JP6499427B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery excellent in non-aqueous electrolyte injection properties and charge / discharge cycle characteristics at high temperatures.

  Lithium ion secondary batteries, which are one type of electrochemical element, are considered to be applied to portable devices, automobiles, electric tools, electric chairs, household and commercial power storage systems because of their high energy density. Yes. In particular, as a portable device, it is widely used as a power source for a mobile phone, a smartphone, or a tablet PC. As these lithium-ion secondary batteries for portable devices, flat rectangular batteries are widely adopted according to the shape of the devices.

  The characteristics required for batteries are diverse, and various measures are required depending on the application. For example, a flat rectangular lithium ion secondary battery used in the above-described portable device is required to have a high capacity in order to extend the battery usage time. Therefore, the size of the battery is inevitably increased.

  In the rectangular lithium ion secondary battery, the size and number of inlets for injecting the non-aqueous electrolyte are limited. As the size of the battery increases, the amount of non-aqueous electrolyte to be injected also increases, so it is necessary to further improve the injectability of the non-aqueous electrolyte. That is, in a battery having a low nonaqueous electrolyte injection property, the electrode body (a wound electrode body formed by stacking a positive electrode and a negative electrode through a separator and winding them in a spiral shape) is manufactured. If the nonaqueous electrolyte solution is sufficiently infiltrated into the electrode, the time required for manufacturing each battery becomes longer, resulting in lower productivity. On the other hand, in order to increase battery productivity, If the next step is advanced when the penetration of the electrolytic solution is not sufficient, it is completed with a small amount of the nonaqueous electrolytic solution in the electrode body, and for example, the generation rate of batteries with inferior charge / discharge cycle characteristics increases.

  However, in order to increase the non-aqueous electrolyte injection property in a lithium ion secondary battery, the battery cost will be increased to cope with changing the shape of the battery itself. It is desirable to adopt a method that improves the injectability of the constituent members to cope with it. Then, about the graphite used for a negative electrode active material, the proposal which improves the impregnation property of the nonaqueous electrolyte to a negative electrode using the aggregate graphite which aggregated the flat graphite particle | grains is made (patent document 1).

In addition, since the lithium ion secondary battery is a secondary battery as the name suggests, it is possible to ensure excellent charge / discharge cycle characteristics so that a large discharge capacity can be maintained over a long period of time even if charge / discharge is repeated. It has been demanded. In addition, lithium ion secondary batteries are used in a variety of forms as their applications expand, and in response to this, there is a demand for rapid charging, for example. Securing is also required. As a technology that meets these requirements, graphite materials in which the surface of graphite used for the negative electrode active material is coated with amorphous carbon have been proposed (Patent Documents 2, 3, 4, and 5).
In addition, the particle diameters of the first active material (carbon material), the second active material (carbon material), and the third active material (material containing silicon and oxygen as constituent elements) as the negative electrode active material A negative electrode that regulates the permeability of the electrolyte by regulating the content and the like, and relaxing the expansion and contraction of the third active material by setting the density of the negative electrode mixture layer to 1.4 g / cm ³ or less. Proposed. (Patent Document 6)

JP 2013-20772 A International Publication No. 2010/106984 International Publication No. 2010/113783 International Publication No. 2012/015054 JP 2011-146365 A International Publication No. 2013/098962

  Considering the environment in which portable devices are used, a lithium ion secondary battery used as a power source or the like is required to have, for example, good charge / discharge cycle characteristics at high temperatures. In the battery using the negative electrode described above, there is no mention of improving charge / discharge cycle characteristics at high temperatures and charge acceptability at low temperatures while ensuring high injectability of the nonaqueous electrolyte. However, a lithium ion secondary battery having these various characteristics has been demanded.

  This invention is made | formed in view of the said situation, The objective is to provide the lithium ion secondary battery excellent in the injection | pouring property of a non-aqueous electrolyte, and the charging / discharging cycling characteristics in high temperature.

  The lithium ion secondary battery of the present invention that can achieve the above object is a lithium ion 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 accommodated in an outer package. In the secondary battery, the negative electrode has, as a negative electrode active material, artificial graphite A having an average particle diameter of more than 15 μm and 25 μm or less, an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles is amorphous. It is characterized by containing at least graphite B coated with carbonaceous.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery excellent in the injectability of a non-aqueous electrolyte and the charge / discharge cycle characteristic under high temperature (for example, 45 degreeC or more high temperature) can be provided.

It is a perspective view showing typically an example of the lithium ion secondary battery of the present invention. It is a side view of the lithium ion secondary battery of FIG. It is a fragmentary longitudinal cross-sectional view which represents typically an example of the lithium ion secondary battery of this 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 electrolytic solution are housed in an outer package, The negative electrode has, as a negative electrode active material, artificial graphite A having an average particle diameter of more than 15 μm and not more than 25 μm, mother particles having an average particle diameter of 8 μm to 15 μm, graphite, and the surface of the graphite particles being non-conductive. It is characterized by containing at least graphite B coated with crystalline carbon.

In a lithium ion secondary battery having a large-capacity outer can (specifically, an outer can having an internal volume of 10 cm ³ or more), a relatively large amount of non-aqueous electrolyte is produced during the manufacture of the outer casing (battery In this case, the time required for the nonaqueous electrolyte to sufficiently permeate into the flat wound electrode body becomes longer.

  In a flat wound electrode body of a lithium ion secondary battery, it has been found that the non-aqueous electrolyte solution is less likely to penetrate the negative electrode (negative electrode mixture layer) 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 μm and 25 μm or less, an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles are amorphous. It was decided to use graphite B coated with carbonaceous carbon.

  Although the reason is not clear, when the negative electrode active material is used together with the artificial graphite A and the graphite B having a relatively hard surface with respect to the artificial graphite A, the negative electrode mixture layer is formed when the negative electrode is pressed during the production of the negative electrode. It is presumed that the size of the pores formed therein is made uniform, and the permeability of the nonaqueous electrolytic solution into the negative electrode (negative electrode mixture layer) can be increased. Therefore, the lithium ion secondary battery of the present invention has a good non-aqueous electrolyte injection property even when the negative electrode density is 1.55 g / cc or more. Further, since the non-aqueous electrolyte can be easily injected, a sufficient amount of the non-aqueous electrolyte can easily penetrate into the flat wound electrode body. Since it can be produced in a short time, it has high productivity, and battery characteristics (particularly charge / discharge cycle characteristics at normal temperature and high temperature) are also good.

  Further, the graphite B has a high lithium ion acceptability (a ratio of a constant current charge capacity to a total charge capacity). Therefore, the lithium ion secondary battery of the present invention using the artificial graphite A and the graphite B in combination has good acceptability of lithium ions not only at room temperature but also at low temperature, and at a low temperature (for example, a low temperature of 0 ° C. or lower). In addition, the charge characteristics at, and the charge / discharge cycle characteristics at normal and high temperatures are also good.

  In particular, when the content of the graphite B in the entire negative electrode active material is 20 to 60% by mass, charge / discharge cycle characteristics are further improved, and the artificial graphite A and the graphite B in the total negative electrode active material It was found that when the content mass ratio (A / B) was adjusted to 0.5 to 1.5, the charge / discharge cycle characteristics were improved. The reason is not clear, but when the content of graphite B in the entire negative electrode active material is 20 to 60% by mass and A / B is adjusted to 0.5 to 1.5, graphite having excellent lithium ion release properties. It is presumed that a good balance between A and graphite B having excellent lithium ion acceptability is secured, and that high charge / discharge cycle characteristics can be obtained.

  As a negative electrode which concerns on the lithium ion secondary battery of this invention, what formed the negative mix layer containing a negative electrode active material in the single side | surface or both surfaces of a collector is mentioned, for example. The negative electrode mixture layer contains, in addition to the negative electrode active material, a binder and, if necessary, a conductive aid, and includes, for example, a negative electrode active material and a binder (further, a conductive aid). A negative electrode mixture-containing composition (slurry etc.) obtained by adding a suitable solvent to the mixture (negative electrode mixture) and kneading thoroughly is applied to the surface of the current collector and dried to obtain a desired thickness. Can be formed. Moreover, the negative electrode after formation of the negative electrode mixture layer can be subjected to press treatment as necessary to adjust the thickness and density of the negative electrode mixture layer.

  As described above, the negative electrode active material includes at least artificial graphite A having an average particle diameter of more than 15 μm and 25 μm or less, an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles is amorphous carbon. And graphite B coated with

Artificial graphite A is artificial graphite other than graphite B. The artificial graphite referred to in the present invention is, for example, one obtained by firing coke or an organic substance at 2800 ° C. or higher, or one obtained by mixing natural graphite and the above coke or organic substance and performing a heat treatment at 2800 ° C. or higher, and further coke or The organic graphite fired at 2800 ° C. or higher is coated on the surface of the natural graphite. The peak intensity appearing at 1340 to 1370 cm ⁻¹ with respect to the peak intensity appearing at 1570 to 1590 cm ⁻¹ in the argon ion laser Raman spectrum. Artificial graphite having an R value of 0.05 to 0.2 can be used. If the average particle diameter is in the above range, the artificial graphite A may be used in combination with two or more kinds of artificial graphite.

Graphite B is composed of graphite particles serving as mother particles and amorphous carbon covering the surface. Specifically, it is graphite in which the R value, which is a peak intensity ratio appearing at 1340 to 1370 cm ⁻¹ with respect to the peak intensity appearing at 1570 to 1590 cm ⁻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 ensure a sufficient coating amount of amorphous carbon. Moreover, since an irreversible capacity | capacitance will increase if there is too much coating amount of amorphous carbon, R value is 0.6 or less. Such graphite B uses, for example, natural graphite having d ₀₀₂ of 0.338 nm or less or graphite obtained by spherically shaping artificial graphite as a base material (base particle), and the surface thereof is coated with an organic compound. It can be obtained by calcining at 0 ° C., pulverizing, and sizing through a sieve. The organic compound covering the base material includes aromatic hydrocarbons; tars or pitches obtained by polycondensation of aromatic hydrocarbons under heat and pressure; tars mainly composed of a mixture of aromatic hydrocarbons. , Pitch or asphalt; In order to coat the base material with the organic compound, a method of impregnating and kneading the base material into the organic compound can be employed. Alternatively, graphite B can 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 μm or less, and graphite B has an average particle size of 15 μm or less. By using artificial graphite A and graphite B of such a size together, the permeability of the non-aqueous electrolyte into the negative electrode (negative electrode mixture layer) is improved. The reason for this is not clear, but when artificial graphite A and graphite B, which is relatively small and has amorphous carbon on the surface as described above, are used in combination, the negative electrode composite can be obtained by performing a press treatment during the production of the negative electrode. Since the size of the pores formed in the agent layer is made uniform, it is presumed that the nonaqueous electrolyte solution is likely to penetrate. In addition, by using artificial graphite A and graphite B having a relatively small particle size as described above, the lithium ion acceptability of the negative electrode is increased, and the charge / discharge cycle characteristics of the lithium ion secondary battery at high temperatures. In addition, the charging characteristics at low temperatures can be improved.

  In addition, since the specific surface area will increase excessively (the irreversible capacity | capacitance will increase) if the particle size of artificial graphite A is too small, it is preferable that the particle size is not so small. Therefore, in the present invention, artificial graphite A having an average particle diameter of more than 15 μm is used. In addition, if the particle size of graphite B is too small, the coating amount of amorphous carbon covering the surface varies, and there are reasons that the features of graphite B cannot be fully exhibited. It is preferable not to be too small. Therefore, in the present invention, graphite B having an average particle diameter of 8 μm or more is used.

  The average particle size of graphite (artificial graphite A, graphite B, and graphite other than these) referred to in the present specification is, for example, a laser scattering particle size distribution meter (for example, Nikkiso Co., Ltd. Microtrac particle size distribution measuring device “HRA9320”). When the integral volume is obtained from particles having a small particle size distribution measured by dispersing graphite in a medium that does not dissolve or swell graphite, the value of 50% diameter in the volume-based cumulative fraction (D50%) The median diameter.

The specific surface area of artificial graphite A and graphite B (according to the BET method. An example of the apparatus is “Bell Soap Mini” manufactured by Nippon Bell Co., Ltd.) is preferably 1.0 m ² / g or more, and 5.0 m ^2. / G or less is preferable.

  The negative electrode active material includes negative electrode active materials other than artificial graphite A and graphite B (for example, graphite having the same particle size as artificial graphite A and having an average particle size of less than 15 μm or more than 25 μm, It is also possible to use artificial graphite A and graphite B) together with artificial graphite A and graphite B.

  From the viewpoint of further enhancing the injectability of the non-aqueous electrolyte in the battery, the charge / discharge cycle characteristics at high temperatures and the charge characteristics at low temperatures, the content of graphite B in the total negative electrode active material contained in the negative electrode is 20 The content is preferably at least mass%, more preferably at least 30 mass%. In addition, the surface of graphite B, which is coated with amorphous carbon on the surface of graphite, has a relatively hard surface. Therefore, if it is excessively added and subjected to press treatment, problems such as destruction of particles of artificial graphite A may occur. There is. Therefore, the content of graphite B in all negative electrode active materials contained in the negative electrode is preferably 60% by mass or less, and more preferably 50% by mass or less.

  Moreover, when using negative electrode active materials other than artificial graphite A and graphite B as a negative electrode active material, a negative electrode contains from a viewpoint of ensuring the said effect by using artificial graphite A and graphite B favorably. The total content of artificial graphite A and graphite B in the total negative electrode active material is preferably 50% by mass or more (that is, negative electrode actives other than graphite A and graphite B in the total negative electrode active material contained in the negative electrode) The content of the substance is preferably 50% by mass or less).

  Examples of the binder relating to the negative electrode include, but are not limited to, a fluororesin such as polyvinylidene fluoride (PVDF), a cellulose ether compound, and a rubber binder. Specific examples of the cellulose ether compound include carboxymethyl cellulose (CMC), carboxyethyl cellulose, hydroxyethyl cellulose, alkali metal salts such as lithium salts, sodium salts, and potassium salts, ammonium salts, and the like. Specific examples of rubber binders include, for example, styrene / conjugated diene copolymers such as styrene / butadiene copolymer rubber (SBR); nitrile / conjugated diene copolymers such as nitrile / butadiene copolymer rubber (NBR). Rubber; Silicone rubber such as polyorganosiloxane; Polymer of alkyl acrylate ester; Acrylic obtained by copolymerization of alkyl acrylate ester with ethylenically unsaturated carboxylic acid and / or other ethylenically unsaturated monomers Rubber; fluororubber 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 conductive aids include acetylene black; ketjen black; carbon blacks such as channel black, furnace black, lamp black, and thermal black; carbon materials such as carbon fibers; and conductive fibers such as metal fibers. Carbon fluoride, metal powders such as copper and nickel, organic conductive materials such as polyphenylene derivatives, and the like. These may be used alone or in combination of two or more. . Among these, acetylene black, ketjen black and carbon fiber are particularly preferable.

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

  The lead portion on the negative electrode side is usually provided by leaving the exposed portion of the current collector without forming the negative electrode mixture layer on a part of the current collector and forming the lead portion at the time of preparing the negative electrode. However, the lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting a copper foil or the like to the current collector later.

The thickness of the negative electrode mixture layer (when formed on both sides of the current collector, the thickness per side) is preferably 50 to 150 μm. Moreover, as a composition of a negative mix layer, it is preferable that content of a negative electrode active material is 90-99 mass%, and it is preferable that content of a binder is 1-10 mass%. Furthermore, when the negative electrode mixture layer contains a conductive additive, the content of the conductive additive in the negative electrode mixture layer is preferably 10% by mass or less from the viewpoint of increasing the capacity. If the density of the negative electrode mixture layer is too low, the capacity of the battery cannot be increased, and charge / discharge cycle characteristics at sufficiently high temperatures and charging characteristics at low temperatures cannot be obtained. For reasons such as reducing the amount of impregnation of the electrolytic solution, it is 1.55 g / cm ³ or more, more preferably 1.58 g / cm ³ or more. Moreover, it is 1.8 g / cm < ³ > or less, More preferably, it is 1.7 g / cm < ³ > or less.
In addition, the density of the negative mix layer prescribed | regulated here is a density of the part in which the negative mix layer is formed in both surfaces of a collector. The density of the negative electrode mixture layer is determined by measuring the mass and thickness of the negative electrode cut into an arbitrary size (for example, 5 × 5 cm square) with a balance or a micrometer, and subtracting the mass and thickness of the current collector from these values. Calculated by dividing the mass per unit area of the negative electrode composite layer (eg, g / cm ² , g / mm ^2, etc.) by the thickness of the negative electrode composite layer (thickness per side of the current collector). The

  There is no restriction | limiting in particular about the separator which concerns on the lithium ion secondary battery of this invention, What is used for the well-known lithium ion secondary battery is applicable. 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 open area ratio of 30 to 70%, a polyethylene polypropylene composite film (polyethylene polypropylene composite) A microporous membrane) is preferably used.

  In addition, the separator according to the lithium ion secondary battery of the present invention includes a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin and a porous body mainly including a filler having a heat resistant temperature of 150 ° C. or higher. A laminated separator having the porous layer (II) can be used. By using such a separator, the safety (safety in a high temperature environment) of the lithium ion secondary battery can be improved, and the non-alignment in the lithium ion secondary battery can be achieved by adjusting the arrangement of the separator. The injectability of the water electrolyte can be further enhanced.

  The porous layer (I) related to the multilayer separator is mainly for ensuring a shutdown function. When the temperature of the lithium ion secondary battery reaches or exceeds the melting point of the thermoplastic resin (hereinafter referred to as “resin (A)”), which is the main component of the porous layer (I), the porous layer (I) The resin (A) melts and closes the pores of the separator, thereby causing a shutdown that suppresses the progress of the electrochemical reaction.

  In addition, the porous layer (II) according to the laminated 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. However, its function is secured by a filler of 150 ° C. or higher. That is, when the battery becomes hot, even if the porous layer (I) shrinks, the porous layer (II) that does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally contracted. It is possible to prevent a short circuit due to the contact. In the case where the porous layer (I) and the porous layer (II) are integrated as will be described later, the heat-resistant porous layer (II) acts as a skeleton of the separator, and is porous. The thermal contraction of the layer (I), that is, the thermal contraction of the entire separator is suppressed.

  The resin (A) related to the porous layer (I) of the separator has electrical insulation properties, is electrochemically stable, and is used for the non-aqueous electrolyte of the battery described in detail later, There is no particular limitation as long as it is a thermoplastic resin that is stable in the solvent used (described later in detail), but polyolefins such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyethylene terephthalate and copolymer Polyester such as polymerized polyester;

  In addition, it is preferable that a separator has the property (namely, shutdown function) which the hole obstruct | occludes in 80 degreeC or more and 150 degrees C or less (more preferably 100 degreeC or more). Therefore, the porous film (I) has a melting point, that is, a melting temperature measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121, more preferably 80 ° C. or more and 150 ° C. or less (more preferably (100 ° C. or higher) thermoplastic resin having a constituent component thereof is more preferable, and it is a single layer microporous film mainly composed of PE or laminated microporous film in which 2 to 5 layers of PE and PP are laminated. A film or the like is preferable.

  As the microporous membrane as described above, for example, a microporous membrane composed of the above-mentioned exemplified thermoplastic resin used in a conventionally known lithium ion secondary battery or the like, that is, a solvent extraction method, dry or wet stretching An ion-permeable microporous membrane produced by a method or the like can be used.

  The content of the resin (A) in the porous layer (I) is preferably as follows, for example, in order to more easily obtain the shutdown effect. The volume of the resin (A) as the main component in all the constituent components of the porous layer (I) (in the entire volume excluding the void portion. The same applies to the content of each component in each layer of the separator) is 50 volumes. % Or more, more preferably 70% by volume or more, and may be 100% by volume. Furthermore, the porosity of the porous layer (II) obtained by the method described later is 20 to 60%, and the volume of the resin (A) is 50% or more of the pore volume of the porous layer (II). Preferably there is.

  The filler related to the porous layer (II) has a heat-resistant temperature of 150 ° C. or higher, is stable with respect to the non-aqueous electrolyte of the battery, and is electrochemically stable that is not easily oxidized or reduced in the battery operating voltage range. Organic particles or inorganic particles may be used as long as they are fine particles, but fine particles are preferable from the viewpoint of dispersion, and inorganic fine particles are more preferably used from the viewpoint of stability (particularly oxidation resistance). Except for the porous substrate described later, “heat-resistant temperature is 150 ° C. or higher” in this specification means that deformation such as softening is not observed at least at 150 ° C.

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 such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or other mineral resource-derived substances or artificial products thereof. In the porous layer (II), the above exemplified filler having a heat resistant temperature of 150 ° C. or more may be used alone or in combination of two or more. Among the fillers having the exemplified heat resistance temperature of 150 ° C. or higher, alumina, silica, and boehmite are preferable.

  The particle size of the filler having a heat resistant temperature of 150 ° C. or higher is an average particle size, and is preferably 0.001 μm or more, more preferably 0.1 μm or more, and preferably 15 μm or less, more preferably 1 μm or less. The average particle diameter of the filler having a heat resistant temperature of 150 ° C. or higher is, for example, a number average measured by dispersing the filler in a medium that does not dissolve, using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). It can be defined as the particle size.

  Moreover, as a form of the filler whose heat-resistant temperature is 150 degreeC or more, for example, it may have a shape close to a sphere or may have a plate shape.

  As the form of the plate-like particles, it is desirable that the aspect ratio is 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 analyzing an image taken with a scanning electron microscope (SEM).

  The amount of filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) is the total volume of the constituent components of the porous layer (II) [However, when using the porous substrate described later, the porous substrate During the entire volume of components excluding. The same applies to the content of each component of the porous layer (II). ], 50% by volume or more, preferably 70% by volume or more, more preferably 80% by volume or more, and still more preferably 90% by volume or more. By making the filler in the porous layer (II) high as described above, the occurrence of a short circuit due to direct contact between the positive electrode and the negative electrode when the lithium ion secondary battery becomes high temperature is improved. In particular, in the case of a separator having a configuration in which the porous layer (I) and the porous layer (II) are integrated, thermal contraction of the entire separator can be satisfactorily suppressed.

  Moreover, the porous layer (II) binds fillers having a heat resistant temperature of 150 ° C. or more, or binds the porous layer (I) and the porous layer (II) as necessary. Therefore, it is preferable to contain an organic binder. From such a viewpoint, the preferred upper limit of the filler amount having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) is, for example, a constituent component of the porous layer (II) Is 99.5% by volume. 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 easily filled with an organic binder, and the function as a separator may be reduced. There is a possibility that the effect of suppressing the heat shrinkage may be reduced due to the excessively large interval.

  The porous layer (II) preferably contains an organic binder in order to ensure the shape stability of the separator and to integrate the porous layer (II) and the porous layer (I). Examples of organic binders include ethylene-vinyl acetate copolymers (EVA, those having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, and fluorine-based binders. Rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, epoxy resin, etc. In particular, a heat-resistant binder having a heat-resistant temperature of 150 ° C. or higher is preferably used. As the organic binder, those exemplified above may be used singly or in combination of two or more.

  Among the organic binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include Mitsui DuPont Polychemical's “Evaflex Series (EVA)”, Nihon Unicar's EVA, Mitsui DuPont Polychemical's “Evaflex-EAA Series (Ethylene). -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

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

  In order to ensure 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 has a heat-resistant temperature of 150 ° C. or higher, has an electrical insulation property, is electrochemically stable, and further uses an electrolyte solution described in detail below and a solvent used in manufacturing a separator. If it is stable, the material is not particularly limited.

  Further, a porous substrate (porous substrate having a heat resistant temperature of 150 ° C. or higher) made of a fibrous material can be used for the porous layer (II). The “heat resistance” of the porous substrate means that a substantial dimensional change due to softening or the like does not occur, and the change in the length of the object, that is, the porous substrate with respect to the length at room temperature. The heat resistance is evaluated based on whether or not the upper limit temperature (heat resistance temperature) at which the shrinkage ratio (shrinkage ratio) can be maintained at 5% or less is sufficiently higher than the shutdown temperature of the separator. In order to increase the safety of the battery after shutdown, the porous substrate desirably has a heat resistance temperature that is 20 ° C. or more higher than the shutdown temperature, and more specifically, the heat resistance temperature of the porous substrate is 150 ° C. or more. It is preferable that it is 180 degreeC or more.

  When the porous layer (II) is formed using a porous substrate, it is preferable that all or a part of the filler having a heat resistant temperature of 150 ° C. or higher is present in the voids of the porous substrate. By setting it as such a form, the effect | action of the said filler can be exhibited more effectively.

  The thickness of the separator (the laminated separator and other separators) is preferably 10 to 30 μm.

  In the laminated separator, the thickness of the porous layer (II) [when the separator has a plurality of porous layers (II), the total thickness] From the viewpoint of exhibiting effectively, it is preferably 3 μm or more. However, if the porous layer (II) is too thick, the energy density of the battery may be lowered. Therefore, the thickness of the porous layer (II) is preferably 8 μm or less.

  The thickness of the porous layer (I) [when the separator has a plurality of porous layers (I), the total thickness thereof. same as below. ] Is preferably 6 μm or more, more preferably 10 μm or more, from the viewpoint of more effectively exerting the above-described action (particularly the shutdown action) due to the 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 may be lowered. In addition, the force that the porous layer (I) tends to shrink by heat increases. In the configuration in which the layer (I) and the porous layer (II) are integrated, the action of suppressing the thermal contraction of the entire separator may be reduced. Therefore, the thickness of the porous layer (I) is preferably 25 μm or less, more preferably 20 μm or less, and further preferably 14 μm or less.

  The porosity of the separator as a whole is preferably 30% or more in a dried state in order to secure the amount of electrolyte solution retained and to improve ion permeability. On the other hand, from the viewpoint of securing separator strength and preventing internal short circuit, the separator porosity is preferably 70% or less in a dry state. Note that the porosity of the separator: P (%) can be calculated by calculating the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following equation (2).

P = {1- (m / t) / (Σa _i · ρ _i )} × 100 (2)

Here, in the formula (2), a _i : the ratio of component i when the total mass is 1, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (G / cm ² ), t: thickness of separator (cm). The mass m per unit area of the separator is a mass obtained by measuring the mass of a separator cut out in a 20 cm square with an electronic balance and calculating the mass per 1 cm ^2. The thickness t of the separator is 10 randomly with a micrometer. It is obtained by measuring the thickness of the measurement points at the points and averaging them.

In the laminated separator, in the formula (2), m is the mass per unit area (g / cm ² ) of the porous layer (I), and t is the thickness of the porous layer (I) ( cm), the porosity: P (%) of the porous layer (I) can also be obtained using the formula (2). The porosity of the porous layer (I) determined by this method is preferably 30 to 70%.

Furthermore, in the laminated separator, in the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (II), and t is the thickness of the porous layer (II) ( cm), the porosity: P (%) of the porous layer (II) can also be obtained using the 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 according to JIS P 8117, and has a Gurley value of 10 to 300 sec indicated by the number of seconds that 100 ml of air passes through the membrane under a pressure of 0.879 g / mm ^2. It is desirable that If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. By employ | adopting the said structure, it can be set as the separator which has the said air permeability.

  The average pore diameter of the separator (the laminated separator and other separators) is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less. . In the case of the laminated separator, the porous layer (I) preferably has an average pore size of 0.01 to 0.5 μm, and the porous layer (II) has an average pore size of 0.05 to 1 μm. Preferably there is.

  The separator according to the present invention preferably has a heat shrinkage rate at 150 ° C. of 5% or less. If the separator has such characteristics, even when the inside of the battery reaches about 150 ° C., the separator hardly contracts, so that a short circuit due to contact between the positive and negative electrodes can be prevented more reliably, and the battery at high temperature The safety of the can be further increased. By adopting the structure shown above for the laminated separator, the separator having the heat shrinkage rate as described above can be obtained.

  When the porous layer (I) and the porous layer (II) are integrated, the heat shrinkage here refers to the shrinkage rate of the integrated separator as a whole, and the porous layer (I) and the porous layer (I) When the layer (II) is independent, the value of the smaller shrinkage rate is indicated. As will be described later, the porous layer (I) and / or the porous layer (II) can be integrated with the electrode. In that case, the measurement was performed in an integrated state with the electrode. Refers to heat shrinkage.

  The “150 ° C. heat shrinkage rate” means that the separator or the porous layer (I) and the porous layer (II) (when integrated with the electrode, in an integrated state with the electrode) , The temperature is raised to 150 ° C. and left for 3 hours, then taken out, and the dimensions required by comparing with the dimensions of the separator or porous layer (I) and porous layer (II) before being put in the thermostatic bath The percentage of decrease is expressed as a percentage.

  Note that the porous layer (I) and the porous layer (II) do not have to be one each, and a plurality of layers may be present in the separator. For example, a configuration in which the porous layer (I) is disposed on both sides of the porous layer (II) or a configuration in which the porous layer (II) is disposed on both sides of the porous layer (I) may be employed. However, increasing the number of layers may increase the thickness of the separator, leading to an increase in the internal resistance of the lithium ion secondary battery and a decrease in energy density, so it is not preferable to increase the number of layers in the separator. The total number of the porous layers (I) and (II) is preferably 5 or less.

  As a positive electrode which concerns on the lithium ion secondary battery of this invention, what formed the positive mix layer containing a positive electrode active material in the single side | surface or both surfaces of a collector is mentioned, for example. In addition to the positive electrode active material, the positive electrode mixture layer contains a binder and, if necessary, a conductive additive, and includes, for example, a positive electrode active material and a binder (and further a conductive additive). Applying a suitable solvent to the mixture (positive electrode mixture) and thoroughly kneading the resulting mixture (slurry, etc.) on the surface of the current collector, followed by drying to obtain a desired thickness Can be formed. In addition, the negative electrode after the positive electrode mixture layer is formed may be subjected to press treatment as necessary to adjust the thickness and density of the positive electrode mixture layer.

As the positive electrode active material, a conventionally known positive electrode active material for a lithium ion secondary battery, for example, an active material capable of inserting and extracting lithium ions is used. As a specific example of such a positive electrode active material, for example, a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.) Lithium-containing transition metal oxide, LiMn ₂ O ₄ and spinel-structured lithium manganese oxide obtained by substituting some of its elements with other elements, LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.) Type compounds. Specific examples of the lithium-containing transition metal oxide having the layered structure include LiCoO ₂ and other oxides including 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.). In particular, when the lithium ion secondary battery is charged at a higher end voltage than usual before its use, in order to increase the stability of the positive electrode active material in a state charged at a high voltage, It is preferable that the various active materials exemplified above further contain a stabilizing element. Examples of such stabilizing elements include Mg, Ak, Ti, Zr, Mo, and Sn.

  As the binder for the positive electrode mixture layer, those conventionally used as positive electrode binders are suitably employed. For example, selected from the group consisting of acrylonitrile, acrylate esters (methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc.) and methacrylate esters (methyl methacrylate, ethyl methacrylate, butyl methacrylate, etc.) A copolymer formed of two or more monomers including at least one monomer; a hydrogenated nitrile rubber; a polyvinylidene fluoride (PVDF); a vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE); a vinylidene fluoride— Tetrafluoroethylene copolymer (VDF-TFE); vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE); and the like.

  Examples of the conductive assistant include graphites such as natural graphite (flaky graphite and the like) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; It is preferable to use carbon materials such as carbon fibers; 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; organic conductive materials such as polyphenylene derivatives;

  Further, as the positive electrode current collector, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used, but usually an aluminum foil having a thickness of 10 to 30 μm is preferably used.

  Similarly to the lead part of the negative electrode, the lead part on the positive electrode side usually leaves an exposed part of the current collector without forming a positive electrode mixture layer on a part of the current collector during the preparation of the positive electrode, To be provided. However, the lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting an aluminum foil or the like to the current collector later.

  The thickness of the positive electrode mixture layer (when formed on both sides of the current collector, the thickness per side) is preferably 50 to 150 μm. Moreover, as a composition of a positive mix layer, it is preferable that content of a positive electrode active material is 90-98 mass%, and it is preferable that content of a binder is 1-7 mass%, and a conductive support agent. The content of is preferably 1 to 8% by mass.

  The positive electrode having the positive electrode mixture layer and the negative electrode having the negative electrode mixture layer as described above are obtained by dispersing the positive electrode mixture in a solvent such as N-methyl-2-pyrrolidone (NMP) as described above. A composition for forming a positive electrode mixture layer (slurry or the like) or a composition for forming a negative electrode mixture layer (slurry or the like) obtained by dispersing the negative electrode mixture in a solvent such as NMP or water is applied to the surface of the current collector, It is produced by drying. In this case, for example, the positive electrode mixture layer-forming composition is applied to the current collector surface, and the porous layer (II) -forming composition is applied before the composition is dried. Prepared by applying an integrated material with layer (II) or a composition for forming a negative electrode mixture layer to the surface of the current collector, and applying the composition for forming porous layer (II) before the composition is dried A lithium ion secondary battery can also be configured using an integrated product of the negative electrode and the porous layer (II).

  In the lithium ion secondary battery of the present invention, the positive electrode and the negative electrode are overlapped with a separator interposed therebetween, wound in a spiral shape, and further shaped into a flat cross-section. Used in the form of a rotating electrode body.

  In addition, when using the said laminated separator for a separator, it is preferable to arrange | position so that the porous layer (II) may oppose a positive electrode, and to form a flat wound electrode body. In the laminated separator, since the porous layer (II) mainly contains a filler having a heat resistant temperature of 150 ° C. or higher, the porous layer (II) is rough and the nonaqueous electrolytic solution easily permeates. The positive electrode mixture layer related to the positive electrode is generally more easily penetrated by the non-aqueous electrolyte than the negative electrode mixture layer related to the negative electrode due to the types of constituent materials thereof, and the positive electrode (positive electrode mixture layer) and the porous layer. By facing (II), this location becomes a non-aqueous electrolyte flow path, so that the entire flat wound electrode body whose size is increased for use in an outer can with a large internal volume The time for the water electrolyte to penetrate can be further shortened. Therefore, in the lithium ion secondary battery of the present invention, when the laminated separator is employed and the flat wound electrode body is formed so that the porous layer (II) faces the positive electrode, The non-aqueous electrolysis is combined with the effect of improving the permeability of the non-aqueous electrolyte into the negative electrode (in the negative electrode mixture layer) by using artificial graphite A and graphite B together as the negative electrode active material. It becomes possible to improve the injection | pouring property of a liquid highly.

As the non-aqueous electrolyte solution according 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 dissociates in a solvent to form Li ⁺ ions and hardly causes side reactions such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-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 Sulfites such as ethylene glycol sulfite; etc., and these should be used as a mixture of two or more. It can be. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, for the purpose of improving safety such as improvement of charge / discharge cycle characteristics, high-temperature storage property and prevention of overcharge, these electrolytic solutions have acid anhydrides, sulfonic acid esters, dinitriles, vinylene carbonates, 1,3-propanesulphate. Ton, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, t-butylbenzene and other additives (including these derivatives) can also be added as appropriate.

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

The lithium ion secondary battery of the present invention contains a nitrile compound containing at least one LiBF ₄ (lithium borofluoride) and a cyano group when the upper limit voltage of the battery is set to 4.35 V or more, particularly 4.4 V or more. It is preferable to use a nonaqueous electrolytic solution.

Specific examples of the nitrile compound include acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, acrylonitrile, lauronitrile, and other mononitriles; malononitrile, 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-dicyanooctane, 2, Dinitriles such as 7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, 2,4-dimethylglutaronitrile; cyclic nitriles such as benzonitrile; Alkoxy substituted nitriles such as methoxyacetonitrile; and the like, and only one of these may be used, or two or more may be used in combination.

  Among the exemplified nitrile compounds, dinitriles are preferable, compounds represented by the general formula (1) (succinonitrile, glutaronitrile, adiponitrile) are more preferable, and charging / discharging of the battery by using in combination with other additives A compound (glutaronitrile, adiponitrile) represented by the general formula (1) and n in the general formula (1) is 3 or 4 is more preferable because the effect of improving the cycle characteristics becomes better.

By adding the nitrile compound, high-temperature storage stability and safety can be improved, but there is a problem that the cycle characteristics are deteriorated (particularly when the charge upper limit voltage is high). Therefore, it has been found that by adding LiBF ₄ , a lithium ion secondary battery excellent in cycle characteristics can be provided while ensuring high high-temperature storage and safety. In particular, at least the above-mentioned artificial graphite A having an average particle diameter of more than 15 μm and not more than 25 μm, and graphite B having an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles coated with amorphous carbon It has been found that a more remarkable effect is recognized when used together with the lithium ion secondary battery of the present invention containing as a negative electrode active material for a negative electrode.

A preferable range for obtaining 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. Further, the content of LiBF ₄ in the non-aqueous electrolyte is 0.05 wt% or more and 2.5 wt% or less.

  And since the exterior body used for the lithium ion secondary battery of the present invention uses a flat wound electrode body, for example, a rectangular (square tube) exterior can that can make the battery thinner can be used. can do.

  In FIG. 1, the perspective view which represents typically the external appearance of an example of the lithium ion secondary battery of this invention is shown. A lithium ion secondary battery 1 shown in FIG. 1 has a columnar (rectangular tube) battery case 10, and the battery case 10 is hollow and has a flat winding formed of a positive electrode, a negative electrode, and a separator. An electrode body and a non-aqueous electrolyte are accommodated.

  The battery case 10 includes an outer can 11 and a lid 20, and the outer can 11 has a bottomed cylindrical shape (square tube shape), and the lid 20 is covered on the opening end portion thereof. It is integrated with the lid 20 by welding. The outer can 11 and the lid 20 are made of, for example, an aluminum alloy.

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

  The side surface portion of the battery case 10, that is, the side surface portion of the outer can 11 has two wide surfaces 111 and 111 that are opposed to each other and wider than the other surfaces (surfaces 112 and 112 in the drawing). doing. At least one of the wide surfaces 111 and 111 (in FIG. 1, the wide surface 111 at the front in the drawing) is provided with a cleavage groove 12 for cleavage when the pressure in the battery case 10 becomes greater than a threshold value. ing.

  FIG. 2 shows a side view of the battery case 10 of the lithium ion secondary battery shown in FIG. 1 as viewed from the wide surface 111 side. As shown in FIG. 2, the cleavage groove 12 is provided so as to intersect with a diagonal line (indicated by a one-dot chain line in the figure) in a side view from the wide surface 111 side. The diagonal line is drawn from the end of the battery case 10 when the side surface of the battery case 10 is viewed from the side of the wide surface 11 as viewed in a side view as a two-dimensional shape.

  As shown in FIGS. 1 and 2, the battery case (exterior can) according to the lithium ion secondary battery of the present invention has two wide surfaces facing each other on its side surface, and the battery case It is preferable that a cleavage groove that is to be cleaved when the pressure in the battery case becomes larger than a threshold value is provided on the side surface portion so as to intersect a diagonal line in a side view from the wide surface side.

  In conventional lithium ion secondary batteries, a lid is usually provided with a cleavage vent, and when the internal pressure rises due to the battery being placed at an excessively high temperature, the cleavage vent is cleaved to release the internal gas to the outside. Safety is ensured by discharging and reducing internal pressure to prevent battery rupture. However, in the case of using a lithium-containing composite oxide containing Ni as a positive electrode active material or in a lithium ion secondary battery that has been increased in capacity by being charged to a voltage exceeding 4.30 V, an excessively high temperature is required. When placed underneath, the reactivity of the lithium-containing composite oxide is high, so there is a concern that the internal pressure of the battery suddenly rises and ruptures before the operation of the cleavage vent provided on the lid.

  Therefore, as shown in FIGS. 1 and 2, the side surface of the battery case is provided with a cleavage groove that is cleaved when the pressure in the battery case becomes larger than a threshold value. By providing them so as to intersect with each other, even if the internal pressure of the battery suddenly increases, the cleavage groove is rapidly opened, so that the battery can be prevented from being ruptured in advance. In particular, in a battery having a large outer can with a large internal volume, such as an outer can preferably used in the lithium ion secondary battery of the present invention, safety by providing the above-mentioned cleavage groove on the side surface of the battery case. The effect of improving the property is significantly exhibited as compared with a battery having a battery case of a smaller size.

  Moreover, the battery of this invention can also use the exterior body which consists of a laminate film which formed the resin layer in the single side | surface or both surfaces of a metal layer other than the said exterior can.

In the outer package according to the lithium ion secondary battery of the present invention, the internal volume is preferably 10 cm ³ or more, and in this case, the effects of the present invention are remarkably exhibited. Moreover, as a concrete external shape of the exterior body which concerns on this invention, it is preferable that width W is 50 mm or more and height H is 55 mm or more. The width W of the exterior body is preferably 300 mm or less, and more preferably 80 mm or less. Further, the height H of the outer package is preferably 500 mm or less, and more preferably 100 mm or less. Furthermore, the thickness T of the exterior body may be set to the same value or less as the width W, for example.

  Since the lithium ion secondary battery of the present invention is excellent in charge / discharge cycle characteristics at high temperatures and charging characteristics at low temperatures, it is known in the art, including power supply applications for devices used in a wide temperature environment. It can be preferably used in the same applications as various applications to which lithium ion secondary batteries are applied.

  In addition, the lithium ion secondary battery of the present invention is used with an upper limit voltage of charging of 4.3 V or higher, and thus, by setting the upper limit voltage of charging higher than usual, the capacity can be increased. However, even if it is repeatedly used over a long period of time, it is possible to stably exhibit excellent characteristics. In addition, it is preferable that the upper limit voltage of charge of a lithium ion secondary battery is 4.5V or less.

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

Example 1
<Production of negative electrode>
The average particle diameter D50% is 22 _{.mu.m, d 002} is 0.338 nm, specific surface area by BET method at 3.8 m ² / g, graphite A1 (surface amorphous R value in the argon ion laser Raman spectrum is 0.12 and artificial graphite) which is not covered with quality carbon, the average particle diameter D50% is 10 [mu] _{m, d 002} is 0.336 nm, specific surface area by BET method at 3.9 m ² / g, the R values in the argon ion laser Raman spectrum 98 parts by mass of a mixture obtained by mixing graphite B1 (graphite whose surface of mother particles made of graphite is coated with amorphous carbon using pitch as a carbon source) at a mass ratio of 50:50, which is 0.40, CMC: 1.0 part by mass and SBR: 1.0 part by mass were mixed with ion-exchanged water to prepare an aqueous negative electrode mixture-containing paste.

The negative electrode mixture-containing paste is intermittently applied to both sides of a 6 μm-thick current collector made of copper foil, dried, and calendered to give a coating layer density of 1.58 g / cm. ^The negative electrode mixture layer was adjusted to have a thickness of ³ to obtain a negative electrode. The negative electrode was cut to a width of 53 mm, and a tab was welded to the exposed portion of the copper foil to form a lead portion.

<Preparation of positive electrode>
LiCo _0.98 Al _0.008 Mg _0.008 Ti _0.004 O _{2 as} a positive electrode active material: 97.0 parts by mass, acetylene black as a conductive auxiliary agent: 1.5 parts by mass, and PVDF as a binder: 1.5 parts by mass was mixed with NMP as a solvent so as to be uniform to prepare a positive electrode mixture-containing paste. This paste is intermittently applied to both sides of a 12 μm thick aluminum foil serving as a current collector, dried, and then subjected to calendering so that the coating film density of the mixture layer becomes 3.80 g / cm ^3. The thickness of the positive electrode mixture layer was adjusted and cut to a width of 52 mm to produce a positive electrode. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

<Preparation of separator>
Add 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40%) to 5 kg of secondary aggregate boehmite, and use a ball mill for 20 hours with an internal volume of 20 L and a rotation speed of 40 times / minute for 10 hours. A dispersion was prepared by crushing treatment. The treated dispersion was vacuum-dried at 120 ° C. and observed by SEM. As a result, the shape of boehmite was almost plate-like. Moreover, when the average particle diameter (D50%) of boehmite was measured as refractive index 1.65 using the laser scattering particle size distribution analyzer ("LA-920" by HORIBA), it was 1.0 micrometer.

  To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added and stirred with a three-one motor for 3 hours to form a uniform slurry. [Porous layer (II) forming slurry a, solid content ratio 50 mass%] was prepared.

PE microporous separator for lithium ion secondary battery [Porous layer (I): thickness 8 μm, porosity 40%, average pore diameter 0.02 μm, PE melting point 135 ° C.] on one side corona discharge treatment (discharge amount) 40 W · min / m ² ) was applied, and the slurry a for forming the porous layer (II) was applied to the treated surface with a microgravure coater and dried to form a porous layer (II) to obtain a separator. The thickness of the porous layer (II) was adjusted to 4 μm. The boehmite content in the total volume of the constituent components of the porous layer (II) was 88% by volume.

<Battery assembly>
The positive electrode, the negative electrode, and the separator obtained as described above were overlapped with the porous layer (II) facing the positive electrode, and wound in a spiral shape to produce a wound electrode body. The obtained wound electrode body was crushed into a flat shape, placed in an aluminum outer can (inner volume: 10 cm ³ ) having a thickness of 4 mm, a height of 58 mm, and a width of 51 mm, and a non-aqueous electrolyte E1 (electrolyte composition: ethylene carbonate) LiPF ₆ was dissolved to a concentration of 1.1 mol / l in a solvent prepared by mixing ethanol, ethyl methyl carbonate and diethyl carbonate in a volume ratio = 1: 1: 1, and 4-fluoro-1,3-dioxolane- 2-one is added at 1.5% by mass, vinylene carbonate is added at 2.0% by mass, and 2-propynyl 2- (diethoxyphosphoryl) acetate is added in an amount of 1.5% by mass) after sealing. Stop,
A lithium ion secondary battery having the structure shown in FIG. 3 and the appearance shown in FIGS. 1 and 2 was produced. This battery is provided with a cleavage vent for lowering the pressure when the internal pressure rises on the wide side surface of the outer can.

  Here, the lithium ion secondary battery will be described with reference to FIG. 1, FIG. 2, and FIG. 3. The lithium ion secondary battery is the wide surface 111 side of the side surface portion of the battery case 10 (exterior can 11). It has the cleavage groove | channel 12 so that it may cross | intersect the diagonal in the side view from. The cleavage groove 12 includes an inwardly curved portion 121 that protrudes in a projecting manner toward the inner side surface of the battery case 10 and an outwardly curved portion 122 that curves in a projecting manner toward the outer side surface of the battery case 10. The inwardly curved portion 121 and the outwardly curved portion 122 have a semicircular shape having substantially the same size, and constitute a substantially S-shaped tear line having one by one. . And the connection part of the inward bending part 121 and the outward bending part 122 is installed so that it may become a location equivalent to the diagonal in the side view from the wide surface 111 side of the side part of the battery case 10 (exterior can 11). Has been. In addition, the cleavage groove 12 was formed such that the depth of the portion located on the diagonal line in the side view from the wide surface 111 side of the side surface portion of the battery case 10 (exterior can 11) was deeper than the other portions.

  In addition, as shown in FIG. 3, the lithium ion secondary battery has a positive electrode 31 and a negative electrode 32 wound in a spiral shape through the separator 33 as described above, and then pressed so as to become flat. The spirally wound electrode body 30 is accommodated in a rectangular tube-shaped outer can 11 together with a non-aqueous electrolyte. However, in FIG. 3, in order to avoid complication, a metal foil, a non-aqueous electrolyte, or the like as a current collector used for manufacturing the positive electrode 31 and the negative electrode 32 is not illustrated. Also, the separator layers are not shown separately. Furthermore, the inner peripheral side portion of the wound electrode body is not cross-sectional.

  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 electrode terminal. A positive electrode lead body 51 and a negative electrode lead body 52 connected to one end of each of the positive electrode 31 and the negative electrode 32 are drawn out from the flat wound electrode body 30 including the positive electrode 31, the negative electrode 32, and the separator 33. A stainless steel terminal 21 is attached to an aluminum alloy lid (sealing lid plate) 20 that seals the opening of the outer can 11 via a PP insulating packing 22. A stainless steel lead plate 25 is attached via an insulator 24.

  And this cover 20 is inserted in the opening part of the armored can 11, and the opening part of the armored can 11 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 3, the lid 20 is provided with a non-aqueous electrolyte inlet, and a sealing member 23 is inserted into the non-aqueous electrolyte inlet, for example, by laser welding or the like. Sealing of the battery is ensured by welding sealing.

  In the battery of Example 1, the outer can 11 and the lid body 20 function as a positive electrode terminal by directly welding the positive electrode lead body 51 to the lid body 20, and the negative electrode lead body 52 is welded to the lead plate 25. By connecting the negative electrode lead body 52 and the terminal 21 through the lead plate 25, the terminal 21 functions as a negative electrode terminal.

Example 2
Instead of graphite B1, average particle diameter D50% is 15 [mu] _{m, d 002} is 0.336 nm, specific surface area by BET method at 3.5 m ² / g, graphite R value in the argon ion laser Raman spectrum is 0.33 A negative electrode was prepared in the same manner as in Example 1 except that B2 (graphite whose surface was coated with amorphous carbon using pitch as a carbon source) was used, and this negative electrode was used. Produced a lithium ion secondary battery in the same manner as in Example 1.

Example 3
A spirally wound electrode body was prepared in the same manner as in Example 2 except that the separator was disposed so that the porous layer (II) was directed to the negative electrode side, and the same as in Example 2 except that this spirally wound electrode body was used. Thus, a lithium ion secondary battery was produced.

Example 4
A negative electrode was produced in the same manner as in Example 1 except that a mixture in which graphite A1 and graphite B1 were mixed at a mass ratio of 33:67 was used, and lithium was produced in the same manner as in Example 1 except that this negative electrode was used. An ion secondary battery was produced.

Example 5
A negative electrode was produced in the same manner as in Example 1 except that a mixture in which graphite A1 and graphite B1 were mixed at a mass ratio of 60:40 was used, and lithium was produced in the same manner as in Example 1 except that this negative electrode was used. An ion secondary battery was produced.

Example 6
Instead of the graphite A1, average particle size D50% is 18 [mu] _{m, d 002} is 0.338 nm, specific surface area by BET method at 3.9 m ² / g, graphite R value in the argon ion laser Raman spectrum is 0.14 A negative electrode was produced in the same manner as in Example 1 except that A2 (artificial graphite whose surface was not coated with amorphous carbon) was used. Lithium ions were produced in the same manner as in Example 1 except that this negative electrode was used. A secondary battery was produced.

Comparative Example 1
Instead of graphite B1, average particle diameter D50% is 20 [mu] _{m, d 002} is 0.336 nm, specific surface area by BET method at 3.7 m ² / g, graphite R value in the argon ion laser Raman spectrum is 0.33 A negative electrode was produced in the same manner as in Example 1 except that C1 (graphite in which the surface of mother particles made of graphite was coated with amorphous carbon using pitch as a carbon source) was used, and this negative electrode was used. Produced a lithium ion secondary battery in the same manner as in Example 1.

  About the lithium ion secondary battery of Examples 1-3 and the comparative example 1, the following liquid-injection property test and the charging / discharging cycle test under 45 degreeC were done.

<Liquid injection test>
For each of the examples and comparative examples, the non-aqueous electrolyte was injected and sealed simply by putting the flat wound electrode body into an aluminum outer can and covering it with a lid while welding the battery. 10 pieces were prepared in a non-existing state, and these were immersed in a bath filled with a non-aqueous electrolyte having the same composition as that used for the production of each battery, and evacuated for 90 seconds (the ultimate vacuum was -98 kPa). Then, the non-aqueous electrolyte was allowed to enter the inside of the battery case from each non-aqueous electrolyte inlet. Then, after releasing the vacuum, each of the examples and comparative examples is taken out from the non-aqueous electrolyte bath at every arbitrary time, and the amount of liquid injected is obtained by measuring the mass of the battery case (the amount of liquid injected = the amount extracted). From the subsequent battery case mass-battery case mass before immersion in the non-aqueous electrolyte), the arrival time at which the predetermined injection amount was injected into the battery case was determined.

<Charge / discharge cycle test at 45 ° C.>
The lithium ion secondary batteries of Examples and Comparative Examples were left in a constant temperature bath at 45 ° C. for 5 hours, and then each battery was charged with a constant current of 1.0 C up to 4.35 V. Then, constant voltage charging was performed at 4.35 V until the current reached 0.05C. Thereafter, discharging was performed at a constant current of 1.0 C until the voltage reached 3.0V. Charging / discharging was repeated with a series of operations of charging and discharging as one cycle, and the number of cycles capable of maintaining 80% or more of the discharge capacity at the first cycle was examined.

  The structure of the negative electrode active material and the form of the outer can according to the negative electrode of each of the lithium ion secondary batteries of Examples 1 to 6 and Comparative Example 1 are shown in Table 1, and each of the evaluation results and the current value during 1C charge / discharge Is shown in Table 2. In Table 2, “Number of cycles” in “Charge / discharge cycle test at 45 ° C.” means the number of cycles that can maintain a discharge capacity of 80% or more of the discharge capacity (initial capacity) of the first cycle. (The same applies to Tables 3 and 6 below.)

  As shown in Table 1 and Table 2, the lithium ion secondary batteries of Examples 1 to 6 in which graphite A and graphite B were used in combination as negative electrode active materials were compared with the battery of Comparative Example 1 that did not use graphite B. Even when an exterior can with a short non-aqueous electrolyte injection time and a large width and height was used, excellent non-aqueous electrolyte injection properties could be secured and high productivity was obtained. In the lithium ion secondary batteries of Examples 2 and 3 having the same configuration except that the electrode facing the porous layer (II) according to the separator was changed, the porous layer (II) was directed to the positive electrode side. The battery of Example 2 had a shorter productivity and higher productivity than the battery of Example 3 in which the battery was directed to the negative electrode side.

  Moreover, the lithium ion secondary battery of Examples 1-6 has many cycles which could maintain the capacity | capacitance of 80% or more of initial capacity at the time of the charge / discharge cycle test in 45 degreeC, and the charge / discharge cycle under high temperature The characteristics were also excellent. 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, the porous layer (II) according to the separator is directed to the positive electrode side, so that the oxidation reaction of the porous layer (I) is performed even under a high voltage such as an upper limit voltage of 4.35 V. This is considered to be because the porous layer (I) could be prevented from locally deteriorating and the local deterioration.

Example 7
<Production of negative electrode>
Graphite A1, graphite B1, average particle diameter D50% is 19 _{.mu.m, d 002} is 0.338 nm, specific surface area by BET method at 3.8 m ² / g, in R value 0.21 in the argon ion laser Raman spectrum Mixture of certain graphite D1 (natural graphite whose surface is not coated with amorphous carbon) at a mass ratio of 30:30:40: 98 parts by mass, CMC: 1.0 part by mass, and SBR: 1 0.0 parts by mass of ion-exchanged water having a specific conductivity of 2.0 × 10 ⁵ Ω / cm or more was mixed as a solvent to prepare an aqueous negative electrode mixture-containing paste.

The negative electrode mixture-containing paste is intermittently applied to both sides of a 6 μm-thick current collector made of copper foil, dried, and calendered to give a coating layer density of 1.58 g / cm. ^The negative electrode mixture layer was adjusted to have a thickness of ³ to obtain a negative electrode. The negative electrode was cut to have a width of 55.5 mm, and a tab was welded to the exposed portion of the copper foil to form a lead portion.

<Preparation of positive electrode>
LiCo _0.98 Al _0.008 Mg _0.008 Ti _0.004 O _{2 as} a positive electrode active material: 97.0 parts by mass, acetylene black as a conductive auxiliary agent: 1.5 parts by mass, and PVDF as a binder: 1.5 parts by mass was mixed with NMP as a solvent so as to be uniform to prepare a positive electrode mixture-containing paste. This paste is intermittently applied to both sides of a 12 μm thick aluminum foil serving as a current collector, dried, and then subjected to calendering so that the coating film density of the mixture layer becomes 3.80 g / cm ^3. The thickness of the positive electrode mixture layer was adjusted to be 54.5 mm in width to produce a positive electrode. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

<Battery assembly>
A flat wound electrode body was prepared in the same manner as in Example 1 except that the negative electrode and the positive electrode were used, and this flat wound electrode body was made of aluminum having a thickness of 5 mm, a height of 61 mm, and a width of 57 mm. A lithium ion secondary battery was produced in the same manner as in Example 1 except that an outer can (internal volume: 15 cm ³ ) was used.

Example 8
A negative electrode was produced in the same manner as in Example 7 except that graphite B2 was used instead of graphite B1, and 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 produced in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B1, and graphite D1 at a mass ratio of 40:20:40 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as Example 7 except for the above.

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

Example 11
A negative electrode was produced in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B1, and graphite D1 at a mass ratio of 20:40:40 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as Example 7 except for the above.

Example 12
A negative electrode was produced in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B1, and graphite D1 at a mass ratio of 30:20:50 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as Example 7 except for the above.

Example 13
A negative electrode was produced in the same manner as in Example 7 except that a mixture obtained by mixing graphite A2, graphite B1, and graphite D1 at a mass ratio of 30:30:40 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as Example 7 except for the above.

Example 14
A negative electrode was produced in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite B1, and graphite D1 at a mass ratio of 40:10:50 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as Example 7 except for the above.

Comparative Example 2
A negative electrode was produced in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite C1, and graphite D1 at a mass ratio of 10:40:50 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as Example 7 except for the above.

Comparative Example 3
A negative electrode was produced in the same manner as in Example 7 except that a mixture obtained by mixing graphite A1, graphite C1, and graphite D1 at a mass ratio of 30:30:40 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as Example 7 except for the above.

Comparative Example 4
Graphite B1, average particle diameter D50% is 35 [mu] _{m, d 002} is 0.338 nm, specific surface area by BET method at 3.6 m ² / g, graphite R value in the argon ion laser Raman spectrum is 0.11 C2 ( A negative electrode was produced in the same manner as in Example 7 except that a mixture of artificial graphite whose surface was not coated with amorphous carbon) and D1 in a mass ratio of 30:30:40 was used. A lithium ion secondary battery was produced in the same manner as in Example 7 except that this negative electrode was used.

Comparative Example 5
Graphite B1, average particle diameter D50% is 10 [mu] _{m, d 002} is 0.338 nm, specific surface area by BET method at 4.5 m ² / g, graphite C3 R value in the argon ion laser Raman spectrum is 0.15 ( A negative electrode was produced in the same manner as in Example 7, except that a mixture of artificial graphite whose surface was not coated with amorphous carbon) and graphite D1 in a mass ratio of 30:30:40 was used. A lithium ion secondary battery was produced in the same manner as in Example 7 except that this negative electrode was used.

Comparative Example 6
A lithium ion secondary battery was produced in the same manner as in Example 7 except that the thickness of the negative electrode mixture layer was adjusted so that the coating film density of the negative electrode mixture layer was 1.45 g / cm ³ .

  For the lithium ion secondary batteries of Examples 7 to 14 and Comparative Examples 2 to 5, a liquid injection test and a charge / discharge cycle test at 45 ° C. were performed in the same manner as the lithium ion secondary battery of Example 1. .

  The structure of the negative electrode active material and the form of the outer can according to the negative electrode of each of the lithium ion secondary batteries of Examples 7 to 14 and Comparative Examples 2 to 5 are shown in Table 3, and each of the evaluation results and the current during 1C charge / discharge Table 4 shows the values.

  As shown in Table 3 and Table 4, artificial graphite A having an average particle diameter of more than 15 μm and 25 μm or less as the negative electrode active material, and an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles are coated with amorphous carbon The lithium ion secondary batteries of Examples 7 to 14 that are used in combination with the graphite B used are the batteries of Comparative Examples 2 and 3 that do not use the graphite B, and the comparative examples 4 and 5 that do not use the graphite A. Compared with the battery of Example 1, the non-aqueous electrolyte injection time is short, and even when an outer can having a larger width and height than that used in Example 1 is used, excellent non-aqueous electrolyte injection It was possible to secure the productivity and high productivity. In addition, the lithium ion secondary batteries of Examples 7 to 14 had many cycles that could maintain a capacity of 80% or more of the initial capacity during the charge / discharge cycle test at 45 ° C., and the charge / discharge cycles at high temperatures. The characteristics were also excellent.

  In addition, among the lithium ion secondary batteries of Examples 7 to 14, the battery of Example 7 having the most excellent charge / discharge cycle characteristics at high temperature and the batteries of Comparative Examples 2, 3, and 6 were described below. A charge acceptance test at −5 ° C. was performed to evaluate the charge characteristics at low temperatures.

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

  Each battery after the discharge was allowed to stand in a thermostatic bath at −5 ° C. for 5 hours, and after that, each battery was charged with a constant current of 0.5 C up to 4.35 V, and reached 4.35 V. Conducted constant voltage charging at 4.35 V until the current reached 0.05C. The charge capacity at this time was defined as a charge capacity at −5 ° C. Then, it left still in a 25 degreeC thermostat for 5 hours, and it discharged until the voltage reached 2.75V with the constant current of 0.2C.

  The series of operations described above is one cycle, and among the charge capacities at −5 ° C. in the fifth cycle, the charge capacities in the constant current charge region and the charge capacities in the constant current charge region among the charge capacities at 25 ° C. The ratio was determined and evaluated as charge acceptability at −5 ° C. (charge characteristics at low temperature). 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 −5 compared to the batteries of Comparative Examples 2 and 3 in which graphite B was not used. The ratio at the time of charge acceptance evaluation at ° C. was high, and the charge characteristics at low temperatures were excellent.

Example 15
A mixture obtained by mixing graphite A1, graphite B1, and graphite D1 at a mass ratio of 30:30:40: 98 parts by mass, CMC: 1.0 part by mass, and SBR: 1.0 part by mass. A water-based negative electrode mixture-containing paste was prepared by mixing 2.0 × 10 ⁵ Ω / cm or more of ion-exchanged water as a solvent.

The negative electrode mixture-containing paste is intermittently applied to both sides of a 6 μm-thick current collector made of copper foil, dried, and calendered to give a coating layer density of 1.58 g / cm. ^The negative electrode mixture layer was adjusted to have a thickness of ³ to obtain a negative electrode. 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.

<Preparation of positive electrode>
LiCo _0.98 Al _0.008 Mg _0.008 Ti _0.004 O _{2 as} a positive electrode active material: 97.0 parts by mass, acetylene black as a conductive auxiliary agent: 1.5 parts by mass, and PVDF as a binder: 1.5 parts by mass was mixed with NMP as a solvent so as to be uniform to prepare a positive electrode mixture-containing paste. This paste is intermittently applied to both sides of a 12 μm thick aluminum foil serving as a current collector, dried, and then subjected to calendering so that the coating film density of the mixture layer becomes 3.80 g / cm ^3. The thickness of the positive electrode mixture layer was adjusted and cut to a width of 70.2 mm to produce a positive electrode. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

<Battery assembly>
A flat wound electrode body was prepared in the same manner as in Example 1 except that the negative electrode and the positive electrode were used. The flat wound electrode body had a thickness of 5.5 mm, a height of 78 mm, and a width of 54 mm. A lithium ion secondary battery was produced in the same manner as in Example 1 except that an aluminum outer can (internal volume: 20 cm ³ ) was used.

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

  For the lithium ion secondary batteries of Example 15 and Comparative Example 6, a liquid injection test and a charge / discharge cycle test at 45 ° C. were performed in the same manner as the lithium ion secondary battery of Example 1.

  The configuration of the negative electrode active material and the form of the outer can according to the negative electrode of each lithium ion secondary battery of Example 15 and Comparative Example 7 are shown in Table 6, and each evaluation result and the current value during 1C charge / discharge are shown in Table 6. 7 shows.

  As shown in Tables 6 and 7, the lithium ion secondary battery of Example 15 that used graphite A and graphite B in combination as the negative electrode active material was non-comparative to the battery of Comparative Example 7 that did not use graphite B. The injection time of the water electrolyte is short, and even when using an outer can whose height is higher than that used in Example 4 etc., excellent injectability of the non-aqueous electrolyte can be secured, and high productivity is achieved. Had. In addition, the lithium ion secondary battery of Example 15 had many cycles that could maintain a capacity of 80% or more of the initial capacity during the charge / discharge cycle test at 45 ° C., and the charge / discharge cycle characteristics at high temperatures were also high. It was excellent.

Example 16
A lithium ion secondary battery was produced in the same manner as in Example 7. (However, the charge / discharge conditions are different from Example 7 as described later.)

Example 17
As the non-aqueous electrolyte, non-aqueous electrolyte E2 (LiPF ₆ was dissolved in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio = 3: 7 to a concentration of 1.1 mol / l, and 4- fluoro-1,3-dioxolan-2-one 1.7 wt%, vinylene carbonate 2.7 weight%, 2-propynyl 2- (diethoxyphosphoryl) acetate 1.2 wt%, a LiBF ₄ 0. A lithium ion secondary battery produced in the same manner as in Example 16 was produced except that 15% by mass and that in which adiponitrile was added in an amount of 0.5% by mass) were used.

Example 18
A negative electrode was produced in the same manner as in Example 16 except that a mixture in which graphite A1 and graphite B1 were mixed at a mass ratio of 50:50 was used as the negative electrode active material. Example 16 was conducted except that this negative electrode was used. In the same manner, a lithium ion secondary battery was produced.

Example 19
A negative electrode was produced in the same manner as in Example 16 except that a mixture in which graphite A1 and graphite B1 were mixed at a mass ratio of 50:50 was used as the negative electrode active material. Example 17 except that this negative electrode was used. In the same manner, a lithium ion secondary battery was produced.

Example 20
A negative electrode was produced in the same manner as in Example 7 except that a mixture obtained by mixing graphite A2, graphite B2, and graphite D1 at a mass ratio of 30:30:40 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was made in the same manner as Example 16 except for the above.

Example 21
A negative electrode was produced in the same manner as in Example 16 except that a mixture obtained by mixing graphite A2, graphite B2, and graphite D1 at a mass ratio of 30:30:40 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as Example 17 except for the above.

Example 22
The nonaqueous electrolytic solution E3 was prepared with the same composition as the nonaqueous electrolytic solution E2 except that succinonitrile was used instead of adiponitrile contained in the nonaqueous electrolytic solution E2. A lithium ion secondary battery was produced in the same manner as in Example 16 except that this non-aqueous electrolyte E3 was used as the non-aqueous electrolyte.

Example 23
The nonaqueous electrolytic solution E4 was prepared with the same composition as the nonaqueous electrolytic solution E2 except that glutaronitrile was used instead of adiponitrile contained in the nonaqueous electrolytic solution E2. A lithium ion secondary battery was produced in the same manner as in Example 16 except that this non-aqueous electrolyte E4 was used as the non-aqueous electrolyte.

Example 24
The nonaqueous electrolytic solution E5 was prepared with the same composition as that of the nonaqueous electrolytic solution E2 except that lauronitrile was used instead of adiponitrile contained in the nonaqueous electrolytic solution E2. A lithium ion secondary battery was produced in the same manner as in Example 16 except that this nonaqueous electrolyte E5 was used as the nonaqueous electrolyte.

Comparative Example 8
A lithium ion secondary battery was produced in the same manner as in Comparative Example 3. (However, the charge / discharge conditions are different from those of Comparative Example 3 as described later.)

Comparative Example 9
A negative electrode was produced in the same manner as in Example 16 except that a mixture obtained by mixing graphite A1, graphite C1, and graphite D1 at a mass ratio of 30:30:40 was used as the negative electrode active material, and this negative electrode was used. A lithium ion secondary battery was produced in the same manner as in Comparative Example 7 except for the above.

<Charge / discharge cycle test at 45 ° C.>
The lithium ion secondary batteries of Examples 16 to 23 and Comparative Examples 8 and 9 were left in a constant temperature bath at 45 ° C. for 5 hours, and then each battery was subjected to a constant current of 1.0 C up to 4.4 V. After charging and reaching 4.4V, constant voltage charging was performed at 4.4V until the current reached 0.05C. Thereafter, discharging was performed at a constant current of 1.0 C until the voltage reached 3.0V. Charging / discharging was repeated with a series of operations of charging and discharging as one cycle, and the number of cycles capable of maintaining 80% or more of the discharge capacity at the first cycle was examined.

  The structure of the negative electrode active material and the form of the outer can according to the negative electrodes of the lithium ion secondary batteries of Examples 16 to 23 and Comparative Examples 8 and 9 are shown in Table 8, and each evaluation result and current during 1C charge / discharge are shown in Table 8. Table 9 shows the values.

As shown in Table 8 and Table 9, artificial graphite A having an average particle diameter of more than 15 μm and not more than 25 μm as the negative electrode active material and an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles are coated with amorphous carbon Lithium ion secondary batteries of Examples 17, 19, 21, 22, 23, and 24, which were used in combination with graphite B, and used an electrolytic solution containing LiBF ₄ and a nitrile compound, used the electrolytic solution E1. The cycle characteristics were even better than the lithium ion secondary battery. On the other hand, in the lithium ion secondary battery of Comparative Example 8 in which no graphite B was used, the cycle characteristics were improved as compared with Comparative Example 9 using the electrolytic solution E2, but the large values seen in Examples 16 to 24 were observed. There was no improvement in cycle characteristics.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 10 Battery case 11 Outer can 111 Wide surface of battery case (outer can) side part 12 Cleavage groove 121 Inwardly curved part 122 Outerly curved part 20 Lid body 30 Flat winding electrode body

Claims (7)

A flat wound electrode body composed of a positive electrode, a negative electrode, and a separator, and a nonaqueous electrolyte solution are lithium ion secondary batteries housed in an exterior body,
The negative electrode has a mixture layer containing at least a negative electrode active material, and the density of the mixture layer is 1.55 g / cm ³ or more,
As the negative electrode active material, artificial graphite A having an average particle diameter of more than 15 μm and 25 μm or less,
It contains at least graphite B having an average particle diameter of 8 μm or more and 15 μm or less, and the surface of the graphite particles coated with amorphous carbon,
R value of the graphite B is 0.3 or more and 0.7 or less,
Wherein said artificial graphite A in the whole anode active material in the negative electrode contains, containing the mass ratio of the graphite B (A / B) is a lithium ion secondary, wherein 0.5-1.5 Der Rukoto Next battery.   2. The lithium ion secondary battery according to claim 1, wherein the content of the graphite B in all the negative electrode active materials contained in the negative electrode is 20 to 60 mass%. The density of the mixture layer containing the negative electrode active material is 1.55 g / cm. ³ 1.7 g / cm or more ³ The lithium ion secondary battery according to claim 1 or 2, wherein the lithium ion secondary battery is less than 3. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the non-aqueous electrolyte contains a nitrile compound including at least one lithium borofluoride (LiBF ₄ ) and a cyano group. The lithium ion secondary battery according to claim 4, wherein the nitrile compound is represented by the following general formula (1).
_{NC- (CH 2) n -CN (} 1)
[In said general formula (1), n is an integer of 2-4. ] The lithium ion secondary battery according to claim 1, wherein a volume of the outer package is 10 cm ³ or more. The separator has a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin, and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher.
In the flat-shaped winding electrode body, at least the so porous layer (II) is opposed to the positive electrode, the lithium ion secondary according to any one of claims 1 to 6, the positive electrode and the separator are arranged Next battery.

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