COMPOSITE METAL OXIDE AND SODIUM RECHARGEABLE BATTERY

摘要

The present invention provides a sodium secondary battery capable of reducing the amount used of a scarce metal element such as lithium and cobalt and moreover, ensuring a larger discharge capacity after repeating charge/discharge as compared with conventional techniques, and a mixed metal oxide usable as the positive electrode active material therefor. The mixed metal oxide of the present invention comprises Na, Mn and M 1 wherein M 1 is Fe or Ni, with a Na:Mn:M 1 molar ratio being a:(1-b):b wherein a is a value falling within the range of more than 0.5 and less than 1, and b is a value falling within the range of from 0.001 to 0.5. Another mixed metal oxide of the present invention is a mixed metal oxide represented by the following formula (1): Na a Mn 1-b M 1 b O 2 (1) wherein M 1 , a and b each have the same meaning as above. The positive electrode active material for sodium secondary batteries of the present invention comprises the mixed metal oxide above.