JP2008257992A - Positive-electrode active material for nonaqueous electrolyte secondary battery, its manufacturing method, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive-electrode active material for a nonaqueous electrolyte secondary battery that can be stably manufactured, has a high initial discharge capacity, high safety, and excellent cycle characteristics, its manufacturing method, and a nonaqueous electrolyte secondary battery using the positive-electrode active material for a positive electrode. <P>SOLUTION: It is possible to obtain the following positive-electrode active material for a nonaqueous electrolyte secondary battery. The positive-electrode active material is expressed by formula of [Li]<SB>3a</SB>[Ni<SB>x</SB>Co<SB>y</SB>Mn<SB>z</SB>]<SB>3b</SB>[O<SB>2</SB>]<SB>6c</SB>(where, suffixes following the [] denote sites and formula satisfies conditions that x=z, x+y+z=1, 0.3≤x≤0.45, 0.1≤y≤0.4, and 0.3≤z≤0.45). The positive-electrode active material is a hexagonal lithium-nickel-cobalt-manganese composite oxide having a layer structure. The positive-electrode active material has ≤5% of a site occupancy of metal ions other than nickel, cobalt, and manganese in a 3b site obtained from the Rietveld analysis of an X-ray diffraction pattern. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery using the same for a positive electrode. More specifically, a lithium nickel cobalt manganese composite oxide having a layered crystal structure having no heterogeneous phase, useful as a positive electrode material for lithium ion secondary batteries, and a method for producing the same, and a non-aqueous electrolyte using the same as a positive electrode The present invention relates to a secondary battery.

With the widespread use of portable devices such as mobile phones and laptop computers, small and lightweight secondary batteries with high energy density are required. As such secondary batteries, there are lithium ion secondary batteries using lithium metal, lithium alloy, metal oxide, or a material capable of detaching and inserting lithium, such as carbon, as a negative electrode, and research and development are actively performed. ing.
Also in the automobile field, demand for electric vehicles has increased due to resource and environmental problems, and lithium-ion batteries that are inexpensive, have a large capacity, and have good cycle characteristics and output characteristics as motor drive batteries for electric cars and hybrid cars. There is a need for secondary batteries.

A lithium ion secondary battery using a lithium-containing composite oxide, particularly a lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize as a positive electrode active material, has a high energy level because a high voltage of 4V is obtained. It is expected as a battery having a high density, and its practical application is progressing. In the lithium ion secondary battery using the above lithium cobalt composite oxide, many developments have been made so far to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. Yes.

However, since the lithium cobalt composite oxide uses an expensive cobalt compound as a main raw material, the cost of the active material and the battery is increased, and improvement of the active material is desired. The unit price per capacity of a battery using this lithium cobalt composite oxide is about four times as high as that of a nickel-metal hydride battery already used as a secondary battery. is there.
Therefore, reducing the cost of active materials and making it possible to manufacture cheaper lithium ion secondary batteries is not only used for small secondary batteries for portable devices, but also for power storage and electric vehicles. It is possible to expand the application to large-sized secondary batteries such as, and this is industrially significant.

Here, examples of new materials for the positive electrode active material for lithium ion secondary batteries include lithium nickel composite oxide (LiNiO ₂ ) using nickel, which is cheaper than cobalt, and lithium manganese composite oxide using manganese. Can do.

  Lithium nickel composite oxides can be expected to have higher capacity than lithium cobalt composite oxides, and because of the high battery voltage similar to lithium ion secondary batteries using lithium cobalt composite oxide as the positive electrode active material, It is actively performed.

  However, the lithium ion secondary battery using this lithium nickel composite oxide as the positive electrode active material has the following drawbacks. That is, when compared with a lithium ion secondary battery using a lithium cobalt composite oxide as a positive electrode active material, the cycle characteristics are inferior, and the battery performance is relatively impaired when used or stored in a high temperature environment. It had the disadvantage of being easy.

Lithium manganese composite oxides can be expected to be safer than lithium cobalt composite oxides, and since they exhibit a high voltage in the same way as lithium ion secondary batteries using lithium manganese composite oxides as positive electrode active materials, It is actively performed.
However, in the lithium ion secondary battery using this lithium manganese composite oxide as the positive electrode active material, manganese is dissolved in the electrolytic solution with charge / discharge, which deteriorates the charge / discharge characteristics, and further has a discharge capacity. The lithium-cobalt composite oxide had a disadvantage of 2/3.

Therefore, various proposals have been made for lithium metal composite oxides with the aim of solving these drawbacks.
For example, Japanese Laid-8-213015 discloses, for the purpose of improving the self-discharge characteristics and cycle characteristics of the lithium ion secondary _{battery, Li X Ni a Co b M} C O 2 ( however, 0.8 ≦ x ≦ 1.2, 0.01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is Al, V, A lithium-containing composite oxide represented by at least one element selected from Mn, Fe, Cu, and Zn has been proposed. The above lithium nickel composite oxide has higher charge capacity and discharge capacity than the above-described lithium cobalt composite oxide, and improved cycle characteristics compared to the conventional lithium nickel composite oxide represented by LiNiO _2. Yes. However, this material is basically a combination of Co and Ni, and is intended to stabilize the crystal structure by adding a third element while retaining the potential characteristics of these elements. Improvements were still inadequate.

Furthermore, in Japanese Patent Application Laid-Open No. 2003-17052, the general formula Li [Li _X (A _P B _Q C _R ) _1-X ] O ₂ (wherein A, B and C are three different transition metal elements, − 0.1 ≦ X ≦ 0.3, 0.2 ≦ P ≦ 0.4, 0.2 ≦ Q ≦ 0.4, 0.2 ≦ R ≦ 0.4) and nickel, cobalt, and manganese in the same ratio Combined cathode materials have also been proposed. In this publication, nitrogen or argon, which is an inert gas, is bubbled into an aqueous solution to remove dissolved oxygen, or a coprecipitation method to which a reducing agent is added to an aqueous solution in advance is added to the atomic level. It is described that a large particle size, high density composite hydroxide or composite oxide in which three kinds of elements are uniformly mixed can be obtained. However, it is difficult to obtain a single phase by powder mixing and firing a raw material containing three kinds of transition metal elements with lithium hydroxide or lithium carbonate, which is a lithium source. In addition, there remains a problem that it is difficult to control the particle shape and crystallinity.

On the other hand, for the purpose of improving the characteristics of the LiNiO ₂ positive electrode active material, Japanese Patent Application Laid-Open No. 9-298061 discloses lithium and nickel site occupancy obtained from a powder X-ray diffraction pattern, lattice constant and discharge capacity, and charge / discharge cycle. Finding a correlation in characteristics, having a layered rock salt structure, and obtaining a diffraction pattern obtained by a powder diffraction method using X-rays by a Rietveld analysis, a lattice constant, an occupation ratio of a 3b site of lithium, When the occupation ratio of the 3a site of nickel is in a specific range, lithium and nickel occupy other sites appropriately, the crystal structure is stabilized, the discharge capacity is stabilized, the discharge capacity is large, and the cycle characteristics It is said that excellent characteristics can be obtained.

Further, in LiCo _x Ni _1-x O ₂ disclosed in Japanese Patent Laid-Open No. 10-270043, the seat occupancy of metal ions other than lithium ions Li ^{+ at the} 3a site is 2 in the Rietveld analysis result by X-ray diffraction. %, A battery using the positive electrode active material has a reduced irreversible capacity and can improve cycle characteristics. Has been issued.

Further, JP-A-2001-68113 discloses a composition formula _{Li X Ni 1-YQ Co Q} M Y O Z (0 ≦ X ≦ 1.1,0 <Y + Q <0.5,0 <Y <0.5, 0 <Q <0.5, 1.8 ≦ Z ≦ 2.2, M is silicon, titanium, vanadium, chromium, manganese, iron, germanium, zirconium, niobium, molybdenum, ruthenium, palladium, tin, tellurium, hafnium, In a double oxide given by one or more elements including any of tungsten, iridium, platinum, and lead), the lithium occupancy ratio in the transition metal main layer mainly composed of Ni in the layer structure is 0.5% or more. It is described that when the content is 15% or less, a positive electrode active material for a lithium battery having a large discharge capacity, excellent safety, and a wide operating temperature range can be obtained. In addition, when the lithium occupancy ratio in the transition metal main layer in the layer structure is less than 0.5%, especially when the voltage is high, such as when fully charged, the environmental temperature becomes high, or the battery causes an internal short circuit. In such a case, nickel, cobalt, element M mainly contained in the transition metal main layer in the structure and lithium contained in the lithium main layer cause free mixing, and nickel, cobalt, element M, and lithium are random. It has been pointed out that the battery generates heat, and in extreme cases, smoke and fire are seen due to the change to the rock salt structure arranged in the.
Japanese Patent Laid-Open No. 8-213015 JP 2003-17052 A Japanese Patent Laid-Open No. 9-298061 JP-A-10-270043 JP 2001-68113 A

  An object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can be stably manufactured, has high initial discharge capacity, high safety, and good cycle characteristics, a method for manufacturing the same, and a non-aqueous system using the same as a positive electrode The object is to provide an electrolyte secondary battery.

Inventor As a result of extensive study for the positive electrode active material for the production method and a non-aqueous electrolyte secondary battery from a variety of perspectives, the positive electrode active material applied to the non-aqueous electrolyte secondary battery, the general formula LiNi _x Co _y Mn _z O ₂ (where x = z, x + y + z = 1, 0.3 ≦ x ≦ 0.45, 0.1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0.45), and In the method for producing a hexagonal lithium-containing composite oxide having a layered structure,
Nickel compound, cobalt compound, and manganese compound are pulverized and mixed to 0.1 μm or less in a solvent, and the resulting slurry is spray-dried to obtain a mixture of nickel compound, cobalt compound, and manganese compound; Step 2 of adjusting the obtained composite salt raw material and the lithium compound so that the total atomic ratio of nickel, cobalt and manganese and the atomic ratio of lithium are substantially 1: 0.95 to 1.05 and heat treating the mixture. Can produce a single phase of lithium-nickel-manganese composite oxide combining three kinds of elements, which has heretofore been difficult with powder-mixed firing, if it is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising I found out that I can do it.

Furthermore, the general formula _{LiNi x Co y Mn z O 2} ( where, x = z, x + y + z = 1,0.3 ≦ x ≦ 0.45,0.1 ≦ y ≦ 0.4,0.3 ≦ z ≦ 0.45) and a layered hexagonal lithium-nickel-cobalt-manganese composite oxide powder. The x-ray diffraction Rietveld analysis results of the powders show that the nickel ions and cobalt on the 3b site are obtained. Site occupancy of metal ions other than ions and manganese ions (hereinafter, the site occupancy of metal ions may be referred to as M seat occupancy. In addition, the site occupancy of nickel ions, cobalt ions, and manganese ions is represented by M (Ni , Co, Mn) may be described as a seat occupancy ratio)) to be 5% or less, so that the elements can be arranged regularly at the atomic level. To provide a secondary battery with good battery characteristics, in which nickel ions that are fixed in divalent rather than trivalent, are fixed in divalent, and cause divalent and tetravalent redox reactions as lithium ions are desorbed and inserted. As a result, the inventors have found out that the present invention can be achieved.

That is, according to the first aspect of the present invention, [Li] _3a [Ni _x Co _y Mn _z ] _3b [O ₂ ] _6c (where the subscript of [] indicates a site, x = z, x + y + z = 1, And satisfies the following conditions: 0.3 ≦ x ≦ 0.45, 0.1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0.45), and has a layered structure Non-aqueous electrolyte secondary characterized in that the site occupancy of metal ions other than nickel, cobalt and manganese at 3b sites obtained from Rietveld analysis of X-ray diffraction patterns in cobalt manganese composite oxide is 5% or less A positive electrode active material for a battery is provided.

The second invention of the present invention has the general formula LiNi _x Co _y Mn _z O ₂ (where x = z, x + y + z = 1, 0.3 ≦ x ≦ 0.45, 0.1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0.45), and a method for producing a hexagonal lithium nickel cobalt manganese composite oxide having a layered structure, the nickel compound, the cobalt compound, and the manganese compound Are mixed in a solvent to a size of 0.1 μm or less, and the obtained compound slurry is spray-dried to obtain a mixture of a nickel compound, a cobalt compound and a manganese compound, and the obtained mixture raw material and lithium compound are mixed. , Nickel, cobalt, and manganese, and a heat treatment is performed by mixing and heat treatment so that the atomic ratio of lithium and the atomic ratio of lithium is substantially 1.0: 0.95 to 1.05. For non-aqueous electrolyte secondary batteries To provide a manufacturing method of electrode active material.

  A third aspect of the present invention is the non-aqueous electrolyte secondary according to the second aspect, wherein the mixture is heat-treated under conditions of 900 ° C. or higher and 1100 ° C. or lower and in an oxygen stream for 4 hours or longer. A method for producing a positive electrode active material for a battery is provided.

  A fourth invention of the present invention is a nonaqueous system comprising a positive electrode using the positive electrode active material for a nonaqueous electrolyte secondary battery obtained by the method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to the first invention. An electrolyte secondary battery is provided.

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode active material applied to a non-aqueous electrolyte secondary battery, a general formula LiNi _x Co _y Mn _z O ₂ (where x = z, x + y + z = 1, 0.3 ≦ x ≦ 0.45, 0.1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0.45), and a hexagonal lithium-containing composite oxide having a layered structure In the manufacturing method, a nickel compound, a cobalt compound, and a manganese compound are pulverized and mixed in a solvent to a size of 0.1 μm or less, and the resulting slurry is spray-dried to obtain a mixture of the nickel compound, the cobalt compound, and the manganese compound. Step 1 obtained, and a mixture prepared by adjusting the obtained composite salt raw material and the lithium compound so that the total atomic ratio of nickel, cobalt, and manganese and the atomic ratio of lithium are substantially 1: 0.95 to 1.05 Heat treat It is a manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries characterized by including the process 2. By this production method, it is possible to synthesize a single phase of a lithium nickel manganese composite oxide combining three kinds of elements, which has been difficult with conventional powder mixing and firing.

Further general formula _{LiNi x Co y Mn z O 2} ( where, x = z, x + y + z = 1,0.3 ≦ x ≦ 0.45,0.1 ≦ y ≦ 0.4,0.3 ≦ z ≦ 0. 45), and a 3b-site nickel ion, cobalt ion, obtained from the result of X-ray diffraction Rietveld analysis of the powder comprising a hexagonal lithium nickel cobalt manganese composite oxide powder having a layered structure, By making the site occupancy (M-seat occupancy) of metal ions other than manganese ions 5% or less, the elements can be surely regularly arranged at the atomic level. As a result, nickel ions in the positive electrode active material are fixed to be divalent rather than trivalent, and nickel ions that generate a bivalent and tetravalent redox reaction as lithium ions are desorbed and inserted are ensured. It has the effect that a good secondary battery can be provided.

  The charge / discharge reaction of a battery is caused by a redox reaction of a transition metal that forms a composite oxide with lithium. For this reason, it is considered that a single phase having good crystallinity in which atoms are regularly arranged even with a material having the same composition is more likely to have a stable charge balance during charge and discharge, and the utilization rate of the redox reaction of the transition metal is increased. However, when trying to synthesize lithium metal composite oxide containing two or more kinds of transition metal elements, the synthesis of a single phase with good crystallinity in which atoms are regularly arranged, even if the raw materials are simply mixed and fired, Not easy.

  As a result of various studies, the present inventors have found the following.

That is, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has [Li] _3a [Ni _x Co _{y as the} sites 3a, 3b, and 6c in the hexagonal lithium nickel cobalt manganese composite oxide having a layered structure. Mn _z ] _3b [O ₂ ] _6c (where x = z, x + y + z = 1, 0.3 ≦ x ≦ 0.45, 0.1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0.45) The site occupancy of metal ions other than nickel, cobalt, and manganese at the 3b site obtained from the Rietveld analysis of the X-ray diffraction of the lithium-containing composite oxide is 5% or less. .

A method of manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention have the general formula _{LiNi x Co y Mn z O 2} ( where, x = z, x + y + z = 1,0.3 ≦ x ≦ 0.45 0.1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0.45), and a method for producing a hexagonal lithium-containing composite oxide having a layered structure, a nickel compound, a cobalt compound, And manganese compound are pulverized and mixed to 0.1 μm or less in a solvent, and the resulting slurry is spray-dried to obtain a mixture of a nickel compound, a cobalt compound, and a manganese compound, and the obtained composite compound raw material and And a step of heat-treating a mixture prepared by adjusting a lithium compound so that a total atomic ratio of nickel, cobalt, and manganese and an atomic ratio of lithium is substantially 1.0: 0.95 to 1.05. That features To.

  The non-aqueous electrolyte secondary battery, that is, the lithium ion secondary battery according to the present invention is composed of the same components as those of a general lithium ion secondary battery, such as a positive electrode, a negative electrode, and a non-aqueous electrolyte.

  Hereinafter, embodiments of the lithium ion secondary battery according to the present invention will be described in detail for each of the items such as the positive electrode, the negative electrode, and other components.

1. Positive electrode active material The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has [Li] _3a [Ni _x ] each site of 3a, 3b, and 6c in a hexagonal lithium nickel cobalt manganese composite oxide having a layered structure. Co _y Mn _z ] _3b [O ₂ ] _6c (where x = z, x + y + z = 1, 0.3 ≦ x ≦ 0.45, 0.1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0. 45), the site occupancy of metal ions other than nickel, cobalt, and manganese at the 3b site obtained from the X-ray diffraction Rietveld analysis of the lithium-containing composite oxide is 5% or less. And

The particles constituting the positive electrode active material powder according to the present invention are mainly composed of secondary particles formed by aggregating a plurality of primary particles, the average particle diameter of the secondary particles is 5 to 10 μm, and the specific surface area is 0.00. The tap density is 2.0 g / cm ^{3 at} about 7 m ² / g.

  When the site occupancy of metal ions other than nickel, cobalt, and manganese on the 3b site is 5% or more outside the above range, the divalent nickel ions in the lithium nickel cobalt manganese composite oxide decrease, and the trivalent nickel. Ions increase. Along with this, the discharge capacity becomes small, which is not preferable.

  In addition, by adjusting the ratio of nickel ions and manganese ions to the same rate, the charge is adjusted to be trivalent on average for divalent nickel ions and tetravalent manganese ions. Cobalt ions play a role in stabilizing the crystal structure.

A positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention the general formula _{LiNi x Co y Mn z O 2} ( where, x = z, x + y + z = 1,0.3 ≦ x ≦ 0.45,0 ≦ y ≦ In order to produce a hexagonal lithium-containing composite oxide represented by 0.4, 0.3 ≦ z ≦ 0.45) and having a layered structure, a nickel compound, a cobalt compound, and a manganese compound are used as a solvent. In step 1, the slurry obtained is pulverized and mixed to 0.1 μm or less, and the resulting slurry is spray-dried to obtain a mixture of a nickel compound, a cobalt compound and a manganese compound, and the obtained composite compound raw material and lithium compound are mixed with nickel and cobalt. And a mixture prepared so that the total atomic ratio of manganese and the atomic ratio of lithium are substantially 1: 0.95 to 1.05 can be synthesized by heat treatment at 900 ° C. to 1100 ° C. .

  When the heat treatment temperature is lower than 900 ° C., the reaction with the lithium compound does not proceed sufficiently, and it becomes difficult to synthesize a lithium nickel cobalt manganese composite oxide having a desired layered structure. If it exceeds 1100 ° C, the crystal structure starts to be disturbed. Therefore, a crystal structure with less disturbance can be realized by setting the heat treatment temperature to 900 ° C. or higher and 1100 ° C. or lower.

  As the lithium compound, lithium hydroxide, lithium carbonate and the like are preferable. As the nickel compound, nickel oxide, nickel carbonate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide, or the like can be used.

  As the cobalt compound, cobalt oxide, cobalt carbonate, cobalt hydroxide, cobalt oxyhydroxide and the like can be used. As the manganese compound, manganese dioxide, manganese hydroxide, manganese carbonate, manganese oxyhydroxide and the like can be used.

  The positive electrode is formed from a positive electrode mixture containing the positive electrode active material, a conductive material, and a binder. Specifically, a powdered positive electrode active material and a conductive material are mixed, a binder is added thereto, and if necessary, a solvent is added for the purpose of adjusting the viscosity to adjust the positive electrode mixture paste. A sheet-like positive electrode can be produced by applying the material paste onto the surface of a current collector made of, for example, an aluminum foil, drying, and pressing as necessary.

  The conductive material is for securing the electrical conductivity of the positive electrode, and for example, a material obtained by mixing one or more carbon material powders such as carbon black, acetylene black, and graphite can be used. .

  The binder plays a role of binding the active material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene can be used. . An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent to be added to the positive electrode mixture as needed, that is, as a solvent for dispersing the active material, conductive material and activated carbon and dissolving the binder. .

  Activated carbon can also be added to increase the electric double layer capacity.

  The above active material, conductive material, and binder are mixed, and if necessary, the above activated carbon and solvent are added and kneaded to prepare a positive electrode mixture paste. The respective mixing ratios in the positive electrode mixture are also important factors that determine the performance of the lithium secondary battery. When the total solid content (meaning excluding solvent) of the positive electrode mixture is 100 wt%, the active material is 60 to 95 wt%, the conductive material is 1 to 20 wt%, respectively, in the same manner as the positive electrode of a general lithium secondary battery. The binder is preferably 1 to 20 wt%.

  The positive electrode is, for example, applied to the surface of a metal foil current collector made of aluminum or the like, the above-mentioned positive electrode mixture paste sufficiently kneaded, dried to disperse the solvent, and then, if necessary, a roll to increase the electrode density By compressing with a press or the like, a sheet-like material can be formed. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery and used for battery production.

2. Negative electrode For the negative electrode, metallic lithium, lithium alloy, etc. Also, a negative electrode mixture made by mixing a binder with a negative electrode active material capable of occluding and desorbing lithium ions, and adding a suitable solvent, is made of copper, etc. The metal foil current collector is coated, dried, and compressed as necessary to increase the electrode density. At this time, as the negative electrode active material, for example, a fired organic compound such as natural graphite, artificial graphite, or a phenol resin, or a powdery carbon material such as coke can be used. In this case, a fluorine-containing resin such as polyvinylidene fluoride is used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone is used as a solvent for dispersing the active material and the binder. be able to.

3. Separator A separator is inserted between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin microporous film such as polyethylene or polypropylene can be used.

4). Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorous compounds such as triethyl phosphate, triethyl phosphate and trioctyl phosphate alone, or two or more kinds It can be used by mixing. As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiASF ₆ , LiN (CF ₃ SO ₂ ) ₂ , or a composite salt thereof can be used. Further, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

  The lithium secondary battery of the present invention configured as described above can have various shapes such as a cylindrical type and a stacked type. Even if any shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal, The battery can be completed by connecting with a current collecting lead or the like, impregnating the electrode body with the non-aqueous electrolyte, and sealing the battery case.

5. Non-aqueous electrolyte secondary battery The present invention provides a non-aqueous electrolyte secondary battery including a positive electrode using the positive electrode active material for the non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery includes a positive electrode using the positive electrode active material for the non-aqueous electrolyte secondary battery, and is charged and discharged at a potential of 3.0 to 4.5 V, whereby lithium cobalt A non-aqueous electrolyte secondary battery that exhibits a discharge capacity larger than that of the composite oxide and that is highly safe can be realized.

6). Other Applications The embodiments described above are merely examples, and the non-aqueous electrolyte secondary battery of the present invention is implemented in various modifications and improvements based on the knowledge of those skilled in the art including the above-described embodiments. can do.

  Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited. If the merit of the non-aqueous electrolyte secondary battery of the present invention that is excellent in safety is utilized, it is suitable as a large-sized secondary battery such as a power source for an electric vehicle that uses a large amount of a positive electrode active material. The electric vehicle power source means not only an electric vehicle driven purely by electric energy but also a so-called hybrid car power source used in combination with a combustion engine such as a gasoline engine or a diesel engine. .

  Hereinafter, an embodiment according to the present invention will be described in detail with reference to the preferred drawings.

Example 1
Commercially available manganese carbonate hexahydrate (MnCO ₃ .6H ₂ O: Wako Pure Chemical Industries, Ltd.) and nickel sulfate, cobalt hydroxide and commercially available manganese carbonate produced from nickel sulfate and cobalt sulfate raw materials Hexahydrate (MnCO ₃ .6H ₂ O: Wako Pure Chemical Industries, Ltd.) was weighed so that the molar ratio of nickel, cobalt, and manganese was 1: 1: 1. A 10 wt% slurry was prepared. While stirring this slurry, using a circulating medium agitation type wet pulverizer, the slurry is pulverized until the average particle size of the solid content in the slurry becomes 0.1 μm or less, and a two-fluid nozzle spray type spray dryer (Fujisaki Electric). The product powder was obtained by spray drying using MDL-050-M). Thereafter, a commercially available lithium hydroxide monohydrate (LiOH.H ₂ O :) is used so that the charged Li / M ratio is Li: M (Ni, Co, Mn) = 1.05: 1.0 (molar ratio). FMC) and the raw material powder were weighed and mixed, and then heat-treated in an oxygen atmosphere at 1000 ° C. for 10 hours. As a result, substantially spherical secondary particles having an average particle diameter of 7 μm, a specific surface area of 0.7 m ² / g, and a tap density of 1.8 g / cm ³ were obtained.

  When the obtained powder was analyzed by powder X-ray diffraction using Cu-Kα rays, it was confirmed to be a hexagonal layered crystal lithium nickel cobalt manganese composite oxide single phase.

  The particle size distribution is measured with a laser diffraction / scattering particle size distribution measuring device (Nikkiso Microtrac HRA), and the specific surface area is measured with a nitrogen adsorption BET method measuring device (Yuta Ionix Kantasorb QS-10). The tap density was measured according to JIS R 1628, and the X-ray diffraction was measured using (Rigaku Electric Co., Ltd .: RINT-1400).

  Furthermore, according to the Rietveld analysis of the obtained X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy of the 3b site was 99.8%.

Using the obtained active material, a battery was prepared as follows, and the charge / discharge capacity was measured. 52.5 mg of active material, 15 mg of acetylene black and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded to a diameter of 11 mm at a pressure of 100 MPa. The produced electrode was dried overnight at 120 ° C. in a vacuum dryer, and assembled into a 2032 type coin battery shown in FIG. 1 in an Ar atmosphere glove box. For the negative electrode, Li metal having a diameter of 17 mm and a thickness of 1 mm was used, and for the electrolytic solution, an equal mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting salt was used. A polyethylene porous film having a film thickness of 25 μm was used for the separator. The coin battery was subjected to a charge / discharge test after assembly, after the open circuit voltage was stabilized, at a current density of 0.1 mA / cm ^2, with charge and discharge end voltages of 4.5 V and 3.0 V, respectively. Table 1 shows the discharge capacity and the discharge maintenance rate of 20 cycles.

(Example 2)
Example 1 except that the molar ratio (Li / M ratio) of charged Li and M (Ni, Co, Mn) was changed to Li: M (Ni, Co, Mn) = 1.0: 1.0 Similarly, lithium nickel cobalt manganese composite oxide was synthesized. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. From the result of Rietveld analysis of the obtained X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy was 95.6%. Table 1 shows the discharge capacity measured using the obtained composite oxide and the discharge maintenance ratio of 20 cycles.

(Example 3)
Example 1 except that the molar ratio (Li / M ratio) of charged Li and M (Ni, Co, Mn) was changed to Li: M (Ni, Co, Mn) = 0.95: 1.0 Similarly, lithium nickel cobalt manganese composite oxide was synthesized.

  It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. From the result of Rietveld analysis of the result of the X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy was 96.3%. Table 1 shows the discharge capacity measured using the obtained composite oxide and the discharge maintenance ratio of 20 cycles.

Example 4
A lithium nickel cobalt manganese composite oxide was synthesized in the same manner as in Example 1 except that the heat treatment temperature was changed to 1100 ° C. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. From the result of Rietveld analysis of the obtained X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy was 97.7%. Table 1 shows the discharge capacity measured using the obtained composite oxide and the discharge maintenance ratio of 20 cycles.

(Example 5)
A lithium nickel cobalt manganese composite oxide was synthesized in the same manner as in Example 1 except that the heat treatment temperature was changed to 1100 ° C. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. From the result of Rietveld analysis of the obtained X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy was 96.8%. Table 1 shows the discharge capacity measured using the obtained composite oxide and the discharge maintenance ratio of 20 cycles.

(Comparative Example 1)
Example 1 except that the molar ratio (Li / M ratio) of charged Li and M (Ni, Co, Mn) was changed to Li: M (Ni, Co, Mn) = 1.1: 1.0 Similarly, lithium nickel cobalt manganese composite oxide was synthesized. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. From the result of Rietveld analysis of the obtained X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy was 92.1%. Table 1 shows the discharge capacity measured using the obtained composite oxide and the discharge maintenance ratio of 20 cycles.

(Comparative Example 2)
Example 1 except that the molar ratio (Li / M ratio) between charged Li and M (Ni, Co, Mn) was changed to Li: M (Ni, Co, Mn) = 0.9: 1.0 Similarly, lithium nickel cobalt manganese composite oxide was synthesized. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. From the result of Rietveld analysis of the obtained X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy was 95.3%. Table 1 shows the discharge capacity measured using the obtained composite oxide and the discharge maintenance ratio of 20 cycles.

(Comparative Example 3)
A lithium nickel cobalt manganese composite oxide was synthesized in the same manner as in Example 1 except that the heat treatment temperature was changed to 850 ° C. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. From the result of Rietveld analysis of the obtained X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy was 93.4%. Table 1 shows the discharge capacity measured using the obtained composite oxide and the discharge maintenance ratio of 20 cycles.

(Comparative Example 4)
A lithium nickel cobalt manganese composite oxide was synthesized in the same manner as in Example 1 except that the heat treatment temperature was changed to 1150 ° C. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. From the result of Rietveld analysis of the obtained X-ray diffraction pattern, the M (Ni, Co, Mn) seat occupancy was 94.1%. Table 1 shows the discharge capacity measured using the obtained composite oxide and the discharge maintenance ratio of 20 cycles.

"Evaluation"
From the results of Examples and Comparative Examples in Table 1, the positive electrode active material has a charged Li / M ratio of 0.95 to 1.05, and the M (Ni, Co, Mn) seat occupancy of the 3b site is 95%. In other words, the site occupancy (M seat occupancy) of metal ions other than nickel ions, cobalt ions, and manganese ions at the 3b site is 5% or less, and the heat treatment temperature is 900 ° C to 1100 ° C. If it exists, it turns out that the non-aqueous electrolyte secondary battery using this positive electrode active material improves both initial discharge capacity and cycle characteristics.

  In the positive electrode material, Li is desorbed and inserted by a bivalent and tetravalent redox reaction of nickel ions, so it is considered that the larger the number of divalent nickel ions, the larger the discharge capacity.

  The fact that the M (Ni, Co, Mn) seat occupancy is small is considered to be because Li ions are mixed in the 3b site. When Li ions are mixed into the 3b site, the divalent nickel ions, the trivalent cobalt ions, and the tetravalent manganese ions are substituted and a positive charge is left by the difference in charge from the monovalent lithium ions. It is thought that the charge balance is maintained by divalent nickel ions which are considered to be most easily oxidized at the 3b site due to the surplus charges to be trivalently oxidized. That is, it is considered that the decrease in the M (Ni, Co, Mn) seat occupancy decreases the number of divalent nickel ions involved in the desorption / insertion of Li ions, thereby reducing the discharge capacity. Therefore, in order to increase the initial discharge capacity, it is better that the M (Ni, Co, Mn) seat occupancy exceeds 95%.

  In Comparative Example 2, the M (Ni, Co, Mn) seat occupancy rate exceeds 95%, but since the Li / M ratio is 0.90 and Li is small, the number of lithium ions entering the M site is small. Therefore, it is considered that the M (Ni, Co, Mn) seat occupancy is high. However, since the amount of lithium ions is small, the crystal structure is not stable, the capacity retention rate after 20 cycles is not good, and the cycle characteristics are slightly deteriorated.

  From the results of the initial discharge capacity and cycle characteristics, in the production method of the present invention, the optimum synthesis condition is particularly when the heat treatment is performed at a temperature near 1000 ° C. with a Li / M ratio of 1.0 to 1.05. It is thought that.

It is a cross section of the coin battery used for battery evaluation.

Explanation of symbols

1 Lithium metal negative electrode 2 Separator (electrolyte impregnation)
3 Positive electrode (Evaluation electrode)
4 Gasket 5 Negative electrode can 6 Positive electrode can 7 Current collector

Claims (4)

[Li] _3a [Ni _x Co _y Mn _z ] _3b [O ₂ ] _6c (where the subscript of [] indicates a site, x = z, x + y + z = 1, 0.3 ≦ x ≦ 0.45, 0 .. 1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0.45), and a hexagonal lithium nickel cobalt manganese composite oxide having a layered structure. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the site occupancy of metal ions other than nickel, cobalt, and manganese at the 3b site obtained from Rietveld analysis is 5% or less. General formula LiNi _x Co _y Mn _z O ₂ (where x = z, x + y + z = 1, 0.3 ≦ x ≦ 0.45, 0.1 ≦ y ≦ 0.4, 0.3 ≦ z ≦ 0.45) and a method for producing a hexagonal lithium nickel cobalt manganese composite oxide having a layered structure, in which a nickel compound, a cobalt compound, and a manganese compound are 0.1 μm or less in a solvent. The obtained compound slurry is spray-dried to obtain a mixture of a nickel compound, a cobalt compound, and a manganese compound, and the obtained mixture raw material and lithium compound are combined with nickel, cobalt, and manganese. A positive electrode active for a non-aqueous electrolyte secondary battery, comprising a step 2 of mixing and heat-treating so that an atomic ratio and an atomic ratio of lithium are substantially 1.0: 0.95 to 1.05. A method for producing a substance.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the mixture is heat-treated under conditions of 900 ° C or higher and 1100 ° C or lower and in an oxygen stream for 4 hours or longer. . A non-aqueous electrolyte secondary battery comprising a positive electrode using the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1.

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