JP5206659B2 - 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. The present invention relates to a non-aqueous electrolyte secondary battery that achieves a high discharge capacity and is excellent in cycle characteristics.

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.

A conventional typical lithium secondary battery uses a carbon material as a negative electrode active material, and is charged and discharged by inserting (intercalating) and desorbing (deintercalating) lithium into the carbon material in an ionic state. It is repeating. However, it is difficult to increase the amount of lithium ions inserted into the carbon material, and there is a problem that the charge / discharge capacity of the secondary battery cannot be increased. For example, when graphite is used as the carbonaceous material, the lithium metal has a composition of CLi ₆ and the theoretical charge / discharge capacity of this material is 372 Ah / kg. This is only a fraction of the theoretical charge / discharge capacity of lithium metal.

  Therefore, an attempt has been made to use a material containing a metal or a metal compound that can be alloyed with lithium as a negative electrode material capable of developing a higher capacity. For example, Patent Document 1 describes that a non-aqueous electrolyte secondary battery with improved discharge capacity is obtained by using a metal that can be alloyed with lithium, such as silicon, as a negative electrode active material.

In addition, the separator used in the lithium secondary battery is required to satisfy requirements such as not impeding ion conduction between both electrodes, being able to hold the electrolytic solution, having resistance to the electrolytic solution, A polymer porous film mainly made of a thermoplastic resin such as polyethylene 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 to perform molding, and then the plasticizer is removed with a suitable solvent to make it porous (Patent Document 2).
(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 3).
(3) An interfacial exfoliation method in which a filler is added to a polymer material, molding is performed, and the interface between the polymer material and the filler is exfoliated by a subsequent stretching operation to form micropores (Patent Document 4).

  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.

  However, conventional separators containing fillers have poor adhesion to the electrodes due to the presence of fillers protruding on the surface, causing non-uniform resistance between electrodes due to non-uniform distance between electrodes, generating lithium dendrites, etc. Therefore, it is common sense to think that the separator is inferior in safety, and for this reason, there has been no example in which a separator including the filler produced by the method (3) has been put to practical use.

  Also in the aforementioned Patent Document 1, it is described that a separator is made of a single microporous film of polyolefin such as polyethylene or polypropylene, a film obtained by bonding them, or a nonwoven fabric such as polyolefin, polyester, polyamide, or cellulose. Also in the examples, a polyethylene microporous membrane is used. This product is generally produced industrially by the extraction method (1) or the stretching method (2). And patent document 1 does not mention at all about the influence of the separator at the time of using the metal alloyable with lithium for a negative electrode.

Japanese Patent Laid-Open No. 10-223221 JP 7-029563 A JP-A-7-304110 JP 2002-201298 A

  As described in Patent Document 1, when a metal or metal compound that can be alloyed with lithium is used as a negative electrode, due to the volume change accompanying the occlusion of lithium, as shown in Comparative Example 1 described later, There was a problem that the discharge capacity was significantly reduced.

  Accordingly, the present invention provides a non-aqueous electrolyte secondary battery that achieves a high capacity by using a metal or metal compound capable of forming an alloy with lithium as a negative electrode and has a small decrease in discharge capacity during cycling. For the purpose.

  As a result of intensive studies, the inventors of the present invention, in particular, are metals or metal compounds having a large volume expansion coefficient when formed into a lithium alloy, and the metal and the metal compound at the time of being formed into a lithium alloy In the case where the negative electrode has a theoretical capacity density per volume of a certain value or more, a high capacity is achieved by using a porous membrane made of a thermoplastic resin containing an inorganic filler as a separator. However, the present invention was completed by finding that a non-aqueous electrolyte secondary battery capable of providing a small reduction in discharge capacity during cycling can be provided.

That is, the gist of the present invention is a non-aqueous electrolyte secondary 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 battery, the separator has a porous film made of a thermoplastic resin containing an inorganic filler, and the separator has a thickness of 5 μm to 100 μm, a porosity of 30% to 80%, and ASTM F316- 86 has an average pore size of 0.05 μm or more and 10 μm or less, a Gurley permeability determined by JIS P8117 of 20 seconds / 100 cc or more and 700 seconds / 100 cc or less, and an average liquid retention rate change of 15% / minute or less. And the negative electrode contains a metal or metal compound capable of forming an alloy with lithium (however, a lithium-aluminum alloy and a lithium-zinc alloy) Except lithium alloy),
i) The volume expansion coefficient of the lithium alloyed product of the metal or the metal compound with respect to the metal or the metal compound is 1.2 or more and 6.0 or less,
ii) satisfy the following condition (a) and / or condition (b), and
(a) The ratio of the theoretical capacity converted from the amount of lithium in the lithium alloyed product of the metal or the metal compound per weight of the metal or the metal compound is 0.4 Ah / g or more and 4.0 Ah / g or less.
(b) The ratio of the theoretical capacity converted from the amount of lithium in the lithium alloyed product of the metal or the metal compound per volume of the metal or the metal compound is 0.7 Ah / cc or more and 2.3 Ah / cc or less.
iii) A dispersion prepared by sintering the metal or metal compound capable of forming an alloy with lithium or having the metal or metal compound capable of forming an alloy with lithium dispersed therein is applied onto a current collector and dried. The present invention resides in a non-aqueous electrolyte secondary battery.

  In the present invention, although the details of the action mechanism of the effect of improving cycle characteristics by combining a specific separator and a negative electrode containing a metal or metal compound capable of forming an alloy with lithium are not clear, the specific mechanism used in the present invention The separator has a higher ability to retain the electrolytic solution than a separator that is generally used in the past, and therefore, it can follow the volume expansion of the negative electrode sufficiently and stably store the electrolytic solution, It is presumed that good cycle characteristics are exhibited.

  That is, as described in Patent Document 1, conventionally, a separator used in a lithium secondary battery is generally obtained by an extraction method or a stretching method. The membrane obtained by such a method is different from a porous membrane made of a thermoplastic resin containing an inorganic filler, which is characterized by the present invention, and has a high rate of change in the amount of liquid retained, so that the electrolytic solution is put into the separator. The ability to hold is low, as shown in Comparative Example 1 described later, a metal or a metal compound having a large volume expansion coefficient when lithium alloyed, the metal and the metal compound when lithium alloyed, Good cycle characteristics cannot be obtained when a negative electrode having a capacity density per weight or volume exceeding a certain value is used.

  On the other hand, a porous film made of a thermoplastic resin containing an inorganic filler used as a separator in the present invention is easily manufactured as a porous film having a relatively large pore diameter by, for example, an interfacial peeling method, as described later. In addition, the liquid retainability is good.

  The reason why the separator used in the present invention is excellent in liquid retention is considered as follows. That is, the movement of the electrolytic solution in the separator can be regarded as a so-called capillary flow in which the liquid penetrates through the fine holes. In capillary flow, the smaller the pore diameter, the greater the permeation distance and the greater the permeation distance.However, conversely, when the liquid comes out due to external pressure, etc. Conceivable. The separator containing the filler used in the present invention has a larger pore size and liquid permeability in comparison with the separator used in Patent Document 1 manufactured by the methods (1) and (2). Although slightly inferior, it is considered that the liquid is likely to be retained in the film because it is difficult for the liquid to move once it has permeated. In addition, since the dielectric constant of the entire separator increases due to the inclusion of the filler, the chemical affinity between the filler and the electrolytic solution is improved by the interaction with the electrolytic solution that is a polar solvent. It is also conceivable that this has the effect of increasing the electrolyte holding capacity in the separator. Furthermore, since the separator used in the present invention forms a gap between the electrode plate and the separator in the battery due to the unevenness of the separator surface formed by the presence of the filler, more electrolytic solution is retained in this gap. Is possible.

  As described above, in the present invention, by using a specific separator with extremely good liquid retention, the negative electrode contains a metal or a metal compound capable of forming an alloy with lithium, and has a large volume expansion when formed into a lithium alloy. In the secondary battery, the electrolyte solution is stably held, and the deterioration of the cycle characteristics is suppressed by compensating for the electrolyte solution deficiency such as depletion and uneven distribution of the electrolyte solution accompanying the expansion and contraction of the negative electrode during the cycle.

  In addition, as described above, the separator containing the filler has poor adhesion between the electrodes due to the presence of the filler protruding on the surface, resulting in non-uniform resistance between the electrodes due to non-uniform distance between the electrodes. There is no example of practical use that is likely to occur and inferior in safety, and even in Patent Document 1, a microporous polyethylene film not containing such a filler is used as a separator. With such a microporous polyethylene membrane separator, the physical properties of the separator in the present invention cannot be achieved, and the effects of the present invention cannot be obtained.

  In the present invention, by combining a negative separator containing a metal or metal compound capable of forming an alloy with lithium with a specific separator that has not been conventionally used, an excellent effect can be obtained with the above-described operation mechanism.

  In the present invention, the metal or metal compound capable of forming an alloy with lithium is at least one selected from the group consisting of Al, Si, Zn, Ga, Ge, Ag, Cd, In, Sn, Sb, Pb, and Bi. A metal of a kind or a compound of the metal is mentioned (claim 2).

The negative electrode is preferably a thin film having a thickness of 100 μm or less (Claim 3). As such a negative electrode, particles containing a metal capable of forming an alloy with lithium on a current collector , a binder, A thin film electrode having a thin layer containing (Claim 4 ).

The negative electrode may include a metal or a metal compound capable of forming an alloy with lithium as a composite material of at least one of a metal other than the metal and a carbonaceous material (Claim 5 ).

Further, the lithium salt of the nonaqueous electrolytic solution is a fluorine-containing lithium salt, it is preferred that the non-aqueous solvent containing a cyclic carbonate and a chain carbonate (Claim 7). Further, it is preferable that the active material of the positive electrode is a lithium-transition metal composite oxide (Claim 8).

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that achieves higher capacity and is less likely to have a reduced discharge capacity during cycling.

  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 includes a negative electrode and a positive electrode capable of inserting and extracting lithium, a specific separator described in detail below, a non-aqueous solvent, and a non-aqueous electrolyte containing a lithium salt. And a negative electrode containing a metal or a metal compound satisfying a specific condition that can form an alloy with lithium.

[Separator]
<Constituent components and physical properties of separator>
The thermoplastic resin as the base resin of the porous membrane 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, and glass powder. Among them, carbonate organic electrolytes used in lithium secondary batteries are decomposed. In particular, barium sulfate and alumina are preferable.

  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. When the number standard average particle diameter of the inorganic filler exceeds 10 μm, the diameter of the pores formed by stretching becomes too large, and the permeability of the electrolytic solution deteriorates, which is not preferable. Moreover, when the hole diameter becomes large, it tends to cause stretching breakage and a decrease in film strength. In addition, when the number average particle size exceeds 10 μm, the number of particles on the separator surface is too small and a gap between the electrode plate and the separator is not sufficiently formed. Is expensive. 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 addition, even if evenly dispersed, the diameter of the pores formed by stretching is too small, so there is no large difference from the pore diameter of the separator obtained by the above-described (1) extraction method and (2) stretching method, and is intended in the present invention. This is not preferable because the liquid retention is not sufficiently improved. Moreover, since the gap between the electrode plate and the separator is not sufficiently formed because the particle size is too small, there is a high possibility that the retention of the electrolytic solution is lowered on this surface as well.

  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 becomes difficult to exhibit a function as a separator. 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.

  Furthermore, the polymer porous membrane according to the present invention has an average liquid retention rate change rate of 15% / min or less, preferably 12% / min or less, more preferably 10% / min or less, obtained as follows. It is. When the average liquid retention rate change rate exceeds 15% / min, sufficient liquid retention cannot be obtained, and a sufficient improvement in cycle characteristics can be obtained by securing the liquid retention of the electrolytic solution by using a specific separator. I can't. The lower the average liquid retention rate, the higher the liquid retention, which is preferable. However, a lower limit of about 5% / minute is sufficient.

<Change rate of average liquid content of separator>
The weight of the separator cut into a size of 4 cm × 4 cm is measured. Next, after the separator is immersed in the electrolytic solution and the electrolytic solution is sufficiently permeated, the electrolytic solution attached to the surface is wiped up and the weight is measured. The difference from the weight before dipping is taken as the weight of the permeated electrolyte. Further, the change in weight is measured every 30 seconds for 2 minutes, and the average liquid retention rate change rate is calculated as shown in the table below.

<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, the liquid retention of the obtained separator is not sufficient. 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. For this reason, it is difficult to increase the pore diameter, and there is a drawback that the liquid retention of the obtained separator is lowered. 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. As described above, the separator having such a large pore diameter has good liquid retentivity as described above, and is effective in preventing cycle characteristics from being deteriorated due to expansion and contraction of the negative electrode. 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 carbonate such as alkylene carbonate such as ethylene carbonate, propylene carbonate, butylene carbonate (preferably alkylene carbonate having 3 to 5 carbon atoms); dialkyl such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, 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 a chain carbonate used for the mixed non-aqueous solvent which mixed said cyclic carbonate and chain carbonate, the dialkyl carbonate which has a C1-C4 alkyl group 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, deoxidizing agent, dehydrating agent, overcharge preventing 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.

  The ratio of the binder in the positive 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 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. Will be lowered.

  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 is formed by applying a slurry obtained by slurrying the positive electrode active material, the binder, the conductive agent, and other additives added as necessary with a solvent onto a current collector. Can do. 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]
The negative electrode according to the present invention contains a metal or metal compound capable of forming an alloy with lithium, and
i) The volume expansion coefficient of the lithium alloyed product is 1.2 or more and 6.0 or less, and
ii) Either the capacity density per weight is 0.4 Ah / g or more and 4.0 Ah / g or the capacity density per volume is 0.7 Ah / cc or more and 2.3 Ah / cc or less. Satisfy at least one of them.

  The above condition i) indicates the ease of expansion during alloying by lithium occlusion of a metal or metal compound, which occurs when charging a lithium secondary battery, which is typical as a non-aqueous electrolyte secondary battery. .

  Further, the condition of the above ii) is that the metal or the metal compound has a theoretical capacity density of a certain value or more per weight or volume when lithium alloyed, that is, the load due to lithium occlusion. It is a value indicating the minimum level of.

  In other words, the fact that the metal or metal compound satisfies the above i) and ii) means that the continuous load of the volume change accompanying charge / discharge is particularly large when acting as the negative electrode of the non-aqueous electrolyte secondary battery. In the case of using such a specific metal or metal compound, it is a feature of the present invention that the combination with a specific separator is important.

  Hereinafter, the conditions i) and ii) will be described in more detail.

Explanation of i) The volume expansion rate is a rate of change of volume accompanying the occlusion of lithium in the metal or metal compound M, and is obtained as follows.
When the composition ratio of the lithium alloy Li _x M (x is a coefficient determined according to the composition ratio when M and lithium are alloyed) formed by the metal or metal compound M occlusion with lithium is known, Calculated using the formula. As the composition ratio of the lithium alloy, the values listed in Reference Document 1 “BINARY ALLOY PHASE DIAGRAMS (Thaddeus B. Massalski)” can be used.
Volume expansion rate = ((W _Li × x + W _M ) / ρ _LiM ) / (W _M / ρ _M )
W _Li and W _M are the molar weights of lithium and metal or metal compound M, and ρ _M and ρ _LiM are the _densities of metal or metal compound M and lithium alloyed product Li _x M, respectively.
The density of the lithium alloyed product is obtained by proportionally distributing the density of Li alone and the metal or metal compound alone to the alloy composition obtained from Reference 1.

Explanation of ii)
Explanation of (a) (capacity density per weight) of ii) The ratio of the theoretical capacity converted from the amount of lithium in the lithium alloyed product of metal or metal compound M per weight of the metal or metal compound. The capacity density (Ah / g) per weight is calculated by the following equation using the molar weight W _M of the coefficient x and metal or metal compound M obtained from the composition ratio of the lithium alloy. As the composition of the lithium alloy, the values listed in Reference 1 can be used. F is a Faraday constant (= 96485 C / mol).
Capacity density per weight = (F × x) / W _M / 3600

Explanation of (b) (capacity density per volume) of ii) Ratio of theoretical capacity converted from the amount of lithium in the lithium alloyed product of metal or metal compound M per volume of lithium alloyed product of the metal and the metal compound It is. The capacity density per volume (Ah / cc) is calculated by the following equation using the coefficient x obtained from the composition ratio of the lithium alloy, the density ρ _LiM of the lithium alloy product, and the molar weight of each substance. As the composition of the lithium alloy, the values listed in Reference 1 can be used. The density of the lithium alloyed product is obtained by proportionally distributing the density of Li alone and the metal or metal compound alone to the alloy composition obtained from Reference 1. F is a Faraday constant (= 96485 C / mol).
Capacity density per volume = ρ _LiM (F × x) / (W _Li × x + W _M ) / 3600

  The values of Al, Si, Zn, Ga, Ge, Ag, Cd, In, Sn, Sb, Pb, and Bi, which are representative examples of metals capable of forming an alloy with lithium, are shown in the following table. .

  The lower limit of the volume expansion coefficient of the negative electrode according to the present invention is 1.2 or more, particularly 2.0 or more, particularly 3.0 or more, and the upper limit is 6.0 or less. If the volume expansion rate is below this lower limit, the rate of change of volume expansion is small, and a high discharge capacity cannot be obtained although it is difficult to obtain the effects of the present invention. To date, no metal or metal compound capable of forming an alloy with lithium has a volume expansion coefficient exceeding 6.0.

  The lower limit of the capacity density per weight of the negative electrode according to the present invention is 0.4 Ah / g or more, especially 0.5 Ah / g or more, particularly 1.0 Ah / g or more, and the upper limit is 4.0 Ah / g or less. When the capacity density per weight is below this lower limit, the load due to charging / discharging is small, and it is difficult to obtain the effect of the present invention, but a high discharge capacity cannot be obtained. To date, no metal or metal compound capable of forming an alloy with lithium has a capacity density per weight exceeding 4.2 Ah / g.

  In addition, the lower limit of the capacity density per volume of the negative electrode according to the present invention is 0.7 Ah / cc or more, particularly 0.8 Ah / cc or more, particularly 1.0 Ah / cc or more, and the upper limit is 2.3 Ah / cc or less. is there. When the capacity density per volume is below this lower limit, the load due to charging / discharging is small, and a high discharge capacity cannot be obtained although it is difficult to obtain the effects of the present invention. To date, no metal or metal compound capable of forming an alloy with lithium has a capacity density per volume exceeding 2.5 Ah / cc.

  The negative electrode according to the present invention is a metal and metal compound capable of forming an alloy with lithium, preferably Al, Si, Zn, Ga, Ge, Ag, Cd, In, Sn, Sb, Pb, Bi, and these metals. It may be comprised only by 1 type of the compounds, and may be comprised combining these 2 or more types.

  The negative electrode material according to the present invention can be used in combination with a negative electrode material other than the metal and metal compound capable of forming an alloy with lithium as long as the effects of the present invention are not impaired. In this case, as other negative electrode materials that can be used in combination, metals and metal compounds other than metals and metal compounds capable of forming an alloy with lithium, for example, metals such as Cu and Ni that do not form an alloy with lithium or compounds thereof, Carbonaceous materials, for example, graphite materials such as natural graphite and artificial graphite, amorphous materials such as fired products of acetylene black and ketchan black petroleum pitch, carbon materials such as fullerene and nanotubes, or a mixture of graphite and amorphous materials 1 type, or 2 or more types, such as a composite_body | complex, can be used.

  When these other negative electrode materials are used in combination, the use ratio is usually about 95% by weight or less based on the metal or metal compound capable of forming an alloy with lithium.

  In addition, as a metal compound capable of forming an alloy with lithium or a metal compound of another negative electrode material, an oxide, nitride, carbide, or the like of each metal can be used.

Although the form of the negative electrode which concerns on this invention is not ask | required, the following are normally mentioned.
(A) A metal capable of forming an alloy with lithium, or in some cases, an electrode containing this and other metals and, if necessary, a conductive agent.
(B) A thin-film electrode having a thin layer containing a metal capable of forming an alloy with lithium on the current collector, or in some cases, another metal and, if necessary, a conductive agent.
(C) On the current collector, particles containing a metal capable of forming an alloy with lithium, or in some cases, particles thereof and carbonaceous material or other metal particles, and further containing a binder or a conductive agent as necessary. Thin film electrode with thin layer

  For the current collector of the negative electrode, for example, a metal foil such as copper, nickel, stainless steel, or nickel-plated steel can be used. Moreover, it is also possible to surface-treat these collectors as needed.

The thickness of the negative electrode, that is, the thickness of the electrode or thin film electrode in the above (A) to (C) (not including the thickness of the current collector) is not particularly limited, but is usually 200 μm or less. In particular, in the case of a thin film of 100 μm or less, the influence of the volume expansion of the negative electrode is large, and the effect of the present invention is easily obtained.
The lower limit of the negative electrode thickness is usually preferably about 1 μm in order to obtain a high discharge capacity.

The negative electrode according to the present invention is produced, for example, as follows.
Preparation of negative electrode in the form of (A) above: particles containing metal capable of forming an alloy with lithium, or the case
And need carbonaceous and other metal particles, by
Accordingly, sintering is performed together with a conductive agent.
Production of negative electrode in the form of (B) above: a metal capable of forming an alloy with lithium on the current collector, or
If other metals are included in some cases,
The raw material containing these is released into the gas layer and deposited on the current collector.
The
Preparation of negative electrode in the form of (C) above: particles containing metal capable of forming an alloy with lithium, or the case
And need carbonaceous and other metal particles, by
Depending on the current, the dispersion with the binder and conductive agent is dispersed on the current collector.
Apply to dry.

  Here, as the shape of the metal particles, the carbonaceous material particles, and the other metal particles, wire-shaped, spherical, scale-shaped, and irregular-shaped particles are usually used.

  As the dispersion medium, 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.

  Further, 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.

  As the conductive agent, carbon materials such as amorphous carbon such as acetylene black and ketjen black and carbon having a graphite structure, nickel, copper, silver, titanium, platinum, aluminum, cobalt, iron, and chromium are used.

[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 spiral, 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.

  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.

  EXAMPLES 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]
<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 0.17 μm] 117.6 parts by weight as an inorganic filler, melt-kneaded, and the resulting resin composition was heated to 210 Inflation molding was performed at 0 ° C. to obtain a raw sheet. The thickness of the original fabric sheet was 110 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 25 μm and porosity. A porous polymer membrane having 61%, an average pore size of 0.19 μm, and a Gurley air permeability of 85 seconds / 100 cc was obtained. This polymer porous membrane is called separator A. During the stretching process, the inorganic filler was not removed from the porous polymer membrane.

  With respect to this separator A, the average liquid retention rate change rate obtained by the measurement method described above was as shown in Table 3.

<Preparation of non-aqueous electrolyte solution>
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. To this mixed solvent, sufficiently dried LiPF ₆ was dissolved at a ratio of 1.0 mol / l to obtain a non-aqueous electrolyte.

<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.

<Production of negative electrode>
An electrolytic copper foil (thickness 18 μm, substrate surface roughness Ra = 0.33 μm) was used, and a silicon thin film was formed on the electrolytic copper foil by RF sputtering to form a negative electrode. The RF sputtering conditions were a sputtering gas (Ar) flow rate of 100 sccm, a reaction pressure of 40 mTorr, and the silicon thin film was deposited until the thickness became 5 μm. The volume expansion rate, capacity density per weight, and capacity density per volume of this negative electrode were as follows.
Volume expansion rate: 4.1
Capacity density per weight: 4.0 Ah / g
Capacity density per volume: 2.3 Ah / cc

<Battery assembly>
A 2032 type coin cell was manufactured using the separator A, the non-aqueous electrolyte, the positive electrode, and the negative electrode. That is, a stainless steel can that also serves as a positive electrode conductor is accommodated with a positive electrode impregnated with an electrolyte by punching into a disk shape having a diameter of 12.5 mm, and a separator having a diameter of 18.8 mm impregnated with the electrolyte A negative electrode impregnated with an electrolyte by punching into a disk shape having a diameter of 12.5 mm was placed. The can body and a sealing plate serving also as a negative electrode conductor were caulked and sealed via an insulating gasket to produce a coin-type battery. Here, the impregnation of the battery member with the electrolytic solution was performed by immersing each member in the electrolytic solution for 2 minutes.

<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) Cycle test 1) After charging the battery that had been initially charged / discharged with a constant current constant voltage method of 2C up to an upper limit voltage of 4.2V, the battery was discharged with a constant current of 2C up to a final discharge voltage of 3.0V. The charge / discharge cycle to be performed was one cycle, and this cycle was repeated 15 cycles. The cycle test is performed at 25 ° C. The ratio of the discharge capacity at the 15th cycle to the discharge capacity at the 1st cycle in this cycle test is shown in Table 3 as the cycle retention rate.

[Example 2]
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" manufactured by the company, weight average molecular weight: 330,000] 8.8 parts by weight, hydrogenated castor oil ["HY-CASTOR OIL" manufactured by Toyokuni Oil Co., Ltd., molecular weight 938] 8.8 parts by weight, barium sulfate as an inorganic filler [ Number reference average particle size 0.18 μm] 176.5 parts by weight were blended and melt-kneaded, and the resulting resin composition was subjected to inflation molding at a temperature of 210 ° 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 B. During the stretching process, the inorganic filler was not removed from the porous polymer membrane.

  With respect to this separator B, the average liquid retention rate change rate obtained by the measurement method described above was as shown in Table 3.

  A coin-type battery was prepared in the same procedure as in Example 1 except that the separator B was used. The coin-type battery was evaluated in the same manner, and the results are shown in Table 3.

[Comparative Example 1]
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 C.

  With respect to this separator C, the average liquid retention rate change rate obtained by the measurement method described above was as shown in Table 3.

  A coin-type battery was prepared in the same procedure as in Example 1 except that the separator C was used. The coin-type battery was evaluated in the same manner, and the results are shown in Table 3.

  In addition, in order to clarify the effect of the presence or absence of the filler, the separator C of Comparative Example 1 has the same area stretch ratio (about 12 times) as compared with the separators A and B of Examples 1 and 2. .

  As is clear from Table 3 above, the lithium secondary batteries of Examples 1 and 2 equipped with the separator containing the inorganic filler in the thermoplastic resin had a pore size not containing the inorganic filler obtained by the extraction method. The cycle characteristics were better than those of Comparative Example 1 using a small separator.

  As described above, the separator C obtained by the extraction method used in Comparative Example 1 is equivalent to the separators A and B produced by the interfacial peeling method used in Examples 1 and 2, and the same sheet stretch sheet with the same area stretch ratio. Although the average pore diameters of the separators A and B are significantly different, the average pore diameters are 0.19 μm and 0.27 μm. 04 μm. The separators A and B have excellent average liquid retention rates of 11.3% / min and 9.2% / min, respectively, while the separator C has an average liquid retention rate. The rate of change is 17.2% / min. Thus, in Examples 1 and 2 using separators A and B having large pore diameters and good liquid retention properties, the average pore diameters are greatly different and the liquid retention properties are also completely different. In addition, the liquid retention due to the chemical affinity effect by the filler is improved, and the depletion and uneven distribution of the electrolyte accompanying the expansion and contraction of the negative electrode during the cycle are suppressed, resulting in excellent cycle characteristics. Can be obtained. On the other hand, in Comparative Example 1 using the separator C having a small hole diameter and poor liquid retention, such an effect cannot be obtained, and the cycle characteristics are deteriorated.

  In addition, in the film formation by the extraction method, even if the stretching ratio is increased, densification (shrinkage in the thickness direction due to stretching) occurs. Therefore, the pore diameter of the obtained porous film is not so large, and on the contrary, the pore diameter is small. Therefore, it is difficult to realize a separator effective for improving liquid retention.

  Such an effect of improving the cycle characteristics is similarly expected for Sn, Al, Ag, Pb, etc., which show a high volume expansion rate like silicon and have a high capacity density per weight or volume. Is.

  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 has excellent cycle characteristics while achieving high capacity, such as various information communication terminals and mobile objects, where high capacity is required and used repeatedly. Particularly excellent effects can be obtained.

Claims (8)

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,
The separator has a thickness of 5 μm to 100 μm, a porosity of 30% to 80%, an average pore size defined by ASTM F316-86 of 0.05 μm to 10 μm, and a Gurley permeability of 20 defined by JIS P8117. Second / 100 cc to 700 second / 100 cc, average liquid retention rate change rate is 15% / minute or less,
The negative electrode contains a metal or metal compound capable of forming an alloy with lithium (except for lithium-aluminum alloys and lithium-zinc alloy lithium alloys),
i) The volume expansion coefficient of the lithium alloyed product of the metal or the metal compound with respect to the metal or the metal compound is 1.2 or more and 6.0 or less,
ii) satisfy the following condition (a) and / or condition (b), and
(a) The ratio of the theoretical capacity converted from the amount of lithium in the lithium alloyed product of the metal or the metal compound per weight of the metal or the metal compound is 0.4 Ah / g or more and 4.0 Ah / g or less.
(b) The ratio of the theoretical capacity converted from the amount of lithium in the lithium alloyed product of the metal or the metal compound per volume of the metal or the metal compound is 0.7 Ah / cc or more and 2.3 Ah / cc or less.
iii) A dispersion prepared by sintering the metal or metal compound capable of forming an alloy with lithium or having the metal or metal compound capable of forming an alloy with lithium dispersed therein is applied onto a current collector and dried. A non-aqueous electrolyte secondary battery characterized by being manufactured.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal or metal compound capable of forming an alloy with lithium is Al, Si, Zn, Ga, Ge, Ag, Cd, In, Sn, Sb, Pb, And a non-aqueous electrolyte secondary battery comprising at least one metal selected from the group consisting of Bi and a compound of the metal.   3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode is a thin film having a thickness of 100 μm or less. 4.   4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode includes particles containing a metal capable of forming an alloy with lithium and a binder on a current collector. A non-aqueous electrolyte secondary battery, which is a thin film electrode having a thin layer. In the non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, the negative electrode is lithium and the alloy capable of forming a metal or metal compound, at least one metal and a carbonaceous material other than the metal And a non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5 , wherein the amount of the inorganic filler in the separator is 100 parts by weight or more with respect to 100 parts by weight of the thermoplastic resin. A non-aqueous electrolyte secondary battery. Wherein in the non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the lithium salt is a fluorine-containing lithium salt, that non-aqueous solvent contains a cyclic carbonate and a chain carbonate A non-aqueous electrolyte secondary battery. In the non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, the positive electrode, a nonaqueous electrolyte secondary battery, which comprises a lithium transition metal composite oxide as an active material.