An Effective Mixed-Salt As Electrolyte Additive to Improve Calendar Life for Si Anode in Lithium Ion Batteries

Abstract

For the next generation of Lithium-ion batteries, Silicon is drawing attention as the upcoming anode materials with higher capacity than commercial graphite ( Silicon : 3590 mA h g-1vs Graphite : 375 mA h g-1). Especially, Si is suitable for long range electric vehicle from being higher theoretical capacity. However, the chronic problem of Si anode such as large expansion with fracture or pulverization has effect on the calendar life performance. In order to achieve the enhanced calendar life, we suggest that Ca and Mg mixed additive with electrolyte for Si anode in this work, based on our previous reports. In this work, analytical techniques such as NMR and Rietveld refinement was conducted to clarify effect of mixed salt. Ca and Mg inserted to bulk Si to cause formation of quaternary Li-Ca-Mg-Si phase with thermodynamic stability, and Ca salt make dense and strong CaF2 SEI layer on the Si particle, which protect the side reaction between Si particle and electrolyte in coin cell system,. The full cell with mixed additive electrolyte (called Gen FMC) shows enhanced calendar life performance with lower measured current and current leakage than that of baseline electrolyte (called Gen F), being brought by less side reaction. In adding to that, full cell with Gen FMC could delivered high specific capacity after 100 cycles with 47.4 % of retention (Gen F : 36.3%) and high columbic efficiency. We were also able to find that Gen FMC tends to have less cracking electrode surface than that of Si electrode with Gen F.