JP2000331709A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery of high energy density capable of minimizing decomposition of electrolyte and having high charge and discharge efficiency and superior cycle characteristics. SOLUTION: This nonaqueous electrolyte secondary battery comprises, at least a negative electrode containing graphite as negative electrode material capable of occluding and emitting lithium, a positive electrode, and electrolyte formed by melting lithium salt in nonaqueous solvent. The nonaqueous solvent is mixed nonaqueous solvent containing cyclic carbonate and chain carbonate, and the nonaqueous solvent contains a condensate of α-hydroxy acid, having a structure shown in the formula of 0.1-10 wt.%. 'R' in the formula represents a hydrogen atom, alkyl of 1-4C, or alkoxyl of 1-4C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to an improvement of a non-aqueous electrolyte secondary battery using an electrolyte containing a specific α-hydroxy acid condensate. Since the battery of the present invention has improved discharge efficiency and excellent cycle characteristics, it can contribute to miniaturization and high performance of a non-aqueous secondary battery.

[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,
It is expected as a material that can improve the energy density per unit volume.

[0003] However, in a non-aqueous electrolyte secondary battery in which various graphite-based electrode materials are used alone or mixed with other negative electrode materials capable of inserting and extracting lithium, a non-aqueous electrolyte secondary battery is generally used as a lithium primary battery. When an electrolyte containing propylene carbonate as a main solvent, which is preferably used, is used, a decomposition reaction of the solvent proceeds vigorously on the surface of the graphite electrode, making it impossible to smoothly insert and release lithium into and from the graphite electrode. On the other hand, ethylene carbonate has little such decomposition,
In an electrolyte of a non-aqueous electrolyte secondary battery using a graphite-based negative electrode, ethylene carbonate is frequently used as a main solvent.
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 anodes greatly differs depending on the type of electrolyte, it is necessary to optimize the composition of the electrolyte. Various electrolytes have been studied in the past. Some proposals have been made on non-aqueous solvent-based electrolytes containing lactides. For example, Japanese Patent Application Laid-Open No. 7-78634 proposes using a non-aqueous solvent containing an oxycarboxylic acid derivative as an electrolyte in a non-aqueous electrolyte secondary battery using lithium metal as a negative electrode. Also, Japanese Patent Application Laid-Open No. 7-1927
No. 61 discloses an example in which lactide is added to a mixed solvent of cyclic carbonate and dimethoxyethane using a graphite electrode.

[0005]

However, the performance of the battery disclosed in the above-mentioned publication using an electrolytic solution obtained by adding a lactide to a non-aqueous solvent is not always satisfactory. The present invention solves these problems of the prior art, and minimizes the decomposition of the electrolyte of a non-aqueous electrolyte secondary battery using a graphite-based negative electrode, has high charge-discharge efficiency, and has high cycle characteristics. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having a high energy density and a 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 mixed solution containing a cyclic carbonate and a chain carbonate as an electrolyte for a non-aqueous electrolyte secondary battery using a graphite-based negative electrode. The present inventors have found that the use of an electrolytic solution in which a condensate of a lithium salt and a specific α-hydroxy acid is dissolved in a non-aqueous solvent can improve charge / discharge efficiency and cycle characteristics, and have completed the present invention.

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 is 0.1 to 1
0% by weight of α having a structure represented by the following general formula (1)
-A non-aqueous electrolyte secondary battery comprising a hydroxy acid condensate.

[0008]

Embedded image

(In the formula, R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms.) The non-aqueous solvent used in the battery of the present invention is as follows:
It is preferable that 70% by volume or more of the mixed non-aqueous solvent is a carbonate. In particular, the mixed non-aqueous solvent is a mixture of a cyclic carbonate selected from the group consisting of alkylene carbonates having 2 to 4 carbon atoms in an alkylene group, It is preferable that each of these carbonates contains at least 20% by volume of a chain carbonate selected from the group consisting of dialkyl carbonates having 1 to 4 carbon atoms, and at least 70% by volume of the mixed nonaqueous solvent is these carbonates.

The negative electrode material used in the battery of the present invention may be a negative electrode material made of graphite alone, or non-graphite carbon or lithium capable of inserting and extracting lithium.
It is preferable that the negative electrode material is a mixture of graphite and at least one selected from the group consisting of a lithium alloy and a metal oxide. In particular, the negative electrode material has a lattice plane (0
02 plane) has a d value of 0.335 to 0.34 nm and a crystallite size (Lc) of 30 nm or more, preferably 5 nm or more.
It is preferable to include a carbon material of 0 nm or more, particularly 100 nm or more.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The secondary battery according to the present invention comprises, as a negative electrode material capable of inserting and extracting lithium, a negative electrode containing graphite, a positive electrode, and an electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent. At least configured. And, in the present invention, the non-aqueous solvent of the electrolytic solution contains 0.1 to 10% by weight of a condensate of an α-hydroxy acid having a structure represented by the formula (1). The non-aqueous solvent used in the present invention is a mixed non-aqueous solvent containing a cyclic carbonate and a chain carbonate. Further, it is preferable that 70% by volume or more of the mixed nonaqueous solvent is carbonate. The cyclic carbonate 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, for example, 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 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 carbonates 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. Carbonate, diethyl carbonate and ethyl methyl carbonate are 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 a cyclic carbonate and dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate as a chain carbonate. The proportions of the cyclic carbonate and the chain carbonate in the mixed non-aqueous solvent are each preferably 20% by volume or more, and more preferably 25% by volume or more. Further, the total amount of the cyclic carbonate and the chain carbonate in the mixed nonaqueous solvent is preferably 70% by volume or more, more preferably 80% by volume or more, and 9% by volume or more.
It is particularly preferred that the content is 0% by volume or more.

The mixed non-aqueous solvent may contain a solvent other than carbonate. As solvents other than carbonate, 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 Examples thereof include chain ethers such as ethane and dimethoxymethane, and sulfur-containing organic solvents such as sulfolane and diethyl sulfone. 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, solids at 25 ° C. are heated to the melting point and measured in a molten state.

The electrolytic solution used in the present invention contains a condensate of an α-hydroxy acid having a structure represented by the formula (1). Here, the condensate of α-hydroxy acid refers to a product obtained by dehydration condensation of α-hydroxy acid between molecules, and includes a dimer or polymer thereof. The condensate of α-hydroxy acid is not particularly limited as long as it has a structure represented by the formula (1).

[0016]

Embedded image

(Wherein, R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms)

In the formula (1), when R is an alkyl group having 1 to 4 carbon atoms, specific examples thereof include a methyl group, an ethyl group, a propyl group and a butyl group.
Of these, a methyl group is preferred. Further, when R has 1 carbon atom,
When it is an alkoxy group of (1) to (4), specific examples thereof include:
Examples include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group. Of these, a methoxy group is preferred.

Specific examples of the α-hydroxy acid include glycolic acid, lactic acid, α-oxybutyric acid, glyceric acid, tartronic acid, malic acid, tartaric acid, citric acid and the like. Of these, glycolic acid and lactic acid are preferred. As specific examples of the condensate of the α-hydroxy acid, when the condensate is an α-hydroxy acid cyclic diester, glycolide which is a cyclic dimer of glycolic acid in which R is hydrogen, or R is a methyl group Lactide, which is a cyclic dimer of lactic acid, and cyclic diesters of glycolic acid and lactic acid. Lactide is preferred among the above-mentioned cyclic diesters.

When the condensate is a polymer, specific examples thereof include polyglycolic acid, polylactic acid, copolymers of glycolic acid and lactic acid, glycolide and lactide with δ-valerolactone, ε-caprolactone and the like. And a copolymer of glycolide and lactide with cyclic carbonates such as ethylene carbonate and trimethylene carbonate, etc., and are not particularly limited as long as they can be dissolved in a mixed non-aqueous solvent. Among them, those having a weight average molecular weight of 1,000 to 100,000 are preferable,
Those having 0 to 20,000 are more preferable. These may be used as a mixture of two or more. The R site of the α-hydroxy acid condensate of the structure represented by the formula (1) may have a substituent within a range that does not unduly inhibit the intended effect of the present invention.

Formula (1) in the electrolytic solution used in the present invention
The content of the condensate of the α-hydroxy acid having the structure represented by is preferably in the range of 0.1 to 10% by weight. Among them, the content is preferably 0.5 to 8% by weight,
Particularly preferred is 7% by weight. 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, LiCl
Inorganic lithium salts selected from O ₄ , LiPF ₆ and LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ ,
LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO
₂ ) Fluorine-containing organic lithium salts such as (C ₄ F ₉ SO ₂ ) and LiC (CF ₃ SO ₂ ) ₃ can be used. Among them, it is preferable to use LiPF ₆ and LiBF ₄ . 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. If it is less than 0.5 mol / liter or exceeds 2 mol / 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. Further, the crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is preferably 30 nm or more, and 50 n
m or more, and particularly preferably 100 nm or more.

The median diameter of the graphite material measured by a laser diffraction / scattering method is preferably 1 to 100 μm, more preferably 3 to 50 μm or less, and 5 to 4 μm.
The thickness is more preferably 0 μm, and particularly preferably 7 to 30 μm. The BET specific surface area of the graphite material is 0.
5 to 25.0 m ² / g, preferably 0.7 to ²
0.0 m ² / g, more preferably 1.0 to 1
5.0 m ² / g is more preferable, and 1.5 to 1
Particularly preferred is 0.0 m ² / g. The intensity of the peak P _A (peak intensity I _A) in a range of 1580～1620Cm ^-1 in the Raman spectrum analysis using an argon ion laser beam and peak in the range of 1350 ^-1 P _B (peak intensity I _B) Ratio R = I _B / I _A
There are 0 to 0.5, the half-value width of the peak in the range of 1580～1620Cm ^-1 is 26cm ^-1 or less, and particularly preferably between 25 cm ^-1 or less. A negative electrode material capable of inserting and extracting 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 may be directly roll-formed into a sheet electrode,
A pellet electrode can be obtained 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. Examples of the thickener 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.

As the material of the current collector for the negative electrode, metals such as copper, nickel, and stainless steel are used, and among them, copper foil is preferable from the viewpoint of easy processing into a thin film and cost. As a 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. 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 having a spiral shape of a sheet electrode and a separator, a cylinder type having an inside-out structure combining a pellet electrode and a separator, and a coin type having a stack of a pellet electrode and a separator are used. It is possible.

[0027]

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.
PF ₆ ) was used as a solute, and a mixture of propylene carbonate and diethyl carbonate (1: 1 by volume) was added with D,
L-lactide is dissolved at a ratio of 5% by weight, and
₆ was dissolved at a rate of 1 mol / liter. The d value of the lattice plane (002 plane) in X-ray diffraction is 0.336 n
m, crystallite size (Lc) is 100 nm or more (264 n
m), ash content: 0.04% by weight, median diameter by laser diffraction / scattering method: 17 μm, BET method specific surface area: 8.9
m ² / g, a peak P _A (peak intensity I _A) in the range of 1580～1620Cm ^-1 in the Raman spectrum analysis using an argon ion laser beam and 1350-137
Intensity ratio R = 1 _B / I _A of the 0 cm ^-1 in the range of peak P _B (peak intensity I _B) is 0.15,1580~1620cm
A styrene-butadiene rubber (SBR) dispersed in 94 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by Timcal Co.) having a half value width of a peak in the range of ^-1 of 22.2 cm ^-1 with distilled water is solid. 6 parts by weight and mixed with a disperser to form a slurry. The slurry is uniformly coated on a 18-μm-thick copper foil as a current collector, dried, and then disc-shaped with a diameter of 12.5 mm. To form a working electrode, and a coin-type half cell having a lithium foil as a counter electrode via a separator impregnated with an electrolytic solution was prepared.

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. (Example 2) A mixture of propylene carbonate and diethyl carbonate (1: 1 by volume) was added with a weight average molecular weight of 59.
Of polylactic acid at a ratio of 5% by weight.
Except for using the F ₆ 1 mol / liter electrolyte solution prepared by dissolving at a rate of in the same manner as in Example 1 to prepare a coin-type half cell. (Example 3) A mixture of propylene carbonate and diethyl carbonate (1: 1 volume ratio) was added with a weight average molecular weight of 98.
80 polylactic acid at a ratio of 5% by weight
Except for using the F ₆ 1 mol / liter electrolyte solution prepared by dissolving at a rate of in the same manner as in Example 1 to prepare a coin-type half cell.

Example 4 A 50:50 lactic acid-glycolic acid copolymer having a weight average molecular weight of 5800 was dissolved in a mixture of propylene carbonate and diethyl carbonate (1: 1 by volume) at a ratio of 5% by weight, and LiPF was further dissolved. _A coin-type half cell was produced in the same manner as in Example 1, except that an electrolytic solution prepared by dissolving ₆ at a ratio of 1 mol / liter was used.

Example 5 A mixture of ethylene carbonate and diethyl carbonate (1: 1 by volume) was mixed with D, L-
A coin-type half cell was prepared in the same manner as in Example 1, except that lactide was dissolved at a ratio of 5% by weight and LiPF ₆ was further dissolved at a ratio of 1 mol / liter.

Comparative Example 2 LiPF was added to a mixture of ethylene carbonate and diethyl carbonate (1: 1 by volume).
_A coin-type half cell was produced in the same manner as in Example 1 except that an electrolytic solution prepared by dissolving ₆ at a ratio of 1 mol / liter was used. Next, with respect to the coin-shaped half cells of Examples 1 to 5 and Comparative Examples 1 and 2 manufactured as described above, at 25 ° C., at a constant current of 0.2 mA, a discharge termination voltage of 0 V, and at a constant current of 0.4 mA. A charge / discharge test was performed at a charge end voltage of 1.5 V. Table 1 shows the dedoping capacity (dedoping capacity of lithium from the working electrode) and efficiency (dedoping capacity / doping capacity) in the first cycle of Examples 1 to 4 and Comparative Example 1.
Shown in Here, the capacity indicates a capacity per weight of graphite used as a working electrode. In addition, since the ethylene carbonate-based electrolyte originally decomposed less of the electrolyte, the change in the undoping capacity with the cycle for Example 5 and Comparative Example 2 using the ethylene carbonate-based electrolyte is shown in FIG. .

Example 6 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. For the negative electrode, the working electrode used in Example 1 was used. For the electrolytic solution, D, L-lactide was added to a mixture of propylene carbonate and diethyl carbonate (1: 1 volume ratio).
% By weight, and LiPF ₆ was further dissolved at a rate of 1 mol / l. These positive electrode, negative electrode,
The positive electrode was accommodated in a stainless steel can that also served as the positive electrode conductor using the electrolytic solution, and the negative electrode was mounted thereon via a separator impregnated with the electrolytic solution. 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.

Comparative Example 3 LiP was added to a mixture of propylene carbonate and diethyl carbonate (1: 1 by volume).
Except for using the F ₆ 1 mol / liter electrolyte solution prepared by dissolving at a rate of in the same manner as in Example 6 was prepared a coin-type battery. The batteries of Example 6 and Comparative Example 3 were subjected to a charge / discharge test at 25 ° C. at a constant current of 0.5 mA, a charge end voltage of 4.2 V, and a discharge end voltage of 2.5 V. Table 2 shows the discharge capacity per charge of the negative electrode and the charge / discharge efficiency in the first cycle in each battery.

[0034]

## EQU1 ## Charge / discharge efficiency (%) = [(discharge capacity) / (charge capacity)] × 100

In Comparative Examples 1 and 3, the electrolytic solution was severely decomposed and did not operate as a battery. From Tables 1 and 2, it is apparent that the capacity and efficiency are improved when the electrolytic solution containing the α-hydroxy acid condensate having the structure represented by the formula (1) is used. Further, it is clear from FIG. 1 that the cycle life is excellent.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

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. By containing a condensate of an α-hydroxy acid having a structure represented by the formula (1) at a ratio of 1 to 10% by weight, excessive decomposition of the electrolytic solution can be suppressed. As a result, a high capacity can be obtained and a battery having excellent cycle characteristics can be manufactured, which can contribute to miniaturization and high performance of the nonaqueous electrolyte secondary battery.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in dedoping capacity according to the cycles of Example 5 and Comparative Example 2 of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H003 AA02 AA04 BB01 BB02 BB04 BC06 BD00 5H014 AA02 EE05 EE08 EE10 HH00 5H029 AJ03 AJ05 AK03 AL02 AL06 AL07 AL12 AM03 AM05 AM07 BJ03 DJ09 EJ11 HJ02

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 0.1 to 10% by weight of α-hydroxy having a structure represented by the following general formula (1). A non-aqueous electrolyte secondary battery comprising an acid condensate. Embedded image (Wherein, R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms) 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. A mixed non-aqueous solvent comprising: a cyclic carbonate selected from the group consisting of alkylene carbonates having 2 to 4 carbon atoms in an alkylene group;
Containing at least 20% by volume of a chain carbonate selected from the group consisting of dialkyl carbonates,
The non-aqueous electrolyte secondary battery according to claim 2, wherein 70% by volume or more of the mixed non-aqueous solvent is these carbonates. 4. The negative electrode material is at least one selected from the group consisting of a negative electrode material consisting only of graphite and a non-graphite carbon capable of inserting and extracting 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 negative electrode material is a mixture of graphite and 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.