Lithium manganese composite oxide, secondary battery, electronic device, and method for forming layer

Abstract

To increase the volume density or weight density of lithium ions that can be received and released in and from a positive electrode active material to achieve high capacity and high energy density of a secondary battery. A lithium manganese composite oxide represented by Li x Mn y M z O w that includes a region belonging to a space group C2/c and is covered with a carbon-containing layer is used as the positive electrode active material. The element M is an element other than lithium and manganese. The lithium manganese composite oxide has high structural stability and high capacity.

1 . A lithium manganese composite oxide represented by Li x Mn y M z O w  comprising:
 a region belonging to a space group C2/c,   wherein element M is an element other than lithium and manganese, and   wherein the lithium manganese composite oxide is covered with a carbon-containing layer.   
     
     
         2 . The lithium manganese composite oxide according to  claim 1 , further comprising: a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26 (y+z)/w<0.5 are satisfied. 
     
     
         3 . The lithium manganese composite oxide according to  claim 1 ,
 wherein the carbon-containing layer includes a region with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm.   
     
     
         4 . A lithium manganese composite oxide represented by Li x Mn y M z O w  comprising:
 a region belonging to a space group C2/c,   wherein element M is an element other than lithium and manganese,   wherein a ratio of the integral intensity of L 3  peak to the integral intensity of L 2  peak of manganese that is obtained by electron energy loss spectroscopy (L 3 /L 2 ) is greater than or equal to 1.4 and less than or equal to 2.3, and   wherein the lithium manganese composite oxide is covered with a carbon-containing layer.   
     
     
         5 . The lithium manganese composite oxide according to  claim 4 , further comprising:
 a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26 (y+z)/w<0.5 are satisfied.   
     
     
         6 . The lithium manganese composite oxide according to  claim 4 , wherein the carbon-containing layer includes a region with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm. 
     
     
         7 . A lithium manganese composite oxide represented by Li x Mn y M z O w  comprising:
 a region where 0≦x/(y+z)<2, y>0, z>0, and 0.26≦(y+z)/w<0.5 are satisfied,   wherein the element M is an element other than lithium and manganese,   wherein the lithium manganese composite oxide includes a region covered with a carbon-containing layer, and   wherein the carbon-containing layer includes a region with a thickness of greater than or equal to 1 nm and less than or equal to 10 nm.   
     
     
         8 . The lithium manganese composite oxide according to  claim 1 , wherein the element M is nickel. 
     
     
         9 . The lithium manganese composite oxide according to  claim 4 , wherein the element M is nickel. 
     
     
         10 . The lithium manganese composite oxide according to  claim 7 , wherein the element M is nickel. 
     
     
         11 . A lithium-ion secondary battery comprising:
 the lithium manganese composite oxide according to  claim 1  as a positive electrode active material.   
     
     
         12 . A lithium-ion secondary battery comprising:
 the lithium manganese composite oxide according to  claim 4  as a positive electrode active material.   
     
     
         13 . A lithium-ion secondary battery comprising:
 the lithium manganese composite oxide according to  claim 7  as a positive electrode active material.   
     
     
         14 . An electronic device comprising:
 the lithium-ion secondary battery according to  claim 9 .   
     
     
         15 . A method for forming a carbon-containing layer on a surface of a lithium manganese composite oxide represented by Li x Mn y M z O w , comprising:
 forming a layer containing graphene oxide on a surface of the lithium manganese composite oxide; and   reducing the graphene oxide,   wherein the element M is an element other than lithium and manganese.