Study on the effect of electrode/electrolyte interface modification on the performance of Si composite electrode and of $LiCoO_2$ electrode at high voltage operation in lithium secondary battery

Abstract

Lithium secondary battery is one of the most widely used energy storage devices. The use of notebook PCs, cellular phones, digital cameras and many other portable electronics require batteries with higher energy density with safety. That resulted in the demand on lithium secondary batteries with higher energy density which be achieved by increasing either the capacity or operation voltage. Both of these approaches can be realized by using new electrode materials with higher capacity or higher operation voltage than before. New battery system with new electrode materials requires electrolyte system with high electrochemical stability suitable for the electrode material, and the control of electrode/electrolyte interface is one of the important researches for new battery system. The effect of electrolyte/electrode interface control for new negative composite electrode materials with high capacity was investigated. The poor cycling characteristics of the electrode materials with high volume change during cycling were to be enhanced by modifying the solid-electrolyte interphase layer on the negative electrode. To modify the SEI layer, an additive was introduced to the liquid electrolyte, and the effect of additive on the cycling performance was studied. Finally, new electrolyte system for composite electrode material was proposed. Also, the effect of surface film modification on positive electrode material for high voltage operation was investigated. Lithium cobalt oxide, commonly used positive electrode material in lithium secondary battery, is not stable over 4.2V and thus it is not suitable for high voltage operation due to the impedance growth caused by the reaction of liquid electrolyte and surface residual moistures. An additive was proposed to prevent the side reactions of electrolyte and residual moistures, and the effect was studied.