JP2008251480A - Cathode active material for nonaqueous electrolyte secondary battery and nonaqueous secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with thermal stability of a lithium-nickel composite oxide enhanced, with high capacity and excellent in reliability and safety at high temperature preservation. <P>SOLUTION: The anode active material for a nonaqueous electrolyte secondary battery includes a lithium-containing composite oxide and a coating layer coating at least a part of a surface of the lithium-containing composite oxide. The lithium-containing composite oxide contains Ni, the coating layer contains a metal element M and a halogen element, and the metal element M contains at least one kind selected from a group of Al, Ta, W, Zr, Nb, Sn and B. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same, and more particularly to improvement of reliability and safety at high temperature storage.

  In recent years, consumer electronic devices such as telephones, personal computers, and video cameras are rapidly becoming portable and cordless. As a power source for driving these devices, there is an increasing demand for a secondary battery that is small and lightweight and has a high energy density. In particular, development of non-aqueous electrolyte secondary batteries that include a lithium-containing composite oxide as a positive electrode active material is active. Since opportunities for exchanging large volumes of data with personal computers and mobile phones have increased, it is desirable to increase the capacity of non-aqueous electrolyte secondary batteries used as power sources for these electronic devices.

As a negative electrode material for a non-aqueous electrolyte secondary battery, a material capable of inserting and extracting lithium ions is generally used. For example, carbon materials, silicon compounds, tin compounds, etc. are used.
As a separator interposed between the positive electrode and the negative electrode, a microporous film containing polyethylene, polypropylene, or the like is generally used.
As the non-aqueous electrolyte, an aprotic organic solvent in which a lithium salt such as LiBF ₄ or LIPF ₆ is dissolved is generally used.

  Conventionally, lithium cobalt composite oxide or the like has been used as a positive electrode active material of a non-aqueous electrolyte secondary battery, but there is a limit in improving the capacity. Therefore, recently, lithium nickel composite oxide has attracted attention because of its large battery capacity per unit weight. However, the lithium nickel composite oxide has a problem of improving thermal stability. When a battery using lithium nickel composite oxide as a positive electrode active material is used in a high temperature environment, the pyrolyzed positive electrode active material reacts with the nonaqueous electrolyte to generate gas. Therefore, battery characteristics may be deteriorated.

Patent Documents 1 and 2 propose that the surface of a positive electrode active material in which a halogen element is dissolved is coated with a certain kind of metal halide.
Patent Documents 3 and 4 propose that the surface of the positive electrode active material is treated with fluorine to form a certain fluoride film.
Patent Documents 5 and 6 propose to coat the surface of the positive electrode active material with a metal oxide.
JP 2000-128539 A JP 2000-203842 A Japanese Patent Laid-Open No. 08-264183 JP 2004-192896 A JP 2003-123750 A JP 2003-173775 A

In the combination of the metal halide and the active material disclosed in Patent Documents 1 and 2, sufficient thermal stability cannot be obtained.
In Patent Documents 3 and 4, a film is formed by a reaction between fluorine and a metal in the positive electrode active material. Therefore, it is considered that the crystal structure on the surface of the active material is impaired.
In Patent Documents 5 and 6, since the positive electrode active material is coated with a metal oxide, oxide ion conductivity is generated in the coating. Therefore, at a high temperature, oxygen atoms are eluted from the positive electrode active material and react with the electrolyte. Therefore, sufficient thermal stability cannot be obtained.

  As described above, the lithium nickel composite oxide has a problem in thermal stability. Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having higher thermal stability of lithium nickel composite oxide, high capacity, and excellent reliability and safety during high-temperature storage. .

  The present invention has a lithium-containing composite oxide and a coating layer that covers at least a part of the surface of the lithium-containing composite oxide, the lithium-containing composite oxide contains Ni, and the coating layer contains the metal element M. And a halogen element, and the metal element M includes at least one selected from the group consisting of Al, Ta, W, Zr, Nb, Sn, and B, and a positive electrode active material for a non-aqueous electrolyte secondary battery About.

The lithium-containing composite oxide has the general formula (1): Li _a Ni _b Me _c O ₂ (where 0 <a ≦ 2, 0 <b ≦ 1, c = 1−b, Me is Al, Ti, V, It is preferable to include a compound represented by at least one selected from the group consisting of Mn, Co, Fe, Cr, Cu, Zn, and Mg.
When the lithium-containing composite oxide is represented by the general formula (1), the metal element M preferably includes at least one selected from the group consisting of Ta, W, Zr, Nb, Sn, and B. .

The coating layer preferably contains a halide of the metal element M.
The thickness of the coating layer is preferably 1 to 100 nm, and more preferably 2 to 5 nm.

When the metal element M contains at least one selected from the group consisting of Al, Ta, Zr, Sn and B, the halogen element preferably contains at least one of F and Cl.
When the metal element M contains at least one of W and Nb, the halogen element preferably contains Cl.

  The present invention further includes a positive electrode, a negative electrode capable of inserting and extracting lithium ions, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode active material for a secondary battery.

  Furthermore, the present invention provides a nonaqueous electrolyte secondary battery in which a gaseous metal halide is brought into contact with a lithium-containing composite oxide to form a coating layer that covers at least a part of the surface of the lithium-containing composite oxide. The present invention relates to a method for producing a positive electrode active material.

  According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery containing Ni having high thermal stability and a high-capacity non-aqueous electrolyte secondary battery excellent in reliability and safety during high-temperature storage are provided. Can do.

  In the present invention, a coating layer containing a metal element M and a halogen element is formed on a lithium-containing composite oxide containing Ni (hereinafter also referred to as lithium nickel composite oxide). Thereby, the thermal stability of the lithium nickel composite oxide can be enhanced, and a nonaqueous electrolyte secondary battery excellent in reliability and safety during high-temperature storage can be obtained.

  The coating layer preferably has a uniform thickness of about several molecular layers. Thereby, the fall of lithium ion conductivity by a coating layer can be suppressed to the minimum. In addition, when the thickness is about several molecular layers, the surface of the positive electrode active material can be inactivated, and elution of the positive electrode active material at a high temperature and decomposition of the nonaqueous electrolyte on the surface of the positive electrode active material can be suppressed.

The coating layer will be described. The coating layer covers at least a part of the surface of the lithium nickel composite oxide. The coating layer includes a metal element M and a halogen element.
The metal element M includes at least one selected from the group consisting of Al, Ta, W, Zr, Nb, Sn, and B from the viewpoint of improving the thermodynamic stability of the surface layer portion of the lithium nickel composite oxide. . Only one type of metal element M may be included in the coating layer alone, or two or more types may be included.
The halogen element is not particularly limited, but preferably contains F or Cl from the viewpoint of withstand voltage. Only one kind of halogen element may be contained in the coating layer, or two or more kinds may be contained.

The metal element M and the halogen element preferably form a metal halide from the viewpoint of further improving the stability of the coating layer. When the coating layer contains an oxide, oxide ion conductivity is generated in the coating layer. Therefore, at a high temperature, oxygen atoms are eluted from the inside of the positive electrode active material and react with the nonaqueous electrolyte. On the other hand, halides are advantageous in that they have lower ionic conductivity than oxides. As the metal halide, any of fluoride, chloride, bromide and iodide can be used, but fluoride and chloride are preferably used. Only one type of metal halide may be included in the coating layer alone, or two or more types may be included. Examples of the fluoride include WF ₆ and NbF ₅ .
Examples of the chloride include AlCl ₃ , TaCl ₃ , ZrCl ₄ , SnCl ₄ , and BCl ₃ .

  The thickness of the coating layer is preferably 1 to 100 nm. If the thickness is less than 1 nm, the surface of the positive electrode active material cannot be sufficiently inactivated and sufficient thermal stability may not be obtained at high temperatures. On the other hand, when the thickness exceeds 100 nm, the lithium ion conductivity of the positive electrode active material may decrease. The thickness of the coating layer is more preferably 2 to 5 nm from the viewpoint of balancing lithium ion conductivity and thermal stability in a balanced manner.

  A method for forming the coating layer will be described. In the present invention, a halide gas containing the metal element M is brought into contact with the lithium nickel composite oxide. This removes lithium carbonate on the surface of the positive electrode active material, which is a source of gas generation during high-temperature storage, and forms a coating layer containing a thin metal halide of about several molecular layers on the surface of the lithium nickel composite oxide. be able to.

Although the detailed mechanism by which lithium carbonate on the surface of the positive electrode active material is removed is unknown, it is considered that the halide reacts with lithium carbonate and the lithium carbonate is decomposed. At this time, it is considered that lithium halide is generated and CO ₂ and O ₂ are eliminated.

The method for bringing the gaseous metal halide into contact with the lithium nickel composite oxide is not particularly limited. For example, gaseous metal halide and lithium nickel composite oxide are stirred and mixed. Thereby, the coating layer containing a metal halide can be formed on the surface of the lithium nickel composite oxide.
When using a metal halide that is gaseous at room temperature, the temperature during stirring is not particularly limited. Examples of such metal halides include WF ₆ and BCl ₃ .

When using a metal halide that is solid at room temperature, the metal halide is gasified. For example, the gaseous metal halide is brought into contact with the lithium nickel composite oxide by stirring with the lithium nickel composite oxide while heating the metal halide. Although the temperature at the time of stirring changes with metal halides, it is preferable that it is 20-450 degreeC.
The gas pressure of the gaseous metal halide is preferably 10 to 100 Torr.

The positive electrode active material will be described.
The lithium nickel composite oxide used in the present invention may be a layered lithium nickelate represented by Li _a NiO ₂ (where 0 <a ≦ 2), and a part of nickel is composed of other atoms Me. It may be a substituted lithium nickelate. For example, the general formula (1): Li _a Ni _b Me _c O ₂ (where 0 <a ≦ 2, 0 <b ≦ 1, c = 1−b, Me is Al, Ti, V, Mn, Co, Fe , At least one selected from the group consisting of Cr, Cu, Zn and Mg). From the viewpoint of sufficiently obtaining the advantage of high capacity of the lithium nickel composite oxide, it is more preferable that 0.45 ≦ b ≦ 0.99.

In the general formula (1), Me preferably contains at least one of Mn and Co. When Mn is contained, for example, it is represented by the general formula Li _a Ni _b Mn _c O ₂ (where 0 <a ≦ 2, 0.45 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.55). Lithium nickel composite oxide is preferred.
When Co is contained, for example, it is represented by the general formula Li _a Ni _b Co _c O ₂ (where 0 <a ≦ 2, 0.45 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.55). Lithium nickel composite oxide is preferred.

In the general formula (1), Me may contain both Mn and Co. For example, the general formula Li _a Ni _b Mn _C Co _d O ₂ (where 0 <a ≦ 2, 0.25 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.65, 0.01 ≦ d ≦ 0) .65) is preferable.
A positive electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.

  The method for preparing the lithium nickel composite oxide is not particularly limited. For example, a method in which a nickel compound and a lithium compound are pulverized and mixed according to a desired composition, and the mixture is fired. The firing temperature is preferably a temperature at which at least a part of the mixture of the nickel compound and the lithium compound is decomposed or melted. For example, it may be 250 ° C to 1500 ° C. The firing time of the mixture is preferably 1 to 80 hours.

The atmosphere gas at the time of firing may be an oxidizing atmosphere, for example, firing in air. The mixture after firing is pulverized and adjusted to a predetermined particle size to obtain a lithium nickel composite oxide.
The nickel compound is not particularly limited. Examples thereof include nickel hydroxide, nickel oxide, nickel sulfate, and nickel carbonate. The lithium compound is not particularly limited. Examples thereof include lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, and lithium oxide.

When the lithium-containing composite oxide is represented by the general formula (1), the metal element M preferably includes at least one selected from the group consisting of Ta, W, Zr, Nb, Sn, and B. . Since these metal elements are hardly dissolved in the lithium-containing composite oxide, it is considered that the thickness of the coating layer can be easily controlled.
When the metal element M includes at least one selected from the group consisting of Al, Ta, Zr, Sn, and B, the halogen element may include at least one of F and Cl from the viewpoint of withstand voltage. preferable.
When the metal element M contains at least one of W and Nb, the halogen element preferably contains Cl.

Next, the nonaqueous electrolyte secondary battery including the positive electrode active material described above will be described.
The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode capable of inserting and extracting lithium ions, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. A positive electrode contains said positive electrode active material.

The positive electrode will be described.
The positive electrode has a positive electrode current collector and a positive electrode mixture layer carried on the positive electrode current collector. The positive electrode mixture layer generally includes a positive electrode active material, a positive electrode binder, and a conductive agent. The method for producing the positive electrode is not particularly limited. Hereinafter, an example of a method for manufacturing the positive electrode will be described.
First, a positive electrode mixture paste is prepared by mixing a positive electrode active material, a positive electrode binder, a conductive agent, and a dispersion medium. A positive electrode mixture paste is applied to both surfaces of a positive electrode current collector, and after drying, rolling is performed to obtain a positive electrode. The positive electrode current collector is not particularly limited. For example, a metal foil containing aluminum, stainless steel or the like is used, but an aluminum foil is preferable.

  The binder for positive electrodes is not particularly limited. For example, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like can be used.

The conductive agent is not particularly limited. For example, natural graphite, artificial graphite, acetylene black and the like can be used.
The dispersion medium for the positive electrode is not particularly limited. For example, N-methyl-2-pyrrolidone, tetrahydrofuran, dimethylformamide and the like can be used.

The negative electrode will be described.
The negative electrode has a negative electrode current collector and a negative electrode mixture layer carried on the negative electrode current collector. The negative electrode mixture layer generally includes a negative electrode active material and a negative electrode binder. The negative electrode active material is not particularly limited. For example, in addition to alloys such as lithium metal and lithium alloy, intermetallic compounds capable of inserting and extracting lithium ions, carbon materials, organic compounds, inorganic compounds, metal complexes, organic polymer compounds, and the like can be given. These may be used alone or in combination of two or more.

Among these, the negative electrode active material is particularly preferably a carbon material. When the carbon material is in a powder form, the average particle size is preferably, for example, 0.1 to 60 μm, and more preferably 0.5 to 30 μm. The specific surface area of the carbon material is preferably 1 to 10 m ² / g. As the carbon material, graphite is preferable, and graphite having a carbon hexagonal plane spacing (d ₀₀₂ ) of 3.35 to 3.40 mm and a crystallite size (L _c ) in the c-axis direction of 100 mm or more is further included. preferable.

The method for producing the negative electrode is not particularly limited. Hereinafter, an example of a method for manufacturing a negative electrode will be described.
First, a negative electrode active material, a negative electrode binder, and a dispersion medium are mixed to prepare a negative electrode mixture paste. The negative electrode is obtained by applying the negative electrode mixture paste on both surfaces of the negative electrode current collector and rolling it after drying. Although the negative electrode current collector is not particularly limited, for example, a copper foil is used.

The nonaqueous electrolyte will be described.
The nonaqueous electrolyte includes, for example, a nonaqueous solvent and a lithium salt dissolved therein. The non-aqueous solvent is not particularly limited. Examples thereof include cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone. These may be used alone or in combination of two or more.
The lithium salt is not particularly limited. Examples thereof include LiPF ₆ and LiBF ₄ . These may be used alone or in combination of two or more.

  A separator is interposed between the positive electrode and the negative electrode. The material used as the separator is not particularly limited. For example, a microporous membrane made of polyolefin such as polyethylene is used.

  The form of the battery is not particularly limited. For example, a cylindrical shape, a flat shape, a square shape, etc. are mentioned. The battery preferably includes, for example, an internal pressure-operated safety valve, a current cutoff safety valve, or the like so that safety can be ensured even in the case of malfunction.

Hereinafter, the present invention will be described in more detail with reference to examples. The content of the present invention is not limited to these examples.
Example 1
A coating layer containing W as the metal element M and F as the halogen element was formed on the surface of the lithium nickel composite oxide.

(1) Fabrication of positive electrode Lithium carbonate powder (average particle size 2 μm) and nickel carbonate powder (average particle size 10 μm) so that the atomic ratio of lithium and nickel is 1.05: 1.00 Mixed. The mixture was calcined in air at 750 ° C. for 5 hours to obtain lithium nickelate.

1 kg of lithium nickelate was placed in an atmosphere-controlled rotary kiln furnace (kiln rotation speed: 4 rpm), and WF ₆ as a coating material was introduced into the furnace at 25 ° C. and a flow rate of 1 L / min for 20 minutes. Thus, by contacting the WF ₆ to the surface of the lithium nickel composite oxide, to form a uniform coating layer containing WF _6. It was 2 nm when the thickness of the coating layer was measured using XPS.

  100 parts by weight of a lithium nickel composite oxide having a coating layer, 3 parts by weight of acetylene black as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to obtain a positive electrode mixture. The positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a dispersion medium to prepare a slurry-like positive electrode mixture paste. The positive electrode mixture paste was applied to both surfaces of a positive electrode current collector (aluminum foil having a thickness of 20 μm) so as to have a predetermined weight after drying, dried and rolled. Then, it cut | judged to the predetermined dimension and obtained the positive electrode of thickness 170 micrometers. In addition, the thickness of the positive electrode is the total thickness of the positive electrode mixture layer and the positive electrode current collector.

(2) Production of negative electrode As the negative electrode active material, flaky graphite ground and classified so as to have an average particle diameter of about 20 μm was used. A slurry-like negative electrode mixture is prepared by mixing 100 parts by weight of flaky graphite, 3 parts by weight of styrene / butadiene rubber as a binder, and 100 parts by weight of an aqueous solution containing 1% by weight of carboxymethyl cellulose as a dispersion medium. A paste was obtained. The negative electrode mixture paste was applied to both sides of a negative electrode current collector (copper foil having a thickness of 15 μm) so as to have a predetermined weight after drying, dried and rolled. Then, it cut | judged to the predetermined dimension and obtained the negative electrode of thickness 165 micrometers. The negative electrode thickness is the total thickness of the negative electrode mixture layer and the negative electrode current collector.

(3) Preparation of non-aqueous electrolyte First, 100 parts by weight of a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3 and 2 parts by weight of vinylene carbonate were mixed. To the resulting mixture, was used LiPF ₆ was dissolved to a concentration of 1.0 mol / L as the non-aqueous electrolyte.

(4) Battery assembly A cylindrical nonaqueous electrolyte secondary battery (diameter 18 mm, height 65 mm) was assembled. FIG. 1 shows a longitudinal sectional view of a cylindrical battery produced in this example. The battery was assembled as follows.

  First, the positive electrode lead 4 made of aluminum was attached to the positive electrode current collector. A negative electrode lead 5 made of nickel was attached to the negative electrode current collector. The positive electrode 1 and the negative electrode 2 were wound through a separator 3 to constitute a jelly roll type electrode group. As the separator 3, a polyethylene microporous film having a thickness of 20 μm was used.

  Insulating plates 6 and 7 made of polypropylene were disposed on the upper and lower portions of the electrode group. The negative electrode lead 5 was welded to a nickel-plated iron battery case 8. The positive electrode lead 4 was welded to a sealing plate 10 having an internal pressure actuated safety valve. The electrode group was housed inside the battery case 8. Thereafter, a nonaqueous electrolyte was injected into the battery case 8 by a reduced pressure method. Finally, the battery case was completed by caulking the opening end of the battery case to the sealing plate 10 via the gasket 9.

(5) Measurement of capacity retention rate The nonaqueous electrolyte secondary battery was charged and discharged at an environmental temperature of 20 ° C. Charging was performed for 2 hours at a current of 400 mA with a charge end potential of 4.2 V. The discharge was performed at a current of 1400 mA and a discharge end potential of 3.0V. The battery capacity at the 10th cycle was defined as the initial capacity of the battery.
Thereafter, the battery was further charged, and the charged battery was stored at 100 ° C. for 2 hours. Next, the battery after storage was discharged under the same conditions as described above, and the capacity after storage was determined. The ratio of the obtained capacity after storage to the initial capacity was obtained as a percentage and used as the capacity maintenance ratio.
Example 2

  A coating layer containing Al as the metal element M and Cl as the halogen element was formed on the surface of the lithium nickel composite oxide prepared in the same manner as in Example 1.

1 kg of lithium nickel composite oxide was placed in an atmosphere-controlled rotary kiln furnace (kiln rotation speed: 4 rpm), heated to 200 ° C. at a heating rate of 5 ° C./min, and held at that temperature. The coating material AlCl ₃ was gasified at 200 ° C. and introduced into the furnace for 20 minutes under the condition of a flow rate of 1 L / min. Thereafter, the introduction of AlCl ₃ was stopped, and the temperature was lowered to 25 ° C. at 5 ° C./min. As a result, AlCl ₃ was brought into contact with the surface of the lithium nickel composite oxide to uniformly form a coating layer containing AlCl ₃ . The thickness of the coating layer was 2 nm.
A battery was assembled in the same manner as in Example 1 except that the lithium nickel composite oxide having the above coating layer was used, and the capacity retention rate was measured.
Example 3

  A coating layer containing Nb as the metal element M and F as the halogen element was formed on the surface of the lithium nickel composite oxide prepared in the same manner as in Example 1.

1 kg of lithium nickel composite oxide was placed in an atmosphere controlled rotary kiln furnace (kiln rotation speed: 4 rpm), heated to 300 ° C. at a temperature rising rate of 5 ° C./min, and held at that temperature. The coating material NbF ₅ was gasified at 300 ° C. and introduced into the furnace at a flow rate of 1 L / min for 20 minutes. Thereafter, the introduction of NbF ₅ was stopped and the temperature was lowered to 25 ° C. at 5 ° C./min. Thus, by contacting the NbF ₅ on the surface of the lithium nickel composite oxide, to form a uniform coating layer containing a NbF _5. The thickness of the coating layer was 4 nm.
A battery was assembled in the same manner as in Example 1 except that the lithium nickel composite oxide having the above coating layer was used, and the capacity retention rate was measured.
Example 4

  A coating layer containing Ta as the metal element M and Cl as the halogen element was formed on the surface of the lithium nickel composite oxide prepared in the same manner as in Example 1.

1 kg of lithium nickel composite oxide was placed in an atmosphere controlled rotary kiln furnace (kiln rotation speed: 4 rpm), heated to 300 ° C. at a temperature rising rate of 5 ° C./min, and held at that temperature. TaCl ₅ was gasified at 300 ° C. and introduced into the furnace at a flow rate of 1 L / min for 20 minutes. Thereafter, the introduction of TaCl ₅ was stopped, and the temperature was lowered to 25 ° C. at 5 ° C./min. Thereby, TaCl ₅ was brought into contact with the surface of the lithium nickel composite oxide, and a coating layer containing TaCl ₅ was uniformly formed. The thickness of the coating layer was 4 nm.
A battery was assembled in the same manner as in Example 1 except that the lithium nickel composite oxide having the above coating layer was used, and the capacity retention rate was measured.
Example 5

  A coating layer containing Zr as the metal element M and Cl as the halogen element was formed on the surface of the lithium nickel composite oxide prepared in the same manner as in Example 1.

1 kg of lithium nickel composite oxide was placed in an atmosphere-controlled rotary kiln furnace (kiln rotation speed: 4 rpm), heated to 400 ° C. at a heating rate of 5 ° C./min, and held at that temperature. ZrCl ₄ was gasified at 400 ° C. and introduced into the furnace at a flow rate of 1 L / min for 20 minutes. Thereafter, introduction of ZrCl ₄ was stopped and the temperature was lowered to 25 ° C. at 5 ° C./min. As a result, ZrCl ₄ was brought into contact with the surface of the lithium nickel composite oxide to uniformly form a coating layer containing ZrCl ₄ . The thickness of the coating layer was 5 nm.
A battery was assembled in the same manner as in Example 1 except that the lithium nickel composite oxide having the above coating layer was used, and the capacity retention rate was measured.
Example 6

  A covering layer containing Sn as the metal element M and Cl as the halogen element was formed on the surface of the lithium nickel composite oxide prepared in the same manner as in Example 1.

1 kg of lithium nickel composite oxide was placed in an atmosphere-controlled rotary kiln furnace (kiln rotation speed: 4 rpm), heated to 200 ° C. at a heating rate of 5 ° C./min, and held at that temperature. SnCl ₄ was gasified at 200 ° C. and introduced into the furnace at a flow rate of 1 L / min for 20 minutes. Thereafter, the introduction of SnCl ₄ was stopped and the temperature was lowered to 25 ° C. at 5 ° C./min. Thus, SnCl ₄ was brought into contact with the surface of the lithium nickel composite oxide to uniformly form a coating layer containing SnCl ₄ . The thickness of the coating layer was 5 nm.
A battery was assembled in the same manner as in Example 1 except that lithium nickel oxide having the above coating layer was used, and the capacity retention rate was measured.
Example 7

  A coating layer containing B as the metal element M and Cl as the halogen element was formed on the surface of the lithium nickel composite oxide prepared in the same manner as in Example 1.

1 kg of lithium nickel composite oxide was placed in an atmosphere-controlled rotary kiln furnace (kiln rotation speed: 4 rpm), and BCl ₃ was introduced into the furnace at 25 ° C. and a flow rate of 1 L / min for 20 minutes. As a result, BCl ₃ was brought into contact with the surface of the lithium nickel composite oxide to uniformly form a coating layer containing BCl ₃ . The thickness of the coating layer was 2 nm.
A battery was assembled in the same manner as in Example 1 except that the lithium nickel composite oxide having the above coating layer was used, and the capacity retention rate was measured.
<< Comparative Example 1 >>

A battery was assembled in the same manner as in Example 1 except that the coating layer was not formed on the surface of the lithium nickel composite oxide, and the capacity retention rate was measured.
The results are shown in Table 1 for Examples 1 to 7 and Comparative Example 1.

  A battery using a lithium nickel composite oxide having a coating layer as a positive electrode active material had a small decrease in capacity even after high-temperature storage. This is because the surface of the positive electrode active material is inactivated by the coating layer containing the metal halide, and the elution of the positive electrode active material at a high temperature and the decomposition of the nonaqueous electrolyte on the surface of the positive electrode are suppressed. For this reason, it is considered that deterioration of battery characteristics is suppressed.

  In addition, it was confirmed that the effects of the present invention can be obtained even when a coating layer containing a metal element M and a halogen element other than those described above is used.

  By using the positive electrode active material containing the lithium nickel composite oxide of the present invention, the reliability and safety of the battery are improved even during high-temperature storage or in an overcharged state.

It is a longitudinal cross-sectional view of the cylindrical nonaqueous electrolyte secondary battery based on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode lead 5 Negative electrode lead 6 Upper insulating plate 7 Lower insulating plate 8 Battery case 9 Gasket 10 Sealing plate

Claims (10)

A lithium-containing composite oxide, and a coating layer covering at least a part of the surface of the lithium-containing composite oxide,
The lithium-containing composite oxide contains Ni;
The coating layer includes a metal element M and a halogen element;
A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the metal element M includes at least one selected from the group consisting of Al, Ta, W, Zr, Nb, Sn, and B. The lithium-containing composite oxide has the general formula Li _a Ni _b Me _c O ₂ (where 0 <a ≦ 2, 0 <b ≦ 1, c = 1−b, Me is Al, Ti, V, Mn, Co 2. A positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, comprising a compound represented by at least one selected from the group consisting of Fe, Cr, Cu, Zn and Mg.   The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 2, wherein the metal element M includes at least one selected from the group consisting of Ta, W, Zr, Nb, Sn, and B.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the coating layer includes a halide of the metal element M.   The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the coating layer has a thickness of 1 to 100 nm.   The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the coating layer has a thickness of 2 to 5 nm.   The non-metallic element according to claim 1, wherein the metal element M includes at least one selected from the group consisting of Al, Ta, Zr, Sn, and B, and the halogen element includes at least one of F and Cl. Positive electrode active material for water electrolyte secondary battery.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the metal element M includes at least one of W and Nb, and the halogen element includes Cl. Comprising a positive electrode, a negative electrode capable of inserting and extracting lithium ions, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte;
The non-aqueous electrolyte secondary battery in which the said positive electrode contains the positive electrode active material for non-aqueous electrolyte secondary batteries in any one of Claims 1-8.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a gaseous metal halide is brought into contact with the lithium-containing composite oxide to coat at least a part of the surface of the lithium-containing composite oxide with the metal halide. For producing a positive electrode active material for use.

Images