Improvement of the Thermal Stability of LiNi[sub 0.8]Co[sub 0.2]O[sub 2] Cathode by a SiO[sub x] Protective Coating

Abstract

The surface of LiNi 0.8 Co 0.2 O 2 particles was protected by a thin layer of SiO x 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 LiNi 0.8 Co 0.2 O 2 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 SiO x (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 LiNi 0.8 Co 0.2 O 2 powder. The CVD process is very reproducible, and despite a small degradation of the electrochemical performance, the SiO x coating is efficient to decrease by 50% the exothermic reaction occurring at around 210°C in the charged state. © 2004 The Electrochemical Society. All rights reserved.