Improvement of structural stability of LiCoO2 cathode during electrochemical cycling by sol-gel coating of SnO2

We report that sol-gel coating of SnO2 and subsequent heat-treatment at rel atively low temperature greatly improve the structural stability of LiCoO2 cathodes. Coated LiCoO2 materials heat-treated at 400 and 500 degrees C exh ibit excellent structural stability, retaining 86 and 84%, respectively, of their initial capacities after 47 cycles between 4.4 and 2.75 V at the 0.5 C rate. This is attributed to the disappearance of the transition to a hex agonal phase from a monoclinic phase at 4.15-4.2 V during cycling, a result of the formation of nonuniform Sn distribution throughout the particle, i. e., higher Sn concentration near the particle surface. In contrast, coated LiCoO2 heat-treated at 600 degrees C that shows uniform Sn distribution thr oughout the particles exhibits this phase transition during cycling, as doe s uncoated LiCoO2, leading to 51% capacity loss after 47 cycles. This phase transition also increases cation disorder upon cycling. (C) 2000 The Elect rochemical Society. S1099-0062(00)03-128-X. All rights reserved.