JP3658517B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

【００４２】
（実施例４および比較例３）
電解液用の溶媒として、エチレンカーボネートとジエチルカーボネートの混合物（容量比１：１）に、表２に記載される酸無水物を表２に記載される割合で溶解した溶媒を使用した。この溶媒に、乾燥アルゴン雰囲気下で十分に乾燥を行ったＬｉＰＦ₆を１モル／リットルの割合で溶解して電解液を調製した。この電解液を用いたこと以外は、上と同じ方法でコイン型電池を作製し、充放電試験を行った。結果は表２に示すとおりであった。
【００４３】
【表２】

【００４４】
表１および表２の結果は、酸無水物を含まない電解液や、酸無水物の含有量が０．５重量％未満の電解液を用いた二次電池は、電池として機能しなかったり、放電容量や充放電効率が低いといった問題があることを示している。これに対して、環状カーボネート、鎖状カーボネートおよび０．５〜１０重量％の環状の酸無水物を含有する電解液を用いた本発明の二次電池は、放電容量と充放電効率が改善されており、二次電池として好ましいことが確認される。
【００４５】
【発明の効果】
黒鉛系負極を用いた非水系電解液二次電池の電解液溶媒として、環状カーボネート、鎖状カーボネートおよび０．５〜１０重量％の環状の酸無水物を含む溶媒を用いれば、放電容量および充放電効率を向上させることができる。また、本発明によれば、電解液の分解を有効に抑制することができるため、プロピレンカーボネートを含む電解液のように分解しやすい電解液の用途を拡大し、その機能を有効に活用することができる。したがって本発明によれば、サイクル特性の優れた電池を作製することが可能であり、非水系電解液二次電池の小型化と高性能化に寄与することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a non-aqueous liquid electrolyte secondary battery having excellent cycle characteristics with improved charge / discharge efficiency by using a specific non-aqueous electrolyte.
[0002]
[Prior art]
With the recent reduction in weight and size of electrical products, development of lithium secondary batteries having high energy density is in progress. In addition, with the expansion of the application field of lithium secondary batteries, improvement of battery characteristics is also demanded.
Secondary batteries that use metallic lithium as a negative electrode have been actively studied since long ago as batteries that can achieve higher capacities. However, there is a problem that metallic lithium grows in a dendrite shape by repeated charging and discharging, eventually reaches the positive electrode, and causes a short circuit inside the battery. This problem is the biggest technical problem when a secondary battery using metallic lithium as a negative electrode is put into practical use.
[0003]
Therefore, a nonaqueous electrolyte secondary battery using a carbonaceous material capable of inserting and extracting lithium ions such as coke, artificial graphite, and natural graphite has been proposed for the negative electrode. In such a non-aqueous electrolyte secondary battery, since lithium does not exist in a metal 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.
[0004]
However, in non-aqueous electrolyte secondary batteries in which various graphite-based electrode materials are used alone or mixed with other negative electrode materials capable of occluding and releasing lithium to form negative electrodes, lithium primary batteries are generally used. When an electrolyte containing propylene carbonate, which is preferably used, is used as the main solvent, the decomposition reaction of the solvent proceeds vigorously on the surface of the graphite electrode, making it impossible to smoothly occlude and release lithium into the graphite electrode. Since ethylene carbonate has little such decomposition, ethylene carbonate is frequently used as a main solvent in the electrolyte solution of a non-aqueous electrolyte secondary battery using a graphite-based negative electrode. However, even when ethylene carbonate is used as the main solvent, the electrolyte solution decomposes on the surface of the electrode during the charge / discharge process, which causes problems such as a decrease in charge / discharge efficiency and a decrease in cycle characteristics. For this reason, even if it is a case where a graphite type negative electrode is used, providing the nonaqueous electrolyte solution secondary battery which does not produce these problems is calculated | required. Since the performance of graphite-based negative electrodes varies greatly depending on the type of electrolytic solution, it is necessary to optimize the composition of the electrolytic solution, but no satisfactory electrolytic solution has been provided so far.
[0005]
Regarding the composition of the electrolytic solution, various studies have been conventionally made to include an acid anhydride in a non-aqueous solvent of a non-aqueous electrolyte secondary battery. For example, JP-A-4-355065 proposes that an acid anhydride is contained in a non-aqueous solvent of a non-aqueous electrolyte secondary battery using lithium metal as a negative electrode. However, knowledge about a non-aqueous electrolyte secondary battery using a graphite-based negative electrode is not shown. Japanese Patent Application Laid-Open No. 5-82168 describes that an acid anhydride is added to a nonaqueous solvent of a nonaqueous electrolyte secondary battery using a lithium alloy or a carbon material as a negative electrode. However, the amount added is very small, 500 ppm or 1000 ppm. Furthermore, JP-A-7-122987 discloses data in which graphite is used for the negative electrode and an acid anhydride is added to a mixed solvent of cyclic carbonate and dimethoxyethane which is a chain ether. However, knowledge about a mixed solvent containing a cyclic carbonate and a chain carbonate is not shown.
As described above, although there are several examples in which acid anhydride is used in the electrolytic solution, an electrolytic solution in which a sufficient amount of acid anhydride is added to a mixed solvent of cyclic carbonate and chain carbonate is used. No specific application to secondary batteries has been reported so far.
[0006]
[Problems to be solved by the invention]
The present invention has been made to solve these problems of the prior art. That is, the present invention minimizes the decomposition of the electrolyte of a non-aqueous electrolyte secondary battery using a graphite-based negative electrode, and has a high energy density and a high energy density with a high charge / discharge efficiency and excellent cycle characteristics. Providing batteries was an issue to be solved.
[0007]
[Means for Solving the Problems]
As a result of repeating various studies to solve the above-mentioned problems, the present inventors have obtained a mixed non-aqueous solution containing a cyclic carbonate and a chain carbonate as an electrolyte solution of a non-aqueous electrolyte secondary battery using a graphite-based negative electrode. It has been found that if an electrolytic solution in which a lithium salt and a predetermined amount of a cyclic acid anhydride are dissolved in a solvent is used, charge / discharge efficiency and cycle characteristics can be improved, and the present invention has been completed.
[0008]
That is, the present invention provides a negative electrode containing graphite as a negative electrode material capable of inserting and extracting lithium, a positive electrode, and a mixed nonaqueous solvent containing 70% by volume or more of the total amount of cyclic carbonate and chain carbonate in total. Provided is a non-aqueous electrolyte secondary battery comprising at least an electrolyte solution in which a lithium salt and 0.5 to 10% by weight of a cyclic acid anhydride are dissolved.
In the non-aqueous electrolyte secondary battery of the present invention, in particular, the mixed non-aqueous solvent is a cyclic carbonate selected from the group consisting of alkylene carbonates having 2 to 4 carbon atoms in the alkylene group, and carbon atoms in the alkyl group having 1 to 4 carbon atoms. It is preferable that each of the chain carbonates selected from the group consisting of dialkyl carbonates is 20% by volume or more, and 70% by volume or more of the mixed nonaqueous solvent is these carbonates.
[0009]
In the non-aqueous electrolyte secondary battery of the present invention, the negative electrode material is made of a negative electrode material made only of graphite, or non-graphite carbon, lithium, lithium alloy and metal oxide capable of occluding and releasing lithium. A negative electrode material in which one or more selected from the group and graphite are mixed is preferable. In particular, the negative electrode material preferably includes a carbon material having a d-value of 0.335 to 0.340 nm on the lattice plane (002 plane) in X-ray diffraction and a crystallite size (Lc) of 30 nm or more. The crystallite size (Lc) is more preferably 100 nm or more, and particularly preferably 150 nm or more.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The non-aqueous electrolyte secondary battery of the present invention includes a negative electrode containing graphite as a negative electrode material capable of inserting and extracting lithium, a positive electrode, and 70% by volume of the total amount of solvent of cyclic carbonate and chain carbonate characterized in that it is composed of at least from the electrolyte by dissolving a lithium salt and 0.5 to 10 wt% of the cyclic acid anhydride in a mixed nonaqueous solvent containing more. In the present specification, “to” means a range including numerical values described before and after.
[0011]
The mixed nonaqueous solvent of the electrolytic solution includes at least a cyclic carbonate and a chain carbonate. The type of the cyclic carbonate used as the mixed non-aqueous solvent is not limited as long as it has a cyclic structure and a carbonate group in the molecule. Preference is given to cyclic carbonates in which the carbonate group forms part of the cyclic structure. More preferred is alkylene carbonate, and alkylene carbonate having an alkylene group with 2 to 4 carbon atoms is particularly preferred. Specific examples of such alkylene carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate and propylene carbonate are preferable. These alkylene groups may have a substituent as long as the desired effects of the present invention are not excessively inhibited.
[0012]
The chain carbonate used as the mixed non-aqueous solvent is a carbonate having no cyclic structure. The chain carbonate is preferably an alkyl carbonate, particularly an alkyl carbonate having an alkyl group having 1 to 4 carbon atoms. Specifically, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, etc. can be mentioned, among which dimethyl carbonate, diethyl carbonate, ethyl Methyl carbonate is preferred. The alkyl group of these alkyl carbonates may have a substituent within a range that does not excessively inhibit the intended effect of the present invention.
[0013]
The combination of the cyclic carbonate and the chain carbonate is not particularly limited. Preferred combinations include a cyclic carbonate selected from the group consisting of alkylene carbonates having 2 to 4 carbon atoms in the alkylene group and a chain carbonate selected from the group consisting of dialkyl carbonates having 1 to 4 carbon atoms in the alkyl group. Mixed non-aqueous solvent. A more preferable 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.
[0014]
The ratio of the cyclic carbonate and the chain carbonate in the mixed non-aqueous solvent is preferably 20% by volume or more, and more preferably 25% by volume or more. The total amount of cyclic carbonate and chain carbonate in the mixed non-aqueous solvent is 70% by volume or more, preferably 80% by volume or more , and particularly preferably 90% by volume or more.
[0015]
The mixed non-aqueous solvent may contain a solvent other than carbonate. Examples of solvents other than carbonate include 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; Examples include chain ethers such as ethane and dimethoxymethane; sulfur-containing organic solvents such as sulfolane and diethylsulfone. Two or more of these solvents may be used in combination.
[0016]
These solvents can be contained in the mixed non-aqueous solvent in an amount that does not impair the properties of the carbonate solvent. Specifically, the solvent other than carbonate is 30% by volume or less, preferably 20% by volume or less , and particularly preferably 10% by volume or less of the mixed non-aqueous solvent.
[0017]
The electrolytic solution used in the present invention contains a cyclic acid anhydride. The type of the cyclic acid anhydride used in the present invention is not particularly limited as long as it is a compound having an acid anhydride structure in a part of the cyclic structure. Further, it may be a compound having a plurality of acid anhydride structures in one molecule. Specific examples of cyclic acid anhydrides that can be used in the present invention include succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, Cyclopentanetetracarboxylic dianhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, phenyl Succinic anhydride, 2-phenylglutaric anhydride, etc. can be mentioned. Of these, succinic anhydride, maleic anhydride, and glutaric anhydride are preferable. Two or more of these acid anhydrides may be mixed and used.
[0018]
The content of the cyclic acid anhydride in the electrolytic solution used in the present invention is in the range of 0.5 to 10% by weight. Among these, 1 to 8% by weight is preferable, and 2 to 7% by weight is particularly preferable.
[0019]
In the electrolytic solution used in the present invention, a lithium salt is used as a solute. The type of lithium salt that can be used is not particularly limited as long as it can be used as a solute of an electrolytic solution. For example, an inorganic lithium salt selected from LiClO ₄ , LiPF ₆ , 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 mentioned. Among them, it is preferable to use LiPF ₆ or LiBF ₄ . Two or more types of lithium salts may be mixed and used.
The molar concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 2.0 mol / liter. If it is less than 0.5 mol / liter or exceeds 2.0 mol / liter, the electric conductivity of the electrolytic solution tends to be low, and the battery performance tends to deteriorate.
[0020]
Without being bound by any theory, graphite is obtained using the above electrolytic solution in which 0.5 to 10% by weight of cyclic acid anhydride and lithium salt are dissolved in a mixed non-aqueous solvent containing cyclic carbonate and chain carbonate. If a non-aqueous electrolyte secondary battery having a system negative electrode is configured, it is considered that excessive decomposition of the electrolyte during the charge / discharge process is suppressed. For this reason, by suppressing the decomposition of the electrolytic solution, the charge / discharge efficiency is improved, and a secondary battery having excellent cycle characteristics can be provided. In particular, not only when used at room temperature, but also when used at a high temperature of about 60 ° C., such characteristics of the present invention are sufficiently exhibited. These characteristics are apparent from the examples described later.
The electrolytic solution used in the present invention may contain components other than cyclic carbonate, chain carbonate, cyclic acid anhydride, and lithium salt within a range that does not excessively inhibit the intended effect of the present invention. Good.
[0021]
The negative electrode constituting the non-aqueous electrolyte secondary battery of the present invention contains graphite as its component. The physical properties of graphite are not particularly limited as long as it can occlude and release thyllium. Preference is given to artificial graphite and purified natural graphite produced by high-temperature heat treatment of graphitizable pitch obtained from various raw materials. These graphite materials preferably have a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.34 nm determined by X-ray diffraction by the Gakushin method, and 0.335 to 0.337 nm. Some are more preferred. These graphite materials preferably have an ash content of 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 by the Gakushin method is preferably 30 nm or more, more preferably 50 nm or more, and particularly preferably 100 nm or more.
[0022]
Further, the median diameter of the graphite material by the laser diffraction / scattering method is preferably 1 to 100 μm, more preferably 3 to 50 μm, further preferably 5 to 40 μm, and 7 to 30 μm. Is particularly preferred. BET specific surface area of the graphite material is preferably from 0.5~25.0m ² / g, more preferably from 0.7~20.0m ² / g, 1.0~15.0m ² / G is even more preferable, and 1.5 to 10.0 m ² / g is particularly preferable. Further, the intensity of the peak P _A (peak intensity I _A ) in the range of 1580 to 1620 cm ⁻¹ and the peak P _B (peak intensity I _B ) in the range of 1350 to 1370 cm ⁻¹ in the Raman spectrum analysis using argon ion laser light. the ratio R = I _B / I _a is 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.
[0023]
A negative electrode material capable of inserting and extracting lithium can be further mixed with these graphite materials. Examples of the negative electrode material capable of occluding and releasing lithium other than graphite include carbon materials such as non-graphitic carbon materials such as non-graphite carbon and low-temperature calcined carbon, and the like, tin oxide having a d (002) exceeding 0.34 nm, tin oxide Examples thereof include metal oxide materials such as silicon oxide, lithium metal, and various lithium alloys. Two or more kinds of these negative electrode materials may be mixed and used.
[0024]
The method for producing a negative electrode using these negative electrode materials is not particularly limited. For example, the electrode can be manufactured by adding a binder, a conductive material, a solvent, or the like to the negative electrode material as necessary to form a slurry, applying the slurry to the substrate of the current collector, and drying. Further, the electrode material can be roll-formed as it is to be formed into a sheet, or can be formed into a pellet by compression molding or the like.
[0025]
If the binder used for manufacture of an electrode is a material stable with respect to the solvent and electrolyte solution used at the time of electrode manufacture, the kind in particular will not be restrict | limited. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, and cellulose; rubbery polymers such as styrene / butadiene rubber, isoprene rubber, butadiene rubber, and ethylene / propylene rubber; styrene / butadiene / Styrene block copolymer and hydrogenated product thereof, styrene / ethylene / butadiene / styrene block copolymer and hydrogenated product thereof; thermoplastic elastomeric polymer such as styrene / isoprene / styrene block copolymer and hydrogenated product thereof Soft resinous polymers such as syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, propylene / α-olefin (2 to 12 carbon atoms) copolymer; polyvinylidene fluoride, polytetrafluoroethylene, Polite It can be exemplified a fluorine-based polymer such as tetrafluoroethylene-ethylene copolymer.
[0026]
As the binder, a polymer composition having alkali metal ion conductivity such as lithium ion can be used. Examples of such an ion-conductive polymer include polyether polymer compounds such as polyethylene oxide and polypropylene oxide, polyether crosslinked polymer compounds, polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinyl pyrrolidone, and polyvinylidene. A system in which a high molecular compound such as carbonate or polyacrylonitrile is combined with a lithium salt or an alkali metal salt mainly composed of lithium, or an organic compound having a high dielectric constant such as propylene carbonate, ethylene carbonate, or γ-butyrolactone. A blended system can be used. These materials may be used in combination.
[0027]
Various forms can be taken as a mixed form of the negative electrode material and the binder. That is, a form in which both particles are mixed, a form in which a fibrous binder is entangled with particles of the negative electrode material, or a form in which a binder layer is attached to the particle surface. The mixing ratio of the binder to the negative electrode material powder is preferably 0.1 to 30% by weight, more preferably 0.5 to 10% by weight, based on the negative electrode material. When an amount of binder exceeding 30% by weight is added, the internal resistance of the electrode tends to increase. Conversely, when the amount of binder is less than 0.1% by weight, the binding property between the current collector and the negative electrode material is increased. It tends to be inferior.
[0028]
Further, when the negative electrode material and the binder are mixed, the conductive material may be mixed together. Since the kind of the conductive material to be used is not particularly limited, it may be a metal or a nonmetal. Examples of the metal conductive material include materials composed of metal elements such as Cu and Ni. Examples of the nonmetallic conductive material include carbon materials such as graphite, carbon black, acetylene black, and ketjen black. The average particle size of the conductive material is preferably 1 μm or less.
[0029]
The mixing ratio of the conductive material is preferably 0.1 to 30% by weight, more preferably 0.5 to 15% by weight with respect to the negative electrode material. By making the mixing ratio of the conductive material 30% by weight or less, the charge / discharge capacity of the electrode per unit volume can be made relatively high. Moreover, the conductive path between the conductive materials can be sufficiently formed in the electrode by setting the mixing ratio of the conductive materials to 0.1 wt% or more.
[0030]
The above mixture containing at least the negative electrode material and the binder is applied on the current collector according to the intended use of the electrode. The shape of the current collector to be applied is not particularly limited, and can be appropriately determined according to the usage mode of the negative electrode. For example, a cylindrical, plate-shaped, or coil-shaped current collector can be used. The material of the current collector is preferably a metal such as copper, nickel, and stainless steel. Among these, it is more preferable to use a copper foil because it is easy to process into a thin film and is inexpensive.
[0031]
Application to the current collector can be performed by means known to those skilled in the art. When the mixture is in the form of a slurry, it can be applied onto the current collector using, for example, a die coater or a doctor blade. Moreover, when a mixture is paste-form, it can apply | coat on a collector by roller coating etc. If a solvent is used, the electrode can be produced by drying to remove the solvent.
[0032]
Examples of the positive electrode constituting the nonaqueous electrolyte secondary battery of the present invention include lithium transition metal composite oxide materials such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide; transition metal oxidation such as manganese dioxide Material materials: Materials capable of inserting and extracting lithium, such as carbonaceous materials such as fluorinated graphite, can be used. Specifically, LiFeO ₂ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and their non-stoichiometric compounds, MnO ₂ , TiS ₂ , FeS ₂ , Nb ₃ S ₄ , Mo ₃ S ₄ , CoS ₂ , V ₂ O ₅ , P ₂ O ₅ , CrO ₃ , V ₃ O ₃ , TeO ₂ , GeO _{2 and the} like can be used.
The manufacturing method in particular of a positive electrode is not restrict | limited, It can manufacture by the method similar to the manufacturing method of said negative electrode.
[0033]
As the positive electrode current collector used in the present invention, it is preferable to use a valve metal or an alloy thereof that forms a passive film on the surface by anodic oxidation in an electrolytic solution. Examples of the valve metal include metals belonging to IIIa, IVa, Va group (3B, 4B, 5B group) and alloys thereof. Specifically, Al, Ti, Zr, Hf, Nb, Ta and alloys containing these metals can be exemplified, and Al, Ti, Ta and alloys containing these metals can be preferably used. . In particular, Al and its alloys are desirable because of their light weight and high energy density.
[0034]
The material and shape of the separator used in the battery of the present invention are not particularly limited. The separator is separated so that the positive electrode and the negative electrode are not in physical contact, and preferably has high ion permeability and low electrical resistance. The separator is preferably selected from materials that are stable with respect to the electrolyte and excellent in liquid retention. Specifically, the electrolyte solution can be impregnated using a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene.
[0035]
The method for producing the non-aqueous electrolyte secondary battery of the present invention having at least a non-aqueous electrolyte, a negative electrode, and a positive electrode is not particularly limited and can be appropriately selected from commonly employed methods. In addition to the non-aqueous electrolyte solution, the negative electrode, and the positive electrode, an outer can, a separator, a gasket, a sealing plate, a cell case, and the like can be used as necessary for the non-aqueous electrolyte secondary battery of the present invention. For example, a negative electrode can be placed on an outer can, an electrolytic solution and a separator can be provided thereon, and a positive electrode can be placed so as to face the negative electrode, and can be caulked together with a gasket and a sealing plate to form a battery. The shape of the battery is not particularly limited, and can be a cylinder type in which the sheet electrode and the separator are spiral, a cylinder type having an inside-out structure in which the pellet electrode and the separator are combined, a coin type in which the pellet electrode and the separator are stacked, and the like. .
[0036]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Test Examples. The materials, reagents, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.
[0037]
(Examples 1-3 and Comparative Examples 1-2)
As a positive electrode active material, 6 parts by weight of carbon black and 9 parts by weight of polyvinylidene fluoride (made by Kureha Chemical Co., Ltd., trade name KF-1000) are added to 85 parts by weight of LiCoO ₂ , mixed, and dispersed with N-methyl-2-pyrrolidone. The slurry was uniformly applied onto a 20 μm thick aluminum foil as a positive electrode current collector, dried, and then punched into a disk shape having a diameter of 12.5 mm to obtain a positive electrode.
[0038]
As the negative electrode active material, the d value of the lattice plane (002 plane) in X-ray diffraction is 0.336 nm, the crystallite size (Lc) is 100 nm or more (264 nm), the ash content is 0.04% by weight, by the laser diffraction / scattering method A median diameter of 17 μm, a BET specific surface area of 8.9 m ² / g, and a peak spectrum P _A (peak intensity I _A ) in the range of 1580 to 1620 cm ⁻¹ and 1350 to 1370 cm ^{− in} a Raman spectrum analysis using an argon ion laser beam. artificial graphite intensity ratio R = I _B / I _a of the ^first range of peak P _B (peak intensity I _B) is the half width of the peak in the range of 0.15,1580～1620Cm ^-1 is 22.2Cm ^-1 6 parts by weight of polyvinylidene fluoride is mixed with 94 parts by weight of powder (trade name KS-44, manufactured by Timcal), and dispersed with N-methyl-2-pyrrolidone to form a slurry. Was uniformly applied onto a 18 μm thick copper foil as a negative electrode current collector, dried, and then punched into a disk shape having a diameter of 12.5 mm to obtain a negative electrode.
[0039]
As a solvent for the electrolytic solution, a solvent in which an acid anhydride described in Table 1 was dissolved in a ratio described in Table 1 in a mixture of propylene carbonate and diethyl carbonate (volume ratio 1: 1) was used. In this solvent, lithium hexafluorophosphate (LiPF ₆ ) sufficiently dried under a dry argon atmosphere was dissolved at a rate of 1 mol / liter to prepare an electrolytic solution.
Using these positive electrode, negative electrode, and electrolytic solution, the positive electrode was accommodated in a stainless steel can that also serves as a positive electrode conductor, and the negative electrode was placed through a separator impregnated with the electrolytic solution thereon. The can body and a sealing plate that also serves as the negative electrode conductor were caulked and sealed via an insulating gasket to produce a coin-type battery.
[0040]
Each manufactured battery was subjected to a charge / discharge test at a constant current of 0.5 mA and a charge end voltage of 4.2 V and a discharge end voltage of 2.5 V at 25 ° C. Table 1 shows the charge / discharge efficiency (%) and discharge capacity per weight of the negative electrode in the first and tenth cycles of each battery. The charge / discharge efficiency here is calculated by the following equation.
[Expression 1]
Charge / discharge efficiency (%) = [(discharge capacity) / (charge capacity)] × 100
[0041]
[Table 1]

[0042]
(Example 4 and Comparative Example 3)
As a solvent for the electrolytic solution, a solvent in which an acid anhydride described in Table 2 was dissolved in a mixture described in Table 2 in a mixture of ethylene carbonate and diethyl carbonate (volume ratio 1: 1) was used. LiPF ₆ sufficiently dried under a dry argon atmosphere was dissolved in this solvent at a rate of 1 mol / liter to prepare an electrolytic solution. A coin-type battery was produced in the same manner as above except that this electrolytic solution was used, and a charge / discharge test was conducted. The results were as shown in Table 2.
[0043]
[Table 2]

[0044]
The results in Table 1 and Table 2 show that the electrolyte solution containing no acid anhydride or the secondary battery using the electrolyte solution having an acid anhydride content of less than 0.5% by weight does not function as a battery. This indicates that there are problems such as low discharge capacity and low charge / discharge efficiency. On the other hand, the secondary battery of the present invention using the electrolytic solution containing cyclic carbonate, chain carbonate and 0.5 to 10% by weight of cyclic acid anhydride has improved discharge capacity and charge / discharge efficiency. It is confirmed that this is preferable as a secondary battery.
[0045]
【The invention's effect】
If a solvent containing a cyclic carbonate, a chain carbonate, and 0.5 to 10% by weight of a cyclic acid anhydride is used as an electrolyte solution solvent for a non-aqueous electrolyte secondary battery using a graphite-based negative electrode, the discharge capacity and charge are reduced. Discharge efficiency can be improved. In addition, according to the present invention, since the decomposition of the electrolytic solution can be effectively suppressed, the application of the electrolytic solution that is easily decomposed like the electrolytic solution containing propylene carbonate is expanded, and the function is effectively utilized. Can do. Therefore, according to the present invention, it is possible to produce a battery having excellent cycle characteristics, which can contribute to the downsizing and high performance of the non-aqueous electrolyte secondary battery.

Claims (6)

A negative electrode containing graphite as a negative electrode material capable of inserting and extracting lithium, a positive electrode, and a mixed non-aqueous solvent containing 70% by volume or more of the total amount of cyclic carbonate and chain carbonate in combination with lithium salt and 0. A non-aqueous electrolyte secondary battery comprising at least an electrolyte solution in which 5 to 10% by weight of a cyclic acid anhydride is dissolved. The cyclic acid anhydride is glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, 4-cyclohexene-1,2 -Dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, phenylsuccinic anhydride or 2-phenylglutaric anhydride. The non-aqueous electrolyte secondary battery according to claim 1. The mixed non-aqueous solvent is a chain selected from the group consisting of a cyclic carbonate selected from the group consisting of alkylene carbonates having 2 to 4 carbon atoms in the alkylene group and a dialkyl carbonate whose alkyl group has 1 to 4 carbon atoms. The nonaqueous electrolyte secondary battery according to claim 1 or 2 , wherein each of the carbonates contains 20% by volume or more, and 70% by volume or more of the mixed nonaqueous solvent is the carbonate.   The negative electrode material is a negative electrode material made only of graphite, or graphite and at least one selected from the group consisting of non-graphitic carbon, lithium, lithium alloy and metal oxide capable of inserting and extracting lithium. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is a mixed negative electrode material.   The negative electrode material includes a carbon material having a d-value of a lattice plane (002 plane) in an X-ray diffraction of 0.335 to 0.340 nm and a crystallite size (Lc) of 30 nm or more. Item 5. A nonaqueous electrolyte secondary battery according to any one of Items 1 to 4.   The negative electrode material includes a carbon material having a d-value of a lattice plane (002 plane) in an X-ray diffraction of 0.335 to 0.337 nm and a crystallite size (Lc) of 50 nm or more. Item 6. The nonaqueous electrolyte secondary battery according to Item 5.