Modifying of LiNi0.8Co0.2O2 Cathode Material by Chemical Vapor Deposition Coating to Improve Thermal Stability

Abstract

In this paper, we tried to find answers to safety problems due to use of transition metal oxide as positive electrodes in the lithium ion batteries. The exothermic reaction at high temperature induced by the contact between positive electrode in the charged state, such as LiNi_0.8Co_0.2O₂ and the liquid electrolyte solution based of LiPF6 (EC, DMC) is reduced by formation of ceramic oxide. Al₂O₃ – and ZnO-coated are synthesized on the surface of LiNi_0.8Co_0.2O₂ particles by chemical vapor deposition. The influences of deposit on the properties of starting material, in particular the thermal stability, are characterized by using, X-ray diffraction, electrochemical measurements and differential scanning calorimeter (DSC). Al₂O₃-coated sample show fading specific capacity during the first cycle. However, after several cycles a retention capacity is observed. ZnO-coated LiNi_0.8Co_0.2O₂ is inactive electrochemically as shown by X-rays diffraction pattern by the existence of two phases. With regard to DSC analysis in Al₂O₃-coated, one observe about 35% of reduction of heat flow during the exothermic reaction. The CVD method must be improved to obtain interesting results with regard to the electrochemical performances of treated material.

Keywords: lithium-ion batteries, CVD coating; alumina, layered cathode; electrochemistry, X-ray diffraction Thermal stability