Effect of Electrolyte Additives on Non-Nano-Si Negative Electrodes Prepared with Polyimide Binder

We investigated the effect of electrolyte additives on an untreated, conventional micro-sized (non-nano) Si electrode prepared with a polyimide (PI) binder (PI-Si electrode). Both additives, vinylene carbonate (VC) and fluoroethylene carbonate (FEC), improved the cycle stability of a PI-Si electrode half-cell. The solid-electrolyte interphase (SEI) formed by FEC includes a large amount of LiF and shows quite low resistance. This SEI effectively suppresses electrolyte decomposition, and an electrolyte containing VC mainly forms a SEI with organic components, and shows a smaller suppression effect on the electrolyte's excessive decomposition. From the AC impedance measurement and SEM observation results, we found that the formation of a massive SEI prevents contacts among Si particles and increases the charge-transfer resistance of the PI-Si electrode. The applied FEC suppresses the revolution of this resistance, meaning that FEC functions as an electrolyte additive suitable for PI-Si electrodes. A PI, Si, and soft-carbon composite (PI-Si-SC) electrode half-cell shows excellent cycle stability and rate performance by an adjusted amount of FEC (10 wt%). A full-cell, which includes a LiNi 1/3 Mn 1/3 Co 1/3 O 2 positive electrode, the PI-Si-SC negative electrode, and the electrolyte containing 10 wt% FEC, also exhibits quite good cycle stability.