In the layered lithium oxide spinel structures, a major problem that is encountered is that of oxygen release due to the overlapping of the 3d band of the transition metal and the 2p band of O 2-. To overcome this problem, Fe 2+ / Fe 3+ as a transition metal has been used as its 3d bands are far above the 2p bands of oxygen. This leads to structural stability and has resulted in the birth of phospho-olivine cathode chemistries with LiFePO4 being the most prominent. In the LFP crystal structure, oxygen atoms form hexagonal close packing with lithium atoms and iron atoms being located at octahedral voids. The tetrahedral voids are occupied by phosphorus atoms. The phosphorus atoms form covalent bonds with four neighbouring oxygen atoms to distort the structure as shown in Figure .