JP2019121607A - Positive electrode active substance material, positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a positive electrode active substance material of a high nickel rate, which is superior in load characteristic, a positive electrode for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery.SOLUTION: Provided is a positive electrode active substance material which comprises: positive electrode active substance particles having a composition represented by the following formula (1), and tetragonal crystal-based BaTiOparticles coating the surface of the positive electrode active substance particles: LiNiCoMO(1). In the formula (1), M represents one or more metal element selected from a group consisting of aluminum, manganese, chromium, iron, vanadium, magnesium, titanium, zirconium, niobium, molybdenum, tungsten, copper, zinc, gallium, indium, tin, lanthanum and cerium; and a, x, y and z are values that satisfy 0.20≤a≤1.20, 0.70≤x<1.00, 0<y≤0.20, 0<z≤0.10 and x+y+z=1.SELECTED DRAWING: Figure 1

Description

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

  A lithium transition metal complex oxide mainly composed of nickel (Ni) is used in a non-aqueous electrolyte secondary battery as a positive electrode active material exhibiting a relatively high potential and a high capacity. When a nickel-based positive electrode using such a nickel-containing lithium transition metal composite oxide as such an active material, and a counter electrode (negative electrode) containing graphite are employed, the non-aqueous electrolyte secondary battery may be used as described in 4. Generally, it is charged at 2V.

  However, recently, higher capacity of non-aqueous electrolyte secondary batteries is required, and along with this, with the improvement of the nickel ratio in the positive electrode active material, a non-aqueous electrolyte secondary capable of charging at a higher voltage. A battery is required. Specifically, in the case where a counter electrode (negative electrode) containing graphite is employed, the amount of lithium ions removed and inserted is improved by setting the charge voltage to 4.3 V, and the nickel ratio is set to about 80%. Also, high capacity of 200 mAh / g or more can be achieved.

  Further, in development of a non-aqueous electrolyte secondary battery, improvement of output characteristics at low temperature, improvement of discharge capacity, improvement of capacity characteristics at high speed charge and discharge rate, and improvement of 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 complex oxide for the purpose of improving output characteristics in a low temperature range.

JP, 2011-210694, A

  However, in the technique described in Patent Document 1, when the positive electrode active material with a high nickel ratio is used, improvement in load characteristics can not be expected.

  An object of the present invention is to provide a high nickel ratio positive electrode active material having excellent load characteristics, and a positive electrode for non-aqueous electrolyte secondary batteries and a non-aqueous electrolyte secondary battery including the same.

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),
There is provided a positive electrode active material comprising tetragonal BaTiO ₃ particles coated on the surface of the positive electrode active material particles.
Li _a Ni _x Co _y M _z O ₂ (1)
In the above 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) And at least one metal element selected from the group consisting of a, x, y and z is such that 0.20 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0 <y ≦ 0. It is a value within the range of 20, 0 <z ≦ 0.10 and x + y + z = 1.

  According to this aspect, the load characteristics of the non-aqueous electrolyte secondary battery can be improved.

Here, the average particle diameter A of the BaTiO ₃ particles may be 20 nm or more and 150 nm or less.
This further improves the load characteristics of the non-aqueous electrolyte secondary battery.

In addition, the coated area of the BaTiO ₃ particles may be 10% or more and 40% or less with respect to the surface area of the positive electrode active material particles.
Thereby, the load characteristics of the non-aqueous electrolyte secondary battery can be more reliably improved.

The relative permittivity of the BaTiO ₃ particles may be 400 or more and 1,500 or less.
Thereby, the load characteristics of the non-aqueous electrolyte secondary battery can be more reliably improved.

According to another aspect of the present invention, there is provided a positive electrode for a non-aqueous electrolyte secondary battery comprising the above-described positive electrode active material.
According to this aspect, the load characteristics of the non-aqueous electrolyte secondary battery can be improved.

According to another aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery comprising the above-described positive electrode for a non-aqueous electrolyte secondary battery.
According to this aspect, the load characteristics of the non-aqueous electrolyte secondary battery can be improved.

  As described above, according to the present invention, it is possible to improve the load characteristics of the non-aqueous electrolyte secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows schematic structure of the non-aqueous electrolyte secondary battery which concerns on embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<1. Examination of the present inventors>
First, prior to the description of the present invention, the examination of the present inventors until the present invention will be described. The present inventors recalled that supporting a barium titanate (BaTiO ₃ ), which is a ferroelectric substance, on positive electrode active material particles, for the purpose of improving load characteristics of a high nickel ratio positive electrode active material. More specifically, by supporting BaTiO ₃ particles, which are ferroelectrics, on the surface of positive electrode active material particles, the possibility of promoting polarization in the positive electrode active material and facilitating the removal and insertion of lithium ions was examined. .

  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 load characteristics of the positive electrode active material. Therefore, as a result of intensive studies, the present inventors have improved the load characteristics of the positive electrode active material by adopting tetragonal barium titanate having a relatively large dielectric constant among barium titanate. I found that I could do it.

  Barium titanate has a crystal structure such as cubic (Cubic type), Cubic-like type, tetragonal (tetragonal type), rhombohedral type, orthorhombic (orthorhomb type) and the like. Among these, barium titanate used in battery materials is mainly cubic, Cubic-like type. It is considered that this is because barium titanate obtained in a general production method of barium titanate, for example, a hydrothermal synthesis method or a sol-gel method is cubic or Cubic-like type. Furthermore, cubic system barium titanate manufactured by the hydrothermal synthesis method is low in crystallinity and small in dielectric constant as compared with tetragonal system barium titanate. On the other hand, the present inventors have made it possible to dramatically improve the load characteristics of the non-aqueous electrolyte secondary battery by employing tetragonal barium titanate which has not been studied conventionally.

  It is not easy to support barium titanate on positive electrode active material particles with a high nickel ratio. For example, when a method of hydrolyzing and reacting Ti and Ba on the surface of a positive electrode active material in gel, baking it, and supporting barium titanate on the surface is adopted for positive electrode active material particles with a high nickel ratio, Ba is a positive electrode. A side reaction that reacts with Li in the active material occurs, and barium titanate is not formed. Moreover, when it bakes after making barium titanate adhere to a positive electrode active material particle, barium titanate may be diffused to the inside of a positive electrode active material particle. However, as a result of intensive investigations, the present inventors succeeded in supporting tetragonal barium titanate on the surface of positive electrode active material particles by the method described later.

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

  As shown in FIG. 1, the non-aqueous electrolyte secondary battery 10 includes a positive electrode 20, a negative electrode 30, and a separator layer 40. 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, square, 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 or the like.

  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. In addition, 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 surface 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).
Li _a Ni _x Co _y M _z O ₂ (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) 1 It is a metallic element of a kind or more,
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 the value in

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

  Further, the average particle diameter of the positive electrode active material particles is not particularly limited, but is, for example, 5 μm or more and 15 μm or less, preferably 8 μm or more and 14 μm or less. This improves the fillability (tap density, etc.).

  The average particle size of the positive electrode active material particles can be determined by laser diffraction / light scattering method (particle size distribution measurement). In the present specification, the “average particle diameter” refers to a particle diameter corresponding to 50% of cumulative particle size from the particle side in a volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction / light scattering method (D50 Also referred to as the median diameter.

Then, tetragonal BaTiO ₃ particles are supported on the surface of the positive electrode active material particles. Thereby, the load characteristics of the non-aqueous electrolyte secondary battery 10 are improved.

The reason why the load characteristics are improved is not clear, but is presumed as follows. That is, tetragonal BaTiO ₃ particles have relatively strong dielectricity among barium titanate, and polarization occurs in the substance when an electric field is applied. And, 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 accelerates the insertion and desorption process of lithium ions on the surface of the positive electrode active material particles.

Further, by covering the surface of the positive electrode active material particles with BaTiO ₃ particles, the side reaction between the positive electrode active material particles and the electrolytic solution is suppressed, and the decomposition of the electrolytic solution is suppressed. Furthermore, by coating the surface of the positive electrode active material particles with BaTiO ₃ particles, it is possible to prevent the phase transition and inactivation of the unstable positive electrode active material from which lithium ions are desorbed.
As described above, the tetragonal BaTiO ₃ particles can promote the lithium ion insertion / extraction process on the surface of the positive electrode active material particles while preventing the deterioration of the positive electrode active material particles and the electrolytic solution. As a result, it is considered that the load characteristics of the non-aqueous electrolyte secondary battery 10 are improved.

The crystal structure of the BaTiO ₃ particles can be identified by X-ray diffraction. Specifically, with respect to the positive electrode active material, X-ray diffraction is performed using a CuKα ray as a radiation source to obtain a diffraction pattern. The obtained diffraction pattern is analyzed by Rietveld method, and then the crystal structure is analyzed. In the case of tetragonal barium titanate, the peaks of (002) and (200) are split around 31.4 ° and 31.6 ° (both are 2θ), and a total of two peaks are detected. Based on this peak position, the lattice constant of the barium titanate crystal can be calculated. The ratio c / a of the lattice constants a (Å) and c (Å) of barium titanate is in the range of 1.000 to 1.010 in any crystal structure. In particular, in the case of tetragonal barium titanate, the ratio c / a is in the range of 1.008 to 1.010. Therefore, when the ratio c / a is in the range of 1.008 to 1.010, it can be identified that the BaTiO ₃ particles are composed of tetragonal barium titanate.

The relative dielectric constant of the BaTiO ₃ particles is not particularly limited, but may be, for example, 400 or more, preferably 400 or more and 1500 or less, and more preferably 800 or more and 1500 or less. Such a relatively large dielectric constant further promotes insertion and desorption of lithium ions. Further, due to the large relative dielectric constant, the lithium ion insertion / extraction effect can be sufficiently obtained even when the coating area of BaTiO ₃ particles described later is relatively small. When the relative dielectric constant exceeds 1,500, the insertion and desorption effect of lithium ions is saturated. When it is difficult to measure the relative dielectric constant of BaTiO ₃ particles in the positive electrode active material, the relative dielectric constant can be the relative dielectric constant of BaTiO ₃ particles before being coated on the positive electrode active material particles. .

The average particle size (nm) of the BaTiO ₃ particles is not particularly limited, but is preferably 20 nm or more and 150 nm or less, more preferably 20 nm or more and 100 nm or less. As a result, it is possible to obtain the effect of improving the load characteristics while preventing excessive coating due to the BaTiO ₃ particles being too small and unintentional detachment of the BaTiO ₃ particles due to the too large particles.

The average particle diameter of BaTiO ₃ particles, can determine the average particle size by laser diffraction and light scattering method (particle size distribution measurement made by Microtrac Inc.). In addition, the BaTiO ₃ particles after adhesion are analyzed by a scanning electron microscope (SEM) image, and the sphere equivalent 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 an average particle size of BaTiO ₃ particles. Such an arithmetic average value is the same value as the average particle diameter D50 obtained by the laser diffraction particle size distribution / light scattering method. The average particle size of the BaTiO ₃ particles, since the change due to the adhesion before and after the positive electrode active material particles is extremely small, the average particle diameter of BaTiO ₃ particles before attachment may be an average particle diameter of BaTiO ₃ particles.

The coating area of the BaTiO ₃ particles is not particularly limited, but is preferably 10% to 40%, more preferably 10% to 30%, of the surface area of the positive electrode active material particles. As a result, a sufficient amount of BaTiO ₃ particles for supporting insertion and desorption of lithium ions is supported on the surface of the positive electrode active material particles. In addition, the area of the positive electrode active material particles in contact with the electrolytic solution can be increased while sufficiently obtaining the effect of suppressing decomposition of the electrolytic solution and covering of the positive electrode active material particles by the coating of BaTiO ₃ particles. Insertion and detachment can be further promoted.

The surface area of the BaTiO ₃ particles was obtained by obtaining a surface image of the positive electrode active material with a scanning electron microscope, for example, an electron emission scanning electron microscope (FE-SEM), and covering the area of the positive electrode active material It can be calculated by measuring the area of BaTiO ₃ particles and determining their ratio.

  Examples of the conductive aid include carbon blacks such as ketjen black, acetylene black, and furnace black. Among these, any one or more carbon black may be contained. Among these carbon blacks, a preferred example 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 under high voltage. When the reaction occurs, gas is generated, and expansion or the like of the non-aqueous electrolyte secondary battery 10 may occur. From such a point of view, the carbon black is preferably acetylene black.

  The binder includes, for example, polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-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 auxiliary onto the positive electrode current collector 21. 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.

  For example, the positive electrode active material layer 22 is obtained by dispersing a positive electrode active material, a conductive aid, and a binder in a suitable organic solvent (for example, N-methyl-2-pyrrolidone). The slurry (slurry) is coated on the positive electrode current collector 21, dried and rolled.

  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 (cupper), nickel or the like.

The negative electrode active material layer 32 may be anything 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 may contain a negative electrode active material and may further contain a binder. In addition, 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 Mixtures of particles of graphite and a graphite active material, 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. . The oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). Moreover, as a negative electrode active material, metal lithium etc. can be used other than these, for example.

  Further, as the binder, for example, styrene butadiene rubber (SBR) or the like is used. The mass ratio of the negative electrode active material to the binder is not particularly limited, and the mass ratio adopted in the conventional non-aqueous electrolyte secondary battery is also applicable to the present invention.

The separator layer 40 includes a separator and an electrolytic solution.
The separator contained in the separator layer 40 is not particularly limited. Any separator may be used in the separator layer 40 as long as it can be used as a separator of a non-aqueous electrolyte secondary battery. For example, as the separator, it is preferable to use, alone or in combination, a porous film, a non-woven fabric, or the like exhibiting excellent high-rate discharge performance. As a material which comprises a separator, it is represented by the polyolefin resin represented by polyethylene (polyethylene), a polypropylene (polypropylene) etc., a polyethylene terephthalate (polyethylene terephthalate), a polybutylene terephthalate (polybutylene terephthalate) etc., for example Polyester (polyester) resin, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether co-polymer Combination, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone (Hexafluoroacetone) copolymer, vinylidene fluoride-ethylene (ethylene) copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetraethylene fluoride Fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene-tetra It can be used Ruoroechiren copolymer. In addition, the porosity in particular of a separator is not restrict | limited, either, The porosity which the separator of a nonaqueous electrolyte secondary battery has is applicable arbitrarily.

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 or Al ₂ O ₃ as an inorganic filler. According to this 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 decomposition and formation of 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, direct contact between the positive electrode and the electrolytic solution can be prevented.

Furthermore, the present invention is not limited to the above-described examples. For example, the coating layer containing the inorganic filler may be formed on the positive electrode, not on the separator. In such a case, the coating layer containing the inorganic filler can prevent direct contact between the positive electrode and the separator by being formed on both sides of the positive electrode. Needless to say, the coating layer containing the inorganic filler may be formed on both the positive electrode and the separator. Also, instead of the separator layer 40, a solid electrolyte may be used. As a solid electrolyte replacing the separator layer 40, for example, a sulfide-based solid electrolyte material is used. As the sulfide-based solid electrolyte material, for example, Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -LiX (X is a halogen element such as I, Cl), Li ₂ S-P ₂ S _{5 -Li 2 O, Li 2 S-} P 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2, Li2 S -SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 _{-LiCl, Li 2 S-SiS 2} -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 S-B 2 S 3, Li 2 S-P 2 S 5 -Z _m S _{n (m, n} is any positive number, Z is Ge, and 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, q} is a positive number, M is P, Si, Ge B, Al, either Ga or In), and the like. Here, the sulfide-based solid electrolyte material is produced by treating a starting material (for example, Li ₂ S, P ₂ S ₅ or the like) by a melt-quenching method, a mechanical milling method, or the like. Further, heat treatment may be further performed after these treatments. The solid electrolyte may be amorphous or crystalline, or may be in a mixed state.
Further, as the solid electrolyte, among the above sulfide solid electrolyte material, sulfur (S) as at least an element, it is preferable to use a material containing phosphorus (P) and lithium (Li), in particular Li _{2 S-P} 2 it is more preferable to use those containing S _5.
Here, in the case of using a material containing Li ₂ S—P ₂ S ₅ as a sulfide-based solid electrolyte material forming a solid electrolyte, the mixing molar ratio of Li ₂ S and P ₂ S ₅ is, for example, Li ₂ S It may be selected in the range of P ₂ S ₅ = 50: 50 to 90:10.

  As the electrolyte solution, the same non-aqueous electrolyte solution conventionally used for lithium secondary batteries can be used without particular limitation. Here, the electrolytic solution has a composition in which a non-aqueous solvent contains an electrolyte salt. As the non-aqueous solvent, for example, cyclic carbonates such as propylene carbonate, ethylene carbonate, buthylene carbonate, chloroethylene carbonate, vinylene carbonate, etc. ; Cyclic esters such as γ-butyrolactone and γ-valerolactone; Dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate linear carbonates such as ethyl carbonate); linear esters such as methyl formate, methyl acetate, methyl butylate; tetrahydrofuran (tetrahydrofuran) or derivatives thereof; 1, 3-dioxane (1,3-dioxane), 1,4-dioxane (1,4-dioxane), 1,2-dimethoxyethane (1,2-dimethoxyethane), 1,4-dibutoxyethane (1,4-dibutoxyane) Ethers such as dibutyloxyne, methyl diglyme, etc .; acetonitrile (acetonitril), benzonitrile (benz) nitriles such as Nitril), dioxolanes or derivatives thereof; ethylene sulfide, sulfolanes, sultones, sultones or derivatives thereof alone or in combination of two or more thereof Although it can be used, it is not limited to these.

In addition, as electrolyte salts, for example, 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) such as KSCN, sodium (Na) or potassium (K), 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 NC lO 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-phtalate, stearyl sulfonic acid Organic ionic salts such as lithium (lithium stearyl sulfate), lithium octyl sulfonate, lithium dodecylbenzene sulfonate and the like can be used. In addition, it is possible to use these ionic compounds individually or in mixture of 2 or more types. The concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte used in the conventional lithium secondary battery, and is not particularly limited. In the present invention, an electrolytic solution containing a suitable lithium compound (electrolyte salt) at a concentration of about 0.5 mol / L to 2.0 mol / L can be used.

<3. Method of manufacturing positive electrode active material>
Next, a method of 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 tetragonal BaTiO ₃ particles on the surface of the positive electrode active material particles.

The method of synthesizing the positive electrode active material particles is not particularly limited, and for example, a coprecipitation method can be used. Specifically, first, positive electrode active material precursor particles are synthesized by coprecipitation method. A mixed powder is produced by mixing the obtained dry powder with a lithium source such as lithium carbonate (Li ₂ CO ₃ ). The obtained mixed powder can be fired, for example, at 800 ° C. to 1050 ° C. in an air atmosphere for 12 hours 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. A commercially available positive electrode active material particle may be obtained and used.

The tetragonal BaTiO ₃ particles may be obtained by heat treatment at a temperature of 700 ° C. or more and 1000 ° C. or less, preferably 900 ° C. or more and 1000 ° C. or less, and then wet disintegrated using a bead mill. it can. A commercially available tetragonal BaTiO ₃ particle may be obtained and used.

Next, tetragonal BaTiO ₃ particles are supported on the surface of the positive electrode active material particles. Specifically, the dispersion medium is removed from the dispersion liquid (slurry) in which tetragonal BaTiO ₃ particles and positive electrode active material particles are mixed in the dispersion medium, and heat treatment is performed, whereby the surface of the positive electrode active material particles is obtained. Can support BaTiO ₃ particles.

The dispersion liquid can be obtained by adding the BaTiO ₃ particles and the 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, and examples thereof include ketone solvents, ester solvents, ether solvents, alcohol solvents, polyhydric alcohol solvents, nonpolar solvents, etc. Can be used.

  Examples of ketone solvents include methyl ethyl ketone, acetyl acetone, acetone and the like. Moreover, as ester solvent, fatty acid ester solvents, such as ethyl acetate and methyl acetate, are mentioned. In addition, as alcohol solvents, 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, isopentyl alcohol and the like And linear or branched alkoxy alcohols such as 1-methoxypropanol. Examples of ether solvents include glycol solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol dimethyl ether (diglyme) and propylene glycol. Further, as polyhydric alcohol solvents, glycerol, thioglycerol and the like can be mentioned. Nonpolar solvents include cyclohexane, hexane, n-heptane and the like.

  Among the above, from the viewpoints of dispersibility and ease of removal of the solvent, alcohol solvents and ketone solvents are preferable, and ketone solvents are more preferable.

  The boiling point of the dispersion medium is preferably 130 ° C. or less at atmospheric pressure (1 atm), and more preferably 80 ° C. or more and 120 ° C. or less. This enables easy removal of the solvent.

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

The content of the dispersant in the dispersion liquid 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.

  Then, the dispersion medium is removed from the obtained dispersion. The removal of the dispersion medium can be performed, for example, by spray drying (spray drying) or reduced pressure drying (evaporator). Among these, spray drying is preferable from the viewpoint of operability and productivity.

  The drying temperature at the time of spray drying can be appropriately set according to the boiling point of the dispersion medium, and can be, for example, 80 ° C. or more and 120 ° C. or less.

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

Although it does not specifically limit as temperature of heat processing, For example, they are 400 degreeC or more and 800 degrees C or less, Preferably they are 500 degreeC or more and 700 degrees C or less. Thus, while preventing that the crystal structure of the BaTiO ₃ particles are involuntarily altered, the BaTiO ₃ particles can be securely fixed on the surface of the positive electrode active material particle. As a result, the effect of improving the load characteristics by tetragonal BaTiO ₃ particles can be obtained more reliably.

The heat treatment time is not particularly limited, and is, for example, 4 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 of Manufacturing Nonaqueous Electrolyte Secondary Battery>
Subsequently, an example of a method of manufacturing the non-aqueous electrolyte secondary battery 10 will be described. The manufacturing method described below is merely an example, and it is needless to say that the nonaqueous 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 the material (for example, positive electrode active material, conductive additive and binder) constituting the positive electrode active material layer 22 in an organic solvent (for example, N-methyl-2-pyrrolidone). .

  Next, the obtained mixture is mixed and mixed, and then the positive electrode active material is added and mixed 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. Furthermore, the positive electrode active material layer 22 is compressed to a desired thickness by 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 the non-aqueous electrolyte secondary battery. The step of applying the positive electrode active material to the current collector may be performed in a dry environment.

  In the negative electrode 30, first, a mixture of a negative electrode active material, carboxymethyl cellulose (CMC) and a conductive auxiliary agent in a desired ratio is added with a predetermined amount of ion-exchanged water, and mixed and mixed. Thereafter, ion exchange 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. Furthermore, the negative electrode active material layer 32 is compressed to a desired thickness by a compressor. Thereby, 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 is the thickness of the negative electrode active material layer of the non-aqueous electrolyte secondary battery. When metal lithium is used as the negative electrode active material layer 32, a metal lithium foil may be stacked on the negative electrode current collector 31.

  Subsequently, the separator is sandwiched between the positive electrode 20 and the negative electrode 30 to manufacture an electrode structure. Next, the electrode structure is processed into a desired form (for example, cylindrical, square, laminate, button, etc.) and inserted into the container of the form. Furthermore, the pores in the separator are impregnated with the electrolytic solution by injecting an electrolytic solution of a desired composition into the container. Thereby, the non-aqueous electrolyte secondary battery 10 is manufactured.

  Below, the Example which concerns on this embodiment is demonstrated concretely. In addition, the Example shown below is an example of this invention, Comprising: This invention is not limited to the following example.

<1. Cell production>
Example 1
(Production of positive electrode active material)
The 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 a composition formula Ni _0.85 Co _0.10 Al _0.05 (OH) ₂ were synthesized by coprecipitation method. A dry powder obtained, by mixing the lithium carbonate (Li 2 _{CO 3),} to produce a mixed powder. The obtained powder was fired at 800 ° C. to 1050 ° C. for 24 hours in the air atmosphere to synthesize positive electrode active material particles. Here, the molar ratio of Li to Ni + Co + M (= Me) is determined according to the composition of the lithium-nickel-cobalt composite oxide, so Li _1.00 Ni _0.85 Co _0.10 Al _0.05 O ₂ The molar ratio of Li to Me, Li: Me, is 1.00: 1.00. The Li: Me ratio of the obtained lithium nickel cobalt composite oxide is confirmed by ICP-OES (for example, HORIBA ULTIMA2), and the Li: Me ratio after firing is 1.00: 1.00, The preparation was carried out by adjusting the amount of lithium carbonate in advance. For example, the molar ratio of Li to Me is adjusted to be between 1.03: 1.00 and 1.07: 1.00, and the ratio of Li: Me after firing is 1.00: 1.00. I made it.

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

Subsequently, the obtained positive electrode active material particles, BaTiO ₃ particles, and sorbitan fatty acid ester (2% with respect to the total amount) as a dispersing agent are added to 1-methoxypropanol as a dispersion medium and stirred. Thus, a dispersion (slurry) was obtained. The addition amounts of the positive electrode active material particles and the BaTiO ₃ particles were adjusted so that the supported BaTiO ₃ particles were coated at an area ratio of 40.0% with respect to the positive electrode active material particles. As the BaTiO ₃ particles, a tetragonal material having an average particle diameter of 20 nm and a relative dielectric constant of 400 was used.

  Then, the dispersion was spray-dried at a drying temperature of 110 ° C. to obtain a powder.

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

About the positive electrode active material material based on Example 1, the scanning electron microscope image was acquired using Nippon Electronics Co., Ltd. FE-SEM. From the obtained scanning electron microscope image, the area of the positive electrode active material and the area of the coated BaTiO ₃ particles were measured, and the ratio of these was determined to calculate the coverage of BaTiO ₃ particles.

In addition, the SEM image of the obtained positive electrode active material material was analyzed, the sphere equivalent diameters of 20 BaTiO ₃ particles were calculated based on the SEM images, and the arithmetic mean value of these was made the average particle diameter of the BaTiO ₃ particles. . The average particle diameter of BaTiO ₃ particles in the positive electrode active material according to Example 1 was 20 nm.

Furthermore, the obtained positive electrode active material was subjected to powder X-ray diffraction analysis using Cu-Kα as a radiation source, and the ratio c / a of lattice constant was calculated from the obtained X-ray diffraction pattern, 1.010 It was confirmed that the BaTiO ₃ particles maintain the tetragonal crystal structure in the positive electrode active material.

(Production of coin full cell)
The coin half cell was produced by the following processing. First, 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 slurry was applied onto the positive electrode current collector 21 and dried to form a positive electrode active material layer 22. The positive electrode 20 was manufactured by rolling so that the thickness of the positive electrode active material layer 22 was 50 μm. The volume density of the positive electrode active material layer 22 was 3.7 g / cc, and the area density was 20 mg / cm ² .

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

  Then, an electrolyte solution was produced by dissolving lithium hexafluorophosphate 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. Subsequently, the coin full cell according to Example 1 was manufactured by injecting the electrolytic solution into the coin full cell and impregnating the electrolytic solution into the separator.

(Examples 2 to 6)
A positive electrode active material and a coin full cell were prepared in the same manner as in Example 1 except that the configuration of the positive electrode active material particles and the BaTiO ₃ particles used and the coverage of the BaTiO ₃ particles 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 produced in the same manner as in Example 1 except that the configuration and coverage of the BaTiO ₃ particles used were changed as shown in Table 1.

  The configuration of the positive electrode active material in each of the above Examples and Comparative Examples is shown together in Table 1.

<2. Evaluation>
Next, load characteristics were evaluated using the coin full cell obtained in each example and each comparative example.
Specifically, for the coin full cell obtained in each example and each comparative example, the charge rate is 0.2 C at constant current and constant voltage (CC-CV), and the discharge rate is 5 at constant current (CC). .0 C, the cutoff value was 2.85 V-4.3 V, charge and discharge were performed multiple times, and the discharge capacity of each cycle was measured. The cycle life (number of cycles) was taken until the first cycle when the discharge capacity was 80% or less of the discharge capacity of the first cycle. And the relative value (%) of the cycle life obtained in each example and each comparative example when the relative value of the cycle life obtained in comparative example 1 is set to 100 was evaluated as load characteristics. The above results are shown in Table 1 together.

<3. Contrast>
Comparing Example 1 to Example 6 with Comparative Example 1, the coin full cell according to Example 1 to Example 6 using tetragonal BaTiO ₃ particles is more loaded than the coin full cell according to Comparative Example 1. It had excellent characteristics.

In addition, in the coin full cell according to Comparative Example 2 and Comparative Example 3 using BaTiO ₃ particles other than tetragonal crystals, the load characteristics are reduced and the coin full cell according to Comparative Example 1 is carried despite that BaTiO ₃ particles are supported. It was inferior to.

<4. Production of cell (all solid secondary battery)>
(Example 7)
First, after weighing the reagents Li ₂ S, Na ₂ S, P ₂ S ₅ , and LiCl so that the target composition is Li ₆ PS ₅ Cl, mechanical milling is performed by mixing with a planetary ball for 20 hours. went. The mechanical milling was performed at a rotational speed of 380 rpm, at room temperature (25 ° C.) in an argon atmosphere for 20 hours.
By pressing 800 mg of a powder sample of Li ₆ PS ₅ Cl composition obtained by the above mechanical milling process (pressure 400 MPa / cm ² ), a pellet having a diameter of 13 mm and a thickness of about 0.8 mm was obtained. The obtained pellet was coated with a gold foil, and further, the gold foil coated pellet was placed in a carbon crucible to prepare a sample for heat treatment. The obtained sample for heat treatment is vacuum sealed using a quartz glass tube, and then heated from room temperature (25 ° C.) to 550 ° C. at 1.0 ° C./min using an electric furnace, and then to 550 ° C. Heat-treated for 6 hours, and then cooled to room temperature (25.degree. C.) at 1.0.degree. C./minute to obtain a sample. The collected sample was pulverized using an agate mortar, and then X-ray crystal diffraction was performed to confirm that the target Argyrodite crystal was formed, and this material was used as a solid electrolyte.
What mixed the positive electrode active material material of Example 1, the solid electrolyte, and the carbon nanofiber (CNF) which is a conductive agent by a mass ratio of 60:30:10 was made into positive mix.
Moreover, as a negative electrode, metal lithium foil with a thickness of 30 micrometers was used.
10 mg of a positive electrode mixture, 150 mg of a solid electrolyte, and a metal lithium foil (negative electrode) were laminated, and pressed at a pressure of 294 MPa to prepare a test cell according to Example 7.

(Examples 8 to 12 and Comparative Examples 4 to 6)
Example 8 to Example 12 and Comparative Example 4 to Comparative Example 6 are the same as Example 7 except that the positive electrode active material of Example 2 to Example 6 and Comparative Example 1 to Comparative Example 3 is used. The test cell according to

<5. Evaluation>
Next, using the test cells obtained in Example 7 to Example 12 and Comparative Example 4 to Comparative Example 6, cycle characteristics at high-speed charge and discharge rates were evaluated.
Specifically, the test cells obtained in each example and each comparative example are charged at a constant current of 0.05 C at 5 ° C. to an upper limit voltage of 4.0 V, and a discharge end voltage of 0 to 2.5 V The charge and discharge cycle of .05C discharge was repeated 50 cycles. Then, the ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle was taken as the maintenance rate of the discharge capacity. The results are shown in Table 2.

<6. Contrast>
Comparing Example 7 to Example 12 with Comparative Example 4 to Comparative Example 6, the test cells according to Example 7 to Example 12 are faster in charging speed than the test cells according to Comparative Example 4 to Comparative Example 6. The cycle characteristics at the discharge rate were excellent.

  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 such examples. It is obvious that those skilled in the art to which the present invention belongs can conceive of various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also fall within 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 (6)

Positive electrode active material particles having a composition represented by the following formula (1):
A positive electrode active material comprising tetragonal BaTiO ₃ particles coated on the surface of the positive electrode active material particles.
Li _a Ni _x Co _y M _z O ₂ (1)
In the above 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) And at least one metal element selected from the group consisting of a, x, y and z is such that 0.20 ≦ a ≦ 1.20, 0.70 ≦ x <1.00, 0 <y ≦ 0. It is a value within the range of 20, 0 <z ≦ 0.10 and x + y + z = 1. The positive electrode active material according to claim 1, wherein an average particle diameter of the BaTiO ₃ particles is 20 nm or more and 150 nm or less. The positive electrode active material according to claim 1, wherein a coating area of the BaTiO ₃ particles is 10% or more and 40% or less with respect to a surface area of the positive electrode active material particles. The positive electrode active material according to any one of claims 1 to 3, wherein the relative dielectric constant of the BaTiO ₃ particles is 400 or more and 1,500 or less.   The positive electrode for nonaqueous electrolyte secondary batteries containing the positive electrode active material material of any one of Claims 1-4.   A non-aqueous electrolyte secondary battery comprising the positive electrode for a non-aqueous electrolyte secondary battery according to claim 5.

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