JP2007265858A - Nonaqueous electrolytic solution, and secondary battery using the electrolytic solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution capable of providing a battery in which a stable coating film is formed wherein decomposition of an additive at a negative electrode is suppressed to the minimum, in which increase in internal resistance at high temperatures is small when arranged in the battery, and which is capable of maintaining high electric capacity and superior in high temperature characteristics, and a nonaqueous electrolytic solution secondary battery using the nonaqueous electrolytic solution. <P>SOLUTION: In the nonaqueous electrolytic solution in which electrolyte salts are dissolved in an organic solvent, at least one kind or more selected from cyclic compounds expressed by either one of general formulas (1) to (5) is made to be contained in the nonaqueous electrolytic solution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte solution containing a cyclic compound having a specific structure and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte solution. More specifically, the electrolyte solution contains a cyclic compound having a specific structure. Thus, when placed in a battery, a non-aqueous electrolyte that can provide a battery having excellent high-temperature characteristics with a small rate of change in electric capacity and internal resistance during high-temperature storage, and a non-aqueous electrolyte using the non-aqueous electrolyte Next battery.

  With the spread of portable electronic devices such as portable personal computers and handy video cameras in recent years, non-aqueous electrolyte secondary batteries having high voltage and high energy density have been widely used as power sources. Also, from the viewpoint of environmental problems, battery cars and hybrid cars using electric power as a part of power have been put into practical use.

However, the non-aqueous electrolyte secondary battery exhibits a decrease in electric capacity and an increase in internal resistance when it is stored at a high temperature or repeatedly charged and discharged, and is not reliable as a stable power supply source.
Various additives have been proposed in order to improve the stability and electrical characteristics of the nonaqueous electrolyte secondary battery. For example, Patent Document 1 discloses that vinylene carbonate and its derivatives, which are cyclic compounds, are used to form a stable coating so-called SEI (Solid Electrolyte Interface) that suppresses reductive decomposition of an electrolytic solution on a graphite-based negative electrode. An electrolytic solution containing has been proposed. However, although the cyclic compound used in this electrolyte solution has a certain effect, when it is added excessively to the electrolyte solution, the battery performance is lowered and the resistance of the generated film component is high, resulting in an increase in resistance. There was a drawback that the rate was large. Further, there is a problem that the charge due to the decomposition of the additive appears as an irreversible capacity component, leading to a decrease in the initial charge / discharge efficiency. In addition, since the film formed of vinylene carbonate is very unstable and decomposes in an environment of 80 ° C. or higher, the electrolytic solution is decomposed again by the exposed negative electrode surface, and high temperature characteristics at 80 ° C. or higher are exhibited. It was not always satisfactory.

  Patent Document 2 proposes a secondary battery that has an excellent capacity retention rate during cycling by adding a cyclic α-oxyacrylate compound to the electrolyte. However, the characteristics of the secondary battery described in Patent Document 2 are all battery characteristics at room temperature, and it is described that there is a certain effect on the cycle characteristics at room temperature. There is no.

  Patent Document 3 proposes a secondary battery excellent in cycle characteristics and storage characteristics by adding a vinyl sulfone compound to an electrolytic solution. However, the characteristics of the secondary battery described in Patent Document 3 are all battery characteristics at room temperature, and it is described that there are certain effects on the cycle characteristics and storage characteristics at room temperature. There is no description for the characteristics.

  Patent Document 4 proposes a secondary battery excellent in cycle life and safety by adding a vinyl cyclic disulfone compound to an electrolytic solution. However, the characteristics of the secondary battery described in Patent Document 4 are all battery characteristics at room temperature, and it is described that there is a certain effect on the cycle characteristics at room temperature. There is no.

JP-A-8-45545 JP 2004-44710 A Japanese Patent Laid-Open No. 2001-23688 JP 2005-135701 A

  Accordingly, an object of the present invention is to form a stable coating with minimal decomposition of the additive at the negative electrode, and to increase the internal resistance at high temperatures when placed in a battery, and to maintain a high electric capacity. An object of the present invention is to provide a non-aqueous electrolyte solution that can provide a battery having excellent high-temperature characteristics, and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte solution.

  As a result of various studies to achieve the above object, the present inventors have added a cyclic compound having a specific structure to the electrolytic solution, and when this is arranged in a battery, the cycle characteristics and the high temperature characteristics are improved. The present inventors have obtained knowledge that a non-aqueous electrolyte that can provide an excellent battery can be obtained.

  The present invention has been made based on the above knowledge, and in a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in an organic solvent, the cyclic compound represented by any one of the following general formulas (1) to (5) is selected. And a non-aqueous electrolyte secondary battery including the non-aqueous electrolyte as the electrolyte.

（式中、Ｒ₁ およびＲ₂ は、各々独立に水素原子、フッ素原子、または炭素原子数１〜６のフッ素原子を含んでもよい炭化水素基を示す。Ｒ₃ およびＲ₄ は、各々独立に水素原子またはフッ素原子を示す。Ｘは、硫黄原子、スルホン、または二硫化物を示す。Ｙは、酸素原子、炭素原子、Ｎ−Ｈ、Ｎ−アルキル、Ｎ−アリール、または硫黄原子を示す。Ｚは、炭素原子数１〜６のフッ素原子を含んでもよい炭化水素基、またはエーテルもしくはカルボニル結合を有する炭化水素基を示す。）

(In the formula, R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or a hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms. R ₃ and R ₄ each independently represent X represents a sulfur atom, a sulfone, or a disulfide, and Y represents an oxygen atom, a carbon atom, NH, N-alkyl, N-aryl, or a sulfur atom. Z represents a hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms, or a hydrocarbon group having an ether or carbonyl bond.)

（式中、Ｒ₅ 〜Ｒ₁₀は、各々独立に水素原子、フッ素原子、または炭素原子数１〜６のフッ素原子を含んでもよい炭化水素基を示す。）

(In the formula, R _{5 to} R ₁₀ each independently represent a hydrogen atom, a fluorine atom, or a hydrocarbon group that may contain a fluorine atom having 1 to 6 carbon atoms.)

（式中、Ｒ₁₁〜Ｒ₂₀は、各々独立に水素原子、フッ素原子、または炭素原子数１〜６のフッ素原子を含んでもよい炭化水素基を示す。ｎは、１〜３の整数を示す。）

(Wherein R _{11 to} R ₂₀ each independently represent a hydrogen atom, a fluorine atom, or a hydrocarbon group that may contain a fluorine atom having 1 to 6 carbon atoms. N represents an integer of 1 to 3). .)

（式中、Ｒ₂₁〜Ｒ₃₀は、各々独立に水素原子、フッ素原子、または炭素原子数１〜６のフッ素原子を含んでもよい炭化水素基を示す。ｎは、１〜２の整数を示す。）

(In the formula, R _{21 to} R ₃₀ each independently represent a hydrogen atom, a fluorine atom, or a hydrocarbon group that may contain 1 to 6 carbon atoms. N represents an integer of 1 to 2). .)

（式中、Ｒ₃₁およびＲ₃₂は、各々独立にシアノ基、フッ素原子、カルボニル基、または炭素原子数１〜６のフッ素原子もしくはカルボニル基を含んでもよい炭化水素基を示す。Ｒ₃₃〜Ｒ₃₇は、各々独立に水素原子、フッ素原子、または炭素原子数１〜６のフッ素原子を含んでもよい炭化水素基を示す。）

(In the formula, R ₃₁ and R ₃₂ each independently represent a cyano group, a fluorine atom, a carbonyl group, or a hydrocarbon group that may contain a fluorine atom or a carbonyl group having 1 to 6 carbon atoms. R _{33 to} R ₃₇ each independently represents a hydrogen atom, a fluorine atom, or a hydrocarbon group that may contain a fluorine atom having 1 to 6 carbon atoms.)

  According to the present invention, a stable coating with minimal decomposition of the additive at the negative electrode is formed, and the increase in internal resistance at a high temperature is small when placed in a battery, and a high temperature at which a high electric capacity can be maintained. It is possible to provide a non-aqueous electrolyte solution that can provide a battery with excellent characteristics, and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte solution.

The nonaqueous electrolyte solution of the present invention and the nonaqueous electrolyte secondary battery using the nonaqueous electrolyte solution will be described in detail below.
In the nonaqueous electrolytic solution of the present invention, the cyclic compound represented by the general formula (1) is, for example, Macromolecules Vol. 27, page 7935 (1994), Japanese Patent Publication No. 8-504771 and the like.
In the general formula (1), examples of the hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms represented by R ₁ and R ₂ include methyl, methyl trifluoride and the like. Examples of N-alkyl represented by Y include N-methyl and the like, and examples of N-aryl include N-phenyl and N-tolyl. Examples of the hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms represented by Z include ethyl, ethyl tetrafluoride, butyl and the like, and examples of the hydrocarbon group having an ether bond include diethyl ether and the like. Examples of the hydrocarbon group having a carbonyl bond include ethyl butyl ester.

  As the cyclic compound represented by the general formula (1), more specifically, the following compound No. 1-No. 5 etc. are mentioned. However, the compound used for this invention is not restrict | limited at all by the following illustrations.

The cyclic α-oxyacrylic acid ester compound represented by the general formula (2) is described in, for example, Chinese Journal of Polymer Science Vol. 11, no. 2, page 153 (1993) and the like.
In the general formula (2), as the hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms represented by R ₅ to R _10, methyl, include methyl fluoride, and the like.

  As the cyclic compound represented by the general formula (2), more specifically, the following compound No. 6-No. 7 etc. are mentioned. However, the compound used for this invention is not restrict | limited at all by the following illustrations.

The vinyl cyclic sulfone compound represented by the general formula (3) is, for example, Journal
of polymer science. Polymer symposia Vol. 74, pages 227 (1986), Journal of Polymer Science. Part C. Polymer Letter Vol. 25, page 309 (1987) and the like.
In the general formula (3), examples of the hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms represented by R _{11 to} R ₂₀ include methyl and methyl fluoride.

  As the cyclic compound represented by the general formula (3), more specifically, the following compound No. 8-No. 9 etc. are mentioned. However, the compound used for this invention is not restrict | limited at all by the following illustrations.

The cyclic compound represented by the general formula (4) is, for example, The Journal of
Organic Chemistry Vol. 43, no. 254826 (1978), Progress in Polymer Science Vol. 25, page 1043 (2000) and the like.
In the general formula (4), examples of the hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms represented by R _{21 to} R ₃₀ include methyl and methyl fluoride.

  As the cyclic compound represented by the general formula (4), more specifically, the following compound No. 10-No. 11 etc. are mentioned. However, the compound used for this invention is not restrict | limited at all by the following illustrations.

The cyclic compound represented by the general formula (5) is, for example, the following compound No. 12 (1-vinyl-5,7-dioxaspiro [2.5] octane-6-one) is charged with 1,1-bis (hydroxymethyl) -2-vinylcyclopropane, ethyl chloroformate and tetrahydrofuran; Triethylamine can be added dropwise, and the resulting white crystals can be filtered and purified.
In the general formula (5), examples of the hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms or a carbonyl group represented by R ₃₁ and R ₃₂ include methyl, ethyl, propyl, butyl, pentyl, trifluoro methyl, pentafluoroethyl, trimethylene, Techiramechiren, pentamethylene, hexamethylene, phenyl, p- fluorophenyl, 2,4-difluorophenyl, 3,5-difluorophenyl, acetyl and the like, represented by R ₃₃ to R ₃₇ Examples of the hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms include methyl, ethyl, propyl, butyl, pentyl, trifluoromethyl, pentafluoroethyl and the like.

  As the cyclic compound represented by the general formula (5), more specifically, the following compound No. 12-No. 15 etc. are mentioned. However, the compound used for this invention is not restrict | limited at all by the following illustrations.

  The cyclic compound represented by any one of the above general formulas (1) to (5) is a compound that accepts electrons at the negative electrode, and is easily ring-opened and polymerized, and undergoes a polymerization reaction at the electrode electrolyte interface at the beginning of the cycle. It is considered that a stable film can be formed and an increase in interfacial resistance associated with cycles due to decomposition of the electrolytic solution and high temperature storage can be suppressed. In order to express this effect, the content of the cyclic compound in the nonaqueous electrolytic solution is preferably 0.05 to 5% by volume, particularly 0.1 to 3% by volume. If the content of the cyclic compound is less than 0.05% by volume, it is difficult to recognize the effect. Even if the content exceeds 5% by volume, the effect is not manifested any more. May adversely affect liquid properties.

  The organic solvent used in the non-aqueous electrolyte of the present invention is not particularly limited, and those conventionally used as the organic solvent for non-aqueous electrolytes can be used, preferably cyclic or chain-like. Examples include carbonate compounds, cyclic or chain ester compounds, sulfone or sulfoxide compounds, amide compounds, and chain or cyclic ether compounds. The organic solvent is specifically exemplified below, but is not limited by the following examples.

  Since the cyclic carbonate compound, the cyclic ester compound, the sulfone or sulfoxide compound, and the amide compound have a high relative dielectric constant, they serve to increase the dielectric constant of the electrolytic solution. Specifically, examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), 1,2-butylene carbonate, and isobutylene carbonate. Examples of the cyclic ester compound include γ-butyrolactone and γ-valerolactone. Examples of the sulfone or sulfoxide compound include sulfolane, sulfolene, tetramethylsulfolane, diphenyl sulfone, dimethyl sulfone, dimethyl sulfoxide, and the like. Among these, sulfolanes are preferable. Examples of the amide compound include N-methylpyrrolidone, dimethylformamide, dimethylacetamide and the like.

  The chain carbonate compound, the chain or cyclic ether compound, and the chain ester compound can lower the viscosity of the nonaqueous electrolytic solution. Therefore, battery characteristics such as power density can be improved, such as the mobility of electrolyte ions can be increased. Moreover, since it is low-viscosity, the performance of the non-aqueous electrolyte at low temperatures can be increased. Specifically, as the chain carbonate compound, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl Examples thereof include carbonate and t-butyl-i-propyl carbonate. Examples of the chain or cyclic ether compound include dimethoxyethane (DME), ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, dioxolane, dioxane, 1,2-bis (methoxycarbonyloxy) ethane, 1,2-bis (ethoxycarbonyloxy). ) Ethane, 1,2-bis (ethoxycarbonyloxy) propane, ethylene glycol bis (trifluoroethyl) ether, i-propylene glycol (trifluoroethyl) ether, ethylene glycol bis (trifluoromethyl) ether, diethylene glycol bis (tri Fluoroethyl) ether and the like. Among these, dioxolanes are preferable.

  In order to impart flame retardancy, halogen-based, phosphorus-based, and other flame retardants can be appropriately added to the nonaqueous electrolytic solution of the present invention. Examples of the phosphorus flame retardant include phosphate esters such as trimethyl phosphate and triethyl phosphate. 5-100 mass% is preferable with respect to the organic solvent which comprises the non-aqueous electrolyte of this invention, and, as for the addition amount of the said flame retardant, 10-50 mass% is especially preferable. If the addition amount of the flame retardant is less than 5% by mass, a sufficient flame retarding effect cannot be obtained.

As the electrolyte salt used in the non-aqueous electrolyte of the present invention, a conventionally known electrolyte salt is used. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC _{(CF 3 SO 2) 3,} LiSbF 6, LiSiF 5, LiAlF 4, like _{LiSCN, LiClO 4, LiCl, LiF} , LiBr, LiI, LiAlF 4, LiAlCl 4, NaClO 4, NaBF 4, NaI, derivatives of these Among these, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCF ₃ SO ₃ derivatives, LiN (CF ₃ SO _{2) 2} derivative, and LiC (CF ₃ SO ₂₎ to use at least one member selected from the group consisting of ₃ derivatives, The preferred because of excellent magnetic characteristics.

  The electrolyte salt is dissolved in the organic solvent so that the concentration in the non-aqueous electrolyte of the present invention is 0.1 to 3.0 mol / liter, particularly 0.5 to 2.0 mol / liter. It is preferable. If the concentration of the electrolyte salt is less than 0.1 mol / liter, a sufficient current density may not be obtained. If the concentration is more than 3.0 mol / liter, the stability of the nonaqueous electrolyte may be impaired. .

  The non-aqueous electrolyte of the present invention can be suitably used as a non-aqueous electrolyte constituting a primary or secondary battery, particularly a non-aqueous electrolyte secondary battery described later.

As the electrode material of the battery, there are a positive electrode and a negative electrode. As the positive electrode, a positive electrode active material, a binder, and a conductive material slurried with an organic solvent or water are applied to a current collector, dried, and then a sheet. The one made into a shape is used. Examples of the positive electrode active material include TiS ₂ , TiS ₃ , MoS ₃ , FeS ₂ , Li _(1-x) MnO ₂ , Li _(1-x) Mn ₂ O ₄ , Li _(1-x) CoO ₂ , Li _{(1 -x) NiO 2, LiV 2 O} 3, V 2 O 5 and the like. In addition, X in these positive electrode active materials shows the number of 0-1. A material obtained by adding or substituting a transition metal such as Li, Mg, Al, or Co, Ti, Nb, or Cr may be used. Moreover, not only these lithium-metal composite oxides are used alone, but also a plurality of them can be mixed and used. Among these, the lithium-metal composite oxide is preferably at least one of a lithium manganese-containing composite oxide having a layered structure or a spinel structure, a lithium nickel-containing composite oxide, and a lithium cobalt-containing composite oxide. Examples of the binder for the positive electrode active material include, but are not limited to, polyvinylidene fluoride, polytetrafluoroethylene, EPDM, SBR, NBR, and fluorine atom rubber. As the negative electrode, a negative electrode active material and a binder slurryed with an organic solvent or water is applied to a current collector and dried to form a sheet. Examples of the negative electrode active material include inorganic compounds such as lithium, lithium alloys, and tin compounds, carbonaceous materials, and conductive polymers. In particular, a carbonaceous material that can occlude and release highly safe lithium ions is preferable. The carbonaceous material is not particularly limited, but graphite, petroleum coke, coal coke, petroleum pitch carbide, coal pitch carbide, phenol resin / crystalline cellulose resin, etc., and partially carbonized thereof. Carbon materials, furnace black, acetylene black, pitch-based carbon fibers, PAN-based carbon fibers, and the like. Examples of the binder for the negative electrode active material include the same binders for the positive electrode active material.

  As the conductive material for the positive electrode, fine particles of graphite, carbon black such as acetylene black, and amorphous carbon fine particles such as needle coke are used, but are not limited thereto. As the organic solvent to be slurried, an organic solvent that dissolves the binder is usually used. Examples of the organic solvent include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like. However, it is not limited to these.

  As the current collector for the negative electrode, copper, nickel, stainless steel, nickel-plated steel or the like is usually used, and as the current collector for the positive electrode, aluminum, stainless steel, nickel-plated steel or the like is usually used.

  In the non-aqueous electrolyte secondary battery of the present invention, a separator is used between the positive electrode and the negative electrode. As the separator, a commonly used polymer microporous film can be used without any particular limitation. Examples of the film include polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethylene oxide and polypropylene oxide. Films composed of ethers, various celluloses such as carboxymethylcellulose and hydroxypropylcellulose, polymer compounds mainly composed of poly (meth) acrylic acid and various esters thereof, derivatives thereof, copolymers and mixtures thereof. Etc. These films may be used alone, or may be used as a multilayer film by superimposing these films. Furthermore, various additives may be used for these films, and the type and content thereof are not particularly limited. Among these films, a microporous film made of polyethylene, polypropylene, polyvinylidene fluoride, or polysulfone is preferably used for the nonaqueous electrolyte secondary battery of the present invention.

  These films are microporous so that the electrolyte can penetrate and ions can easily pass therethrough. The microporosity method includes a phase separation method in which a polymer compound and a solvent solution are formed into a film while microphase separation is performed, and the solvent is extracted and removed to make it porous. The film is extruded and then heat-treated, the crystals are aligned in one direction, and a gap is formed between the crystals by stretching to make it porous, and so on.

  The shape of the non-aqueous electrolyte secondary battery of the present invention having the above configuration is not particularly limited, and can be various shapes such as a coin shape, a cylindrical shape, and a square shape. FIG. 1 shows an example of a coin-type battery of the nonaqueous electrolyte secondary battery of the present invention, and FIGS. 2 and 3 show examples of a cylindrical battery, respectively.

  In the coin-type non-aqueous electrolyte secondary battery 10 shown in FIG. 1, 1 is a positive electrode capable of releasing lithium ions, 1a is a positive electrode current collector, and 2 is a carbonaceous material capable of inserting and extracting lithium ions released from the positive electrode. The negative electrode current collector, 2a is a negative electrode current collector, 3 is a non-aqueous electrolyte of the present invention, 4 is a stainless steel positive electrode case, 5 is a stainless steel negative electrode case, 6 is a polypropylene gasket, and 7 is a polyethylene separator. It is.

  Further, in the cylindrical nonaqueous electrolyte secondary battery 10 ′ shown in FIGS. 2 and 3, 11 is a negative electrode, 12 is a negative electrode assembly, 13 is a positive electrode, 14 is a positive electrode current collector, and 15 is a non-electrode of the present invention. Water electrolyte, 16 separator, 17 positive electrode terminal, 18 negative electrode terminal, 19 negative electrode plate, 20 negative electrode lead, 21 positive electrode plate, 22 positive electrode lead, 23 case, 24 insulating plate, 25 gasket , 26 are safety valves, and 27 is a PTC element.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not restrict | limited by a following example.

  In the examples and comparative examples, nonaqueous electrolyte secondary batteries (lithium secondary batteries) were produced according to the following production procedure.

<Production procedure>

(Preparation of positive electrode)
85 parts by mass of LiNi _0.8 Co _0.17 Al _0.03 O ₂ as a positive electrode active material, 10 parts by mass of acetylene black as a conductive material, and 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder were mixed to obtain a positive electrode material. This positive electrode material was dispersed in N-methyl-2-pyrrolidone (NMP) to form a slurry. This slurry was applied to both sides of a positive electrode current collector made of aluminum, dried and press-molded to obtain a positive electrode plate. Then, this positive electrode plate was cut into a predetermined size, and a sheet-like positive electrode was produced by scraping off the electrode mixture at a portion that became a lead tab weld for extracting current.

(Preparation of negative electrode)
A negative electrode material was prepared by mixing 92.5 parts by mass of graphite carbon material powder as a negative electrode active material and 7.5 parts by mass of PVDF as a binder. This negative electrode material was dispersed in NMP to form a slurry. This slurry was applied to both sides of a copper negative electrode current collector, dried and press-molded to obtain a negative electrode plate. Then, this negative electrode plate was cut into a predetermined size, and a sheet-like negative electrode was produced by scraping off a portion of the electrode mixture that would become a lead tab weld for extracting current.

(Preparation of non-aqueous electrolyte)
The nonaqueous electrolytic solution was prepared by dissolving 1 mol / liter of LiPF ₆ in a mixed solvent of 30% by volume of ethylene carbonate (EC) and 70% by volume of diethyl carbonate (DEC). 1) was added in the amount (volume%) shown in Table 1 to obtain a non-aqueous electrolyte.

(Battery assembly)
The obtained sheet-like positive electrode and sheet-like negative electrode were wound through a polyethylene microporous film having a thickness of 25 μm to form a wound electrode body. The obtained wound electrode body was inserted into the case and held in the case. At this time, the current collecting lead having one end welded to the lead tab weld portion of the sheet-like positive electrode or sheet-like negative electrode was joined to the positive electrode terminal or the negative electrode terminal of the case, respectively. Thereafter, a non-aqueous electrolyte was poured into the case holding the wound electrode body, and the case was sealed and sealed to produce a cylindrical lithium secondary battery having a diameter of 18 mm and an axial length of 65 mm.

(Initial charge / discharge, initial discharge capacity measurement method)
The initial charge / discharge of the produced secondary battery was performed under the following conditions. First, a constant current and constant voltage charge is performed up to 4.1 V at a charging current of 0.25 mA / cm ² (current value corresponding to 1/4 C, 1 C is a current value that discharges the battery capacity in one hour), and a discharge current of 0.33 mA / Constant current discharge was performed up to 3.0 V at cm ² (current value corresponding to 1/3 C). Then, constant current constant voltage to 4.1V at a charging current 1.1 mA / cm ² (current value of 1C equivalent) charged, up to 3.0V discharge current 1.1 mA / cm ² (current value of 1C equivalent) The operation of discharging with constant current was performed 4 times. Thereafter, 3.0 V at a charging current 1.1 mA / cm ² at (1C equivalent current value) to 4.1V charging constant current constant voltage, discharge current 0.33mA / cm ² (1 / 3C equivalent current value) The discharge capacity at this time was defined as the initial discharge capacity of the battery. The measurement was performed in an atmosphere at 20 ° C.

(Initial internal resistance measurement method)
First, a constant current and constant voltage charge up to 3.75 V with a charging current of 1.1 mA / cm ² (current value equivalent to 1 C), an AC impedance measurement device (manufactured by Toyo Technica: frequency response analyzer solartron 1260, potentio / galvanostat) Using a solartron 1287), scanning was performed from a frequency of 100 kHz to 0.02 Hz, and a Cole-Cole plot showing the imaginary part on the vertical axis and the real part on the horizontal axis was created. Subsequently, in this Cole-Cole plot, as shown in FIG. 4, the arc portion is fitted with a circle, and the larger value of the two points intersecting the real part (horizontal axis) of this circle is the resistance value. And the initial internal resistance of the battery.

(High temperature storage characteristics test method)
The lithium secondary battery was kept at 20 ° C. and charged at a constant current and a constant voltage up to 4.1 V (SOC 100%) at a charging current of 1.1 mA / cm ² . It preserve | saved for 720 hours (30 days) in an 80 degreeC thermostat. Thereafter, the ambient temperature is returned to 20 ° C., and a constant current is discharged to 3.0 V once at a discharge current of 0.33 mA / cm ² (current value corresponding to 1/3 C), and the charge current is 1.1 mA / cm ² again. (Current value equivalent to 1C) is constant current and constant voltage charge up to 4.1V, discharge current is 0.33mA / cm ² (current value equivalent to 1 / 3C) and constant current is discharged to 3.0V. Discharge at this time The capacity was defined as the discharge capacity of the battery after the high temperature storage test. Similarly to the initial internal resistance measurement, the internal resistance was charged at a constant current and a constant voltage up to 3.75 V with a charging current of 1.1 mA / cm ² (current value equivalent to 1 C), and the frequency was measured from 100 kHz to A Cole-Cole plot was created by scanning to 0.02 Hz and showing the imaginary part on the vertical axis and the real part on the horizontal axis. Subsequently, in this Cole-Cole plot, the arc part is fitted with a circle, and the larger value of the two points intersecting the real part (horizontal axis) of this circle is taken as the resistance value, and the battery after high temperature storage. Of internal resistance.

From these measurement results, the discharge capacity recovery rate (%) and the internal resistance increase rate (%) were determined by the following formula.
Discharge capacity recovery rate (%) = [(discharge capacity after storage at high temperature) / (initial discharge capacity)] × 100
Internal resistance increase rate (%) = [{(internal resistance after high temperature storage) − (initial internal resistance)} / (initial internal resistance)] × 100

<Example 1 to Example 9>
As described above (preparation of non-aqueous electrolyte solution), non-aqueous electrolyte solutions were prepared. Using these non-aqueous electrolytes, lithium secondary batteries were respectively produced as described above (battery assembly), and the lithium secondary batteries were subjected to a high-temperature storage characteristic test according to the above operation procedure. The results are shown in Table 1.

<Comparative Example 1>
A lithium secondary battery was produced in the same manner as in the example except that the base electrolyte was used as the non-aqueous electrolyte, and the lithium secondary battery was subjected to a high-temperature storage characteristic test in the same manner as in the example. The results are shown in Table 1.

<Comparative example 2>
A lithium secondary battery was produced in the same manner as in Example except that a nonaqueous electrolyte solution in which 0.6% by volume of vinylene carbonate (VC) was added to the base electrolyte solution was used as the nonaqueous electrolyte solution. About this, the high temperature storage characteristic test was done like the Example. The results are shown in Table 1.

  As is clear from the results of [Table 1], in the batteries of Examples 1 to 9 in which the cyclic compound represented by any one of the above general formulas (1) to (5) was added to the electrolyte, the added cyclic The compound received electrons at the negative electrode during initial charging and ring-opening polymerization, and formed a stable coating before decomposition of the electrolytic solution. Therefore, it is considered that the discharge capacity recovery rate at high temperature storage was improved. It was also confirmed that the increase in internal resistance can be suppressed while maintaining a high discharge capacity recovery rate by minimizing the amount of the compound to be added. On the other hand, the battery of Comparative Example 1 using only the base electrolyte solution has a low discharge capacity recovery rate and a high increase rate of internal resistance because a stable film is not formed and decomposition of the electrolyte solution proceeds. In the battery of Comparative Example 2 in which VC is added to the electrolytic solution, although the high temperature characteristics are higher than the battery of Comparative Example 1 having only the base electrolytic solution, the coating formed by VC is decomposed in an environment of 80 ° C. It was confirmed that the discharge capacity recovery rate was low and the internal resistance increase rate was high.

FIG. 1 is a longitudinal sectional view schematically showing an example of the structure of a coin-type battery of the nonaqueous electrolyte secondary battery of the present invention. FIG. 2 is a schematic diagram showing a basic configuration of a cylindrical battery of the nonaqueous electrolyte secondary battery of the present invention. FIG. 3 is a perspective view showing the internal structure of the cylindrical battery of the nonaqueous electrolyte secondary battery of the present invention as a cross section. FIG. 4 is a graph showing a Cole-Cole plot created in the measurement of the internal resistance of the battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 2 Negative electrode 2a Negative electrode collector 3 Electrolyte 4 Positive electrode case 5 Negative electrode case 6 Gasket 7 Separator 10 Coin type nonaqueous electrolyte secondary battery 10 'Cylindrical nonaqueous electrolyte secondary battery DESCRIPTION OF SYMBOLS 11 Negative electrode 12 Negative electrode assembly 13 Positive electrode 14 Positive electrode assembly 15 Electrolytic solution 16 Separator 17 Positive electrode terminal 18 Negative electrode terminal 19 Negative electrode plate 20 Negative electrode lead 21 Positive electrode 22 Positive electrode lead 23 Case 24 Insulating plate 25 Gasket 26 Safety valve 27 PTC element

Claims (3)

A nonaqueous electrolytic solution in which an electrolyte salt is dissolved in an organic solvent contains at least one selected from cyclic compounds represented by any one of the following general formulas (1) to (5). Non-aqueous electrolyte.

(In the formula, R ₁ and R ₂ each independently represent a hydrogen atom, a fluorine atom, or a hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms. R ₃ and R ₄ each independently represent X represents a sulfur atom, a sulfone, or a disulfide, and Y represents an oxygen atom, a carbon atom, NH, N-alkyl, N-aryl, or a sulfur atom. Z represents a hydrocarbon group which may contain a fluorine atom having 1 to 6 carbon atoms, or a hydrocarbon group having an ether or carbonyl bond.)

(In the formula, R _{5 to} R ₁₀ each independently represent a hydrogen atom, a fluorine atom, or a hydrocarbon group that may contain a fluorine atom having 1 to 6 carbon atoms.)

(Wherein R _{11 to} R ₂₀ each independently represent a hydrogen atom, a fluorine atom, or a hydrocarbon group that may contain a fluorine atom having 1 to 6 carbon atoms. N represents an integer of 1 to 3). .)

(In the formula, R _{21 to} R ₃₀ each independently represent a hydrogen atom, a fluorine atom, or a hydrocarbon group that may contain 1 to 6 carbon atoms. N represents an integer of 1 to 2). .)

(In the formula, R ₃₁ and R ₃₂ each independently represent a cyano group, a fluorine atom, a carbonyl group, or a hydrocarbon group that may contain a fluorine atom or a carbonyl group having 1 to 6 carbon atoms. R _{33 to} R ₃₇ each independently represents a hydrogen atom, a fluorine atom, or a hydrocarbon group that may contain a fluorine atom having 1 to 6 carbon atoms.)   The nonaqueous electrolytic solution according to claim 1, wherein the content of the cyclic compound represented by any one of the general formulas (1) to (5) is 0.05 to 5% by volume with respect to the nonaqueous electrolytic solution. . A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte according to claim 1 as an electrolyte.

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