The synthesis and characterization of for a 4 V secondary lithium cell was done. The was prepared by ten different methods and characterized by x‐ray diffraction and electrochemical methods. prepared from and [or ] exhibited more than 150 mAh · g−1 of rechargeable capacity in the voltage range between 2.5 and 4.2 V in 1M propylene carbonate solution. The reaction mechanism was also examined and explained in terms of topotactic reaction. Lithium nickelate(III) (R3̅m; , in hexagonal setting) was oxidized to nickel dioxide (R3̅m; , ) via having a monoclinic lattice (C2/m). The nickel dioxide could be reversibly reduced to lithium nickelate(III). Factors affecting the electrochemical reactivity of are given and the possibility of using for 4 V secondary lithium cells is described.