JP7051312B2 - Manufacturing method of positive electrode active material, non-aqueous secondary battery, and positive electrode active material - Google Patents

Description

The present invention relates to a positive electrode active material, a non-aqueous secondary battery, and a method for producing a positive electrode active material.

In recent years, with the miniaturization and weight reduction of various electronic devices, there is a demand for higher capacity and higher potential of non-aqueous secondary batteries used as power sources for these electronic devices. For example, a lithium composite oxide containing nickel (Ni) as a main component is known as a positive electrode active material exhibiting a relatively high potential and a high capacity. Such a lithium composite oxide containing nickel as a main component is generally used at a charging voltage of 4.2 V with graphite as a counter electrode.

In recent years, in order to increase the capacity, it has been studied to increase the nickel ratio and the charging voltage in a non-aqueous secondary battery using a lithium composite oxide containing nickel as a main component.

Specifically, by increasing the charging voltage to 4.3 V with graphite as the counter electrode, a high capacity of 200 mAh / g or more can be realized with a nickel ratio of 80%. However, at the high charging voltage as described above, the oxidizing power of the lithium composite oxide becomes extremely high. As a result, the stability of the crystal structure of the delithiumized lithium composite oxide is lost, and the cycle characteristics of the non-aqueous secondary battery are deteriorated.

Therefore, in a non-aqueous secondary battery using a lithium composite oxide containing nickel as a main component, various improvements have been attempted in order to improve the cycle characteristics.

For example, Patent Document 1 below discloses doping a lithium nickel cobalt (LiNiCo) composite oxide with a halogen element. This makes it possible to improve the cycle characteristics of the non-aqueous secondary battery. Further, Patent Document 2 below discloses that one or more elements of B, Al, In and Sn are added to a lithium nickel cobalt (LiNiCo) composite oxide. This makes it possible to improve the cycle characteristics of the non-aqueous secondary battery. Further, Patent Document 3 below discloses that a lithium nickel cobalt aluminum (LiNiCoAl) composite oxide is coated with a sulfate and a boric acid compound. This makes it possible to improve the cycle characteristics of the non-aqueous secondary battery.

Japanese Unexamined Patent Publication No. 2006-261127 Japanese Unexamined Patent Publication No. 8-78006 Japanese Unexamined Patent Publication No. 2009-146739

However, in the techniques disclosed in Patent Documents 1 to 3, a different element is added to the positive electrode active material. Therefore, the range in which lithium can be intercalated and deintercalated in the positive electrode active material is narrowed. Therefore, in the non-aqueous secondary batteries disclosed in Patent Documents 1 to 3, the cycle characteristics are improved, but the discharge capacity is lowered.

Therefore, the present invention has been made in view of the above problems. An object of the present invention is to provide a positive electrode active material, a non-aqueous secondary battery, and a method for producing a positive electrode active material, which can further improve cycle characteristics while maintaining a discharge capacity.

In order to solve the above problems, according to a certain viewpoint of the present invention, an active material particle containing a lithium composite oxide represented by the following chemical formula 1 and a coating layer covering the surface of the active material particle are provided. The coating layer contains Li and La as essential elements, and further contains one or more elements E selected from the group consisting of Al, Zr, Nb, Sc, Ti, Ta and Y. Provided is a positive electrode active material containing an oxide containing the presenting oxide and having a ratio of the coating layer of 0.3% by mass or more and 1.0% by mass or less with respect to the total mass of the positive electrode active material.
Li _a Ni _{x Coy} M _z O ₂ ... Chemical formula 1
In the above chemical formula 1, M is selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. It is one kind or two or more kinds of metal elements, 0.10 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0 <y ≦ 0.20, and 0 ≦ z ≦ 0. .10 and x + y + z = 1.

With the above configuration, it is possible to improve the cycle characteristics while maintaining the discharge capacity of the non-aqueous secondary battery.

The element E may be Zr or Ti.

With the above configuration, it is possible to further suppress a decrease in the discharge capacity of the non-aqueous secondary battery.

The coating layer may be formed of particles of the oxide having an average particle size of 0.1 μm or more and 1 μm or less.

With the above configuration, the coating layer formed by the dry process can improve the cycle characteristics while maintaining the discharge capacity of the non-aqueous secondary battery.

The oxide particles may contain Li ₇ La ₃ Zr ₂ O ₁₂ , which is a garnet-type solid electrolyte.

With the above configuration, it is possible to further suppress a decrease in the discharge capacity of the non-aqueous secondary battery.

The oxide particles may contain La _0.5 Li _0.3 TiO ₃ , which is a perovskite-type solid electrolyte.

With the above configuration, it is possible to further suppress a decrease in the discharge capacity of the non-aqueous secondary battery.

The thickness of the coating layer may be 0.1 μm or more and 1 μm or less.

With the above configuration, the coating layer formed by the wet process can improve the cycle characteristics while maintaining the discharge capacity of the non-aqueous secondary battery.

A resin coating layer containing polyacrylonitrile having a mass average molecular weight of 500,000 or more and 800,000 or less and further coating the active material particles may be provided on the coating layer.

With the above configuration, the cycle characteristics can be further improved while maintaining the discharge capacity of the non-aqueous secondary battery.

The active material particles are secondary particles in which a plurality of primary particles are bonded, the average length of the major axis of the primary particles is 0.1 μm or more and 2 μm or less, and the average particle diameter of the secondary particles is 3 μm. It may be 20 μm or more and 20 μm or less.

With the above configuration, the battery characteristics of the non-aqueous secondary battery can be further improved.

Further, in order to solve the above-mentioned problems, according to another viewpoint of the present invention, a positive electrode containing the positive electrode active material described in any of the above and an alkali metal ion, an alkaline earth metal ion or an aluminum ion are cations. A non-aqueous secondary battery comprising an electrolytic solution containing a salt, a fluoroethylene carbonate, a fluoroether and a fluorocarbonate is provided.

With the above configuration, the non-aqueous secondary battery can improve the cycle characteristics while maintaining the discharge capacity.

Further, a separator coated with ceramic may be provided.

With the above configuration, the non-aqueous secondary battery can improve the reliability.

The separator may contain Mg or Al as an element.

With the above configuration, the non-aqueous secondary battery can improve the reliability.

Further, in order to solve the above-mentioned problems, according to another viewpoint of the present invention, a step of forming an active material particle containing a lithium composite oxide represented by the following chemical formula 1 and a surface of the active material particle are formed. A method for producing a positive electrode active material including a step of forming a coating layer, wherein the coating layer contains Li and La as essential elements and is a group consisting of Al, Zr, Nb, Sc, Ti, Ta and Y. It contains an oxide further containing one or more selected elements E, and the coating layer is obtained by a wet or dry process in an amount of 0.3% by mass or more and 1.0% by mass based on the total mass of the positive electrode active material. Hereinafter, a method for producing a positive electrode active material, which covers the surface of the active material particles, is provided.
Li _a Ni _{x Coy} M _z O ₂ ... Chemical formula 1
In the above chemical formula 1, M is selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. One or more kinds of metal elements, 0.10 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0 <y ≦ 0.20, and 0 ≦ z ≦ 0.10. And x + y + z = 1.

With the above configuration, it is possible to produce a positive electrode active material capable of improving the cycle characteristics while maintaining the discharge capacity of the non-aqueous secondary battery.

The coating layer may be formed by coating the surface of the active material particles with the oxide and then heat-treating the active material particles at 500 ° C. or higher and 600 ° C. or lower.

With the above configuration, it is possible to produce a positive electrode active material capable of improving the cycle characteristics while maintaining the discharge capacity of the non-aqueous secondary battery.

The active material particles may be formed by a coprecipitation method.

With the above configuration, it is possible to produce a positive electrode active material capable of improving the cycle characteristics while maintaining the discharge capacity of the non-aqueous secondary battery.

As described above, according to the present invention, it is possible to improve the cycle characteristics while maintaining the discharge capacity of the non-aqueous secondary battery.

It is explanatory drawing which shows typically the structure of the non-aqueous secondary battery which concerns on one Embodiment of this invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

<1. Configuration of non-water secondary battery>
First, with reference to FIG. 1, the configuration of the non-aqueous secondary battery 10 according to the embodiment of the present invention will be specifically described.

As shown in FIG. 1, the non-aqueous secondary battery 10 includes a positive electrode 20, a negative electrode 30, and a separator layer 40 impregnated with an electrolytic solution. The form of the non-aqueous secondary battery 10 is not particularly limited. For example, the form of the non-aqueous secondary battery 10 may be any of a cylindrical type, a square type, a laminated type, a button type, and the like.

The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22. The current collector 21 may be any conductor as long as it is a conductor. For example, the current collector 21 may be aluminum, stainless steel, nickel-plated steel, or the like.

The positive electrode active material layer 22 contains at least a positive electrode active material and a binder resin, and may further contain a conductive auxiliary agent. The ratio of the contents of the positive electrode active material, the conductive auxiliary agent, and the binder resin is not particularly limited. As the content ratio, it is possible to use the content ratio used in a general non-aqueous secondary battery.

The conductive auxiliary agent enhances the conductivity of the positive electrode. Conductive auxiliaries include, for example, carbon black such as ketjen black and acetylene black, natural graphite, artificial graphite, carbon nanotubes, graphene, and Fibrous carbon such as carbon nanofibers, or a composite of these fibrous carbon and carbon black can be used. However, the conductive auxiliary agent is not limited to the above-mentioned substances as long as the conductivity of the positive electrode can be enhanced, and other substances can be used.

The binder resin binds the positive electrode active material and the conductive auxiliary agent onto the current collector 21. Examples of the binder resin include polyvinylidene fluoride (polyvinylidene fluoride), ethylenepropylene diene ternary copolymer (ethylene-polyethylene-diene terpolymer), styrene butadiene rubber (styrene-butadiene rubber), and acrylonitrile. , Fluororelastomer, polyvinyl acetate, polymethylmethacrylate, polyethylene, nitrocellulose and the like can be used. However, the binder resin is not limited to the above-mentioned substances as long as the positive electrode active material and the conductive agent can be bound onto the current collector 21. For example, other substances can be used as the binder resin.

In the present embodiment, the positive electrode active material includes active material particles and a coating layer that covers the surface of the active material particles. Further, the positive electrode active material may further include a resin coating layer for coating the active material particles on the coating layer.

The active material particles contain a lithium composite oxide containing nickel as a main component, and specifically, a lithium composite oxide represented by the following chemical formula 1.
Li _a Ni _{x Coy} M _z O ₂ ... Chemical formula 1
In the above chemical formula 1, M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), niobium ( Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), and cerium (Ce). One or more metal elements selected from the group, 0.10 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, and 0 <y ≦ 0.20, and 0. ≦ z ≦ 0.10. And x + y + z = 1.

In the above chemical formula 1, M is preferably one or more metal elements selected from the group consisting of Al, Mn, Mg and Ti. Further, a is preferably 0.10 ≦ a ≦ 1.00, and x, y, z are preferably 0.80 ≦ x ≦ 0.95 and 0.05 ≦ y ≦ 0.20. And 0 ≦ z ≦ 0.10. And x + y + z = 1.

Active material particles containing the lithium composite oxide represented by the above chemical formula 1 may be used. As a result, the non-aqueous secondary battery 10 can be used with a high charging voltage of 4.3 V or more with graphite as the counter electrode.

The active material particles may further contain another lithium composite oxide in addition to the lithium composite oxide represented by the above chemical formula 1. Examples of other lithium composite oxides include Li / Ni / Co / Mn-based composite oxides such as LiNi _{x Coy Mn z O 2} , Li / Ni-based composite oxides such as LiNiO ₂ , and LiMn ₂ O ₄ . Li / Mn-based composite oxides such as LiMn _1.5 Ni _0.5 O ₄ or Li _a Mn _x Coy Ni _z O ₂ ( _1.150 ≦ a ≦ 1.430, 0.45 ≦ x ≦ 0. 6, 0.10 ≦ y ≦ 0.15, 0.20 ≦ _z ≦ 0.28) or LiMn _x Coy Ni _z O ₂ (0.3 ≦ x ≦ 0.85, 0.10 ≦ y ≦ 0. 3. Solid solution oxides such as 0.10 ≦ z ≦ 0.3) can be exemplified.

Further, the active material particles are formed as secondary particles in which a large number of primary particles are bonded. The average length of the major axis of the primary particles may be 0.1 μm or more and 2 μm or less, and more preferably 0.1 μm or more and 1 μm or less. Further, the average particle diameter of the secondary particles of the active material particles may be 3 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less.

When the average length of the major axis of the primary particles of the active material particles is less than 0.1 μm, the crystallinity of the active material particles is lowered, which causes a large decrease in the battery capacity. Further, in such a case, the internal resistance may increase, which is not preferable. Further, when the average length of the major axis of the primary particles of the active material particles is more than 2 μm, the shear stress of the active material particles becomes large. This is not preferable because the active material particles are likely to be cracked and the battery characteristics may be deteriorated.

Further, when the average particle size of the secondary particles of the active material particles is less than 3 μm, the handling of the active material particles becomes complicated, and the manufacturing cost (cost) of the non-aqueous secondary battery 10 increases. When the average particle size of the secondary particles of the active material particles is more than 20 μm, it becomes difficult to secure a sufficient reaction area between the active material particles and the electrolytic solution, and the discharge capacity of the non-aqueous secondary battery 10 becomes high. It will drop.

Here, the average length of the major axis of the primary particle of the active material particle and the average particle diameter of the secondary particle are measured by image analysis of the image of the active material particle observed by SEM (Scanning Electron Microscope). Can be done. The average length of the major axis of the primary particle represents the arithmetic mean value of the length of the longest part of the primary particle in the observation image of the active material particle. Further, the average particle diameter of the secondary particles represents, for example, an arithmetic mean value of the diameter when the secondary particles are regarded as spheres.

The coating layer contains Li and La as essential elements and further contains an oxide containing one or more elements E selected from the group consisting of Al, Zr, Nb, Sc, Ti, Ta and Y. Since such oxides exhibit high lithium ion conductivity, the coating layer protects the surface of the active material particles without inhibiting ion conduction from the active material particles. Therefore, the coating layer can stabilize the crystal structure of the active material particles and improve the cycle characteristics of the non-aqueous secondary battery 10 without deteriorating the battery characteristics of the non-aqueous secondary battery 10.

Further, the coating layer may cover the surface of the active material particles with 0.3% by mass or more and 1.0% by mass or less with respect to the total mass of the positive electrode active material including the active material particles. When the coating amount of the coating layer is less than 0.3% by mass, the effect of improving the cycle characteristics of the non-aqueous secondary battery 10 according to the present embodiment is difficult to obtain, which is not preferable. Further, when the coating amount of the coating layer exceeds 1.0% by mass, the discharge capacity of the non-aqueous secondary battery 10 decreases and the surface resistance of the positive electrode active material increases, which is not preferable.

Here, the element E contained in the oxide constituting the coating layer may be Zr or Ti. When the element E is Zr or Ti, the coating layer can have higher lithium ion conductivity. Thereby, the battery characteristics of the non-aqueous secondary battery 10 can be further improved.

A case where the element E contained in the oxide constituting the coating layer is Zr will be described. At this time, it is more preferable that the coating layer covers the surface of the active material particles with 0.3% by mass or more and 0.8% by mass or less with respect to the total mass of the positive electrode active material including the active material particles. When the coating amount of the coating layer is less than 0.3% by mass, the effect of improving the cycle characteristics of the non-aqueous secondary battery 10 according to the present embodiment is difficult to obtain, which is not preferable. Further, when the coating amount of the coating layer exceeds 0.8% by mass, the discharge capacity of the non-aqueous secondary battery 10 decreases and the surface resistance of the positive electrode active material increases, which is not preferable.

Further, a case where the element E contained in the oxide constituting the coating layer is Ti will be described. At this time, it is more preferable that the coating layer covers the surface of the active material particles with 0.3% by mass or more and 1.0% by mass or less with respect to the total mass of the positive electrode active material including the active material particles. When the coating amount of the coating layer is less than 0.3% by mass, the effect of improving the cycle characteristics of the non-aqueous secondary battery 10 according to the present embodiment is difficult to obtain, which is not preferable. Further, when the coating amount of the coating layer exceeds 1.0% by mass, the discharge capacity of the non-aqueous secondary battery 10 decreases and the surface resistance of the positive electrode active material increases, which is not preferable.

The coating layer may be formed on the surface of the active material particles by either a wet process or a dry process. Specifically, the coating layer may be formed by a wet process using an alkoxide. Further, the coating layer may be formed by a dry process such as a mechanical method.

When the coating layer is formed by a wet process, the coverage of the coating layer with respect to the active material particles can be further increased. Thereby, the cycle characteristics of the non-aqueous secondary battery 10 can be further improved. In such a case, the coating layer is formed as a mixture of oxides containing at least one of Li, La, and element E.

Further, the thickness of the coating layer formed by the wet process may be 0.1 μm or more and 1 μm or less. When the thickness of the coating layer is less than 0.1 μm, the effect of improving the cycle characteristics of the non-aqueous secondary battery 10 according to the present embodiment is difficult to obtain, which is not preferable. Further, when the thickness of the coating layer exceeds 1 μm, the discharge capacity of the non-aqueous secondary battery 10 decreases and the surface resistance of the positive electrode active material increases, which is not preferable. For the thickness of the coating layer, for example, an image obtained by observing a cross section of an active material particle obtained by a CP (Cross-section Electron Microsher) method using SEM or TEM (Transmission Electron Microscope) is analyzed. It can be measured by.

On the other hand, when the coating layer is formed by a dry process, the coating layer can be formed by using a solid electrolyte having higher lithium ion conductivity. Specifically, the solid electrolyte is pulverized into fine powder, and then the pulverized fine powder is bonded to the surface of the active material particles by a dry process to form a coating layer.

Examples of the oxide-based solid electrolyte having high lithium ion conductivity include Li ₇ La ₃ Zr ₂ O ₁₂ which is a garnet type solid electrolyte, and La _0.5 Li ₀ which is a perovskite type solid electrolyte. _.3 TiO ₃ can be exemplified. Oxide-based solid electrolytes are stable in the atmosphere and exhibit very high lithium ion conductivity at room temperature. Therefore, by forming the coating layer with the oxide-based solid electrolyte, the ionic conductivity of the coating layer can be further improved. According to this, the non-aqueous secondary battery 10 can further improve the battery characteristics.

Further, the average particle size of the fine powder of the solid electrolyte bonded to the surface of the active material particles in the dry process may be 0.1 μm or more and 1 μm or less. When the average particle size of the fine powder of the solid electrolyte is less than 0.1 μm, the effect of improving the cycle characteristics of the non-aqueous secondary battery 10 according to the present embodiment is difficult to obtain, which is not preferable. Further, when the average particle size of the fine powder of the solid electrolyte is more than 1 μm, the discharge capacity of the non-aqueous secondary battery 10 decreases and the surface resistance of the positive electrode active material increases, which is not preferable. The average particle size of the fine powder of the solid electrolyte can be measured by image analysis of the image of the positive electrode active material observed by SEM. The average particle size of the fine powder of the solid electrolyte is, for example, the arithmetic mean value of the diameter of the fine powder of the solid electrolyte when it is assumed to be a sphere.

The resin coating layer is formed on the coating layer and further coats the active material particles from above the coating layer. Specifically, the resin coating layer may be formed of polyacrylonitrile. By further protecting the surface of the active material particles, the resin coating layer can further stabilize the crystal structure of the active material particles and further improve the cycle characteristics of the non-aqueous secondary battery 10.

In addition, in this embodiment, polyacrylonitrile represents a polymer polymerized with acrylonitrile as a main monomer (monomer). Specifically, the polyacrylonitrile represents a polymer polymerized using 90% or more of acrylonitrile as a monomer.

The mass average molecular weight of polyacrylonitrile is preferably 200,000 or more and 800,000 or less. Further, it is more preferably 500,000 or more and 800,000 or less. When the mass average molecular weight of polyacrylonitrile is less than 200,000, the effect of improving the cycle characteristics of the non-aqueous secondary battery 10 is difficult to obtain, which is not preferable. When the mass average molecular weight of polyacrylonitrile is more than 800,000, the handling of polyacrylonitrile becomes complicated and the manufacturing cost of the non-aqueous secondary battery 10 increases, which is not preferable.

In the non-aqueous secondary battery 10 according to the present embodiment, the crystal structure of the lithium composite oxide contained in the positive electrode active material can be stabilized by the coating layer described above. Therefore, the non-aqueous secondary battery 10 according to the present embodiment can improve the cycle characteristics.

The positive electrode active material layer 22 can be formed, for example, by forming a positive electrode slurry, applying the positive electrode slurry onto the current collector 21, and then drying and rolling the positive electrode slurry. The positive electrode slurry is formed by dispersing the above-mentioned positive electrode active material, conductive auxiliary agent, and binder resin in a suitable organic solvent (for example, N-methyl-2-pyrrolidone). be able to. The density of the positive electrode active material layer 22 after rolling is not particularly limited, and may be any density as long as it is used in the positive electrode active material layer of a general non-aqueous secondary battery.

The negative electrode 30 includes a current collector 31 and a negative electrode active material layer 32. The current collector 31 may be any conductor as long as it is a conductor, and may be, for example, copper, a copper alloy, aluminum, stainless steel, nickel-plated steel, or the like.

The negative electrode active material layer 32 contains at least the negative electrode active material, and may further contain a conductive auxiliary agent and a binder resin. The ratio of the contents of the negative electrode active material, the conductive auxiliary agent, and the binder is not particularly limited, and the ratio of the contents used in a general non-aqueous secondary battery can be used.

As the negative electrode active material, for example, a graphite active material, a silicon (Si) or tin (Sn) -based active material, a titanium oxide (TiO _x ) -based active material, or the like can be used. Also, a mixture of these can be used. Specifically, the graphite-based active material is artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, or the like. The silicon (Si) or tin (Sn) -based active material is silicon (Si) or tin (Sn) fine particles, silicon (Si) or tin (Sn) oxide fine particles, or an alloy of silicon or tin. .. The titanium oxide (TiO _x ) -based active material is Li ₄ Ti ₅ O ₁₂ or the like. Further, as the negative electrode active material, for example, metallic lithium (Li) or the like can be used in addition to these.

The conductive auxiliary agent enhances the conductivity of the negative electrode. For example, as the conductive auxiliary agent, the same conductive auxiliary agent used in the positive electrode active material layer 22 can be used.

The binder resin binds the negative electrode active material and the conductive auxiliary agent onto the current collector 21. For example, as the binder resin, styrene-butadiene rubber (Stylene-Butagene Rubber: SBR) or the like can be used.

The negative electrode active material layer 32 can be formed, for example, by forming a negative electrode slurry, applying the negative electrode slurry onto the current collector 31, and then drying and rolling the negative electrode slurry. The negative electrode slurry can be formed by dispersing the above-mentioned negative electrode active material, the conductive auxiliary agent, and the binder resin in an appropriate solvent (for example, water). The density of the negative electrode active material layer 32 after rolling is not particularly limited, and may be any density as long as it is used in the negative electrode active material layer of a general non-aqueous secondary battery.

The separator layer 40 contains a separator and an electrolytic solution.

The separator is not particularly limited as long as it is used as a separator for a non-aqueous secondary battery, and any separator can be used. As the separator, for example, it is preferable to use a porous membrane or a non-woven fabric showing excellent high rate discharge performance alone or in combination.

Further, at least one surface of the separator may be coated with ceramic. Specifically, at least one surface of the separator may be coated with polyvinylidene fluoride or the like containing an inorganic substance such as Mg (OH) ₂ or Al ₂ O ₃ . Further, the separator may contain an inorganic substance such as Mg (OH) ₂ or Al ₂ O ₃ as a filler. That is, it is preferable that the separator contains an inorganic compound of Mg or Al inside or on the surface. In such a case, the separator can improve the strength and heat resistance, so that the reliability of the non-aqueous secondary battery can be improved. The ceramic coating may be formed on both sides of the separator, or may be formed on only one side of the separator.

Examples of the material constituting the separator include a polyolefin resin typified by polyethylene or polypropylene, a polymer terephthalate represented by a polymer terephthalate, a polybutylene terephthalate represented by a polybutylene terephthalate, and the like. Polyester-based resin, polyvinylidene difluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether (vinylidene-perfluorovinyl ether). Vinylidene-tetrafluoroethylene (vinylidene difluoride-tetrafluoroethylene) copolymer, vinylidene fluoride-trifluoroethylene (vinylidene difluoride-trifluoroethylene) copolymer, vinylidene fluoride-fluoroethylene (vinylidene fluoride) Vinylidene-hexafluoroacetone polymer, vinylidene fluoride-ethylene polymer, vinylidene fluoride copolymer, vinylidene fluoride copolymer, vinylidene fluoride Trifluoropropylene (vinylidene difluoride-trifluoropropylene) copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene (vinylidene difluoride-tellafluoroethylene-hexafluoropeline) copolymer -Tetrafluoroet hylene) Copolymers and the like can be used. The porosity of the separator is not particularly limited, and the porosity used in a general non-aqueous secondary battery separator can be used.

The electrolytic solution contains an electrolyte salt and a non-aqueous electrolyte.

The electrolyte salt enhances the electrical conductivity of the electrolyte. Specifically, the electrolyte salt may be a salt having an alkali metal ion, an alkaline earth metal ion, or an aluminum ion as a cation. For example, the electrolyte salts include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN and the like. It may be salt of. These electrolyte salts may be used alone or in combination of two or more. The concentration of the electrolyte salt may be any concentration as long as it is used in a general non-aqueous secondary battery, and may be, for example, 0.5 mol / L to 2.0 mol / L.

The electrolyte salts are, for example, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC. (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClo ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-malate, (C ₂ H) ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phaltate, lithium styl sulfate, lithium octyl sulfate, lithium benzene sulfonate, dodecylbenzene sulphonate, etc. It may be an organic ion salt.

Examples of the non-aqueous electrolyte include propylene carbonate (propylene carbonate), ethylene carbonate (ethylene carbononate), butylene carbonate (butyrene carbononate), chloroethylene carbonate (chloroethylene carbononate), vinylene carbonate (vinylene carbonate), and the like. ), Cyclic esters such as γ-butyrolactone or γ-valerolactone, dimethyl carbonate, diethyl carbonate or ethercarbonate chains, etc. Carbonates, chain esters such as methyl formate, methyl acetate or methyl butyrate, tetrahydrofuran (tetrahydrofuran) or derivatives thereof, 1,3-dioxane. ), 1,4-dioxane (1,4-dioxane), 1,2-dimethoxyethane (1,2-dimethoxyethane), 1,4-dibutoxyethane (1,4-dibutoxyethane) or methyldiglyclyme. Ethers such as ester, nitriles such as acetonitrile or benzonitrile, dioxolane or derivatives thereof, ethylene sulfide, sulfolane, sultone. Alternatively, these derivatives can be used alone or in admixture of two or more.

The non-aqueous electrolyte preferably contains a fluorine compound such as fluoroethylene carbonate, fluoroether, and fluorocarbonate. When the non-aqueous electrolyte contains a fluorine compound, the acid resistance of the non-aqueous electrolyte is improved, so that the stability of the non-aqueous secondary battery 10 under high temperature or high charging voltage is improved.

In the present embodiment, it is particularly preferable to contain a salt having an alkali metal ion, an alkaline earth metal ion, or an aluminum ion as a cation as the electrolyte salt. Further, in the present embodiment, it is preferable to contain fluoroethylene carbonate, fluoroether and fluorocarbonate as the non-aqueous electrolyte. In such a case, the non-aqueous secondary battery according to the present embodiment can further improve the stability under high temperature or high charging voltage.

Further, the electrolytic solution may contain various additives such as a negative electrode SEI (Solid Electrolyte Interface) forming agent or a surfactant.

Examples of various additives include succinic anhydride, lithium bis oxalate borone, lithium tetrafluoroborate, propane sultone, and propane sultone. Examples thereof include butane sultone, propene sultone, 3-sulfolene, fluorinated allylether, and fluorinated methyllate. As the content of these various additives, it is possible to use the content of the additive in a general non-aqueous secondary battery.

<2. Manufacturing method of non-water secondary battery ＞
(Manufacturing method of positive electrode active material)
First, a method for producing a positive electrode active material according to the present embodiment will be described. The positive electrode active material according to the present embodiment can be produced by producing active material particles by a coprecipitation method or the like, and then forming a coating layer on the surface of the active material particles by a wet or dry process.

For example, active material particles can be produced by the coprecipitation method. Specifically, a compound containing nickel sulfate hexahydrate (NiSO _{4.6H 2} O), cobalt sulfate pentahydrate ₍ CoSO 4.5H ₂ O), and the metal element M is dissolved in ion-exchanged water. , Form a mixed aqueous solution. Here, the total mass of the compound containing nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and the metal element M may be, for example, about 20% by mass with respect to the total mass of the mixed aqueous solution. Further, the compound containing nickel sulfate hexahydrate, cobalt sulfate pentahydrate, and the metal element M is mixed so that the molar ratio of Ni, Co, and M becomes the composition of the desired active material particles.

As described above, the metal element M includes aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), gallium (Mg), titanium (Ti), and zirconium (Zr). ), Niob (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), and cerium ( One or more metal elements selected from the group consisting of Ce). Further, the compound containing the metal element M may be, for example, a sulfate, a nitrate, an oxide, a nitride and a hydroxide of the metal element M.

Next, a predetermined amount (for example, 500 ml) of ion-exchanged water is charged into the reaction vessel, and the dissolved oxygen in the ion-exchanged water is removed by bubbling an inert gas (gas) such as nitrogen.

Subsequently, while maintaining the temperature of the ion-exchanged water in the reaction vessel at 50 ° C. and stirring the ion-exchanged water, the above-mentioned mixed aqueous solution is dropped onto the ion-exchanged water. Further, while maintaining the pH at 11.5 and the temperature at 50 ° C., a saturated aqueous solution of NaCO ₃ is added dropwise to the ion-exchanged water. The saturated aqueous solution of NaCO ₃ is added dropwise so as to be excessive with respect to Ni, Co and the metal element M of the mixed aqueous solution.

The dropping speed of the mixed aqueous solution and the saturated aqueous solution of NaCO ₃ is not particularly limited, but if it is too fast, a uniform precursor (co-precipitated oxide salt) may not be obtained. Therefore, the dropping speed may be, for example, about 3 ml / min. Further, the mixed aqueous solution and the saturated aqueous solution of NaCO ₃ may be added dropwise in about 10 hours, for example. As a result, the hydroxide salt of each metal element is co-precipitated.

Next, by performing solid-liquid separation (for example, suction filtration), the co-precipitated hydroxide salt is taken out from the aqueous solution in the reaction vessel, and the taken-out hydroxide salt is washed with ion-exchanged water. Further, the hydroxide salt is vacuum dried at a predetermined temperature (for example, about 100 ° C.) for a predetermined time (for example, about 10 hours).

Next, the dried hydroxide salt is pulverized in a mortar for several minutes to obtain a dry powder. Then, the dry powder and lithium hydroxide (LiOH) are mixed to produce a mixed powder. The molar ratio of Li and Ni + Co + M is determined according to the composition of the active material particles.

Subsequently, the produced mixed powder is fired in an oxygen atmosphere to produce active material particles. The firing time and firing temperature can be arbitrarily adjusted, but for example, the firing temperature may be about 700 ° C. to 800 ° C., and the firing time may be, for example, about 10 hours.

Next, a method of forming a coating layer on the surface of the active material particles will be described.

When using a wet process, first, isopropanol is charged into the reaction vessel as a dispersion medium. Then, lithium alkoxide and lanthanum alkoxide, which are constituent elements of the coating layer, and alkoxide of one or more elements E selected from the group consisting of Al, Zr, Nb, Sc, Ti, Ta and Y are added to the reaction vessel. To form a mixed solution. In addition, these alkoxides are added so that the molar ratio of each element of Li, La and element E becomes a desired coating layer composition.

Subsequently, the active material particles prepared above are charged into the reaction vessel, and then the mixture is stirred. Then, spray dry or an evaporator is used to remove the dispersion medium isopropanol. Further, by firing the active material particles in an oxygen atmosphere, a positive electrode active material on which a coating layer is formed can be produced.

The firing temperature is preferably about 500 ° C. to 600 ° C., and the firing time is preferably about 6 hours, for example. When the firing temperature is less than 500 ° C., the removal of the dispersion medium and the composite of the coating layer and the active material particles are insufficient, which deteriorates the battery characteristics of the non-aqueous secondary battery 10, which is not preferable. Further, when the firing temperature is more than 600 ° C., the cycle characteristics of the non-aqueous secondary battery 10 are deteriorated due to the deterioration of the active material particles, which is not preferable.

On the other hand, when the dry process is used, first, Li ₇ La ₄ Zr ₃ O ₁₂ or La _0.5 Li _0.3 TiO ₃ which is a solid electrolyte constituting the coating layer is pulverized to form fine powder. As a method for pulverizing the solid electrolyte, for example, a jet mill (jet mill), a ball mill (ball mill), a beads mill (beads mill), an emulsified dispersion, or the like can be used. However, in order to form the coating layer entirely by a dry process, it is preferable to use a jet mill for pulverizing the solid electrolyte.

The pulverized solid electrolyte fine powder is bonded to the surface of the active material particles by using a dry coating device such as Nobilta (manufactured by Hosokawa Micron Co., Ltd.) to form a coating layer. The coating condition of the solid electrolyte by the dry coating device may be, for example, 2000 rpm for 5 minutes. Then, the positive electrode active material can be produced by firing the active material particles on which the coating layer is formed in an oxygen atmosphere.

The firing temperature is preferably about 500 ° C. to 600 ° C., and the firing time is preferably about 6 hours, for example. When the firing temperature is less than 500 ° C., the composite of the coating layer and the active material particles is insufficient, and the battery characteristics of the non-aqueous secondary battery 10 are deteriorated, which is not preferable. Further, when the firing temperature is more than 600 ° C., the cycle characteristics of the non-aqueous secondary battery 10 are deteriorated due to the deterioration of the active material particles, which is not preferable.

By the above method, the positive electrode active material on which the coating layer is formed can be produced.

(Manufacturing method of non-water secondary battery)
Subsequently, a method for manufacturing the non-aqueous secondary battery 10 will be described. However, the method for manufacturing the non-aqueous secondary battery 10 is not limited to the following method, and a known manufacturing method can also be used.

First, the positive electrode 20 is manufactured as follows. First, a positive electrode slurry is formed by dispersing a mixture of the positive electrode active material, the conductive auxiliary agent, and the binder resin prepared above in a desired ratio in an organic solvent. Next, the positive electrode slurry is applied onto the current collector 21 and dried to form the positive electrode active material layer 22. The coating method is not particularly limited, but for example, a knife coater method, a gravure coater method, or the like can be used.

Further, the positive electrode active material layer 22 is compressed to a desired density or thickness by a roll press machine. Thereby, the positive electrode 20 can be manufactured. Here, the density or thickness of the positive electrode active material layer 22 is not particularly limited, and may be any as long as it is the density or thickness of the positive electrode active material layer of a general non-aqueous secondary battery.

The negative electrode 30 is also manufactured by the same method as that of the positive electrode 20. First, a negative electrode slurry is formed by dispersing a mixture of a negative electrode active material, a conductive auxiliary agent, and a binder resin in a desired ratio in a solvent (for example, water). Next, the negative electrode slurry is applied onto the current collector 31 and dried to form the negative electrode active material layer 32. The coating method is not particularly limited, but for example, a knife coater method, a gravure coater method, or the like can be used.

Further, the negative electrode active material layer 32 is compressed to a desired density or thickness by a roll press machine. As a result, the negative electrode 30 can be manufactured. Here, the density or thickness of the negative electrode active material layer 32 is not particularly limited, and may be any as long as it is the density or thickness of the negative electrode active material layer of a general non-aqueous secondary battery. When metallic lithium is used as the negative electrode active material layer 32, the negative electrode 30 can be manufactured by bonding the metallic lithium foil to the current collector 31.

Subsequently, the electrode structure is manufactured by sandwiching the separator between the positive electrode 20 and the negative electrode 30. The prepared electrode structure is processed into a shape suitable for a desired shape (for example, cylindrical type, square type, laminated type, button type, etc.), and then inserted into a container of the desired shape. Further, by injecting an electrolytic solution containing the above-mentioned electrolyte salt and non-aqueous electrolyte into the container, the separator is impregnated with the electrolytic solution. After that, the electrode structure and the container in which the electrolytic solution is injected are sealed. As a result, the non-aqueous secondary battery 10 can be manufactured.

Hereinafter, the positive electrode active material, the method for producing the positive electrode active material, and the non-aqueous secondary battery according to the present embodiment will be specifically described with reference to Examples and Comparative Examples. The examples shown below are merely examples, and the positive electrode active material, the method for producing the positive electrode active material, and the non-aqueous secondary battery according to the present embodiment are not limited to the following examples.

<Test Example 1>
(Manufacturing of positive electrode active material)
First, nickel sulfate hexahydrate ₍ NiSO _{4.6H 2} O), cobalt sulfate pentahydrate (CoSO 4.5H ₂ O), aluminum nitrate (Al (NO ₃ ) ₃ ), and magnesium sulfate heptahydrate. (Hydrate _{4.7H 2 O} ) was dissolved in ion-exchanged water to prepare a mixed aqueous solution. Here, the total mass of nickel sulfate hexahydrate, cobalt sulfate pentahydrate, aluminum nitrate, and magnesium sulfate heptahydrate was set to about 20% by mass with respect to the total mass of the mixed aqueous solution. The molar ratio of each element, Ni: Co: Al: Mg, was 88: 10: 1: 1.

In addition, 500 ml of ion-exchanged water was charged into the reaction vessel. Dissolved oxygen in the ion-exchanged water was removed by bubbling the ion-exchanged water with an inert gas such as nitrogen while maintaining the temperature of the ion-exchanged water at 50 ° C.

Next, the above mixed aqueous solution was added dropwise to the ion-exchanged water while stirring the ion-exchanged water while maintaining the temperature in the reaction vessel at 50 ° C. Further, an excess amount of saturated NaCO ₃ aqueous solution with respect to Ni, Co, Al and Mg in the mixed aqueous solution was added dropwise to the ion-exchanged water. During the dropping, the pH of the aqueous solution in the reaction vessel was maintained at 11.5, and the temperature was maintained at 50 ° C. The dropping rate of the mixed aqueous solution and the saturated aqueous solution of NaCO ₃ was about 3 ml / min. The mixed aqueous solution and the saturated aqueous solution of NaCO ₃ were added dropwise over 10 hours. As a result, the hydroxide salt of each metal element was co-precipitated.

Subsequently, the co-precipitated hydroxide salt was taken out from the aqueous solution in the reaction vessel by suction filtration, and the taken-out hydroxide salt was washed with ion-exchanged water. Further, the hydroxide salt was vacuum dried at a drying temperature of 100 ° C. for about 10 hours.

Next, the dried hydroxide salt was pulverized in a mortar to obtain a dry powder. Then, the dry powder and lithium hydroxide (LiOH) were mixed to form a mixed powder. The molar ratio Li: Me of Li and Ni, Co, Al and Mg (= Me) was 1.0: 1.0. Further, the mixed powder was calcined in an oxygen atmosphere and at a calcining temperature of 700 ° C. to 800 ° C. for 10 hours.

As a result, active material particles were produced. The composition of the active material particles was LiNi _0.88 Co _0.1 Al _0.01 Mg _0.01 O ₂ . In addition, the average length of the major axis of the primary particles of the active material particles and the average particle diameter of the secondary particles were measured using the SEM image.

Subsequently, a wet or dry process was used to form a coating layer on the prepared active material particles.

When the wet process is used, specifically, isopropanol is charged as a dispersion medium into the reaction vessel, and then the constituent material of the coating layer is added to the reaction vessel. When the composition of the coating layer is Li ₇ La ₃ Zr ₂ O ₁₂ , lithium methoxide (Lithium methoxide), lanthanum isopropoxide, and 70 mass% zirconium propoxide (zirconium propoxide) 7: 4 It was added to the reaction vessel at a molar ratio of 3. Further, when the composition of the coating layer is La _0.5 Li _0.3 TiO ₃ , lanthanopropoxide, lithium methoxydo, and tetraisopropyl orthotitantate are added in an amount of 0.5: 0.3: 1. Was added to the reaction vessel at the molar ratio of.

Next, the active material particles prepared above were added to the reaction vessel to which the constituent materials of the coating layer were added, and then the mixed solution was stirred. Subsequently, isopropanol was removed from the active material particles using spray drying or an evaporator. Then, the active material particles were fired for 6 hours in an oxygen atmosphere and at a firing temperature of 500 ° C. to 600 ° C. to prepare a positive electrode active material on which a coating layer was formed. The composition of the coating layer in the wet process indicates the ratio of the amount of each element charged, and the coating layer may not have the composition described above strictly.

On the other hand, when using a dry process, first, a commercially available solid electrolyte, Li ₇ La ₃ Zr ₂ O ₁₂ or La _0.5 Li _0.3 TiO ₃ , is pulverized with a jet mill until the average particle size becomes 1 μm or less. bottom. Next, using Novirta (manufactured by Hosokawa Micron Co., Ltd.), the pulverized solid electrolyte was bonded to the active material particles prepared above at 2000 rpm to 3000 rpm for 5 minutes to prepare a coating layer. Then, the active material particles were fired for 6 hours in an oxygen atmosphere and at a firing temperature of 500 ° C. to 600 ° C. to prepare a positive electrode active material on which a coating layer was formed.

(Manufacturing of half cell)
Subsequently, a half cell non-aqueous secondary battery was produced by the following method. First, the positive electrode active material prepared above, acetylene black (manufactured by Denka), and polyvinylidene fluoride (PVdF), weighed at a mass ratio of 96: 2: 2, are dispersed in N-methyl-2-pyrrolidone to form a positive electrode. A slurry was formed. The positive electrode slurry was applied to a current collector of aluminum foil so that the coating amount after drying was 13 mg / cm ² , and dried to form a positive electrode active material layer. Then, a positive electrode was produced by rolling so that the density of the positive electrode active material layer was 3.0 g / cm ³ .

The negative electrode was manufactured by placing a metallic lithium foil on a copper foil which is a current collector. Then, a separator (thickness 12 μm) was prepared in which both sides were coated with a coating liquid in which aluminum oxide (Al ₂ O ₃ ) and polyvinylidene fluoride (PVdF) were mixed at a mass ratio of 70:30. An electrode structure was produced by arranging the separator between the positive electrode and the negative electrode.

Further, lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a non-aqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a volume ratio of 3: 7 at a concentration of 1.3 M to dissolve an electrolytic solution. Was produced. Next, the electrode structure was processed and stored in a coin half cell container, and then an electrolytic solution was injected to seal the container. As a result, a non-aqueous secondary battery was produced.

Further, for the test of the capacity retention rate at 45 ° C., an electrolytic solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a non-aqueous solvent at a concentration of 1.4 M. As the non-aqueous solvent, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), fluoroether (FE), and fluorocarbonate (FC) were mixed in a volume ratio of 15:45:20:20. Next, the electrode structure was processed and stored in a coin half cell container, and then an electrolytic solution was injected to seal the container. As a result, a non-aqueous secondary battery for testing with a capacity retention rate of 45 ° C. was produced.

(Charge / discharge evaluation)
The non-aqueous secondary battery was charged and discharged at the charge / discharge rate (rate) shown in Table 1 below. The cut-off voltage was set to 3.0 V to 4.4 V. Further, CC-CV means a constant current constant voltage, and CC means a constant current. Charging and discharging to the non-aqueous secondary battery was performed at 25 ° C. However, only in the test of the capacity retention rate at 45 ° C., charging / discharging up to 2 cycles was performed at 25 ° C., and charging / discharging after 3 cycles was performed at 45 ° C.

Here, the charge capacity of the first cycle is defined as the initial charge capacity, and the value obtained by dividing the discharge capacity of the first cycle by the charge capacity of the first cycle is defined as the initial efficiency. Further, the discharge capacity of the second cycle was defined as the initial capacity, and the value obtained by dividing the discharge capacity of the 53rd cycle by the discharge capacity of the second cycle was defined as the capacity retention rate (that is, cycle characteristics). The results of these evaluations are summarized in Table 2.

In Table 2, the "average particle size" represents the average particle size of the secondary particles of the active material particles. Further, the embodiment in which the "dry process rotation speed" is described indicates that the coating layer was formed by the dry process. Examples in which "dry process rotation speed" is not described indicate that the coating layer was formed by a wet process. Further, the ratio of "coating amount" is calculated as a ratio to the total mass of the positive electrode active material, and "-" in the column of "coating layer" indicates that the process is not carried out.

Referring to the results in Table 2, in Examples 1 to 13, since the active material particles are coated with the coating layer, the initial charge capacity and the initial capacity which are almost the same as those of Comparative Examples 1, 2 and 13 are maintained. .. In addition, it can be seen that Examples 1 to 13 have a 25 ° C. capacity retention rate and a 45 ° C. capacity retention rate higher than those of Comparative Examples 1, 2 and 13. Further, in Examples 1 to 13, since the process of forming the coating layer is included in the range of the present embodiment, the initial charge capacity and the initial capacity substantially equivalent to those of Comparative Examples 3 to 12 are maintained. In addition, it can be seen that Examples 1 to 13 have a 25 ° C. capacity retention rate and a 45 ° C. capacity retention rate higher than those of Comparative Examples 3 to 12.

When a cycle test was conducted to evaluate the capacity retention rate at 45 ° C. using the half-cell non-aqueous secondary batteries for the 25 ° C. test of Comparative Examples 1 and 2, the capacity retention rate may drop sharply. have understood. Therefore, it can be seen that the cycle characteristics are improved particularly at high temperatures by containing the fluorine compounds of fluoroethylene carbonate, fluoroether (FE), and fluorocarbonate (FC) in the electrolytic solution.

<Test Example 2>
(Manufacturing of full cell)
Next, a full cell non-aqueous secondary battery was produced by the following method. First, the positive electrode active material prepared in Test Example 1, acetylene black (manufactured by Denka), and polyvinylidene fluoride (PVdF) weighed at a mass ratio of 96: 2: 2 were weighed and dispersed in N-methyl-2-pyrrolidone. To form a positive electrode slurry. The positive electrode slurry was applied to a current collector of aluminum foil so that the coating amount after drying was 13 mg / cm ² , and dried to form a positive electrode active material layer. Then, a positive electrode was produced by rolling so that the density of the positive electrode active material layer was 3.0 g / cm ³ .

Graphite was used for the negative electrode. Then, a separator (thickness 12 μm) was prepared in which both sides were coated with a coating liquid in which magnesium hydroxide (Mg (OH) ₂ ) and polyvinylidene fluoride (PVdF) were mixed at a mass ratio of 70:30. An electrode structure was produced by arranging the separator between the positive electrode and the negative electrode.

Further, an electrolytic solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a non-aqueous solvent at a concentration of 1.3 M. As the non-aqueous solvent, ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3: 7. Next, the electrode structure was processed and stored in a coin full cell container, and then an electrolytic solution was injected to seal the container. As a result, a non-aqueous secondary battery was produced.

(Charge / discharge evaluation)
The non-aqueous secondary battery was charged and discharged at the charge / discharge rate (rate) shown in Table 3 below. The cutoff voltage was 2.85V to 4.35V. Further, CC-CV means a constant current constant voltage, and CC means a constant current. Charging and discharging to the non-aqueous secondary battery was performed at 25 ° C. However, only in the test of the capacity retention rate at 45 ° C., charging / discharging up to 2 cycles was performed at 25 ° C., and charging / discharging after 3 cycles was performed at 45 ° C.

Here, the charge capacity of the first cycle is defined as the initial charge capacity, and the value obtained by dividing the discharge capacity of the first cycle by the charge capacity of the first cycle is defined as the initial efficiency. Further, the discharge capacity of the third cycle was defined as the initial capacity, and the value obtained by dividing the discharge capacity of the 101st cycle by the discharge capacity of the third cycle was defined as the capacity retention rate (that is, the cycle characteristic). The results of these evaluations are summarized in Table 4.

In Table 4, the "average particle size" represents the average particle size of the secondary particles of the active material particles. Further, the embodiment in which the "dry process rotation speed" is described indicates that the coating layer was formed by the dry process. Examples in which "dry process rotation speed" is not described indicate that the coating layer was formed by a wet process. Further, the ratio of "coating amount" is calculated as a ratio to the total mass of the positive electrode active material, and "-" in the column of "coating layer" indicates that the process is not carried out.

Referring to the results in Table 4, even in the case of a full-cell non-aqueous secondary battery, in Examples 14 to 17, since the active material particles are coated with the coating layer, the initial charge is almost the same as that of Comparative Examples 14 and 15. Maintains capacity and initial capacity. In addition, it can be seen that Examples 14 to 17 have a 25 ° C. capacity retention rate and a 45 ° C. capacity retention rate higher than those of Comparative Examples 14 and 15.

<Test Example 3>
(Manufacturing of full cell)
Subsequently, a full cell non-aqueous secondary battery was produced by the following method. First, polyvinylidene fluoride (PVdF) was dispersed in N-methyl-2-pyrrolidone (NMP). On the other hand, polyacrylonitrile having a mass average molecular weight of 500,000 obtained by polymerizing acrylonitrile and acrylic acid at a molar ratio of 97.5: 2.5 was dispersed in N-methyl-2-pyrrolidone (NMP). Then, NMP in which polyvinylidene fluoride (PVdF) was dispersed and NMP in which polyacrylonitrile was dispersed were mixed. Further, acetylene black and the positive electrode active material prepared in Test Example 1 were sequentially mixed with the mixture, and the mixture was kneaded. The mixing ratio of the final positive electrode active material, acetylene black, polyvinylidene fluoride, and polyacrylonitrile was 96: 2: 2: 1 by mass ratio. Then, NMP was added to the above mixture to adjust the viscosity to form a positive electrode slurry.

The positive electrode slurry was applied to a current collector of aluminum foil so that the coating amount after drying was 20 mg / cm ² , and dried to form a positive electrode active material layer. Then, a positive electrode was produced by rolling so that the density of the positive electrode active material layer was 3.6 g / cm ³ .

Graphite was used for the negative electrode. Then, a separator (thickness 12 μm) was prepared in which both sides were coated with a coating liquid in which magnesium hydroxide (Mg (OH) ₂ ) and polyvinylidene fluoride (PVdF) were mixed at a mass ratio of 70:30. An electrode structure was produced by arranging the separator between the positive electrode and the negative electrode.

Further, an electrolytic solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a non-aqueous solvent at a concentration of 1.3 M. As the non-aqueous solvent, ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3: 7. Next, the electrode structure was processed and stored in a coin full cell container, and then an electrolytic solution was injected to seal the container. As a result, a non-aqueous secondary battery was produced.

(Charge / discharge evaluation)
The non-aqueous secondary battery was charged and discharged at the charge / discharge rate (rate) shown in Table 5 below. The cutoff voltage was 2.85 to 4.35V. Further, CC-CV means a constant current constant voltage, and CC means a constant current. Charging and discharging to the non-aqueous secondary battery was performed at 25 ° C. However, only in the test of the capacity retention rate at 45 ° C., charging / discharging up to 2 cycles was performed at 25 ° C., and charging / discharging after 3 cycles was performed at 45 ° C.

Here, the charge capacity of the first cycle is defined as the initial charge capacity, and the value obtained by dividing the discharge capacity of the first cycle by the charge capacity of the first cycle is defined as the initial efficiency. Further, the discharge capacity of the third cycle was defined as the initial capacity, and the value obtained by dividing the discharge capacity of the 101st cycle by the discharge capacity of the third cycle was defined as the capacity retention rate (that is, the cycle characteristic). The results of these evaluations are summarized in Table 6.

In Table 6, the "average particle size" represents the average particle size of the secondary particles of the active material particles. Further, "PAN" represents the above-mentioned polyacrylonitrile having a mass average molecular weight of 500,000. Further, the ratio of "coating amount" is calculated as a ratio to the total mass of the positive electrode active material, and "-" in the columns of "coating layer" and "resin coating layer" indicates that the process is not carried out.

Referring to the results in Table 6, in Examples 18 and 19, since the active material particles are coated with a resin coating layer containing polyacrylonitrile in addition to the coating layer, the initial charge capacity is almost the same as that of Comparative Example 14. And maintain the initial capacity. In addition, it can be seen that Examples 18 and 19 have a 25 ° C. capacity retention rate and a 45 ° C. capacity retention rate higher than those of Comparative Example 14. Further, in Examples 18 and 19, the active material particles are coated with a coating layer and a resin coating layer. Therefore, Examples 18 and 19 have a higher 5 ° C. capacity retention rate and a 45 ° C. capacity retention rate due to the synergistic effect of both, as compared with the case where they are coated with only one of the coating layer and the resin coating layer. I understand.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. .. It is naturally understood that these also belong to the technical scope of the present invention.

10 Non-aqueous secondary battery 20 Positive electrode 21 Current collector 22 Positive electrode active material layer 30 Negative electrode 31 Current collector 32 Negative electrode active material layer 40 Separator layer

Claims (12)

Active material particles containing a lithium composite oxide represented by the following chemical formula 1 and
A coating layer that covers the surface of the active material particles, and
It is a positive electrode active material equipped with
The coating layer contains an oxide, and the particles of the oxide contain a lithium lanthanum zirconium oxide.
The ratio of the coating layer is 0.3% by mass or more and less than 0.9% by mass with respect to the total mass of the positive electrode active material.
The active material particles and the coating layer are composites.
The coating layer has a thickness of 0.1 μm or more and 1 μm or less, or the coating layer is formed of particles of the oxide having an average particle size of 0.1 μm or more and 1 μm or less. , Positive electrode active material.
Li _a Ni _x Coy _{MzO 2} ... Chemical formula 1
In the above chemical formula 1, M is selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. It is one kind or two or more kinds of metal elements, 0.10 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0 <y ≦ 0.20, and 0 ≦ z ≦ 0. .10 and x + y + z = 1. Active material particles containing a lithium composite oxide represented by the following chemical formula 1 and
A coating layer that covers the surface of the active material particles, and
It is a positive electrode active material equipped with
The coating layer contains an oxide, and the particles of the oxide contain lithium titanate lanthanum.
The ratio of the coating layer is 0.3% by mass or more and 1.0% by mass or less with respect to the total mass of the positive electrode active material .
The active material particles and the coating layer are composites.
The coating layer has a thickness of 0.1 μm or more and 1 μm or less, or the coating layer is formed of particles of the oxide having an average particle size of 0.1 μm or more and 1 μm or less. , Positive electrode active material.
Li _a Ni _x Coy _{MzO 2} ... Chemical formula 1
In the above chemical formula 1, M is selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. It is one kind or two or more kinds of metal elements, 0.10 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0 <y ≦ 0.20, and 0 ≦ z ≦ 0. .10 and x + y + z = 1. The positive electrode active material according to claim 1, wherein the lithium lanthanum zirconium oxide is Li ₇ La ₃ Zr ₂ O ₁₂ , which is a garnet-type solid electrolyte. The positive electrode active material according to claim 2, wherein the lithium titanate lanthanum is La _0.5 Li _0.3 TiO ₃ , which is a perovskite-type solid electrolyte. The invention according to any one of claims 1 to 4 , which contains a polyacrylonitrile having a mass average molecular weight of 500,000 or more and 800,000 or less, and further comprises a resin coating layer for coating the active material particles from above the coating layer. The positive positive active material described. The active material particles are secondary particles in which a plurality of primary particles are bonded.
The item according to any one of claims 1 to 5 , wherein the average length of the major axis of the primary particles is 0.1 μm or more and 2 μm or less, and the average particle diameter of the secondary particles is 3 μm or more and 20 μm or less. Positive electrode active material. A positive electrode containing the positive electrode active material according to any one of claims 1 to 6 and a positive electrode.
An electrolytic solution containing an alkali metal ion, an alkaline earth metal ion or a salt having an aluminum ion as a cation, a fluoroethylene carbonate, a fluoroether and a fluorocarbonate,
Equipped with a non-water secondary battery. The non-aqueous secondary battery according to claim 7 , further comprising a ceramic coated separator. The non-aqueous secondary battery according to claim 8 , wherein the separator contains Mg or Al as an element. The step of forming active material particles containing a lithium composite oxide represented by the following chemical formula 1 and
The step of forming a coating layer on the surface of the active material particles,
A step of firing the active material particles at a firing temperature of 500 to 600 ° C. after coating the surface of the active material particles with the oxide.
It is a manufacturing method of a positive electrode active material including
The coating layer contains an oxide, and the particles of the oxide contain a lithium lanthanum zirconium oxide.
A method for producing a positive electrode active material, wherein the coating layer covers the surface of the active material particles in an amount of 0.3% by mass or more and less than 0.9% by mass with respect to the total mass of the positive electrode active material by a wet or dry process. ..
Li _a Ni _{x Coy} M _z O ₂ ... Chemical formula 1
In the above chemical formula 1, M is selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. One or more kinds of metal elements, 0.10 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0 <y ≦ 0.20, and 0 ≦ z ≦ 0.10. And x + y + z = 1. The step of forming active material particles containing a lithium composite oxide represented by the following chemical formula 1 and
The step of forming a coating layer on the surface of the active material particles,
A step of firing the active material particles at a firing temperature of 500 to 600 ° C. after coating the surface of the active material particles with the oxide.
It is a manufacturing method of a positive electrode active material including
The coating layer contains an oxide, and the particles of the oxide contain lithium titanate lanthanum.
A method for producing a positive electrode active material, wherein the coating layer covers the surface of the active material particles in an amount of 0.3% by mass or more and 1.0% by mass or less with respect to the total mass of the positive electrode active material by a wet or dry process. ..
Li _a Ni _{x Coy} M _z O ₂ ... Chemical formula 1
In the above chemical formula 1, M is selected from the group consisting of Al, Mn, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. One or more kinds of metal elements, 0.10 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0 <y ≦ 0.20, and 0 ≦ z ≦ 0.10. And x + y + z = 1. The method for producing a positive electrode active material according to claim 10 or 11 , wherein the active material particles are formed by a coprecipitation method.

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