JP4586374B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more specifically, includes a negative electrode and a positive electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte containing a non-aqueous solvent and a lithium salt. Non-aqueous electrolyte secondary battery with stable and good load characteristics, and can also prevent deterioration due to so-called trickle charge used to compensate for capacity reduction due to self-discharge of batteries such as personal computers The present invention relates to a non-aqueous electrolyte secondary battery.

2. Description of the Related Art Lithium secondary batteries, which are light nonaqueous electrolyte secondary batteries that have a high energy density with the reduction in weight and size of electrical products, are used in a wide range of fields. Lithium secondary batteries usually have a positive electrode in which an active material layer containing a positive electrode active material such as a lithium compound typified by lithium cobaltate is formed on a current collector, and lithium occlusion / representative typified by graphite. A negative electrode in which an active material layer containing a negative electrode active material such as a carbon material that can be released is formed on a current collector, and an electrolyte such as a lithium salt such as LiPF ₆ are dissolved in a normal aprotic non-aqueous solvent. It is mainly composed of a non-aqueous electrolyte and a separator made of a polymer porous membrane.

Separators used in lithium secondary batteries are required to satisfy requirements such as not impeding ion conduction between both electrodes, being able to hold an electrolytic solution, and having resistance to an electrolytic solution. A porous polymer membrane made of a thermoplastic resin such as polypropylene or polypropylene is used. Conventionally, as a method for producing these polymer porous membranes, for example, the following methods are known as known techniques.
(1) An extraction method in which a plasticizer that can be easily extracted and removed in a post-process is added to a polymer material, followed by molding, and then the plasticizer is removed with a suitable solvent to make it porous (Patent Document 1).
(2) A stretching method in which after forming a crystalline polymer material, a structurally weak amorphous portion is selectively stretched to form micropores (Patent Document 2).
(3) Interfacial exfoliation method in which an inorganic filler is added to a thermoplastic resin as a polymer material, molding is performed, and then the interface between the polymer material and the filler is exfoliated by a stretching operation to form micropores (patent Reference 3).

  However, the extraction method (1) requires treatment of a large amount of waste liquid, and has problems in both environmental and economic aspects. Further, it is difficult to obtain a uniform film due to the contraction of the film generated in the extraction process, and there is a problem in productivity such as yield. The stretching method (2) requires a long heat treatment in order to control the pore size distribution by controlling the crystal phase / amorphous phase structure before stretching, which is problematic in terms of productivity.

  On the other hand, the interfacial peeling method (3) does not generate waste liquid and is an excellent method in both environmental and economic aspects. In addition, since the interface between the polymer material and the filler can be easily peeled off by a stretching operation, a porous film can be obtained without the need for a pretreatment such as heat treatment, which is excellent in terms of productivity. It is a technique.

In addition, Patent Document 4 discloses an inorganic material in order to prevent fluorine from being generated by the reaction between moisture in the battery and the fluorine-containing electrolyte, and the battery capacity from being reduced due to deterioration of the electrolytic solution or electrode plate by the generated fluorine. When using a porous membrane containing powder as a separator for a lithium secondary battery, it is necessary to use an inorganic powder with an equilibrium moisture content of less than 4% and a low moisture adsorption amount in order to minimize the amount of moisture brought into the separator. Are listed.
JP 7-029563 A JP-A-7-304110 JP 2002-201298 A JP 2000-208123 A

  As described above, the porous film formed by the interfacial peeling method has no waste liquid and is excellent in both environment and economy, and does not require pretreatment such as heat treatment, and is excellent in productivity. A battery using a porous membrane as a separator by this interfacial peeling method often has a phenomenon that the electrode interface resistance increases and the load characteristics deteriorate, making it difficult to produce a battery having stable performance.

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that does not have a problem of deterioration in load characteristics and can maintain stable performance.

A non-aqueous electrolyte secondary battery of the present invention comprises a non-aqueous electrolyte comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte containing a non-aqueous solvent and a lithium salt. In the electrolytic solution secondary battery, the separator has a porous film made of a thermoplastic resin containing an inorganic filler, and the moisture contained in the battery is 200 as the concentration in the electrolytic solution in the battery. ~500ppm der is, the negative electrode is characterized that you active material a carbon material (claim 1).

  That is, as a result of intensive studies, the present inventors have determined that the moisture brought into the battery mainly through the separator and the electrode during the assembly of the battery has a great influence on the electrode interface resistance, and the moisture range is within a specific range. As a result, it was found that a battery having stable and good load characteristics was obtained, and the present invention was completed. In addition, the reason for this is not clear, but the secondary battery of the present invention is used to prevent battery performance deterioration due to so-called trickle charging, which is used to compensate for capacity reduction due to self-discharge of batteries such as personal computers. It was also found that this is effective.

  As described above, Patent Document 4 describes that the equilibrium moisture content of the inorganic powder contained in the separator is reduced to less than 4% in order to minimize the moisture content that the separator brings into the battery. According to the study by the present inventors, it is found that the lower the moisture in the battery, the better, but the presence within a certain range rather reduces the electrode interface resistance and improves the load characteristics. did. That is, the present invention is intended to improve performance by actively utilizing moisture that has been conventionally excluded as much as possible, and not only the moisture of the separator but also all of the cells brought into the battery. It is managed including moisture, and is completely different from the technique disclosed in Patent Document 4 which simply attempts to reduce the amount of moisture as much as possible.

  In the present invention, the amount of water in the battery is not the water concentration of the electrolyte used for battery assembly, but is included in the separator, electrode material, electrolyte, battery assembly work atmosphere, etc. at the time of battery assembly. It is the total amount of all moisture brought into the battery and contained in the battery as a product. Therefore, the amount of moisture in the battery can be obtained from the total amount of moisture that is attached to or contained in the material used for assembling the battery, and further brought into the battery as a product as moisture in the assembly atmosphere. Since most of the water brought into the battery as a product in this way is concentrated in the electrolyte, disassemble the assembled battery, take out the electrolyte, and measure its moisture concentration It can ask for.

  The moisture brought into the battery is mainly due to the separator and the electrode material. In other words, the water content in the electrolyte is usually kept at several tens of ppm or less to prevent decomposition of the contained salt. Therefore, generally, the amount of water contained in the electrolyte and brought into the battery as a product. There is almost no.

  In the present invention, the reason why the electrode interface resistance is lowered due to the presence of a specific amount of water in the battery is not clear, but any by-product (hereinafter referred to as “contributing substance”) generated by the reaction between the water and a salt in the electrolytic solution. It may be referred to as “.”). The reason why this effect is limited to a specific water content range is that the ratio of such contributing substances to be generated is usually compared to hydrofluoric acid generated by the reaction between water and a salt in the electrolyte. Since it is low, it is presumed that there is no contributing substance amount that produces a sufficient effect when the water content is less than 200 ppm. On the contrary, if the amount of water is excessively large, the active material is deteriorated by hydrofluoric acid and the resistance is increased by the generation of lithium fluoride.

  Further, although details of the reason why the battery of the present invention is effective in suppressing the battery deterioration due to trickle charge, that is, the increase in the self-discharge amount, it is not clear, but in the same manner as the contributing substance effective in reducing the electrode interface resistance, some by-product is generated. It is presumed that things are contributing.

  Here, the trickle current is defined as a charging current value when the battery is continuously charged with 4.2 V-CCCV for 672 hours in an atmosphere of 60 ° C.

  In the present invention, as the separator, the thickness is 5 μm to 100 μm, the porosity is 30% to 80%, the average pore size defined by ASTM F316-86 is 0.05 μm to 10 μm, and the Gurley defined by JIS P8117. It is preferable that the air permeability is 20 seconds / 100 cc or more and 700 seconds / 100 cc or less.

Further, it is preferable that the active material of the upper Symbol positive electrode is a lithium-transition metal composite oxide (claim 3).

  According to the present invention, a non-aqueous electrolyte secondary battery having stable and good load characteristics can be obtained. The secondary battery of the present invention is also effective in preventing deterioration of battery performance due to so-called trickle charge used to compensate for capacity reduction due to self-discharge of a battery such as a personal computer.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

  The non-aqueous electrolyte secondary battery of the present invention comprises a specific separator as described in detail below, a non-aqueous electrolyte, a positive electrode and a negative electrode capable of occluding and releasing lithium, and a specific amount in the battery. Of water.

[Separator]
<Constituent components and physical properties of separator>
The thermoplastic resin as the base resin of the porous film constituting the separator of the present invention is not particularly limited as long as the inorganic filler described later can be uniformly dispersed. For example, a polyolefin resin, Examples thereof include fluorine resins, styrene resins such as polystyrene, ABS resins, vinyl chloride resins, vinyl acetate resins, acrylic resins, polyamide resins, acetal resins, and polycarbonate resins. The above thermoplastic resins such as polyolefin resins may be used alone or in combination of two or more.

  Among these, polyolefin resin is particularly preferable because of its excellent balance of heat resistance, solvent resistance, and flexibility. Examples of the polyolefin resin include monoolefin polymers such as ethylene, propylene, 1-butene, 1-hexene, 1-octene or 1-decene, ethylene, propylene, 1-butene, 1-hexene, 1-octene or The main component is a copolymer of 1-decene and another monomer such as 4-methyl-1-pentene or vinyl acetate. Specifically, low-density polyethylene, linear low-density polyethylene, Examples thereof include high-density polyethylene, polypropylene, crystalline ethylene-propylene block copolymer, polybutene, and ethylene-vinyl acetate copolymer. In the present invention, it is preferable to use polyethylene or polypropylene among the polyolefin resins.

  The weight average molecular weight of such a thermoplastic resin has a lower limit of usually 50,000 or more, especially 100,000 or more, and an upper limit of usually 500,000 or less, preferably 400,000 or less, more preferably 300,000 or less, especially 200,000 or less. I just need it. When this upper limit is exceeded, melt molding becomes difficult because the melt viscosity of the resin increases in addition to the decrease in fluidity due to the addition of filler. Further, even when a molded product is obtained, the filler is not evenly dispersed in the resin, and pore formation due to interfacial peeling becomes nonuniform, which is not preferable. Below this lower limit, the mechanical strength decreases, which is not preferable.

Examples of the inorganic filler contained in the polymer porous membrane according to the present invention include calcium carbonate, magnesium carbonate, barium carbonate, talc, clay, mica, kaolin, silica, hydrotalcite, diatomaceous earth, calcium sulfate, magnesium sulfate, Examples include barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide, alumina, zinc oxide, zeolite, glass powder, etc. Among them, it is difficult to be decomposed by non-aqueous electrolyte and non-aqueous electrolysis In particular, barium sulfate and alumina are preferable because the electrolytic solution composed of LiPF ₆ and a carbonate-based solvent, which is most commonly used as the solution, is difficult to decompose.

  As the particle size of the inorganic filler, the lower limit of the number-based average particle size is usually 0.01 μm or more, preferably 0.1 μm or more, especially 0.2 μm or more, and the upper limit is usually 10 μm or less, preferably 5 μm or less, More preferably, it is 3 μm or less, and particularly preferably 1 μm or less. If the number-based average particle diameter of the inorganic filler exceeds 10 μm, the diameter of the holes formed by stretching becomes too large, and it tends to cause stretching breakage and a decrease in film strength. If the number reference average particle size is smaller than 0.01 μm, the filler is likely to aggregate, and it is difficult to uniformly disperse the filler in the base resin.

  In the present invention, one kind of inorganic filler can be used alone, or two or more kinds can be mixed and used as long as they satisfy the above conditions.

  The blending amount of the inorganic filler in the polymer porous membrane according to the present invention is such that the lower limit is usually 40 parts by weight or more, preferably 50 parts by weight or more, especially 60 parts by weight or more, relative to 100 parts by weight of the thermoplastic resin. More preferably, it is 100 parts by weight or more, and the upper limit is usually 300 parts by weight or less, preferably 200 parts by weight or less, more preferably 150 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin. When the blending amount of the inorganic filler with respect to 100 parts by weight of the thermoplastic resin in the polymer porous membrane is less than 40 parts by weight, it is difficult to form a communication hole and it is difficult to express the function as a separator. Moreover, the antioxidant effect of the separator cannot be sufficiently obtained by reducing the contact area between the base resin of the separator and the positive electrode due to the addition of the inorganic filler. On the other hand, if it exceeds 300 parts by weight, not only the viscosity at the time of film forming becomes high and the processability is inferior, but also the film breaks during stretching for making it porous, which is not preferable. In the present invention, since the filler blended in the production of the porous membrane remains in the substantially molded porous membrane, the blending amount range of the filler is within the range of the porous membrane. It becomes a filler content range.

  As the inorganic filler, one that has been surface-treated with a surface treatment agent in order to enhance dispersibility in the thermoplastic resin can also be used. As the surface treatment, when the thermoplastic resin is a polyolefin resin, for example, a treatment with a fatty acid such as stearic acid or a metal salt thereof, polysiloxane, or a silane coupling agent can be given.

  At the time of molding the porous polymer membrane according to the present invention, a low molecular weight compound having compatibility with the thermoplastic resin may be added. This low molecular weight compound enters between the molecules of the thermoplastic resin, lowers the interaction between molecules and inhibits crystallization, and as a result, improves the stretchability of the resin composition during sheet molding. In addition, the low molecular weight compound moderately enhances the interfacial adhesive force between the thermoplastic resin and the inorganic filler and prevents the pores from becoming coarse due to stretching, and the interfacial adhesive force between the thermoplastic resin and the inorganic filler. The effect of preventing the inorganic filler from falling off from the film is obtained.

  As this low molecular weight compound, those having a molecular weight of 200 to 3000 are preferably used. When the molecular weight of the low molecular weight compound exceeds 3000, the low molecular weight compound is difficult to enter between the molecules of the thermoplastic resin, so that the effect of improving stretchability is insufficient. On the other hand, when the molecular weight is less than 200, the compatibility is improved, but so-called blooming, in which a low molecular weight compound is precipitated on the surface of the polymer porous membrane, is likely to occur, and the membrane properties are easily deteriorated and blocking is not preferable.

  As the low molecular weight compound, when the thermoplastic resin is a polyolefin resin, an aliphatic hydrocarbon or glyceride is preferably used. In particular, when the polyolefin resin is polyethylene, liquid paraffin or low melting point wax is preferably used.

  In the resin composition as a film forming material for the polymer porous membrane according to the present invention, the lower molecular weight compound is added at a lower limit of usually 1 part by weight or more, preferably 5 parts by weight with respect to 100 parts by weight of the thermoplastic resin. The upper limit is usually 20 parts by weight or less, preferably 15 parts by weight or less, relative to 100 parts by weight of the thermoplastic resin. When the blending amount of the low molecular weight compound is less than 1 part by weight with respect to 100 parts by weight of the thermoplastic resin, the above effect by blending the low molecular weight compound cannot be sufficiently obtained, and when the blending amount exceeds 20 parts by weight, thermoplasticity is obtained. The interaction between the molecules of the resin is reduced too much and sufficient strength cannot be obtained. In addition, smoke generation occurs during sheet forming, and slipping occurs at the screw portion, making it difficult to form a stable sheet.

  If necessary, other additives such as a heat stabilizer can be added to the resin composition as a film forming material for the polymer porous membrane according to the present invention. The additive is not particularly limited as long as it is a known additive. The compounding quantity of these additives is 0.05-1 weight% normally with respect to the whole quantity of a resin composition.

  The porosity of the polymer porous membrane according to the present invention is usually 30% or more, preferably 40% or more, more preferably 50% or more as the lower limit of the porosity of the polymer porous membrane, and usually 80 as the upper limit. % Or less, preferably 70% or less, and more preferably 65% or less. If the porosity is less than 30%, the ion permeability is not sufficient, and the function as a separator cannot be achieved. On the other hand, if the porosity exceeds 80%, the actual strength of the film is lowered, which is not preferable because breakage or short-circuiting due to the active material and short-circuiting occur during battery production.

The porosity of the polymer porous membrane is a value calculated by the following calculation formula.
Porosity Pv (%) = 100 × (1−w / [ρ · S · t])
S: Area of polymer porous membrane t: Thickness of polymer porous membrane w: Weight of polymer porous membrane ρ: True specific gravity of polymer porous membrane

In addition, when the blend weight of the component i (resin, filler, etc.) constituting the polymer porous membrane is Wi and the specific gravity is ρi, the true specific gravity ρ can be obtained by the following formula (where Σ is all components) Represents the sum of
True specific gravity ρ = ΣWi / Σ (Wi / ρi)

  The upper limit of the thickness of the polymer porous membrane according to the present invention is usually 100 μm or less, preferably 40 μm or less, and the lower limit is usually 5 μm or more, preferably 10 μm or more. If the thickness is less than 5 μm, the actual strength is low, and therefore, it is not preferable because breakage at the time of producing the battery, punch-through due to the active material, and short circuit occur. Moreover, since the electrical resistance of a separator will become high when thickness exceeds 100 micrometers, the capacity | capacitance of a battery falls and it is unpreferable. On the other hand, when the thickness exceeds 100 μm, the amount of the active material put into the battery is reduced, so that the capacity of the whole battery is also lowered, which is not preferable. By setting the thickness of the separator to a range of 5 to 100 μm, a separator having good ion permeability can be obtained.

  The lower limit of the average pore diameter of the polymer porous membrane according to the present invention is 0.05 μm or more, preferably 0.1 μm or more, and more preferably 0.2 μm or more. The upper limit is 10 μm or less, preferably 5 μm or less, more preferably 3 μm or less, and particularly preferably 1 μm or less. If the average pore size is smaller than 0.05 μm, it is difficult to ensure sufficient connectivity of the porous membrane, and if it is larger than 10 μm, it is difficult to ensure practical film strength. As will be described later, the pore diameter of the polymer porous membrane can be arbitrarily changed by selecting the properties (particle size, etc.) and the filling amount of the inorganic filler as necessary. Here, the average pore diameter of the polymer porous membrane is determined by ASTM F316-86.

  The polymer porous membrane according to the present invention has a lower limit value of Gurley air permeability of 20 seconds / 100 cc or more, particularly 100 seconds / 100 cc or more, and an upper limit value of 700 seconds / 100 cc or less, particularly 300 seconds / 100 cc or less. It is preferable that When the Gurley permeability is below this lower limit, the porosity is often too high or the thickness is too thin, and as described above, the actual strength of the film is low, and breakage during battery creation and penetration by active material A short circuit occurs, which is not preferable. When the upper limit is exceeded, ion permeability is not sufficient, and the function as a separator cannot be achieved, which is not preferable. The Gurley air permeability is measured according to JIS P8117, and indicates the number of seconds that 100 cc of air passes through the membrane at a pressure of 1.22 kPa.

<Manufacturing method of separator>
A separator used in a lithium secondary battery is required to satisfy requirements such as not impeding ion conduction between both electrodes, being able to hold an electrolytic solution, and having resistance to an electrolytic solution. Is a polymer porous film mainly made of a thermoplastic resin such as polyethylene or polypropylene, and the method for producing these polymer porous films includes (1) extraction method and (2) stretching as described above. (3) Interfacial peeling method.

  However, in the extraction method of (1), it is necessary to select a plasticizer that has good compatibility with the polymer material. Therefore, even if extraction or subsequent stretching is performed, sufficiently large pores cannot be formed. Therefore, there is a drawback that the electric resistance of the obtained separator is increased. Moreover, a method for enlarging the pores by adding a plasticizer having poor compatibility is also known as a known technique. However, in this method, it is difficult to obtain a film having good properties because of unstable molding. In any method, it is necessary to treat a large amount of waste liquid in the extraction process, and there are problems in both environmental and economic aspects. Further, it is difficult to obtain a uniform film due to the contraction of the film generated in the extraction process, and there is a problem in productivity such as yield. In the stretching method (2), since only the amorphous part between the crystal domains is selectively stretched, it is difficult to stretch at a high magnification. Therefore, it is difficult to increase the hole diameter, and there is a drawback that the electric resistance of the obtained separator is increased. Further, in order to control the pore size distribution by controlling the structure of the crystalline phase / amorphous phase before stretching, heat treatment for a long time is required, which is problematic in terms of productivity.

  In contrast, the interfacial exfoliation method (3) can easily exfoliate the interface between the polymer material and the filler by a stretching operation as compared with the methods (1) and (2). A porous membrane having a large pore diameter can be easily produced without requiring a pretreatment such as the above. Thus, a separator having a large pore diameter has high pore communication properties, excellent liquid retention of a non-aqueous electrolyte, and is effective in stabilizing battery performance. Moreover, there is no generation of waste liquid, and it is an excellent method in terms of both environment and economy.

  Therefore, the separator of the present invention is preferably produced by an interfacial peeling method, and more specifically, produced by the following method.

  First, a resin composition is prepared by blending a predetermined amount of an additive such as an inorganic filler, a thermoplastic resin, and a low molecular weight compound or an antioxidant that is added as necessary, and kneading. Here, the resin composition may be premixed by a Henschel mixer or the like, and then prepared using a commonly used single screw extruder, twin screw extruder, mixing roll or twin screw kneader, etc. Alternatively, the preliminary kneading may be omitted and the resin composition may be directly prepared using the extruder or the like.

  Next, the resin composition is formed into a sheet. Sheet forming can be performed by a T-die method using a commonly used T-die or an inflation method using a circular die.

  Next, the formed sheet is stretched. For the stretching, longitudinal uniaxial stretching for stretching in the sheet take-up direction (MD), transverse uniaxial stretching for stretching in the transverse direction (TD) with a tenter stretching machine, etc., uniaxial stretching to MD, followed by TD with a tenter stretching machine, etc. There is a sequential biaxial stretching method in which stretching is performed, or a simultaneous biaxial stretching method in which the longitudinal direction and the transverse direction are simultaneously stretched. The uniaxial stretching can be performed by roll stretching. The stretching can be performed at any temperature at which the resin composition constituting the sheet can be easily stretched to a predetermined stretching ratio, and the resin composition does not melt and block the pores to lose the connectivity. However, it is preferably stretched in the temperature range of the melting point of the resin—70 ° C. to the melting point of the resin—5 ° C. The stretching ratio is arbitrarily set according to the required pore diameter and strength, but preferably, stretching is performed at least 1.2 times in a uniaxial direction. In addition, although there is no restriction | limiting in particular about the upper limit of this draw ratio, Usually, it is 7 times or less in a uniaxial direction. If the stretching exceeds this upper limit, the porosity of the obtained porous film becomes too high, the strength is lowered, and there is a possibility that it cannot be put into practical use.

[Non-aqueous electrolyte]
The non-aqueous electrolyte used for the non-aqueous electrolyte secondary battery of the present invention contains a non-aqueous solvent and a lithium salt.

<Non-aqueous solvent>
As the non-aqueous solvent of the electrolyte used in the non-aqueous electrolyte secondary battery of the present invention, any known solvent can be used as the solvent for the non-aqueous electrolyte secondary battery. For example, cyclic carbonates such as alkylene carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate (preferably alkylene carbonates having 3 to 5 carbon atoms); dialkyls such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, and ethyl methyl carbonate Chain carbonates such as carbonates (preferably dialkyl carbonates having an alkyl group having 1 to 4 carbon atoms); cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; chain ethers such as dimethoxyethane and dimethoxymethane; γ-butyrolactone, γ -Cyclic carboxylic acid esters such as valerolactone; and chain carboxylic acid esters such as methyl acetate, methyl propionate, and ethyl propionate. These may be used alone or in combination of two or more.

  Among the above exemplified solvents, a mixed non-aqueous solvent in which a cyclic carbonate and a chain carbonate are mixed is preferable from the viewpoint of improving overall battery performance such as charge / discharge characteristics and battery life. The mixed non-aqueous solvent contains cyclic carbonate and chain carbonate in an amount of 15% by volume or more of the whole non-aqueous solvent, and the total of these volumes is 70% by volume or more of the whole non-aqueous solvent. It is preferable to do.

  As the cyclic carbonate used in the mixed non-aqueous solvent in which the cyclic carbonate and the chain carbonate are mixed, an alkylene carbonate having 2 to 4 carbon atoms in the alkylene group is preferable. Specific examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate and the like. Of these, ethylene carbonate and propylene carbonate are preferable.

  Moreover, as the chain carbonate used for the mixed non-aqueous solvent in which the cyclic carbonate and the chain carbonate are mixed, a dialkyl carbonate having an alkyl group having 1 to 4 carbon atoms is preferable. Specific examples thereof include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate and the like. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.

  Each of these cyclic carbonates and chain carbonates may be used independently, or a plurality of types may be used in any combination and ratio. The ratio of the cyclic carbonate in the mixed non-aqueous solvent is 15% by volume or more, particularly 20 to 50% by volume, and the ratio of the chain carbonate is 30% by volume or more, particularly 40 to 80% by volume. The content ratio is preferably cyclic carbonate: chain carbonate = 1: 1 to 4 (volume ratio).

  Furthermore, the mixed non-aqueous solvent may contain a solvent other than the cyclic carbonate and the chain carbonate as long as the battery performance of the manufactured lithium battery is not deteriorated. The ratio of the solvent other than the cyclic carbonate and the chain carbonate in the mixed non-aqueous solvent is usually 30% by volume or less, preferably 10% by volume or less.

<Lithium salt>
Arbitrary things can be used as lithium salt which is a solute of nonaqueous system electrolyte. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ ; LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C _{4 F 9 SO 2), LiC} (CF 3 SO 2) 3, LiPF 4 (CF 3) 2, LiPF 4 (C 2 F 5) 2, LiPF 4 (CF 3 SO 2) 2, LiPF 4 (C 2 F ₅ SO ₂ ) ₂ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F ₅ SO ₂ ) _2, etc. Examples include lithium salts. Of these, fluorine-containing lithium salts such as LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (C ₂ F ₅ SO ₂ ) ₂ , particularly LiPF ₆ and LiBF ₄ are preferable. In addition, about lithium salt, 1 type may be used independently and 2 or more types may be used together.

  The lower limit of the concentration of these lithium salts in the non-aqueous electrolyte is usually 0.5 mol / l or more, especially 0.75 mol / l or more, and the upper limit is usually 2 mol / l or less, especially 1.5 mol / l. l or less. When the concentration of the lithium salt exceeds this upper limit value, the viscosity of the nonaqueous electrolytic solution increases and the electrical conductivity also decreases. Moreover, since electrical conductivity will become low if less than this lower limit, it is preferable to prepare a non-aqueous electrolyte within the said concentration range.

<Other additives>
In addition to the non-aqueous solvent and the lithium salt, the non-aqueous electrolyte solution according to the present invention includes other useful components as necessary, for example, conventionally known vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, phenyl ethylene carbonate, Negative electrode film forming agent such as succinic anhydride, ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methanesulfonate, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethylsulfone, diethylsulfone, dimethyl Various additives such as positive electrode protective agents such as sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide, overcharge prevention agent, deoxidizing agent, dehydrating agent may be included. .

[Positive electrode]
As the positive electrode, a material in which an active material layer containing a positive electrode active material and a binder is usually formed on a current collector is used.

  The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. Preferable examples include lithium transition metal composite oxides.

Specific examples of the lithium-transition metal composite oxide, lithium cobalt complex oxides such as LiCoO _2, lithium-nickel composite oxide such as LiNiO _2, include lithium-manganese composite oxides such as LiMnO _2. In these lithium transition metal composite oxides, some of the main transition metal atoms are Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, etc. Replacing with other metals is preferable because it can be stabilized. Any one of these positive electrode active materials may be used alone, or two or more thereof may be used in any combination and ratio.

  The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), Examples thereof include fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, and nitrocellulose. These may be used individually by 1 type, or may use multiple types together.

  As for the ratio of the binder in the positive electrode active material layer, the lower limit is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and the upper limit is usually 80% by weight or less, preferably 60% by weight or less, more preferably 40% by weight or less, and still more preferably 10% by weight or less. If the proportion of the binder is small, the active material cannot be sufficiently retained, so that the mechanical strength of the positive electrode is insufficient, and the battery performance such as cycle characteristics may be deteriorated. On the contrary, if the amount is too large, the battery capacity and conductivity are lowered. It will be.

  The positive electrode active material layer usually contains a conductive agent in order to increase conductivity. Examples of the conductive agent include carbonaceous materials such as graphite fine particles such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon fine particles such as needle coke. These may be used individually by 1 type, or may use multiple types together.

  The ratio of the conductive agent in the positive electrode active material layer is such that the lower limit is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and the upper limit is usually 50% by weight or less. , Preferably 30% by weight or less, more preferably 15% by weight or less. If the proportion of the conductive agent is small, the conductivity may be insufficient, and conversely if too large, the battery capacity may be reduced.

  In addition, the positive electrode active material layer can contain additives for a normal active material layer such as a thickener.

  The thickener is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. These may be used individually by 1 type, or may use multiple types together.

  Aluminum, stainless steel, nickel-plated steel or the like is used for the current collector of the positive electrode.

  The positive electrode can be formed by applying a slurry obtained by slurrying the above-described positive electrode active material, a binder, a conductive agent, and other additives added as necessary with a solvent onto a current collector, and drying the positive electrode active material. . As the solvent used for slurrying, an organic solvent that dissolves the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like are used, but not limited thereto. These may be used individually by 1 type, or may use multiple types together. Moreover, a dispersing agent, a thickener, etc. can be added to water, and an active material can also be slurried with latex, such as SBR.

  Thus, the thickness of the positive electrode active material layer formed is about 10-200 micrometers normally. The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

[Negative electrode]
As the negative electrode, a material in which an active material layer containing a negative electrode active material and a binder is usually formed on a current collector is used.

  As a negative electrode active material, a carbonaceous material capable of occluding / releasing lithium such as organic pyrolysate, artificial graphite and natural graphite under various pyrolysis conditions; capable of occluding / releasing lithium such as tin oxide and silicon oxide Metal oxide materials; lithium metal; various lithium alloys, metal materials capable of forming an alloy with lithium, such as Si and Sn, and the like can be used. These negative electrode active materials may be used individually by 1 type, and may mix and use 2 or more types.

  The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene / butadiene rubber, isoprene rubber, and butadiene rubber. These may be used individually by 1 type, or may use multiple types together.

  The ratio of the binder in the negative electrode active material layer is such that the lower limit is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and the upper limit is usually 80% by weight or less. Preferably it is 60 weight% or less, More preferably, it is 40 weight% or less, More preferably, it is 10 weight% or less. If the ratio of the binder is small, the active material cannot be sufficiently retained, so that the negative electrode mechanical strength may be insufficient, and the battery performance such as cycle characteristics may be deteriorated. become.

  In addition, the negative electrode active material layer may contain additives for a normal active material layer such as a thickener.

  The thickener is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. These may be used individually by 1 type, or may use multiple types together.

  Copper, nickel, stainless steel, nickel-plated steel, or the like is used for the negative electrode current collector.

  The negative electrode can be formed by applying a slurry obtained by slurrying the above-described negative electrode active material, a binder, and other additives added as necessary with a solvent, and then drying the current collector. As the solvent used for slurrying, an organic solvent that dissolves the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like are used, but not limited thereto. These may be used individually by 1 type, or may use multiple types together. Moreover, a dispersing agent, a thickener, etc. can be added to water, and an active material can also be slurried with latex, such as SBR.

  Thus, the thickness of the negative electrode active material layer formed is about 10-200 micrometers normally. The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

[Battery configuration]
The lithium secondary battery of the present invention is manufactured by assembling the above-described positive electrode, negative electrode, non-aqueous electrolyte, and separator into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary.

  The battery shape is not particularly limited, and can be appropriately selected from various commonly used shapes according to the application. Examples of commonly used shapes include a cylinder type with a sheet electrode and separator in a spiral shape, an inside-out cylinder type with a combination of pellet electrode and separator, a coin type with a stack of pellet electrode and separator, and a sheet Examples include a laminate type in which electrodes and separators are laminated. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

[Moisture content in the battery]
The non-aqueous electrolyte secondary battery of the present invention is characterized in that the amount of water contained in the battery is in a specific range with respect to the electrolyte. This water content is usually 200 ppm or more, preferably 250 ppm or more, and usually 500 ppm or less, preferably 300 ppm or less.

  If the amount of water in the battery is less than the above range, the amount of contributing substances effective in reducing the electrode interface resistance described above is small, and the interface resistance cannot be reduced. When the amount of water in the battery is larger than the above range, the capacity is reduced due to deterioration of the electrode active material due to hydrofluoric acid generated by the reaction between the water and the salt in the electrolyte, which is not preferable.

  For the measurement of the amount of moisture in the battery, any known method can be used. If the battery is not assembled, the amount of moisture for each constituent member is measured and the sum is obtained. Further, after the battery is assembled, the moisture in the battery is quickly concentrated in the electrolyte as described above, and therefore, the amount of moisture in the electrolyte in the battery may be measured.

The moisture content of the electrode material and separator used for battery assembly is measured as follows.
<Moisture content of electrode material and separator>
A measurement sample is put in a 130 ° C. heating furnace in which nitrogen gas is flowed and held for 20 minutes. The flowing nitrogen gas is introduced into a measurement cell of a Karl Fischer moisture meter, and the amount of moisture is measured. The integrated value for 20 minutes is defined as the total water content. The measurement is performed in a glove box having a dew point of -75 ° C. to prevent moisture from entering.

Moreover, the moisture content in electrolyte solution is measured as follows.
<Moisture content of electrolyte>
Since a small amount of water in the electrolytic solution quickly reacts with the Li salt in the electrolytic solution to become HF, for example, HF is quantified by acid content measurement, and the amount of water can be calculated from the value. Moreover, although there is no restriction | limiting in the measuring method of the water | moisture content of the electrolyte solution in a battery, what is necessary is just to decompose | disassemble a battery, take out electrolyte solution, and to use for the measurement of the said water | moisture content within the airtight container without water mixing.

  Moreover, although there is no restriction | limiting in the measuring method of the water | moisture content of the electrolyte solution in a battery, what is necessary is just to use for the measurement of the said moisture content, disassembling a battery in an airtight container, taking out electrolyte solution.

  In the present invention, in order to keep the amount of moisture in the battery within a specific range, it is important to control the moisture conditions of the moisture brought in from each member, the assembly atmosphere, etc. when assembling the battery of the present invention. It is. That is, the member to be used is devised, for example, appropriately managing the moisture in the storage atmosphere or protecting it with a material that does not absorb moisture according to the total moisture content in the battery. Also, when assembling the battery, it is necessary to devise measures such as paying attention to moisture management in an atmosphere such as dry air. Thus, the total water content contained in the positive electrode material, the negative electrode material, and the separator is usually 200 ppm or more, preferably 250 ppm or more, usually 500 ppm or less, particularly 300 ppm or less based on the electrolytic solution. A battery can be fabricated.

  The general embodiment of the lithium secondary battery of the present invention has been described above. However, the lithium secondary battery of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist thereof. Can be implemented.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples as long as the gist thereof is not exceeded.

[Example 1]
A battery was prepared according to the following procedure.
<Manufacture of separator>
High density polyethylene [“HI-ZEX7000FP” manufactured by Mitsui Chemicals, Inc., weight average molecular weight: 200,000, density: 0.956 g / cm ³ , melt flow rate: 0.04 g / 10 min], 100 parts by weight, soft polypropylene [Idemitsu Petrochemical "PER R110E", weight average molecular weight: 330,000] 8.8 parts by weight, hydrogenated castor oil ["HY-CASTOR" manufactured by Toyokuni Oil Co., Ltd.
OIL ", molecular weight 938] 8.8 parts by weight, barium sulfate [number-based average particle size 0.18 μm] 176.5 parts by weight as an inorganic filler were blended and melt-kneaded, and the resulting resin composition was heated to 210 ° C. Inflation molding was performed at 0 ° C. to obtain a raw sheet. The thickness of the original fabric sheet was 105 μm on average. Next, the obtained raw sheet was successively stretched at 90 ° C. in the sheet longitudinal direction (MD) 4 times, and then at 120 ° C. in the width direction (TD) 2.9 times to obtain a film thickness of 26 μm and porosity. A porous polymer membrane having a molecular weight of 64%, an average pore diameter (average pore diameter determined by ASTM F316-86) of 0.27 μm, and a Gurley air permeability (Gurley air permeability determined by JIS P8117) of 44 seconds / 100 cc was obtained. This polymer porous membrane is called separator A. Note that, during the stretching process, the inorganic filler was not removed from the porous polymer membrane.

  This separator A was dried under the drying conditions shown in Table 1 to obtain a moisture content separator shown in Table 1.

<Preparation of non-aqueous electrolyte>
Purified ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 in a dry argon atmosphere to prepare a mixed solvent. Into this mixed solvent, sufficiently dried LiPF ₆ was dissolved at a ratio of 1.0 mol / l to obtain a non-aqueous electrolyte. The water content of the electrolytic solution was 40 ppm.

<Preparation of positive electrode>
LiCoO ₂ was used as the positive electrode active material, and 6 parts by weight of carbon black and 9 parts by weight of polyvinylidene fluoride (trade name “KF-1000” manufactured by Kureha Chemical Co., Ltd.) were added to 85 parts by weight of LiCoO ₂ and mixed. Disperse with 2-pyrrolidone to form a slurry. This was uniformly applied to one side of a 20 μm-thick aluminum foil as a positive electrode current collector, dried, and then pressed by a press machine so that the density of the positive electrode active material layer was 3.0 g / cm ^3. It was. Table 1 shows the drying conditions of the positive electrode and the moisture content of the obtained positive electrode.

<Production of negative electrode>
Using natural graphite powder as a negative electrode active material, 94 parts by weight of natural graphite powder was mixed with 6 parts by weight of polyvinylidene fluoride, and dispersed with N-methyl-2-pyrrolidone to form a slurry. This was uniformly applied to one side of a 18 μm-thick copper foil as a negative electrode current collector, dried, and then pressed by a pressing machine so that the density of the negative electrode active material layer was 1.5 g / cm ^3. did. Table 1 shows the drying conditions of the negative electrode and the water content of the obtained negative electrode.

<Battery assembly>
A 18650 type cylindrical battery was fabricated using the separator, the non-aqueous electrolyte, the positive electrode, and the negative electrode. That is, the positive electrode and the negative electrode were wound through the separator to form an electrode group, which was sealed in a battery can. Thereafter, 4.5 g of the electrolyte solution was poured into a battery can loaded with the electrode group, and the electrode was sufficiently infiltrated, followed by caulking.

[Examples 2 and 3, Comparative Examples 1 and 2]
In Example 1, the separator drying conditions were changed as shown in Table 1 (but not in Comparative Example 2), and the same procedure was performed except that the separator had the moisture content shown in Table 1. Was made.

[Comparative Example 3]
A battery was produced in the same manner as in Example 1 except that the separator B produced by the following method was used as the separator.

<Manufacture of separator B>
A mixture film of 25 parts by weight of polyethylene having a viscosity average molecular weight of 1,000,000 and 75 parts by weight of paraffin wax (average molecular weight 389) was extruded using a 40 mmφ twin screw extruder at an extrusion temperature of 170 ° C. to prepare a raw film. The obtained raw film was immersed in isopropanol at 60 ° C. to extract and remove paraffin wax. The obtained film was longitudinally stretched 2.0 times at a temperature of 90 ° C. using a roll stretching machine, and then stretched 6.0 times at a temperature of 100 ° C. using a tenter stretching machine, and the film thickness was 22 μm and pores were obtained. A porous membrane having a rate of 50%, an average pore size of 0.04 μm, and a Gurley air permeability of 440 seconds / 100 cc was obtained. This polymer porous membrane is called separator B.

  The separator B was dried under the drying conditions shown in Table 1 to obtain a separator having a moisture content shown in Table 1.

  The batteries obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated as follows, and the results are shown in Table 2. The trickle charge test was performed only for the batteries of Example 2 and Comparative Example 3, and the results are shown in Table 3.

  Moreover, about each battery, after 12 hours passed from assembly, the electrolytic solution was taken out and the moisture concentration measured by the above-described moisture content measuring method is shown in Table 2.

<Battery evaluation>
1) Initial charging / discharging End-of-charge voltage of 4.2 V at a constant current corresponding to 0.2 C at 25 ° C. (the rated capacity due to the discharge capacity at 1 hour rate is assumed to be 1 C, and the same applies hereinafter) Charge and discharge 3 cycles at an end-of-discharge voltage of 3V, stabilize the 4th cycle with a current corresponding to 0.5C to a charge-end voltage of 4.2V, and the charge current value becomes a current value corresponding to 0.05C. After charging 4.2V-constant current constant voltage charging (CCCV charging) (0.05C cut), 3V discharging was performed at a constant current value corresponding to 0.2C.

2) Interfacial resistance measurement 1) A battery that has been initially charged and discharged is charged to a charge end voltage of 4.2 V at a current corresponding to 0.5 C at 25 ° C., and a charging current value corresponds to 0.05 C. 4.2V-constant current constant voltage charging (CCCV charging) (0.05C cut) for charging until the current value was reached was performed. Then, electrode interface resistance was calculated | required with the alternating current impedance method, and the result was shown in Table 2. The measurement temperature is 25 ° C., the measurement frequency is 20 kHz to 0.01 Hz, and the applied voltage is 10 mV. The measurement of the interface resistance by the AC impedance method is described in, for example, Japanese Patent Application Laid-Open No. 9-11001.

3) Rate measurement 2) The battery whose interface resistance was measured was discharged at 3 ° C. at a constant current value corresponding to 0.2 C at 25 ° C. Next, the battery is charged to a charge end voltage of 4.2 V with a current corresponding to 0.5 C, and charged until the charge current value reaches a current value corresponding to 0.05 C. 4.2 V—constant current constant voltage charging (CCCV Charge) (0.05 C cut). Thereafter, 3V discharge was performed at a constant current value corresponding to 0.2C. The discharge capacity at this time is shown in Table 2. Also, based on this discharge capacity, Table 2 shows the ratio of the discharge capacity when a similarly charged battery was discharged at 3 V at a constant current value corresponding to 2 C as discharge efficiency.

4) Trickle charge test Above 1) A battery that had been initially charged and discharged was charged to a charge end voltage of 4.2 V at a current corresponding to 0.5 C at 25 ° C., and a current corresponding to a charge current value of 0.05 C. 4.2V-constant current constant voltage charging (CCCV charging) (0.05C cut) for charging until the value is reached was performed. Next, the charged battery is placed in an atmosphere of 60 ° C. for 672 hours, and 4.2 V-CCCV is continuously charged to compensate for the voltage drop due to self-discharge. Changes were measured. The results are shown in Table 3.

  From Tables 1 to 3, if the secondary battery is prepared using a specific separator and the water concentration of the electrolyte in the battery is 200 to 500 ppm, the load characteristics are excellent, and the problem of deterioration due to trickle charging It can be seen that an excellent battery can be obtained.

  The use of the lithium secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. , Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, small devices such as watches, strobes, cameras, and large devices such as electric cars and hybrid cars Can be mentioned.

  In particular, the lithium secondary battery of the present invention is useful as a secondary battery for a personal computer because it is effective in preventing deterioration due to so-called trickle charge used to compensate for capacity reduction due to self-discharge of a battery such as a personal computer.

Claims (3)

In a non-aqueous electrolyte secondary battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte containing a non-aqueous solvent and a lithium salt,
The separator has a porous film made of a thermoplastic resin containing an inorganic filler,
Water contained within the cell, Ri 200~500ppm der as the concentration of the electrolytic solution of the electrolyte Ikeuchi,
Nonaqueous electrolyte secondary battery negative electrode is characterized that you active material a carbon material.   2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator has a thickness of 5 μm to 100 μm, a porosity of 30% to 80%, and an average pore diameter defined by ASTM F316-86 of 0.05 μm. A non-aqueous electrolyte secondary battery characterized by having a Gurley air permeability defined by JIS P8117 of 20 seconds / 100 cc or more and 700 seconds / 100 cc or less. 3. The non-aqueous electrolyte secondary battery according to claim 1 , wherein the positive electrode uses a lithium transition metal composite oxide as an active material. 4.