Cathode active material

1 . A cathode active material containing:

a transition metal oxide, having a two-dimensional layered crystal structure when being discharged and a three-dimensional crystal structure when being charged, wherein

an organic molecule that is a glycol ether or a dialkyl ether is disposed between two or more unit layers of the two-dimensional layered crystal structure, and

wherein

when being charged, an oxygen of the organic molecule is bonded reversibly with a transition metal of the transition metal oxide to transform the two-dimensional layered crystal structure into the three-dimensional crystal structure,

the two-dimensional layered crystal structure is thermodynamically stable, where a unit lattice of the transition metal oxide contains the transition metal and oxygen bonded with each other, and transition metal filling octahedral sites of the unit lattice is two-dimensionally extended,

the three-dimensional crystal structure is thermodynamically metastable, where the unit lattice having the transition metal filling octahedral sites and a unit lattice having transition metal filling tetrahedral sites are mixed, and

the cathode active material is expressed by a following Chemical Formula 1:

Me x AO 2 ·y OC

wherein, in Chemical Formula 1,

Me is at least one metal element selected from a group consisting of an alkali metal element and an alkaline earth metal element,

A is transition metal,

OC is the glycol ether or the dialkyl ether, and

0.23≤x≤1, and 0.01≤y≤0.5.

2 . The cathode active material of claim 1 , wherein the two-dimensional crystal structure includes two or more unit layers composed of the transition metal oxide, and contains at least one metal element disposed between the two or more unit layers and selected from a group of metals other than transition metal.

3 . The cathode active material of claim 1 , wherein the Me is at least one element selected from Li, Na, K, Ca, and Mg.

4 . A cathode active material containing:

a transition metal oxide, having a two-dimensional layered crystal structure when being discharged and a three-dimensional crystal structure when being charged, wherein

an organic molecule is disposed between two or more unit layers of the two-dimensional layered crystal structure, and

wherein

when being charged, oxygen of the organic molecule is bonded reversibly with a transition metal of the transition metal oxide to transform the two-dimensional layered crystal structure into the three-dimensional crystal structure,

the two-dimensional layered crystal structure is thermodynamically stable, where a unit lattice of the transition metal oxide contains the transition metal and oxygen bonded with each other, and transition metal filling octahedral sites of the unit lattice is two-dimensionally extended,

the three-dimensional crystal structure is thermodynamically metastable, where the unit lattice having the transition metal filling octahedral sites and a unit lattice having transition metal filling tetrahedral sites are mixed, and

the cathode active material has a composition Na 0.27 MnO 2 ·0.54C 6 H 14 O 3 .