Structure and electrochemistry of Li1±yNiO2 and a new Li2NiO2 phase with the Ni (OH)2 structure

Abstract We discuss the preparation and structure of 3R-Li x Ni 2- x O 2 for x near 1 and report the variation of the voltage of Li/Li 1± y NiO 2 cells versus y . Using electrochemical techniques and in situ X-ray diffraction we show that Li can be reversibly intercalated in Li 1- y NiO 2 for 0≤ y ≤0.6 and that over this range of y the lattice constants of the 3R phase change reversibly. Additional lithium can also be inserted electrochemically into LiNiO 2 to form a new Li 2 phase with the Ni(OH) 2 structure. When the additional Li is removed from Li 2 NiO 2 , the host lattice reverts to the LiNiO 2 structure, but there is substantial hysteresis in the voltage of Li/Li 1± y NiO 2 cells during this phase transition. The analogous phase, Li 2 CoO 2 , does not form when additional Li is added to LiCoO 2 by electrochemical methods.