JP2007048711A - Anode active material, manufacturing method of the same, and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode active material of which chemical stability can be further improved, and manufacturing method of the same, and a battery. <P>SOLUTION: A coated layer containing at least either one of Ni or Mn is formed on Co-containing compound not containing Li (step S110), afterwards, mixed with Li compound and heat treatment is applied (step S120). By this, the surface of particles of the positive electrode active material can be covered more homogeneously with a stable complex oxide containing at least either one of Ni or Mn. Moreover, it can be synthesized by one time of heat-treatment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a positive electrode active material comprising composite oxide particles containing lithium (Li) and cobalt (Co), a method for producing the same, and a battery using the same.

  In recent years, with the widespread use of portable devices such as video cameras or laptop computers, the demand for small, high-capacity secondary batteries has increased. Currently used secondary batteries include nickel-cadmium batteries using an alkaline electrolyte, but the battery voltage is as low as 1.2 V, and it is difficult to improve the energy density. Therefore, development of a so-called lithium metal secondary battery using lithium metal having a specific gravity of 0.534, which is the lightest among solid solids, has a very low potential, and has the largest current capacity per unit mass among metal anode materials. Has been studied. However, the lithium metal secondary battery has a problem that lithium is dendriticly grown on the negative electrode with charge / discharge and cycle characteristics are deteriorated or an internal short circuit is caused by breaking through the separator. Therefore, a secondary battery that repeats charge and discharge by using a carbon material such as coke for the negative electrode and occludes and releases alkali metal ions has been developed, and deterioration of the negative electrode due to charge and discharge has been improved (for example, Patent Document 1). reference).

  On the other hand, transition metal chalcogenides containing alkali metals are known as positive electrode active materials that can obtain a battery voltage of around 4V. Among these, composite oxides such as lithium cobaltate or lithium nickelate are promising in terms of high potential, stability, and long life. In particular, lithium cobaltate exhibits high potential, so by increasing the charging voltage. It is expected to improve the energy density.

  However, when the charging voltage is increased, the oxidizing atmosphere in the vicinity of the positive electrode becomes strong, and there is a problem that the electrolyte is likely to be deteriorated by oxidative decomposition or cobalt is easily eluted from the positive electrode. As a result, the charge / discharge efficiency is lowered, the cycle characteristics are lowered, the high temperature characteristics are lowered, and it is difficult to increase the charge voltage.

Conventionally, as a means for improving the stability of the positive electrode active material, it is known to form a coating layer on the surface of the composite oxide particles. As a method for forming a coating layer, a method is known in which a metal oxide is deposited on the surface of a lithium cobalt composite oxide by dry mixing and heat-treated (see, for example, Patent Document 2).
JP 62-90863 A JP 2003-221234 A

  However, in order to increase the charging voltage, it is necessary to further improve the chemical stability, and further improvement has been demanded.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a positive electrode active material capable of further improving chemical stability, a method for producing the same, and a battery.

The positive electrode active material according to the present invention is in the form of particles whose average composition is represented by chemical formula 1, and includes cobalt-containing compound particles containing cobalt and not containing lithium, of nickel (Ni) and manganese (Mn). It is obtained by forming a coating layer containing at least one and then heat-mixing with a lithium compound, and at least one of nickel and manganese is more concentrated in the particle surface layer than inside the particle. It is expensive.
(Chemical formula 1)
_{Li (1 + a) Co (} 1-xyz) Ni x Mn y M z O (2-b) F c
(In chemical formula 1, M is magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn ), Molybdenum (Mo), tin (Sn), tungsten (W), zirconium (Zr), yttrium (Y), niobium (Nb), calcium (Ca) and strontium (Sr) X, y, and z are values within the ranges of 0 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, and 0 ≦ z ≦ 0.10, and at least one of x and y is zero. And a, b, and c are values in the ranges of −0.10 ≦ a ≦ 0.10, −0.10 ≦ b ≦ 0.20, and 0 ≦ c ≦ 0.10, respectively.

A method for producing a positive electrode active material according to the present invention is a method for producing a particulate positive electrode active material having an average composition represented by chemical formula 1, wherein cobalt-containing compound particles containing cobalt and not containing lithium are mixed with nickel and manganese. And forming a coating layer containing at least one of the above, followed by heat treatment by mixing with a lithium compound.
(Chemical formula 1)
_{Li (1 + a) Co (} 1-xyz) Ni x Mn y M z O (2-b) F c
(In Chemical Formula 1, M is at least one member selected from the group consisting of magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium, and strontium. X, y, and z are values within the ranges of 0 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, and 0 ≦ z ≦ 0.10, respectively, and at least one of x and y is less than zero. A, b, and c are values in the ranges of -0.10≤a≤0.10, -0.10≤b≤0.20, and 0≤c≤0.10, respectively.)

A battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, the positive electrode contains a particulate positive electrode active material having an average composition represented by Chemical Formula 1, and the positive electrode active material contains cobalt. It is obtained by forming a coating layer containing at least one of nickel and manganese on cobalt-containing compound particles not containing lithium, and then mixing and heat-treating with a lithium compound. The concentration of at least one of manganese is higher in the particle surface layer than in the particles.
(Chemical formula 1)
_{Li (1 + a) Co (} 1-xyz) Ni x Mn y M z O (2-b) F c
(In Chemical Formula 1, M is at least one member selected from the group consisting of magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium, and strontium. X, y, and z are values within the ranges of 0 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, and 0 ≦ z ≦ 0.10, respectively, and at least one of x and y is less than zero. A, b, and c are values in the ranges of -0.10≤a≤0.10, -0.10≤b≤0.20, and 0≤c≤0.10, respectively.)

  According to the positive electrode active material and the method for producing the same of the present invention, since the coating layer is formed on the cobalt-containing compound particles and then mixed with the lithium compound and heat-treated, at least one of nickel and manganese is coated on the particle surface. It can be uniformly covered with the stable complex oxide. Therefore, the capacity can be increased and the chemical stability can be further improved. Therefore, according to the battery of the present invention using this positive electrode active material, a high capacity can be obtained and the charge / discharge efficiency can be improved. Further, the positive electrode active material can be manufactured by a single heat treatment, so that the manufacturing process can be simplified and the manufacturing cost can be reduced.

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

  The positive electrode active material according to an embodiment of the present invention is a particulate material having an average composition represented by Chemical Formula 1, and at least one of nickel and manganese has a concentration in the particle surface layer that is higher than that in the particle. Is higher. This is because a composite oxide containing at least one of nickel and manganese has high chemical stability and contributes to charge / discharge, but the capacity is lowered when it is uniformly dissolved into the inside of the particles.

(Chemical formula 1)
_{Li (1 + a) Co (} 1-xyz) Ni x Mn y M z O (2-b) F c
In Chemical Formula 1, M is at least one member selected from the group consisting of magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium, and strontium. .

  x and y are values within the range of 0 ≦ x ≦ 0.30 and 0 ≦ y ≦ 0.30, respectively, and at least one of x and y is greater than zero. By including at least one of nickel and manganese, the chemical stability can be improved. On the other hand, if the content increases, the capacity decreases.

  z is a value within the range of 0 ≦ z ≦ 0.10, and the element M may or may not be included. By including the element M, the crystal structure can be stabilized and chemical stability or thermal stability can be improved, but the capacity decreases as the content increases.

  a and b are values in the range of −0.10 ≦ a ≦ 0.10 and −0.10 ≦ b ≦ 0.20, respectively. This is because a high capacity can be obtained within these ranges. C is in the range of 0 ≦ c ≦ 0.10, and fluorine (F) may or may not be included. This is because the chemical stability can be further improved by containing fluorine, but the capacity decreases as the content increases.

The average particle size of the positive electrode active material is preferably in the range of 1.0 μm or more and less than 50 μm. If the thickness is less than 1.0 μm, the filling property of the positive electrode active material is deteriorated and the capacity is reduced, and if it is 50 μm or more, the load characteristics are deteriorated. The specific surface area of the positive electrode active material is preferably in the range of less than 0.1 m ² / g or more 3m ² / g. If it is less than 0.1 m ² / g, it is difficult to obtain sufficient load characteristics, and if it is 3 m ² / g or more, the thermal stability is lowered.

  Further, the positive electrode active material is obtained by forming a coating layer containing at least one of nickel and manganese on cobalt-containing compound particles containing cobalt and not containing lithium, and then mixing and heat-treating with the lithium compound. It is a thing. Thereby, in this positive electrode active material, the particle surface can be uniformly covered with a stable composite oxide containing at least one of nickel and manganese, and the chemical stability can be further improved. Yes.

  FIG. 1 shows a process of one manufacturing method of this positive electrode active material. First, a coating layer containing at least one of nickel and manganese is formed on cobalt-containing compound particles that contain cobalt and do not contain lithium (step S110).

  For the cobalt-containing compound particles, it is preferable to use at least one selected from the group consisting of hydroxides, oxides and oxyhydroxides. This is because a positive electrode active material with few impurities can be synthesized, crystallinity can be improved more than other compounds such as carbonates, and higher characteristics can be obtained. In addition to cobalt, the cobalt-containing compound particles may include those containing at least one selected from the group consisting of manganese, nickel, and element M shown in Chemical Formula 1. This is because the crystal structure can be stabilized as described above. Such cobalt-containing compound particles can be synthesized by a coprecipitation method or the like. The average particle size of the cobalt-containing compound particles is preferably 0.5 μm or more and 50 μm or less. Thereby, the average particle diameter of the positive electrode active material can be within the preferable range described above.

  The coating layer is preferably formed of at least one selected from the group consisting of hydroxide and oxyhydroxide. This is because a uniform film can be easily formed. The covering layer may also be formed so as to include at least one of the group consisting of cobalt and the element M shown in Chemical Formula 1 in addition to at least one of nickel and manganese.

  The coating layer is preferably formed in an alkaline aqueous solution containing the components of the coating layer. This is because a uniform film can be easily formed. Specifically, for example, cobalt-containing compound particles are dispersed in an alkaline aqueous solution (step S111), and an aqueous solution containing the components of the coating layer is added to the dispersion while stirring to form a coating layer (step S112). . As the alkaline aqueous solution, for example, a solution in which at least one of the group consisting of sodium hydroxide, lithium hydroxide and potassium hydroxide is dissolved is used. Among these, it is preferable to use a solution in which lithium hydroxide is dissolved. This is because contamination of impurities can be suppressed.

  The hydrogen ion exponent pH of the alkaline aqueous solution when forming the coating layer is preferably in the range of 8 or more and 14 or less. If the hydrogen ion index pH is lower than this, the manganese component is difficult to settle, and it is difficult to obtain the target composition. If the hydrogen ion index pH is higher, the amount of alkali used is increased and the production cost is reduced. It will be expensive.

  As the aqueous solution containing the components of the coating layer, for example, a solution in which at least one of nickel and manganese is dissolved in pure water is used, and when the element M shown in Chemical Formula 1 is further added, the element M A compound in which the above compound is dissolved is used.

  As the nickel compound, if it is an inorganic compound, nickel hydroxide, nickel carbonate, nickel nitrate, nickel fluoride, nickel chloride, nickel bromide, nickel iodide, nickel perchlorate, nickel bromate, nickel iodate, Examples include nickel oxide, nickel peroxide, nickel sulfide, nickel sulfate, nickel hydrogen sulfate, nickel nitride, nickel nitrite, nickel phosphate, or nickel thiocyanate. For organic compounds, nickel oxalate or nickel acetate Etc. A nickel compound may be used individually by 1 type, but 2 or more types may be mixed and used for it.

  As the manganese compound, if it is an inorganic compound, manganese hydroxide, manganese carbonate, manganese nitrate, manganese fluoride, manganese chloride, manganese bromide, manganese iodide, manganese chlorate, manganese perchlorate, manganese bromate, Examples include manganese iodate, manganese oxide, manganese phosphinate, manganese sulfide, manganese hydrogen sulfide, manganese sulfate, manganese hydrogen sulfate, manganese thiocyanate, manganese nitrite, manganese phosphate, manganese dihydrogen phosphate, or manganese hydrogen carbonate. Examples of organic compounds include manganese oxalate and manganese acetate. A manganese compound may be used individually by 1 type, but 2 or more types may be mixed and used for it.

  When adding an aqueous solution containing the components of the coating layer to the dispersion in which the cobalt-containing compound particles are dispersed, an aqueous alkaline solution may be added simultaneously to control the hydrogen ion exponent pH to be within a predetermined range. preferable. Even if the hydrogen ion exponent pH of the alkaline aqueous solution is adjusted when dispersing the cobalt-containing compound particles, if the hydrogen ion exponent pH is lowered by the addition of the aqueous solution containing the components of the coating layer, the uniformity of the coating layer is reduced. Because there are cases.

  Moreover, when adding the aqueous solution containing the component of a coating layer, you may make it add the compound which forms a complex simultaneously. This is because the formation of the coating layer can be further stabilized. The compound that forms the complex is preferably ammonia or hydrazine, and may be used as a mixture.

  Next, the cobalt-containing compound particles on which the coating layer is formed and the lithium compound are mixed and subjected to heat treatment to synthesize a positive electrode active material (step S120). Since the coating layer is formed on the cobalt-containing compound particles in this way and then synthesized with the lithium compound, the surface of the particles can be easily formed with nickel and nickel as compared with the case where the coating layer is formed after the synthesis with the lithium compound. It can be uniformly covered with a stable complex oxide containing at least one of manganese. In addition, the positive electrode active material can be manufactured by a single heat treatment.

  The lithium compound is preferably at least one selected from the group consisting of lithium hydroxide, lithium carbonate, lithium nitrate, lithium chloride and lithium fluoride. Among these, it is preferable to use lithium hydroxide or lithium carbonate because the manufacturing cost can be reduced. In addition, it is preferable to use lithium fluoride because fluorine can be added to the positive electrode active material and the stability of the positive electrode active material can be further improved. The heat treatment is preferably performed at a temperature of 700 ° C. or higher and lower than 1000 ° C. in an oxygen-containing atmosphere such as oxygen or air. This is because a good positive electrode active material can be synthesized.

  This positive electrode active material is used for a secondary battery as follows, for example.

(First secondary battery)
FIG. 2 shows a cross-sectional structure of a first secondary battery using the positive electrode active material according to the present embodiment. This secondary battery is a so-called lithium ion secondary battery in which lithium is used as an electrode reactant and the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium. This secondary battery is called a so-called cylindrical type, and is a winding in which a pair of strip-like positive electrode 21 and strip-like negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. A rotating electrode body 20 is provided. Inside the battery can 11, an electrolytic solution that is a liquid electrolyte is injected and impregnated in the separator 23. The battery can 11 is made of, for example, iron plated with nickel, and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  FIG. 3 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The cathode active material layer 21B includes, for example, a particulate cathode active material according to the present embodiment, and a conductive agent such as graphite and a binder such as polyvinylidene fluoride as necessary. Furthermore, you may contain the other 1 type, or 2 or more types of positive electrode active material.

  The negative electrode 22 has, for example, a structure in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A having a pair of opposed surfaces. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil having good electrochemical stability, electrical conductivity, and mechanical strength.

  The negative electrode active material layer 22B includes one or more negative electrode materials capable of inserting and extracting lithium as the negative electrode active material, and the positive electrode active material layer 21B as necessary. It is comprised including the binder similar to.

  In this secondary battery, the charge capacity of the negative electrode material capable of inserting and extracting lithium is larger than the charge capacity of the positive electrode 21 so that lithium metal does not deposit on the negative electrode 22 during the charge. It has become.

  Examples of the negative electrode material capable of inserting and extracting lithium include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, and fired organic polymer compounds , Carbon materials such as carbon fiber or activated carbon. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body is a carbonized material obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature, and part of it is non-graphitizable carbon or graphitizable carbon. Some are classified as: These carbon materials are preferable because the change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Further, non-graphitizable carbon is preferable because excellent cycle characteristics can be obtained. Furthermore, those having a low charge / discharge potential, specifically, those having a charge / discharge potential close to that of lithium metal are preferable because a high energy density of the battery can be easily realized.

  Examples of the negative electrode material capable of inserting and extracting lithium include materials capable of inserting and extracting lithium and containing at least one of a metal element and a metalloid element as a constituent element. . This is because a high energy density can be obtained by using such a material. In particular, the use with a carbon material is more preferable because a high energy density can be obtained and excellent cycle characteristics can be obtained. The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more of these phases. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

  Examples of metal elements or metalloid elements constituting the negative electrode material include magnesium, boron, aluminum, gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin, lead (Pb), bismuth ( Bi), cadmium (Cd), silver (Ag), zinc, hafnium (Hf), zirconium, yttrium, palladium (Pd) or platinum (Pt). These may be crystalline or amorphous.

  Among these, as the negative electrode material, a material containing a 4B group metal element or a semimetal element in the short-period type periodic table as a constituent element is preferable, and at least one of silicon and tin is particularly preferable as a constituent element. This is because silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained.

  Examples of the negative electrode material capable of inserting and extracting lithium further include other metal compounds or polymer materials. Other metal compounds include oxides such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide or tin oxide, sulfides such as nickel sulfide or molybdenum sulfide, or nitrides such as lithium nitride, Examples of the polymer material include polyacetylene and polypyrrole.

  The separator 23 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. May be. Among these, a porous film made of polyolefin is preferable because it is excellent in short-circuit preventing effect and can improve the safety of the battery due to the shutdown effect.

  The electrolytic solution includes, for example, a nonaqueous solvent such as an organic solvent and an electrolyte salt dissolved in the nonaqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, N-methylpyrrolidone, acetonitrile, N, N— Dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, propionitrile, anisole, acetate ester, butyrate ester, or A propionic acid ester is mentioned. One non-aqueous solvent may be used alone, or two or more non-aqueous solvents may be mixed and used.

As electrolyte salt, lithium salt is mentioned, for example, 1 type may be used independently, and 2 or more types may be mixed and used for it. The lithium _{salt, LiPF 6, LiBF 4, LiAsF} 6, LiClO 4, LiB (C 6 H 5) 4, LiCH 3 SO 3, LiCF 3 SO 3, LiN (SO 2 CF 3) 2, LiC (SO 2 CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, difluoro [oxolato-O, O ′] lithium borate, lithium bisoxalate borate, or LiBr.

  Note that the open circuit voltage (that is, the battery voltage) at the time of full charge of the secondary battery may be 4.20V, but it is designed to be higher than 4.20V and not lower than 4.25V and lower than 4.80V. It is preferable. The energy density can be increased by increasing the battery voltage, and according to the present embodiment, the chemical stability of the positive electrode active material is improved, so that an excellent cycle even if the battery voltage is increased. This is because characteristics can be obtained. In that case, since the amount of lithium released per unit mass increases even with the same positive electrode active material than when the battery voltage is set to 4.20 V, the amounts of the positive electrode active material and the negative electrode active material are adjusted accordingly. .

  For example, the secondary battery can be manufactured as follows.

  First, for example, the positive electrode active material layer 21B is formed on the positive electrode current collector 21A to produce the positive electrode 21. The positive electrode active material layer 21B is prepared, for example, by mixing a positive electrode active material, a conductive agent, and a binder to prepare a positive electrode mixture, and then using the positive electrode mixture in a solvent such as N-methyl-2-pyrrolidone. It is formed by dispersing to form a paste-like positive electrode mixture slurry, applying this positive electrode mixture slurry to the positive electrode current collector 21A, drying the solvent, and compression molding with a roll press or the like.

  Further, for example, the negative electrode active material layer 22B is formed on the negative electrode current collector 22A to produce the negative electrode 22. The negative electrode active material layer 22B may be formed by, for example, any one of a vapor phase method, a liquid phase method, a baking method, and coating, or a combination of two or more thereof. As the vapor phase method, for example, a physical deposition method or a chemical deposition method can be used. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a thermal CVD (Chemical Vapor Deposition) A chemical vapor deposition method) or a plasma CVD method can be used. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. As for the firing method, a known method can be used. For example, an atmosphere firing method, a reaction firing method, or a hot press firing method can be used. In the case of application, it can be formed in the same manner as the positive electrode 21.

  Subsequently, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIGS. 2 and 3 is formed.

  In this secondary battery, when charged, lithium ions are released from the positive electrode active material layer 21B, and the negative electrode material that can occlude and release lithium contained in the negative electrode active material layer 22B via the electrolytic solution. Occluded. Next, when discharging is performed, lithium ions stored in the negative electrode material capable of inserting and extracting lithium in the negative electrode active material layer 22B are released, and are inserted into the positive electrode active material layer 21B through the electrolytic solution. . In this embodiment, since the positive electrode active material described above is used, the chemical stability of the positive electrode 21 is high, and even if the open circuit voltage during full charge is increased, the positive electrode 21 and the electrolyte are deteriorated. The reaction is suppressed.

(Secondary secondary battery)
FIG. 4 illustrates a configuration of a second secondary battery using the positive electrode active material according to the present embodiment. In this secondary battery, a wound electrode body 30 to which a positive electrode lead 31 and a negative electrode lead 32 are attached is accommodated in a film-like exterior member 40, and can be reduced in size, weight, and thickness. ing.

  The positive electrode lead 31 and the negative electrode lead 32 are led out from the inside of the exterior member 40 to the outside, for example, in the same direction. The positive electrode lead 31 and the negative electrode lead 32 are each made of a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior member 40 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. For example, the exterior member 40 is disposed so that the polyethylene film side and the wound electrode body 30 face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesive film 41 is inserted between the exterior member 40 and the positive electrode lead 31 and the negative electrode lead 32 to prevent intrusion of outside air. The adhesion film 41 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 5 shows a cross-sectional structure taken along line II of the spirally wound electrode body 30 shown in FIG. The wound electrode body 30 is obtained by stacking and winding a positive electrode 33 and a negative electrode 34 with a separator 35 and an electrolyte layer 36 interposed therebetween, and the outermost peripheral portion is protected by a protective tape 37.

  The positive electrode 33 has a structure in which a positive electrode active material layer 33B is provided on both surfaces of a positive electrode current collector 33A, and the negative electrode 34 has a structure in which a negative electrode active material layer 34B is provided on both surfaces of the negative electrode current collector 34A. have. The configurations of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, the negative electrode active material layer 34B, and the separator 35 are respectively the positive electrode current collector 21A, the positive electrode active material layer 21B, and the negative electrode current collector 22A. The same as the negative electrode active material layer 22B and the separator 23.

  The electrolyte layer 36 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 36 is preferable because high ion conductivity can be obtained and liquid leakage can be prevented. The configuration of the electrolytic solution is the same as that of the first secondary battery. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, from the viewpoint of electrochemical stability, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable.

  For example, the secondary battery can be manufactured as follows.

  First, after the positive electrode 33 and the negative electrode 34 are manufactured in the same manner as the first secondary battery, a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 33 and the negative electrode 34. Then, the mixed solvent is volatilized to form the electrolyte layer 36. After that, the positive electrode lead 31 is attached to the positive electrode current collector 33A, and the negative electrode lead 32 is attached to the negative electrode current collector 34A. Next, the positive electrode 33 and the negative electrode 34 on which the electrolyte layer 36 is formed are laminated via a separator 35 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and a protective tape 37 is adhered to the outermost peripheral portion. Thus, the wound electrode body 30 is formed. Finally, for example, the wound electrode body 30 is sandwiched between the exterior members 40, and the outer edges of the exterior members 40 are sealed and sealed by heat fusion or the like. At that time, the adhesion film 41 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 4 and 5 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 33 and the negative electrode 34 are prepared as described above, and after the positive electrode lead 31 and the negative electrode lead 32 are attached to the positive electrode 33 and the negative electrode 34, the positive electrode 33 and the negative electrode 34 are stacked via the separator 35 and wound. Rotate and adhere the protective tape 37 to the outermost periphery to form a wound body that is a precursor of the wound electrode body 30. Next, the wound body is sandwiched between the exterior members 40, and the outer peripheral edge portion excluding one side is heat-sealed to form a bag shape, and is stored inside the exterior member 40. Subsequently, an electrolyte composition containing an electrolytic solution, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as required is injected into the exterior member 40. The opening of the exterior member 40 is sealed. Thereafter, heat is applied to polymerize the monomer to form a polymer compound, thereby forming a gel electrolyte layer 36, and assembling the secondary battery shown in FIGS.

  This secondary battery operates in the same manner as the first secondary battery.

  As described above, according to the present embodiment, since the coating layer is formed on the cobalt-containing compound particles and then mixed with the lithium compound and heat-treated, the particle surface is stable including at least one of nickel and manganese. It can be uniformly covered with the composite oxide. Therefore, chemical stability can be improved, high capacity can be obtained, and charge / discharge efficiency can be improved. Further, the positive electrode active material can be manufactured by a single heat treatment, so that the manufacturing process can be simplified and the manufacturing cost can be reduced.

  In particular, if at least one member selected from the group consisting of hydroxides, oxides and oxyhydroxides is used as the cobalt-containing compound particles, a positive electrode active material with few impurities can be synthesized, and carbonic acid can be synthesized. Crystallinity can be improved more than other compounds such as salts, and higher characteristics can be obtained.

  Moreover, if the coating layer is formed of at least one selected from the group consisting of hydroxide and oxyhydroxide, a more uniform film can be easily formed.

  Further, specific embodiments of the present invention will be described in detail with reference to the drawings.

(Examples 1-1 to 1-10)
As Examples 1-1 to 1-10 and Comparative Examples 1-1 and 1-2 corresponding thereto, positive electrode active materials were prepared as follows.

  In Example 1-1, first, commercially available cobalt hydroxide having an average particle diameter of 7.2 μm as measured by the laser scattering method is prepared as the cobalt-containing compound particles, and the temperature is set to a slurry concentration of 200 g / l. It was dispersed in an aqueous solution of sodium hydroxide having a hydrogen ion index of pH 10.5 at 50 ° C. (Step S111; see FIG. 1). Next, while stirring the dispersion in a nitrogen stream, an aqueous sulfate solution having an atomic ratio of nickel to manganese of 1: 1 and a metal salt concentration of 1.5 mol / l, an aqueous ammonia solution of 25% by mass, Is continuously dropped at a constant flow rate, and a 25% by mass aqueous sodium hydroxide solution is dropped intermittently so that the hydrogen ion exponent pH of the dispersion is maintained between 10.5 and 11.0. A coating layer made of nickel and manganese hydroxide was formed (step S112; see FIG. 1).

  Thereafter, the slurry was filtered, washed, and vacuum dried at 70 ° C. When the obtained powder was dissolved in hydrochloric acid and the composition was examined by inductively coupled plasma (ICP) spectroscopy, it was found that Co: Ni: Mn = 90: 5: 5 and the desired atomic ratio. confirmed. In addition, the particle size distribution was measured by the laser scattering method, and almost the same distribution as the cobalt hydroxide used was observed. Further, when the particle surface was qualitatively analyzed using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDX), cobalt, nickel and manganese were analyzed. Were uniformly distributed, and no portion where nickel or manganese was liberated was observed. In addition, the obtained powder was embedded in an epoxy resin, and a cross section of the particle was cut out using a microtome, and then qualitative analysis was performed. As a result, nickel and manganese existed to cover the surface of the cobalt hydroxide particles. It was confirmed.

  Subsequently, the cobalt-containing compound particles that formed the coating layer and commercially available lithium hydroxide were mixed so that the atomic ratio of the metal element was Li / (Ni + Co + Mn) = 1.05, and 950 in an air stream. After calcining at 0 ° C. for 8 hours, the mixture was pulverized and sieved to obtain a positive electrode active material.

  When the obtained positive electrode active material was dissolved in hydrochloric acid and the composition was examined by ICP spectroscopy, Li: Co: Ni: Mn = 1.05: 0.90: 0.05: 0.05 and the desired atomic ratio It turns out that. Further, the particle size distribution was measured by a laser scattering method, and the average particle size was 9.5 μm. Furthermore, when observed by SEM, a granular pattern was seen uniformly on the entire surface of the particles of about 10 μm. Further, when the positive electrode active material was embedded in an epoxy resin and a particle cross section was cut out using a microtome, qualitative analysis was performed. As a result, nickel and manganese were detected in a high concentration near the surface. In addition, the element composition ratio on the particle surface was examined by X-ray photoelectron spectroscopy (XPS) (X-ray source; monochromatic Al-Kα ray, beam diameter 100 μm, step size 0.2 eV). The atomic ratio of Co: Ni: Mn was 75:12:13. That is, it was found that the concentrations of nickel and manganese were higher on the particle surface than inside the particle.

In Example 1-2, a positive electrode active material was produced in the same manner as in Example 1-1 except that synthetic cobalt hydroxide was used in place of commercially available cobalt hydroxide as the cobalt-containing compound particles. did. Cobalt hydroxide is continuously added dropwise to a sodium hydroxide aqueous solution having a hydrogen ion exponent of pH 10.5 while stirring with a 1 mol / l cobalt sulfate aqueous solution and a 25% by mass ammonia aqueous solution at a constant flow rate. % Aqueous sodium hydroxide solution was dropped intermittently to maintain the hydrogen ion exponent pH between 10.5 and 11.0 while reacting at 50 ° C., followed by filtration, washing with water, and vacuum at 70 ° C. It was produced by drying. When the obtained powder was analyzed by X-ray diffraction, it was confirmed that it coincided with the pattern of Co (OH) ₂ . Further, when the particle size distribution was measured by a laser scattering method, the average particle size was 12 μm, which was a distribution close to a normal distribution.

  The composition of the positive electrode active material of Example 1-2 was examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn = 1.05: 0.90: 0.05: 0.05 Of atomic ratio. Similarly, the particle size distribution was measured, and the average particle size was 12.3 μm. Further, when the elemental composition ratio on the particle surface was examined by XPS in the same manner, the atomic ratio of Co: Ni: Mn was 77: 9: 14. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  In Example 1-3, cobalt hydroxide produced in the same manner as in Example 1-2 was used as the cobalt-containing compound particles, and the atomic ratio was Co: Ni: Mn = 95: 2.5: 2.5. A positive electrode active material was prepared in the same manner as in Example 1-1 except that a coating layer made of nickel and manganese hydroxide was formed.

  The composition of the positive electrode active material of Example 1-3 was also examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn = 1.05: 0.95: 0.025: 0.025 Of atomic ratio. Similarly, when the elemental composition ratio on the particle surface was examined by XPS, the atomic ratio of Co: Ni: Mn was 79: 9: 12. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  In Example 1-4, cobalt hydroxide produced in the same manner as in Example 1-2 was used as the cobalt-containing compound particles, and the atomic ratio was Co: Ni: Mn = 75: 12.5: 12.5. A positive electrode active material was prepared in the same manner as in Example 1-1 except that a coating layer made of nickel and manganese hydroxide was formed.

  The composition of the positive electrode active material of Example 1-4 was examined in the same manner as in Example 1-1. Li: Co: Ni: Mn = 1.05: 0.75: 0.125: 0.125 Of atomic ratio. Similarly, when the elemental composition ratio on the particle surface was examined by XPS, the atomic ratio of Co: Ni: Mn was 58:20:22. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  In Example 1-5, cobalt hydroxide produced in the same manner as in Example 1-2 was used as the cobalt-containing compound particles, and nickel was used so as to have an atomic ratio of Co: Ni: Mn = 90: 7: 3. A positive electrode active material was produced in the same manner as in Example 1-1 except that a coating layer made of manganese hydroxide was formed.

  The composition of the positive electrode active material of Example 1-5 was examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn = 1.05: 0.90: 0.07: 0.03 Of atomic ratio. Similarly, when the elemental composition ratio on the particle surface was examined by XPS, the atomic ratio of Co: Ni: Mn was 67:15:18. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  In Example 1-6, cobalt hydroxide produced in the same manner as in Example 1-2 was used as the cobalt-containing compound particles, and nickel was used so as to have an atomic ratio of Co: Ni: Mn = 90: 4: 6. A positive electrode active material was produced in the same manner as in Example 1-1 except that a coating layer made of manganese hydroxide was formed.

  The composition of the positive electrode active material of Example 1-6 was examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn = 1.05: 0.90: 0.04: 0.06 Of atomic ratio. Similarly, when the elemental composition ratio on the particle surface was examined by XPS, the atomic ratio of Co: Ni: Mn was 55:20:25. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  In Example 1-7, a positive electrode active material was produced in the same manner as in Example 1-1 except that synthesized magnesium solid solution cobalt hydroxide was used as the cobalt-containing compound particles. Magnesium solid solution cobalt hydroxide is mixed with a sodium hydroxide aqueous solution having a hydrogen ion exponent of pH 10.5 with stirring, an aqueous sulfate solution having an atomic ratio of cobalt to magnesium of 99: 1 and a metal salt concentration of 1 mol / l. 25% by mass of ammonia aqueous solution is continuously dropped at a constant flow rate, and 25% by mass of sodium hydroxide aqueous solution is intermittently dropped to adjust the hydrogen ion exponent pH between 10.5 and 11.0. While maintaining, the reaction was carried out at 50 ° C., followed by filtration, washing with water, and vacuum drying at 70 ° C.

  The composition of the positive electrode active material of Example 1-7 was examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn: Mg = 1.05: 0.89: 0.05: 0 .05: 0.01 atomic ratio. Similarly, when the elemental composition ratio on the particle surface was examined by XPS, the atomic ratio of Co: Ni: Mn was 50:23:27. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  In Example 1-8, a positive electrode active material was produced in the same manner as in Example 1-1 except that synthesized aluminum solid solution cobalt hydroxide was used as the cobalt-containing compound particles. The aluminum solid solution cobalt hydroxide is stirred in a sodium hydroxide aqueous solution having a hydrogen ion index of pH 8, while stirring, an aqueous sulfate solution having an atomic ratio of cobalt to aluminum of 99: 1 and a metal salt concentration of 1 mol / l; While continuously dropping a mass% aqueous ammonia solution at a constant flow rate and intermittently dropping a 25 mass% aqueous sodium hydroxide solution to maintain the hydrogen ion exponent pH between 8 and 10.0, After making it react at 50 degreeC, it filtered and washed with water, It produced by vacuum-drying at 70 degreeC.

  The composition of the positive electrode active material of Example 1-8 was examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn: Al = 1.05: 0.89: 0.05: 0 .05: 0.01 atomic ratio. Similarly, when the elemental composition ratio on the particle surface was examined by XPS, the atomic ratio of Co: Ni: Mn was 48:22:30. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  Example 1-9 was the same as Example 1-1 except that commercially available tricobalt tetroxide having an average particle size of 6.5 μm as measured by the laser scattering method was used as the cobalt-containing compound particles. Thus, a positive electrode active material was produced.

  The composition of the positive electrode active material of Example 1-9 was also examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn = 1.05: 0.90: 0.05: 0.05 Of atomic ratio. Similarly, when the elemental composition ratio on the particle surface was examined by XPS, the atomic ratio of Co: Ni: Mn was 50:24:26. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  In Example 1-10, except that the commercially available cobalt oxyhydroxide having an average particle diameter measured by a laser scattering method of 13 μm was used as the cobalt-containing compound particles, the same as in Example 1-1. A positive electrode active material was prepared.

  The composition of the positive electrode active material of Example 1-10 was examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn = 1.05: 0.90: 0.05: 0.05 Of atomic ratio. Similarly, when the elemental composition ratio on the particle surface was examined by XPS, the atomic ratio of Co: Ni: Mn was 51:24:25. That is, it was confirmed that the concentration of nickel and manganese was higher on the particle surface than inside the particle.

  In Comparative Example 1-1, a commercially available tricobalt tetroxide having an average particle diameter measured by a laser scattering method of 6.5 μm and a commercially available lithium hydroxide are set to have an atomic ratio of Li / Co = 1.05. The mixture was baked at 950 ° C. for 8 hours in an air stream, pulverized, and sieved to prepare a positive electrode active material.

  In Comparative Example 1-2, first, a commercially available lithium cobaltate having an average particle diameter measured by a laser scattering method of 13 μm, a commercially available lithium nitrate, a commercially available nickel nitrate, and a commercially available manganese nitrate, Li: Co: Ni: Mn = 1.05: 0.90: 0.05: 0.05 is weighed so as to have an atomic ratio, and water is evaporated to dryness while stirring by adding water to obtain a solid. It was. Next, the solid was lightly pulverized, and commercial lithium hydroxide was added so that the atomic ratio of the metal element was Li / (Co + Ni + Mn) = 1.05, followed by firing at 950 ° C. for 8 hours in an air stream. The positive electrode active material was prepared by pulverizing and sieving.

  The composition of the positive electrode active material of Comparative Example 1-2 was also examined in the same manner as in Example 1-1. As a result, Li: Co: Ni: Mn = 1.05: 0.90: 0.05: 0.05 Of atomic ratio. Moreover, when observed by SEM, it was in the state where the microparticles around 1 micrometer adhered to the surface of the lithium cobalt oxide particle. Further, when the elemental composition ratio on the particle surface was examined by XPS in the same manner, the atomic ratio of Co: Ni: Mn was 92: 3: 5.

  Using the produced positive electrode active materials of Examples 1-1 to 1-10 and Comparative Examples 1-1 and 1-2, secondary batteries shown in FIGS. First, 86% by mass of the prepared positive electrode active material powder, 10% by mass of graphite as a conductive agent, and 4% by mass of polyvinylidene fluoride as a binder are mixed and dispersed in N-methyl-2-pyrrolidone as a solvent. After that, it was applied to both surfaces of a positive electrode current collector 21A made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and compression-molded to form a positive electrode active material layer 21B, whereby the positive electrode 21 was produced. Next, the positive electrode lead 25 made of aluminum was attached to the positive electrode current collector 21A.

  Further, 90% by mass of artificial graphite powder as a negative electrode active material and 10% by mass of polyvinylidene fluoride as a binder are mixed and dispersed in N-methyl-2-pyrrolidone which is a solvent. The negative electrode current collector 22A made of a foil was applied on both sides, dried, and compression molded to form a negative electrode active material layer 22B to produce a negative electrode 22. Next, a negative electrode lead 26 made of nickel was attached to the negative electrode current collector 22A. At that time, the amount of the positive electrode active material and the negative electrode active material is adjusted, the open circuit voltage at the time of full charge is 4.40 V, and the capacity of the negative electrode 22 is expressed by the capacity component due to insertion and extraction of lithium. did.

Next, the produced positive electrode 21 and negative electrode 22 were wound many times through a separator 23 made of a porous polyolefin film, to produce a wound electrode body 20. Subsequently, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15, and is stored inside the battery can 11. did. After that, by injecting an electrolyte into the battery can 11 and caulking the battery can 11 through the gasket 17, the safety valve mechanism 15, the heat sensitive resistance element 16 and the battery lid 14 are fixed, and the outer diameter is 18 mm. A cylindrical secondary battery having a height of 65 mm was obtained. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt to 1.0 mol / l in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 was used.

  The produced secondary battery was charged and discharged at 23 ° C., and the discharge capacity at the first cycle was determined as the initial capacity, and the discharge capacity retention rate at the 200th cycle relative to the first cycle was examined. Charging is performed at a constant current of 1000 mA until the battery voltage reaches 4.40 V, and then charged at a constant voltage of 4.40 V until the total charging time is 2.5 hours. The discharge was performed at a constant current of 800 mA until the battery voltage reached 2.75V. The obtained results are shown in Table 1.

  As shown in Table 1, according to Examples 1-1 to 1-10, Comparative Example 1-1 using lithium cobaltate and Comparative Example 1 in which a coating layer was formed and fired on lithium cobaltate Compared to 2, it was possible to improve the discharge capacity retention rate. In other words, if a coating layer is formed on cobalt-containing compound particles that do not contain lithium and then mixed with a lithium compound and heat-treated, the chemical stability of the positive electrode active material can be further improved and cycle characteristics improved. I found out that Moreover, it turned out that it is preferable to use any of hydroxide, oxide or oxyhydroxide for the cobalt-containing compound particles.

  Furthermore, in Examples 1-1 to 1-6 and Examples 1-7 and 1-8, Examples 1-7 and 1-8 in which the element M shown in Chemical Formula 1 is included are larger in capacity. The maintenance rate could be further improved. That is, it has been found that the capacity maintenance rate can be further improved by including the element M.

(Example 2-1)
Except that the same positive electrode active material as in Example 1-1 was used and the amounts of the positive electrode active material and the negative electrode active material were adjusted so that the open circuit voltage at the time of full charge was 4.2 V. A secondary battery was produced in the same manner as in 1-1. Moreover, as Comparative Example 2-1 for this example, the same positive electrode active material as in Comparative Example 1-1, lithium cobaltate was used as the positive electrode active material, and the open circuit voltage at the time of full charge was 4.2V. A secondary battery was fabricated in the same manner as in Example 1-1 except that the amounts of the positive electrode active material and the negative electrode active material were adjusted.

  The fabricated secondary batteries of Example 2-1 and Comparative Example 2-1 were charged and discharged in the same manner as in Example 1-1, and the initial capacity and cycle characteristics were examined. At that time, the charging voltage was 4.2V. The results are shown in Table 2 together with the results of Example 1-1 and Comparative example 1-1.

  As shown in Table 2, also in Example 2-1, the capacity retention rate could be improved as compared with Comparative Example 2-1, as in Example 1-1. However, the degree of improvement was greater in Example 1-1 where the battery voltage was 4.4V. That is, it was found that a higher effect can be obtained when the battery voltage is higher than 4.2V.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiment or example, the case of using an electrolyte solution that is a liquid electrolyte or a gel electrolyte in which an electrolyte solution is held in a polymer compound has been described. However, other electrolytes may be used. Good. Other electrolytes include, for example, a polymer electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, an inorganic solid electrolyte made of ion conductive ceramics, ion conductive glass, or ionic crystals, or a molten salt electrolyte. Or a mixture thereof.

  In the above embodiments and examples, a so-called lithium ion secondary battery in which the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium has been described. However, the present invention relates to lithium metal as the negative electrode active material. The capacity of the negative electrode used is a so-called lithium metal secondary battery whose capacity is represented by the deposition and dissolution of lithium, or the negative electrode material capable of occluding and releasing lithium is more charged than the positive electrode. The same applies to a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is expressed by the sum thereof, by reducing the capacity. be able to.

  Further, in the above embodiments and examples, the secondary battery having a winding structure has been described, but the present invention is similarly applied to a secondary battery having another structure in which the positive electrode and the negative electrode are folded or stacked. can do. In addition, the present invention can also be applied to secondary batteries having other shapes such as a so-called coin type, button type, or square type. Moreover, not only a secondary battery but a primary battery is applicable.

It is a flowchart showing the manufacturing method of the positive electrode active material which concerns on one embodiment of this invention. It is sectional drawing showing the structure of the 1st secondary battery using the positive electrode active material which concerns on one embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the secondary battery shown in FIG. It is a disassembled perspective view showing the structure of the 2nd secondary battery using the positive electrode active material which concerns on one embodiment of this invention. It is sectional drawing along the II line of the winding electrode body shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20, 30 ... Winding electrode body, 21, 33 ... Positive electrode, 21A, 33A ... Positive electrode current collector, 21B, 33B ... Positive electrode active material layer, 22, 34 ... Negative electrode, 22A, 34A ... Negative electrode current collector, 22B, 34B ... Negative electrode active material layer, 23, 35 ... Separator , 24 ... Center pin, 25, 31 ... Positive electrode lead, 26, 32 ... Negative electrode lead, 36 ... Electrolyte layer, 37 ... Protective tape, 40 ... Exterior member, 41 ... Adhesion film.

Claims (18)

A particulate positive electrode active material having an average composition represented by Chemical Formula 1,
A coating layer containing at least one of nickel (Ni) and manganese (Mn) is formed on cobalt-containing compound particles containing cobalt (Co) but not lithium (Li), and then mixed with a lithium compound and heat-treated. It was obtained by
A positive electrode active material characterized in that at least one of nickel and manganese has a higher concentration in the particle surface layer than in the particles.
(Chemical formula 1)
_{Li (1 + a) Co (} 1-xyz) Ni x Mn y M z O (2-b) F c
(In chemical formula 1, M is magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn ), Molybdenum (Mo), tin (Sn), tungsten (W), zirconium (Zr), yttrium (Y), niobium (Nb), calcium (Ca) and strontium (Sr) X, y, and z are values within the ranges of 0 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, and 0 ≦ z ≦ 0.10, and at least one of x and y is zero. And a, b, and c are values in the ranges of −0.10 ≦ a ≦ 0.10, −0.10 ≦ b ≦ 0.20, and 0 ≦ c ≦ 0.10, respectively. A method for producing a particulate positive electrode active material having an average composition represented by Chemical Formula 1,
A coating layer containing at least one of nickel (Ni) and manganese (Mn) is formed on cobalt-containing compound particles containing cobalt (Co) but not lithium (Li), and then mixed with a lithium compound and heat-treated. A process for producing a positive electrode active material comprising a step.
(Chemical formula 1)
_{Li (1 + a) Co (} 1-xyz) Ni x Mn y M z O (2-b) F c
(In chemical formula 1, M is magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn ), Molybdenum (Mo), tin (Sn), tungsten (W), zirconium (Zr), yttrium (Y), niobium (Nb), calcium (Ca) and strontium (Sr) X, y, and z are values within the ranges of 0 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, and 0 ≦ z ≦ 0.10, and at least one of x and y is zero. And a, b, and c are values in the ranges of −0.10 ≦ a ≦ 0.10, −0.10 ≦ b ≦ 0.20, and 0 ≦ c ≦ 0.10, respectively.   The method for producing a positive electrode active material according to claim 2, wherein at least one selected from the group consisting of hydroxide, oxide and oxyhydroxide is used as the cobalt-containing compound particles.   The cobalt-containing compound particles include, in addition to cobalt, magnesium, aluminum, boron, titanium, vanadium, chromium, manganese, iron, nickel, copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium, and strontium. The method for producing a positive electrode active material according to claim 2, wherein a material containing at least one member of the group is used.   The method for producing a positive electrode active material according to claim 2, wherein an average particle size of the cobalt-containing compound particles is 0.5 μm or more and 50 μm or less.   The method for producing a positive electrode active material according to claim 2, wherein the coating layer is formed of at least one selected from the group consisting of hydroxide and oxyhydroxide.   In addition to at least one of nickel and manganese, the cobalt-containing compound particles include magnesium, aluminum, boron, titanium, vanadium, chromium, iron, cobalt, copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, and niobium. The method for producing a positive electrode active material according to claim 2, wherein a coating layer containing at least one member selected from the group consisting of calcium, strontium, and calcium is formed.   The method for producing a positive electrode active material according to claim 2, wherein the coating layer is formed in an alkaline aqueous solution containing a component of the coating layer.   9. The method for producing a positive electrode active material according to claim 8, wherein the hydrogen ion exponent pH of the alkaline aqueous solution when forming the coating layer is in the range of 8 or more and 14 or less.   9. The method for producing a positive electrode active material according to claim 8, wherein the alkaline aqueous solution is prepared by dissolving at least one selected from the group consisting of sodium hydroxide, lithium hydroxide and potassium hydroxide.   The method for producing a positive electrode active material according to claim 8, wherein a compound that forms a complex is added to the alkaline aqueous solution.   The method for producing a positive electrode active material according to claim 11, wherein at least one of ammonia and hydrazine is added as a compound that forms a complex.   9. The positive electrode active material according to claim 8, wherein the coating layer is formed by dispersing the cobalt-containing compound particles in an alkaline aqueous solution and adding an aqueous solution containing the components of the coating layer to the dispersion. Manufacturing method.   14. The method for producing a positive electrode active material according to claim 13, wherein when adding the aqueous solution containing the component of the coating layer, an aqueous alkaline solution is added to control the hydrogen ion exponent pH.   3. The method for producing a positive electrode active material according to claim 2, wherein at least one selected from the group consisting of lithium hydroxide, lithium carbonate, lithium nitrate, lithium chloride, and lithium fluoride is used as the lithium compound.   The method for producing a positive electrode active material according to claim 2, wherein a temperature of the heat treatment is set to 700 ° C. or higher and lower than 1000 ° C.   The method for producing a positive electrode active material according to claim 2, wherein the heat treatment is performed in an oxygen-containing atmosphere. A battery including an electrolyte together with a positive electrode and a negative electrode,
The positive electrode contains a particulate positive electrode active material having an average composition represented by Chemical Formula 1,
The positive electrode active material is formed by forming a coating layer containing at least one of nickel (Ni) and manganese (Mn) on cobalt-containing compound particles containing cobalt (Co) and not containing lithium (Li), and then forming a lithium compound It was obtained by mixing and heat-treating with
The battery wherein the concentration of at least one of nickel and manganese in the positive electrode active material is higher in the particle surface layer than in the particles.
(Chemical formula 1)
_{Li (1 + a) Co (} 1-xyz) Ni x Mn y M z O (2-b) F c
(In chemical formula 1, M is magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn ), Molybdenum (Mo), tin (Sn), tungsten (W), zirconium (Zr), yttrium (Y), niobium (Nb), calcium (Ca) and strontium (Sr) X, y, and z are values within the ranges of 0 ≦ x ≦ 0.30, 0 ≦ y ≦ 0.30, and 0 ≦ z ≦ 0.10, and at least one of x and y is zero. And a, b, and c are values in the ranges of −0.10 ≦ a ≦ 0.10, −0.10 ≦ b ≦ 0.20, and 0 ≦ c ≦ 0.10, respectively.

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