WO2015015883A1 - Lithium secondary battery and electrolyte solution for lithium secondary batteries - Google Patents

Lithium secondary battery and electrolyte solution for lithium secondary batteries Download PDF

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Publication number
WO2015015883A1
WO2015015883A1 PCT/JP2014/064058 JP2014064058W WO2015015883A1 WO 2015015883 A1 WO2015015883 A1 WO 2015015883A1 JP 2014064058 W JP2014064058 W JP 2014064058W WO 2015015883 A1 WO2015015883 A1 WO 2015015883A1
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Prior art keywords
negative electrode
active material
electrode active
lithium secondary
secondary battery
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PCT/JP2014/064058
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French (fr)
Japanese (ja)
Inventor
洋子 橋詰
井上　和彦
信也 須藤
須黒　雅博
緑 志村
滝　敬之
裕知 渡辺
厚輝 渋谷
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日本電気株式会社
株式会社Adeka
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Application filed by 日本電気株式会社, 株式会社Adeka filed Critical 日本電気株式会社
Priority to JP2015529426A priority Critical patent/JPWO2015015883A1/en
Priority to CN201480042497.1A priority patent/CN105409047B/en
Priority to KR1020167004102A priority patent/KR20160036577A/en
Publication of WO2015015883A1 publication Critical patent/WO2015015883A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a lithium secondary battery having a high capacity, particularly excellent in cycle characteristics for use in a high temperature environment, and having a long life, and an electrolyte for a lithium secondary battery used therefor.
  • Lithium secondary batteries are widely used in portable electronic devices and personal computers, and are required to be smaller and lighter.
  • lithium secondary batteries have a high energy density that can be used for high-performance electronic devices and electric vehicles. Deterioration is suppressed, cycle characteristics are excellent, and long life is required.
  • a positive electrode active material layer containing a positive electrode active material formed on a current collector and a negative electrode active material layer containing a negative electrode active material are arranged to face each other with a separator therebetween. A charge / discharge cycle is performed when the electrode active material reversibly stores and releases lithium ions by being immersed in an electrolytic solution and housed in an exterior body.
  • negative electrode active material As this type of negative electrode active material, from the viewpoint of high energy density, low cost, and safety, metals such as silicon and silicon oxide, tin that forms an alloy with lithium, and metal oxides are used instead of carbon-based materials. It has been.
  • the negative electrode active material containing silicon has a large volume expansion / contraction due to charging / discharging, and falls off as a fine powder from the negative electrode active material layer with repeated charging / discharging, resulting in a decrease in battery capacity. In particular, when used in a high temperature environment of 45 ° C. or higher, deterioration due to a decrease in battery capacity tends to become remarkable.
  • a film is formed on the negative electrode active material layer, and the negative electrode active material from the negative electrode active material layer is formed. It has been done to suppress the loss of material. However, it is difficult to form a stable coating having a uniform thickness on the silicon-based negative electrode active material that can sufficiently suppress deterioration of cycle characteristics due to use.
  • the cycle characteristics are improved by adding a specific substance to the electrolytic solution to be used.
  • a specific substance such as graphite as an active material and a polymer carboxylic oxide as a binder, an organic solvent, Non-aqueous electrolytes using electrolyte salts and electrolytes containing specific unsaturated phosphate esters (Patent Documents 1 and 2), lithium ion batteries and the like, alkoxy groups substituted with halogen atoms, A substance containing a halogen-containing phosphate ester compound having an alkoxy group containing a saturated bond and suppressing gas generation during storage at high temperature of a charged secondary battery has been reported (Patent Document 3).
  • a lithium secondary having a negative electrode formed by depositing an active material thin film on a current collector A battery including a non-electrolyte containing at least one of a phosphate ester compound, a phosphite ester, and a borate ester (Patent Document 4) has been reported.
  • An object of the present invention is to form a stable film having a uniform thickness, having flexibility to follow a volume change accompanying charging / discharging of a silicon-based negative electrode active material having a large volume expansion / shrinkage ratio due to insertion and extraction of lithium.
  • a silicon-based negative electrode active material having a large volume expansion / shrinkage ratio due to insertion and extraction of lithium.
  • the present inventors As a substance capable of forming a flexible and stable film capable of following a change in volume accompanying charge / discharge on a silicon-based negative electrode active material, the present inventors have unsaturated at the terminal of three alkoxy groups of phosphate ester. It has been found that by adding an unsaturated phosphate ester having a triple bond to the electrolytic solution, the capacity retention rate in the charge / discharge cycle can be improved, and the present invention has been completed based on such knowledge.
  • the present invention is a lithium secondary battery having an electrolyte solution that immerses a positive electrode and a negative electrode that occlude and release lithium during charge and discharge, and the negative electrode includes a silicon-based negative electrode active material,
  • the electrolyte is the formula (1)
  • R 1 to R 3 independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms
  • a lithium secondary battery comprising an unsaturated phosphate ester About.
  • the present invention also relates to an electrolyte for a lithium secondary battery in which a positive electrode and a negative electrode that absorb and release lithium in accordance with charge and discharge are immersed,
  • R 1 to R 3 independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms
  • the present invention relates to an electrolytic solution.
  • the lithium secondary battery of the present invention and the electrolyte for a lithium secondary battery suppress deterioration due to charging / discharging of a silicon-based negative electrode active material having a large volume expansion / contraction rate due to insertion and extraction of lithium, particularly in a high temperature environment. As a result, the cycle characteristics can be improved and the life can be extended.
  • the lithium secondary battery of the present invention has a positive electrode and a negative electrode, and an electrolytic solution for immersing them.
  • the negative electrode includes a silicon-based negative electrode active material capable of reversibly occluding and releasing lithium ions during charge and discharge, and is laminated on the current collector as a negative electrode active material layer integrated with a negative electrode binder. Has a structured.
  • the negative electrode active material may be any material as long as it contains a silicon-based negative electrode active material.
  • Examples of the silicon-based negative electrode active material include silicon and silicon oxide (SiOx: 0 ⁇ x ⁇ 2). . Any one of these may be used, but it is preferable to include both of them. These have different lithium ion charge / discharge potentials as a negative electrode active material.
  • silicon has a lower lithium ion charge / discharge potential than silicon oxide.
  • Lithium ions can be gradually released as the voltage changes, and rapid volume shrinkage of the negative electrode active material layer due to lithium ions being released at a specific potential at a time can be suppressed.
  • Silicon oxide hardly reacts with the electrolyte and can exist stably. Specific examples include SiO and SiO 2 .
  • the content of silicon in the negative electrode active material may be 100% by mass, and may be 0% by mass when silicon oxide is contained in the negative electrode active material, but is preferably 5% by mass or more and 95% by mass or less. More preferably, they are 10 mass% or more and 90 mass% or less, More preferably, they are 20 mass% or more and 50 mass% or less.
  • the content of silicon oxide in the negative electrode active material may be 100% by mass, and may be 0% by mass when silicon is contained in the negative electrode active material, but may be 5% by mass or more and 90% by mass or less. More preferably, it is 40 mass% or more and 80 mass% or less, More preferably, it is 50 mass% or more and 70 mass% or less.
  • the negative electrode active material may contain a metal other than silicon or a metal oxide.
  • the metal other than silicon include metals capable of forming an alloy with lithium, and capable of releasing lithium ions from the lithium alloy during discharging and forming the lithium alloy during charging.
  • Specific examples include aluminum, lead, tin, indium, bismuth, silver, barium, calcium, mercury, palladium, platinum, tellurium, zinc, and lanthanum. These can select 1 type (s) or 2 or more types. Of these, tin is preferred.
  • the metal oxide as the negative electrode active material include aluminum oxide, tin oxide, indium oxide, zinc oxide, and lithium oxide, and these can be used alone or in combination of two or more. . These metal oxides are preferably used together with the above metals, and in particular, when used together with the same metal as the metal contained in the metal oxide, occlusion / release of lithium ions is performed at different potentials during charging and discharging, It is preferable to use a tin oxide together with the tin because a rapid volume change of the negative electrode active material layer can be suppressed.
  • silicon oxides and metal oxides are preferably at least partially amorphous.
  • the silicon oxide or the metal oxide is amorphous, it is possible to suppress pulverization of the negative electrode active material layer and to suppress reaction with the electrolytic solution.
  • the negative electrode active material layer having amorphous silicon oxide or metal oxide elements due to non-uniformity such as defects and crystal grain boundaries included in the crystal structure are reduced, and non-uniform volume change is suppressed. it is conceivable that.
  • the silicon oxide and the metal oxide are amorphous, since the peak specific to the crystal structure observed when having a crystal structure is broad.
  • a carbon material is included as the negative electrode active material.
  • the carbon material include graphite, amorphous carbon, diamond-like carbon, and carbon nanotube.
  • Graphite with high crystallinity has high electrical conductivity and can improve the current collecting performance of the negative electrode active material layer.
  • Amorphous carbon with low crystallinity suppresses deterioration of the negative electrode active material layer due to charge / discharge. can do.
  • the content of the carbon material in the negative electrode active material is preferably 2% by mass or more and 50% by mass or less, and more preferably 2% by mass or more and 30% by mass or less.
  • the silicon, silicon oxide, metal, metal oxide, and carbon material are in a particulate form because deterioration due to charging / discharging of the negative electrode active material can be suppressed.
  • the particulate negative electrode active material the larger the volume change associated with charging / discharging, the smaller the diameter is preferable because the volume change of the negative electrode active material layer due to the volume change of these particles can be suppressed.
  • the average particle diameter of silicon oxide is smaller than the average particle diameter of the carbon material.
  • the average particle diameter of silicon oxide is preferably 1 ⁇ 2 or less of the average particle diameter of the carbon material.
  • the average particle diameter of silicon is smaller than the average particle diameter of silicon oxide.
  • the average particle diameter of silicon is preferably 1 ⁇ 2 or less of the average particle diameter of silicon oxide.
  • the average particle diameter of silicon is preferably 20 ⁇ m or less, for example, because it can ensure contact with the current collector, and more preferably 15 ⁇ m or less.
  • amorphous silicon oxide exists around the silicon cluster, and its surface is in the form of particles coated with carbon. May be.
  • the thickness of the carbon film covering the surface of the silicon-based material particles is preferably 0.1 to 5 ⁇ m because it is possible to suppress deterioration of the negative electrode active material due to charge and discharge and increase conductivity. .
  • the thickness of the carbon coating can be measured by observation with a transmission electron microscope (TEM), and an average value of measured values for 100 particles can be adopted.
  • a method for producing a negative electrode active material having a carbon film in which silicon or metal is dispersed in the amorphous silicon oxide a method described in JP-A-2004-47404 can be exemplified. Specifically, silicon oxide or metal oxide is formed around silicon or metal nanoclusters by CVD treatment of silicon oxide or metal oxide in an organic gas atmosphere such as methane gas. A carbon coating can be formed around. Moreover, the method of mixing a silicon oxide, a metal oxide, silicon, a metal, and a carbon material by mechanical milling can be mentioned. The average particle diameter of the negative electrode active material having such a carbon film can be about 1 to 20 ⁇ m.
  • Examples of the negative electrode binder that binds the negative electrode active material include polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and styrene-butadiene copolymer.
  • PVdF polyvinylidene fluoride
  • Examples thereof include polymer rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide and the like. These can be used alone or in combination of two or more.
  • polyimide and polyamideimide are included from the viewpoint of binding force.
  • the amount of the binder for the negative electrode to be used is 5 to 25 parts by mass with respect to 100 parts by mass of the negative electrode active material from the viewpoints of “sufficient binding force” and “high energy” which are in a trade-off relationship. It is preferable.
  • the current collector that supports the negative electrode active material layer in which the negative electrode active material is integrated with the negative electrode binder may be any material that has electrical conductivity that enables electrical connection to the external terminal.
  • Aluminum, nickel, copper, silver, or an alloy thereof is preferable.
  • Examples of the shape include foil, flat plate, and mesh.
  • the thickness of the current collector can be about 5 to 30 ⁇ m.
  • the negative electrode can be manufactured using a negative electrode active material layer material including a negative electrode active material and a negative electrode binder on a current collector.
  • a method for producing the negative electrode active material layer include a coating method such as a doctor blade method and a die coater method, a CVD method, and a sputtering method.
  • a thin film of aluminum, nickel, or an alloy thereof may be formed by a method such as vapor deposition or sputtering to form a negative electrode current collector.
  • the thickness of the negative electrode active material layer can be about 10 to 200 ⁇ m.
  • the positive electrode includes a positive electrode active material capable of reversibly occluding and releasing lithium ions during charge and discharge, and the positive electrode active material is laminated on the current collector as a positive electrode active material layer integrated with a positive electrode binder. It has a structure.
  • the positive electrode active material releases lithium ions into the electrolytic solution during charging and occludes lithium from the electrolytic solution during discharging, and is layered such as LiMnO 2 and Li x Mn 2 O 4 (0 ⁇ x ⁇ 2).
  • a positive electrode active material can be used individually by 1 type or in combination of 2 or more types.
  • the positive electrode binder that binds and integrates the positive electrode active material specifically, the same negative electrode binder as that described above can be used.
  • the positive electrode binder polyvinylidene fluoride is preferable from the viewpoint of versatility and low cost.
  • the amount of the positive electrode binder used is preferably 2 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.
  • the content of the positive electrode binder is 2 parts by mass or more, the adhesion between the active materials or between the active material and the current collector is improved, and the cycle characteristics are improved.
  • the substance ratio is improved and the positive electrode capacity can be improved.
  • a conductive auxiliary material may be added for the purpose of reducing the impedance of the positive electrode active material.
  • the conductive auxiliary material carbonaceous fine particles such as graphite, carbon black, and acetylene black can be used.
  • the current collector that supports the positive electrode active material layer in which the positive electrode active material is integrated with the positive electrode binder may be any material that can conduct electricity with the external terminal.
  • the same collector as that used for the negative electrode can be used.
  • the positive electrode can be produced on a current collector using a positive electrode active material layer material including a positive electrode active material and a positive electrode binder.
  • a method for manufacturing the positive electrode active material layer a method similar to the method for manufacturing the negative electrode active material layer can be used.
  • the electrolyte solution can absorb and release lithium in the positive electrode and the negative electrode during charge and discharge, so that the lithium ion can be dissolved by immersing the positive electrode and the negative electrode, and the electrolyte is dissolved in a non-aqueous organic solvent. .
  • the solvent of the electrolytic solution is stable at the operating potential of the battery and has a low viscosity so that the electrode can be immersed in the usage environment of the battery.
  • cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC); dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate
  • aprotic organic solvents such as chain carbonate esters such as (EMC) and dipropyl carbonate (DPC); propylene carbonate derivatives; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, and ethyl propionate; .
  • EC ethylene carbonate
  • PC propylene carbonate
  • BC butylene carbonate
  • VC vinylene carbonate
  • DMC dimethyl carbonate
  • DEC diethyl carbonate
  • MEC ethyl methyl carbonate
  • DPC dipropyl carbonate
  • DPC dipropyl carbonate
  • a lithium salt As an electrolyte contained in the electrolytic solution, a lithium salt is preferable.
  • the lithium salt include LiPF 6 , LiAsF 6 , LiAlCl 4 , LiClO 4 , LiBF 4 , LiSbF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , Li (CF 3 SO 2 ) 3 , LiN ( CF 3 SO 2 ) 2 and the like.
  • the concentration of the electrolyte in the electrolytic solution is preferably 0.01 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 1.5 mol / L or less.
  • concentration is within this range, safety can be improved, and a battery having high reliability and contributing to reduction of environmental load can be obtained.
  • the above electrolytic solution contains an unsaturated phosphate ester represented by the formula (1).
  • the unsaturated phosphoric acid ester represented by the formula (1) is a polymer produced by the progress of a polymerization reaction in which an unsaturated triple bond becomes a radical on the surface of the negative electrode active material as the battery is charged and discharged. It is considered that the active material is coated to form a uniform film made of a polymer. This polymer coating permeates lithium ions and inhibits the permeation of the electrolytic solution, and consequently suppresses the reaction between the negative electrode active material and the electrolytic solution, and suppresses the decrease in battery capacity due to repeated charge and discharge. It is thought that you can.
  • R 1 to R 3 independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms.
  • the unsaturated phosphoric acid ester represented by the formula (1) is a compound represented by the formula (2) in which R 1 to R 3 represent methylene groups. Is preferable in forming.
  • the content of the unsaturated phosphate ester represented by the formula (1) in the electrolyte is appropriately selected so that a film having an appropriate thickness is formed on the negative electrode active material.
  • the unsaturated phosphate ester represented by the formula (1) contained in the electrolytic solution is polymerized or decomposed during the initial charge / discharge of the battery and the subsequent relatively early charge / discharge. For this reason, when the amount of the unsaturated phosphate ester represented by the formula (1) contained in the electrolytic solution is excessive, the unsaturated phosphate ester represented by the formula (1) at an early stage of the charge / discharge cycle.
  • the concentration of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution may be, for example, about 0.005 to 10% by mass, preferably 0.01 to 5.0% by mass, and more preferably Is about 0.5 to 3.0% by mass.
  • the upper limit of the content of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution can be defined by the impedance (charge transfer resistance) between the electrodes at the end of charging.
  • the content of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution is the same as that at the end of charging when the unsaturated phosphate ester represented by the formula (1) is added. It is preferable that the impedance between the electrodes is less than about 10 times that in the case of no addition because the rate characteristic or charge / discharge characteristic is not deteriorated.
  • separator Any separator may be used as long as it suppresses the conduction between the positive electrode and the negative electrode, does not inhibit the permeation of the charged body, and has durability against the electrolytic solution.
  • the material that can be used include polyolefin microporous membranes such as polypropylene and polyethylene, cellulose, polyethylene terephthalate, polyimide, and polyvinylidene fluoride. These can be used as porous films, woven fabrics, non-woven fabrics and the like.
  • the outer package those having a strength capable of stably holding the positive electrode, the negative electrode, the separator, and the electrolytic solution, electrochemically stable with respect to these substances, and watertight are preferable.
  • a laminate film coated with stainless steel, nickel-plated iron, aluminum, silica, and alumina can be used.
  • a resin used for the laminate film polyethylene, polypropylene, polyethylene terephthalate, or the like is used. Can do. These may be a structure of one layer or two or more layers.
  • the shape of the secondary battery may be any of a cylindrical type, a flat wound square type, a laminated square type, a coin type, a flat wound laminated type, and a laminated laminate type.
  • the laminated laminate type secondary battery includes a negative electrode 3 having a negative electrode active material layer 1 provided on a negative electrode current collector 2 made of metal such as copper foil, and a positive electrode current collector 5 made of metal such as aluminum foil.
  • the positive electrode 6 having the positive electrode active material layer 4 provided on the substrate is disposed so as to face each other through a separator 7 made of a polypropylene microporous film that avoids these contacts, and these are accommodated in a laminate outer package 8. .
  • the laminate outer package is filled with an electrolytic solution, and the negative electrode active material layer 1 and the positive electrode active material layer 4 are immersed in the electrolytic solution, and each is electrically connected to the current collector portion where no active material layer is formed. Connected, the negative electrode terminal 9 and the positive electrode terminal 10 are pulled out to the outside of the laminate outer package, and are connected to an external power source or equipment used during charging and discharging.
  • Example 1 a silicon-based negative electrode active material in which a carbon coating was formed on the surface of silicon-based particles in which silicon was dispersed in amorphous silicon oxide (SiOx, 0 ⁇ x ⁇ 2) was obtained.
  • the mass ratio of silicon, amorphous silicon oxide, and carbon in the silicon-based negative electrode active material was 29:61:10.
  • This negative electrode active material and polyamic acid, which is a precursor of polyimide as a negative electrode binder, were weighed at a mass ratio of 90:10 and mixed with n-methylpyrrolidone to obtain a negative electrode slurry.
  • the negative electrode slurry was applied to a copper foil having a thickness of 10 ⁇ m, dried, and then subjected to a heat treatment in a nitrogen atmosphere at 300 ° C. to produce a negative electrode.
  • Lithium nickelate (LiNi0.80Co0.15Al0.05O2) as a positive electrode active material, carbon black as a conductive auxiliary, and polyvinylidene fluoride as a positive electrode binder in a mass ratio of 90: 5: 5 They were weighed and mixed with n-methylpyrrolidone to form a positive electrode slurry.
  • the positive electrode slurry was applied to an aluminum foil having a thickness of 20 ⁇ m, dried, and then pressed to prepare a positive electrode.
  • 3 layers of the positive electrode and 4 layers of the negative electrode obtained were alternately stacked while sandwiching a polypropylene porous film as a separator.
  • the ends of the positive electrode current collector not covered with the positive electrode active material are welded to each other, and the aluminum positive electrode terminal is welded to the welded portion, while the end of the negative electrode current collector not covered with the negative electrode active material
  • the parts were welded together, and a negative electrode terminal made of nickel was welded to the welded portion to obtain an electrode element having a planar laminated structure.
  • the obtained electrode element was wrapped with an aluminum laminate film as an outer package, and an electrolyte solution was injected therein, and then sealed while reducing the pressure to 0.1 atm to prepare a secondary battery.
  • Example 1 A lithium secondary battery was produced in the same manner as in Example 1 except that the compound (1) represented by the formula (2) was not used, and the charge / discharge cycle characteristics were evaluated. The results are shown in Table 1.
  • Example 3 A lithium secondary battery was fabricated in the same manner as in Example 1 except that the compound (3) represented by the formula (4) was used instead of the compound (1) represented by the formula (2). The charge / discharge cycle characteristics were evaluated. The results are shown in Table 1.
  • the charge / discharge capacity retention rate at 60 ° C. of the lithium secondary battery of the example is higher than that of the lithium secondary battery of the comparative example, and the electrolytic solution containing the unsaturated compound represented by the formula (1) It can be seen that the lithium secondary battery of the present invention using this has excellent charge / discharge cycle characteristics.
  • the lithium secondary battery of the present invention can be used in all industrial fields that require a power source and industrial fields related to the transport, storage, and supply of electrical energy. Specifically, it can be used as a power source for mobile devices such as mobile phones and notebook computers, and a power source for driving motors of vehicles.

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Abstract

The present invention provides: a lithium secondary battery which is suppressed in deterioration of a negative electrode active material due to charging and discharging and has excellent cycle characteristics, while having a long service life especially for use in a high-temperature environment; and an electrolyte solution which is used in this lithium secondary battery. A lithium secondary battery according to the present invention contains an electrolyte solution, in which a positive electrode and a negative electrode that absorb and desorb lithium during charging and discharging are immersed, and has a negative electrode that contains a silicon-based negative electrode active material. The electrolyte solution contains an unsaturated phosphoric acid ester that is represented by formula (1) (wherein each of R1-R3 independently represents a direct bond or an alkylene group having 1-5 carbon atoms).

Description

リチウム二次電池及びリチウム二次電池用電解液Lithium secondary battery and electrolyte for lithium secondary battery
　本発明は、高容量で、特に、高温環境下での使用に対するサイクル特性に優れ、長寿命のリチウム二次電池や、これに用いるリチウム二次電池用電解液に関する。 The present invention relates to a lithium secondary battery having a high capacity, particularly excellent in cycle characteristics for use in a high temperature environment, and having a long life, and an electrolyte for a lithium secondary battery used therefor.
　リチウム二次電池は、携帯型電子機器やパソコン等に広く利用され、小型化、軽量化が求められる一方において、高機能電子機器や電気自動車等に利用可能なエネルギー密度が高く、充放電に伴う劣化が抑制されサイクル特性に優れ、長寿命であることが求められている。リチウム電池は、それぞれ集電体上に形成された正極活物質を含有する正極活物質層と、負極活物質を含有する負極活物質層とが、セパレーターを介して対向して配置され、これらが電解液に浸漬されて外装体に収納された構造を有し、電極活物質がリチウムイオンを可逆的に収蔵、放出することにより、充放電サイクルが行われる。 Lithium secondary batteries are widely used in portable electronic devices and personal computers, and are required to be smaller and lighter. On the other hand, lithium secondary batteries have a high energy density that can be used for high-performance electronic devices and electric vehicles. Deterioration is suppressed, cycle characteristics are excellent, and long life is required. In each lithium battery, a positive electrode active material layer containing a positive electrode active material formed on a current collector and a negative electrode active material layer containing a negative electrode active material are arranged to face each other with a separator therebetween. A charge / discharge cycle is performed when the electrode active material reversibly stores and releases lithium ions by being immersed in an electrolytic solution and housed in an exterior body.
　この種の負極活物質として、高エネルギー密度、低コスト、安全性の観点から、炭素系材料に代わり、ケイ素やケイ素酸化物、リチウムと合金を形成するスズ等の金属や、金属酸化物が用いられている。しかしながら、ケイ素を含む負極活物質は充放電に伴う体積の膨張収縮が大きく、反復される充放電に伴い負極活物質層から微粉となって脱落し、電池の容量の低下が生じる。特に、４５℃以上の高温環境で使用すると、電池の容量の低下による劣化が顕著になる傾向にある。 As this type of negative electrode active material, from the viewpoint of high energy density, low cost, and safety, metals such as silicon and silicon oxide, tin that forms an alloy with lithium, and metal oxides are used instead of carbon-based materials. It has been. However, the negative electrode active material containing silicon has a large volume expansion / contraction due to charging / discharging, and falls off as a fine powder from the negative electrode active material layer with repeated charging / discharging, resulting in a decrease in battery capacity. In particular, when used in a high temperature environment of 45 ° C. or higher, deterioration due to a decrease in battery capacity tends to become remarkable.
　このようなリチウムの吸蔵放出に伴う体積膨張収縮率が大きいケイ素系負極活物質の充放電に伴う劣化を抑制するため、負極活物質層上に被膜を形成し、負極活物質層からの負極活物質の脱落を抑制することが行われている。しかしながら、使用に伴うサイクル特性の劣化を充分に抑制することができる均一な厚さの安定した被膜をケイ素系負極活物質に形成することは困難である。 In order to suppress deterioration due to charging / discharging of the silicon-based negative electrode active material having a large volume expansion / contraction rate due to such occlusion / release of lithium, a film is formed on the negative electrode active material layer, and the negative electrode active material from the negative electrode active material layer is formed. It has been done to suppress the loss of material. However, it is difficult to form a stable coating having a uniform thickness on the silicon-based negative electrode active material that can sufficiently suppress deterioration of cycle characteristics due to use.
　一方、リチウム二次電池の充放電サイクル特性の向上を図るため、使用する電解液に特定の物質を添加することにより、サイクル特性の向上を図ることが行われている。具体的には、グラファイト等の結晶性の高い結晶性炭素材料を活物質とし高分子カルボン酸化物を結着剤として製造された負極を使用した非水電解液二次電池において、有機溶媒と、電解質塩と、特定の不飽和リン酸エステルを含有する電解液を用いたもの（特許文献１、２）、リチウムイオン電池等の非水電解液として、ハロゲン原子により置換されたアルコキシ基と、不飽和結合を含むアルコキシ基とを有するハロゲン含有リン酸エステル化合物を含み、充電状態の二次電池の高温保存時におけるガス発生を抑制したもの（特許文献３）等が報告されている。また、上述のようにリチウムの吸蔵放出に伴う体積膨張収縮率が大きいケイ素系負極活物質に適用可能な方法として、集電体上に活物質薄膜を堆積して形成した負極を有するリチウム二次電池において、リン酸エステル化合物、亜リン酸エステル、及びホウ酸エステルの少なくとも１種を含む非電解質を含むもの（特許文献４）が報告されている。 On the other hand, in order to improve the charge / discharge cycle characteristics of the lithium secondary battery, the cycle characteristics are improved by adding a specific substance to the electrolytic solution to be used. Specifically, in a non-aqueous electrolyte secondary battery using a negative electrode manufactured using a crystalline carbon material with high crystallinity such as graphite as an active material and a polymer carboxylic oxide as a binder, an organic solvent, Non-aqueous electrolytes using electrolyte salts and electrolytes containing specific unsaturated phosphate esters (Patent Documents 1 and 2), lithium ion batteries and the like, alkoxy groups substituted with halogen atoms, A substance containing a halogen-containing phosphate ester compound having an alkoxy group containing a saturated bond and suppressing gas generation during storage at high temperature of a charged secondary battery has been reported (Patent Document 3). In addition, as a method applicable to a silicon-based negative electrode active material having a large volume expansion / shrinkage ratio due to insertion and extraction of lithium as described above, a lithium secondary having a negative electrode formed by depositing an active material thin film on a current collector A battery including a non-electrolyte containing at least one of a phosphate ester compound, a phosphite ester, and a borate ester (Patent Document 4) has been reported.
　しかしながら、エネルギー密度の高い電池を実現するためには、単位面積当たりの負極活物質量が充分になるように電極の厚みを厚くする必要があり、エネルギー密度の高いケイ素系負極を利用する場合においても、充放電に伴う体積変化に追従できる柔軟性を有し、均一で安定した被膜の形成により充放電に伴う負極活物質の劣化を抑制し、特に、高温環境下での使用に対し、サイクル特性の向上、長寿命化を図ることができるリチウム二次電池が要請されている。 However, in order to realize a battery having a high energy density, it is necessary to increase the thickness of the electrode so that the amount of the negative electrode active material per unit area is sufficient. In addition, it has the flexibility to follow the volume change associated with charge / discharge, and suppresses the deterioration of the negative electrode active material associated with charge / discharge by forming a uniform and stable film, especially for use in high-temperature environments. There is a demand for a lithium secondary battery capable of improving characteristics and extending the life.
特開２０１１－１２４０３９JP2011-124039 特開２０１１－７７０２９JP2011-77029A 特開２０１１－９６４６２JP2011-96462 特開２００２－３１９４３１JP 2002-319431 A
　本発明の課題は、リチウムの吸蔵放出に伴う体積膨張収縮率が大きいケイ素系負極活物質の充放電に伴う体積変化に追従できる柔軟性を有し、均一な厚さの安定した被膜を形成し、充放電に伴う負極活物質の劣化を抑制し、特に、高温環境下での使用に対し、サイクル特性の向上を図り、長寿命化を図ることができるリチウム二次電池やリチウム二次電池用電解液を提供することにある。 An object of the present invention is to form a stable film having a uniform thickness, having flexibility to follow a volume change accompanying charging / discharging of a silicon-based negative electrode active material having a large volume expansion / shrinkage ratio due to insertion and extraction of lithium. For lithium secondary batteries and lithium secondary batteries that can suppress deterioration of the negative electrode active material due to charge and discharge, improve cycle characteristics and extend the life, especially for use in high temperature environments It is to provide an electrolytic solution.
　本発明者らは、ケイ素系負極活性物質に、充放電に伴う体積変化に追従可能な柔軟で安定した被膜を形成することができる物質として、リン酸エステルの三つのアルコキシ基の末端に不飽和三重結合を有する不飽和リン酸エステルを電解液に添加することにより、充放電サイクルにおける容量維持率を向上させることができることを見出し、かかる知見に基づき、本発明を完成させた。 As a substance capable of forming a flexible and stable film capable of following a change in volume accompanying charge / discharge on a silicon-based negative electrode active material, the present inventors have unsaturated at the terminal of three alkoxy groups of phosphate ester. It has been found that by adding an unsaturated phosphate ester having a triple bond to the electrolytic solution, the capacity retention rate in the charge / discharge cycle can be improved, and the present invention has been completed based on such knowledge.
　即ち、本発明は、充放電に伴いリチウムを吸蔵放出する正極及び負極を浸漬する電解液を有し、負極がケイ素系負極活物質を含むリチウム二次電池であって、
電解液が、式（１） That is, the present invention is a lithium secondary battery having an electrolyte solution that immerses a positive electrode and a negative electrode that occlude and release lithium during charge and discharge, and the negative electrode includes a silicon-based negative electrode active material,
The electrolyte is the formula (1)
Figure JPOXMLDOC01-appb-C000005
Figure JPOXMLDOC01-appb-C000005
（式中、Ｒ1～Ｒ3は、独立して直接結合、又は炭素数１～５のアルキレン基を示す。）で表される不飽和リン酸エステルを含むことを特徴とするリチウム二次電池に関する。 (Wherein R 1 to R 3 independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms), and a lithium secondary battery comprising an unsaturated phosphate ester About.
　また、本発明は、充放電に伴いリチウムを吸蔵放出する正極及び負極を浸漬するリチウム二次電池用電解液であって、式（１） The present invention also relates to an electrolyte for a lithium secondary battery in which a positive electrode and a negative electrode that absorb and release lithium in accordance with charge and discharge are immersed,
Figure JPOXMLDOC01-appb-C000006
Figure JPOXMLDOC01-appb-C000006
（式中、Ｒ1～Ｒ3は、独立して直接結合、又は炭素数１～５のアルキレン基を示す。）で表される不飽和リン酸エステルを含むことを特徴とするリチウム二次電池用電解液に関する。 (Wherein R 1 to R 3 independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms), and a lithium secondary battery comprising an unsaturated phosphate ester The present invention relates to an electrolytic solution.
　本発明のリチウム二次電池や、リチウム二次電池用電解液は、リチウムの吸蔵放出に伴う体積膨張収縮率が大きいケイ素系負極活物質の充放電に伴う劣化を抑制し、特に、高温環境下での使用に対し、サイクル特性の向上を図り、長寿命化を図ることができる。 The lithium secondary battery of the present invention and the electrolyte for a lithium secondary battery suppress deterioration due to charging / discharging of a silicon-based negative electrode active material having a large volume expansion / contraction rate due to insertion and extraction of lithium, particularly in a high temperature environment. As a result, the cycle characteristics can be improved and the life can be extended.
本発明のリチウム二次電池の一例の構成を示す構成図である。It is a block diagram which shows the structure of an example of the lithium secondary battery of this invention.
１　負極活物質層
２　負極集電体
３　負極
４　正極活物質層
５　正極集電体
６　正極
７　セパレーター
８　外装体
１１　リチウム二次電池 DESCRIPTION OF SYMBOLS 1 Negative electrode active material layer 2 Negative electrode collector 3 Negative electrode 4 Positive electrode active material layer 5 Positive electrode collector 6 Positive electrode 7 Separator 8 Exterior body 11 Lithium secondary battery
　本発明のリチウム二次電池は、正極及び負極と、これらを浸漬する電解液とを有する。　　　 The lithium secondary battery of the present invention has a positive electrode and a negative electrode, and an electrolytic solution for immersing them. *
　［負極］
　負極は、充放電に伴いリチウムイオンを可逆的に吸蔵、放出可能なケイ素系負極活物質を含み、負極活物質が負極結着剤により一体化された負極活物質層として集電体上に積層された構造を有する。 [Negative electrode]
The negative electrode includes a silicon-based negative electrode active material capable of reversibly occluding and releasing lithium ions during charge and discharge, and is laminated on the current collector as a negative electrode active material layer integrated with a negative electrode binder. Has a structured.
　負極活物質は、ケイ素系負極活物質を含むものであればいずれであってもよく、ケイ素系負極活物質としては、ケイ素や、酸化ケイ素（ＳｉＯｘ：０＜ｘ≦２）を挙げることができる。これらの何れか一方を含むものであればよいが、これらの双方を含むことが好ましい。これらは、負極活物質としてリチウムイオンの充放電の電位が異なり、具体的には、ケイ素は酸化ケイ素よりリチウムイオンの充放電の電位が低く、これらを含有する負極活物質層において、放電時の電圧の変化に伴い徐々にリチウムイオンを放出することができ、特定の電位で一時にリチウムイオンが放出されることによる負極活物質層の急激な体積収縮を抑制することができる。酸化ケイ素は電解液との反応が生じにくく、安定して存在することができる。具体的には、ＳｉＯ、ＳｉＯ2等を挙げることができる。 The negative electrode active material may be any material as long as it contains a silicon-based negative electrode active material. Examples of the silicon-based negative electrode active material include silicon and silicon oxide (SiOx: 0 <x ≦ 2). . Any one of these may be used, but it is preferable to include both of them. These have different lithium ion charge / discharge potentials as a negative electrode active material. Specifically, silicon has a lower lithium ion charge / discharge potential than silicon oxide. Lithium ions can be gradually released as the voltage changes, and rapid volume shrinkage of the negative electrode active material layer due to lithium ions being released at a specific potential at a time can be suppressed. Silicon oxide hardly reacts with the electrolyte and can exist stably. Specific examples include SiO and SiO 2 .
　負極活物質中、ケイ素の含有量は、１００質量％でもよく、負極活物質に酸化ケイ素が含まれる場合は、０質量％でもよいが、５質量％以上、９５質量％以下であることが好ましく、より好ましくは、１０質量％以上、９０質量％以下であり、更に好ましくは、２０質量％以上、５０質量％以下である。また、負極活物質中の酸化ケイ素の含有量は、１００質量％でもよく、負極活物質にケイ素が含まれる場合は、０質量％でもよいが、５質量％以上、９０質量％以下であることが好ましく、より好ましくは、４０質量％以上、８０質量％以下であり、更に好ましくは、５０質量％以上、７０質量％以下である。 The content of silicon in the negative electrode active material may be 100% by mass, and may be 0% by mass when silicon oxide is contained in the negative electrode active material, but is preferably 5% by mass or more and 95% by mass or less. More preferably, they are 10 mass% or more and 90 mass% or less, More preferably, they are 20 mass% or more and 50 mass% or less. In addition, the content of silicon oxide in the negative electrode active material may be 100% by mass, and may be 0% by mass when silicon is contained in the negative electrode active material, but may be 5% by mass or more and 90% by mass or less. More preferably, it is 40 mass% or more and 80 mass% or less, More preferably, it is 50 mass% or more and 70 mass% or less.
　また、負極活物質として、ケイ素以外の金属や、金属酸化物を含んでいてもよい。ケイ素以外の金属としては、リチウムと合金を形成することができる金属であって、放電時にリチウム合金からリチウムイオンを放出し、充電時にリチウム合金を形成することができる金属を挙げることができる。具体的には、アルミニウム、鉛、スズ、インジウム、ビスマス、銀、バリウム、カルシウム、水銀、パラジウム、白金、テルル、亜鉛、ランタンを挙げることができる。これらは１種又は２種以上を選択することができる。これらのうち、スズが好ましい。 Further, the negative electrode active material may contain a metal other than silicon or a metal oxide. Examples of the metal other than silicon include metals capable of forming an alloy with lithium, and capable of releasing lithium ions from the lithium alloy during discharging and forming the lithium alloy during charging. Specific examples include aluminum, lead, tin, indium, bismuth, silver, barium, calcium, mercury, palladium, platinum, tellurium, zinc, and lanthanum. These can select 1 type (s) or 2 or more types. Of these, tin is preferred.
　負極活物質としての金属酸化物は、具体的には、酸化アルミニウム、酸化スズ、酸化インジウム、酸化亜鉛、酸化リチウムを挙げることができ、これらは１種又は２種以上を組み合わせて用いることができる。これらの金属酸化物は、上記金属と共に用いられることが好ましく、特に、金属酸化物に含まれる金属と同じ金属と共に、用いられることが、充放電時に異なる電位でリチウムイオンの吸蔵放出が行われ、負極活物質層の急激な体積変化を抑制できることから、好ましく、上記スズと共に酸化スズを用いることが好ましい。 Specific examples of the metal oxide as the negative electrode active material include aluminum oxide, tin oxide, indium oxide, zinc oxide, and lithium oxide, and these can be used alone or in combination of two or more. . These metal oxides are preferably used together with the above metals, and in particular, when used together with the same metal as the metal contained in the metal oxide, occlusion / release of lithium ions is performed at different potentials during charging and discharging, It is preferable to use a tin oxide together with the tin because a rapid volume change of the negative electrode active material layer can be suppressed.
　これらの酸化ケイ素や、金属酸化物は、その少なくとも一部が非晶質であることが好ましい。酸化ケイ素や金属酸化物が非晶質であることにより、負極活物質層の微粉化を抑制すると共に、電解液との反応を抑制することができる。非晶質酸化ケイ素や金属酸化物を有する負極活物質層においては、結晶構造に含まれる欠陥や結晶粒界等の不均一性に起因する要素が減少し、不均一な体積変化が抑制されると考えられる。 These silicon oxides and metal oxides are preferably at least partially amorphous. When the silicon oxide or the metal oxide is amorphous, it is possible to suppress pulverization of the negative electrode active material layer and to suppress reaction with the electrolytic solution. In the negative electrode active material layer having amorphous silicon oxide or metal oxide, elements due to non-uniformity such as defects and crystal grain boundaries included in the crystal structure are reduced, and non-uniform volume change is suppressed. it is conceivable that.
　酸化ケイ素や金属酸化物が非晶質であることは、Ｘ線回折測定により、結晶構造を有する場合に観察される結晶構造固有のピークがブロードとなることから、確認することができる。 It can be confirmed from the X-ray diffraction measurement that the silicon oxide and the metal oxide are amorphous, since the peak specific to the crystal structure observed when having a crystal structure is broad.
　また、負極活物質として、炭素材料を含むことが好ましい。炭素材料としては、黒鉛、非晶質炭素、ダイヤモンド状炭素、カーボンナノチューブ等を挙げることができる。結晶性の高い黒鉛は電気伝導性が高く、負極活物質層の集電性の向上を図ることができ、結晶性の低い非晶質炭素は、充放電に伴う負極活物質層の劣化を抑制することができる。負極活物質中の炭素材料の含有量は、２質量％以上、５０質量％以下であることが好ましく、より好ましくは、２質量％以上、３０質量％以下である。 Further, it is preferable that a carbon material is included as the negative electrode active material. Examples of the carbon material include graphite, amorphous carbon, diamond-like carbon, and carbon nanotube. Graphite with high crystallinity has high electrical conductivity and can improve the current collecting performance of the negative electrode active material layer. Amorphous carbon with low crystallinity suppresses deterioration of the negative electrode active material layer due to charge / discharge. can do. The content of the carbon material in the negative electrode active material is preferably 2% by mass or more and 50% by mass or less, and more preferably 2% by mass or more and 30% by mass or less.
　上記ケイ素や酸化ケイ素、金属、金属酸化物、炭素材料は粒子状であることが、負極活物質の充放電に伴う劣化を抑制できるため、好ましい。粒子状の負極活物質としては、充放電に伴う体積変化の大きいもの程、小径とすることが、これらの粒子の体積変化による負極活物質層の体積変化を抑制することができるため、好ましい。具体的には、酸化ケイ素の平均粒子径は炭素材料の平均粒子径より小さく、例えば、酸化ケイ素の平均粒子径が炭素材料の平均粒子径の１／２以下であることが好ましい。ケイ素の平均粒子径は、酸化ケイ素の平均粒子径より小さく、例えば、ケイ素の平均粒子径が酸化ケイ素の平均粒子径の１／２以下であることが好ましい。平均粒子径をこのような範囲に制御すれば、充放電による体積変化が大きい粒子が小径となり、負極活物質層の体積変化の緩和効果が大きく、エネルギー密度、サイクル寿命と効率のバランスに優れた二次電池を得ることができる。ケイ素の平均粒子径としては、具体的には、例えば２０μｍ以下であることが、集電体との接触を担保し得ることから好ましく、より好ましくは１５μｍ以下である。 It is preferable that the silicon, silicon oxide, metal, metal oxide, and carbon material are in a particulate form because deterioration due to charging / discharging of the negative electrode active material can be suppressed. As the particulate negative electrode active material, the larger the volume change associated with charging / discharging, the smaller the diameter is preferable because the volume change of the negative electrode active material layer due to the volume change of these particles can be suppressed. Specifically, the average particle diameter of silicon oxide is smaller than the average particle diameter of the carbon material. For example, the average particle diameter of silicon oxide is preferably ½ or less of the average particle diameter of the carbon material. The average particle diameter of silicon is smaller than the average particle diameter of silicon oxide. For example, the average particle diameter of silicon is preferably ½ or less of the average particle diameter of silicon oxide. By controlling the average particle size in such a range, particles with large volume change due to charge / discharge become small diameter, the effect of relaxing the volume change of the negative electrode active material layer is large, and the balance between energy density, cycle life and efficiency is excellent A secondary battery can be obtained. Specifically, the average particle diameter of silicon is preferably 20 μm or less, for example, because it can ensure contact with the current collector, and more preferably 15 μm or less.
　また、導電性の低下を抑制し充放電サイクルによる負極活物質の劣化を抑制する観点から、ケイ素のクラスターの周囲に非晶質酸化ケイ素が存在し、その表面を炭素が被覆した粒子状であってもよい。ケイ素系材料の粒子の表面を被覆する炭素被膜の厚さとしては、０．１～５μｍであることが充放電に伴う負極活物質の劣化を抑制すると共に導電性を高めることができることから、好ましい。炭素被膜の厚さの測定は、透過型電子顕微鏡（ＴＥＭ）観察により測定し、１００粒子についての測定値の平均値を採用することができる。 In addition, from the viewpoint of suppressing the decrease in conductivity and suppressing the deterioration of the negative electrode active material due to the charge / discharge cycle, amorphous silicon oxide exists around the silicon cluster, and its surface is in the form of particles coated with carbon. May be. The thickness of the carbon film covering the surface of the silicon-based material particles is preferably 0.1 to 5 μm because it is possible to suppress deterioration of the negative electrode active material due to charge and discharge and increase conductivity. . The thickness of the carbon coating can be measured by observation with a transmission electron microscope (TEM), and an average value of measured values for 100 particles can be adopted.
　上記非晶質の酸化ケイ素中にケイ素や金属が分散した炭素被膜を有する負極活物質の製造方法としては、特開２００４－４７４０４記載の方法を挙げることができる。具体的には、メタンガス等の有機物ガス雰囲気中で酸化ケイ素や金属酸化物をＣＶＤ処理することにより、ケイ素や金属のナノクラスターの周囲に非晶質の酸化ケイ素や金属酸化物を形成し、その周囲に炭素被膜を形成することができる。また、酸化ケイ素や金属酸化物と、ケイ素や金属と、炭素材料とをメカニカルミリングで混合する方法を挙げることができる。このような炭素被膜を有する負極活物質の平均粒子径としては、１～２０μｍ程度を挙げることができる。 As a method for producing a negative electrode active material having a carbon film in which silicon or metal is dispersed in the amorphous silicon oxide, a method described in JP-A-2004-47404 can be exemplified. Specifically, silicon oxide or metal oxide is formed around silicon or metal nanoclusters by CVD treatment of silicon oxide or metal oxide in an organic gas atmosphere such as methane gas. A carbon coating can be formed around. Moreover, the method of mixing a silicon oxide, a metal oxide, silicon, a metal, and a carbon material by mechanical milling can be mentioned. The average particle diameter of the negative electrode active material having such a carbon film can be about 1 to 20 μm.
　上記負極活物質を結着する負極結着剤としては、例えば、ポリフッ化ビニリデン（ＰＶｄＦ）、ビニリデンフルオライド－ヘキサフルオロプロピレン共重合体、ビニリデンフルオライド－テトラフルオロエチレン共重合体、スチレン－ブタジエン共重合ゴム、ポリテトラフルオロエチレン、ポリプロピレン、ポリエチレン、ポリイミド、ポリアミドイミド等を挙げることができる。これらは1種を単独で又は２種以上を組み合わせて使用することができる。これらの中、結着力の観点から、ポリイミド、ポリアミドイミドを含むことが好ましい。使用する負極用結着剤の量は、トレードオフの関係にある「十分な結着力」と「高エネルギー化」の観点から、負極活物質１００質量部に対して、５～２５質量部であることが好ましい。 Examples of the negative electrode binder that binds the negative electrode active material include polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and styrene-butadiene copolymer. Examples thereof include polymer rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide and the like. These can be used alone or in combination of two or more. Among these, it is preferable that polyimide and polyamideimide are included from the viewpoint of binding force. The amount of the binder for the negative electrode to be used is 5 to 25 parts by mass with respect to 100 parts by mass of the negative electrode active material from the viewpoints of “sufficient binding force” and “high energy” which are in a trade-off relationship. It is preferable.
　負極活物質が負極結着剤により一体とされた負極活物質層を支持する集電体は、外部端子との導通を可能とする導電性を有するものであればよく、電気化学的安定性から、アルミニウム、ニッケル、銅、銀、又は、これらの合金が好ましい。その形状としては、箔、平板状、メッシュ状が挙げられる。集電体の厚さとしては５～３０μｍ程度を挙げることができる。 The current collector that supports the negative electrode active material layer in which the negative electrode active material is integrated with the negative electrode binder may be any material that has electrical conductivity that enables electrical connection to the external terminal. Aluminum, nickel, copper, silver, or an alloy thereof is preferable. Examples of the shape include foil, flat plate, and mesh. The thickness of the current collector can be about 5 to 30 μm.
　上記負極は、集電体上に、負極活物質と負極結着剤とを含む負極活物質層用材料を用いて作製することができる。負極活物質層の作製方法としては、ドクターブレード法、ダイコーター法等の塗工法、ＣＶＤ法、スパッタリング法等を挙げることができる。予め負極活物質層を形成した後に、蒸着、スパッタ等の方法でアルミニウム、ニッケルまたはそれらの合金の薄膜を形成して、負極集電体としてもよい。負極活物質層の厚さとしては１０～２００μｍ程度を挙げることができる。 The negative electrode can be manufactured using a negative electrode active material layer material including a negative electrode active material and a negative electrode binder on a current collector. Examples of a method for producing the negative electrode active material layer include a coating method such as a doctor blade method and a die coater method, a CVD method, and a sputtering method. After forming a negative electrode active material layer in advance, a thin film of aluminum, nickel, or an alloy thereof may be formed by a method such as vapor deposition or sputtering to form a negative electrode current collector. The thickness of the negative electrode active material layer can be about 10 to 200 μm.
　［正極］
　正極は、充放電に伴いリチウムイオンを可逆的に吸蔵、放出可能な正極活物質を含み、正極活物質が正極結着剤により一体化された正極活物質層として集電体上に積層された構造を有する。 [Positive electrode]
The positive electrode includes a positive electrode active material capable of reversibly occluding and releasing lithium ions during charge and discharge, and the positive electrode active material is laminated on the current collector as a positive electrode active material layer integrated with a positive electrode binder. It has a structure.
　正極活物質は、充電時にリチウムイオンを電解液中へ放出し、放電時に電解液中からリチウムを吸蔵するものであり、ＬｉＭｎＯ2、ＬｉxＭｎ2Ｏ4（０＜ｘ＜２）等の層状構造を持つマンガン酸リチウム、又はスピネル構造を有するマンガン酸リチウム；ＬｉＣｏＯ2、ＬｉＮｉＯ2、又はこれらの遷移金属の一部を他の金属で置き換えたもの；ＬｉＮｉ1/3Ｃｏ1/3Ｍｎ1/3Ｏ2等の特定の遷移金属が半数を超えないリチウム遷移金属酸化物；これらのリチウム遷移金属酸化物において化学量論組成よりもＬｉを過剰にしたもの等が挙げられる。特に、ＬｉαＮｉβＣｏγＡｌδＯ2（１≦α≦１．２、β＋γ＋δ＝１、β≧０．７、γ≦０．２）又はＬｉαＮｉβＣｏγＭｎδＯ2（１≦α≦１．２、β＋γ＋δ＝１、β≧０．６、γ≦０．２）が好ましい。正極活物質は、１種を単独で、又は２種以上を組み合わせて使用することができる。 The positive electrode active material releases lithium ions into the electrolytic solution during charging and occludes lithium from the electrolytic solution during discharging, and is layered such as LiMnO 2 and Li x Mn 2 O 4 (0 <x <2). Lithium manganate having a structure, or lithium manganate having a spinel structure; LiCoO 2 , LiNiO 2 , or a part of these transition metals replaced with another metal; LiNi 1/3 Co 1/3 Mn 1 / Examples thereof include lithium transition metal oxides in which a specific transition metal such as 3 O 2 does not exceed half; those lithium transition metal oxides in which Li is more excessive than the stoichiometric composition. In particular, LiαNiβCoγAlδO 2 (1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.7, γ ≦ 0.2) or LiαNiβCoγMnδO 2 (1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.6). Γ ≦ 0.2) is preferable. A positive electrode active material can be used individually by 1 type or in combination of 2 or more types.
　上記正極活物質を結着して一体化する正極結着剤としては、具体的には、上記負極結着剤と同様のものを用いることができる。正極結着剤としては、汎用性、低コストの観点から、ポリフッ化ビニリデンが好ましい。使用する正極結着剤の量は、正極活物質１００質量部に対して、２～１０質量部であることが好ましい。正極結着剤の含有量が２質量部以上であれば、活物質同士あるいは活物質と集電体との密着性が向上し、サイクル特性が良好になり、１０質量部以下であれば、活物質比率が向上し、正極容量を向上させることができる。 As the positive electrode binder that binds and integrates the positive electrode active material, specifically, the same negative electrode binder as that described above can be used. As the positive electrode binder, polyvinylidene fluoride is preferable from the viewpoint of versatility and low cost. The amount of the positive electrode binder used is preferably 2 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. When the content of the positive electrode binder is 2 parts by mass or more, the adhesion between the active materials or between the active material and the current collector is improved, and the cycle characteristics are improved. The substance ratio is improved and the positive electrode capacity can be improved.
　上記正極活物質層には、正極活物質のインピーダンスを低下させる目的で、導電補助材を添加してもよい。導電補助材としては、グラファイト、カーボンブラック、アセチレンブラック等の炭素質微粒子を用いることができる。 In the positive electrode active material layer, a conductive auxiliary material may be added for the purpose of reducing the impedance of the positive electrode active material. As the conductive auxiliary material, carbonaceous fine particles such as graphite, carbon black, and acetylene black can be used.
　正極活物質が正極結着剤により一体とされた正極活物質層を支持する集電体は、外部端子との導通を可能とする導電性を有するものであればよく、具体的には、上記負極に用いる集電体と同様のものを用いることができる。 The current collector that supports the positive electrode active material layer in which the positive electrode active material is integrated with the positive electrode binder may be any material that can conduct electricity with the external terminal. The same collector as that used for the negative electrode can be used.
　上記正極は、集電体上に、正極活物質と正極結着剤とを含む正極活物質層用材料を用いて作製することができる。正極活物質層の作製方法には、負極活物質層の作製方法と同様の方法を適用することができる。 The positive electrode can be produced on a current collector using a positive electrode active material layer material including a positive electrode active material and a positive electrode binder. As a method for manufacturing the positive electrode active material layer, a method similar to the method for manufacturing the negative electrode active material layer can be used.
　［電解液］
　電解液は、充放電時に正極負極においてリチウムの吸蔵放出を可能とするため、正極と負極を漬浸してリチウムイオンを溶解可能なものであり、非水系の有機溶媒に電解質を溶解したものである。 [Electrolyte]
The electrolyte solution can absorb and release lithium in the positive electrode and the negative electrode during charge and discharge, so that the lithium ion can be dissolved by immersing the positive electrode and the negative electrode, and the electrolyte is dissolved in a non-aqueous organic solvent. .
　上記電解液の溶媒は、電池の動作電位において安定であり、電池の使用環境において、電極を漬浸できるように低粘度であることが好ましい。具体的には、プロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ブチレンカーボネート（ＢＣ）、ビニレンカーボネート（ＶＣ）等の環状炭酸エステル類；ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）、ジプロピルカーボネート（ＤＰＣ）等の鎖状炭酸エステル；プロピレンカーボネート誘導体；ギ酸メチル、酢酸メチル、プロピオン酸エチル等の脂肪族カルボン酸エステル；などの非プロトン性有機溶媒を挙げることができる。これらは１種を単独で、又は２種以上を組み合わせて使用することができる。これらの中、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ビニレンカーボネート（ＶＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＭＥＣ）、ジプロピルカーボネート（ＤＰＣ）等の環状又は鎖状炭酸エステルが好ましい。 It is preferable that the solvent of the electrolytic solution is stable at the operating potential of the battery and has a low viscosity so that the electrode can be immersed in the usage environment of the battery. Specifically, cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC); dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate And aprotic organic solvents such as chain carbonate esters such as (EMC) and dipropyl carbonate (DPC); propylene carbonate derivatives; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, and ethyl propionate; . These can be used alone or in combination of two or more. Among these, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), dipropyl carbonate A cyclic or chain carbonate such as (DPC) is preferred.
　電解液に含まれる電解質としては、リチウム塩が好ましい。リチウム塩としては、具体的に、ＬｉＰＦ6、ＬｉＡｓＦ6、ＬｉＡｌＣｌ4、ＬｉＣｌＯ4、ＬｉＢＦ4、ＬｉＳｂＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＣ4Ｆ9ＳＯ3、Ｌｉ（ＣＦ3ＳＯ2）3、ＬｉＮ（ＣＦ3ＳＯ2）2等を挙げることができる。 As an electrolyte contained in the electrolytic solution, a lithium salt is preferable. Specific examples of the lithium salt include LiPF 6 , LiAsF 6 , LiAlCl 4 , LiClO 4 , LiBF 4 , LiSbF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , Li (CF 3 SO 2 ) 3 , LiN ( CF 3 SO 2 ) 2 and the like.
　電解液中の電解質の濃度としては、０．０１ｍｏｌ／Ｌ以上、３ｍｏｌ／Ｌ以下であることが好ましく、より好ましくは、０．５ｍｏｌ／Ｌ以上、１．５ｍｏｌ／Ｌ以下である。電解質濃度がこの範囲であると、安全性の向上を図ることができ、信頼性が高く、環境負荷の軽減に寄与する電池を得ることができる。 The concentration of the electrolyte in the electrolytic solution is preferably 0.01 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 1.5 mol / L or less. When the electrolyte concentration is within this range, safety can be improved, and a battery having high reliability and contributing to reduction of environmental load can be obtained.
　上記電解液は、式（１）で表される不飽和リン酸エステルを含む。 The above electrolytic solution contains an unsaturated phosphate ester represented by the formula (1).
Figure JPOXMLDOC01-appb-C000007
Figure JPOXMLDOC01-appb-C000007
式（１）で表される不飽和リン酸エステルは、電池の充放電に伴い負極活物質表面で不飽和三重結合がラジカルとなって、重合反応が進行して生成される重合体が、負極活物質を被覆し、重合体からなる均一な厚さの被膜を形成すると考えられる。この重合体被膜は、リチウムイオンを透過させ、電解液の透過を阻害し、結果として負極活物質と電解液との反応を抑制し、反復される充放電による電池の容量の低下を抑制することができると考えられる。 The unsaturated phosphoric acid ester represented by the formula (1) is a polymer produced by the progress of a polymerization reaction in which an unsaturated triple bond becomes a radical on the surface of the negative electrode active material as the battery is charged and discharged. It is considered that the active material is coated to form a uniform film made of a polymer. This polymer coating permeates lithium ions and inhibits the permeation of the electrolytic solution, and consequently suppresses the reaction between the negative electrode active material and the electrolytic solution, and suppresses the decrease in battery capacity due to repeated charge and discharge. It is thought that you can.
　式（１）中、Ｒ1～Ｒ3は、独立して直接結合、又は炭素数１～５のアルキレン基を示す。式（１）で表される不飽和リン酸エステルが、式中、Ｒ1～Ｒ3がメチレン基を示す、式（２）で表される化合物であることが、負極活物質に均一な膜を形成する上で好ましい。 In formula (1), R 1 to R 3 independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms. The unsaturated phosphoric acid ester represented by the formula (1) is a compound represented by the formula (2) in which R 1 to R 3 represent methylene groups. Is preferable in forming.
Figure JPOXMLDOC01-appb-C000008
Figure JPOXMLDOC01-appb-C000008
　式（１）で表される不飽和リン酸エステルの電解液中の含有量は、負極活物質上に適切な厚さの被膜が形成される含有量を適宜選択することが好ましい。電解液中に含まれる式（１）で表される不飽和リン酸エステルは、電池の初期の充放電及びそれに続く比較的早期の充放電において重合、あるいは、分解する。このため、電解液中に含まれる式（１）で表される不飽和リン酸エステル量が過多であると、充放電サイクルの早い段階において、式（１）で表される不飽和リン酸エステルが分解され、分解生成物が電極に付着するなどして、その後の充放電サイクルにおけるリチウムイオンの吸蔵放出が阻害され、却って電池の放電容量を減少させ、あるいは、レート特性を悪化させてしまう。電解液中の式（１）で表される不飽和リン酸エステルの濃度は、例えば０．００５～１０質量％程度であればよく、好ましくは、０．０１～５．０質量％、より好ましくは、０．５～３．０質量％程度である。 It is preferable that the content of the unsaturated phosphate ester represented by the formula (1) in the electrolyte is appropriately selected so that a film having an appropriate thickness is formed on the negative electrode active material. The unsaturated phosphate ester represented by the formula (1) contained in the electrolytic solution is polymerized or decomposed during the initial charge / discharge of the battery and the subsequent relatively early charge / discharge. For this reason, when the amount of the unsaturated phosphate ester represented by the formula (1) contained in the electrolytic solution is excessive, the unsaturated phosphate ester represented by the formula (1) at an early stage of the charge / discharge cycle. Is decomposed, and decomposition products adhere to the electrode, so that occlusion / release of lithium ions in the subsequent charge / discharge cycle is hindered. On the contrary, the discharge capacity of the battery is reduced, or the rate characteristics are deteriorated. The concentration of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution may be, for example, about 0.005 to 10% by mass, preferably 0.01 to 5.0% by mass, and more preferably Is about 0.5 to 3.0% by mass.
　また、電解液中の式（１）で表される不飽和リン酸エステルの含有量の上限は、充電終了時の電極間のインピーダンス（電荷移動抵抗）によって規定することもできる。具体的には、電解液中の式（１）で表される不飽和リン酸エステルの含有量は、式（１）で表される不飽和リン酸エステルを添加した場合の上記充電終了時の電極間のインピーダンスが、未添加の場合の概ね１０倍未満となる量であることが、レート特性あるいは充放電特性を低下させないことから好ましい。 Further, the upper limit of the content of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution can be defined by the impedance (charge transfer resistance) between the electrodes at the end of charging. Specifically, the content of the unsaturated phosphate ester represented by the formula (1) in the electrolytic solution is the same as that at the end of charging when the unsaturated phosphate ester represented by the formula (1) is added. It is preferable that the impedance between the electrodes is less than about 10 times that in the case of no addition because the rate characteristic or charge / discharge characteristic is not deteriorated.
　［セパレーター］
　セパレーターは、正極及び負極の導通を抑制し、荷電体の透過を阻害せず、電解液に対して耐久性を有するものであれば、いずれであってもよい。具体的な材質としては、ポリプロピレン、ポリエチレン等のポリオレフィン系微多孔膜、セルロース、ポリエチレンテレフタレート、ポリイミド、ポリフッ化ビニリデン等を採用することができる。これらは、多孔質フィルム、織物、不織布等として用いることができる。 [separator]
Any separator may be used as long as it suppresses the conduction between the positive electrode and the negative electrode, does not inhibit the permeation of the charged body, and has durability against the electrolytic solution. Specific examples of the material that can be used include polyolefin microporous membranes such as polypropylene and polyethylene, cellulose, polyethylene terephthalate, polyimide, and polyvinylidene fluoride. These can be used as porous films, woven fabrics, non-woven fabrics and the like.
　［セル外装体］
　外装体としては、上記正極及び負極、セパレーター、電解液を安定して保持可能な強度を有し、これらの物質に対して電気化学的に安定で、水密性を有するものが好ましい。具体的には、例えば、ステンレス、ニッケルメッキを施した鉄、アルミニウム、シリカ、アルミナをコーティングしたラミネートフィルムを用いることができ、ラミネートフィルムに用いる樹脂としては、ポリエチレン、ポリプロピレン、ポリエチレンテレフタレート等を用いることができる。これらは、１層又は２層以上の構造体であってもよい。 [Cell exterior body]
As the outer package, those having a strength capable of stably holding the positive electrode, the negative electrode, the separator, and the electrolytic solution, electrochemically stable with respect to these substances, and watertight are preferable. Specifically, for example, a laminate film coated with stainless steel, nickel-plated iron, aluminum, silica, and alumina can be used. As a resin used for the laminate film, polyethylene, polypropylene, polyethylene terephthalate, or the like is used. Can do. These may be a structure of one layer or two or more layers.
　［二次電池］
　上記二次電池の形状は、円筒型、扁平捲回角型、積層角型、コイン型、扁平捲回ラミネート型、及び積層ラミネート型のいずれでもよい。 [Secondary battery]
The shape of the secondary battery may be any of a cylindrical type, a flat wound square type, a laminated square type, a coin type, a flat wound laminated type, and a laminated laminate type.
　上記二次電池の一例として、図１に示す積層ラミネート型二次電池１１を挙げることができる。この積層ラミネート型二次電池は、銅箔等の金属からなる負極集電体２上に設けられた負極活物質層１を有する負極３と、アルミニウム箔等の金属からなる正極集電体５上に設けられた正極活物質層４を有する正極６とが、これらの接触を回避するポリプロピレン微多孔質膜からなるセパレーター７を介して対向配置され、これらがラミネート外装体８内に収納されている。ラミネート外装体内部には電解液が充填され、負極活物質層１と、正極活物質層４は電解液に浸漬され、それぞれ、活物質層が形成されていない集電体の部分で電気的に接続され、負極端子９、正極端子１０がラミネート外装体の外部へ引き出され、充放電時に、外部電源や、使用機器に接続されるようになっている。 As an example of the secondary battery, a laminated laminate type secondary battery 11 shown in FIG. 1 can be given. The laminated laminate type secondary battery includes a negative electrode 3 having a negative electrode active material layer 1 provided on a negative electrode current collector 2 made of metal such as copper foil, and a positive electrode current collector 5 made of metal such as aluminum foil. The positive electrode 6 having the positive electrode active material layer 4 provided on the substrate is disposed so as to face each other through a separator 7 made of a polypropylene microporous film that avoids these contacts, and these are accommodated in a laminate outer package 8. . The laminate outer package is filled with an electrolytic solution, and the negative electrode active material layer 1 and the positive electrode active material layer 4 are immersed in the electrolytic solution, and each is electrically connected to the current collector portion where no active material layer is formed. Connected, the negative electrode terminal 9 and the positive electrode terminal 10 are pulled out to the outside of the laminate outer package, and are connected to an external power source or equipment used during charging and discharging.
　以下に、本発明のリチウム二次電池を詳細に説明する。
［実施例１］
［リチウム二次電池の作製］
　負極活物質として、ケイ素が非晶質酸化ケイ素（ＳｉＯｘ、０＜ｘ≦２）中に分散したケイ素系粒子表面に炭素被覆が形成されたケイ素系負極活物質を得た。ケイ素系負極活物質の、ケイ素、非晶質酸化ケイ素、炭素の質量比は２９：６１：１０であった。この負極活物質と、負極用結着剤としてのポリイミドの前駆体であるポリアミック酸とを、９０：１０の質量比で計量し、それらをｎ－メチルピロリドンと混合して、負極スラリーとした。負極スラリーを厚さ１０μｍの銅箔に塗布した後に乾燥し、さらに窒素雰囲気３００℃の熱処理を行い、負極を作製した。 Hereinafter, the lithium secondary battery of the present invention will be described in detail.
[Example 1]
[Production of lithium secondary battery]
As the negative electrode active material, a silicon-based negative electrode active material in which a carbon coating was formed on the surface of silicon-based particles in which silicon was dispersed in amorphous silicon oxide (SiOx, 0 <x ≦ 2) was obtained. The mass ratio of silicon, amorphous silicon oxide, and carbon in the silicon-based negative electrode active material was 29:61:10. This negative electrode active material and polyamic acid, which is a precursor of polyimide as a negative electrode binder, were weighed at a mass ratio of 90:10 and mixed with n-methylpyrrolidone to obtain a negative electrode slurry. The negative electrode slurry was applied to a copper foil having a thickness of 10 μm, dried, and then subjected to a heat treatment in a nitrogen atmosphere at 300 ° C. to produce a negative electrode.
　正極活物質としてのニッケル酸リチウム（ＬｉＮｉ０．８０Ｃｏ０．１５Ａｌ０．０５Ｏ２）と、導電補助材としてのカーボンブラックと、正極用結着剤としてのポリフッ化ビニリデンとを、９０：５：５の質量比で計量し、それらをｎ－メチルピロリドンと混合して、正極スラリーとした。正極スラリーを厚さ２０μｍのアルミ箔に塗布した後に乾燥し、さらにプレスして、正極を作製した。 Lithium nickelate (LiNi0.80Co0.15Al0.05O2) as a positive electrode active material, carbon black as a conductive auxiliary, and polyvinylidene fluoride as a positive electrode binder in a mass ratio of 90: 5: 5 They were weighed and mixed with n-methylpyrrolidone to form a positive electrode slurry. The positive electrode slurry was applied to an aluminum foil having a thickness of 20 μm, dried, and then pressed to prepare a positive electrode.
　得られた正極の３層と負極の４層を、セパレーターとしてポリプロピレン多孔質フィルムを挟みつつ交互に重ねた。正極活物質に覆われていない正極集電体の端部同士を溶接し、さらにその溶接箇所にアルミニウム製の正極端子を溶接し、一方、負極活物質に覆われていない負極集電体の端部同士を溶接し、さらにその溶接箇所にニッケル製の負極端子を溶接して、平面的な積層構造を有する電極素子を得た。 3 layers of the positive electrode and 4 layers of the negative electrode obtained were alternately stacked while sandwiching a polypropylene porous film as a separator. The ends of the positive electrode current collector not covered with the positive electrode active material are welded to each other, and the aluminum positive electrode terminal is welded to the welded portion, while the end of the negative electrode current collector not covered with the negative electrode active material The parts were welded together, and a negative electrode terminal made of nickel was welded to the welded portion to obtain an electrode element having a planar laminated structure.
　ＬｉＰＦ6を１モル／ｌの濃度で溶解したＥＣ／ＤＥＣ＝３０／７０（体積比）からなるカーボネート系非水電解液を９９質量部と、式（２）で表される化合物（１）を１質量部（電解液中の含有率：１質量％）とを混合し電解液を得た。 99 parts by mass of a carbonate-based non-aqueous electrolyte composed of EC / DEC = 30/70 (volume ratio) in which LiPF 6 was dissolved at a concentration of 1 mol / l, and a compound (1) represented by the formula (2) 1 part by mass (content ratio in electrolytic solution: 1% by mass) was mixed to obtain an electrolytic solution.
Figure JPOXMLDOC01-appb-C000009
Figure JPOXMLDOC01-appb-C000009
　得られた電極素子を外装体としてのアルミニウムラミネートフィルムで包み、内部に電解液を注液した後、０．１気圧まで減圧しつつ封止し、二次電池を作製した。 The obtained electrode element was wrapped with an aluminum laminate film as an outer package, and an electrolyte solution was injected therein, and then sealed while reducing the pressure to 0.1 atm to prepare a secondary battery.
　［充放電サイクル特性の評価］
　得られたリチウム二次電池についてサイクル特性を評価した。６０℃に保った恒温槽中で２．５Ｖから４．２Ｖの電圧範囲で充放電を繰り返した。充放電サイクル１００回後の放電容量（ＤＣ１００）を測定し、初回の放電容量（ＤＣ１）に対する１００回後の放電容量比（ＤＣ１００／ＤＣ１）を算出し、１００サイクル後の容量維持率を得た。同様に充放電サイクル２５０回後の放電容量（ＤＣ２５０）を測定し、初回の放電容量（ＤＣ１）に対する２５０回後の放電容量比（ＤＣ２５０／ＤＣ１）を算出し、２５０サイクル後のサイクル維持率を得た。結果を表１に示す。 [Evaluation of charge / discharge cycle characteristics]
The cycle characteristics of the obtained lithium secondary battery were evaluated. Charging / discharging was repeated in a voltage range of 2.5 V to 4.2 V in a thermostat kept at 60 ° C. The discharge capacity (DC100) after 100 charge / discharge cycles was measured, the discharge capacity ratio (DC100 / DC1) after 100 times to the initial discharge capacity (DC1) was calculated, and the capacity retention rate after 100 cycles was obtained. . Similarly, the discharge capacity (DC250) after 250 charge / discharge cycles is measured, the discharge capacity ratio (DC250 / DC1) after 250 times to the initial discharge capacity (DC1) is calculated, and the cycle maintenance rate after 250 cycles is calculated. Obtained. The results are shown in Table 1.
　［比較例１］
　式（２）で表される化合物（１）を用いなかったこと以外は、実施例１と同様にしてリチウム二次電池を作製し、充放電サイクル特性の評価を行った。結果を表１に示す。 [Comparative Example 1]
A lithium secondary battery was produced in the same manner as in Example 1 except that the compound (1) represented by the formula (2) was not used, and the charge / discharge cycle characteristics were evaluated. The results are shown in Table 1.
　［比較例２］
　式（２）で表される化合物に変えて、式（３）で表される化合物（２）を用いたこと以外は、実施例１と同様にして、リチウム二次電池を作製し、充放電サイクル特性の評価を行った。結果を表１に示す。 [Comparative Example 2]
A lithium secondary battery was produced and charged / discharged in the same manner as in Example 1 except that the compound (2) represented by the formula (3) was used instead of the compound represented by the formula (2). The cycle characteristics were evaluated. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-C000010
Figure JPOXMLDOC01-appb-C000010
　［比較例３］
　式（２）で表される化合物（１）に変えて、式（４）で表される化合物（３）を用いたこと以外は、実施例１と同様にして、リチウム二次電池を作製し、充放電サイクル特性の評価を行った。結果を表１に示す。 [Comparative Example 3]
A lithium secondary battery was fabricated in the same manner as in Example 1 except that the compound (3) represented by the formula (4) was used instead of the compound (1) represented by the formula (2). The charge / discharge cycle characteristics were evaluated. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-C000011
Figure JPOXMLDOC01-appb-C000011
Figure JPOXMLDOC01-appb-T000012
Figure JPOXMLDOC01-appb-T000012
　結果から、実施例のリチウム二次電池の６０℃における充放電容量維持率は、比較例のリチウム二次電池と比較して高く、式（１）で表される不飽和化合物を含有する電解液を用いた本発明のリチウム二次電池は充放電サイクル特性に優れたものであることが分かる。 From the results, the charge / discharge capacity retention rate at 60 ° C. of the lithium secondary battery of the example is higher than that of the lithium secondary battery of the comparative example, and the electrolytic solution containing the unsaturated compound represented by the formula (1) It can be seen that the lithium secondary battery of the present invention using this has excellent charge / discharge cycle characteristics.
　本願は、２０１３年７月３１日出願の特願２０１３－１５９３９７に記載した総ての事項を、その内容として含むものである。 This application includes all matters described in Japanese Patent Application No. 2013-15997 filed on July 31, 2013 as its contents.
　本発明のリチウム二次電池は、電源を必要とするあらゆる産業分野、並びに電気的エネルギーの輸送、貯蔵および供給に関する産業分野にて利用することができる。具体的には、携帯電話、ノートパソコン等のモバイル機器の電源、車両のモーター駆動用電源等に利用することができる。 The lithium secondary battery of the present invention can be used in all industrial fields that require a power source and industrial fields related to the transport, storage, and supply of electrical energy. Specifically, it can be used as a power source for mobile devices such as mobile phones and notebook computers, and a power source for driving motors of vehicles.

Claims (4)

  1. 　充放電に伴いリチウムを吸蔵放出する正極及び負極を浸漬する電解液を有し、負極がケイ素系負極活物質を含むリチウム二次電池であって、
    電解液が、式（１）
    Figure JPOXMLDOC01-appb-C000001
     （式中、Ｒ1～Ｒ3は、独立して直接結合、又は炭素数１～５のアルキレン基を示す。）で表される不飽和リン酸エステルを含むことを特徴とするリチウム二次電池。     A lithium secondary battery having a positive electrode that occludes and releases lithium with charge and discharge, and an electrolyte that immerses the negative electrode, the negative electrode including a silicon-based negative electrode active material,
    The electrolyte is the formula (1)
    Figure JPOXMLDOC01-appb-C000001
     (Wherein R 1 to R 3 independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms), and a lithium secondary battery comprising an unsaturated phosphate ester .
  2. 　式（１）で表される不飽和リン酸エステルが、式（２）
    Figure JPOXMLDOC01-appb-C000002
     で表される請求項1に記載のリチウム二次電池。     The unsaturated phosphate ester represented by formula (1) is represented by formula (2)
    Figure JPOXMLDOC01-appb-C000002
     2. The lithium secondary battery according to claim 1, represented by:
  3. 　充放電に伴いリチウムを吸蔵放出する正極及び負極を浸漬するリチウム二次電池用電解液であって、式（１）
    Figure JPOXMLDOC01-appb-C000003
     （式中、Ｒ1～Ｒ3は、独立して直接結合、又は炭素数１～５のアルキレン基を示す。）で表される不飽和リン酸エステルを含むことを特徴とするリチウム二次電池用電解液。     An electrolyte for a lithium secondary battery that immerses a positive electrode and a negative electrode that occlude and release lithium in accordance with charge and discharge, wherein the formula (1)
    Figure JPOXMLDOC01-appb-C000003
     (Wherein R 1 to R 3 independently represent a direct bond or an alkylene group having 1 to 5 carbon atoms), and a lithium secondary battery comprising an unsaturated phosphate ester Electrolyte.
  4. 　式（１）で表される不飽和リン酸エステルが、式（２）
    Figure JPOXMLDOC01-appb-C000004
     で表される請求項３に記載のリチウム二次電池用電解液。     The unsaturated phosphate ester represented by formula (1) is represented by formula (2)
    Figure JPOXMLDOC01-appb-C000004
     The electrolyte solution for lithium secondary batteries of Claim 3 represented by these.
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