Ethylene Carbonate Free Sulfone-Based Electrolyte for Enabling Superior Performance of High Ni-containing Li-Transition Metal Oxide Cathodes at High Voltage and High Temperature

Abstract

The present study introduces an ethylene carbonate (EC) free electrolyte, composed of 1 M LiPF₆ in ethyl methyl sulfone (EMS) and dimethyl carbonate (DMC) (3 : 7 by volume), for Li-ion batteries, which is better suited for usage with higher upper cut-off potentials, with high Ni-containing ‘layered’ Li- transition metal oxide cathodes (like Li−NMC811), and at elevated temperature. The as-designed and developed sulfone-based electrolyte exhibits superior anodic stability and lower electrolyte resistance, while suppressing the decomposition of LiPF₆ and facilitating the formation of a S-containing, more passivating, thinner and uniform CEI layer on Li−NMC811, despite the usage of a high upper cut-off potential of 4.5 V (vs. Li/Li⁺). Compared with conventional EC-based electrolyte, the sulfone-based electrolyte results in notably suppressed rise in impedance and improved cyclic-stability, with capacity retentions of ~87 % (vs. ~78 % for EC-based electrolyte) after 50 cycles @ C/10 at room temperature (going up to 4.5 V). Even at 45 °C, the sulfone-based electrolyte results in significantly higher initial Coulombic efficiency (viz., >80 % vs. ~40 %), higher reversible capacity (~230 mAh/g vs. ~178 mAh/g) and superior cyclic stability (~74 % vs. ~46 % retention after 50 cycles @ C/10); thus, revealing its superiority for usage at elevated temperature.