Cathode material for lithium ion secondary batteries, cathode member for lithium ion secondary batteries, and lithium ion secondary battery

1. A cathode material for a lithium ion secondary battery comprising an oxide represented by a composition formula Li 2+x (M,M A )(Si,M B )O 4 ; Li 2+x (M,M A )SiO 4 ; or Li 2+x M(Si,M B )O 4 ,

wherein M represents at least one element selected from the group consisting of Fe, Mn, Co and Ni; M A and M B substitute parts of M and Si, respectively, to compensate for an electric charge equivalent to x of Li + ,

wherein the M A represents a monovalent element, and the M B represents a trivalent element, a divalent element, or a monovalent element,

wherein in the composition formula representing the oxide, 0<x≦0.25, and

wherein a value of the x is a multiple of 0.03125.

2. The cathode material for a lithium ion secondary battery according to claim 1 , wherein the M A represents at least one element selected from Li, Na and K, and the M B represents at least one element selected from B, Al, Ga, In, Sc, Y, Mg, Ca, Na and K.

3. The cathode material for a lithium ion secondary battery according to claim 1 , wherein the oxide is represented by a composition formula Li 2+x Fe(Si,M B )O 4 or Li 2+x Mn(Si,M B )O 4 , wherein M B represents at least one element selected from B, Al and Ga.

4. The cathode material for a lithium ion secondary battery according to claim 1 , wherein

the cathode material is a composite composed of the oxide and a carbon material, and

the composite shows a sea-islands structure in which the oxide is scattered like islands in the carbon material, and an average circle-equivalent diameter of the islands of the sea-islands structure is 3 nm or more and 15 nm or less.

5. The cathode material for a lithium ion secondary battery according to claim 4 , wherein

the composite is a grain having a size of 1 μm or more and 20 μm or less, and

a void exists inside the grain.

6. The cathode material for a lithium ion secondary battery according to claim 5 , wherein the void having a size of 200 nm or more and less than the size of the grain exists inside the grain.

7. The cathode material for a lithium ion secondary battery according to claim 6 , wherein an abundance of the void is 20% or more and 80% or less in terms of an area rate in a section of the grain.

8. A cathode member for a lithium ion secondary battery comprising a metal foil provided with a cathode layer including: the cathode material for a lithium ion secondary battery according to claim 1 ; and a binder.

9. A lithium ion secondary battery comprising the cathode material for a lithium ion secondary battery according to claim 1 .