Regulating the solvation chemistry of non-flammable high voltage electrolyte through salt-solvent ratio modulation

Boosting the energy density and safety issue of lithium-ion batteries has become ever more important to satisfy the diverse applications such as energy storage and mobile electronic devices. Herein, we present a new high voltage polyether-based electrolyte (HVPEE) by solvation structure design that can endure high-voltage operations and also possess non-flammable features. Especially, HVPEEs 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 HVPEEs, rather than the free solvent and ions. In this way, the oxidative decomposition of HVPEE on the cathode interface can be suppressed significantly due to the reduced 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 LiFePO₄//Li full cells 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 4.5 V, the discharge capacity of the LiNi_0.6Mn_0.2Co_0.2O₂//Li full cell can reach 170 mA h g^-1.