JP7262998B2 - Positive electrode active material, positive electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for producing positive electrode active material - Google Patents

Description

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

Lithium transition metal composite oxides containing nickel (Ni) as a main component are used in non-aqueous electrolyte secondary batteries as positive electrode active materials exhibiting relatively high potential and high capacity. When a nickel-based positive electrode using such a nickel-containing lithium-transition metal composite oxide as an active material and a counter electrode (negative electrode) containing graphite are employed, the non-aqueous electrolyte secondary battery, when used, has the following problems: 4. It is common to charge at 2V.

However, in recent years, there has been a demand for even higher capacities for non-aqueous electrolyte secondary batteries. Batteries are required. Specifically, when a counter electrode (negative electrode) containing graphite is employed, the charging voltage is set to 4.3 V to improve the amount of lithium ion desorption and insertion, and the nickel ratio is about 80%. can also achieve a high capacity of 200 mAh/g or more.

Further, in the development of non-aqueous electrolyte secondary batteries, improvement in output characteristics at low temperatures, improvement in discharge capacity, improvement in capacity characteristics at high charge/discharge rates, and improvement in cycle characteristics are also required. Patent Document 1 proposes a positive electrode active material in which a ferroelectric is sintered on the surface of a lithium-containing transition metal composite oxide for the purpose of improving output characteristics in a low temperature range.

JP 2011-210694 A

However, with the technique described in Patent Document 1, when a positive electrode active material with a high nickel ratio is used, improvement in cycle characteristics at a high charge/discharge rate could not be expected.

An object of the present invention is to provide a positive electrode active material having a high nickel ratio and excellent cycle characteristics at a high charge/discharge rate, a positive electrode for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery, and a positive electrode active material containing the same. It is to provide a manufacturing method.

In order to solve the above problems, according to one aspect of the present invention, positive electrode active material particles having a composition represented by the following formula (1) and BaTiO ₃ particles supported on the surface of the positive electrode active material particles and satisfying the relationship represented by the following formula (2) is provided.
_{LiaNixCoyMzO2 ( 1 ) _}
In the formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), from Niobium (Nb), Molybdenum (Mo), Tungsten (W), Copper (Cu), Zinc (Zn), Gallium (Ga), Indium (In), Tin (Sn), Lanthanum (La), Cerium (Ce) one or more metal elements selected from the group consisting of a, x, y and z, 0.20≤a≤1.20, 0.70≤x<1.00, 0<y≤0. 20, values within the range 0<z≦0.10 and x+y+z=1.
0.001A≤Y≤0.01A+1 (2)
In the formula (2), A is the average particle size (nm) of the BaTiO ₃ particles, and Y is the amount of the BaTiO ₃ particles supported on the positive electrode active material particles on a mol % basis.

According to this aspect, it is possible to improve the cycle characteristics of the non-aqueous electrolyte secondary battery at a high charge/discharge rate.

Here, the BaTiO ₃ particles may have an average particle diameter A of 10 nm or more and 100 nm or less.
This further improves the cycle characteristics of the non-aqueous electrolyte secondary battery at high charge/discharge rates.

According to another aspect of the present invention, there is provided a positive electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material described above.
According to this aspect, it is possible to improve the cycle characteristics of the non-aqueous electrolyte secondary battery at a high charge/discharge rate.

According to another aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery comprising the positive electrode for a non-aqueous electrolyte secondary battery described above.
According to this aspect, it is possible to improve the cycle characteristics of the non-aqueous electrolyte secondary battery at a high charge/discharge rate.

According to another aspect of the present invention, the BaTiO ₃ particles are coated on the surface of the positive electrode active material particles having the composition represented by the following formula (1), and then heat treated at a temperature of 700° C. or less to obtain the above-mentioned A method for manufacturing a positive electrode active material is provided, which includes a step of supporting the BaTiO ₃ particles on the positive electrode active material particles.
_{LiaNixCoyMzO2 ( 1 ) _}
In the formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), from Niobium (Nb), Molybdenum (Mo), Tungsten (W), Copper (Cu), Zinc (Zn), Gallium (Ga), Indium (In), Tin (Sn), Lanthanum (La), Cerium (Ce) one or more metal elements selected from the group consisting of a, x, y and z, 0.20≤a≤1.20, 0.70≤x<1.00, 0<y≤0. 20, values within the range 0<z≦0.10 and x+y+z=1.
According to this aspect, the cycle characteristics of the non-aqueous electrolyte secondary battery at a high charge/discharge rate are more reliably improved.

As described above, according to the present invention, it is possible to improve the cycle characteristics of a non-aqueous electrolyte secondary battery at a high charge/discharge rate.

1 is an explanatory diagram showing a schematic configuration of a non-aqueous electrolyte secondary battery according to an embodiment of the invention; FIG.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

<1. Study by the present inventors>
First, prior to describing the present invention, the inventors' studies up to the present invention will be described. For the purpose of improving the cycle characteristics of a positive electrode active material with a high nickel ratio at a high charge/discharge rate, the present inventors have proposed that the positive electrode active material particles support barium titanate (BaTiO ₃ ), which is a ferroelectric. remembered. More specifically, the inventors investigated the possibility that by supporting _BaTiO particles, which are ferroelectrics, on the surface of the positive electrode active material particles, the polarization of the positive electrode active material is promoted and the insertion and removal of lithium ions is facilitated. .

However, simply applying the method described in Patent Document 1 to positive electrode active material particles with a high nickel ratio did not improve the cycle characteristics of the positive electrode active material at high charge/discharge rates. Therefore, as a result of intensive studies, the present inventors found that the particle size and coating amount of the BaTiO ₃ particles supported on the surface of the positive electrode active material particles affect the cycle characteristics at high charge/discharge rates. rice field. Furthermore, the inventors have found the possibility that the particle size and the coating amount do not independently affect the performance of the positive electrode active material, but have a certain correlation and affect the performance of the positive electrode active material.

Therefore, the positive electrode active material according to the present invention includes positive electrode active material particles having a composition represented by the following formula (1),
BaTiO ₃ particles supported on the surface of the positive electrode active material particles,
A positive electrode active material that satisfies the relationship represented by the following formula (2).
_{LiaNixCoyMzO2 ( 1 ) _}
In 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), cerium (Ce) one or more metal elements selected from the group, and a, x, y and z are 0.20≤a≤1.20, 0.70≤x<1.00, 0<y≤0.20 , 0<z≦0.10 and x+y+z=1.
0.001A≤Y≤0.01A+1 (2)
In formula (2), A is the average particle size (nm) of BaTiO ₃ particles, and Y is the amount of BaTiO ₃ particles supported on the positive electrode active material particles on a mol % basis.

<2. Configuration of Nonaqueous Electrolyte Secondary Battery>
A specific configuration of the above-described non-aqueous electrolyte secondary battery 10 according to one embodiment of the present invention will be described below with reference to FIG. FIG. 1 is an explanatory diagram illustrating the configuration of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

As shown in FIG. 1, the nonaqueous electrolyte secondary battery 10 includes a positive electrode 20, a negative electrode 30, and a separator layer 40. As shown in FIG. The form of the non-aqueous electrolyte secondary battery 10 is not particularly limited. For example, the non-aqueous electrolyte secondary battery 10 may be cylindrical, prismatic, laminate, button, or the like.

The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22 . The positive electrode current collector 21 is made of, for example, aluminum.

Moreover, the positive electrode active material layer 22 contains at least a positive electrode active material. The positive electrode active material layer 22 may further contain other additives such as a conductive aid and/or a binder. Moreover, the positive electrode active material layer 22 may contain a solid electrolyte.

The positive electrode active material according to the present embodiment includes positive electrode active material particles and BaTiO ₃ particles supported on the surfaces of the positive electrode active material particles.
Moreover, in the present embodiment, the positive electrode active material particles have a composition represented by the following formula (1).
_{LiaNixCoyMzO2 ( 1 ) _}
In 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), 1 selected from the group consisting of cerium (Ce) is a metallic element of at least one species,
a, x, y and z are in the range of 0.20≦a≦1.20, 0.70≦x<1.00, 0<y≦0.20, 0<z≦0.10 and x+y+z=1 is a value within

Such positive electrode active material particles have a relatively high nickel content and a high capacity density. Therefore, such positive electrode active material particles greatly contribute to increasing the capacity of the non-aqueous electrolyte secondary battery 10 .

The average particle size of the positive electrode active material particles is not particularly limited, but is, for example, 5 μm or more and 20 μm or less, preferably 8 μm or more and 15 μm or less. Thereby, a suitable conductive path (conductive path) can be formed between the particles. Therefore, the resistance (for example, charge transfer resistance) of the positive electrode active material layer can be reduced, and high battery performance can be achieved.

The average particle size of the positive electrode active material particles can be determined by a laser diffraction/light scattering method (particle size distribution measurement manufactured by Microtrack). As used herein, the term "average particle size" refers to a particle size (D50 , also called median diameter). The particle size in the product may be image-analyzed by scanning electron microscope (SEM) measurement to determine the average particle size. Here, it almost agrees with the value of the average particle size obtained by the laser scattering method.

BaTiO ₃ particles are supported on the surfaces of the positive electrode active material particles under conditions that satisfy the relationship represented by the following formula (2).
0.001A≤Y≤0.01A+1 (2)
In formula (2), A is the average particle size (nm) of BaTiO ₃ particles, and Y is the amount of BaTiO ₃ particles supported on the positive electrode active material particles on a mol % basis.

This improves the cycle characteristics of the non-aqueous electrolyte secondary battery 10 at high charge/discharge rates. The reason why the cycle characteristics are improved at a high charge/discharge rate is not clear, but is presumed as follows. That is, the BaTiO ₃ particles have ferroelectricity and polarization occurs inside the substance. By supporting such BaTiO ₃ particles on the surface of the positive electrode active material particles, polarization in the positive electrode active material particles is promoted. This promotes the intercalation/deintercalation process of lithium ions on the surface of the positive electrode active material particles.

In addition, since the surfaces of the positive electrode active material particles are coated with the BaTiO ₃ particles, side reactions between the positive electrode active material particles and the electrolytic solution are suppressed, and decomposition of the electrolytic solution is suppressed. Furthermore, since the surfaces of the positive electrode active material particles are coated with the BaTiO ₃ particles, it is possible to prevent phase transition and inactivation of the unstable positive electrode active material from which lithium ions are detached.

On the other hand, BaTiO ₃ particles have no ionic conductivity. Therefore, if BaTiO ₃ particles excessively cover the surface of the positive electrode active material particles, desorption and insertion of lithium ions become difficult. Therefore, it is considered preferable that the BaTiO ₃ particles appropriately cover the surface of the positive electrode active material particles. Here, it is considered that the BaTiO ₃ particles cover the surfaces of the positive electrode active material particles depending on the particle size of the BaTiO ₃ particles. That is, when the BaTiO ₃ particles have a large particle size, gaps are likely to form between the BaTiO ₃ particles to be coated, and even when a relatively large amount of BaTiO ₃ particles are coated, the surface of the positive electrode active material particles is uniform. part exposed. On the other hand, when the BaTiO ₃ particles have a small particle size, the positive electrode active material particles are densely coated with the BaTiO ₃ particles even when the BaTiO ₃ particles are coated in a relatively small amount.

Therefore, as represented by the above formula (2), there is an appropriate adhesion amount (loading amount) of the BaTiO ₃ particles depending on the average particle size (nm) of the BaTiO ₃ particles. It is believed that the cycle characteristics of the battery 10 at high charge/discharge rates are improved.

As described above, the supported amount Y (mol %) of the BaTiO ₃ particles is within a range that satisfies the relationship represented by the above formula (2). If the loading amount Y (mol%) of the BaTiO ₃ particles is less than 0.001 A, the effect of coating the positive electrode active material particles with the BaTiO ₃ particles cannot be sufficiently obtained, and the non-aqueous electrolyte secondary battery 10 cannot be produced. Cycle characteristics do not improve at high charge/discharge rates. On the other hand, when the supported amount Y (mol%) of the BaTiO ₃ particles exceeds (0.01A+1), the BaTiO ₃ particles excessively cover the positive electrode active material particles, making it difficult to desorb and insert lithium ions. As a result, the cycle characteristics at a high charge/discharge rate are rather deteriorated.

Y should be 0.001A or more, preferably 0.002A or more. Y should be (0.01A+1) or less, preferably (0.01A+0.9) or less.

The average particle size A (nm) of the BaTiO ₃ particles is not particularly limited, but is preferably 10 nm or more and 100 nm or less, more preferably 10 nm or more and 80 nm or less. As a result, excessive coating due to too small BaTiO ₃ particles and unintentional detachment of the BaTiO ₃ particles due to too large BaTiO 3 particles are prevented, and the effect of improving cycle characteristics at the above-mentioned high-speed charge-discharge rate is achieved. Obtainable.

In addition, the ratio of the average particle size of the BaTiO ₃ particles to the average particle size of the positive electrode active material particles is not particularly limited, but is preferably 0.0011 or more and 0.0068 or less, more preferably 0.0012 or more and 0.0050 or less. be. As a result, the amount of BaTiO ₃ particles supported on the positive electrode active material particles can be set in a more appropriate range, and the cycle characteristics of the non-aqueous electrolyte secondary battery 10 at high charge/discharge rates are further improved.

The average particle size A of the BaTiO ₃ particles can be obtained by measuring the BaTiO ₃ particles by a laser diffraction particle size distribution/light scattering method (particle size distribution measurement) manufactured by Microtrack. Also, since the average particle size A of the BaTiO ₃ particles changes very little before and after the positive electrode active material particles are attached, the average particle size of the BaTiO ₃ particles before attachment may be used as the average particle size A of the BaTiO ₃ particles. In addition, the BaTiO ₃ particles after adhesion are analyzed with a scanning electron microscope (SEM) image, and the equivalent sphere diameters of a plurality of, for example, 20 BaTiO ₃ particles are calculated based on the SEM image, and their arithmetic mean The value may be the average particle size A of the BaTiO ₃ particles. Such an arithmetic mean value is the same value as the average particle size D50 obtained by the laser diffraction particle size distribution/light scattering method. However, since the BaTiO ₃ particles supported on the surface of the positive electrode active material particles are very small, there is almost no difference in the laser diffraction particle size distribution and light scattering method. It is preferable to obtain the average particle size of _{the three} particles.

Also, the amount Y of BaTiO ₃ particles supported in the positive electrode active material can be obtained from the amount of BaTiO ₃ added to 1 mol of the positive electrode active material made of a lithium-containing transition metal oxide. In addition, quantitative analysis of Ba and Ti by scanning electron microscope (SEM) image analysis and inductively coupled plasma-mass spectrometry (ICP-MS) positive electrode active material made of lithium-containing transition metal oxide BaTiO ₃ loading per 1 mol can also be specified.

Also, in the positive electrode active material, the BaTiO ₃ particles are coated on the surface of the positive electrode active material particles, and then heat-treated at a temperature of 700° C. or less, so that the BaTiO ₃ particles are supported on the positive electrode active material particles. is preferred. The heat treatment is performed for fixing the BaTiO ₃ particles to the surfaces of the positive electrode active material particles. Here, by performing the heat treatment at a relatively low temperature as described above, the crystal structure of the BaTiO ₃ particles is prevented from changing during the heat treatment, and the effect of improving the cycle characteristics at the above-mentioned high-speed charge-discharge rate is more reliably achieved. Obtainable.

Examples of conductive aids include carbon black such as ketjen black, acetylene black, and furnace black. Among these, any one or more kinds of carbon black may be contained. A preferred example of these carbon blacks is acetylene black. Acetylene black has fewer defects than other carbon blacks. Defective portions of carbon black may react with the electrolyte when the non-aqueous electrolyte secondary battery 10 is charged and discharged at high voltage. When the reaction occurs, gas is generated, and expansion of the non-aqueous electrolyte secondary battery 10 and the like may occur. From such a viewpoint, the carbon black is preferably acetylene black.

Binders include, for example, polyvinylidene difluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber. ), fluoroelastomer, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, and the like. The binder is not particularly limited as long as it can bind the positive electrode active material and the conductive aid onto the positive electrode current collector 21 . Moreover, the content of the binder is not particularly limited, and may be any content as long as it is applied to the positive electrode active material layer of the non-aqueous electrolyte secondary battery.

The positive electrode active material layer 22 is formed by, for example, dispersing a positive electrode active material, a conductive aid, and a binder in an appropriate organic solvent (eg, N-methyl-2-pyrrolidone). It is formed by coating a slurry on the positive electrode current collector 21, drying it, and rolling it.

The negative electrode 30 includes a negative electrode current collector 31 and a negative electrode active material layer 32 . The negative electrode current collector 31 is made of, for example, copper (copper), nickel, or the like.

The negative electrode active material layer 32 may be of any type as long as it is used as a negative electrode active material layer of a non-aqueous electrolyte secondary battery. For example, the negative electrode active material layer 32 contains a negative electrode active material and may further contain a binder. Further, the negative electrode active material layer 32 may contain a solid electrolyte. The negative electrode active material is, for example, a graphite active material (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), silicon (Si) or tin (Sn), or oxides thereof and a graphite active material, fine particles of silicon or tin, alloys based on silicon or tin, and titanium oxide (TiO _x ) compounds such as Li ₄ Ti ₅ O ₁₂ can be used. . Silicon oxide is represented by SiO _x (0≦x≦2). In addition to these, for example, metal lithium or the like can be used as the negative electrode active material.

As the binder, for example, styrene-butadiene rubber (SBR) is used. The mass ratio between the negative electrode active material and the binder is not particularly limited, and the mass ratio employed in conventional non-aqueous electrolyte secondary batteries can also be applied to the present invention.

Separator layer 40 includes a separator and an electrolytic solution.
The separator contained in separator layer 40 is not particularly limited. Any separator can be used as the separator included in the separator layer 40 as long as it is used as a separator for a non-aqueous electrolyte secondary battery. For example, as the separator, it is preferable to use a porous film, a non-woven fabric, or the like, which exhibits excellent high-rate discharge performance, alone or in combination. Materials constituting the separator include, for example, polyolefin resins such as polyethylene and polypropylene, polyethylene terephthalate, and polybutylene terephthalate. polyester resin, polyvinylidene difluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinylether copolymer, vinylidene fluoride-tetrafluoroethylene (tetrafluoroethylene) copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, fluoride vinylidene-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer , vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like can be used. The porosity of the separator is also not particularly limited, and any porosity of the separator of the non-aqueous electrolyte secondary battery can be applied.

Moreover, the separator may have a coating layer containing an inorganic filler. Specifically, the coating layer may contain at least one of Mg(OH) ₂ and Al ₂ O ₃ as an inorganic filler. According to such a configuration, the coating layer containing the inorganic filler prevents direct contact between the positive electrode and the separator, thereby preventing oxidation and decomposition of the electrolytic solution generated on the surface of the positive electrode during high-temperature storage, and decomposing the electrolytic solution. It is possible to suppress the generation of gas, which is a substance.

Here, the coating layer containing the inorganic filler may be formed on both sides of the separator, or may be formed only on one side of the separator on the positive electrode side. If the coating layer containing the inorganic filler is formed at least on the positive electrode side, it is possible to prevent direct contact between the positive electrode and the electrolytic solution.

Moreover, the present invention is not limited to the above examples. For example, a coating layer containing an inorganic filler may be formed on the positive electrode instead of on the separator. In this case, the coating layers containing the inorganic filler are formed on both sides of the positive electrode, thereby preventing direct contact between the positive electrode and the separator. Needless to say, the coating layer containing the inorganic filler may be formed on both the positive electrode and the separator. A solid electrolyte may be used instead of the separator layer 40 . A solid electrolyte that replaces the separator layer 40 is composed of, for example, a sulfide-based solid electrolyte material. Sulfide-based solid electrolyte materials include, for example, Li ₂ SP ₂ S ₅ , Li ₂ SP ₂ S ₅ -LiX (X is a halogen element, such as I, Cl), Li ₂ SP ₂ S _{5 -Li2O ,} Li2SP2S5- _Li2O -LiI, _Li2S - _SiS2 , _{Li2S - SiS2} - _{LiI ,} Li2S _-SiS2 -LiBr, _Li2S - _SiS2 -LiCl, _Li2S - _SiS2 - _{B2S3 - LiI} , _{Li2S - SiS2 - P2S5} -LiI, _Li2S - _B2S3 , _{Li2SP2S5 -} Z _m S _n (m and n are positive numbers, Z is either Ge, Zn or Ga), Li ₂ S—GeS ₂ , Li ₂ S—SiS ₂ —Li ₃ PO ₄ , Li ₂ S—SiS ₂ — Li _p MO _q (p and q are positive numbers; M is any one of P, Si, Ge, B, Al, Ga and In). Here, the sulfide-based solid electrolyte material is produced by processing a starting material (for example, Li ₂ S, P ₂ S _{5 ,} etc.) by a melt quenching method, a mechanical milling method, or the like. Further, heat treatment may be performed after these treatments. The solid electrolyte may be amorphous, crystalline, or a mixture of both.
Further, as the solid electrolyte, it is preferable to use, among the above sulfide solid electrolyte materials, those containing at least sulfur (S), phosphorus (P) and lithium (Li) as constituent elements, particularly Li ₂ SP _{2 .} It is more preferable to use those containing _S5 .
Here, when a material containing Li ₂ S—P ₂ S ₅ is used as the sulfide-based solid electrolyte material forming the solid electrolyte, the mixing molar ratio of Li ₂ S and P ₂ S ₅ is, for example, Li ₂ S :P ₂ S ₅ =50:50 to 90:10.

As the electrolytic solution, the same non-aqueous electrolytic solution conventionally used in lithium secondary batteries can be used without particular limitation. Here, the electrolytic solution has a composition in which an electrolyte salt is contained in a non-aqueous solvent. Examples of non-aqueous solvents include cyclic ester carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate, and the like. ); cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate ( chain esters such as methyl formate, methyl acetate, and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane ), 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyldiglyme nitriles such as acetonitrile, benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof can be used singly or in combination of two or more thereof, but the present invention is not limited to these.

Examples of 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 , inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K) such as KSCN, LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN( _{CF3SO2 )} ( _{C4F9SO2 )} , LiC( _{CF3SO2 ) 3} , LiC _{( C2F5SO2 ) 3 ,} ( _CH3 ) _{4NBF4 ,} ( _CH3 ) _4NBr , (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (nC ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, lithium stearyl sulfate, octyl sulfonic acid Organic ion salts such as lithium octyl sulfate and lithium dodecylbenzene sulfonate can be used. These ionic compounds can be used alone or in combination of two or more. Moreover, the concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte used in conventional lithium secondary batteries, and is not particularly limited. In the present invention, an electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.5 mol/L to 2.0 mol/L can be used.

<3. Method for producing positive electrode active material>
Next, a method for manufacturing the positive electrode active material will be described. The positive electrode active material can be obtained by synthesizing positive electrode active material particles and further supporting BaTiO ₃ particles on the surfaces of the positive electrode active material particles.

A method for synthesizing the positive electrode active material particles is not particularly limited, but for example, a coprecipitation method can be used. Specifically, first, cathode active material precursor particles are synthesized by a coprecipitation method. The dry powder obtained is mixed with a lithium source such as lithium carbonate (Li ₂ CO ₃ ) to form a mixed powder. The mixed powder thus obtained is sintered, for example, at 800 to 1050° C. for 12 hours in an air atmosphere to synthesize positive electrode active material particles. Here, the molar ratio of Li to other elements such as Ni, Co, and M is determined according to the composition of the lithium-cobalt composite oxide. Incidentally, commercially available positive electrode active material particles may be obtained and used.

Next, BaTiO ₃ particles are supported on the surfaces of the positive electrode active material particles. Specifically, a dispersion (slurry) obtained by mixing BaTiO ₃ particles and positive electrode active material particles in a dispersion medium is subjected to heat treatment after removing the dispersion medium, thereby forming BaTiO ₃ particles on the surfaces of the positive electrode active material particles. can be carried.

The dispersion can be obtained by adding BaTiO ₃ particles and positive electrode active material particles to a dispersion medium and dispersing them by stirring or the like. The dispersion medium is not particularly limited as long as the BaTiO ₃ particles and the positive electrode active material particles are insoluble. can be used.

Examples of ketone-based solvents include methyl ethyl ketone, acetylacetone, and acetone. Examples of ester solvents include fatty acid ester solvents such as ethyl acetate and methyl acetate. Examples of alcohol solvents include linear or branched aliphatic alcohols such as 2-propanol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, pentyl alcohol and isopentyl alcohol. , 1-methoxypropanol, and other linear or branched alkoxy alcohols. Examples of ether-based solvents include glycol-based solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol dimethyl ether (diglyme), and propylene glycol. Examples of polyhydric alcohol solvents include glycerol and thioglycerol. Non-polar solvents include cyclohexane, hexane, n-heptane and the like.

Among the above-mentioned solvents, alcohol solvents and ketone solvents are preferred, and ketone solvents are more preferred, from the viewpoint of dispersibility and ease of solvent removal.

The boiling point of the dispersion medium is preferably 130° C. or lower, more preferably 90° C. or higher and 120° C. or lower under atmospheric pressure (1 atm). This makes it possible to easily remove the solvent.

Moreover, the dispersion liquid may contain a dispersing agent. The dispersant contributes to improving the dispersion stability of the BaTiO ₃ particles and/or the positive electrode active material particles. As the dispersant, various dispersants such as C4-C24 fatty acids such as oleic acid and nonionic surfactants can be used. Examples of nonionic surfactants include fatty acid ester surfactants such as sorbitan fatty acid esters (e.g. Ionet S, Sanyo Chemical Industries), polyoxyethylene sorbitan fatty acid monoesters (e.g. Ionet T, Sanyo Chemical Industries), and SN sparse , SN Dispersant (San Nopco) and the like.

The content of the dispersant in the dispersion is not particularly limited, and can be set according to the required dispersion stability of the BaTiO ₃ particles and the positive electrode active material particles.

Next, the dispersion medium is removed from the resulting dispersion. The dispersion medium can be removed by, for example, spray drying (spray drying) or vacuum drying (evaporator). Among these, spray drying is preferable from the viewpoint of operability and productivity.

The drying temperature during spray drying can be appropriately set according to the boiling point of the dispersion medium, and can be, for example, 80° C. or higher and 160° C. or lower.

Finally, heat treatment (baking) is performed to fix (neck) the BaTiO ₃ particles on the surfaces of the positive electrode active material particles. Thereby, a positive electrode active material can be obtained.

Although the temperature of the heat treatment is not particularly limited, it is preferably 700° C. or less. As a result, the crystal structure of the BaTiO ₃ particles can be prevented from being unintentionally altered, and the effect of improving the cycle characteristics at a high charge/discharge rate by the BaTiO ₃ particles can be obtained more reliably. The heat treatment temperature is preferably 300° C. or higher and 700° C. or lower, more preferably 400° C. or higher and 700° C. or lower.

The heat treatment time is not particularly limited, and is, for example, 2 hours or more and 24 hours or less, preferably 4 hours or more and 12 hours or less.
The atmosphere during the heat treatment can be an oxygen-containing atmosphere, such as an air atmosphere.

<4. Method for manufacturing non-aqueous electrolyte secondary battery>
Next, an example of a method for manufacturing the non-aqueous electrolyte secondary battery 10 will be described. The manufacturing method described below is merely an example, and it goes without saying that the non-aqueous electrolyte secondary battery 10 can be manufactured by other methods.

The positive electrode 20 is manufactured as follows. First, a slurry is formed by dispersing materials (eg, positive electrode active material, conductive aid, and binder) constituting the positive electrode active material layer 22 in an organic solvent (eg, N-methyl-2-pyrrolidone). .

Next, the obtained mixture is kneaded and mixed, and then the positive electrode active material is added and kneaded and mixed. Finally, an organic solvent is added to adjust the viscosity to obtain a slurry.

Next, the slurry is applied onto the positive electrode current collector 21 and dried to form the positive electrode active material layer 22 . Further, the positive electrode active material layer 22 is compressed to a desired thickness using a compressor. Thereby, the positive electrode 20 is manufactured. Here, the thickness of the positive electrode active material layer 22 is not particularly limited as long as it is the thickness of the positive electrode active material layer of a non-aqueous electrolyte secondary battery. Note that the step of applying the positive electrode active material to the current collector may be performed in a dry environment.

For the negative electrode 30, first, a mixture of a negative electrode active material, carboxymethyl cellulose (CMC), and a conductive aid at a desired ratio is mixed with a predetermined amount of ion-exchanged water and kneaded. Thereafter, ion-exchanged water is further added to adjust the viscosity, and a styrene-butadiene rubber (SBR) binder is added to form a negative electrode slurry. Next, the slurry is applied onto the negative electrode current collector 31 and dried to form the negative electrode active material layer 32 . Further, the negative electrode active material layer 32 is compressed to a desired thickness using a compressor. Thus, the negative electrode 30 is manufactured. Here, the thickness of the negative electrode active material layer 32 is not particularly limited as long as it has the thickness of the negative electrode active material layer of a non-aqueous electrolyte secondary battery. When metallic lithium is used as the negative electrode active material layer 32 , a metallic lithium foil may be stacked on the negative electrode current collector 31 .

Subsequently, an electrode structure is manufactured by sandwiching the separator between the positive electrode 20 and the negative electrode 30 . Next, the electrode structure is processed into a desired shape (for example, a cylindrical shape, a square shape, a laminated shape, a button shape, etc.) and inserted into a container of that shape. Further, by injecting an electrolytic solution having a desired composition into the container, each pore in the separator is impregnated with the electrolytic solution. Thereby, the non-aqueous electrolyte secondary battery 10 is manufactured.

Examples of the present embodiment will be specifically described below. The examples shown below are examples of the present invention, and the present invention is not limited to the following examples.

<1. Manufacture of cells>
(Example 1)
(Preparation of positive electrode active material)
Positive electrode active material particles having a composition formula of Li _1.00 Ni _0.85 Co _0.10 Al _0.05 O ₂ were synthesized by the following method. First, positive electrode active material precursor particles having a composition represented by the composition formula Ni _0.85 Co _0.10 Al _0.05 (OH) ₂ were synthesized by a coprecipitation method. A mixed powder was produced by mixing the obtained dry powder and lithium carbonate (Li ₂ CO ₃ ). The obtained powder was calcined at 800° C. to 1050° C. for 24 hours in an oxygen atmosphere to synthesize positive electrode active material particles. Here, since the molar ratio of Li to Ni+Co+M (=Me) is determined according to the composition of the lithium-nickel-cobalt composite oxide, Li _1.00 Ni _0.85 Co _0.10 Al _0.05 O ₂ is produced, the molar ratio Li:Me between Li and Me is 1.00:1.00. The Li:Me ratio of the obtained lithium-nickel-cobalt composite oxide was confirmed by ICP-OES (for example, HORIBA ULTIMA2), and the Li:Me ratio after firing was 1.00:1.00. The amount of lithium carbonate was adjusted in advance for production. For example, the molar ratio of Li and Me is adjusted between 1.03:1.00 and 1.07:1.00 so that the Li:Me ratio after firing is 1.00:1.00. manufactured.

The average particle size of the positive electrode active material particles was measured by a laser diffraction particle size distribution/light scattering method (particle size distribution measurement). As a result, the average particle size was 12 μm.

Next, to acetone as a dispersion medium, the obtained positive electrode active material particles, BaTiO ₃ particles, and SN sparse (2% of the total amount) as a dispersant are added and stirred to obtain a dispersion liquid. (slurry) was obtained. The amounts of the positive electrode active material particles and BaTiO ₃ particles added were adjusted so that the supported BaTiO ₃ particles were 0.010 mol % with respect to the positive electrode active material particles.

Then, the dispersion liquid was spray-dried at a drying temperature of 100° C. to obtain a powder.

The obtained powder was sintered at 700° C. for 12 hours in an oxygen atmosphere to fix the BaTiO ₃ particles on the surface of the positive electrode active material particles, thereby obtaining the positive electrode active material according to Example 1.

The resulting positive electrode active material was analyzed by SEM images, the spherical equivalent diameters of 20 BaTiO ₃ particles were calculated based on the SEM images, and the arithmetic mean value of these was taken as the average particle diameter A of the BaTiO ₃ particles. The average particle size A of the BaTiO ₃ particles in the positive electrode active material according to Example 1 was 10 nm.

(Preparation of coin full cell)
A coin half cell was produced by the following treatment. First, a positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 96:2:2. This mixture (positive electrode mixture) was dispersed in N-methyl-2-pyrrolidone to form a slurry.

The positive electrode active material layer 22 was formed by applying the slurry onto the positive electrode current collector 21 and drying it. Then, the positive electrode 20 was produced by rolling so that the thickness of the positive electrode active material layer 22 was 50 μm. The positive electrode active material layer 22 had a volume density of 3.7 g/cc and an area density of 20 mg/cm ² .

The negative electrode 30 was produced by applying negative electrode slurry in which graphite was dispersed in ion-exchanged water onto a copper foil, which is the negative electrode current collector 31, and drying the slurry. Then, a porous polypropylene film having a thickness of 12 μm (both sides of which are coated with magnesium hydroxide, manufactured by Teijin Ltd.) was prepared as a separator, and the separator was placed between the positive electrode 20 and the negative electrode 30 to obtain an electrode. A structure was manufactured. Next, the electrode structure was processed into the size of a coin full cell and housed in a coin full cell container.

Then, lithium hexafluorophosphate was dissolved at a concentration of 1.3 M in a non-aqueous solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 3:7 to prepare an electrolytic solution. Then, the coin full cell according to Example 1 was manufactured by injecting the electrolyte into the coin full cell and impregnating the separator with the electrolyte.

(Examples 2 to 7)
A positive electrode active material and a coin full cell were prepared in the same manner as in Example 1, except that the average particle diameter and the amount of BaTiO ₃ particles carried were changed as shown in Table 1.

(Comparative example 1)
A positive electrode active material and a coin full cell were prepared in the same manner as in Example 1, except that the BaTiO ₃ particles were not supported on the positive electrode active material.

(Comparative Example 2, Comparative Example 3)
A positive electrode active material and a coin full cell were prepared in the same manner as in Example 1, except that the average particle diameter and the amount of BaTiO ₃ particles carried were changed as shown in Table 1.

Table 1 summarizes the production conditions in the above Examples and Comparative Examples. Table 1 also shows the permissible range of the supported amount calculated by substituting the average particle diameter into the formula (2).

<2. Evaluation>
Next, using the coin-full cells obtained in each example and each comparative example, cycle characteristics at a high charge/discharge rate were evaluated.
Specifically, the coin full cells obtained in each example and each comparative example were charged and discharged at 100 at the charge/discharge rate and cutoff voltage (unit: V) shown in Table 2. went on a cycle. The temperature during charging and discharging was room temperature (25° C.). CC-CV means constant current constant voltage and CC means constant current. Then, the discharge capacity at the 1st cycle was measured, and this value was used as the initial discharge capacity to obtain the capacity retention rate of the discharge capacity at the 100th cycle with respect to the discharge capacity at the 1st cycle. Then, when the capacity retention rate obtained in Comparative Example 1 was set to 100, the rate (%) of the capacity retention rate obtained in each example and each comparative example was evaluated as cycle characteristics at a high charge/discharge rate. The above results are also shown in Table 1.

<3. Comparison>
Comparing Examples 1 to 7 with Comparative Example 1, the coin full cells according to Examples 1 to 7 are superior to the coin full cell according to Comparative Example 1 in cycle characteristics at a high charge/discharge rate. rice field.
In addition, the coin full cells according to Comparative Examples 2 and 3 were rather inferior to the coin full cell according to Comparative Example 1 in terms of cycle characteristics at a high charge/discharge rate, although BaTiO ₃ particles were supported. .

<4. Production of cell (all-solid secondary battery)>
(Example 8)
First, the reagents Li ₂ S, Na ₂ S, P ₂ S ₅ , and LiCl were weighed so as to obtain the target composition of Li ₆ PS ₅ Cl, and then mixed with a planetary ball for 20 hours to perform mechanical milling. gone. The mechanical milling process was performed at a rotational speed of 380 rpm, room temperature (25° C.), and an argon atmosphere for 20 hours.
800 mg of the Li ₆ PS ₅ Cl composition powder sample obtained by the mechanical milling treatment was pressed (at a pressure of 400 MPa/cm ² ) to obtain a pellet having a diameter of 13 mm and a thickness of about 0.8 mm. The obtained pellet was coated with gold foil, and the pellet coated with gold foil was placed in a carbon crucible to prepare a sample for heat treatment. The obtained sample for heat treatment was vacuum sealed using a quartz glass tube, heated from room temperature (25°C) to 550°C at a rate of 1.0°C/min using an electric furnace, and then heated to 550°C. After the heat treatment was performed for 6 hours, the sample was obtained by cooling to room temperature (25° C.) at 1.0° C./min. After pulverizing the collected sample using an agate mortar, X-ray crystal diffraction was performed to confirm that the desired Argyrodite crystal was formed, and this material was used as a solid electrolyte.
A positive electrode mixture was prepared by mixing the positive electrode active material of Example 1, the solid electrolyte, and carbon nanofibers (CNF) as a conductive agent at a mass ratio of 60:30:10.
A metal lithium foil having a thickness of 30 μm was used as the negative electrode.
10 mg of the positive electrode mixture, 150 mg of the solid electrolyte and a metallic lithium foil (negative electrode) were laminated and pressed at a pressure of 294 MPa to prepare a test cell according to Example 8.

(Examples 9 to 14, Comparative Examples 4 to 6)
Examples 9 to 14 and Comparative Examples 4 to 6 were prepared in the same manner as in Example 8, except that the positive electrode active materials of Examples 2 to 7 and Comparative Examples 1 to 3 were used. A test cell according to was produced.

<5. Evaluation>
Next, using the test cells obtained in Examples 8 to 14 and Comparative Examples 4 to 6, cycle characteristics at a high charge/discharge rate were evaluated.
Specifically, the test cells obtained in each example and each comparative example were charged at a constant current of 0.05 C at 5° C. to an upper limit voltage of 4.0 V, and the discharge end voltage was 0 to 2.5 V. A charge/discharge cycle of discharging at 0.05 C was repeated for 50 cycles. The ratio of the discharge capacity at the 50th cycle to the discharge capacity at the 1st cycle was defined as the discharge capacity retention rate. Table 3 shows the results.

<6. Comparison>
Comparing Examples 8 to 14 with Comparative Examples 4 to 6, the test cells according to Examples 8 to 14 charge faster than the test cells according to Comparative Examples 4 to 6. Excellent cycle characteristics at discharge rate.

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

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

Claims (5)

Positive electrode active material particles having a composition represented by the following formula (1);
BaTiO ₃ particles supported on the surface of the positive electrode active material particles,
The ratio of the average particle size of the BaTiO ₃ particles to the average particle size of the positive electrode active material particles is 0.5. 0011 or more and 0.0050 or less,
A positive electrode active material that satisfies the relationship represented by the following formula (2).
_{LiaNixCoyMzO2 ( 1 ) _}
In the formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), from Niobium (Nb), Molybdenum (Mo), Tungsten (W), Copper (Cu), Zinc (Zn), Gallium (Ga), Indium (In), Tin (Sn), Lanthanum (La), Cerium (Ce) one or more metal elements selected from the group consisting of a, x, y and z, 0.20≤a≤1.20, 0.70≤x<1.00, 0<y≤0. 20, values within the range 0<z≦0.10 and x+y+z=1.
0.001A≤Y≤0.01A+1 (2)
In the formula (2), A is the average particle size (nm) of the BaTiO ₃ particles, and Y is the amount of the BaTiO ₃ particles supported on the positive electrode active material particles on a mol % basis. 2. The cathode active material according to claim 1, wherein the BaTiO ₃ particles have an average particle size A of 10 nm or more and 100 nm or less. A positive electrode for a non-aqueous electrolyte secondary battery, comprising the positive electrode active material according to claim 1 . A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to claim 3 . After coating the surface of the positive electrode active material particles having the composition represented by the following formula (1) with the BaTiO ₃ particles, a heat treatment is performed at a temperature of 700° C. or less to coat the BaTiO ₃ particles on the positive electrode active material particles. and the ratio of the average particle size of the BaTiO ₃ particles to the average particle size of the positive electrode active material particles is 0.5. 0011 or more and 0.0050 or less , a method for producing a positive electrode active material.
_{LiaNixCoyMzO2 ( 1 ) _}
In the formula (1), M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), from Niobium (Nb), Molybdenum (Mo), Tungsten (W), Copper (Cu), Zinc (Zn), Gallium (Ga), Indium (In), Tin (Sn), Lanthanum (La), Cerium (Ce) one or more metal elements selected from the group consisting of a, x, y and z, 0.20≤a≤1.20, 0.70≤x<1.00, 0<y≤0. 20, values within the range 0<z≦0.10 and x+y+z=1.

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