JP6103419B2 - Cathode active material - Google Patents

Description

  The present invention relates to a positive electrode active material. In particular, the present invention relates to a positive electrode active material used for a non-aqueous electrolyte secondary battery.

  Lithium composite metal oxides are used as positive electrode active materials for nonaqueous electrolyte secondary batteries, particularly as positive electrode active materials for lithium secondary batteries. Lithium secondary batteries have already been put into practical use as small power sources for mobile phones and laptop computers, and are also being applied to medium and large power sources for automobiles and power storage.

  As a conventional lithium composite metal oxide, Patent Document 1 describes a lithium-nickel-manganese composite oxide having a layered structure. Here, the compound is obtained by mixing a transition metal composite oxide obtained by a coprecipitation method and lithium hydroxide and firing in air at 900 ° C. for 12 hours.

JP 2005-187282 A

  However, the nonaqueous electrolyte secondary battery using the above lithium-nickel-manganese composite oxide as the positive electrode active material is not sufficient in terms of discharge capacity and cycle characteristics. Further, in the synthesis method as described above, elements such as Al, Mg, Ca, Zn, Si, Sn, and V are doped with elements that can be expected to improve battery characteristics such as discharge capacity and cycle characteristics by doping transition metals. It was difficult to do. The objective of this invention is providing the positive electrode active material which gives the nonaqueous electrolyte secondary battery excellent in discharge capacity and cycling characteristics.

  As a result of various studies, the present inventors have found that the following inventions meet the above object, and have reached the present invention.

That is, the present invention provides the following inventions.
<1> a lithium compound, M ¹¹ (M ¹¹ is one or more elements selected from the group consisting of Al, Mg, Ca, Zn, Si, Sn and V) and M ²¹ (M ²¹ is an element other than M ^11, and a positive electrode comprising the step of a raw material containing a one or more transition metal elements selected from transition metal elements excluding Fe.), calcined in the presence of an inert molten agent A method for producing an active material.
<2> Carbonate, A sulfate, A nitrate, A phosphate, A hydroxide, A chloride, A molybdate, and A tungstate, where the inert melting agent is A carbonate One or more inert melting agents selected from the group consisting of (where A represents one or more metal elements selected from the group consisting of Na, K, Rb, Cs, Ca, Mg, Sr and Ba) The method for producing a positive electrode active material according to <1>, wherein
<3> The method for producing a positive electrode active material according to <1> or <2>, wherein the inert melting agent is a carbonate of A (where A has the same meaning as described above).
The manufacturing method of the positive electrode active material in any one of said <1>-<3> whose <4> baking temperature is 650-950 degreeC.
<5> The method for producing a positive electrode active material according to any one of <1> to <4>, wherein M ¹¹ is V.
<6> The method for producing a positive electrode active material according to any one of <1> to <5>, wherein M ²¹ is at least one transition metal element selected from the group consisting of Ni, Co, and Mn.
<7> A positive electrode active material obtained by the production method according to any one of <1> to <6>.
<8> The positive electrode active material according to <7>, wherein the positive electrode active material is represented by the following formula (I).
Li _x M ¹¹ _y M ²¹ _1-y O ₂ (I)
(M ¹¹ is one or more elements selected from the group consisting of Al, Mg, Ca, Zn, Si, Sn and V, M ²¹ is an element other than M ¹¹ , and a transition excluding Fe One or more transition metal elements selected from metal elements have the same meaning as above, x is 0.9 or more and 1.3 or less, and y is more than 0 and 0.1 or less.
<9> The positive electrode active material according to <8>, wherein y is greater than 0 and not greater than 0.01.
<10> A positive electrode having the positive electrode active material according to any one of <7> to <9>.
<11> A nonaqueous electrolyte secondary battery having the positive electrode according to <10>.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material which gives the nonaqueous electrolyte secondary battery excellent in discharge capacity and cycling characteristics can be obtained.

The positive electrode active material of the present invention includes a lithium compound, M ¹¹ (M ¹¹ is one or more elements selected from the group consisting of Al, Mg, Ca, Zn, Si, Sn, and V) and M ^21. (M ²¹ is an element other than M ¹¹ and one or more transition metal elements selected from transition metal elements other than Fe) and is fired in the presence of an inert melting agent. It is a manufacturing method of the positive electrode active material which has the process to do.

  In the present invention, the inert melting agent is difficult to react with the lithium composite metal oxide raw material during firing, and includes A carbonate, A sulfate, A nitrate, A phosphate, A One or more inert melting agents selected from the group consisting of: a hydroxide of A, a chloride of A, a molybdate of A, and a tungstate of A (where A is Na, K, Rb, Cs, It preferably represents one or more elements selected from the group consisting of Ca, Mg, Sr and Ba.

Examples of the carbonate of A include Na ₂ CO ₃ , K ₂ CO ₃ , Rb ₂ CO ₃ , Cs ₂ CO ₃ , CaCO ₃ , MgCO ₃ , SrCO ₃ , and BaCO ₃ .

As the sulfate _A, mention may be made of _{Na 2 SO 4, K 2 SO} 4, Rb 2 SO 4, Cs 2 SO 4, CaSO 4, MgSO 4, SrSO 4, BaSO 4.

Examples of the nitrate of A include NaNO ₃ , KNO ₃ , RbNO ₃ , CsNO ₃ , Ca (NO ₃ ) ₂ , Mg (NO ₃ ) ₂ , Sr (NO ₃ ) ₂ , and Ba (NO ₃ ) _2. .

As the phosphate of A, Na ₃ PO ₄ , K ₃ PO ₄ , Rb ₃ PO ₄ , Cs ₃ PO ₄ , Ca ₃ (PO ₄ ) ₂ , Mg ₃ (PO ₄ ) ₂ , Sr ₃ (PO ₄ ) ₂ and Ba ₃ (PO ₄ ) ₂ .

Examples of the hydroxide of A include NaOH, KOH, RbOH, CsOH, Ca (OH) ₂ , Mg (OH) ₂ , Sr (OH) ₂ , and Ba (OH) ₂ .

Examples of the chloride of A include NaCl, KCl, RbCl, CsCl, CaCl ₂ , SrCl ₂ , BaCl ₂ and MgCl ₂ .

Examples of A molybdate include Na ₂ MoO ₄ , K ₂ MoO ₄ , Rb ₂ MoO ₄ , Cs ₂ MoO ₄ , CaMoO ₄ , MgMoO ₄ , SrMoO ₄ , and BaMoO ₄ .

Examples of the tungstate of A include Na ₂ WO ₄ , K ₂ WO ₄ , Rb ₂ WO ₄ , Cs ₂ WO ₄ , CaWO ₄ , MgWO ₄ , SrWO ₄ , and BaWO ₄ .

Two or more of these inert melting agents can also be used. Among these inert melting agents, as the inert melting agent for obtaining a fine positive electrode active material having higher crystallinity and less agglomeration between primary particles, carbonate of A is preferable, and Na _{2 is} particularly preferable. CO ₃ and K ₂ CO ₃ are preferable. By using these inert melting agents, a positive electrode active material that provides a non-aqueous electrolyte secondary battery having a higher discharge capacity can be obtained. Moreover, you may use together inert melt agents other than the inert melt agent quoted above as needed. Examples of the inert melting agent include inert melting agents such as KF, NH ₄ F, and NH ₄ Cl.

  In the present invention, the amount of the inert melting agent during firing is usually 0.1 to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material raw material. A preferable amount of the inert melting agent is 0.5 to 90 parts by weight, more preferably 1 to 80 parts by weight.

  The holding temperature in the calcination is an important factor in the sense of adjusting the BET specific surface area of the obtained lithium composite metal oxide. Usually, the higher the holding temperature, the smaller the BET specific surface area tends to be. The BET specific surface area tends to increase as the holding temperature is lowered. The holding temperature in normal firing can be in the range of 200 to 1050 ° C, and the preferable holding temperature can be in the range of 650 to 950 ° C. The setting of the holding temperature depends on the kind of the inert melting agent to be used, and the melting point of the inert melting agent may be taken into consideration, and it is preferable to perform the holding temperature in the range of melting point minus 100 ° C. or higher and melting point plus 100 ° C. or lower. The holding time at the holding temperature is usually 0.1 to 20 hours, preferably 0.5 to 8 hours. The rate of temperature rise to the holding temperature is usually 50 to 400 ° C./hour, and the rate of temperature drop from the holding temperature to room temperature is usually 10 to 400 ° C./hour. As the firing atmosphere, air, oxygen, nitrogen, argon, or a mixed gas thereof can be used, but an air atmosphere is preferable. The inert melting agent may remain in the lithium composite metal oxide or may be removed by washing, evaporation, or the like.

  Further, after firing, the positive electrode active material may be pulverized using a ball mill or a jet mill, or pulverization and firing may be repeated twice or more. Further, the positive electrode active material can be washed or classified as necessary.

Moreover, it is preferable that the positive electrode active material of this invention is shown by following formula (I).
Li _x M ¹¹ _y M ²¹ _1-y O ₂ (I)

  In the present invention, x is preferably 0.9 or more and 1.3 or less in the sense of further improving the cycle characteristics and discharge capacity of the battery obtained.

M ¹¹ is one or more elements selected from the group consisting of Al, Mg, Ca, Zn, Si, Sn and V. In order to increase the discharge capacity of the obtained nonaqueous electrolyte secondary battery, V, One or more transition metal elements selected from the group consisting of Al and Mg are preferable, and V is more preferable.

M ²¹ is one other than M ¹¹ and one or more transition metal elements selected from transition metal elements excluding Fe, and contains one or more selected from the group consisting of Ni, Co, and Mn. Is preferred.

  Further, y is preferably more than 0 and 0.1 or less, and more preferably more than 0 and 0.01 or less.

As the lithium compound in the present invention, lithium hydroxide, lithium hydroxide monohydrate, and lithium carbonate are preferably used. As raw materials containing M ¹¹ and M ²¹ , oxides, hydroxides (also oxyhydroxides may be used). Including the same.), Chloride, carbonate, sulfate, nitrate, oxalate, acetate, and the like. Two or more of these may be mixed. The raw material containing M ¹ and M ² can also be obtained by coprecipitation.

  The above positive electrode active material is useful for a non-aqueous electrolyte secondary battery excellent in high discharge capacity and cycle characteristics.

  In the positive electrode active material of the present invention, a part of the transition metal element may be substituted with another element within a range not impairing the effects of the present invention. Here, examples of other elements include elements such as B, Ga, In, and Ge.

  In addition, a compound different from the active material may be attached to the particle surface of the positive electrode active material in the present invention as long as the effects of the present invention are not impaired. As the compound, a compound containing at least one element selected from the group consisting of B, Al, Ga, In, Si, Ge, Sn, Mg and a transition metal element, preferably B, Al, Mg, Ga, A compound containing one or more elements selected from the group consisting of In and Sn, more preferably an Al compound, and specific examples of the compound include oxides, hydroxides, and oxywater of the elements. Examples thereof include oxides, carbonates, nitrates, and organic acid salts, and oxides, hydroxides, and oxyhydroxides are preferable. Moreover, you may use these compounds in mixture. Among these compounds, a particularly preferred compound is alumina. Moreover, you may heat after adhesion.

  The positive electrode active material of the present invention is suitable for a nonaqueous electrolyte secondary battery. In the present invention, the positive electrode active material may have different compounds attached to the particle surface as described above.

  As a method of manufacturing the positive electrode using the positive electrode active material, a case of manufacturing a positive electrode for a non-aqueous electrolyte secondary battery will be described as an example.

  The positive electrode is manufactured by supporting a positive electrode mixture containing a positive electrode active material, a conductive material and a binder on a positive electrode current collector. A carbon material can be used as the conductive material, and examples of the carbon material include graphite powder, carbon black such as acetylene black, and fibrous carbon material. Moreover, you may use these in mixture of 2 or more types. Since carbon black such as acetylene black is fine and has a large surface area, it can improve the electrical conductivity inside the positive electrode and improve the charge / discharge efficiency and rate characteristics by adding it in a small amount in the positive electrode mixture. As a result, the binding property by the binder of the positive electrode mixture and the positive electrode current collector is lowered, and the internal resistance is increased. Usually, the ratio of the conductive material in the positive electrode mixture is 5 to 20 parts by weight with respect to 100 parts by weight of the positive electrode active material. When a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive material, this ratio can be lowered.

  As the binder, a thermoplastic resin can be used. Specifically, polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), and four fluorine. Fluoropolymers such as fluorinated ethylene / hexafluoropropylene / vinylidene fluoride copolymers, propylene hexafluoride / vinylidene fluoride copolymers, tetrafluoroethylene / perfluorovinyl ether copolymers, polyethylene, polypropylene, etc. Polyolefin resin and the like. Moreover, you may use these 2 types or more in mixture. Further, by using a fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin to the positive electrode mixture is 1 to 10% by weight, and the ratio of the polyolefin resin is 0.1 to 2% by weight, A positive electrode mixture excellent in binding property with the positive electrode current collector can be obtained.

  As the positive electrode current collector, Al, Ni, stainless steel or the like can be used, but Al is preferable in that it is easily processed into a thin film and is inexpensive. As a method of supporting the positive electrode mixture on the positive electrode current collector, there is a method of pressure molding, or a method of pasting using an organic solvent or the like, applying onto the positive electrode current collector, drying and pressing to fix the positive electrode current collector. Can be mentioned. In the case of forming a paste, a slurry composed of a positive electrode active material, a conductive material, a binder, and an organic solvent is prepared. Examples of the organic solvent include amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; ester solvents such as methyl acetate; dimethylacetamide, N-methyl- Examples include amide solvents such as 2-pyrrolidone.

  Examples of the method for applying the positive electrode mixture to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. By the method mentioned above, the positive electrode for nonaqueous electrolyte secondary batteries can be manufactured.

  As a method for manufacturing a non-aqueous electrolyte secondary battery using the above positive electrode, a case of manufacturing a lithium secondary battery will be described as an example. That is, the electrode group obtained by laminating and winding the separator, the negative electrode, and the positive electrode can be manufactured by impregnating the electrolytic solution after the electrode group is housed in the battery case.

  As the shape of the electrode group, for example, a shape in which the cross section when the electrode group is cut in a direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, a rectangle with rounded corners, etc. Can be mentioned. In addition, examples of the shape of the battery include a paper shape, a coin shape, a cylindrical shape, and a square shape.

  The negative electrode only needs to be capable of doping and dedoping lithium ions at a lower potential than the positive electrode, and an electrode in which a negative electrode mixture containing a negative electrode material is supported on a negative electrode current collector, or an electrode made of a negative electrode material alone Can be mentioned. Examples of the negative electrode material include carbon materials, chalcogen compounds (oxides, sulfides, and the like), nitrides, metals, and alloys that can be doped and dedoped with lithium ions at a lower potential than the positive electrode. Moreover, you may use these negative electrode materials in mixture.

The negative electrode material is exemplified below. Specific examples of the carbon material include graphite such as natural graphite and artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fiber, and fired organic polymer compound. Examples oxide, _{specifically,} (wherein, x represents a positive real number) SiO 2, SiO, etc. formula SiO _x oxides of silicon represented by; TiO _2, TiO, etc. by the formula TiO _x (wherein, x Is an oxide of titanium represented by a positive real number; an oxide of vanadium represented by a formula VO _x (where x is a positive real number) such as V ₂ O ₅ and VO ₂ ; Fe ₃ O ₄ , Fe ₂ O ₃ , FeO, etc. Iron oxide represented by the formula FeO _x (where x is a positive real number); SnO ₂ , SnO, etc. represented by the formula SnO _x (where x is a positive real number) Tin oxide; tungsten oxide represented by the general formula WO _x (where x is a positive real number) such as WO ₃ and WO ₂ ; Li ₄ Ti ₅ O ₁₂ , LiVO ₂ (Li _1.1 V _0.9 O ₂ Composite metal oxides containing lithium and titanium and / or vanadium, etc. Can. Specific examples of the sulfide include titanium sulfide represented by the formula TiS _x (where x is a positive real number) such as Ti ₂ S ₃ , TiS ₂ , and TiS; V ₃ S ₄ , VS _2, Vanadium sulfide represented by the formula VS _x (where x is a positive real number), such as VS; FeS _x (where x is a positive real number), such as Fe ₃ S ₄ , FeS ₂ , FeS Iron sulfide; molybdenum sulfide represented by the formula MoS _x (where x is a positive real number) such as Mo ₂ S ₃ , MoS ₂ ; SnS _x such as SnS _2, SnS where x is A sulfide of tin represented by a positive real number; a sulfide of tungsten represented by WS _{2 and the} like WS _x (where x is a positive real number); and a formula SbS _x such as Sb ₂ S ₃ (where x is antimony represented by a positive real _{number); Se 5 S 3, SeS} 2, SeS formula SeS _x (wherein such, Mention may be made of such sulfide selenium represented by a positive real number). Specific examples of the nitride include lithium-containing nitrides such as Li ₃ N, Li _3-x A _x N (where A is Ni and / or Co, and 0 <x <3). Can be mentioned. These carbon materials, oxides, sulfides, and nitrides may be used in combination, and may be crystalline or amorphous. Further, these carbon materials, oxides, sulfides and nitrides are mainly carried on the negative electrode current collector and used as electrodes.

Specific examples of the metal include lithium metal, silicon metal, and tin metal. Examples of the alloy include lithium alloys such as Li—Al, Li—Ni, and Li—Si; silicon alloys such as Si—Zn; Sn—Mn, Sn—Co, Sn—Ni, Sn—Cu, and Sn—La. In addition to tin alloys such as Cu ₂ Sb, La ₃ Ni ₂ Sn _{7 and the} like. These metals and alloys are mainly used alone as electrodes (for example, used in a foil shape).

  Among the negative electrode materials, from the viewpoint of high potential flatness, low average discharge potential, good cycle characteristics, and the like, a carbon material mainly composed of graphite such as natural graphite or artificial graphite is preferably used. The shape of the carbon material may be any of a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder.

  The negative electrode mixture may contain a binder as necessary. Examples of the binder include thermoplastic resins, and specific examples include PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyethylene, and polypropylene.

  Examples of the negative electrode current collector include Cu, Ni, and stainless steel. Cu may be used because it is difficult to form an alloy with lithium and it is easy to process into a thin film. The method of supporting the negative electrode mixture on the negative electrode current collector is the same as in the case of the positive electrode. The method is a method of pressure molding, pasted using a solvent, etc., coated on the negative electrode current collector, dried, pressed and pressed. And the like.

  As the separator, for example, a material having a form such as a porous membrane, a nonwoven fabric, a woven fabric made of a polyolefin resin such as polyethylene and polypropylene, a fluororesin, a nitrogen-containing aromatic polymer, and the like can be used. Moreover, it is good also as a separator using 2 or more types of the said material, and the said material may be laminated | stacked. Examples of the separator include separators described in JP 2000-30686 A, JP 10-324758 A, and the like. The thickness of the separator is preferably about 5 to 200 μm, and preferably about 5 to 40 μm, as long as the mechanical strength is maintained because the volume energy density of the battery is increased and the internal resistance is reduced.

  The separator preferably has a porous film containing a thermoplastic resin. In a non-aqueous electrolyte secondary battery, normally, when an abnormal current flows in the battery due to a short circuit between the positive electrode and the negative electrode, the function of shutting down the current and preventing the excessive current from flowing (shut down) It is preferable to have. Here, the shutdown is performed by closing the micropores of the porous film in the separator when the normal use temperature is exceeded. After the shutdown, even if the temperature in the battery rises to a certain high temperature, it is preferable to maintain the shutdown state without breaking the film due to the temperature. Examples of such a separator include a laminated film in which a heat-resistant porous layer and a porous film are laminated. By using the film as a separator, the heat resistance of the secondary battery in the present invention can be further increased. . Here, the heat-resistant porous layer may be laminated on both surfaces of the porous film.

  Hereinafter, a laminated film in which the heat-resistant porous layer and the porous film are laminated will be described.

  In the laminated film, the heat resistant porous layer is a layer having higher heat resistance than the porous film, and the heat resistant porous layer may be formed of an inorganic powder or may contain a heat resistant resin. When the heat resistant porous layer contains a heat resistant resin, the heat resistant porous layer can be formed by an easy technique such as coating. Examples of the heat resistant resin include polyamide, polyimide, polyamideimide, polycarbonate, polyacetal, polysulfone, polyphenylene sulfide, polyetherketone, aromatic polyester, polyethersulfone, and polyetherimide, from the viewpoint of further improving heat resistance. , Polyamide, polyimide, polyamideimide, polyethersulfone, and polyetherimide are preferable, and polyamide, polyimide, and polyamideimide are more preferable. Even more preferred are nitrogen-containing aromatic polymers such as aromatic polyamides (para-oriented aromatic polyamides, meta-oriented aromatic polyamides), aromatic polyimides, aromatic polyamideimides, and particularly preferred are aromatic polyamides and production surfaces. Particularly preferred is para-oriented aromatic polyamide (hereinafter sometimes referred to as para-aramid). Further, examples of the heat resistant resin include poly-4-methylpentene-1 and cyclic olefin polymers. By using these heat resistant resins, the heat resistance of the laminated film, that is, the thermal film breaking temperature of the laminated film can be further increased. Among these heat-resistant resins, when using a nitrogen-containing aromatic polymer, because of the polarity in the molecule, compatibility with the electrolyte, that is, the liquid retention in the heat-resistant porous layer may be improved, The rate of impregnation of the electrolyte during production of the nonaqueous electrolyte secondary battery is also high, and the discharge capacity of the nonaqueous electrolyte secondary battery is further increased.

  The thermal film breaking temperature of such a laminated film depends on the type of heat-resistant resin, and is selected and used according to the use scene and purpose of use. More specifically, as the heat resistant resin, the cyclic olefin polymer is used at about 400 ° C. when the nitrogen-containing aromatic polymer is used, and at about 250 ° C. when poly-4-methylpentene-1 is used. When using, the thermal film breaking temperature can be controlled to about 300 ° C., respectively. In addition, when the heat resistant porous layer is made of an inorganic powder, the thermal film breaking temperature can be controlled to, for example, 500 ° C. or higher.

  The para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4,4′- It consists essentially of repeating units bonded at opposite orientations, such as biphenylene, 1,5-naphthalene, 2,6-naphthalene, etc., oriented in the opposite direction coaxially or in parallel. Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly ( Para-aligned or para-oriented such as paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer Examples include para-aramid having a structure according to the type.

  The aromatic polyimide is preferably a wholly aromatic polyimide produced by condensation polymerization of an aromatic dianhydride and a diamine. Specific examples of the dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic Examples thereof include acid dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and the like. Specific examples of the diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, 1,5 -Naphthalene diamine etc. are mentioned. Moreover, a polyimide soluble in a solvent can be preferably used. Examples of such a polyimide include a polycondensate polyimide of 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride and an aromatic diamine.

  As the above-mentioned aromatic polyamideimide, those obtained from condensation polymerization using aromatic dicarboxylic acid and aromatic diisocyanate, those obtained from condensation polymerization using aromatic diacid anhydride and aromatic diisocyanate Is mentioned. Specific examples of the aromatic dicarboxylic acid include isophthalic acid and terephthalic acid. Specific examples of the aromatic dianhydride include trimellitic anhydride. Specific examples of the aromatic diisocyanate include 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, orthotolylane diisocyanate, m-xylene diisocyanate, and the like.

  In order to further enhance the ion permeability, the heat-resistant porous layer is preferably a thin heat-resistant porous layer having a thickness of 1 to 10 μm, more preferably 1 to 5 μm, and particularly 1 to 4 μm. The heat-resistant porous layer has fine pores, and the size (diameter) of the pores is usually 3 μm or less, preferably 1 μm or less. Moreover, when a heat resistant porous layer contains a heat resistant resin, a heat resistant porous layer can also contain the below-mentioned filler.

  In the laminated film, the porous film preferably has fine pores and has a shutdown function. In this case, the porous film contains a thermoplastic resin. The size of the micropores in the porous film is usually 3 μm or less, preferably 1 μm or less. The porosity of the porous film is usually 30 to 80% by volume, preferably 40 to 70% by volume. In the nonaqueous electrolyte secondary battery, when the normal use temperature is exceeded, the porous film containing the thermoplastic resin can close the micropores by softening the thermoplastic resin constituting the porous film.

  What is necessary is just to select the thermoplastic resin which does not melt | dissolve in the electrolyte solution in a nonaqueous electrolyte secondary battery. Specific examples include polyolefin resins such as polyethylene and polypropylene, and thermoplastic polyurethane resins, and a mixture of two or more of these may be used. In order to soften and shut down at a lower temperature, it is preferable to contain polyethylene. Specific examples of the polyethylene include polyethylene such as low density polyethylene, high density polyethylene, and linear polyethylene, and ultra high molecular weight polyethylene having a molecular weight of 1,000,000 or more. In order to further increase the puncture strength of the porous film, the thermoplastic resin constituting the film preferably contains at least ultra high molecular weight polyethylene. In addition, in terms of production of the porous film, the thermoplastic resin may preferably contain a wax made of polyolefin having a low molecular weight (weight average molecular weight of 10,000 or less).

  Moreover, the thickness of the porous film in a laminated | multilayer film is 3-30 micrometers normally, Preferably it is 3-25 micrometers. In the present invention, the thickness of the laminated film is usually 40 μm or less, preferably 30 μm or less. Moreover, when the thickness of the heat resistant porous layer is A (μm) and the thickness of the porous film is B (μm), the value of A / B is preferably 0.1 or more and 1 or less.

  Moreover, when the heat resistant porous layer contains a heat resistant resin, the heat resistant porous layer may contain one or more fillers. The filler may be selected from organic powder, inorganic powder, or a mixture thereof as the material thereof. The average particle diameter of the particles constituting the filler is preferably 0.01 to 1 μm.

  Examples of the organic powder include styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl acrylate, or a copolymer of two or more kinds, polytetrafluoroethylene, 4 fluorine. Examples include fluorine-containing resins such as fluorinated ethylene-6-propylene-propylene copolymer, tetrafluoroethylene-ethylene copolymer, and polyvinylidene fluoride; melamine resin; urea resin; polyolefin; and powders made of organic substances such as polymethacrylate. . The organic powder may be used alone or in combination of two or more. Among these organic powders, polytetrafluoroethylene powder is preferable from the viewpoint of chemical stability.

  Examples of the inorganic powder include powders made of inorganic substances such as metal oxides, metal nitrides, metal carbides, metal hydroxides, carbonates, sulfates, etc. Among these, they are made of inorganic substances having low conductivity. Powder is preferably used. Specific examples include powders made of alumina, silica, titanium dioxide, calcium carbonate, or the like. The inorganic powder may be used alone or in combination of two or more. Among these inorganic powders, alumina powder is preferable from the viewpoint of chemical stability. Here, it is more preferable that all of the particles constituting the filler are alumina particles, and it is even more preferable that all of the particles constituting the filler are alumina particles, and part or all of them are substantially spherical alumina particles. It is embodiment which is. Incidentally, when the heat-resistant porous layer is formed from an inorganic powder, the inorganic powder exemplified above may be used, and may be mixed with a binder as necessary.

  The filler content when the heat-resistant porous layer contains a heat-resistant resin depends on the specific gravity of the filler material. For example, when all of the particles constituting the filler are alumina particles, When the total weight is 100, the weight of the filler is usually 5 or more and 95 or less, preferably 20 or more and 95 or less, more preferably 30 or more and 90 or less. These ranges can be appropriately set depending on the specific gravity of the filler material.

  Examples of the shape of the filler include a substantially spherical shape, a plate shape, a columnar shape, a needle shape, a whisker shape, and a fibrous shape, and any particle can be used. It is preferable that Examples of the substantially spherical particles include particles having a particle aspect ratio (long particle diameter / short particle diameter) of 1 or more and 1.5 or less. The aspect ratio of the particles can be measured by an electron micrograph.

  In the present invention, from the viewpoint of ion permeability, the separator preferably has an air permeability of 50 to 300 seconds / 100 cc, more preferably 50 to 200 seconds / 100 cc in terms of air permeability by the Gurley method. preferable. Moreover, the porosity of a separator is 30-80 volume% normally, Preferably it is 40-70 volume%. The separator may be a laminate of separators having different porosity.

In the secondary battery, the electrolytic solution usually contains an electrolyte and an organic solvent. Examples of the electrolyte include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LIBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (COCF ₃ ), Li (C ₄ F ₉ SO ₃ ), LiC (SO ₂ CF ₃ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiBOB (where BOB is bis (oxalato) borate) .), Lithium salts such as lower aliphatic carboxylic acid lithium salts and LiAlCl _4, and a mixture of two or more of these may be used. The lithium salt is usually selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ and LiC (SO ₂ CF ₃ ) ₃ containing fluorine among them. Those containing at least one selected are used.

In the electrolytic solution, examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di ( Carbonates such as methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2-methyl Ethers such as tetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetate Amides such as amides; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or those obtained by further introducing a fluorine substituent into the above organic solvent Usually, two or more of these are used in combination. Among these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate or cyclic carbonate and ether is more preferable. The mixed solvent of cyclic carbonate and non-cyclic carbonate has a wide operating temperature range, excellent load characteristics, and is hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material. In this respect, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable. Further, it is preferable to use an electrolytic solution containing a lithium salt containing fluorine such as LiPF ₆ and an organic solvent having a fluorine substituent. A mixed solvent containing ethers having fluorine substituents such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl carbonate has excellent high-current discharge characteristics, preferable.

A solid electrolyte may be used instead of the above electrolytic solution. As the solid electrolyte, for example, an organic polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used. Moreover, what is called a gel type which hold | maintained the non-aqueous electrolyte in the high molecular compound can also be used. The _{Li 2 S-SiS 2, Li} 2 S-GeS 2, Li 2 S-P 2 S 5, Li 2 S-B 2 S 3, Li 2 S-SiS 2 -Li 3 PO 4, Li 2 S-SiS _An inorganic solid electrolyte containing a sulfide such as _2- Li ₂ SO ₄ may be used. In the nonaqueous electrolyte secondary battery of the present invention, when a solid electrolyte is used, the solid electrolyte may serve as a separator, and in that case, the separator may not be required.

  Next, the present invention will be described in more detail with reference to examples. The evaluation of the positive electrode active material, the charge / discharge test, and the cycle test were performed as follows.

1. Charge / Discharge Test PVdF as a binder is sometimes referred to as N-methyl-2-pyrrolidone (hereinafter, NMP) in a mixture of a positive electrode active material and a conductive material (a mixture of acetylene black and graphite at 9: 1). The Al foil with a thickness of 40 μm to be a current collector is prepared by adding the solution dissolved in) to a composition of active material: conductive material: binder = 87: 10: 3 (weight ratio) and kneading. The paste was applied to the substrate and vacuum dried at 150 ° C. for 8 hours to obtain a positive electrode.

1-1.25 ° C. Test The obtained positive electrode was subjected to an electrolyte solution (ethylene carbonate (hereinafter sometimes referred to as EC), dimethyl carbonate (hereinafter sometimes referred to as DMC) and ethyl methyl carbonate (hereinafter referred to as EMC). In a mixture of 30:35:35 (volume ratio) of LiPF ₆ dissolved at a concentration of 1 mol / liter (hereinafter sometimes referred to as LiPF ₆ / EC + DMC + EMC)). Thus, a coin-type battery (R2032) was fabricated by combining a polypropylene porous membrane as a separator and metal lithium as a negative electrode.

Using the above coin-type battery, a cycle test was carried out under the conditions shown below while maintaining at 25 ° C. The cycle characteristics were compared by calculating the discharge capacity retention rate according to the following.
<25 ° C cycle test>
A charge / discharge test was conducted with a maximum charge voltage of 4.3 V and a minimum discharge voltage of 2.5 V, 50 cycles, the 1st, 10th, 20th, and 50th cycles at a 0.2C rate and the other at a 1C rate.
<25 ° C discharge capacity maintenance rate>
Discharge capacity retention rate (25 ° C.) (%) = (discharge capacity at 50th cycle under 25 ° C. condition) / (initial discharge capacity under 25 ° C. condition) × 100

1-2.60 ° C. Test 50:50 (volume ratio) of ethylene carbonate (hereinafter sometimes referred to as EC) and ethyl methyl carbonate (hereinafter sometimes referred to as EMC) as an electrolytic solution to the obtained positive electrode. Combining a mixture with LiPF ₆ dissolved to 1 mol / liter (hereinafter sometimes referred to as LiPF ₆ / EC + EMC), a polypropylene porous film as a separator, and metallic lithium as a negative electrode A type battery (R2032) was produced.

Using the above coin-type battery, a cycle test was performed under the conditions shown below while maintaining at 60 ° C. The cycle characteristics were compared by calculating the discharge capacity retention rate according to the following.
<60 ° C cycle test>
A charge / discharge test was conducted at a 0.2 C rate with a maximum charge voltage of 4.3 V and a minimum discharge voltage of 3.0 V.
<60 ° C discharge capacity retention rate>
Discharge capacity retention rate (60 ° C.) (%) = (discharge capacity at 50th cycle under 60 ° C. condition) / (initial discharge capacity under 60 ° C. condition) × 100

2. Composition analysis of positive electrode active material After the powder was dissolved in hydrochloric acid, it was measured using an inductively coupled plasma emission analysis method (SPS3000 manufactured by SII Nanotechnology Inc., hereinafter sometimes referred to as ICP-AES).

3. Powder X-ray diffraction measurement of the positive electrode active material The powder X-ray diffraction measurement of the positive electrode active material was performed using RINT2500TTR type manufactured by Rigaku Corporation. The measurement was performed by filling a positive electrode active material in a dedicated holder and using a CuKα ray source in a diffraction angle range of 2θ = 10 to 90 ° to obtain a powder X-ray diffraction pattern.

4). BET specific surface area measurement About 0.2 g of the powder was dried in a nitrogen atmosphere at 150 ° C. for 15 minutes, and then measured using a flow sorb II 2300 manufactured by Micromeritics.

Example 1
In a polypropylene beaker, 40.4 g of potassium hydroxide was added to 600 ml of distilled water and dissolved by stirring to completely dissolve potassium hydroxide, thereby preparing an aqueous potassium hydroxide solution (alkali aqueous solution). In a glass beaker, 14.3 g of nickel (II) chloride hexahydrate, 12.1 g of manganese (II) chloride tetrahydrate and 0.814 g of vanadyl sulfate trihydrate were added to 250 ml of distilled water. The mixture was dissolved by stirring to obtain a nickel-manganese-vanadium mixed aqueous solution. While stirring the potassium hydroxide aqueous solution, the nickel-manganese-vanadium mixed aqueous solution was added dropwise thereto, thereby forming a coprecipitate and obtaining a coprecipitate slurry.

Next, the coprecipitate slurry was filtered and washed with distilled water, and dried at 100 ° C. to obtain a coprecipitate. 4.00 g of the coprecipitate, 2.01 g of lithium carbonate, and 0.308 g of potassium carbonate were dry-mixed using an agate mortar to obtain a mixture. Next, the mixture is put in an alumina firing container, and is fired by holding it in an air atmosphere at 800 ° C. for 6 hours using an electric furnace, cooled to room temperature to obtain a fired product, pulverized, and distilled water. Was washed by decantation, filtered, and dried at 100 ° C. for 8 hours to obtain a powdered positive electrode active material S ¹ . The BET specific surface area of the positive electrode active material ^{S 1} was 7.0 m ² / g.

Composition analysis of the ^{S 1,} Li: Ni: Mn: molar ratio of V is 1.13: 0.48: 0.51: was 0.01. As a result of powder X-ray diffraction measurement, the crystal structure of S ¹ was found to be a layered structure belonging to the R-3m space group.

A coin-type battery was produced using S ¹ and subjected to a 60 ° C. cycle test. As a result, the initial discharge capacity (mAh / g) was 163, and the discharge capacity retention rate (%) was 92.3. It was. They A coin type battery was produced by using the R ¹ in later comparative example 1, it was higher than the discharge capacity and the discharge capacity retention ratio in the case of the 60 ° C. cycle test.

A coin-type battery was prepared using S ¹ and subjected to a 25 ° C. cycle test. As a result, the initial discharge capacity (mAh / g) was 145, and the discharge capacity retention rate (25 ° C.) (%) was 92. .5. They A coin type battery was produced by using the R ¹ in later comparative example 1, it was higher than the discharge capacity and the discharge capacity retention ratio in the case of the 25 ° C. cycle test.

Example 2
Except that firing with 900 ° C. · 8 hours to obtain a powdery positive electrode active material S ² in the same manner as in Example 1. The BET specific surface area of the positive electrode active material ^{S 1} was 6.8 m ² / g.

Composition analysis of the ^{S 2,} Li: Ni: Mn: molar ratio of V is 1.14: 0.49: 0.50: was 0.01. As a result of the powder X-ray diffraction measurement, it was found that the crystal structure of S ² was a layered structure belonging to the R-3m space group.

When a coin-type battery was produced using S ² and subjected to a 60 ° C. cycle test, the initial discharge capacity (mAh / g) was 165, and the discharge capacity retention rate (60 ° C.) (%) was 92. 0. They A coin type battery was produced by using the R ¹ in later comparative example 1, it was higher than the discharge capacity and the discharge capacity retention ratio in the case of the 60 ° C. cycle test.

When a coin-type battery was produced using S ² and a 25 ° C. cycle test was conducted, the initial discharge capacity (mAh / g) was 148, and the discharge capacity retention rate (25 ° C.) (%) was 92. .7. They A coin type battery was produced by using the R ¹ in later comparative example 1, it was higher than the discharge capacity and the discharge capacity retention ratio in the case of the 25 ° C. cycle test.

Example 3
In a polypropylene beaker, 59.4 g of potassium hydroxide was added to 300 ml of distilled water and dissolved by stirring to completely dissolve potassium hydroxide to prepare an aqueous potassium hydroxide solution (alkali aqueous solution). In a glass beaker, 39.2 g of nickel (II) sulfate hexahydrate, 25.2 g of manganese (II) sulfate monohydrate and 0.353 g of vanadyl sulfate tetrahydrate were added to 300 ml of distilled water. The mixture was dissolved by stirring to obtain a nickel-manganese-vanadium mixed aqueous solution. While stirring the potassium hydroxide aqueous solution, the nickel-manganese-vanadium mixed aqueous solution was added dropwise thereto, thereby forming a coprecipitate and obtaining a coprecipitate slurry.

Next, the coprecipitate slurry was filtered and washed with distilled water, and dried at 100 ° C. to obtain a coprecipitate. A mixture was obtained by dry-mixing 5.00 g of the coprecipitate, 2.64 g of lithium carbonate, and 0.480 g of potassium sulfate using an agate mortar. Next, the mixture is placed in an alumina firing container and fired by holding it in an air atmosphere at 850 ° C. for 6 hours using an electric furnace, cooled to room temperature to obtain a fired product, pulverized, and distilled water. Was decanted, filtered, and dried at 100 ° C. for 8 hours to obtain a powdered positive electrode active material S ³ .

As a result of the composition analysis of S ³ , the molar ratio of Li: Ni: Mn: V was 1.09: 0.50: 0.50: 0.001. As a result of powder X-ray diffraction measurement, the crystal structure of S ³ was found to be a layered structure belonging to the R-3m space group.

A coin type battery was produced by using the ^{S 3,} was subjected to 25 ° C. cycle test, the initial discharge capacity (mAh / g) is 148, the discharge capacity retention ratio (%) was 97.8 . It was higher than the discharge capacity and the discharge capacity maintenance rate when A coin type battery was produced by using the R ¹ in later comparative example 1.

Comparative Example 1
In a polypropylene beaker, 40.4 g of potassium hydroxide was added to 600 ml of distilled water and dissolved by stirring to completely dissolve potassium hydroxide, thereby preparing an aqueous potassium hydroxide solution (alkali aqueous solution). In a glass beaker, 14.3 g of nickel (II) chloride hexahydrate, 12.1 g of manganese (II) chloride tetrahydrate and 0.814 g of vanadyl sulfate trihydrate were added to 250 ml of distilled water. The mixture was dissolved by stirring to obtain a nickel-manganese-vanadium mixed aqueous solution. While stirring the potassium hydroxide aqueous solution, the nickel-manganese-vanadium mixed aqueous solution was added dropwise thereto, thereby forming a coprecipitate and obtaining a coprecipitate slurry.

Next, the coprecipitate slurry was filtered and washed with distilled water, and dried at 100 ° C. to obtain a coprecipitate. 4.00 g of the coprecipitate and 2.01 g of lithium carbonate were dry-mixed using an agate mortar to obtain a mixture. Next, the mixture is put in an alumina firing container, and is fired by holding it in an air atmosphere at 800 ° C. for 6 hours using an electric furnace. The mixture is cooled to room temperature to obtain a fired product, which is pulverized and powdered. to obtain a positive electrode active material R ¹ in. The BET specific surface area of the positive electrode active material ^{R 1} was 4.8 m ² / g.

As a result of the compositional analysis of R ¹ , the molar ratio of Li: Ni: Mn: V was 1.07: 0.48: 0.49: 0.03. As a result of the powder X-ray diffraction measurement, the crystal structure of R ¹ is not limited to the layered oxide belonging to the R-3m space group, but is also an impurity such as a Li-deficient layered oxide or Li ₃ VO _4. Was observed.

When a coin-type battery was produced using R ¹ and subjected to a 60 ° C. cycle test, the initial discharge capacity (60 ° C.) (mAh / g) was 126, and the discharge capacity retention rate (60 ° C.) (% ) Was 83.6.

When a coin-type battery was produced using the R ¹ and subjected to a 25 ° C. cycle test, the initial discharge capacity (25 ° C.) (mAh / g) was 107, and the discharge capacity retention rate (25 ° C.) (% ) Was 76.6.

Comparative Example 2
In a polypropylene beaker, 59.4 g of potassium hydroxide was added to 300 ml of distilled water and dissolved by stirring to completely dissolve potassium hydroxide to prepare an aqueous potassium hydroxide solution (alkali aqueous solution). In a glass beaker, 39.4 g of nickel (II) sulfate hexahydrate and 25.4 g of manganese (II) sulfate monohydrate were added to 300 ml of distilled water, dissolved by stirring, and mixed with nickel-manganese. An aqueous solution was obtained. While stirring the aqueous potassium hydroxide solution, the nickel-manganese mixed aqueous solution was added dropwise thereto, whereby a coprecipitate was generated, and a coprecipitate slurry was obtained.

Next, the coprecipitate slurry was filtered and washed with distilled water, and dried at 100 ° C. to obtain a coprecipitate. A mixture was obtained by dry-mixing 5.00 g of the coprecipitate, 2.64 g of lithium carbonate, and 0.480 g of potassium sulfate using an agate mortar. Next, the mixture is placed in an alumina firing container and fired by holding it in an air atmosphere at 850 ° C. for 6 hours using an electric furnace, cooled to room temperature to obtain a fired product, pulverized, and distilled water. Was decanted, filtered, and dried at 100 ° C. for 8 hours to obtain a powdered positive electrode active material R ² .

As a result of the composition analysis of R ² , the molar ratio of Li: Ni: Mn was 1.1: 0.50: 0.50. As a result of powder X-ray diffraction measurement, the crystal structure of R ² was found to be a layered structure belonging to the R-3m space group.

A coin-type battery was fabricated using R ² and subjected to a 25 ° C. cycle test. As a result, the initial discharge capacity (mAh / g) was 149, and the discharge capacity retention rate (%) was 70.6. . That is, the initial discharge capacity is about the same as in Examples 1 to 3, but the discharge capacity retention rate is lower than those in Examples 1 to 3 and Comparative Example 1, and the discharge capacity and cycle characteristics are excellent. A positive electrode active material giving a water electrolyte secondary battery could not be obtained.

Production Example 1 (Production of laminated film)
(1) Production of coating solution After 272.7 g of calcium chloride was dissolved in 4200 g of NMP, 132.9 g of paraphenylenediamine was added and completely dissolved. To the obtained solution, 243.3 g of terephthalic acid dichloride was gradually added and polymerized to obtain para-aramid, which was further diluted with NMP to obtain a para-aramid solution (A) having a concentration of 2.0% by weight. To 100 g of the obtained para-aramid solution, 2 g of alumina powder (a) (manufactured by Nippon Aerosil Co., Ltd., Alumina C, average particle size 0.02 μm) and 2 g of alumina powder (b) (Sumitomo Chemical Co., Ltd. Sumiko Random, AA03, average particles) 4 g in total as a filler is added and mixed, treated three times with a nanomizer, filtered through a 1000 mesh wire net, and degassed under reduced pressure to produce a slurry coating solution (B) did. The weight of alumina powder (filler) with respect to the total weight of para-aramid and alumina powder is 67% by weight.

(2) Production and Evaluation of Laminated Film As the porous film, a polyethylene porous film (film thickness 12 μm, air permeability 140 seconds / 100 cc, average pore diameter 0.1 μm, porosity 50%) was used. The polyethylene porous film was fixed on a PET film having a thickness of 100 μm, and the slurry-like coating liquid (B) was applied onto the porous film by a bar coater manufactured by Tester Sangyo Co., Ltd. The coated porous film on the PET film is integrated into a poor solvent and immersed in water to precipitate a para-aramid porous film (heat resistant porous layer), and then the solvent is dried to form a heat resistant porous film. A laminated film in which a layer and a porous film were laminated was obtained. The thickness of the laminated film was 16 μm, and the thickness of the para-aramid porous film (heat resistant porous layer) was 4 μm. The laminated film had an air permeability of 180 seconds / 100 cc and a porosity of 50%. When the cross section of the heat-resistant porous layer in the laminated film was observed with a scanning electron microscope (SEM), a relatively small micropore of about 0.03 to 0.06 μm and a relatively large micropore of about 0.1 to 1 μm It was found to have The laminated film was evaluated by the following method.

<Evaluation of laminated film>
(A) Thickness measurement The thickness of the laminated film and the thickness of the porous film were measured in accordance with JIS standards (K7130-1992). Moreover, as the thickness of the heat resistant porous layer, a value obtained by subtracting the thickness of the porous film from the thickness of the laminated film was used.
(B) Measurement of air permeability by Gurley method The air permeability of the laminated film was measured by a digital timer type Gurley type densometer manufactured by Yasuda Seiki Seisakusho Co., Ltd. based on JIS P8117.
(C) Porosity A sample of the obtained laminated film was cut into a 10 cm long square and the weight W (g) and thickness D (cm) were measured. Obtain the weight (Wi (g)) of each layer in the sample, and obtain the volume of each layer from Wi and the true specific gravity (true specific gravity i (g / cm ³ )) of the material of each layer, The porosity (volume%) was obtained from the following formula.
Porosity (volume%) = 100 × {1− (W1 / true specific gravity 1 + W2 / true specific gravity 2 + ·· + Wn / true specific gravity n) / (10 × 10 × D)}

  In each of the above examples, when the laminated porous film obtained in Production Example 1 is used as a separator, a lithium secondary battery capable of further increasing the thermal membrane breaking temperature can be obtained.

Claims (2)

^{_{Li x M 11 y M 21 1}} -y O 2 (M 11 is ^{.M 21} is V is .x is Ni and Mn is 0.9 to 1.3, y is greater than 0 0.1 The following is a method for producing a positive electrode active material represented by:
A lithium compound and a raw material containing M ¹¹ (M ¹¹ is V) and M ²¹ (M ²¹ is Ni and Mn) are mixed with A carbonate, A sulfate, A nitrate, A Presence of one or more inert melting agents (where A represents K) selected from the group consisting of: phosphates of A, hydroxides of A, molybdates of A, and tungstates of A. The manufacturing method of the positive electrode active material which has a process which the baking temperature is 650 to 950 degreeC below, and the baking atmosphere bakes with air | atmosphere, oxygen, nitrogen, argon, or those mixed gas.   The method for producing a positive electrode active material according to claim 1, wherein the inert melting agent is a carbonate of A (where A has the same meaning as described above).