Decent Fast-Charging Performance of Li-Ion Battery Achieved by Modifying Electrolyte Formulation and Charging Protocol

Abstract

In this work, two strategies have been attempted to achieve decent fast-charging performances of Li-ion batteries. The first is to combine lithium bis(fluorosulfonyl)imide (LiFSI) and dimethoxyethane (DME) into an electrolyte for high ionic conductivity of the bulk electrolyte and the electrolyte-electrode interphases, and the second is to limit charging capacity within 80% state-of-charge (SOC) for stable capacity retention by lowering charging rate without increasing total charging time in the standard constant current-constant voltage (CC-CV) charging protocol. It is found that using 5 wt% fluoroethylene carbonate (FEC) as an additive enables the hybridization of 20 wt% DME into the electrolyte without adverse effects on the initial formation cycles and ongoing cycling in terms of coulombic efficiency and reversible capacity, and adding 2 wt% LiPF6 is beneficial to reducing charge-transfer resistance and stabilizing capacity retention. As a result, decent fast-charging performances are obtained from the 200 mAh graphite/LiNi0.80Co0.15Al0.05O2 pouch cells by using a 1.2 m (molality) LiFSI 3:5:2 ethylene carbonate (EC)/ethylmethyl carbonate (EMC)/DME + 5% FEC + 2% LiPF6 electrolyte (all by wt) and a modified CC-CV charging protocol consisting of CC charging at 4 C for a total of 12 min, which is the charging time equivalent to a 5 C charging protocol.