Manganese oxide, lithium manganese complex oxide and cobalt-coated lithium manganese complex oxide, and preparation processes thereof

Abstract

A manganese oxide which has a calcium or/and magnesium content of 0.01 to 2.50 mol % based on the moles of manganese, a lithuim manganese complex oxide using the manganese oxide, and a cobalt-coated lithuim manganese complex oxide are disclosed. These provide a particularly high discharge capacity and are useful for the improvement of cycle characteristics of a secondary battery as an active material of a positive electrode for a secondary battery with a nonaqueous electrolyte.

What is claimed is:  
     
         1 . A manganese oxide which has a calcium or/and magnesium content of 0.01 to 2.50 mol % based on the moles of manganese.  
     
     
         2 . The manganese oxide of  claim 1  which has a BET specific surface area of 1 to 100 m 2 /g.  
     
     
         3 . The manganese oxide of  claim 1  or  2  which has a particle size distribution of not greater than 0.4.  
     
     
         4 . A process for preparing the manganese oxide, comprising the steps of: 
 adding to an aqueous magnesium salt solution, a calcium salt or/and magnesium salt such that the calcium or/and magnesium content based on the moles of manganese is 0.01 to 2.50 mol % and an aqueous alkali solution at an alkali equivalent ratio of between 0.1 and 10 based on the total of the manganese and the calcium or/and magnesium to obtain an aqueous suspension of manganese (II) hydroxide,    supplying an oxygen-containing gas into the aqueous suspension heated to a temperature of 20 to 100° C. to produce a precipitate by the oxidation of the manganese ions, and    collecting the precipitate after filtration, washing and drying.    
     
     
         5 . A lithium manganese complex oxide using the manganese oxide defined in any one of  claims 1  to  3  as a precursor.  
     
     
         6 . A process for preparing the lithium manganese complex oxide, which comprises the steps of: 
 mixing the manganese oxide of any one of  claims 1  to  3  with a lithium compound such that the molar ratio of lithium to manganese (Li/Mn) is 0.505 to 0.550,    compression molding the mixture to obtain a formed body, sintering the formed body in an oxidizing atmosphere, and pulverizing the sintered body.    
     
     
         7 . The process for preparing the lithium manganese complex oxide of  claim 6 , wherein the density of the formed body after the compression molding is not less than 1.5 g/cc.  
     
     
         8 . A cobalt-coated lithium manganese complex oxide, wherein the coating amount of cobalt (Z wt %) in relation to a BET specific surface area (S m 2 /g) of the lithium manganese complex oxide is within the range expressed by the following equation (1): 
       0.05× S≦Z≦ 1.50 ×S   (1) 
     
     
         9 . The cobalt-coated lithium manganese complex oxide of  claim 8 , wherein the cobalt is a spinel-structured cobalt oxide.  
     
     
         10 . The cobalt-coated lithium manganese complex oxide of  claim 9 , wherein a lattice constant of the cobalt oxide is 8.10±0.05 Å.  
     
     
         11 . The cobalt-coated lithium manganese complex oxide of any one of  claims 8  to  10 , a lattice constant of the lithium manganese complex oxide is 8.15 to 8.24 Å.  
     
     
         12 . A process for preparing the cobalt-coated lithium manganese complex oxide, comprising the steps of: 
 oxidizing lithium manganese complex oxide particles dispersed in an aqueous alkali solution and a cobalt compound at a temperature of 20 to 100° C. so that a cobalt oxide epitaxially grows on the lithium magnesium complex oxide, and    collecting the resulting oxide after filtration, washing and drying.