Factors limiting the electrochemical performance of oxide cathodes

An overview of the current understanding of the factors limiting the electrochemical performances of the layered, spinel, and olivine oxide cathodes is presented with a particular focus on the chemical and structural instabilities. The wide variations in the reversible capacity limits of LiMO2 layered oxide cathodes (140 mA h/g for LiCoO2 VS 160-200 mA h/g for LiNi1/3Mn1/3Co1/3O2 and LiNi0.5Mn0.5O2) could be explained on the basis of differences in chemical instabilities arising from an overlap of Mn+/(n+1)+:3d and O2-:2p bands. Degree of cation disorder and lithium extraction rate are found to influence the type of phases formed for the chemically delithiated Li1-xMO2 and the electrochemical rate capability. On the other hand, the lattice parameter difference between the two cubic phases formed during the charge-discharge process is found to play a significant role on the capacity retention, rate capability, and storage characteristics of the spinel oxide cathodes in addition to the well-known Mn dissolution problem. Despite excellent structural and chemical stabilities, the olivine LiFePO4 suffers from poor electrical conductivity and consequent low rate capability. (c) 2006 Elsevier B.V. All rights reserved.