Improvement of the thermal stability of LiNi0.8Co0.2O2 cathode by a SiOx protective coating

The surface of LiNi0.8Co0.2O2 particles was protected by a thin layer of SiOx deposited via chemical vapor deposition (CVD). The aim was to enable lithium ions to intercalate into the cathode material through the coating layer while preventing the surface of the cathode to be directly in contact with the electrolyte media. The structure of LiNi0.8Co0.2O2 is only slightly modified by the CVD process. The film deposited around the cathode particles was characterized. It consists of an amorphous layer of understoichiometric silicon dioxide SiOx (x<2) which is 3-5 nm thick. The initial charge capacity of the starting material is not affected by the protective coating; nevertheless, the capacity fade is slightly increased upon cycling compared to the uncoated LiNi0.8Co0.2O2 powder. The CVD process is very reproducible, and despite a small degradation of the electrochemical performance, the SiOx coating is efficient to decrease by 50% the exothermic reaction occurring at around 210 degrees C in the charged state. (C) 2004 The Electrochemical Society.