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 relatively low temperature greatly improve the structural stability of LiCoO2 cathodes. Coated LiCoO2 materials heat-treated at 400 and 500°C exhibit 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 hexagonal 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°C that shows uniform Sn distribution throughout the particles exhibits this phase transition during cycling, as does uncoated LiCoO2, leading to 51% capacity loss after 47 cycles. This phase transition also increases cation disorder upon cycling. © 2000 The Electrochemical Society. S1099-0062(00)03-128-X. All rights reserved.