Layered oxide materials for batteries

Abstract

Materials are presented of the formula: A x M y M i zi O 2−d , where A is sodium or a mixed alkali metal including sodium as a major constituent; x>0; M is a metal or germanium; y>0; M i , for i=1, 2, 3 . . . n, is a transition metal or an alkali metal; z i ≧0 for each i=1, 2, 3 . . . n; 0<d≦0.5; the values of x, y, z i and d are such as to maintain charge neutrality; and the values of x, y, z i and d are such that x+y+Σz i >2−d. The formula includes compounds that are oxygen deficient. Further the oxidation states may or may not be integers i.e. they may be whole numbers or fractions or a combination of whole numbers and fractions and may be averaged over different crystallographic sites in the material. Such materials are useful, for example, as electrode materials in rechargeable battery applications. Also presented is a method of preparing a compound having the formula A x M y M i zi O 2−d .

1 . A method of preparing a compound having the formula A x M y M i   zi O 2−d , where A is an sodium or a mixed alkali metal including sodium, x>0, M is a transition metal, y>0, M i , for i=1, 2, 3 . . . n is a transition metal or an alkali metal, z i ≧0 for each i=1, 2, 3 . . . n, 0<d≦0.5, and the values of x, y, z i  and d are such as to maintain charge neutrality, the method comprising:
 a) mixing starting materials together, 
 b) heating the mixed starting materials at a temperature of between 400° C. and 1500° C., to obtain an oxygen-deficient reaction product having the formula A x M y M i   zi O 2−d′ ; and 
 c) cooling the reaction product, or allowing the reaction product to cool, under conditions that prevent significant re-incorporation of oxygen into the oxygen-deficient reaction product. 
 
     
     
         2 . A method as claimed in  claim 1  wherein cooling the reaction product comprises cooling the reaction product in one of an inert atmosphere and a reducing atmosphere. 
     
     
         3 . A method as claimed in  claim 1  wherein cooling the reaction product comprises cooling the reaction product in an inert atmosphere, the inert atmosphere being, or consisting substantially of, one or more inert gases. 
     
     
         4 . A method as claimed in  claim 1  wherein heating the mixed starting materials to obtain an oxygen-deficient reaction product comprises heating the mixed starting materials in an oxidising atmosphere. 
     
     
         5 . A method as claimed in  claim 1  wherein heating the mixed starting materials to obtain an oxygen-deficient reaction product comprises heating the mixed starting materials in air.