NiO2 Obtained by Electrochemical Lithium Deintercalation from Lithium Nickelate: Structural Modifications

A study of the Li/Li{sub x}Ni{sub 1.02}O{sub 2} system at high potential has shown the successive formation of two phases with O3 (AB CA BC) and O1 (AB) oxygen packings, respectively, near the NiO{sub 2} composition. For the Li{sub x}Ni{sub 1+z}O{sub 2} phases with z {ge} 0.07, only the O3 packing is observed at the end of lithium deintercalation: the extra nickel ions present in the interslab spaces destabilize the O1 type packing. The nonhomogeneous distribution of extra nickel ions from one interslab space to another leads to the presence of stacking faults in both phases. Lithium can be reversibly reintercalated into the NiO{sub 2} phase. Good stability is observed at low charge-discharge rates during long-term cycling of the Li/Li{sub x}Ni{sub 1.02}O{sub 2} system over a large potential range. This study also provided evidence for inhomogeneity in the starting material at the crystallite scale. The Li{sub 0.98}Ni{sub 1.02}O{sub 2} material corresponds to a mixture of various phases with very similar stoichiometries. The crystallites which are closest to the ideal stoichiometry form an O1 type phase which is stable at high potential, whereas those which are farthest from stoichiometry lead to an O1 type phase which is slowly transformed into amore » new phase, characterized by an O3 type packing, through a Ni{sup 3+} migration from the slab to the interslab space.« less