KR20150070971A - Lithium ion secondary battery - Google Patents

Abstract

The present invention provides a lithium ion secondary battery having excellent non-aqueous electrolyte injection properties and excellent charging-discharging cycle properties. The lithium ion secondary battery includes: a flat wound electrode body comprising a positive electrode, a negative electrode, and a separator; and non-aqueous electrolyte in an external body. The negative electrode is a negative electrode active material and includes at least graphite A, which has an average diameter of greater than 15 μm and 25 μm or smaller, and graphite B, which has an average diameter of 8-15 μm and has the particle surface covered by amorphous carbon.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a lithium ion secondary battery,

The present invention relates to a lithium ion secondary battery having excellent injectability of a non-aqueous electrolyte and excellent charge-discharge cycle characteristics at a high temperature.

The lithium ion secondary battery, which is a type of electrochemical device, is considered to be applied to a portable electronic device, an automobile, a power tool, a power storage device, a home electric power storage system, and a business electric power storage system because of its high energy density. Particularly, portable devices are widely used as power sources for mobile phones, smart phones, tablet PCs, and the like. In these lithium ion secondary batteries for portable devices, flat-shaped batteries are widely adopted in accordance with the shape of the apparatus and the like.

The characteristics required for a battery are various, and a variety of measures are required for each application. For example, a lithium ion secondary battery of a flat rectangular shape used in the above-described portable equipment is required to have a high capacity for a long time to use the battery. Therefore, the size of the battery necessarily increases.

The prismatic lithium ion secondary battery has a limitation in the size and number of the injection ports into which the nonaqueous electrolyte solution is injected. As the size of the battery increases, the amount of the non-aqueous electrolyte to be injected also increases, so that it is necessary to further increase the injectability of the non-aqueous electrolyte. That is, in a battery in which the non-aqueous electrolyte has low injectability, the electrode body (the wound electrode body formed by winding the positive electrode and the negative electrode through a separator and wound in a spiral shape) The productivity is lowered because the time required for the manufacture of individual batteries becomes longer. On the other hand, when the penetration of the non-aqueous electrolyte into the electrode body is insufficient, the next step is carried out to increase the productivity of the battery The amount of the nonaqueous electrolyte solution in the electrode body is reduced to a small amount, for example, the generation rate of the battery in which the charge-discharge cycle characteristics are deteriorated becomes large.

However, in order to improve the injectability of the nonaqueous electrolyte in the lithium ion secondary battery, the cost of the battery is increased for changing the shape of the battery itself, so that the injectability of the constituent members of the battery such as the electrode and the separator is improved Corresponding techniques are preferred. Therefore, proposals have been made to improve impregnability of a non-aqueous electrolyte to a negative electrode by using bulk graphite aggregated with flat graphite particles with respect to graphite used for the negative electrode active material (Patent Document 1).

In addition, the lithium ion secondary battery is required to have excellent charge / discharge cycle characteristics so that a large discharge capacity can be maintained over a long period of time even if charging and discharging are repeated in terms of being a secondary battery as the name suggests. In addition, lithium ion secondary batteries are used in various forms in accordance with the expansion of their applications. For this reason, for example, there is a demand for quick charging, and in order to enable this, ) Is also required. As a technique to meet such a demand, graphite materials coated with amorphous carbon on the surface of graphite used for an anode active material have been proposed (Patent Documents 2, 3, 4 and 5).

The particle size and content of the first active material (carbon material), the second active material (carbon material), and the third active material (material containing silicon and oxygen constituent elements) are specified as the negative electrode active material, A negative electrode for improving the permeability of an electrolyte solution by reducing the expansion and contraction of the third active material by setting the density of the mixed layer to 1.4 g / cm 3 or less has been proposed. (Patent Document 6)

Japanese Patent Application Laid-Open No. 2013-20772 International Publication No. 2010/106984 International Publication No. 2010/113783 International Publication No. 2012/015054 Japanese Patent Application Laid-Open No. 11-146365 International Publication No. 2013/098962

Considering the environment in which portable equipment is used, a lithium ion secondary battery used as the power source or the like is required to have good charge-discharge cycle characteristics at high temperatures, for example. In the battery using the above-described negative electrode, there is no mention of improving the charging / discharging cycle characteristics under high temperature and improving the charge-importing property at low temperature while ensuring high injectability of the non-aqueous electrolyte. Lithium ion 2 A car battery was required.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lithium ion secondary battery excellent in injection properties of a non-aqueous electrolyte and excellent charge-discharge cycle characteristics under a high temperature.

The lithium ion secondary battery of the present invention which can achieve the above object is a lithium ion secondary battery in which a flat wound electrode body composed of a positive electrode, a negative electrode and a separator, and a nonaqueous electrolyte solution are contained in an external body, The negative electrode comprises, as the negative electrode active material, at least an artificial graphite A having an average particle diameter of more than 15 占 퐉 and 25 占 퐉 or less and graphite B having an average particle diameter of 8 占 퐉 or more and 15 占 퐉 or less and a surface of the graphite particle being coated with amorphous carbon .

According to the present invention, it is possible to provide a lithium ion secondary battery having excellent non-aqueous electrolyte injection performance and excellent charge / discharge cycle characteristics under a high temperature (for example, at a high temperature of 45 캜 or higher).

1 is a perspective view schematically showing an example of a lithium ion secondary battery of the present invention.
2 is a side view of the lithium ion secondary battery of FIG.
3 is a partial vertical cross-sectional view schematically showing an example of the lithium ion secondary battery of the present invention.

The lithium ion secondary battery of the present invention is a lithium ion secondary battery in which a flat wound electrode body composed of a positive electrode, a negative electrode and a separator and a nonaqueous electrolyte solution are contained in an external body, and the negative electrode is an anode active material Artificial graphite A having a particle diameter of more than 15 占 퐉 and 25 占 퐉 or less; mother particles (mother particles) having an average particle diameter of 8 占 퐉 to 15 占 퐉 and made of graphite; , And at least one of them.

In a lithium ion secondary battery having a large external can (specifically, an external can having an internal volume of 10 cm 3 or more), a relatively large amount of non-aqueous electrolyte is introduced into the external body (battery case) at the time of its production, , The time for sufficiently penetrating the non-aqueous electrolyte into the flat-rolled electrode body becomes long.

In the flat-rolled electrode body of the lithium ion secondary battery, it has been found that the non-aqueous electrolyte solution hardly permeates the negative electrode (negative electrode mixture layer) side than the positive electrode (positive electrode mixture layer). Therefore, in the present invention, as the negative electrode active material related to the negative electrode, at least an artificial graphite A having an average particle diameter of more than 15 占 퐉 and not more than 25 占 퐉, an artificial graphite A having an average particle diameter of not less than 8 占 퐉 and not more than 15 占 퐉, And the graphite B which was formed was used.

The reason for this is not clear. However, when artificial graphite A and graphite B having a comparatively hard surface for artificial graphite A are jointly used as a negative electrode active material, And the permeability of the nonaqueous electrolyte solution into the negative electrode (negative electrode material mixture layer) can be enhanced. Therefore, the lithium ion secondary battery of the present invention has good injectability of the nonaqueous electrolyte even when the density of the negative electrode is 1.55 g / cc or more. In addition, since the filler of the non-aqueous electrolyte is improved, a sufficient amount of the nonaqueous electrolytic solution easily penetrates into the flat wound electrode body, so that the lithium ion secondary battery of the present invention can be produced in a shorter time And the battery characteristics (particularly, charge / discharge cycle characteristics under normal temperature and high temperature) are also good.

In addition, the graphite B has a high water solubility (ratio of the constant current charging capacity to the total charging capacity) of the lithium ion. Therefore, the lithium ion secondary battery of the present invention, in which artificial graphite A and graphite B are used in combination, is excellent in water solubility at low temperature as well as at room temperature, and is excellent in charge characteristics under a low temperature (for example, And charge / discharge cycle characteristics at room temperature and at high temperature are good.

Particularly, when the content of the graphite B in the entire negative electrode active material is 20 to 60 mass%, the charging / discharging cycle characteristics become better, and further, the total mass of the artificial graphite A and the graphite B It has been found that when the ratio (A / B) is adjusted to 0.5 to 1.5, the charge-discharge cycle characteristics become better. The reason for this is not clear. However, when the content of graphite B in the entire negative electrode active material is adjusted to 20 to 60 mass% and the A / B ratio is adjusted to 0.5 to 1.5, the ratio of graphite A and lithium ion It is presumed that the balance of the graphite B having excellent water solubility is satisfactorily secured and a high charge-discharge cycle characteristic is obtained.

Examples of the negative electrode relating to the lithium ion secondary battery of the present invention include a negative electrode mixture layer containing a negative electrode active material formed on one surface or both surfaces of the current collector. The negative electrode material mixture layer contains, in addition to the negative electrode active material, a binder and, if necessary, a conductive auxiliary agent, and is suitably used in a mixture (negative electrode material mixture) containing, for example, a negative electrode active material and a binder (Slurry or the like), which is obtained by adding a solvent and sufficiently kneading it, to the surface of the current collector and drying it, so as to obtain a desired thickness. The negative electrode after the negative electrode mixture layer is formed may be subjected to pressing treatment as necessary to adjust the thickness and density of the negative electrode material mixture layer.

As described above, the negative electrode active material includes artificial graphite A having an average particle size of more than 15 占 퐉 and 25 占 퐉 or less, graphite B having an average particle size of 8 占 퐉 or more and 15 占 퐉 or less and the surface of graphite particles being coated with amorphous carbon Lt; / RTI >

Artificial graphite A is artificial graphite other than graphite B. The artificial graphite in the present invention means, for example, a graphite obtained by calcining a coke or an organic material at 2800 DEG C or higher, or a graphite or a mixture of the above coke or an organic material and subjected to heat treatment at 2800 DEG C or higher, that the baked at more than 2800 ℃ and the like having been coated on the surface of the natural graphite, an argon ion laser Raman spectrum to that of indicated by 1340~1370cm ^-1 to the peak intensity represented by ^-1 in 1570~1590cm Artificial graphite having an R value of 0.05 to 0.2 which is a peak intensity ratio can be used. If the average particle size is within the above-mentioned range, two or more kinds of artificial graphite may be used in combination with the artificial graphite A.

The graphite B is composed of graphite particles which become the parent particles and amorphous carbon which covers the surface of the graphite particles. Specifically, the graphite, the peak intensity ratio R value expressed by 1340~1370cm ^-1 to the peak intensity expressed by 1570~1590cm ^-1 in the argon ion laser Raman spectrum is 0.1 to 0.7. The R value is more preferably 0.3 or more in order to secure a sufficient covering amount of the amorphous carbon. The R value is preferably 0.6 or less because the irreversible capacity increases when the coverage amount of the amorphous carbon is too large. Such graphite B can be obtained, for example, by using natural graphite having a d ₀₀₂ of 0.338 nm or less or graphite obtained by embedding artificial graphite in a spherical shape as a base material (parent particle) Firing at ~ 1500 ° C, followed by disintegration and sieving through a sieve. Examples of the organic compound coating the base material include aromatic hydrocarbons; Tar or pitch obtained by polycondensing aromatic hydrocarbons under heating and pressure; Tar, pitch or asphalt mainly containing a mixture of aromatic hydrocarbons; And the like. In order to coat the base material with the organic compound, a method of impregnating and kneading the base material with the base material may be employed. Graphite B can also be produced by a vapor phase method in which a hydrocarbon gas such as propane or acetylene is carbonized by pyrolysis and deposited on the surface of graphite having d ₀₀₂ of 0.338 nm or less.

Artificial graphite A has an average particle size of 25 占 퐉 or less and graphite B has an average particle size of 15 占 퐉 or less. By using artificial graphite A and graphite B of the same size in combination, permeability of the non-aqueous electrolyte solution into the negative electrode (negative electrode mixture layer) improves. When the artificial graphite A and graphite B having a relatively small size and having amorphous carbon on its surface are used in combination with the artificial graphite A, a pressing process is performed at the time of manufacturing the negative electrode, It is presumed that the nonaqueous electrolytic solution is likely to permeate. By using artificial graphite A and graphite B having a relatively small particle size as described above, it is possible to improve the water solubility of lithium ions in the negative electrode and to improve the charging / discharging cycle characteristics under high temperature and the charging characteristics at low temperature of the lithium ion secondary battery have.

Further, it is preferable that the artificial graphite A has a particle size not too small in that the specific surface area becomes excessively large (the irreversible capacity increases) when the particle size is too small. Therefore, in the present invention, artificial graphite A having an average particle diameter of more than 15 mu m is used. If the particle size of the graphite B is too small, the coating amount of the amorphous carbon covering the surface is uneven and the advantage of the graphite B can not be sufficiently exhibited. Therefore, the particle size is not so small desirable. Therefore, in the present invention, graphite B having an average particle diameter of 8 탆 or more is used.

The average particle diameter of graphite (artificial graphite A, graphite B and graphite other than the above) referred to in the present specification can be measured by a laser scattering particle size distribution analyzer (for example, Microtrack particle size distribution measuring apparatus "HRA9320" manufactured by Nikkiso Co., ) And a value of 50% diameter (D50%) in the integrated fraction based on volume when the integral volume is obtained from particles having a small particle size distribution measured by dispersing graphite in a medium which does not dissolve or swell the graphite, Diameter.

The specific surface area of artificial graphite A and graphite B (according to the BET method, for example, "BELSORP-mini" manufactured by Nippon-Belle) is preferably 1.0 m 2 / g or more and more preferably 5.0 m 2 / g or less.

The negative electrode active material may be a negative electrode active material other than the artificial graphite A and the graphite B (for example, the same kind as the artificial graphite A and having an average particle size of less than 15 占 퐉 or a graphite exceeding 25 占 퐉) And graphite not corresponding to graphite B) may be used together with artificial graphite A and graphite B.

It is preferable that the content of graphite B in the entire negative electrode active material contained in the negative electrode is 20% by mass or more from the viewpoint of the filling ability of the non-aqueous electrolyte in the battery, the charging / discharging cycle characteristics under high temperature, And more preferably 30 mass% or more. In addition, graphite B coated with amorphous carbon on the surface of graphite is relatively hard on the surface, and when it is excessively added and subjected to press treatment, there is a possibility that problems such as destruction of particles of artificial graphite A may occur. Therefore, the content of graphite B in the entire negative electrode active material contained in the negative electrode is preferably 60 mass% or less, and more preferably 50 mass% or less.

When the negative electrode active material other than artificial graphite A and graphite B is used for the negative electrode active material, from the viewpoint of satisfactorily securing the above effect of using artificial graphite A and graphite B, (That is, the content of the negative electrode active material other than graphite A and graphite B in the entire negative electrode active material contained in the negative electrode is preferably 50 mass% or less), and the total content of artificial graphite A and graphite B in the negative electrode is preferably 50 mass% Do).

Examples of the binder relating to the negative electrode include, but are not limited to, fluorine resins such as polyvinylidene fluoride (PVDF), cellulose ether compounds, and rubber binders. Specific examples of the cellulose ether compound include, for example, carboxymethyl cellulose (CMC), carboxyethyl cellulose, hydroxyethyl cellulose, alkali metal salts such as lithium salt, sodium salt and potassium salt thereof, and ammonium salt. Specific examples of the rubber-based binder include styrene / conjugated diene copolymers such as styrene / butadiene copolymer rubber (SBR); Nitrile-conjugated diene copolymer rubbers such as nitrile-butadiene copolymer rubber (NBR); Silicone rubbers such as polyorganosiloxane; Polymers of alkyl acrylate esters; An acrylic rubber obtained by copolymerization of an alkyl acrylate with an ethylenically unsaturated carboxylic acid and / or other ethylenically unsaturated monomer; Fluorine rubber such as vinylidene fluoride copolymer rubber; And the like.

The conductive auxiliary agent related to the negative electrode is not particularly limited as long as it is an electron conductive material and may not be used. Specific examples of the conductive auxiliary agent include carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Carbon fiber; And conductive fibers such as metal fibers; Carbon fluoride; Metal powders such as copper and nickel; Organic conductive materials such as polyphenylene derivatives; These may be used singly or in combination of two or more. Of these, acetylene black, Ketjen black and carbon fiber are particularly preferable.

As the negative electrode current collector, copper foil, nickel foil, punching metal, net, expanded metal, or the like can be used, but copper foil is usually used. In order to obtain a lithium ion secondary battery having a high energy density, the cathode current collector preferably has an upper limit of thickness of 30 占 퐉 and a lower limit of 5 占 퐉 when the thickness of the entire cathode is reduced.

The lead portion on the cathode side is usually formed by leaving the exposed portion of the current collector without forming the negative electrode mixture layer on a part of the current collector when the negative electrode is manufactured and making the lead portion as the exposed portion. However, it is not always required that the lead portion is integrated with the current collector from the beginning, and a copper foil or the like may be connected later to the current collector.

It is preferable that the thickness of the negative electrode material mixture layer (the thickness per side surface when formed on both sides of the current collector) is 50 to 150 mu m. The composition of the negative electrode mixture layer is preferably 90 to 99% by mass, and the content of the binder is preferably 1 to 10% by mass. When the conductive additive is contained in the negative mix material layer, the content of the conductive additive in the negative mix material layer is preferably 10 mass% or less from the viewpoint of high capacity. If the density of the negative electrode material mixture layer is too low, the capacity of the battery can not be increased, and the charging / discharging cycle characteristics at a sufficient high temperature and the charging property at low temperature can not be obtained. If the density is too high, Cm3 or more, and more preferably 1.58 g / cm3 or more. It is 1.8 g / cm 3 or less, and more preferably 1.7 g / cm 3. The density of the negative electrode material mixture layer defined here is the density of the portion where the negative electrode material mixture layer is formed on both surfaces of the current collector. The density of the negative electrode material mixture layer is determined by measuring the mass and thickness of the negative electrode cut out to an arbitrary size (for example, 5 x 5 cm square) with a balance or a micrometer, and subtracting the mass and thickness of the collector from the measured values (G / cm 2, g / mm 2, etc.) of the negative electrode mixture layer by the thickness of the negative electrode mixture layer (the thickness per side of the collector).

The separator related to the lithium ion secondary battery of the present invention is not particularly limited, and those used in a known lithium ion secondary battery can be applied. For example, a microporous polyethylene film (polyethylene microporous membrane) or a microporous polypropylene film (polypropylene microporous membrane) having a thickness of 5 to 30 μm and an opening ratio of 30 to 70%, a polyethylene polypropylene composite film Propylene-based microporous membrane) and the like are suitably used.

In the separator relating to the lithium ion secondary battery of the present invention, a porous layer (I) composed of a microporous membrane composed mainly of a thermoplastic resin and a porous porous layer containing a filler having a heat resistance temperature of 150 deg. II) can be used as the separator. By using such a separator, the safety (safety in a high-temperature environment) of the lithium ion secondary battery can be enhanced and the injectability of the non-aqueous electrolyte in the lithium ion secondary battery can be improved by adjusting the arrangement of the separator. Can be increased.

The porous layer (I) related to the laminated separator is mainly intended to secure a shutdown function. When the temperature of the lithium ion secondary battery reaches the melting point or higher of a thermoplastic resin (hereinafter referred to as " resin (A) ") which is a main component of the porous layer (I) (A) melts and blocks the pores of the separator, thereby causing shutdown which suppresses the progress of the electrochemical reaction.

The porous layer (II) relating to the laminate-type separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the battery rises. The filler having a heat- And the function is secured by this. That is, when the battery becomes hot, the porous layer (II), which is difficult to shrink even if the porous layer (I) is shrunk, is prevented from being short-circuited by direct contact between the positive and negative electrodes can do. In the case of a structure in which the porous layer (I) and the porous layer (II) are integrated as described later, the heat resistant porous layer (II) acts as a skeleton of the separator, The heat shrinkage of the entire separator is suppressed.

The resin (A) related to the porous layer (I) of the separator has electrical insulation, is electrochemically stable, and is used later in a nonaqueous electrolyte solution of a battery or a solvent used in the production of a separator (PE), polypropylene (PP), and ethylene-propylene copolymer; polyolefins such as ethylene-propylene copolymer; Polyesters such as polyethylene terephthalate and copolymerized polyesters; .

Further, it is preferable that the separator has a property that the hole is closed (that is, a shutdown function) at 80 ° C or more and 150 ° C or less (more preferably 100 ° C or more). Therefore, the porous film (I) has a melting temperature measured by a differential scanning calorimeter (DSC) of 80 ° C or more and 150 ° C or less (more preferably 100 ° C or more) according to JIS K 7121 It is more preferable to use a thermoplastic resin as a constituent component, and it is preferably a single-layered microporous membrane containing PE as a main component, or a laminated microporous membrane in which 2 to 5 layers of PE and PP are laminated.

Examples of the microporous membrane include a microporous membrane composed of the thermoplastic resin of the above-described example used in a conventionally known lithium ion secondary battery or the like, that is, a microporous membrane made of an ion permeable membrane produced by solvent extraction, dry or wet drawing Microporous membrane can be used.

The content of the resin (A) in the porous layer (I) is preferably, for example, as follows in order to make it easier to obtain an effect of shutdown. The volume of the resin (A) as the main component in the entire constituent components of the porous layer (I in the following description with respect to the content of each component in each layer of the separator among the entire volume excluding the vacant portion) is 50 volumes Or more, more preferably 70 vol% or more, and even more preferably 100 vol%. It is also preferable that the porosity of the porous layer (II) obtained by the later method is 20 to 60% and the volume of the resin (A) is 50% or more of the void volume of the porous layer (II).

The filler relating to the porous layer (II) has a heat-resistant temperature of 150 DEG C or higher and is stable to a non-aqueous electrolyte contained in the battery, and if it is electrochemically stable which is difficult to be oxidized and reduced in an operating voltage range of a battery, The inorganic fine particles may be fine particles in terms of dispersion and the like, and more preferably, inorganic fine particles are used in terms of stability (particularly, oxidation resistance). The term "heat-resistant temperature of not lower than 150 ° C" in this specification means that no deformation such as softening is observed at least at 150 ° C, except for the later-described porous substrate.

Specific examples of the filler having a heat-resistant temperature of 150 ° C or higher include inorganic oxide fine particles such as iron oxide, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), TiO ₂ and BaTiO ₂ . The inorganic oxide fine particles may be fine particles of mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica and the like or artificial organics thereof. As the porous layer (II), one filler having a heat resistance temperature of 150 deg. C or higher may be used alone, or two or more fillers may be used in combination. Of the fillers having a heat-resistant temperature of 150 DEG C or higher in the above example, alumina, silica and boehmite are preferable.

The particle diameter of the filler having a heat-resistant temperature of 150 占 폚 or higher is preferably 0.001 占 퐉 or larger, more preferably 0.1 占 퐉 or larger, preferably 15 占 퐉 or smaller, and more preferably 1 占 퐉 or smaller. The average particle diameter of the filler having a heat-resistant temperature of 150 占 폚 or higher can be measured by dispersing the filler in a medium which does not dissolve the filler by using a laser scattering particle size distribution analyzer (for example, "LA-920" Can be defined as the number average particle diameter.

In the form of a filler having a heat-resistant temperature of 150 ° C or higher, for example, it may have a shape close to a sphere or a plate-like shape.

The aspect ratio of the plate-like particles is preferably 5 or more, more preferably 10 or more, and 100 or less, more preferably 50 or less. The aspect ratio of the plate-like particles can be obtained, for example, by image analysis of an image taken by a scanning electron microscope (SEM).

The amount of the filler having a heat-resistant temperature of not lower than 150 占 폚 in the porous layer (II) is not particularly limited as long as the total volume of the constituent components of the porous layer (II) Of the total volume. Is 50 vol% or more, preferably 70 vol% or more, more preferably 80 vol% or more, and further preferably 90 vol% or more, with respect to the content of each component of the porous layer (II). By setting the filler in the porous layer (II) to have a high content as described above, occurrence of a short circuit due to direct contact between the positive electrode and the negative electrode when the lithium ion secondary battery has reached a high temperature can be suppressed more preferably, In the case of a separator having a structure in which the porous layer (I) and the porous layer (II) are integrated, the heat shrinkage of the entire separator can be satisfactorily suppressed.

It is preferable that an organic binder is contained in the porous layer (II) in order to bond the pellets having a heat-resistant temperature of not lower than 150 ° C or bind the porous layer (I) and the porous layer (II) , The upper limit value of the amount of the filler having a heat-resistant temperature of not less than 150 ° C in the porous layer (II) is, for example, 99.5% by volume of the total volume of the constituent components of the porous layer (II). If the amount of the filler having a heat-resistant temperature of 150 ° C or higher in the porous layer (II) is less than 70% by volume, for example, it is necessary to increase the amount of the organic binder in the porous layer (II) , The pores of the porous layer (II) are liable to be filled with the organic binder, and the function as the separator may be deteriorated. In the case where the porous layer (II) is made porous by using a pore former or the like, There is a possibility that the effect of suppressing heat shrinkage is lowered.

The porous layer (II) preferably contains an organic binder for securing the shape stability of the separator and integrating the porous layer (II) and the porous layer (I). Examples of the organic binder include ethylene-vinyl acetate copolymer (EVA, 20 to 35 mol% of structural unit derived from vinyl acetate), ethylene-acrylic acid copolymer such as ethylene-ethyl acrylate copolymer, fluorine rubber, styrene butadiene rubber (SBR), carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), crosslinked acrylic resin, polyurethane, Epoxy resins and the like. Among them, a heat-resistant binder having a heat-resistant temperature of 150 ° C or higher is preferably used. As the organic binder, one of the above-mentioned examples may be used alone, or two or more of them may be used in combination.

Of the organic binders exemplified above, a highly flexible binder such as EVA, an ethylene-acrylic acid copolymer, a fluorine-based rubber, or SBR is preferable. Specific examples of such flexible organic binders include EVA Flex series (EVA) manufactured by Mitsui DuPont Polychemical, EVA manufactured by Nippon Unicar Co., EVA Flex-EEE series (ethylene-acrylic acid copolymer) manufactured by Mitsui DuPont Polychemical Co., (EBR) of Nippon Unicar Co., Ltd., "Daier Latex Series" (fluororubber) of Daikin Industries, "TRD-2001 (SBR)" of JSR Corporation and "BM-400B (SBR)" of Nippon Zeon Corporation.

When the organic binder is used for the porous layer (II), it may be used in the form of an emulsion dissolved or dispersed in a solvent of a composition for forming a porous layer (II) described below.

In order to secure the shape stability and flexibility of the separator, a fibrous material or the like may be mixed with the filler in the porous layer (II). The fibrous material is preferably a material having a heat-resistant temperature of not less than 150 ° C, having electrical insulation, being electrochemically stable, stable to a solvent used in the production of the electrolytic solution described above and a separator, There is no.

Further, a porous substrate made of a fibrous substance (a porous substrate having a heat-resistant temperature of 150 ° C or higher) may be used for the porous layer (II). The " heat resistance " of the porous substrate means that no substantial dimensional change occurs due to softening or the like, and a change in length of the object, that is, a ratio of shrinkage (shrinkage ratio) (Heat-resistant temperature) which is capable of maintaining the heat-resistance of the separator is sufficiently higher than the shutdown temperature of the separator. In order to enhance the safety of the battery after shutdown, it is preferable that the porous substrate has a heat-resistant temperature higher than the shutdown temperature by 20 ° C or higher. More specifically, the heat resistant temperature of the porous substrate is preferably 150 ° C or higher, desirable.

When the porous layer (II) is constituted by using a porous substrate, it is preferable that all or part of the filler having a heat-resistant temperature of 150 ° C or higher is present in the pores of the porous substrate. By adopting such a configuration, the action of the filler can be more effectively exerted.

It is preferable that the thickness of the separator (the separator of the laminate type and the other separator) is 10 to 30 占 퐉.

In the laminate type separator, the thickness of the porous layer (II) (the total thickness when the separator has a plurality of porous layers (II)) is set so that the above-mentioned actions by the porous layer (II) , It is preferable that the thickness is 3 mu m or more. However, if the thickness of the porous layer (II) is too thick, it is preferable that the thickness of the porous layer (II) is 8 占 퐉 or less because there is a possibility that the energy density of the battery is lowered.

The thickness of the porous layer (the total thickness when the separator has a plurality of porous layers (I). The same shall apply hereinafter) is preferably 6 占 퐉 or more and more preferably 10 占 퐉 or more from the viewpoint of more effectively exhibiting the action (in particular, the shutdown action) by use of the porous layer (I). However, if the porous layer (I) is too thick, there is a possibility that the energy density of the battery is lowered. In addition, the porous layer (I) In the structure in which the porous layer (II) is integrated, the action of suppressing the heat shrinkage of the whole separator may be reduced. Therefore, the thickness of the porous layer (I) is preferably 25 占 퐉 or less, more preferably 20 占 퐉 or less, and even more preferably 14 占 퐉 or less.

The porosity of the entire separator is preferably 30% or more in a dried state in order to secure the amount of electrolytic solution to maintain a sufficient ion permeability. On the other hand, from the viewpoints of securing the strength of the separator and preventing the internal short circuit, the porosity of the separator is preferably 70% or less in a dried state. The porosity P (%) of the separator can be calculated from the thickness of the separator, the mass per unit area, and the density of the constituent components, by calculating the sum for each component i using the following expression (2).

P = {1- (m / t) / (? _{I i} ? _I )} 100 (2)

Here, the above-mentioned (2) wherein, a _i: ratio, ρ _i of component i at the time when the total mass of a 1: density of component i (g / ㎤), m: mass per unit area of the separator (g / Lt; 2 >), and t: thickness (cm) of the separator. The mass per unit area (m) of the separator is calculated by mass per 1 cm 2 of the separator cut out in 20 cm square and the mass is measured with an electronic balance. The thickness t of the separator is 10 points And the average thickness was measured.

In the above-mentioned laminated separator, it is preferable that m is a mass per unit area (g / cm 2) of the porous layer (I) and t is a thickness (cm) of the porous layer (I) , The porosity P (%) of the porous layer (I) can be obtained by using the above-mentioned formula (2). The porosity of the porous layer (I) obtained by this method is preferably 30 to 70%.

In the above laminated separator, it is preferable that m is a mass per unit area (g / cm 2) of the porous layer (II) and t is a thickness (cm) of the porous layer (II) , The porosity P (%) of the porous layer (II) can be obtained by using the above formula (2). The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

The separator according to the present invention is measured by a method in accordance with JIS P 8117, and preferably has a Gurley value of 10 to 300 sec as expressed by a supernatant of 100 ml of air permeable to air under a pressure of 0.879 g / . If the air permeability is too large, the ion permeability becomes small. On the other hand, if the air permeability is too small, the strength of the separator may be small. By employing the above-described configuration, a separator having the above described degree of permeability can be obtained.

The average pore diameter of the separator (the above-described laminated separator and the other separator) is preferably 0.01 占 퐉 or more, more preferably 0.05 占 퐉 or more, preferably 1 占 퐉 or less, more preferably 0.5 占 퐉 or less. In the case of the laminated separator, the average pore diameter of the porous layer (I) is preferably 0.01 to 0.5 mu m, and the average pore diameter of the porous layer (II) is preferably 0.05 to 1 mu m.

The separator according to the present invention preferably has a heat shrinkage at 150 캜 of 5% or less. With such a separator having such characteristics, it is possible to more reliably prevent a short circuit due to contact between the positive and negative electrodes because the separator hardly shrinks even when the inside of the cell becomes about 150 DEG C, . The separator having the above-described heat shrinkage ratio can be made by employing the above-described structure for the laminate separator.

Here, the heat shrinkage rate refers to the shrinkage percentage of the whole of the integral separator when the porous layer (I) and the porous layer (II) are integrated, and when the porous layer (I) and the porous layer , It indicates the smaller value of each shrinkage ratio. As described later, the porous layer (I) and / or porous layer (II) may be integrated with the electrode, but in this case, it indicates the heat shrinkage ratio measured in a state integrated with the electrode.

The term " heat shrinkage rate at 150 占 폚 " as used herein means a ratio of the heat shrinkage rate at 150 占 폚 when the separator or the porous layer I and the porous layer II (integrated with the electrode when integrated with the electrode) are placed in a thermostatic chamber, Is raised to 150 DEG C, left for 3 hours, taken out, and compared with the dimensions of the separator or the porous layer (I) and the porous layer (II) before being placed in the thermostatic chamber.

The porous layer (I) and the porous layer (II) need not be one layer each, and a plurality of layers may be contained in the separator. For example, the porous layer (I) may be disposed on both surfaces of the porous layer (II), or the porous layer (II) may be disposed on both surfaces of the porous layer (I). However, increasing the number of layers may increase the thickness of the separator to increase the internal resistance of the lithium ion secondary battery or lower the energy density. Therefore, it is not desirable to increase the number of layers too much, and the number of layers of the porous layer I ) And the porous layer (II) is preferably 5 layers or less.

Examples of the positive electrode relating to the lithium ion secondary battery of the present invention include a positive electrode mixture layer containing a positive electrode active material formed on one surface or both surfaces of the current collector. The positive electrode material mixture layer contains, in addition to the positive electrode active material, a binder and, if necessary, a conductive auxiliary agent, and a suitable solvent is added to a mixture (positive electrode material mixture) containing, for example, a positive electrode active material and a binder (A slurry or the like) obtained by sufficiently kneading a composition of the positive electrode material mixture is applied to the surface of the current collector and dried to form a desired thickness. The thickness and density of the positive electrode material mixture layer may be adjusted by subjecting the negative electrode after the positive electrode material mixture layer is formed to a pressing treatment as necessary.

As the cathode active material, there is used a conventionally known cathode active material for a lithium ion secondary battery, for example, an active material capable of absorbing and desorbing lithium ions. Specific examples of such a cathode active material include a layered lithium containing transition represented by Li _{1 + x} MO ₂ (-0.1 <x <0.1, M: Co, Ni, Mn, Al, A metal oxide, a lithium manganese oxide having a spinel structure in which LiMn ₂ O ₄ or a part of the element is replaced with another element, and an olivine-type compound represented by LiMPO ₄ (M: Co, Ni, Mn, Fe and the like) . Specific examples of the lithium-containing transition metal oxide of the layer structure example, LiCoO _2, in addition, an oxide containing at least Co, Ni and _{Mn (LiMn 1/3 Ni 1} /3 Co 1/3 O 2, LiMn 5/12 _{Ni 5/12 Co 1/6} O 2, LiNi 3/5 Mn 1/5 Co 1/5 O 2 , etc.) and the like can be given. In particular, when the lithium ion secondary battery is charged with a higher end voltage than usual before use, in order to enhance the stability of the positive electrode active material in a state of being filled with a high voltage, various kinds of active materials in the above- . Examples of such a stabilizing element include Mg, Ak, Ti, Zr, Mo, Sn and the like.

As the binder for the positive electrode mixture layer, those conventionally known as used for a positive electrode binder are suitably employed. (Methacrylic acid esters such as methyl acrylate, ethyl methacrylate, butyl methacrylate and the like), acrylonitrile, acrylic esters (such as methyl acrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate) A copolymer formed by two or more kinds of monomers including at least one kind of monomer selected from the group consisting of Hydrogenated nitrile rubber; Polyvinylidene fluoride (PVDF); Vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE); Vinylidene fluoride-tetrafluoroethylene copolymer (VDF-TFE); Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE); And the like.

Examples of the conductive additive include graphite such as natural graphite (flake graphite and the like), artificial graphite and the like; Carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Carbon fiber; , And conductive fibers such as metal fibers; Carbon fluoride; Metal powders such as aluminum; Zinc oxide; Conductive whiskers such as potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives; May be used.

As the collector of the positive electrode, a metal foil such as aluminum, a punching metal, a mesh, or an expanded metal may be used, but an aluminum foil with a thickness of 10 to 30 m is preferably used.

Similarly to the lead portion of the negative electrode, the lead portion on the positive electrode side is usually formed by leaving the exposed portion of the current collector without forming the positive electrode mixture layer on a part of the current collector in the production of the positive electrode, However, the lead portion is not necessarily one integrated with the current collector from the outset, and may be provided by connecting a foil or the like made of aluminum later to the current collector.

It is preferable that the thickness of the positive electrode material mixture layer (the thickness per side surface when formed on both sides of the current collector) is 50 to 150 mu m. The content of the positive electrode active material is preferably 90 to 98 mass%, the content of the binder is preferably 1 to 7 mass%, the content of the conductive auxiliary is 1 to 8 mass% .

In addition, the negative electrode having the positive electrode mixture layer and the positive electrode mixture layer as described above can be obtained by forming the positive electrode mixture layer formed by dispersing the positive electrode mixture in a solvent such as N-methyl-2-pyrrolidone (NMP) (Slurry or the like) for forming a negative electrode mixture layer in which a negative electrode mixture is dispersed in a solvent such as NMP or water is applied to the surface of the collector and then dried. In this case, for example, a positive electrode mixture layer forming composition is applied onto the surface of the current collector, and the positive electrode prepared by applying the composition for forming the porous layer (II) before the composition is dried, Alternatively, it is also possible to use a composite of the negative electrode and the porous layer (II) prepared by applying the composition for forming the negative electrode mixture layer onto the surface of the current collector and coating the composition for forming the porous layer (II) before the composition is dried, Ion secondary battery may be constructed.

In the lithium ion secondary battery of the present invention, the positive electrode and the negative electrode are used in the form of a flat-shaped wound electrode body formed by being rolled in a spiral shape while being interposed with a separator interposed therebetween and further shaping the cross- .

When the above-mentioned laminated separator is used for the separator, it is preferable that the porous layer (II) is arranged so as to face the anode, and the flat wound electrode body is formed. In the above-mentioned laminated separator, since the porous layer (II) contains a filler having a heat-resistant temperature of 150 ° C or more as a main component, the scale is rough and the nonaqueous electrolyte solution tends to permeate. In the positive electrode material mixture layer related to the positive electrode, the nonaqueous electrolyte solution is more likely to permeate than the negative electrode material mixture layer generally associated with the negative electrode in the kind of the constituent material or the like. By making the positive electrode (positive electrode material mixture layer) and the porous layer , This point serves as the flow path of the non-aqueous electrolyte, so that the time during which the non-aqueous electrolyte penetrates into the entire flat-rolled electrode body having a larger size for use in an external can having a large content can be further shortened. Therefore, in the lithium ion secondary battery of the present invention, when the laminated separator is used and the flat wound electrode body is formed so that the porous layer (II) faces the positive electrode, The action of improving the permeability of the non-aqueous electrolyte to the negative electrode (in the negative electrode mixture layer) by using the graphite A and the graphite B in combination is combined, and the injectability of the non-aqueous electrolyte can be enhanced to a high degree.

As the non-aqueous electrolyte relating to the lithium ion secondary battery of the present invention, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it is dissociated in a solvent to form Li ⁺ ions and it is difficult to cause side reactions such as decomposition in a voltage range used as a battery. For _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, inorganic lithium salts such as _{LiSbF 6, LiCF 3 SO 3,} LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF 3 An organic lithium salt such as SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n? 2), LiN (RfOSO ₂ ) ₂ (wherein Rf is a fluoroalkyl group) Can be used.

The organic solvent used in the nonaqueous electrolyte solution is not particularly limited as long as it dissolves the lithium salt and does not cause side reactions such as decomposition in a voltage range used as a battery. Examples thereof include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; Chain esters such as methyl propionate; cyclic esters such as? -butyrolactone; Chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; Cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; Nitriles such as acetonitrile, propionitrile and methoxypropionitrile; Sulfurous acid esters such as ethylene glycol sulfite; These may be used in combination of two or more. In addition, in order to obtain a cell having better characteristics, it is preferable to use a combination such as a mixed solvent of ethylene carbonate and chain carbonate in which a high conductivity can be obtained. For the purpose of improving the charge-discharge cycle characteristics of such electrolytic solution and improving safety such as high-temperature storability and prevention of overcharging, anhydrous acid, sulfonic acid ester, dinitrile, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide , Cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene and the like (including these derivatives) may be suitably added.

The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 1.5 mol / l, more preferably 0.9 to 1.25 mol / l.

In the lithium ion secondary battery of the present invention, when the charging upper limit voltage is set to 4.35 V or more, particularly 4.4 V or more, a nitrile compound containing at least one of LiBF ₄ (lithium tetrafluoroborate) and a cyano group It is preferable to use a non-aqueous electrolyte solution.

Specific examples of the nitrile compound include mononitriles such as acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, acrylonitrile, and lairylonitrile; Malononitrile, represented by the following general formula (1)

NC- (CH ₂ ) _n -CN (1)

[In the general formula (1), n is an integer of 2 to 4)

, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8- Dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, 2,4-dimethyl Dinitriles such as glutaronitrile; Cyclic nitriles such as benzonitrile; Alkoxy substituted nitriles such as methoxy acetonitrile; , And the like. Any one of them may be used, or two or more of them may be used in combination.

Among the above-mentioned nitrile compounds, dinitrile is preferable, and the compounds represented by the above general formula (1) (succinonitrile, glutaronitrile, adiponitrile) are more preferable, (Glutaronitrile, adiponitrile) represented by the above-mentioned general formula (1) and having n of 3 or 4 in the general formula (1) from the viewpoint that the effect of improving the charge- More preferable.

By adding the nitrile compound, there is a problem that the cycle characteristics are deteriorated (in particular, the charge upper limit voltage is high), while high temperature storability and safety can be improved. Thus, by adding the above-mentioned LiBF ₄ , it has been found that a lithium ion secondary battery excellent in cycle characteristics can be provided while ensuring high-temperature storage stability and safety. Particularly, the artificial graphite A having an average particle size of more than 15 占 퐉 and not more than 25 占 퐉 and the graphite B having an average particle diameter of not less than 8 占 퐉 and not more than 15 占 퐉 and the surface of the graphite particles being coated with amorphous carbon, It has been found that a remarkable effect can be recognized by using the lithium ion secondary battery of the present invention as an active material.

A preferable range for achieving the above effect is that the content of the nitrile compound in the non-aqueous electrolyte is 0.05 wt% or more and 5.0 wt% or less. The content of LiBF _{4 in} the non-aqueous electrolyte is 0.05 wt% or more and 2.5 wt% or less.

The external body used in the lithium ion secondary battery of the present invention uses a square-shaped wound electrode body, for example, a square-shaped external can that can make the battery thinner .

1 is a perspective view schematically showing an appearance of an example of a lithium ion secondary battery of the present invention. The lithium ion secondary battery 1 shown in Fig. 1 has a columnar (square-shaped) battery case 10, and the battery case 10 is hollow and has an anode, a cathode, and a separator A flat wound electrode body constituted by the non-aqueous electrolyte, and the like.

The battery case 10 is composed of an outer can 11 and a lid 20. The outer can 11 has a bottomed cylindrical shape and has an opening at its end, Body 20 is written and integrated with the lid body 20 by welding. The outer can 11 and the cover 20 are made of, for example, an aluminum alloy.

A terminal 21 made of stainless steel or the like protrudes from the lid body 20 and an insulating packing 22 made of PP or the like is interposed between the terminal 21 and the lid body 20. The terminal 21 functions as a negative terminal and the case 11 and the cover 20 are connected to the positive terminal 21. The terminal 21 is connected to the negative electrode, for example, in the battery case 10. In this case, . However, depending on the material of the battery case 10, the terminal 21 is connected to the anode in the battery case 10 to function as a positive terminal, and the external can 11 and the lid 20 function as negative terminals Sometimes it works. In addition, a non-aqueous electrolyte injection port is provided in the lid body 20, and after the non-aqueous electrolyte is injected into the battery case 10, it is sealed with the sealing member 23.

The side surface portion of the battery case 10, that is, the side surface portion of the external can 11, faces two mutually opposed light-shielding surfaces (width-wise surfaces) 111, and 111, respectively. When the pressure in the battery case 10 is greater than the threshold value at least one of the light-absorbing surfaces 111 and 111 (the light-absorbing surface 111 on the front surface in FIG. 1) A cleavage groove 12 is formed.

Fig. 2 shows a side view of the battery case 10 of the lithium ion secondary battery shown in Fig. 1 viewed from the side of the light-incoming surface 111. Fig. 2, the cleavage grooves 12 are provided so as to intersect with diagonal lines (indicated by a dot-and-dash line in the figure) as viewed from the side from the light-incoming surface 111 side. The diagonal line is drawn from the end of the battery case 10 when the side surface portion of the battery case 10 is recognized as a two-dimensional shape recognized when viewed from the side of the light-incoming surface 111 side.

As shown in Figs. 1 and 2, a battery case (outer can) related to the lithium ion secondary battery of the present invention has two side surfaces of mutually opposing light-exposing planes, It is preferable that the cleansing grooves opened when the pressure in the battery case is larger than the threshold value are provided so as to intersect the diagonal line when viewed from the side from the side of the collapsing surface.

In the conventional lithium ion secondary battery, a heat-releasing vent is usually provided in the lid, and when the internal pressure is increased, for example, the battery is placed at an excessively high temperature, the heat-releasing vent is opened to discharge the internal gas to the outside, The battery is prevented from being ruptured and the safety is ensured. By the way, in a lithium ion secondary battery in which a lithium-containing complex oxide containing Ni is used for a positive electrode active material or a lithium ion secondary battery which is charged at a voltage exceeding 4.30 V and used at a high capacity, if the lithium- There is a concern that the internal pressure of the battery rises sharply due to high reactivity and tears may occur before the operation of the heat shielding vent provided on the lid body.

Therefore, as shown in Figs. 1 and 2, the heat-releasing groove, which is opened when the pressure in the battery case is larger than the threshold value, intersects the diagonal line when viewed from the side from the light-incoming surface side It is possible to prevent the battery from being ruptured and the like due to the rapid opening of the cleavage grooves even if a sudden rise in the cell internal pressure occurs. Particularly, in a battery having a large external can having a large content, such as an outer can which is preferably used in the lithium ion secondary battery of the present invention, the safety improvement effect by providing the above- , And is significantly more expressed than a battery having a battery case smaller than this.

In the battery of the present invention, an external body made of a laminated film in which a resin layer is formed on one side or both sides of a metal layer in addition to the external can can be used.

In the case of the outer body relating to the lithium ion secondary battery of the present invention, the content thereof is preferably 10 cm 3 or more, and in this case, the effect of the present invention is remarkably manifested. The external shape of the outer body according to the present invention preferably has a width W of 50 mm or more and a height H of 55 mm or more. Further, the width W of the outer body is preferably 300 mm or less, more preferably 80 mm or less. The height (H) of the external body is preferably 500 mm or less, more preferably 100 mm or less. Further, the thickness T of the external body may be set to a value equal to or less than the width W, for example.

Since the lithium ion secondary battery of the present invention is excellent in charge / discharge cycle characteristics at a high temperature and charging characteristics at a low temperature, the conventional lithium ion secondary battery as well as the power source for equipment used in a wide temperature environment It can be suitably used for various applications and applications.

Further, the lithium ion secondary battery of the present invention is used with the upper limit voltage of the charge of 4.3 V or higher. By setting the upper limit voltage of the charge higher than usual in this way, It is possible to stably exhibit excellent characteristics. The upper limit of the charging of the lithium ion secondary battery is preferably 4.5 V or less.

(Example)

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1

<Fabrication of negative electrode>

Graphite A1 having an average particle size (D50%) of 22 mu m, a d _{002 value} of 0.338 nm, a specific surface area of 3.8 m &lt; 2 &gt; / g determined by the BET method and an R value of 0.12 in an argon ion laser Raman spectrum (D50%) of 10 mu m, d ₀₀₂ of 0.336 nm, and specific surface area of 3.9 m &lt; 2 &gt; / g according to the BET method, and an R value in the argon ion laser Raman spectrum of 0.40 , 98 parts by mass of a mixture of graphite B1 (graphite coated with amorphous carbon whose surface is made of graphite) with amorphous carbon at a mass ratio of 50:50, 1.0 part by mass of CMC, and 1.0 part by mass of SBR: 1.0 Mass part was mixed with ion-exchanged water to prepare a paste containing a negative electrode mixture of water.

The negative electrode material mixture containing paste was intermittently coated on both sides of a current collector having a thickness of 6 mu m made of copper foil and dried to perform calendering so that the thickness of the negative electrode material mixture layer was adjusted to be 1.58 g / To obtain a negative electrode. Further, the negative electrode was cut so as to have a width of 53 mm, and a tab was further welded to the exposed portion of the copper foil to form a lead portion.

<Fabrication of positive electrode>

97.0 parts by mass of LiCo _{0 .98} Al _{0 .008} Mg _{0 .008} Ti _{0 .004} O _{2 as a} positive electrode active material, 1.5 parts by mass of acetylene black as a conductive additive, and 1.5 parts by mass of PVDF as a binder were mixed with NMP as a solvent The mixture was mixed to prepare a paste containing a positive electrode mixture so as to be uniform. This paste was intermittently coated on both sides of an aluminum foil having a thickness of 12 mu m serving as a current collector and dried and calendered to adjust the thickness of the positive electrode material mixture layer so that the coating density of the positive electrode mixture layer was 3.80 g / 52 mm to prepare a positive electrode. Further, a tab was welded to the exposed portion of the aluminum foil of this anode to form a lead portion.

<Fabrication of Separator>

5 kg of the secondary aggregate boehmite was added with 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration: 40%) and subjected to a crushing treatment for 10 hours with a ball mill at an internal volume of 20 L and a rotation speed of 40 revolutions per minute To prepare a dispersion. The dispersion after the treatment was vacuum-dried at 120 캜 and SEM observation revealed that the boehmite had a substantially plate-like shape. The average particle size (D50%) of the boehmite was measured using a laser scattering particle size distribution analyzer ("LA-920" manufactured by HORIBA) at a refractive index of 1.65.

0.5 g of xanthan gum as a thickening agent and 17 g of a resin binder dispersant (modified polybutyl acrylate, solid content: 45% by mass) as a binder were added to 500 g of the above dispersion, and the mixture was stirred for 3 hours with a three- (A), solid content ratio of 50 mass%] was prepared.

(Discharging amount: 40 W · min / min) on one side of a microporous separator made of PE for lithium ion secondary battery (porous layer (I): thickness 8 μm, porosity 40%, average pore size 0.02 μm, The slurry (a) for forming the porous layer (II) was coated on the treated surface by a micro gravure coater and dried to form a porous layer (II) to obtain a separator. The thickness of the porous layer (II) was adjusted to 4 탆. The content of boehmite in the total volume of the constituent components of the porous layer (II) was 88% by volume.

<Assembly of Battery>

The thus obtained positive electrode, negative electrode and separator were superimposed with the porous layer (II) interposed therebetween so as to face the positive electrode side, and were wound in a spiral shape to produce a wound electrode body. The obtained wound electrode body was pressed into a flat shape and placed in an aluminum can (inner volume: 10 cm 3) made of aluminum having a thickness of 4 mm, a height of 58 mm, and a width of 51 mm to prepare a nonaqueous electrolytic solution E1 (electrolytic solution composition: ethylene carbonate, a carbonate volume ratio = 1: 1: 1 in a mixed solvent, was dissolved to a concentration of the LiPF ₆ 1.1㏖ / ℓ, 1.5% by weight of 1,3-dioxolane-2-one 4-fluoro, 2.0% by mass of vinylene carbonate, and 1.5% by mass of 2-propynyl 2- (diethoxyphosphoryl) acetate)

A lithium ion secondary battery having the appearance shown in Figs. 1 and 2 was fabricated with the structure shown in Fig. Further, this battery is provided with a heat-dissipating vent for lowering the pressure when the internal pressure of the external can increases on the wide side portion.

Here, the lithium ion secondary battery will be described with reference to Figs. 1, 2, and 3. The lithium ion secondary battery is a lithium ion secondary battery having a side surface of the battery case 10 (outer can 11) (12) so as to cross the diagonal line when viewed from the side from the side of the base plate (111). The cleavage groove 12 has an inner curved portion 121 curved in a protruding shape toward the inner side of the battery case 10 and an outer curved portion 122 curved in a protruding shape toward the outer side of the side surface of the battery case 10 The inner curved portion 121 and the outer curved portion 122 are semicircular shapes having substantially the same size and constitute a substantially S-shaped opening line having one each of them. The connecting portion between the inner curved portion 121 and the outer curved portion 122 corresponds to the diagonal line when viewed from the side of the side of the battery case 10 (outer can 11) It is installed to be a point. The cleavage groove 12 is formed such that the depth of a portion of the side surface of the battery case 10 (outer can 11) located on the diagonal line when viewed from the side from the light-incoming surface 111 side is deeper than other portions .

3, the positive electrode 31 and the negative electrode 32 are wound in a spiral shape via the separator 33 as described above, and then pressed so as to have a flat shape And is housed in a flat-type external can 11 together with a non-aqueous electrolytic solution. However, in Fig. 3, a metallic foil or a nonaqueous electrolytic solution or the like as a current collector used in manufacturing the positive electrode 31 and the negative electrode 32 is not shown in order to avoid a burden. In addition, the respective layers of the separator are not separately shown. Further, the inner peripheral side of the wound electrode body is not formed as a section.

The outer can 11 is made of an aluminum alloy and constitutes a battery case together with the lid 20. The outer can 11 also serves as a positive terminal. The positive electrode 31 and the negative electrode 32 are connected to one end of the positive electrode 31 and the negative electrode 32 from the flat wound electrode body 30 composed of the positive electrode 31, the negative electrode 32 and the separator 33, The cathode lead body 51 and the cathode lead body 52 are drawn out. A terminal 21 made of stainless steel is attached to a lid (sealing lid plate) 20 made of an aluminum alloy for sealing an opening of the outer can 11 via an insulating packing 22 made of PP, A lead plate 25 made of stainless steel is attached to this terminal 21 via an insulator 24. [

The lid body 20 is inserted into the opening of the outer can 11 and welded to the joint of the outer can 11 to seal the opening of the outer can 11 to seal the inside of the battery. 3, the non-aqueous electrolyte injection port is provided in the cover 20. The non-aqueous electrolyte injection port is welded and sealed by laser welding or the like in a state in which the sealing member 23 is inserted, The hermeticity of the battery is secured.

In the battery of the first embodiment, the cathode can 11 and the cover 20 function as positive terminals by directly welding the cathode lead body 51 to the cover body 20, The terminal 21 is welded to the plate 25 and the cathode lead 52 and the terminal 21 are made conductive through the lead plate 25 so that the terminal 21 functions as a negative terminal.

Example 2

Graphite B2 having an average particle diameter (D50%) of 15 mu m, a d _{002 value} of 0.336 nm, a specific surface area of 3.5 m &lt; 2 &gt; / g according to the BET method and an R value of 0.33 in an argon ion laser Raman spectrum Was used instead of the graphite in which the surface of the parent particles was coated with amorphous carbon having a pitch of carbon source) was used in place of the negative electrode and the negative electrode was used. Ion secondary battery was fabricated.

Example 3

A wound electrode body was fabricated in the same manner as in Example 2 except that the porous layer (II) of the separator was disposed so as to face the negative electrode side. In the same manner as in Example 2 except that the wound electrode body was used, A battery was produced.

Example 4

A negative electrode was prepared in the same manner as in Example 1 except that a mixture obtained by mixing graphite A1 and graphite B1 in a mass ratio of 33:67 was used and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used Respectively.

Example 5

A negative electrode was prepared in the same manner as in Example 1 except that a mixture obtained by mixing graphite A1 and graphite B1 in a mass ratio of 60:40 was used and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used Respectively.

Example 6

And in place of the graphite A1 having an average particle size (D50%) is 18㎛, d ₀₀₂ 0.338nm, a specific surface area by the BET method 3.9㎡ / g, whose R value in the argon ion laser Raman spectrum of graphite 0.14 A2 (surface Was replaced with amorphous carbon), a negative electrode was fabricated in the same manner as in Example 1, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

Comparative Example 1

And an average particle diameter (D50%) is 20㎛, d ₀₀₂ in place of the graphite B1 0.336nm, a specific surface area by the BET method 3.7㎡ / g, an argon ion laser Raman R value is 0.33 in graphite C1 (graphite in the spectrum Was used in place of graphite in which the surface of the parent particles was coated with amorphous carbon having a pitch of carbon atoms) was used in place of the negative electrode, and the negative electrode was produced in the same manner as in Example 1. In the same manner as in Example 1, Ion secondary battery was fabricated.

The lithium ion secondary batteries of Examples 1 to 6 and Comparative Example 1 were subjected to the following main liquid test and the charge / discharge cycle test at 45 캜.

<Main Liquid Test>

For each of the examples and the comparative example, ten flat electrodes were placed in an aluminum can outer case, covered with a lid, welded and sealed with no non-aqueous electrolyte, , And these were immersed in a bath filled with a nonaqueous electrolyte solution having the same composition as that used for the preparation of each cell, evacuated for 90 seconds (with an ultimate vacuum degree of -98 kPa), and the nonaqueous electrolyte solution was injected from each non- Lt; / RTI &gt; After releasing the vacuum, one of each of the examples and the comparative examples was taken out from the bath of the nonaqueous electrolyte solution at an arbitrary time, and the amount of the main liquid was obtained from the measurement of the mass of the battery case (main liquid amount = The battery case mass before immersion), and the arrival time at which the predetermined main liquid amount was injected into the battery case was obtained from the main liquid amount per time.

<Charge and discharge cycle test at 45 ° C>

The lithium ion secondary batteries of the examples and comparative examples were left in a thermostatic chamber at 45 캜 for 5 hours and then charged to a constant current of 1.0 C to 4.35 V for each battery. After reaching 4.35 V, C at a constant voltage of 4.35V. Thereafter, discharging was carried out until the voltage reached 3.0 V at a constant current of 1.0C. A series of such charging and discharging operations were repeated to charge and discharge one cycle, and the number of cycles capable of maintaining 80% or more of the discharge capacity in the first cycle was examined.

Table 1 shows the configuration of the negative electrode active material related to the negative electrode of each of the lithium ion secondary batteries of Examples 1 to 6 and Comparative Example 1 and the shape of the external can. The evaluation results and current values at 1C charge / 2. The "number of cycles" in the "charge and discharge cycle test at 45 ° C." in Table 2 means the number of cycles in which a discharge capacity of 80% or more of the discharge capacity (initial capacity) of the first cycle could be maintained (The same holds true in Tables 3 and 6).

As shown in Tables 1 and 2, the lithium ion secondary batteries of Examples 1 to 6 in which graphite A and graphite B were used in combination as the negative electrode active material, compared with the battery of Comparative Example 1 in which graphite B was not used, The liquid immersion time of the nonaqueous electrolytic solution was short, and excellent cannulaity of the nonaqueous electrolytic solution was secured even when using an external can having a large width and a high height. In the lithium ion secondary batteries of Examples 2 and 3 having the same constitution except that the electrode in which the porous layer (II) related to the separator was opposed was changed, the porous layer (II) in the battery of Example 2 , The liquid time of the nonaqueous electrolyte solution was shorter than that of the battery of Example 3, which was directed to the negative electrode side, and the productivity was higher.

Further, the lithium ion secondary batteries of Examples 1 to 6 had a large number of cycles capable of maintaining a capacity of 80% or more of the initial capacity at the time of the charge-discharge cycle test at 45 캜, and were excellent in charge- Respectively. In the battery of Example 2, the charge-discharge cycle characteristics were improved as compared with the battery of Example 3. [ This is because, in the battery of Example 2, since the porous layer (II) related to the separator is directed toward the anode side, the oxidation reaction of the porous layer (I) is suppressed even at a high voltage such as the upper limit voltage of 4.35 V, It is believed that it is possible to prevent the layer (I) from being deteriorated.

Example 7

<Fabrication of negative electrode>

Graphite A1 and graphite B1, an average particle size (D50%) of 19 mu m, a d ₀₀₂ of 0.338 nm, a specific surface area of 3.8 m &lt; 2 &gt; / g by the BET method, an R value of 0.21 in an argon ion laser Raman spectrum , 98 parts by mass of a mixture of graphite D1 (natural graphite whose surface was not coated with amorphous carbon) at a mass ratio of 30:30:40, 1.0 part by mass of CMC, and 1.0 part by mass of SBR, 10 &lt; ⁵ &gt; OMEGA / cm or more as a solvent to prepare a paste containing a negative electrode mixture of water.

The negative electrode material mixture containing paste was intermittently coated on both sides of a collector having a thickness of 6 mu m made of copper foil and dried and calendered to adjust the thickness of the negative electrode material mixture layer so that the coating film density of the mixture layer was 1.58 g / To obtain a negative electrode. Further, the negative electrode was cut to a width of 55.5 mm, and a tab was welded to the exposed portion of the copper foil to form a lead portion.

<Fabrication of positive electrode>

97.0 parts by mass of LiCo _{0 .98} Al _{0 .008} Mg _{0 .008} Ti _{0 .004} O _{2 as a} positive electrode active material, 1.5 parts by mass of acetylene black as a conductive additive, and 1.5 parts by mass of PVDF as a binder were mixed with NMP as a solvent To prepare a paste containing a positive electrode mixture. This paste was intermittently coated on both sides of an aluminum foil having a thickness of 12 mu m serving as a current collector and dried and calendered to adjust the thickness of the positive electrode material mixture layer so that the coating density of the positive electrode mixture layer was 3.80 g / 54.5 mm to prepare a positive electrode. Further, a tab was welded to the exposed portion of the aluminum foil of this anode to form a lead portion.

<Assembly of Battery>

A flat-rolled electrode body was fabricated in the same manner as in Example 1 except that the cathode and the anode were used. An aluminum outer can (thickness: 15 cm) having a thickness of 5 mm, a height of 61 mm, ) Was used as a positive electrode active material, a lithium ion secondary battery was fabricated.

Example 8

A negative electrode was prepared in the same manner as in Example 7 except that graphite B2 was used instead of graphite B1. A lithium ion secondary battery was produced in the same manner as in Example 7 except that this negative electrode was used.

Example 9

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B1 and graphite D1 as a negative electrode active material in a mass ratio of 40:20:40 was used and the same as Example 7 To prepare a lithium ion secondary battery.

Example 10

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B2 and graphite D1 as a negative electrode active material in a mass ratio of 10:40:50 was used and the same as Example 7 To prepare a lithium ion secondary battery.

Example 11

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B1 and graphite D1 as a negative electrode active material in a mass ratio of 20:40:40 was used and the same as Example 7 To prepare a lithium ion secondary battery.

Example 12

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B1 and graphite D1 as a negative electrode active material in a mass ratio of 30:20:50 was used and the same as Example 7 To prepare a lithium ion secondary battery.

Example 13

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A2, graphite B1 and graphite D1 as a negative electrode active material in a mass ratio of 30:30:40 was used and the same as Example 7 To prepare a lithium ion secondary battery.

Example 14

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B1 and graphite D1 as a negative electrode active material in a mass ratio of 40:10:50 was used and the same as Example 7 To prepare a lithium ion secondary battery.

Comparative Example 2

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite C1 and graphite D1 as a negative electrode active material in a mass ratio of 10:40:50 was used and the same as Example 7 To prepare a lithium ion secondary battery.

Comparative Example 3

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite C1 and graphite D1 as a negative electrode active material in a mass ratio of 30:30:40 was used and the same as Example 7 To prepare a lithium ion secondary battery.

Comparative Example 4

Graphite B1 having an average particle size (D50%) of 35 mu m, a d _{002 value} of 0.338 nm, a specific surface area of 3.6 m &lt; 2 &gt; / g according to the BET method and an R value of 0.11 in an argon ion laser Raman spectrum And graphite D1 were mixed in a mass ratio of 30:30:40 was used in place of the negative electrode, and a negative electrode was prepared in the same manner as in Example 7 except that the negative electrode was used. A lithium ion secondary battery was fabricated in the same manner as in Example 7.

Comparative Example 5

And B1 and the graphite having an average particle size (D50%) is 10㎛, d ₀₀₂ 0.338nm, a specific surface area by the BET method 4.5㎡ / g, whose R value in the argon ion laser Raman spectrum of graphite 0.15 C3 (surface And graphite D1 were mixed at a mass ratio of 30:30:40 was used in place of the mixture of the graphite D1 and graphite D1 in the mass ratio of 30:30:40. A lithium ion secondary battery was fabricated in the same manner as in Example 7.

Comparative Example 6

A lithium ion secondary battery was fabricated in the same manner as in Example 7 except that the thickness of the negative electrode mixture layer was adjusted so that the coating density of the negative electrode mixture layer was 1.45 g / cm 3.

The lithium ion secondary batteries of Examples 7 to 14 and Comparative Examples 2 to 6 were subjected to the liquation test and the charge / discharge cycle test at 45 캜 in the same manner as in the lithium ion secondary battery of Example 1 and the like.

Table 3 shows the configuration of the negative electrode active material related to the negative electrode of each of the lithium ion secondary batteries of Examples 7 to 14 and Comparative Examples 2 to 6 and the shape of the external can. The evaluation results and the current The values are shown in Table 4.

As shown in Tables 3 and 4, artificial graphite A having an average particle size of more than 15 占 퐉 and 25 占 퐉 or less as an anode active material, artificial graphite A having an average particle size of 8 占 퐉 or more and 15 占 퐉 or less and graphite particles whose surfaces were coated with amorphous carbon The lithium ion secondary batteries of Examples 7 to 14 in which the graphite B was used were compared with the batteries of Comparative Examples 2 and 3 which did not use the graphite B and the batteries of Comparative Examples 4 and 5 which did not use the graphite A And the external can having a larger width and height than those used in Example 1 and the like can be used to ensure excellent injectability of the nonaqueous electrolyte solution, and thus the productivity is high. The lithium ion secondary batteries of Examples 7 to 14 had a large number of cycles capable of maintaining a capacity of 80% or more of the initial capacity at the time of the charging / discharging cycle test at 45 캜 and were excellent in charge / Respectively.

Further, among the lithium ion secondary batteries of Examples 7 to 14, the battery of Example 7 and the batteries of Comparative Examples 2, 3, and 6, which had the best charge-discharge cycle characteristics at a high temperature, The chargeability test was conducted to evaluate the charging characteristics at low temperatures.

&Lt; Testing of charge importability at -5 ° C>

The lithium ion secondary batteries of Example 7 and Comparative Examples 2 and 3 were left to stand in a constant temperature bath at 25 캜 for 5 hours and then charged to a constant current of 0.5 C to 4.35 V for each battery. Thereafter, constant-voltage charging was performed at 4.35 V until the current reached 0.05C. The charging capacity at this time was defined as the charging capacity at 25 캜. Thereafter, discharging was performed until the voltage reached 2.75 V at a constant current of 0.2C.

Each battery after the discharge was allowed to stand in a thermostatic chamber at -5 DEG C for 5 hours. Thereafter, each battery was charged at a constant current of 0.5 C up to 4.35 V. After reaching 4.35 V, the current reached 0.05 C The battery was charged at a constant voltage of 4.35V. The charging capacity at this time was defined as the charging capacity at -5 [deg.] C. Thereafter, the resultant was allowed to stand in a constant temperature bath at 25 DEG C for 5 hours, and discharge was carried out until the voltage reached 2.75 V at a constant current of 0.2C.

The charge capacity in the constant current charging region of the charging capacity at -5 ° C in the fifth cycle and the charging capacity in the constant current charging region among the charging capacity at 25 ° C The ratio was evaluated and evaluated as chargeability (charge characteristics under low temperature) at -5 ° C. These results are shown in Table 5.

As shown in Table 5, the lithium ion secondary battery of Example 7 in which graphite A and graphite B were used in combination as the negative electrode active material was found to have a lower temperature at -5 캜 than the batteries of Comparative Examples 2 and 3 which did not use graphite B And the charging characteristics at low temperature were excellent.

Example 15

A mixture of graphite and graphite A1 B1 D1 with the graphite in a mass ratio of 30:30:40 mixture of: 98 parts by mass of CMC: 1.0 parts by mass, and SBR: 1.0 parts by mass, the conductivity is 2.0 × 10 ⁵ Ω / ㎝ or more ion Exchanged water as a solvent to prepare a paste containing a negative electrode mixture of water.

The negative electrode material mixture containing paste was intermittently coated on both sides of a collector having a thickness of 6 mu m made of copper foil and dried and calendered to adjust the thickness of the negative electrode material mixture layer so that the coating film density of the mixture layer was 1.58 g / To obtain a negative electrode. Further, the negative electrode was cut to a width of 71.2 mm, and a tab was welded to the exposed portion of the copper foil to form a lead portion.

<Fabrication of positive electrode>

97.0 parts by mass of LiCo _{0 .98} Al _{0 .008} Mg _{0 .008} Ti _{0 .004} O _{2 as a} positive electrode active material, 1.5 parts by mass of acetylene black as a conductive additive, and 1.5 parts by mass of PVDF as a binder were mixed with NMP as a solvent To prepare a paste containing a positive electrode mixture. This paste was intermittently coated on both sides of an aluminum foil having a thickness of 12 mu m serving as a current collector and dried and then calendered to adjust the thickness of the positive electrode material mixture layer to a coating film density of 3.80 g / mm to produce a positive electrode. Further, a tab was welded to the exposed portion of the aluminum foil of this anode to form a lead portion.

<Assembly of Battery>

A flat-rolled electrode body was fabricated in the same manner as in Example 1 except that the cathode and the anode were used. An aluminum outer can (thickness: 20 cm 3) having an average thickness of 5.5 mm, a height of 78 mm, ) Was used as a positive electrode active material, a lithium ion secondary battery was fabricated.

Comparative Example 7

A negative electrode was prepared in the same manner as in Example 15 except that a mixture obtained by mixing graphite A1, graphite C1 and graphite D1 as a negative electrode active material in a mass ratio of 10:40:50 was used and the same as Example 7 To prepare a lithium ion secondary battery.

The lithium ion secondary battery of Example 15 and Comparative Example 7 was subjected to the liquation test and the charge and discharge cycle test at 45 캜 in the same manner as in the lithium ion secondary battery of Example 1 and the like.

Table 6 shows the configuration of the negative electrode active material related to the negative electrode of each lithium ion secondary battery of Example 15 and Comparative Example 7 and the shape of the external can. The evaluation results and current values at 1 C charge / .

As shown in Tables 6 and 7, the lithium ion secondary battery of Example 15 in which graphite A and graphite B were used in combination as the negative electrode active material, compared with the battery of Comparative Example 7 which did not use graphite B, The liquid injection time was short and the external can having a height larger than that used in Example 4 or the like was used, the injectability of the excellent non-aqueous electrolyte could be ensured and the productivity was high. Further, the lithium ion secondary battery of Example 15 had a large number of cycles capable of maintaining a capacity of 80% or more of the initial capacity at the time of the charge-discharge cycle test at 45 占 폚, and was excellent in charge-discharge cycle characteristics under high temperature.

Example 16

A lithium ion secondary battery was fabricated in the same manner as in Example 7. (However, charging and discharging conditions were different from those in Example 7 as described later.)

Example 17

As the non-aqueous electrolyte The non-aqueous electrolytic solution E2 (ethylene carbonate and the di-ethyl carbonate volume ratio = 3: 7 in a mixed solvent, the LiPF ₆ was dissolved to a concentration of 1.1㏖ / ℓ, 4-fluoro-1,3-dioxo , 2.7 mass% of vinylene carbonate, 1.2 mass% of 2-propynyl 2- (diethoxyphosphoryl) acetate, 0.15 mass% of LiBF ₄ , and 0.5 mass% of adiponitrile %) Was used as the positive electrode active material, a lithium ion secondary battery produced in the same manner as in Example 16 was fabricated.

Example 18

A negative electrode was prepared in the same manner as in Example 16 except that a mixture obtained by mixing graphite A1 and graphite B1 as a negative electrode active material in a mass ratio of 50:50 was used. A battery cell was fabricated.

Example 19

A negative electrode was prepared in the same manner as in Example 16 except that a mixture obtained by mixing graphite A1 and graphite B1 as a negative electrode active material in a mass ratio of 50:50 was used and lithium ion 2 A battery cell was fabricated.

Example 20

A negative electrode was prepared in the same manner as in Example 7 except that a mixture obtained by mixing graphite A2, graphite B2 and graphite D1 as a negative electrode active material in a mass ratio of 30:30:40 was used and the same as Example 16 To prepare a lithium ion secondary battery.

Example 21

A negative electrode was prepared in the same manner as in Example 16 except that a mixture obtained by mixing graphite A2, graphite B2 and graphite D1 as a negative electrode active material in a mass ratio of 30:30:40 was used and the same as Example 17 To prepare a lithium ion secondary battery.

Example 22

Aqueous electrolyte E3 was prepared in the same composition as that of the non-aqueous electrolyte E2 except that succinonitrile was used instead of the adiponitrile contained in the non-aqueous electrolyte E2 described above. A lithium ion secondary battery was fabricated in the same manner as in Example 16 except that this non-aqueous electrolyte E3 was used as the non-aqueous electrolyte.

Example 23

A non-aqueous electrolyte E4 was prepared in the same composition as the non-aqueous electrolyte E2 except that glutaronitrile was used instead of the adiponitrile contained in the non-aqueous electrolyte E2 described above. A lithium ion secondary battery was produced in the same manner as in Example 16 except that the nonaqueous electrolyte E4 was used as the nonaqueous electrolyte.

Example 24

A non-aqueous electrolyte E5 was prepared in the same composition as the non-aqueous electrolyte E2 except that laurylonitrile was used in place of the adiponitrile contained in the non-aqueous electrolyte E2 described above. A lithium ion secondary battery was fabricated in the same manner as in Example 16 except that this non-aqueous electrolyte E5 was used as the non-aqueous electrolyte.

Comparative Example 8

A lithium ion secondary battery was fabricated in the same manner as in Comparative Example 3. (However, charge / discharge conditions were different from Comparative Example 3 as described later.)

Comparative Example 9

A negative electrode was prepared in the same manner as in Example 16 except that a mixture obtained by mixing graphite A1, graphite C1 and graphite D1 as a negative electrode active material in a mass ratio of 30:30:40 was used and the same as Example 17 To prepare a lithium ion secondary battery.

<Charge and discharge cycle test at 45 ° C>

The lithium ion secondary batteries of Examples 16 to 24 and Comparative Examples 8 and 9 were placed in a thermostatic chamber at 45 캜 for 5 hours and then charged to 4.4 V at a constant current of 1.0 V until they reached 4.4 V After reaching, constant-voltage charging was performed at 4.4 V until the current reached 0.05 C. Thereafter, discharging was carried out until the voltage reached 3.0 V at a constant current of 1.0C. A series of such charging and discharging operations were repeated to charge and discharge one cycle, and the number of cycles capable of maintaining 80% or more of the discharge capacity in the first cycle was examined.

Table 8 shows the configuration of the negative electrode active material related to the negative electrode of each of the lithium ion secondary batteries of Examples 16 to 24 and Comparative Examples 8 and 9 and the shape of the external can. The evaluation results and the current value Are shown in Table 9.

As shown in Tables 8 and 9, artificial graphite A having an average particle size of more than 15 μm but not more than 25 μm as an anode active material, graphite Lithium ion secondary batteries of Examples 17, 19, 21, 22, 23, and 24 in which an electrolyte solution containing LiBF ₄ and a nitrile compound were used in combination with the lithium ion secondary battery And exhibited better cycle characteristics. On the other hand, in the lithium ion secondary battery of Comparative Example 9 in which the graphite B was not used, the cycle characteristics were improved as compared with Comparative Example 8 using the electrolyte E2, but the improvement of the large cycle characteristics shown in Examples 16 to 24 was seen I did.

1: Lithium ion secondary battery
10: Battery case
11: External can
111: Battery case (exterior can)
12: Cleft groove
121:
122:
20:
30: flat-type wound electrode body

Claims (9)

A flat lithium ion secondary battery comprising a flat wound electrode body composed of an anode, a cathode and a separator, and a non-aqueous electrolyte contained in an external body,
Wherein the negative electrode has a mixture layer including at least an anode active material, a density of the mixture layer is 1.55 g / cm 3 or more,
An artificial graphite A having an average particle size of more than 15 占 퐉 and not more than 25 占 퐉,
A graphite B having an average particle size of not less than 8 μm and not more than 15 μm and a surface of which is coated with amorphous carbon. The method according to claim 1,
Wherein the content of the graphite B in the total negative electrode active material contained in the negative electrode is 20 to 60 mass%. 3. The method according to claim 1 or 2,
Wherein the mass ratio (A / B) of the artificial graphite A and the graphite B in the total negative electrode active material contained in the negative electrode is 0.5 to 1.5. 3. The method according to claim 1 or 2,
Wherein the non-aqueous electrolyte contains a nitrile compound containing at least one lithium tetrafluoroborate (LiBF ₄ ) and a cyano group. 5. The method of claim 4,
Wherein the nitrile compound is represented by the following general formula (1).
NC- (CH ₂ ) _n -CN (1)
[In the general formula (1), n is an integer of 2 to 4) 3. The method according to claim 1 or 2,
Wherein a volume of the external body is 10 cm 3 or more. 3. The method according to claim 1 or 2,
The separator has a porous layer (I) comprising a microporous membrane composed mainly of a thermoplastic resin and a porous layer (II) comprising a filler having a heat resistance temperature of 150 ° C or higher as a main component,
In the flat wound electrode body, the positive electrode and the separator are disposed such that at least the porous layer (II) faces the positive electrode. 3. The method according to claim 1 or 2,
The volume of the external body is 10 cm 3 or more,
The separator has a porous layer (I) comprising a microporous membrane composed mainly of a thermoplastic resin and a porous layer (II) comprising a filler having a heat resistance temperature of 150 ° C or higher as a main component,
In the flat wound electrode body, the positive electrode and the separator are disposed such that at least the porous layer (II) faces the positive electrode. 3. The method according to claim 1 or 2,
Wherein the non-aqueous electrolyte contains at least one lithium tetrafluoroborate (LiBF ₄ ) and a cyano group,
The volume of the outer body is 10 cm 3 or more,
The separator has a porous layer (I) comprising a microporous membrane composed mainly of a thermoplastic resin and a porous layer (II) comprising a filler having a heat resistance temperature of 150 ° C or higher as a main component,
In the flat wound electrode body, the positive electrode and the separator are disposed such that at least the porous layer (II) faces the positive electrode.

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