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[Display omitted] 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 LiFePO 4 //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 0.6 Mn 0.2 Co 0.2 O 2 //Li full cell can reach 170 mA h g−1. [ABSTRACT FROM AUTHOR]

[Display omitted] Solid-state polymer electrolytes are outstanding candidates for next-generation lithium metal batteries in the realm of high specific energy densities, high safeties and tight contact with electrodes. However, their applications are still hindered by the limitations that no single polymer is electrochemically stable with the oxidizing high-voltage cathode and the highly reductive Li anode, simultaneously. Herein, a bilayer asymmetric polymer electrolyte (SL-SPE) without accessional interface resistance that using poly (ethylene glycol) diacrylate (PEGDA) as a "bridge" to connect the sulfonyl (O S = O)-contained oxidation-tolerated layer and polyether-derived reduction-tolerated layer (SPE), is proposed and synthesized by sequential two-step UV polymerizations. SL-SPE can provide widened electrochemical stability window up to 5 V, while simultaneously deploying a stable Janus interface property. Eventually, the superior high-voltage (4.4 V) cycling durability can be displayed in LiNi 0.6 Co 0.2 Mn 0.2 O 2 |SL-SPE|Li batteries. This finding provides a bran-new idea for designing multifunctional polymer electrolytes in the application of solid-state batteries. [ABSTRACT FROM AUTHOR]