LT-LiC0.9Ni0.1O2 prepared at 400 degrees C with a structure that is intermediate between an ideal lithiated spinel and a layered structure has been investigated as an electrode in rechargeable Lithium cells; it delivers a voltage vs. pure lithium that is significantly lower than the voltage provided by its high-temperature analogue, HT-LiCo0.9Ni0.1O2, (synthesized at 900 degrees C). The rechargeability of Li/LT-LiCo0.9Ni0.1O2 cells can be improved by leaching some lithium and a small amount of cobalt from LT-LiCo0.9Ni0.1O2 by acid treatment and loading the cells in a charged state. The improvement in electrochemical performance is attributed to the formation of a defect spinel phase Li-0.8[Co1.6Ni0.2]O-4 in which the lithium ions adopt the tetrahedral A sites and the cobalt and nickel ions the B sites of an A[B-2]O-4 spinel.