by volume) was mixed with Li
A coin-type battery was produced in the same manner as in Example 2, except that an electrolytic solution prepared by dissolving PF ₆ at a rate of 1 mol / liter was used. The batteries prepared in Examples 2 to 5 and Comparative Examples 2 and 3 were charged at 25 ° C. with a constant current of 0.5 mA at a charge end voltage of 4.2 V and a discharge end voltage of 2.5 V.
A charge / discharge test was performed. Table 1 shows the discharge capacity per charge of the negative electrode in the first cycle, the charge / discharge efficiency, and the capacity retention rate (%) as a measure of the cycle characteristics in each battery. Here, the charge / discharge efficiency and the capacity retention rate are obtained from the following equations. Charge / discharge efficiency (%) = [(discharge capacity) / (charge capacity)] × 1
00 capacity retention rate (%) = [(discharge capacity at 100th cycle) /
(1st cycle discharge capacity)] × 100

[0032]

[Table 1]

From Table 1, it is clear that the use of the electrolytic solution of the present example improves the initial charge / discharge efficiency, improves the capacity retention ratio, and excels in cycle characteristics.
In the case of the propylene carbonate-based electrolyte solution of Comparative Example 3, propylene carbonate decomposed violently on the graphite material surface of the negative electrode and did not operate as a battery, but contained a cyclic sulfone having a carbon-carbon double bond in the ring. By doing so, operation becomes possible, and the discharge capacity and cycle characteristics are significantly improved.

[0034]

As described above, a mixed non-aqueous solvent containing a cyclic carbonate and a chain carbonate is used as a non-aqueous solvent for an electrolyte of a non-aqueous electrolyte secondary battery using a graphite-based negative electrode. 1% by volume or more and less than 5% by volume of carbon-
By containing a cyclic sulfone having a carbon double bond, a considerably stable lithium ion permeable composite protection derived from a cyclic sulfone having a carbon-carbon double bond and a carbonate is provided on the graphite surface in contact with the electrolytic solution. It is believed that a coating forms. Due to this coating, excessive decomposition of the electrolyte is suppressed, and a battery having excellent cycle characteristics can be manufactured, which can contribute to miniaturization and high performance of the nonaqueous electrolyte secondary battery.

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Claims (6)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising at least a negative electrode containing graphite as a negative electrode material capable of inserting and extracting lithium, a positive electrode, and an electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent. Wherein the non-aqueous solvent is a mixed non-aqueous solvent containing a cyclic carbonate and a chain carbonate, and the non-aqueous solvent has a carbon-carbon double bond in the ring of 0.1% by volume or more and less than 5% by volume. A non-aqueous electrolyte secondary battery comprising a cyclic sulfone. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein 70% by volume or more of the mixed non-aqueous solvent is carbonate. 3. The mixed non-aqueous solvent is selected from the group consisting of a cyclic carbonate selected from the group consisting of alkylene carbonates having 2 to 4 carbon atoms of an alkylene group and a dialkyl carbonate consisting of 1 to 4 carbon atoms of an alkyl group. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery contains at least 20% by volume of the chain carbonate, and 70% by volume or more of the mixed non-aqueous solvent is these carbonates. . 4. The negative electrode material comprises at least one selected from the group consisting of a negative electrode material consisting of graphite alone, a non-graphite carbon capable of occluding and releasing lithium, lithium, a lithium alloy, and a metal oxide. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the non-aqueous electrolyte secondary battery is a negative electrode material obtained by mixing graphite. 5. The method according to claim 1, wherein the negative electrode material has a lattice plane (0
The non-aqueous system according to any one of claims 1 to 4, wherein the d-value of the (02 plane) is 0.335 to 0.34 nm, and the carbon material has a crystallite size (Lc) of 30 nm or more. Electrolyte secondary battery. 6. The negative electrode material has a lattice plane (0
02 surface) is 0.335 to 0.337 nm,
The non-aqueous electrolyte secondary battery according to claim 5, wherein the non-aqueous electrolyte secondary battery is made of a carbon material having a crystallite size (Lc) of 50 nm or more.