JPWO2015045350A1 - Lithium ion secondary battery - Google Patents

Abstract

Provided is a lithium ion secondary battery in which a coating layer having pores and no large size pores is provided on a negative electrode active material layer. A lithium ion secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode is disposed on the surface of the current collector, and includes a negative electrode active material and an organic solvent-based binder It has a negative electrode active material layer and a coating layer that is disposed on the surface of the negative electrode active material layer and includes ceramic powder and a water-based binder and has pores.

Description

  The present invention relates to a lithium ion secondary battery.

  A lithium ion secondary battery is a secondary battery having a high charge / discharge capacity and capable of high output. Currently, it is mainly used as a power source for portable electronic devices, and further expected as a power source for electric vehicles that are expected to be widely used in the future. A lithium ion secondary battery has an active material capable of inserting and extracting lithium (Li) in a positive electrode and a negative electrode, respectively. The lithium ion secondary battery operates by moving lithium ions in the electrolytic solution provided between both electrodes.

In order to improve the safety of the lithium ion secondary battery, it has been studied to prevent an internal short circuit by providing an insulating layer on the surface of the negative electrode active material layer. In order to suppress an increase in resistance of the electrode, it is disclosed that an exposed portion is provided in the insulating layer. For example, Patent Document 1 (Japanese Patent Laid-Open No. 2010-192365) discloses a technique in which an insulating layer is provided on a negative electrode active material layer while leaving an exposed portion where the negative electrode active material layer is exposed. Patent Document 1, the area of the exposed portion is preferably 3μm ² ~100μm ^2, the number of the exposed portion is disclosed that it is preferable 50 to 500 per 1 mm ^2, the individual size of the exposed portion from the numerical value It is clear that the number of exposed parts is considerably large.

  In the technique disclosed in Patent Document 1, a large hole (exposed portion) having a diameter of several μm to several tens of μm as described above is provided in the insulating layer in order to suppress an increase in resistance of the electrode. However, if the insulating layer provided on the surface of the negative electrode active material layer has a large hole having a diameter of several μm to several tens of μm as described in Patent Document 1, for example, current concentration occurs in the hole, and Li Precipitates. When Li is deposited in the holes, there is a possibility that an internal short circuit of the lithium ion secondary battery occurs through the Li. Further, if the insulating layer has a large-sized hole as described above, the mechanical strength of the insulating layer is lowered, and the insulating layer may be broken to cause an internal short circuit.

  Patent Document 2 discloses a non-aqueous electrolyte secondary battery including an inorganic particle layer including a dispersant composed of inorganic particles and polycarboxylate and an aqueous binder on the surface of a positive electrode. Patent Document 2 discloses that an inorganic particle is uniformly dispersed in an inorganic particle layer since a dispersant is contained in the inorganic particle layer. Further, Patent Document 2 discloses that the water-based binder is preferably polytetrafluoroethylene (abbreviation PTFE), polyacrylonitrile (abbreviation PAN), or styrene butadiene rubber (abbreviation SBR).

  Here, PTFE and PAN, which are water-based binders described in Patent Document 2, are both resins that are easily reduced, and SBR is poor in binding properties, so that it is not suitable for use in a negative electrode with large expansion and contraction. Therefore, the technique disclosed in Patent Document 2 cannot be easily applied to the coating layer formed on the negative electrode surface. Moreover, it is estimated that a suitable dispersing agent changes with kinds of aqueous binder. Since PTFE, PAN, and SBR are water-dispersible binders, it is presumed that they exhibit dispersibility of inorganic particles different from the water-soluble binder.

JP 2010-192365 A JP 2009-302009 A

  The present invention has been made in view of such circumstances, and provides a lithium ion secondary battery in which a coating layer having pores and not having large-sized pores is provided on a negative electrode active material layer. For the purpose. Furthermore, the present invention provides a lithium ion secondary battery that has high safety and is unlikely to cause a significant decrease in battery capacity by providing a coating layer with a uniform thickness in which inorganic particles are uniformly dispersed on the negative electrode active material layer. The purpose is to provide.

  As a result of intensive studies by the present inventors, if a coating layer having a ceramic powder and an aqueous binder is disposed on the surface of the negative electrode active material layer containing the negative electrode active material and the organic solvent-based binder, it has pores, It has been found that it is possible to provide a lithium ion secondary battery that can form a coating layer having no large pores, has high safety, and does not cause a significant decrease in battery capacity.

  That is, the lithium ion secondary battery of the present invention is a lithium ion secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the negative electrode is disposed on the surface of the current collector and the current collector. A negative electrode active material layer including a negative electrode active material and an organic solvent-based binder; and a coating layer disposed on a surface of the negative electrode active material layer, including a ceramic powder and an aqueous binder, and having pores. And

  The diameter of the pores is preferably 50 nm or more and 2 μm or less.

  The mass ratio of the ceramic powder and the aqueous binder in the coating layer is preferably 88:12 to 99: 1.

  The glass transition point of the aqueous binder is preferably 60 ° C. or higher.

  The aqueous binder is preferably at least one selected from polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone and carboxymethyl cellulose.

  The thickness of the coating layer is preferably 2 μm or more and 10 μm or less.

It is preferable that the average particle diameter _{D 50} of the ceramic powder is 100nm or more 1μm or less.

The negative electrode active material preferably contains Si or SiO _x (0.3 ≦ x ≦ 1.6).

  The organic solvent-based binder is preferably one selected from polyamide, polyamideimide, and polyimide.

The non-aqueous electrolyte preferably contains an additive composed of LiPF ₂ (C ₂ O ₄ ) ₂ .

  Furthermore, as a result of intensive studies by the present inventors, on the surface of the negative electrode active material layer containing the negative electrode active material and the organic solvent-based binder, a dispersant composed of ceramic powder, a water-soluble binder, and a polycarboxylic acid having a hydrophobic portion is added. If the covering layer is disposed, lithium ion can form a coating layer having pores with a uniform thickness in which ceramic powder is uniformly dispersed, has high safety, and is unlikely to cause a significant decrease in battery capacity. We found that we can provide secondary batteries.

  In the lithium ion secondary battery of the present invention, it is preferable that the water-based binder is a water-soluble binder, and the coating layer further includes a dispersant composed of a polycarboxylic acid having a hydrophobic portion.

  The polycarboxylic acid is composed of a copolymer of styrene and acrylic acid, and the molecular weight of the polycarboxylic acid is preferably from 5,000 to 500,000.

  The water-soluble binder is preferably at least one selected from polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone and carboxymethyl cellulose.

  The thickness unevenness of the coating layer is preferably 2 μm or less.

  The content of the dispersant in the coating layer is preferably 1 part by mass or more and 10 parts by mass or less when the ceramic powder is 100 parts by mass.

  The thickness of the coating layer is preferably 2 μm or more and 10 μm or less.

It is preferable that the average particle diameter _{D 50} of the ceramic powder is 100nm or more 1μm or less.

  The lithium ion secondary battery of the present invention has a high safety and a remarkable battery because the coating layer provided on the negative electrode active material layer contains ceramic powder, has pores, and does not have large-sized pores. Does not cause a decrease in capacity. Furthermore, in the lithium ion secondary battery of the present invention, since the coating layer provided on the negative electrode active material layer contains ceramic powder, has pores, and has little thickness unevenness, the safety is high and the battery capacity is remarkable. It is difficult to cause a decline.

It is a schematic diagram explaining the negative electrode for lithium ion secondary batteries of this embodiment. The observation result of the scanning electron microscope on the surface of the negative electrode of Test Example F4 is shown. The observation result of the scanning electron microscope on the surface of the negative electrode of Test Example F1 is shown. The observation result of the scanning electron microscope on the surface of the negative electrode of Test Example F2 is shown. It is a schematic diagram explaining the other negative electrode for lithium ion secondary batteries of this embodiment.

<Lithium ion secondary battery>
The lithium ion secondary battery of this invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte.

(Negative electrode)
The negative electrode has a current collector, a negative electrode active material layer, and a coating layer.

  The current collector is responsible for taking out electricity in the lithium ion secondary battery, and is made of a material that has high electron conductivity and is electrochemically inactive during charge and discharge. Examples of the current collector material include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. In particular, from the viewpoint of electrical conductivity, workability, and cost, the material for the current collector is preferably aluminum or copper. The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. As the current collector, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, or a stainless steel foil can be suitably used. When the current collector is a foil, sheet or film, the thickness of the current collector is preferably 10 μm to 50 μm. The thickness of the current collector is particularly preferably 15 μm to 30 μm from the viewpoint of increasing the battery capacity while maintaining high strength in the current collector.

  The negative electrode active material layer includes a negative electrode active material and an organic solvent-based binder, and includes a conductive additive as necessary.

  As the negative electrode active material, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, a compound that includes an element that can be alloyed with lithium, a polymer material, or the like can be used.

  Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, natural graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Examples of elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb and Bi are mentioned. Among these, as an element that can be alloyed with lithium, silicon (Si) or tin (Sn) is preferable, and silicon (Si) is particularly preferable.

Examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , and CaSi. _{2, CrSi 2, Cu 5 Si} , FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO 2 and LiSnO. As the compound having an element that can be alloyed with lithium, a silicon compound or a tin compound is preferable. As the silicon compound, SiO _x (0.3 ≦ x ≦ 1.6) is preferable. Examples of the tin compound include tin alloys (Cu—Sn alloy, Co—Sn alloy, etc.).

  Examples of the polymer material include polyacetylene and polypyrrole.

In order to obtain a high-capacity lithium ion secondary battery, the negative electrode active material preferably contains Si or SiO _x (0.3 ≦ x ≦ 1.6). In addition to the above materials, it is preferable to use natural graphite in combination as the negative electrode active material.

In order to obtain a high-capacity lithium ion secondary battery, the content ratio of Si or SiO _x (0.3 ≦ x ≦ 1.6) in the negative electrode active material layer when the entire negative electrode active material layer is 100% by mass Is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more.

  Moreover, when the whole negative electrode active material layer is 100 mass%, it is preferable that the content rate of the negative electrode active material in a negative electrode active material layer is 60 mass% or more and 97 mass% or less, and 70 mass% or more and 95 mass% or less. It is more preferable that it is 75 mass% or more and 90 mass% or less.

The negative electrode active material is preferably in powder form. If the anode active material is in powder form, have an average particle diameter _{D 50} of the negative electrode active material is preferably 0.5μm or more 30μm or less, more preferably 3μm or more 15μm or less is 2μm or more 8μm or less Further preferred. When the average particle diameter D ₅₀ of the negative electrode active material is too small, the anode active material specific surface area of the powder becomes larger, it increases the contact area between the powder and the non-aqueous electrolyte of the negative electrode active material, a nonaqueous electrolyte Since decomposition easily proceeds, cycle characteristics may be deteriorated. If the average particle diameter D ₅₀ of the negative electrode active material is too large, the reaction resistance during charging and discharging increases, the output characteristic may be deteriorated. The average particle diameter D ₅₀ of the negative electrode active material is too large, the surface roughness of the negative electrode active material layer becomes large, it may become difficult to apply a coating layer on the negative electrode active material layer. The average particle diameter D ₅₀ can be measured by particle size distribution measurement method. The average particle diameter D ₅₀ is that the particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50%. That is, the average particle diameter D ₅₀ means the median size measured by volume.

  A conductive additive is added to the negative electrode active material layer as necessary in order to increase the conductivity of the electrode. Examples of the conductive assistant include carbon black, graphite, acetylene black (abbreviation AB), ketjen black (registered trademark) (abbreviation KB), and vapor grown carbon fiber (abbreviation VGCF). These conductive assistants can be used alone or in combination of two or more. The amount of the conductive auxiliary agent used is not particularly limited, but can be, for example, about 1 part by mass to 30 parts by mass with respect to 100 parts by mass of the active material contained in the negative electrode.

  In the present invention, the binder contained in the negative electrode active material layer is an organic solvent-based binder. The organic solvent binder is a resin that is dissolved or dispersed in an organic solvent or a rubber that is dissolved or dispersed in an organic solvent. The organic solvent-based binder plays a role of connecting the negative electrode active material and the conductive additive to the current collector.

  Examples of the organic solvent binder include fluorine-containing resins such as polyvinylidene fluoride (abbreviation PVDF), polytetrafluoroethylene (abbreviation PTFE) and fluororubber, thermoplastic resins such as polypropylene, polyethylene and polyvinyl acetate resin, polyimide, and the like. Examples thereof include imide resins such as polyamideimide, alkoxysilyl group-containing resins, and rubbers such as styrene butadiene rubber (abbreviated as SBR). The organic solvent binder is particularly preferably a resin that dissolves in N-methyl-2-pyrrolidone (abbreviation NMP). Examples of the resin that dissolves in NMP include PVDF, polyamide, polyamideimide, and polyimide. Preferred organic solvent-based binders for suppressing the expansion and contraction of the negative electrode active material include polyamide, polyamideimide, and polyimide.

  In order to dispose the negative electrode active material layer on the surface of the current collector, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. The negative electrode active material may be applied directly on the surface. Specifically, a negative electrode active material layer-forming composition containing a negative electrode active material, an organic solvent-based binder and, if necessary, a conductive additive is prepared, and an appropriate solvent is added to the composition to form a slurry. The organic solvent-based binder may be used as a solution in which an organic solvent-based binder is dissolved in a solvent or a dispersed suspension. Examples of the solvent include NMP, methanol, ethanol, methyl isobutyl ketone (abbreviation MIBK), N, N-dimethylformamide (abbreviation DMF), dimethyl sulfoxide (abbreviation DMSO), γ-butyrolactone, and acetone. The slurry is applied to the surface of the current collector and then dried. Drying may be performed under normal pressure conditions, or under reduced pressure conditions using a vacuum dryer. What is necessary is just to set drying temperature suitably, and the temperature beyond the boiling point of the solvent to be used is preferable. When polyamideimide or polyimide is used as the organic solvent-based binder, the drying temperature is more preferably 150 ° C. or higher and particularly preferably 180 ° C. or higher because it is necessary to close the imide ring. What is necessary is just to set drying time suitably according to an application quantity and drying temperature. In order to increase the density of the negative electrode active material layer, a compression step may be added to the current collector after the negative electrode active material layer is formed by drying.

  The coating layer is disposed on the surface of the negative electrode active material layer, includes ceramic powder and an aqueous binder, and has pores.

  A number of ceramic powders are arranged in the coating layer. The aqueous binder is disposed between the negative electrode active material layer and the coating layer and between the ceramic powders in the coating layer, and binds between the negative electrode active material layer and the coating layer and between the ceramic powders in the coating layer. Since the coating layer contains powder, it has pores formed between the ceramic powder, between the negative electrode active material layer and the ceramic powder, and between the ceramic powder and the aqueous binder. Note that the coating layer does not have a large-sized hole on the order of μm, for example.

  Since the surface of the negative electrode active material layer is covered with the coating layer, the negative electrode active material is less likely to come into direct contact with the non-aqueous electrolyte. Therefore, the decomposition reaction of the nonaqueous electrolytic solution by the negative electrode active material is suppressed, and deterioration of the cycle characteristics of the lithium ion secondary battery can be suppressed. Moreover, since the eluate of the metal component contained in the non-aqueous electrolyte and the decomposition product of the non-aqueous electrolyte can be physically trapped by the coating layer, it is possible to suppress the deposition of the decomposition product on the surface of the negative electrode active material. As a result, deterioration of the cycle characteristics of the lithium ion secondary battery can be suppressed.

  Further, if large-sized holes are present in the coating layer, the current density is locally increased at the hole portions during charge / discharge, which may easily induce Li precipitation. The precipitated Li may further cause an internal short circuit between the positive and negative electrodes and a deterioration in life such as cycle characteristics. In this invention, since a coating layer does not have a large-sized hole, the internal short circuit of a lithium ion secondary battery can be suppressed, and the safety | security of a lithium ion secondary battery can be improved.

  Further, since the ceramic powder has low conductivity and high heat resistance, a coating layer having both insulation and heat resistance is disposed on the surface of the negative electrode active material layer. Therefore, the lithium ion secondary battery can suppress an internal short circuit even at a high temperature, and can improve safety.

  Further, since the coating layer has pores, the coating layer does not have a large resistance in the lithium ion secondary battery, and the coating layer does not cause a significant decrease in battery capacity of the lithium ion secondary battery.

  If an organic solvent-based binder is used for the negative electrode active material layer and an organic solvent-based binder is also used for the coating layer, the organic solvent-based binder of the negative electrode active material layer is partially included in the organic solvent used when forming the coating layer. Since there exists a possibility of melt | dissolving, it is not preferable.

  The aqueous binder refers to a resin that dissolves or disperses in an aqueous solvent or a rubber that dissolves or disperses in an aqueous solvent. Examples of the water-based binder include a water-soluble binder and a water-dispersed binder. Here, examples of the aqueous solvent include water or a mixture of water and alcohol. Examples of the alcohol include ethanol, methanol, isopropanol, and butanol. The mixing ratio of the mixture of water and alcohol is preferably water: alcohol = 50: 50 or more and 100: 0 or less by mass ratio.

  As the aqueous binder, those having a glass transition point of 60 ° C. or higher are preferable, and those having a glass transition point of 80 ° C. or higher are more preferable. Since the actual use range of the lithium ion secondary battery is about 60 ° C. or less, it is desirable that the aqueous binder is not softened to about 60 ° C. If the glass transition point of the aqueous binder is 60 ° C. or higher, the following effects can be expected. If the glass transition point of the water-based binder is 60 ° C. or higher, a strong coating layer can be formed because the polymer skeleton of the water-based binder is hard or the cohesion between molecules is high. Therefore, even if the negative electrode active material that expands and contracts with the insertion and extraction of Li is used, the coating layer can suppress the expansion and contraction of the negative electrode active material. Moreover, since the aqueous binder does not soften even at a high temperature of about 60 ° C. and the strength of the coating layer is high, the life and safety of the lithium ion secondary battery at a high temperature can be ensured.

  The water-soluble binder refers to a resin that dissolves in an aqueous solvent. Since the water-soluble binder is used for the negative electrode, a resin having sufficient reduction resistance against the negative electrode potential is preferable. As an index of the oxidation resistance and reduction resistance of the resin, the HOMO (Highest Occupied Molecular Orbital) level (eV) of the resin and the LUMO (Lowest Unoccupied Molecular Orbital: lowest vacant molecular orbital energy) ) The level value (eV) can be used. The smaller the HOMO level value, the higher the oxidation resistance, and the higher the LUMO level value, the higher the reduction resistance. The value of the HOMO level and the value of the LUMO level can be calculated by a molecular orbital calculation (ab initio method) using a commercially available program. For example, it can be calculated by a commercially available general purpose program “Gaussian 94”. First, the molecular structure optimization calculation is performed to determine the stable structure of the molecule. Thereafter, the energy level of HOMO / LUMO is calculated using the stable structure. The water-soluble binder preferably has a LUMO level value of 0.2 eV or more.

  Examples of the water-soluble binder include methyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, polystyrene sulfonic acid, polyvinyl sulfonic acid, polyacrylic acid, sodium polyacrylate, polystyrene styrene copolymer, methyl vinyl ether / maleic anhydride copolymer, Polyacrylamide, polyethylene oxide, polyvinyl alcohol, acrylic acid / maleic acid copolymer, acrylic acid / sulfonic acid monomer, hydroxyethyl cellulose, acrylamide-diallyldimethylammonium chloride, diallyldimethylammonium chloride, poly (trimethylaminoethyl methyl methacrylate) Sulfate), isobutyl / maleic anhydride, chitosan, polyvinyl butyral, polyethylene glycol Call, gelatin, polyvinyl ethyl ether, polyvinyl acetate, polyvinyl pyrrolidone, polypropylene oxide.

  Among the water-soluble binders, those having a glass transition point of 60 ° C. or higher are more preferable. As a water-soluble binder having a glass transition point of 60 ° C. or more, for example, methyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, polystyrene sulfonic acid, polyvinyl sulfonic acid, polyacrylic acid may vary depending on the degree of polymerization and the composition ratio of the copolymer. , Sodium polyacrylate, polystyrene styrene copolymer, methyl vinyl ether / maleic anhydride copolymer, polyacrylamide, polyvinyl alcohol, acrylic acid / maleic acid copolymer, acrylic acid / sulfonic acid monomer, hydroxyethyl cellulose, acrylamide Examples include diallyldimethylammonium chloride, isobutyl / maleic anhydride, chitosan, polyvinyl butyral, gelatin, and polyvinylpyrrolidone.

  The water-soluble binder is preferably at least one selected from polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone and carboxymethyl cellulose. These binders have high water solubility and are less likely to adversely affect electrochemically.

  If the water-soluble binder is polyvinyl alcohol or carboxymethyl cellulose, the cycle life of the lithium ion secondary battery can be improved.

  If the water-soluble binder is polyacrylic acid or carboxymethylcellulose, the high-temperature storage characteristics of the lithium ion secondary battery can be improved.

  If the water-soluble binder is a mixture of polyvinyl pyrrolidone and polyvinyl alcohol, the ceramic powder can be easily dispersed and the pot life can be lengthened. Here, pot life refers to pot life, and specifically refers to the time during which particles are dispersed without being settled.

  Examples of the water-dispersed binder include acrylic polymers, methacrylic polymers, polyurethanes, epoxy polymers, styrene polymers, and vinyl polymers. These water-dispersed polymers may be used alone, but may be used as a combination of two or more types or as a copolymer.

  The coating layer may further contain a dispersant as necessary. A commercially available dispersant can be used as appropriate. When the coating layer contains a dispersant, the ceramic powder is uniformly dispersed in the coating layer by the dispersant, and as a result, the thickness unevenness of the coating layer is reduced.

  When a water-soluble binder is used as the aqueous binder, examples of the dispersant include polycarboxylic acids having a hydrophobic portion. Since the polycarboxylic acid having a hydrophobic portion has both a hydrophobic group and a hydrophilic group, a dispersion effect due to hydrophilicity / hydrophobicity is added in addition to an electrostatic dispersion effect due to electric charge. Therefore, the polycarboxylic acid having a hydrophobic portion has a large dispersion effect.

  The hydrophobic portion of the polycarboxylic acid is preferably, for example, a phenyl group, an alkylphenyl group, a linear or branched alkyl group having 5 to 20 carbon atoms, or a cycloalkyl group. The hydrophobic functional group may have a structure further having a substituent having a low polarity, for example, an alkyl group such as a methyl group.

  The polycarboxylic acid having a hydrophobic part can be obtained, for example, by polymerizing a monomer raw material containing a monomer capable of introducing a hydrophobic part and a monomer capable of introducing a carboxyl group by an appropriate method.

  Monomers capable of introducing carboxyl groups (hereinafter referred to as carboxyl group-containing monomers) include: tyrenic unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid; maleic acid and its anhydride, itaconic acid And its anhydride, unsaturated dicarboxylic acid such as citraconic acid and its anhydride, fumaric acid and its anhydride; unsaturated dicarboxylic acid monoester such as itaconic acid monomethyl, itaconic acid monobutyl, 2-acryloyloxyethylphthalic acid; 2 -Unsaturated tricarboxylic acid monoesters such as methacryloyloxyethyl trimellitic acid and 2-methacryloyloxyethyl pyromellitic acid; and carboxyalkyl acrylates such as carboxyethyl acrylate and carboxypentyl acrylate. As the carboxyl group-containing monomer, acrylic acid and carboxyethyl acrylate can be preferably used.

  As a monomer capable of introducing a hydrophobic part (hereinafter referred to as a hydrophobic functional group-containing monomer), a monomer having a hydrophobic functional group and an ethylenically unsaturated group as described above in one molecule, such as styrene, α -Methylstyrene, vinyltoluene, cyclohexyl acrylate, isobornyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, phenoxyethyl acrylate, cinnamic acid.

  The polycarboxylic acid having a hydrophobic portion is preferably made of a copolymer of styrene and acrylic acid.

  The preferred mass average molecular weight of the polycarboxylic acid having a hydrophobic part is from 5,000 to 500,000, more preferably from 6,000 to 200,000, and even more preferably from 7,500 to 150,000. If the mass average molecular weight is larger than 500,000, the dispersing agent bridges between the ceramic powders and the ceramic powder is agglomerated, which is not preferable. If the mass average molecular weight is smaller than 5000, a repulsive effect due to steric hindrance of the dispersing agent molecules can be obtained. Since it becomes difficult, it is not preferable. The mass average molecular weight can be measured using gel permeation chromatography (abbreviation GPC) using polystyrene having a known molecular weight as a standard substance.

  A preferable content of the dispersant in the coating layer is 1 part by mass or more and 10 parts by mass or less, more preferably 2 parts by mass or more and 6 parts by mass or less, and more preferably, when the ceramic powder is 100 parts by mass. 3 parts by mass or more and 5 parts by mass or less.

A ceramic powder that does not dissolve in an aqueous solvent can be used. That is, oxides, nitrides, and carbides are desirable as the ceramic powder. Specific examples of the ceramic powder include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , MgO, SiC, AlN, BN, talc, mica, kaolinite, CaO, ZnO, and zeolite. As the ceramic powder, Al ₂ O ₃ , SiO ₂ , and TiO ₂ are preferable from the viewpoint of availability, and Al ₂ O ₃ is particularly preferable.

It is preferable that the average particle size _{D 50} of the ceramic powder is 100nm or more 1μm or less,
More preferably, it is 200 nm or more and 800 nm or less, and particularly preferably 300 nm or more and 600 nm or less. When the average particle diameter D ₅₀ of the ceramic powder is too large, there is a possibility that the thickness of the coating layer is greater than the desired thickness. Further, the ceramic powder tends to settle in the slurry during the formation of the coating layer, and is difficult to disperse. When the average particle diameter D ₅₀ of the ceramic powder is too small, there is a possibility that the ceramic powder when creating the coating layer penetrates into the negative electrode active material layer.

  A preferable mass ratio of the ceramic powder and the aqueous binder in the coating layer is 88:12 to 99: 1, more preferably 90:10 to 98: 2, and still more preferably 92: 8 to 97: 3. If the content of the aqueous binder in the coating layer is too small, there is a risk of the coating layer collapsing due to a decrease in the binding force of the coating layer to the negative electrode active material layer or a reduction in the binding force between ceramic powders in the coating layer. This is not preferable. In addition, the flexibility of the entire coating layer is lost, and the coating layer may be broken by the pressure applied to the electrode. If the content of the aqueous binder in the coating layer is too large, there is a concern that the heat resistance of the coating layer is lowered, which is not preferable.

  When the dispersant is used, the preferable content of the dispersant in the coating layer is 1 part by mass or more and 10 parts by mass or less, more preferably 2 parts by mass or more and 6 parts by mass when the ceramic powder is 100 parts by mass. Or less, more preferably 3 parts by mass or more and 5 parts by mass or less.

  A preferable mass ratio of the ceramic powder and the water-soluble binder in the coating layer is 99: 1 to 85:15, more preferably 98: 2 to 88:12, and still more preferably 97: 3 to 90:10. .

  If the content of the water-soluble binder in the coating layer is too small, there is a risk of the coating layer collapsing due to a decrease in the binding force of the coating layer to the negative electrode active material layer or a reduction in the binding force between the ceramic powders in the coating layer. Therefore, it is not preferable. In addition, the flexibility of the entire coating layer is lost, and the coating layer may be broken by the pressure applied to the electrode. If the content of the water-soluble binder in the coating layer is too large, there is a concern that the hardness of the coating layer itself may be lowered or the heat resistance of the coating layer may be lowered, which is not preferable.

  The thickness of the coating layer is preferably 2 μm or more and 10 μm or less, more preferably 2 μm or more and 8 μm or less, and particularly preferably 3 μm or more and 6 μm or less. If the thickness of the coating layer is too thin, the effect of preventing a short circuit of the lithium ion secondary battery may not be exhibited. If the thickness of the coating layer is too thick, the ratio of the coating layer in the entire battery increases, so the charge / discharge capacity per volume / mass of the lithium ion secondary battery may be reduced.

  The thickness unevenness of the coating layer is preferably 2 μm or less, more preferably 1 μm or less, and further preferably 0.5 μm or less. If the thickness unevenness of the coating layer is too large, the current tends to concentrate on the thin portion, which tends to cause capacity deterioration during the cycle test. In addition, the thickness unevenness of the coating layer was determined by measuring the thickness of the electrode at 10 points at intervals of 5 mm and determining the difference between the maximum value and the minimum value.

  The pores contained in the coating layer preferably have a diameter of 20 nm to 2 μm, more preferably 20 nm to 1 μm, and still more preferably 20 nm to 300 nm. If the diameter of the pores is too small, the ionic conductivity may decrease and the resistance may increase. On the other hand, if the diameter of the pore is too large, current concentration occurs in the pore and Li may be deposited.

  The method for disposing the coating layer on the negative electrode active material layer is not particularly limited. For example, the coating layer can be disposed on the negative electrode active material layer by the following method. The coating layer can be disposed on the negative electrode active material layer by preparing a mixture by dispersing the material of the coating layer in an aqueous solvent, applying the mixture onto the negative electrode active material layer, and drying after application. As a coating method, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used.

  The solid concentration in the mixture of the coating layer material and the aqueous solvent is preferably 20% by mass or more and 70% by mass or less, and more preferably 30% by mass or more and 60% by mass or less. If the solid content concentration is in the above range, the solid content is easily dispersed in the mixture, and the pot life of the mixture can be prolonged.

In order to disperse the material of the coating layer in the aqueous solvent, it is preferable to use a wet dispersion method using a mixer. A commercially available product can be used as the mixer. Since the average particle diameter D ₅₀ of the ceramic powder is preferably 1μm or less, such fine ceramic powder to be uniformly dispersed in an aqueous solvent, it is better subjected to mechanical dispersion treatment. As a dispersion method, for example, a dispersion method used for dispersion of paint is preferably used.

  FIG. 1 is a schematic diagram illustrating a negative electrode for a lithium ion secondary battery according to this embodiment. In FIG. 1, a negative electrode active material 3 is bound on a current collector 1 by an organic solvent-based binder 2. The negative electrode active material layer 4 includes a negative electrode active material 3 and an organic solvent-based binder 2. The coating layer 5 is disposed on the negative electrode active material layer 4.

  In the coating layer 5 of FIG. 1, the plurality of ceramic powders 51 are arranged along the unevenness of the surface of the negative electrode active material layer 4, and the aqueous binder 521 is between the ceramic powders 51 and between the ceramic powder 51 and the negative electrode active material layer 4. It is arranged between. A plurality of ceramic powders 51 are bound together by the aqueous binder 521, and the ceramic powder 51 and the negative electrode active material layer 4 are bound together. The pores 6 are formed between the ceramic powders 51, between the negative electrode active material layer 4 and the ceramic powder 51, and between the ceramic powder 51 and the aqueous binder 521. As shown in FIG. 1, the coating layer 5 has no large size holes.

  FIG. 5 is a schematic diagram illustrating another negative electrode for a lithium ion secondary battery according to this embodiment. A coating layer of another negative electrode for a lithium ion secondary battery illustrated in FIG. 5 includes a dispersant 53 and a water-soluble binder 522 is used. In FIG. 5, the negative electrode active material 3 is bound on the current collector 1 by the organic solvent binder 2. The negative electrode active material layer 4 includes a negative electrode active material 3 and an organic solvent-based binder 2. The coating layer 5 is disposed on the negative electrode active material layer 4.

  In the coating layer 5 of FIG. 5, the plurality of ceramic powders 51 are arranged along the unevenness of the surface of the negative electrode active material layer 4, and the water-soluble binder 522 is between the ceramic powders 51 and between the ceramic powder 51 and the negative electrode active material layer 4. The dispersing agent 53 is disposed between the ceramic powders 51 and between the ceramic powder 51 and the negative electrode active material layer 4. The plurality of ceramic powders 51 or the ceramic powder 51 and the negative electrode active material layer 4 are bound by the water-soluble binder 522. The dispersant 53 works to repel the ceramic powders 51 so that the ceramic powders 51 are uniformly dispersed in the coating layer 5. The pores 6 are formed between the ceramic powders 51, between the negative electrode active material layer 4 and the ceramic powder 51, and between the ceramic powder 51 and the water-soluble binder 522.

  The lithium ion secondary battery of this invention has the said negative electrode for lithium ion secondary batteries, It is characterized by the above-mentioned. The lithium ion secondary battery having the negative electrode for a lithium ion secondary battery has high safety and does not cause a significant decrease in battery capacity.

  The lithium ion secondary battery of the present invention has a positive electrode and a non-aqueous electrolyte in addition to the above-described negative electrode for a lithium ion secondary battery as battery components.

(Positive electrode)
The positive electrode has a current collector and a positive electrode active material layer bound to the surface of the current collector. The positive electrode active material layer includes a positive electrode active material and a binder, and includes a conductive additive as necessary. The current collector and conductive additive are the same as those described in the negative electrode for lithium ion secondary batteries. As a binder, what was demonstrated as an organic-solvent binder in the above-mentioned negative electrode for lithium ion secondary batteries can be used suitably.

As the positive electrode active material, a lithium-containing compound or another metal compound can be used. Examples of the lithium-containing compound, for example, lithium-cobalt composite oxide having a layered structure, the lithium nickel composite oxide having a layered structure, the lithium manganese composite oxide having a spinel structure represented by the general _{formula: Li a Co p Ni q Mn} r D _s O _x (D is at least one selected from Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe and Na, p + q + r + s = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r <1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) ≦ 0.2) Olivine-type lithium phosphate complex oxide represented by LiMPO ₄ (M is at least one of Mn, Fe, Co and Ni), represented by general formula: Li ₂ MPO ₄ F Fluorine olivine type lithium phosphate complex oxide (M is at least one of Mn, Fe, Co and Ni), silicate type lithium complex oxide represented by general formula: Li ₂ MSiO ₄ (M is Mn , Fe, Co, and Ni). Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide, and manganese dioxide, and sulfides such as titanium sulfide and molybdenum sulfide.

The positive electrode active material is preferably made of a lithium-containing oxide represented by the chemical formula: LiMO ₂ (M is at least one selected from Ni, Co, and Mn), and further has a general formula: Li _a Co _{p Ni q Mn r D s O x} (D is, Al, Mg, Ti, Sn , Zn, W, Zr, Mo, at least one, p + q + r + s = 1,0 <p <1,0 ≦ selected from Fe and Na Lithium having a layered structure represented by q <1, 0 ≦ r <1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) ≦ 0.2) It is preferably made of a cobalt-containing composite metal oxide.

Examples of the lithium-containing oxide include LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _{0. 3 O 2, LiCoO 2, LiNi} 0.8 Co 0.2 O 2, LiCoMnO 2 and the like. Lithium-containing oxides are preferably LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ from the viewpoint of thermal stability.

The positive electrode active material preferably has an average particle diameter _{D 50} is a powder shape is 1 m to 20 m. When the average particle diameter D ₅₀ of the positive electrode active material is too small specific surface area of the cathode active material increases the reaction area with the greater becomes the positive electrode active material and the nonaqueous electrolyte will proceed decomposition of the electrolytic solution, poor cycle characteristics There is a risk. When the average particle diameter D ₅₀ of the positive electrode active material is too large resistance of the lithium ion secondary battery increases, there is a possibility that the output characteristics of the lithium ion secondary battery decreases.

(Nonaqueous electrolyte)
The nonaqueous electrolytic solution includes a solvent and an electrolyte dissolved in the solvent. An additive may be further added to the non-aqueous electrolyte.

  As the solvent, for example, cyclic esters, chain esters, and ethers can be used. Examples of the cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane.

Examples of the electrolyte dissolved in the non-aqueous electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As the non-aqueous electrolyte, for example, a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 is} added in a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate to 0.5 mol / l to 1.7 mol. A solution dissolved at a concentration of about 1 / l is mentioned.

Examples of the additive include a substance having a property that is higher in oxidation-reduction potential than other solvents and electrolytes, which are other components contained in the nonaqueous electrolytic solution, and is easily reductively decomposed. In a lithium ion secondary battery, a substance having the property of being easily reductively decomposed is reductively decomposed before the solvent or electrolyte, thereby suppressing the reductive decomposition of the solvent or electrolyte. By using such an additive in combination with an active material that easily reduces and decomposes a non-aqueous electrolyte, for example, an Si-based active material, decomposition of a solvent or an electrolyte can be remarkably suppressed. The battery life can be improved. Examples of such additives include fluoroethylene carbonate, LiPF ₂ (C ₂ O ₄ ) ₂ (abbreviation LPFO), LiPF ₄ C ₂ O ₄ (abbreviation LPFTO), and LiB (C ₂ O ₄ ) ₂ .

  The additive is preferably added so that the molar concentration per liter of the non-aqueous electrolyte is 0.01 mol / L or more and 0.3 mol / L or less. It is more preferable to add such that the concentration is 0.03 mol / L or more and 0.2 mol / L or less.

  The lithium ion secondary battery of the present invention may further have a separator.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. Examples of the separator include a porous film made of a synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, and a porous film made of a ceramic. The separator may be composed of a plurality of laminated porous membranes. In addition, an insulating layer or a heat-resistant layer may be disposed on the surface on the positive electrode side and / or the negative electrode side. Examples of the constituent member of the insulating layer or the heat-resistant layer include alumina, titanium oxide, zirconium oxide, magnesium oxide, zinc oxide, and silicon dioxide. The material of the porous membrane is preferably polyethylene or polypropylene, and the constituent member of the heat-resistant layer is preferably alumina. More preferably, the porous film has a three-layer structure of polypropylene / polyethylene / polypropylene, and it is particularly preferable that at least one surface of the porous film has a heat-resistant layer containing alumina of 1 μm or more.

  The lithium ion secondary battery can be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.

  As mentioned above, although embodiment for lithium ion secondary batteries of the present invention was described, the present invention is not limited to the above-mentioned embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Production of negative electrode>
(Preparation of copper foil with a negative electrode active material layer)
As an anode active material, the average particle diameter _{D 50} of 5.3 .mu.m SiO (Aldrich) and natural graphite (average particle diameter _{D 50} of SMG (manufactured by Hitachi Chemical Co., Ltd.) of 20.1Myuemu) was prepared. A polyamide-imide resin (abbreviated as PAI) (manufactured by Arakawa Chemical Industries, Ltd.) was prepared as a binder resin. Acetylene black (abbreviation AB) was prepared as a conductive additive.

  A mixture was prepared by mixing at a ratio of SiO / natural graphite / AB / PAI = 32/50/8/10 (mass ratio). This mixture was dispersed in an appropriate amount of NMP to prepare a slurry.

  Using a doctor blade, this slurry was applied in a film shape to a copper foil having a thickness of 20 μm, which is a current collector for a negative electrode. The current collector coated with the slurry was dried and pressed to obtain a bonded product. The joined product was heated and dried with a vacuum dryer at 200 ° C. for 2 hours to obtain a copper foil on which a negative electrode active material layer was formed. This was designated as negative electrode A. The thickness of the negative electrode active material layer of the negative electrode A was 18 μm. This negative electrode A is used as the negative electrode of Test Example F5.

(Negative electrode of Test Example F1)
Polyacrylic acid (abbreviated as PAA), which is a water-soluble binder, is dissolved in water, and Al ₂ O ₃ powder (manufactured by Sumitomo Chemical Co., Ltd., average particle diameter D ₅₀ is 540 nm) is mixed. 1 was obtained. The mass ratio of water, PAA, and Al ₂ O ₃ was water / PAA / Al ₂ O ₃ = 60 / 1.6 / 38.4 as a percentage. Mixture No. for coating layer The solid content concentration of 1 was 40% by mass.

  Using an applicator, the negative electrode A was coated with the mixture no. 1 was applied. Mixture No. for coating layer The negative electrode A coated with No. 1 was heat-dried at 120 ° C. for 6 hours, cut into a predetermined shape (25 mm × 30 mm rectangular shape), and used as the negative electrode of Test Example F1. The thickness of the coating layer of the negative electrode of Test Example F1 was 5 μm.

(Negative electrode of Test Example F2)
Carboxymethylcellulose (abbreviated as CMC), which is a water-soluble binder, is dissolved in water, and Al ₂ O ₃ powder is mixed. 2 was obtained. The mass ratio of water, CMC, and Al ₂ O ₃ was water / CMC / Al ₂ O ₃ = 60 / 1.6 / 38.4 as a percentage. Mixture No. for coating layer The solid content concentration of 2 was 40% by mass.

  Using an applicator, the negative electrode A was coated with the mixture no. 2 was applied. Mixture No. for coating layer The negative electrode A coated with No. 2 was heat-dried at 120 ° C. for 6 hours, cut into a predetermined shape (25 mm × 30 mm rectangular shape), and used as the negative electrode of Test Example F2. The thickness of the coating layer of the negative electrode of Test Example F2 was 3 μm.

(Negative electrode of Test Example F3)
Polyvinyl alcohol (abbreviated as PVA), which is a water-soluble binder, is dissolved in water, and Al ₂ O ₃ powder is mixed. 3 was obtained. The mass ratio of water, PVA, and Al ₂ O ₃ was water / PVA / Al ₂ O ₃ = 60 / 1.6 / 38.4 as a percentage. Mixture No. for coating layer The solid content concentration of 3 was 40% by mass.

  Using an applicator, the negative electrode A was coated with the mixture no. 3 was applied. Mixture No. for coating layer The negative electrode A coated with No. 3 was heat-dried at 120 ° C. for 6 hours, cut into a predetermined shape (rectangular shape of 25 mm × 30 mm), and used as the negative electrode of Test Example F3. The thickness of the coating layer of the negative electrode of Test Example F3 was 4 μm.

(Negative electrode of Test Example F4)
Polyvinylidene fluoride (abbreviated as PVDF), which is an organic solvent binder, is dissolved in NMP, Al ₂ O ₃ powder is mixed, and coating layer mixture No. 4 was obtained. The mass ratio of NMP, PVDF, and Al ₂ O ₃ was NMP / PVDF / Al ₂ O ₃ = 60 / 1.6 / 38.4 as a percentage.

  Using an applicator, the negative electrode A was coated with the mixture no. 4 was applied. Mixture No. for coating layer The negative electrode A coated with No. 4 was dried by heating at 120 ° C. for 6 hours, and cut into a predetermined shape (rectangular shape of 25 mm × 30 mm) to obtain a negative electrode of Test Example F4. The thickness of the coating layer of the negative electrode of Test Example F4 was 4 μm.

<Scanning electron microscope (abbreviation SEM) observation of the surface of the coating layer>
The surface of the negative electrode of Test Example F1, the surface of the negative electrode of Test Example F2, and the surface of the negative electrode of Test Example F4 were observed by SEM. The SEM observation result of the negative electrode surface of Test Example F4 is shown in FIG. 2, the SEM observation result of the negative electrode surface of Test Example F1 is shown in FIG. 3, and the SEM observation result of the negative electrode surface of Test Example F2 is shown in FIG.

  As shown in FIG. 2, on the surface of the negative electrode of Test Example F4, a large number of micron-order holes including a hole having a maximum diameter of 30 μm were observed. Moreover, this hole in the surface of the negative electrode of Test Example F4 penetrated to the negative electrode active material layer, and a portion where the negative electrode active material layer was exposed was observed. On the other hand, as can be seen from FIGS. 3 and 4, pores having a diameter of 100 nm to 600 nm were observed on the surface of the negative electrode of Test Example F1 and the surface of the negative electrode of Test Example F2, but the diameter was larger than 2 μm. No holes were observed.

  Although not shown in the figure, SEM observation of the surface of the negative electrode of Test Example F3 was also performed. As a result, pores having a diameter of 200 nm to 500 nm were observed, but no pores having a diameter larger than 2 μm were observed.

  From this, it was confirmed that if PAA, CMC or PVA was included in the coating layer, a coating layer having pores with a diameter of 50 nm to 2 μm but having no pores with a diameter larger than 2 μm could be formed.

(Production of laminated lithium ion secondary battery)
(Laminated lithium ion secondary battery of Test Example D1)
A laminate type lithium ion secondary battery of Test Example D1 using the negative electrode of Test Example F1 as the negative electrode was produced as follows.

The positive electrode was produced as follows. LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (abbreviation NCM523) having an average particle diameter D ₅₀ of 5 μm as a positive electrode active material, and acetylene black (product number HS100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive additive, As a binder, PVDF (manufactured by Kureha Co., Ltd., product number 7208) was mixed as 94 parts by mass, 3 parts by mass, and 3 parts by mass to prepare a mixture. This mixture was dispersed in an appropriate amount of NMP to prepare a slurry.

An aluminum foil having a thickness of 20 μm was prepared as a current collector. The slurry was placed on the current collector, and applied using a doctor blade so that the slurry became a film. The obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were firmly and closely joined by a roll press. At this time, the electrode density was set to 3.2 g / cm ² . The bonded product was heated in a vacuum dryer at 120 ° C. for 6 hours. The bonded product after heating was cut into a predetermined shape (rectangular shape of 25 mm × 30 mm) to obtain a positive electrode. The thickness of the positive electrode active material layer was about 30 μm.

  A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode of Test Example F1. Specifically, a separator was sandwiched between the positive electrode and the negative electrode of Test Example F1 to form an electrode plate group. As the separator, a rectangular sheet (27 × 32 mm, thickness 25 μm) having a three-layer porous membrane structure of polypropylene resin / polyethylene resin / polypropylene resin and coated with alumina on both the positive electrode side and the negative electrode side was used.

The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then a non-aqueous electrolyte was poured into the bag-like laminated film. Fluoroethylene carbonate (abbreviated as FEC), ethylene carbonate (abbreviated as EC), ethyl methyl carbonate (abbreviated as EMC), and dimethyl carbonate (abbreviated as DMC) as non-aqueous electrolytes were FEC: EC: EMC: DMC = 0.4: 2. LiPF ₆ is dissolved in a solvent mixed at a ratio of 6: 3: 4 (volume ratio) so as to be 1 mol / l, and LiPF ₂ (C ₂ O ₄ ) ₂ (abbreviation LPFO) is 0.01 mol / l. The solution dissolved in was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the non-aqueous electrolyte were sealed. Note that the positive electrode and the negative electrode each have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. Through the above steps, a laminate type lithium ion secondary battery of Test Example D1 was produced.

(Laminated lithium ion secondary battery of Test Example D2)
A laminated lithium ion secondary battery of Test Example D2 was produced in the same manner as Test Example D1, except that the negative electrode of Test Example F1 in the laminated lithium ion secondary battery of Test Example D1 was changed to the negative electrode of Test Example F2.

(Laminated lithium ion secondary battery of Test Example D3)
A laminated lithium ion secondary battery of Test Example D3 was produced in the same manner as Test Example D1, except that the negative electrode of Test Example F1 in the laminated lithium ion secondary battery of Test Example D1 was changed to the negative electrode of Test Example F3.

(Laminated lithium ion secondary battery of Test Example D4)
A laminated lithium ion secondary battery of Test Example D4 was produced in the same manner as Test Example D1, except that the negative electrode of Test Example F1 in the laminated lithium ion secondary battery of Test Example D1 was changed to the negative electrode of Test Example F4.

(Laminated lithium ion secondary battery of Test Example D5)
A laminated lithium ion secondary battery of Test Example D5 was produced in the same manner as Test Example D1, except that the negative electrode of Test Example F1 in the laminated lithium ion secondary battery of Test Example D1 was changed to the negative electrode of Test Example F5.

<Safety evaluation of lithium ion secondary batteries>
In the laminated lithium ion secondary batteries of Test Example D1, Test Example D4, and Test Example D5, each battery was sealed with a non-aqueous electrolyte solution. Each laminated lithium ion secondary battery is set on an autograph (product number AGS-500D, manufactured by Shimadzu Corporation) with a nail with a nail diameter of 0.8 mm, and nail penetration is performed while forcibly applying a voltage to the battery from the outside. The load, current, and voltage applied to the nail when it was inserted at a speed of 1 mm / second were measured. Table 1 shows the current value when each laminated lithium ion secondary battery is short-circuited.

  From the results of Table 1, when comparing the current value at the time of short circuit of the laminate type lithium ion secondary battery of Test Example D4 and the laminate type lithium ion secondary battery of Test Example D5, if there is a coating layer, the current at the time of short circuit It was found that the value could be greatly suppressed and the short-circuit prevention function was working. Furthermore, according to the test example D1, the short-circuit current of the laminate type lithium ion secondary battery of test example D1 and the laminate type lithium ion secondary battery of test example D4 is compared with that of test example D4. It was found that it can be reduced to / 10. Therefore, when the negative electrode of Test Example F1 having no hole with a diameter larger than 2 μm is used on the surface of the coating layer, the short circuit prevention function is more effective than the negative electrode of Test Example F4 having a hole with a maximum diameter of 30 μm on the surface of the coating layer. It was proved that the safety is high.

<60 ° C storage test>
Using the laminate type lithium ion secondary battery of Test Example D1, Test Example D2, and Test Example D5, the 60 ° C. storage characteristics were evaluated. The 60 ° C. storage test was held for 18 days at a temperature of 60 ° C. with a voltage of 4.32 V applied.

  A conditioning process was performed before the storage test. In the conditioning treatment, each laminated lithium ion secondary battery was charged stepwise to 4.5V, finally charged to 4.5V at a 1C rate, and then CV charged (constant voltage charging) for 5 hours. Then, after discharging to 2.5 V at a 0.33 C rate, CV discharging (constant voltage discharging) was performed at 2.5 V for 5 hours.

  Further, aging was performed after the conditioning treatment. In aging, each laminated lithium ion secondary battery was held at 4.32 V at 60 ° C. for 12 hours.

  After this aging, CCCV charge (constant current constant voltage charge) to 25V and 0.2C to 4.5V, hold for 10 minutes, and CC discharge (constant current discharge) to 2.5V at 0.33C And held for 10 minutes. The discharge capacity at 0.33 C at this time was defined as the initial capacity. The initial capacity was not significantly different in the laminated lithium ion secondary battery of Test Example D1, Test Example D2, and Test Example D5 in which no coating layer was formed. From this, it was confirmed that even when a coating layer having pores of 50 nm to 2 μm on the surface and having no pores with a diameter larger than 2 μm was used, the capacity of the battery was hardly lowered.

  Each laminate type lithium ion secondary battery after the storage test was measured for discharge capacity at 0.33 C in the same manner as the initial capacity measurement, and this was taken as the capacity after the 60 ° C. storage test. The capacity retention rate of the 60 ° C. storage test was determined by the following formula: Capacity maintenance rate (%) after 60 ° C. storage test = (capacity after 60 ° C. storage test / initial capacity) × 100. The results are shown in Table 2.

  As can be seen from Table 2, the capacity retention rate (%) after the 60 ° C. storage test of the laminate type lithium ion secondary batteries of Test Example D1 and Test Example D2 as compared to the laminate type lithium ion secondary battery of Test Example D5 ) Greatly improved. Both PAA and CMC have a glass transition point of 100 ° C. or more, and it was found that the use of PAA or CMC as the coating layer binder improves the 60 ° C. storage characteristics of the laminated lithium ion secondary battery.

<Cycle test>
A cycle test was performed using the laminated lithium ion secondary batteries of Test Example D2, Test Example D3, and Test Example D5. As a cycle test, a cycle test in which charging and discharging were repeated under the following conditions was performed, and the discharge capacity after 200 cycles was measured. When charging, CC charging (constant current charging) was performed at 60 ° C. at a 1 C rate and a voltage of 4.32 V. When discharging, CC discharge (constant current discharge) was performed at a rate of 3.26 V and 1 C. This charging / discharging was made into 1 cycle, and the cycle test was done to 200 cycles.

  In addition, the conditioning process was implemented before performing cycle measurement. In the conditioning treatment, each laminated lithium ion secondary battery was charged stepwise to 4.5V, finally charged to 4.5V at a 1C rate, and then CV charged (constant voltage charging) for 5 hours. Then, after discharging to 2.5 V at a 0.33 C rate, CV discharging (constant voltage discharging) was performed at 2.5 V for 5 hours.

  Further, aging was performed after the conditioning treatment. In aging, each laminated lithium ion secondary battery was held at 4.32 V at 60 ° C. for 12 hours.

  After this aging, CCCV charge (constant current constant voltage charge) to 25V and 0.2C to 4.5V, hold for 10 minutes, and CC discharge (constant current discharge) to 2.5V at 0.33C And held for 10 minutes. The discharge capacity at 0.33 C at this time was defined as the initial capacity. Here, the initial capacities of the laminated lithium ion secondary batteries of Test Example D2, Test Example D3, and Test Example D5 were almost equal values.

  Each laminate type lithium ion secondary battery after the 200 cycle test was measured for the discharge capacity at 0.33 C in the same manner as the initial capacity measurement, and this was taken as the capacity after 200 cycles.

  The capacity retention ratio after the cycle test was determined by the capacity retention ratio (%) after the cycle test = (capacity after 200 cycles / initial capacity) × 100. The results are shown in Table 3.

  As can be seen from Table 3, as compared with the laminated lithium ion secondary battery of Test Example D5, the laminate type lithium ion secondary batteries of Test Example D2 and Test Example D3 have improved capacity retention after the cycle test. From this, it was found that the coating layer containing CMC or PVA satisfactorily protects the surface of the negative electrode active material layer and can maintain the capacity of the lithium ion secondary battery even after the 200-cycle test.

<Dispersibility test (without dispersant)>
When the mixture for the coating layer is more dispersible in water, a more uniform coating layer can be formed, and the coating layer can be formed stably. Therefore, the dispersibility of the ceramic powder was tested.

The binder was dissolved in water, and Al ₂ O ₃ powder was mixed to obtain a slurry for each test example. The mass ratio of water, binder, and Al ₂ O ₃ was a percentage, water / binder / Al ₂ O ₃ = 60 / 1.6 / 38.4. The solid content concentration of the slurry of each test example was 40% by mass.

  As Test Example 1, polyvinyl pyrrolidone (abbreviation: PVP) was used as a binder, as Test Example 2, polyvinyl alcohol (abbreviation: PVA) was used as a binder, and as Test Example 3, a mixture of PVP and PVA was used as a binder. The mixing ratio of PVP and PVA was 50:50 by mass ratio.

Each sample bottle was allowed to stand for 1 day in a state where the mixture of each test example was placed, and it was visually confirmed whether or not the aqueous phase and the solid phase were separated. Furthermore the sample bottle after standing 1 day was determined by dynamic light scattering cumulant average particle diameter of each Al ₂ O ₃ in the liquid. The results are shown in Table 4. The cumulant average particle diameter is an average particle diameter calculated by analyzing the data obtained by the dynamic light scattering method by the Cumulant method. Incidentally, the grain size of the _Al 2 _{O 3} powder material an average particle diameter _{D 50} is 540 nm.

Comparing Test Example 1 to Test Example 3, in Test Example 1, Al ₂ O ₃ had the smallest cumulant average particle diameter, but separated into an aqueous phase and a solid phase over time. Test Example 2 is considered to have a large cumulant average particle size and aggregate and enlarge. In Test Example 3, the cumulant average particle size was relatively small, and separation into an aqueous phase and a solid phase was not observed even after a 1-day static test. Therefore, it was found that by using PVP and PVA in combination as an aqueous binder, the ceramic powder is easily dispersed and the pot life is long. The combination of PVP and PVA disperses the ceramic powder and is difficult to settle. The ceramic powder is coated with PVP, which promotes the dispersion of the ceramic powder due to the steric repulsion between the PVP, and further between the ceramic powder and the PVA. It is considered that the ceramic powder and the PVA form a network in the solution due to the hydrogen bond acting on, and a stable solution that is difficult to separate into an aqueous phase and a solid phase is obtained.

<Dispersibility test (with dispersant)>
The dispersibility test of the ceramic powder according to the type of the dispersant was performed.
A water-soluble binder is dissolved in water, Al ₂ O ₃ powder and each dispersant are added, and they are mixed for 2 hours with a mixer (manufactured by Sinky Co., Ltd., product number: AR-100). A slurry was obtained. In Test Examples 4 to 12, the mass ratio of water, binder, Al ₂ O _3, and dispersant was percentage, and water / binder / Al ₂ O ₃ / dispersant = 50/2/46/2. The solid content concentration of the slurry of Test Examples 4 to 12 was 50% by mass.

An Al ₂ O ₃ powder having an average particle diameter D ₅₀ = 600 nm was prepared as an Al ₂ O ₃ powder, and polyvinyl alcohol (abbreviated as PVA) (Mw = 2200) was prepared as a water-soluble binder.

  As a dispersant, a styrene-acrylic acid copolymer (manufactured by BASF Japan, product number: HPD96J, Mw = 16,500), a styrene-acrylic acid copolymer (manufactured by BASF Japan, product number: J-60J, Mw). = 8,500), styrene-acrylic acid copolymer (manufactured by BASF Japan, product number: J-63J, Mw = 12,500), polyacrylic acid (abbreviation PAA) (manufactured by Wako Pure Chemical Industries, Ltd., Mw) = 250,000), carboxymethyl cellulose (abbreviation CMC), polyvinyl alcohol (abbreviation PVA) (manufactured by Wako Pure Chemical Industries, Ltd., Mw = 2,200), phosphate ester polymer (manufactured by BYK Japan Japan, product number BYK180) ) And polyethylene glycol (abbreviation PEG) (Mw = 20,000).

Each sample bottle was allowed to stand for 1 day in a state where the slurry of each of Test Examples 4 to 12 was put, and the cumulant average particle size of each Al ₂ O ₃ powder in the slurry of the sample bottle after standing for 1 day was changed. Measured by dynamic light scattering. The results are shown in Table 5. The cumulant average particle diameter is an average particle diameter calculated by analyzing the data obtained by the dynamic light scattering method by the Cumulant method. Incidentally, _Al 2 _{O 3} powder having an average particle diameter _{D 50} of the material is 600 nm.

First, it was found that the Al ₂ O ₃ powder in the slurry of Test Example 12 in which no dispersant was added had an average cumulant particle size of 1961 nm, and the Al ₂ O ₃ powder was agglomerated. On the other hand, the cumulant average particle diameters of the Al ₂ O ₃ powders in the slurries of Test Examples 4 to 6 were all small. Also a slurry of Test Examples 7-11, when comparing the cumulant average particle size of the _Al 2 _{O 3} powder slurry in Test Example 4-6, the cumulant average particle size of the _Al 2 _{O 3} powder slurry of Test Example 4-6 Was found to be significantly smaller. Since _Al 2 _{O 3} powder having an average particle diameter _{D 50} of which put the material is at 600 nm, _Al 2 _{O 3} powder in the slurry in Test Example 4-6, hardly aggregate, to be well dispersed all right.

Here, the dispersant used in the slurry of Test Example 10 is a phosphoric acid dispersant. The average cumulant particle diameter of the Al ₂ O ₃ powder of the slurry of Test Example 10 is 1804 nm, which is almost the same as the average particle diameter of the Al ₂ O ₃ powder of the slurry of Test Example 12 that does not use a dispersant. From this, it was found that the phosphoric acid dispersant has no dispersion effect when the material of the coating layer is used. The average particle size of the Al ₂ O ₃ powder in the slurry of Test Examples 8, 9, and 11 was slightly smaller than the average particle size of the Al ₂ O ₃ powder in the slurry of Test Example 12 without using a dispersant. There was no significant decline. Moreover, the average cumulant particle diameter of the Al ₂ O ₃ powder of the slurry of Test Example 7 was 7094 nm, which was significantly larger than the average particle diameter of the Al ₂ O ₃ powder of the slurry of Test Example 12 not using the dispersant. . The dispersant added to the slurry of Test Example 7 is polyacrylic acid. Polyacrylic acid has a carboxylic acid group, but does not have a hydrophobic portion, and has a very large molecular weight of 250,000. It is predicted that the dispersant added to the slurry of Test Example 7 has a molecular weight that is too large to bridge between the Al ₂ O ₃ powders, and instead of being dispersed, it is aggregated.

Moreover, even if it left still for one day, the slurry of Test Examples 4-6 was not isolate | separated into the water phase and the solid phase. In the slurry, _Al 2 _{O 3} powder hardly agglomerate, a slurry of _Al 2 _{O 3} powder Test example since hardly settle 4-6, the pot life was found to longer.

<Production of negative electrode>
(Preparation of copper foil with a negative electrode active material layer)
As the negative electrode active material, SiO having an average particle diameter D ₅₀ of 5 μm and natural graphite (SMG having an average particle diameter D ₅₀ of 20 μm (manufactured by Hitachi Chemical Co., Ltd.)) were prepared. A polyamide-imide resin (abbreviated as PAI) (manufactured by Arakawa Chemical Industries, Ltd.) was prepared as a binder resin. Acetylene black (abbreviation AB) was prepared as a conductive additive.

  Mixing was performed at a ratio of SiO / SMG / AB / PAI = 32/50/8/10 (mass ratio) to obtain a mixture. This mixture was dispersed in an appropriate amount of NMP to prepare a slurry.

  This slurry was applied to a copper foil having a thickness of 20 μm, which is a negative electrode current collector, in a film shape using a doctor blade. The current collector coated with the slurry was dried and pressed to obtain a bonded product. The joined product was heated and dried with a vacuum dryer at 200 ° C. for 2 hours to obtain a copper foil on which a negative electrode active material layer was formed. This was designated as negative electrode B. The thickness of the negative electrode active material layer of the negative electrode B was 17 μm. This negative electrode B is designated as the negative electrode of Test Example F15. The negative electrode of Test Example F15 is a negative electrode on which no coating layer is formed.

(Negative electrode of Test Example F6)
The slurry of Test Example 4 was applied to the negative electrode B using an applicator. The negative electrode B on which the slurry of Test Example 4 was applied was heat-dried at 200 ° C. for 2 hours, cut into a predetermined shape (25 mm × 30 mm rectangular shape), and used as the negative electrode of Test Example F6. The thickness of the coating layer of the negative electrode of Test Example F6 was 5.1 μm, and the thickness unevenness was 1 μm.

  Here, the thickness of the coating layer was determined by subtracting the thickness of the negative electrode B from the thickness of the negative electrode of Test Example F6. The thickness of each negative electrode was an average value of the results of measuring each negative electrode at 10 points at intervals of 5 mm. The thickness unevenness of the coating layer was determined by measuring the thickness of each negative electrode at 10 points at intervals of 5 mm, and determining the difference between the maximum value and the minimum value.

(Negative electrode of Test Example F7)
A negative electrode of Test Example F7 was produced in the same manner as the negative electrode of Test Example F6 except that the slurry of Test Example 4 was replaced with the slurry of Test Example 5. The thickness of the coating layer of the negative electrode of Test Example F7 was 4.6 μm, and the thickness unevenness was 1 μm.

(Negative electrode of Test Example F8)
A negative electrode of Test Example F8 was produced in the same manner as the negative electrode of Test Example F6 except that the slurry of Test Example 4 was replaced with the slurry of Test Example 6. The thickness of the coating layer of the negative electrode of Test Example F8 was 4.4 μm, and the thickness unevenness was 1 μm.

(Negative electrode of Test Example F9)
A negative electrode of Test Example F9 was produced in the same manner as the negative electrode of Test Example F6 except that the slurry of Test Example 4 was replaced with the slurry of Test Example 7. The thickness of the coating layer of the negative electrode of Test Example F9 was 5.8 μm, and the thickness unevenness was 5 μm.

(Negative electrode of Test Example F10)
A negative electrode of Test Example F10 was produced in the same manner as the negative electrode of Test Example F6 except that the slurry of Test Example 4 was replaced with the slurry of Test Example 8. The thickness of the coating layer of the negative electrode of Test Example F10 was 5.6 μm, and the thickness unevenness was 3 μm.

(Negative electrode of Test Example F11)
A negative electrode of Test Example F11 was produced in the same manner as the negative electrode of Test Example F6 except that the slurry of Test Example 4 was replaced with the slurry of Test Example 9. The thickness of the coating layer of the negative electrode of Test Example F11 was 5.1 μm, and the thickness unevenness was 3 μm.

(Negative electrode of Test Example F12)
A negative electrode of Test Example F12 was produced in the same manner as the negative electrode of Test Example F6 except that the slurry of Test Example 4 was replaced with the slurry of Test Example 10. The thickness of the coating layer of the negative electrode of Test Example F12 was 5.7 μm, and the thickness unevenness was 3 μm.

(Negative electrode of Test Example F13)
A negative electrode of Test Example F13 was produced in the same manner as the negative electrode of Test Example F6 except that the slurry of Test Example 4 was replaced with the slurry of Test Example 11. The thickness of the coating layer of the negative electrode of Test Example F13 was 6.2 μm, and the thickness unevenness was 4 μm.

(Negative electrode of Test Example F14)
A negative electrode of Test Example F14 was produced in the same manner as the negative electrode of Test Example F6 except that the slurry of Test Example 4 was replaced with the slurry of Test Example 12. The thickness of the coating layer of the negative electrode of Test Example F14 was 5.8 μm, and the thickness unevenness was 4 μm.

Table 6 shows the results of the thickness and thickness unevenness of the coating layer of the negative electrode of each test example F6 to F14, and the average particle size of the Al ₂ O ₃ powder in each slurry.

  From Table 6, it was found that the thickness unevenness of the negative electrode coating layers of Test Examples F6 to F8 was significantly smaller than the thickness unevenness of the negative electrode coating layers of Test Examples F9 to F14.

(Production of laminated lithium ion secondary battery)
(Laminated lithium ion secondary battery of Test Example D6)
A laminate type lithium ion secondary battery of Test Example D6 using the negative electrode of Test Example F6 as the negative electrode was produced as follows.

The positive electrode was produced as follows. LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (abbreviation NCM523) having an average particle diameter D ₅₀ of 5 μm as a positive electrode active material, acetylene black (product number HS100) as a conductive additive, and polyvinylidene fluoride as a binder (Abbreviation PVDF) was mixed as 94 parts by mass, 3 parts by mass, and 3 parts by mass, respectively, to obtain a mixture. This mixture was dispersed in an appropriate amount of NMP to prepare a slurry.

An aluminum foil having a thickness of 20 μm was prepared as a current collector. The slurry was placed on the current collector, and applied using a doctor blade so that the slurry became a film. The obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were firmly and closely joined by a roll press. At this time, the electrode density was set to 3.2 g / cm ² . The bonded product was heated in a vacuum dryer at 120 ° C. for 6 hours. The bonded product after heating was cut into a predetermined shape (rectangular shape of 25 mm × 30 mm) to obtain a positive electrode. The thickness of the positive electrode active material layer was about 42 μm.

  A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode of Test Example F6. Specifically, a separator was sandwiched between the positive electrode and the negative electrode of Test Example F6 to form an electrode plate group. As the separator, a rectangular sheet (27 × 32 mm, thickness 25 μm) having a three-layer porous membrane structure of polypropylene resin / polyethylene resin / polypropylene resin and coated with alumina on both the positive electrode side and the negative electrode side was used.

The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then a non-aqueous electrolyte was poured into the bag-like laminated film. Fluoroethylene carbonate (abbreviated as FEC), ethylene carbonate (abbreviated as EC), ethyl methyl carbonate (abbreviated as EMC), and dimethyl carbonate (abbreviated as DMC) as non-aqueous electrolytes were FEC: EC: EMC: DMC = 0.4: 2. A solution prepared by dissolving LiPF ₆ in a solvent mixed at a ratio of 6: 3: 4 (volume ratio) to 1 mol / l and dissolving LiPF ₂ (C ₂ O ₄ ) ₂ to 0.01 mol / l. Was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the non-aqueous electrolyte were sealed. Note that the positive electrode and the negative electrode each have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. Through the above steps, a laminate type lithium ion secondary battery of Test Example D6 was produced.

(Laminated lithium ion secondary battery of Test Example D7)
A laminated lithium ion secondary battery of Test Example D7 was produced in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F7.

(Laminated lithium ion secondary battery of Test Example D8)
A laminated lithium ion secondary battery of Test Example D8 was produced in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F8.

(Laminated lithium ion secondary battery of Test Example D9)
A laminated lithium ion secondary battery of Test Example D9 was prepared in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F9.

(Laminated lithium ion secondary battery of Test Example D10)
A laminated lithium ion secondary battery of Test Example D10 was produced in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F10.

(Laminated lithium ion secondary battery of Test Example D11)
A laminated lithium ion secondary battery of Test Example D11 was produced in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F11.

(Laminated lithium ion secondary battery of Test Example D12)
A laminated lithium ion secondary battery of Test Example D12 was prepared in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F12.

(Laminated lithium ion secondary battery of Test Example D13)
A laminated lithium ion secondary battery of Test Example D13 was produced in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F13.

(Laminated lithium ion secondary battery of Test Example D14)
A laminated lithium ion secondary battery of Test Example D14 was produced in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F14.

(Laminated lithium ion secondary battery of Test Example D15)
A laminated lithium ion secondary battery of Test Example D15 was produced in the same manner as Test Example D6 except that the negative electrode of Test Example F6 in the laminated lithium ion secondary battery of Test Example D6 was changed to the negative electrode of Test Example F15.

<60 ° C storage test>
The 60 ° C. storage characteristics were evaluated using the laminate type lithium ion secondary batteries of Test Example D6, Test Example D7, Test Example D9, Test Example D10, and Test Example D15. The 60 ° C. storage test was held for 18 days at a temperature of 60 ° C. with a voltage of 4.32 V applied.

  A conditioning process was performed before the storage test. In the conditioning treatment, each laminated lithium ion secondary battery was charged stepwise to 4.5V, finally charged to 4.5V at a 1C rate, and then CV charged for 5 hours. Then, after discharging to 2.5 V at a 0.33 C rate, CV discharging was performed at 2.5 V for 5 hours.

  Further, aging was performed after the conditioning treatment. In aging, each laminated lithium ion secondary battery was held at 4.32 V at 60 ° C. for 12 hours. After this aging, CCCV charge was performed at 25 ° C. to 4.5 V at 0.2 C, held for 10 minutes, CC discharged to 0.3 V at 0.33 C, and held for 10 minutes. The discharge capacity at 0.33 C was measured and used as the initial capacity.

  Each laminate type lithium ion secondary battery after the storage test was measured for discharge capacity at 0.33 C in the same manner as the initial capacity measurement, and this was taken as the capacity after the 60 ° C. storage test. The capacity retention rate of the 60 ° C. storage test was determined by the following formula: Capacity maintenance rate (%) after 60 ° C. storage test = (capacity after 60 ° C. storage test / initial capacity) × 100. The results are shown in Table 7.

  As can be seen from Table 7, the laminated lithium ion secondary batteries of Test Example D6 and Test Example D7 are stored at 60 ° C. as compared with the laminated lithium ion secondary batteries of Test Example D15, Test Example D9, and Test Example D10. The capacity retention rate (%) after the test was greatly improved. It was found that the 60 ° C. storage characteristics of the laminated lithium ion secondary battery were improved by reducing the thickness unevenness of the coating layer.

  1: current collector, 2: organic solvent-based binder, 3: negative electrode active material, 4: negative electrode active material layer, 5: coating layer, 51: ceramic powder, 521: aqueous binder, 522: water-soluble binder, 53: dispersion Agent, 6: pores.

Claims (17)

A lithium ion secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The negative electrode is
A current collector,
A negative electrode active material layer disposed on a surface of the current collector and including a negative electrode active material and an organic solvent-based binder;
A coating layer that is disposed on the surface of the negative electrode active material layer, includes ceramic powder and an aqueous binder, and has pores;
A lithium ion secondary battery comprising:   The lithium ion secondary battery according to claim 1, wherein the pore has a diameter of 50 nm to 2 μm.   3. The lithium ion secondary battery according to claim 1, wherein a mass ratio of the ceramic powder and the aqueous binder in the coating layer is 88:12 to 99: 1.   The lithium ion secondary battery according to any one of claims 1 to 3, wherein the glass transition point of the aqueous binder is 60 ° C or higher.   The lithium ion secondary battery according to any one of claims 1 to 4, wherein the aqueous binder is at least one selected from polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone, and carboxymethyl cellulose.   The thickness of the said coating layer is 2 micrometers or more and 10 micrometers or less, The lithium ion secondary battery as described in any one of Claims 1-5. The average particle diameter D ₅₀ of the lithium ion secondary battery according to any one of claims 1 to 6 is 100nm or more 1μm or less of the ceramic powder. The lithium ion secondary battery according to claim 1, wherein the negative electrode active material contains Si or SiO _x (0.3 ≦ x ≦ 1.6).   The lithium ion secondary battery according to any one of claims 1 to 8, wherein the organic solvent-based binder is one selected from polyamide, polyamideimide, and polyimide. The lithium ion secondary battery according to any one of claims 1-9 containing an additive the non-aqueous electrolyte consisting of _{LiPF 2 (C 2 O 4)} 2.   The lithium ion secondary battery according to claim 1, wherein the aqueous binder is a water-soluble binder, and the coating layer further includes a dispersant made of a polycarboxylic acid having a hydrophobic portion.   The lithium ion secondary battery according to claim 11, wherein the polycarboxylic acid is made of a copolymer of styrene and acrylic acid, and the molecular weight of the polycarboxylic acid is from 5,000 to 500,000.   The lithium ion secondary battery according to claim 11 or 12, wherein the water-soluble binder is at least one selected from polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone, and carboxymethyl cellulose.   The lithium ion secondary battery according to any one of claims 11 to 13, wherein thickness unevenness of the coating layer is 2 m or less.   The content of the dispersant in the coating layer is 1 part by mass or more and 10 parts by mass or less when the ceramic powder is 100 parts by mass. Next battery.   The thickness of the said coating layer is 2 micrometers or more and 10 micrometers or less, The lithium ion secondary battery as described in any one of Claims 11-15. The average particle diameter _{D 50} is a lithium-ion secondary battery according to any one of claims 11 to 16 is 100nm or more 1μm or less of the ceramic powder.

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