Lithium secondary battery

Abstract

A lithium secondary battery has small internal resistance and has good charge-discharge cycle characteristics, with a lithium transition metal compound being used as a positive active material. A portion of transition element Me, which comprises Ni, Co or both Ni and Co, in a lithium transition metal compound LiMeO 2 to be used as a positive active material is substituted for with at least two elements selected from among Ti, Li and Mn. The compound also corresponds to the formula LiM z (Ni X1 Co X2 ) 1-Z O 2 , in which: 0≦X1≦1; 0≦X2≦1; X1+X2=1; M comprises at least two elements selected from among Ti, Li and Mn; and 0<Z<1.

1 . A lithium secondary battery, comprising: 
 a positive active material comprising lithium transition metal compound corresponding to the formula LiMeO 2 ,    wherein Me comprises Ni, Co or both Ni and Co, a portion of which is substituted for with at least two elements selected from among Ti, Li and Mn, said compound also corresponding to the formula LiM z (Ni X1 Co X2 ) 1-Z O 2 , in which:    0≦X1≦1;    0≦X2≦1;    X1+X2=1;    M comprises at least two elements selected from among Ti, Li and Mn; and    0<Z<1.    
     
     
         2 . A lithium secondary battery as recited in  claim 1 , wherein said lithium transition metal compound has a two-dimensionally layered configuration.  
     
     
         3 . A lithium secondary battery as recited in  claim 1 , wherein a ratio of Z/(X1+X2) is not less than 0.05 and not more than 0.3.  
     
     
         4 . A lithium secondary battery as recited in  claim 1 , further comprising a negative active material which comprises carbon.  
     
     
         5 . A lithium secondary battery as recited in  claim 1 , further comprising a negative active material selected from the group consisting of amorphous carbon material, artificial graphite and natural graphite.  
     
     
         6 . A lithium secondary battery as recited in  claim 1 , wherein the lithium transition metal compound is composed by firing a mixed compound comprising salts and/or oxides having been prepared with a predetermined ratio in the presence of oxygen within a temperature range of 600° C. to 1000° C. for 5 hours to 50 hours.  
     
     
         7 . A lithium secondary battery as recited in  claim 1 , wherein the lithium transition metal compound has been synthesized and obtained by conducting at least first and second firing steps, with the firing temperature of the second step being higher than that of the first step.