NiO2 obtained by electrochemical lithium deintercalation from lithium nickelate:: Structural modifications

A study of the Li//LixNi1.02O2 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 NiO2 composition. For the LixNi1+zO2 phases with z greater than or equal to 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 lends to the presence of stacking faults in both phases. Lithium can be reversibly reintercalated into the NiO2 phase. Good stability is observed at low charge-discharge rates during long-term cycling of the Li//LixNi1.02O2 system over a large potential range. This study also provided evidence fur inhumogeneity in the starting material at the crystallite scale. The Li0.98Ni1.02O2 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 a new phase, characterized by an O3 type packing, through a Ni3+ migration from the slab to the interslab space. (C) 2000 The Electrochemical Society. S0013-4651(99)08-013-1. All rights reserved.