Lithium-cobalt composite oxide, process for its production, positive electrode for lithium secondary cell employing it, and lithium secondary cell

Abstract

A composite oxide suitable for an active material of a positive electrode for a lithium secondary cell which can be used in a wide range of voltage, has a large electric capacity and excellent low temperature performance and is excellent in the durability for charge-discharge cycles and highly safe, a process for its production, and a positive electrode and a cell employing it, are presented. The composite oxide is a lithium-cobalt composite oxide which is represented by the formula LiCo 1-x M x O 2 , (wherein 0≦x≦0.02 and M is at least one member selected from the group consisting of Ta, Ti, Nb, Zr and Hf), and which has a half-width of the diffraction peak for (110) face at 2θ=66.5±1°, of from 0.070 to 0.180°, as measured by the X-ray diffraction using CuK α as a ray source.

1 : A hexagonal lithium-cobalt composite oxide for a lithium secondary cell, which is represented by the formula LiCo 1-x M x O 2 , wherein x is 0.0005≦x≦0.02 and M is at least one member selected from the group consisting of Ta, Ti, Nb, Zr and Hf, and which has a half-width of the diffraction peak for (110) face at 2θ=66.5±1°, of from 0.070 to 0.180°, as measured by the X-ray diffraction using CuK α  as a ray source.  
   
   
       2 : The hexagonal lithium-cobalt composite oxide for a lithium secondary cell according to  claim 1 , wherein 0.001≦x≦0.01.  
   
   
       3 : The hexagonal lithium-cobalt composite oxide for a lithium secondary cell according to  claim 1 , wherein 0.002≦x≦0.007.  
   
   
       4 : The hexagonal lithium-cobalt composite oxide for a lithium secondary cell according to  claim 1 , wherein the half-width of the diffraction peak for (110) face is from 0.100 to 0.165°.  
   
   
       5 : The hexagonal lithium-cobalt composite oxide for a lithium secondary cell according to  claim 1 , wherein the packing press density of the hexagonal lithium-cobalt composite oxide is from 2.90 to 3.35 g/cm 3 .  
   
   
       6 : The hexagonal lithium-cobalt composite oxide for a lithium secondary cell according to  claim 1 , wherein the packing press density of the hexagonal lithium-cobalt composite oxide is from 3.05 to 3.25 g/cm 3 .  
   
   
       7 : A positive electrode for a lithium secondary cell, which contains the hexagonal lithium-cobalt composite oxide for a lithium secondary cell as defined in  claim 1 , as an active material.  
   
   
       8 : The positive electrode for a lithium secondary cell according to  claim 7 , having a mixture comprising the active material, an electrically conductive material and a binder, supported on a current collector.  
   
   
       9 : The positive electrode for a lithium secondary cell according to  claim 8 , wherein the current collector is aluminum or stainless steel.  
   
   
       10 : A lithium secondary cell employing a positive electrode which contains the hexagonal lithium-cobalt composite oxide for a lithium secondary cell as defined in  claim 1 , as an active material.  
   
   
       11 : The lithium secondary cell according to  claim 10 , wherein a cyclic or chain carbonic ester is used as a solvent for the electrolyte.  
   
   
       12 : The hexagonal lithium-cobalt composite oxide for a lithium secondary cell according to  claim 1 , which is obtained by a process which comprises dry blending a cobalt oxyhydroxide powder having an average particle size of from 1 to 20 μm and a specific surface area of from 2 to 200 m 2 /g, a lithium carbonate powder having an average particle size of from 1 to 50 μm and a specific surface area of from 0.1 to 10 m 2 /g, and a powder of an oxide of metal element M having an average particle size of at most 10 μm and a specific surface area of from 1 to 100 m 2 /gm, and firing the mixture at a temperature of from 850 to 1,000° C. in an oxygen-containing atmosphere.