Research for High Initial Coulombic efficiency of Silicon Monoxide for Li-ion batteries Anode

Abstract

Silicon has attracted attention as a substitute for existing carbon-based anode materials because it has a high charge / discharge capacity through an alloy reaction with lithium. In particular, the theoretical capacity of silicon has about 4200mAh/g. Unfortunately, the lifetime characteristic such as electrode breakage were remarkable due to the large volume change due to the alloying reaction in the charge / discharge. To solve this problem silicon oxide has been developed as a solution. Oxide matrix in SiO can accommodate huge expansion but, large 1st cycle irreversible capacity lead to poor initial coulombic efficiency. Almost previous studies have developed materials with low irreversible capacity loss. However before that is meaningful, silicon reaction is completely performed. We study initial coulombic efficiency of the silicon oxide form the perspective reversible capacity not of irreversible capacity, and to understand the reason of reversible capacity shortage. The insufficient reaction due to kinetic factor and the thermodynamic properties of insufficient reversible capacity, silicon suffer strong compressive stress during the lithiation that could drop the reaction potential of silicon. As a result, we confirm residual c-Si that makes insufficient reversible capacity and compressive stress on c-Si derived from Rama peak shift. Since SiO is not fully lithiatied by stress, a reversible capacity shortage lowers initial coulombic efficiency. The proper disproportion and pre-reaction were performed to release the stress of SiO. As a result, the stress was released and the fully lithiated reaction was confirmed. Also, the initial coulombic efficiency was improved without changing the reversible capacity and high lifetime characteristics.