Regulating the Solvation Chemistry of Poly-Ether Based Non-Flammable High Voltage Electrolyte Through Salt-Solvent Ratio Modulation

Abstract

Boosting the energy density and safety issue of lithium-ion batteries (LIBs) have become ever more important to satisfy the diverse applications. Herein, we present a new high voltage polyether-based electrolyte (HVPEE) by molecular design that can endure high-voltage operations and also present non-flammable features. Especially, HPVEEs show better compatibility and stability with electrode than conventional electrolyte. We find that the solvent separated ion pair (SSIP) and contact ion pair (CIP) dominate the ion-solvent structure of HPVEEs, rather than the free solvent and ions. In this way, the oxidative decomposition of HPVEE on the cathode interface can be suppressed significantly due to the lower highest occupied molecular orbital of SSIP complex structure than that of free TFSI - . As a result, the oxidation voltage can achieve as high as 5.35 V when the ether group/Li is optimized at 10/1 in the HVPEE, enabling the LiFePO 4 //Li full cell deliver a capacity of 165 mA h g -1 with a capacity retention of 98 % after 200 cycles. Moreover, when the cut-off voltage is 4.4 V, the discharge capacity of the LiNi 0.6 Mn 0.2 Co 0.2 O 2 //Li full cell can still reach 143 mA h g -1 after 80 cycles.

Keywords: PEGDME, poly-ether electrolytes, high-voltage, solvation structure, molecular dynamics simulation