JP5206914B2 - Positive electrode active material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for a lithium ion secondary battery containing a composite oxide containing lithium (Li) and cobalt (Co), and a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same. About.

  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. Accordingly, a secondary battery that repeats charge and discharge by using a carbon material such as coke as 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 them, lithium cobaltate or lithium nickelate is promising in terms of high potential, stability, and long life, and in particular, lithium cobaltate exhibits high potential, so energy density is improved by increasing the charging voltage. It is expected that

  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, and it is difficult to increase the charge voltage.

Conventionally, as a means for improving the stability of the positive electrode active material, a different element such as aluminum (Al), magnesium (Mg), zirconium (Zr) or titanium (Ti) is dissolved (see Patent Document 2). ), Using a mixture of a small amount of lithium nickel manganese composite oxide (see Patent Document 3), or coating the surface of lithium cobaltate with lithium manganate or nickel cobalt composite oxide having a spinel structure (Patent Document) 4 and 5) are reported.
JP 62-90863 A JP 2004-303459 A JP 2002-1003007 A JP-A-10-333573 JP-A-10-372470

  However, the technique of dissolving different elements in a solid solution has a problem that the cycle characteristics cannot be sufficiently improved if the amount of the solid solution is small, and the capacity decreases if the amount of the solid solution is large. In addition, the technology using a mixture of lithium nickel manganese composite oxide, etc., and the technology of coating with lithium manganate or nickel cobalt composite oxide cannot sufficiently improve the characteristics, and further improvement is required. It was.

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 for a lithium ion secondary battery that can increase the capacity and improve the charge / discharge efficiency, and uses the same. An object of the present invention is to provide a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery.

The positive electrode active material for a lithium ion secondary battery according to the present invention is a composite oxide particle in which a coating layer is provided on at least a part of the composite oxide particle, and the composite oxide particle has an average composition of Li _{(1 + x)} Co _{(1-y) MyO (2-z)} (where M is magnesium, aluminum, boron (B), titanium, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel) (Ni), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), tungsten (W), zirconium, yttrium (Y), niobium (Nb), calcium (Ca) and strontium (Sr) At least one of the group consisting of: x, y, and z satisfy −0.10 ≦ x ≦ 0.10, 0 ≦ y <0.50, and −0.10 ≦ z ≦ 0.20, respectively. is a value within the range.) are represented by, the coating layer, And lithium, nickel, Ri name of an oxide containing manganese, the composition ratio of nickel and manganese in the covering layer is a nickel: a molar ratio of manganese, 95: 5 to 65: Ri 35 range der of The oxide of the coating layer is composed of lithium, nickel, manganese, and oxygen, or lithium, nickel, manganese, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, cobalt (Co ), Copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium and strontium, and the content of at least one element of the group is , 30mo with respect to the sum of nickel and manganese and at least one element of the group in the coating layer 1% or less .

The positive electrode for a lithium ion secondary battery according to the present invention contains a positive electrode active material in which a coating layer is provided on at least a part of the composite oxide particles, and the composite oxide particles have an average composition of Li _{(1 + x)} Co _{(1-y) MyO (2-z)} (where M is magnesium, aluminum, boron, titanium, vanadium, chromium, manganese, iron, nickel, copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, At least one member selected from the group consisting of niobium, calcium, and strontium, and x, y, and z are −0.10 ≦ x ≦ 0.10, 0 ≦ y <0.50, and −0.10 ≦ z, respectively. The coating layer is made of an oxide containing lithium, nickel, and manganese, and the composition ratio of nickel and manganese in the coating layer is Nikke. : A molar ratio of manganese, 95: 5 to 65: Ri 35 range der of the oxide of the coating layer is composed of a lithium nickel, and manganese, and oxygen, or lithium, and nickel, At least one selected from the group consisting of manganese and magnesium, aluminum, boron, titanium, vanadium, chromium, iron, cobalt (Co), copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium, and strontium And the content of at least one element in the group is 30 mol% or less based on the total of nickel and manganese in the coating layer and at least one element in the group .

A lithium ion secondary battery according to the present invention is provided with an electrolyte together with a positive electrode and a negative electrode, and the positive electrode contains a positive electrode active material in which a coating layer is provided on at least a part of the composite oxide particles. oxide particles, average composition _{Li (1 + x) Co (} 1-y) M y O (2-z) ( where, M is magnesium, aluminum, boron, titanium, vanadium, chromium, manganese, iron, nickel , Copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium, and strontium, and x, y, and z are −0.10 ≦ x ≦ 0.10, respectively. , 0 ≦ y <0.50, −0.10 ≦ z ≦ 0.20), and the coating layer is made of an oxide containing lithium, nickel, and manganese. ,this The composition ratio of nickel and manganese in Kutsugaeso is nickel: a molar ratio of manganese, 95: 5 to 65: Ri 35 range der of the oxide coating layer, lithium, nickel, and manganese, Consists of oxygen, or lithium, nickel, manganese, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, cobalt (Co), copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium And at least one element of the group consisting of calcium and strontium, and the content of at least one element of the group is at least one element of nickel and manganese in the coating layer and the group Is 30 mol% or less with respect to the total .

According to the positive electrode active material for lithium ion secondary battery of the present invention, the composite oxide particles having an average composition represented by _{Li (1 + x) Co (} 1-y) M y O (2-z), nickel a molar ratio of manganese 95: 5 to 65: a 35 range of, and consisting of lithium, nickel and manganese and oxygen, or a element such as magnesium lithium, nickel and manganese and an amount A coating layer made of an oxide containing it was provided . Thereby , the chemical stability of the positive electrode active material can be improved while taking advantage of the high capacity and high potential of the composite oxide particles. Therefore, according to the lithium ion secondary battery positive electrode and a lithium ion secondary battery of the present invention using the positive electrode active material for the lithium ion secondary battery, it is possible to obtain a high capacity, improved charge and discharge efficiency be able to.

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

  The positive electrode active material according to one embodiment of the present invention has a coating layer provided on at least a part of the composite oxide particles having an average composition represented by Chemical Formula 1. In this positive electrode active material, a high capacity and a high discharge potential can be obtained by configuring the average composition of the composite oxide particles as shown in Chemical Formula 1.

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

  x is a value in the range of −0.10 ≦ x ≦ 0.10, more preferably in the range of −0.08 ≦ x ≦ 0.08, and −0.06 ≦ x ≦ 0.06. It is more preferable if it is within the range. If it is smaller than this, the discharge capacity will be reduced, and if it is larger than this, lithium will diffuse when the coating layer is formed, and it may be difficult to control the process.

  y is a value within the range of 0 ≦ y <0.50, more preferably within the range of 0 ≦ y <0.40, and even more preferably within the range of 0 ≦ y <0.30. That is, M in Chemical Formula 1 is not an essential constituent element. Lithium cobalt oxide is preferable because it can obtain a high capacity and has a high discharge potential, and is preferable because it can improve stability if it contains M. However, if the amount of M increases, lithium cobalt oxide is preferable. This is because the above characteristics are impaired and the capacity and the discharge potential are lowered.

  z is a value in the range of −0.10 ≦ z ≦ 0.20, more preferably in the range of −0.08 ≦ z ≦ 0.18, and −0.06 ≦ z ≦ 0.16. It is more preferable if it is within the range. This is because the discharge capacity can be further increased within this range.

  A coating layer functions as a reaction suppression layer, and is comprised with the oxide containing lithium, nickel, and manganese. The composition ratio of nickel and manganese in the coating layer is preferably a molar ratio of nickel: manganese in the range of 99: 1 to 40:60, more preferably in the range of 95: 5 to 60:40. Preferably, it is more preferably in the range of 70:30 to 90:10. This is because the capacity and charge / discharge efficiency can be further improved within this range. In addition, when nickel is increased, the capacity should be improved, but when the manganese content is low, the interdiffusion between nickel contained in the coating layer and cobalt contained in the composite oxide particles increases, It is considered that the capacity and charge / discharge efficiency are thereby reduced. On the other hand, it is considered that when the manganese content is large, a phase having a small capacity is generated.

  Thus, when the molar ratio of nickel: manganese in the coating layer is in the range of 99: 1 to 40:60, the capacity per unit mass in the coating layer is about 50% of the capacity per unit mass of the composite oxide particles. %, And when the molar ratio of nickel: manganese is in the range of 95: 5 to 60:40, the capacity per unit mass in the coating layer can be reduced per unit mass of the composite oxide particles. It can be almost equal to or greater than the capacity. That is, according to this positive electrode active material, charge / discharge efficiency can be improved by the coating layer while suppressing a decrease in capacity due to the provision of the coating layer.

  The oxide of the covering layer further includes magnesium, aluminum, boron, titanium, vanadium, chromium, iron, cobalt, copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium and strontium. May be contained as a constituent element. This is because the stability of the positive electrode active material can be further improved and the diffusibility of lithium ions can be further improved. In this case, the total content of these elements is preferably 40 mol% or less, more preferably 30 mol% or less, and more preferably 20 mol% or less with respect to the total of nickel, manganese and these elements in the coating layer. If it is more preferable. This is because when the content of these elements increases, the amount of occlusion of lithium decreases and the capacity of the positive electrode active material decreases. Note that these elements may or may not be dissolved in the oxide.

  The amount of the coating layer is preferably in the range of 0.5% by mass or more and 50% by mass or less of the composite oxide particles, more preferably in the range of 1.0% by mass or more and 40% by mass or less. More preferably, it is in the range of 0.0 mass% or more and 35 mass% or less. This is because when the amount of the coating layer is large, the capacity decreases, and when the amount is small, the stability cannot be sufficiently improved.

  Note that the coating layer means a region until the change in concentration of nickel and manganese is substantially not seen when the change in concentration of nickel and manganese is examined from the surface to the inside of the positive electrode active material. Concentration change from the surface of nickel and manganese in the positive electrode active material toward the inside, for example, while the positive electrode active material is scraped by sputtering or the like, the composition thereof is Auger Electron Spectroscopy (AES) or SIMS (Secondary Ion Mass Spectrometry; Secondary ion mass spectrometry). It is also possible to slowly dissolve the positive electrode active material in an acidic solution or the like, and to measure the time change of the eluted portion by inductively coupled plasma (ICP) spectroscopic analysis or the like.

  The average particle diameter of the positive electrode active material is preferably in the range of 2.0 μm to 50 μm. If the thickness is less than 2.0 μm, the positive electrode active material is easily peeled off from the positive electrode current collector in the pressing step when the positive electrode is produced, and the surface area of the positive electrode active material is increased, so that a conductive agent or a binder is added. This is because the amount must be increased, and the energy density per unit mass becomes small. On the other hand, when the thickness exceeds 50 μm, there is a high possibility that the positive electrode active material penetrates the separator and causes a short circuit.

  The positive electrode active material is obtained, for example, by forming a precursor layer of a coating layer on the above-described composite oxide particles and firing at a temperature of 300 ° C. to 1000 ° C. in an oxidizing atmosphere such as air or pure oxygen. be able to. As a material for the precursor layer, a material that can be converted into an oxide by firing such as hydroxide, carbonate or nitrate containing an element constituting the coating layer can be used, and the oxide or coating layer constituting the coating layer can be used. A plurality of oxides containing the element to be used may be used. Further, the precursor layer can be applied by, for example, using a ball mill, a jet mill, a pulverizer or a fine powder pulverizer, and pulverizing and mixing the composite oxide particles and the material of the precursor layer. A dispersion medium such as water or a solvent may be used. Alternatively, it may be deposited by a mechanochemical treatment such as mechanofusion, or a vapor phase method such as sputtering or chemical vapor deposition (CVD), or a precursor layer of hydroxide by a neutralization titration method. You may make it adhere. In addition, after forming a coating layer, you may adjust a particle size by performing a light grinding | pulverization or classification operation as needed.

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

(First secondary battery)
FIG. 1 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. 2 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-dikilolane, diethyl ether, sulfolane, methylsulfolane, propionitrile, anisole, acetate, butyrate, 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. Lithium salts include 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) when the secondary battery is fully charged may be 4.20V, but 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. 1 and 2 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. 3 shows 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. 4 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. 3 and 4 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 obtain a polymer compound, thereby forming the 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.

  Thus, according to the present embodiment, since the cathode active material provided with a coating layer made of an oxide having a nickel: manganese molar ratio of 99: 1 to 40:60 is used for the composite oxide particles, The chemical stability can be improved while taking advantage of the high capacity and high potential of the composite oxide particles. Therefore, high capacity can be obtained and cycle characteristics can be improved.

  Further, specific embodiments of the present invention will be described in detail.

A positive electrode active material was prepared as follows. First, 20 parts by mass of composite oxide particles having an average composition of Li _1.03 Co _0.98 Al _0.01 Mg _0.01 O _2.02 and an average particle diameter of 13 μm measured by a laser scattering method were added at 80 ° C., 2N aqueous lithium hydroxide solution 300 The mixture was stirred and dispersed in parts by mass for 2 hours. Then, commercially available reagents such as nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O) and manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O), or one of them, Ni _v Mn _{(1-v )} Weighed so as to be 5% by mass of the composite oxide particles in terms of O ₂ , dissolved in pure water, dropped into the dispersion solution of the composite oxide particles, and stirred at 80 ° C. for 3 hours. did. At that time, the molar ratio of nickel: manganese was changed within the range of 0: 100 to 100: 0.

  Subsequently, the dispersion solution was filtered and washed, and dried at 120 ° C., thereby forming a hydroxide precursor layer on the surface of the composite oxide particles. Next, 10 parts by mass of this precursor sample was impregnated with 2 parts by mass of a 2N aqueous lithium hydroxide solution, mixed and dried, and then heated at a rate of 5 ° C / min, a heating temperature of 950 ° C, and a holding time of 8 hours. Then, a heat treatment was performed to form a coating layer. About the obtained positive electrode active material, the density | concentration change which goes to the inside from the surface of nickel and manganese was investigated by the time-of-flight type secondary ion mass spectrometer (TOF-SIMS analyzer), sputtering with an ion beam. As a result, the contents of nickel and manganese rapidly decreased from the surface to the inside, and were below the detection limit at a depth of 300 nm or more. That is, it was confirmed that a coating layer containing nickel and manganese was formed on the surface of the composite oxide particle.

  Next, a coin-type secondary battery shown in FIG. 5 was produced using these produced positive electrode active materials, and the characteristics were evaluated. This secondary battery is formed by laminating a positive electrode 51 and a negative electrode 52 via a separator 53 impregnated with an electrolytic solution, sandwiching between an outer can 54 and an outer cup 55 and caulking via a gasket 56. is there. The positive electrode 54 comprises 86% by mass of the produced positive electrode active material powder, 10% by mass of graphite as a conductive agent, and 4% by mass of polyvinylidene fluoride as a binder in N-methyl-2-pyrrolidone as a solvent. It was dispersed and applied to a positive electrode current collector 21A made of an aluminum foil, dried, compression-molded with a roll press machine to form a positive electrode active material layer 21B, and then punched into a pellet.

Also, a lithium metal foil for anode 52, using a porous polyolefin film separator 53, the electrolyte, LiPF the ethylene carbonate and ethylmethyl carbonate mixed solvent in an equal volume, as an electrolyte salt ₆ Was dissolved so as to be 1.0 mol / l.

  The produced secondary battery was charged / discharged at 23 ° C., and the discharge capacity at the first cycle and the charge / discharge efficiency at the first cycle, that is, the ratio of the discharge capacity to the charge capacity were examined. Charging is performed at a constant current of 1 mA until the battery voltage reaches 4.45 V, and then charged at a constant voltage until the total charging time reaches 15 hours. The discharging is performed at a constant current of 1 mA. The constant current discharge was performed until the battery voltage reached 2.5 V by current. FIG. 6 shows the relationship between the molar ratio of nickel and manganese in the coating layer of the positive electrode active material, the discharge capacity, and the discharge capacity retention rate.

  As shown in FIG. 6, when the nickel content in the coating layer was increased, the discharge capacity increased and showed a tendency to decrease after showing the maximum value. In addition, the charge / discharge efficiency increased after decreasing once, and showed a tendency to decrease again after showing the maximum value.

In addition, for the secondary battery in which the above-described composite oxide particles having an average composition of Li _1.03 Co _0.98 Al _0.01 Mg _0.01 O _2.02 were used as they were as a positive electrode active material without providing a coating layer, the first cycle was performed as described above. When the discharge capacity was measured, the discharge capacity was about 174 mAh / g. That is, when the molar ratio of nickel: manganese in the coating layer is in the range of 99: 1 to 40:60, the capacity per unit mass in the coating layer is about 50% of the capacity per unit mass of the composite oxide particles. When the molar ratio of nickel: manganese is in the range of 95: 5 to 60:40, the capacity per unit mass in the coating layer is almost equal to the capacity per unit mass of the composite oxide particles. It turned out that it can be equivalent or better.

  Therefore, if the molar ratio of nickel: manganese in the coating layer is in the range of 99: 1 to 40:60, the charge / discharge efficiency is improved by the coating layer while suppressing a decrease in capacity due to the provision of the coating layer. When the molar ratio of nickel: manganese in the coating layer is within the range of 95: 5 to 60:40, and further within the range of 70:30 to 90:10, the capacity and charge / discharge efficiency are further improved. I found out that I could do it.

  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 electrolytic solution that is a liquid electrolyte or a gel electrolyte in which the electrolytic solution is held in a polymer compound has been described, but other electrolytes may be used. Also 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.

  Furthermore, although the secondary battery having a winding structure has been described in the above embodiment, the present invention can be similarly applied to a secondary battery having another structure in which the positive electrode and the negative electrode are folded or stacked. . 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 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 | wire of the winding electrode body shown in FIG. It is sectional drawing showing the structure of the secondary battery produced in the Example. It is a characteristic view showing the relationship between nickel, manganese and molar ratio in a coating layer, discharge capacity, and charging / discharging efficiency.

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, 56 ... Gasket, 20, 30 ... Winding electrode body, 21 , 33, 51 ... positive electrode, 21A, 33A, 51A ... positive electrode current collector, 21B, 33B, 51B ... positive electrode active material layer, 22, 34, 52 ... negative electrode, 22A, 34A ... negative electrode current collector, 22B, 34B ... Negative electrode active material layer, 23, 35, 53 ... 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, 54 ... exterior can, 55 ... exterior cup.

Claims (12)

A positive electrode active material for a lithium ion secondary battery in which a coating layer is provided on at least a part of the composite oxide particles,
The composite oxide particles have an average composition of _{Li (1 + x) Co (} 1-y) M y O (2-z) ( where, M is magnesium (Mg), aluminum (Al), boron (B), Titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), It is at least one member selected from the group consisting of tungsten (W), zirconium (Zr), yttrium (Y), niobium (Nb), calcium (Ca), and strontium (Sr), and x, y, and z are each − 0.10 ≦ x ≦ 0.10,0 ≦ y < 0.50, is represented by a.) a value in the range of -0.10 ≦ z ≦ 0.20,
The coating layer includes a lithium (Li), nickel, Ri name of an oxide containing manganese,
The composition ratio of nickel and manganese in the covering layer is a nickel: a molar ratio of manganese, 95: 5 to 65: Ri 35 range der of
The oxide of the coating layer is
Consisting of lithium, nickel, manganese and oxygen,
Or from lithium, nickel, manganese, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, cobalt (Co), copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium and strontium At least one element of the group, and the content of at least one element of the group is the sum of nickel and manganese in the coating layer and at least one element of the group On the other hand, the positive electrode active material for lithium ion secondary batteries which is 30 mol% or less . The composition ratio of nickel and manganese in the coating layer is nickel: a molar ratio of manganese, 90: 10 to 70: a 30 range of the positive electrode active material for a lithium ion secondary battery according to claim 1, wherein. The amount of the said coating layer is a positive electrode active material for lithium ion secondary batteries of Claim 1 which exists in the range of 0.5 mass% or more and 50 mass% or less of the said complex oxide particle. Average particle diameter in the range of 2.0μm or more 50μm or less, the positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the positive active material for a lithium ion secondary battery. Containing a positive electrode active material provided with a coating layer on at least a part of the composite oxide particles;
The composite oxide particles have an average composition of _{Li (1 + x) Co (} 1-y) M y O (2-z) ( where, M is magnesium (Mg), aluminum (Al), boron (B), Titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), It is at least one member selected from the group consisting of tungsten (W), zirconium (Zr), yttrium (Y), niobium (Nb), calcium (Ca), and strontium (Sr), and x, y, and z are each − 0.10 ≦ x ≦ 0.10, 0 ≦ y <0.50, and −0.10 ≦ z ≦ 0.20.)
The coating layer is made of an oxide containing lithium (Li), nickel, and manganese,
The composition ratio of nickel and manganese in the covering layer is a nickel: a molar ratio of manganese, 95: 5 to 65: Ri 35 range der of
The oxide of the coating layer is
Consisting of lithium, nickel, manganese and oxygen,
Or from lithium, nickel, manganese, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, cobalt (Co), copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium and strontium At least one element of the group, and the content of at least one element of the group is the sum of nickel and manganese in the coating layer and at least one element of the group On the other hand, the positive electrode for lithium ion secondary batteries which is 30 mol% or less . The composition ratio of nickel and manganese in the coating layer is nickel: a molar ratio of manganese, 90: 10 to 70: a 30 range of the lithium ion secondary battery positive electrode according to claim 5, wherein. The amount of the said coating layer is a positive electrode for lithium ion secondary batteries of Claim 5 which exists in the range of 0.5 mass% or more and 50 mass% or less of the said complex oxide particle. The positive electrode for a lithium ion secondary battery according to claim 5 , wherein an average particle diameter of the positive electrode active material is in a range of 2.0 μm or more and 50 μm or less. A cathode and an anode, e Bei electrolyte,
The positive electrode contains a positive electrode active material in which a coating layer is provided on at least a part of the composite oxide particles,
The composite oxide particles have an average composition of _{Li (1 + x) Co (} 1-y) M y O (2-z) ( where, M is magnesium (Mg), aluminum (Al), boron (B), Titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), It is at least one member selected from the group consisting of tungsten (W), zirconium (Zr), yttrium (Y), niobium (Nb), calcium (Ca), and strontium (Sr), and x, y, and z are each − 0.10 ≦ x ≦ 0.10, 0 ≦ y <0.50, and −0.10 ≦ z ≦ 0.20.)
The coating layer is made of an oxide containing lithium (Li), nickel, and manganese,
The composition ratio of nickel and manganese in the covering layer is a nickel: a molar ratio of manganese, 95: 5 to 65: Ri 35 range der of
The oxide of the coating layer is
Consisting of lithium, nickel, manganese and oxygen,
Or from lithium, nickel, manganese, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, cobalt (Co), copper, zinc, molybdenum, tin, tungsten, zirconium, yttrium, niobium, calcium and strontium At least one element of the group, and the content of at least one element of the group is the sum of nickel and manganese in the coating layer and at least one element of the group On the other hand, the lithium ion secondary battery which is 30 mol% or less . The composition ratio of nickel and manganese in the coating layer is nickel: a molar ratio of manganese, 90: 10 to 70: a 30 range of the lithium ion secondary battery according to claim 9, wherein. Wherein the amount of the coating layer, said a composite oxide in the range of 0.5 wt% to 50 wt% of the particles, the lithium ion secondary battery of claim 9. The lithium ion secondary battery according to claim 9 , wherein an average particle diameter of the positive electrode active material is in a range of 2.0 μm to 50 μm.

Images