Degradation suppression effect of amorphous-hard-carbon-bundled Si-based negative electrode

Abstract

To improve the electrode calendar life of high-capacity Si, a non-core–shell type Si negative electrode (hard-carbon-bundled Si, HCS) was investigated for preventing volume changes and particle breakage of nano-sized Si particles. This modified electrode, which consists of hard-carbon (HC)-bundled multiple nano-sized Si particles, prevents direct contact between Si and a liquid electrolyte and enables suppression of physical changes to the core HC. In this study, HCS samples were prepared at various carbonization temperatures and their physical and electrochemical properties were also evaluated. The charge–discharge properties of electrochemical cells with a HCS/C₆ mixed negative electrode gave adequate cycling performances and coulombic efficiencies, i.e. almost flat capacity retention and more than 99% coulombic efficiency over 100 cycles. The effects of the HCS carbonization temperature on the charge–discharge properties were investigated by determining the reaction electrode potential of the HCS. The physical and electrochemical properties of the HC phase in the HCS particle surface contributed to the charge–discharge capacity and good cycling properties. The reactivity of the nano-Si in HC effectively suppressed electrochemical cell degradation. The developed HCS is an appropriate material for protecting negative electrodes against significant volume changes in the Si and improving their electrochemical performances.