Double-phase electrolyte enabling the long-lasting redox mediation in Li–O2 batteries

Abstract

The achievement of practical Li–O2 batteries is impeded by their low discharge capacity, large charge overpotential, and short lifespan. In general, the use of electrolyte with a high-donor-number solvent such as dimethyl sulfoxide (DMSO) is able to drive the solution-mediated pathway, alleviating the premature passivation of cathode from the surface-mediated Li2O2 film growth, gaining large Li2O2 toroidal particles, and extending the discharge lifetime. However, direct electrochemical decomposition of Li2O2 toroidal products typically occurs at a high charge potential owing to the poor solid-solid contact between cathode catalysts and Li2O2 toroids. Besides, DMSO-based electrolytes are unstable to Li anode, leading to undesired parasitic reactions. To overcome above issues, herein, a double-phase electrolyte composed of 10-methylphenothiazine (MPT)-dissolved DMSO-based catholyte and octyltrimethoxysilane (TOOS)-based anolyte is designed taking advantages of the immiscibility of DMSO and TOOS solvents and the insolubility of MPT in TOOS. Benefiting from the rapid liquid-solid reaction between MPT+ and Li2O2 products, the blocked MPT shuttling in TOOS, and the good compatibility of TOOS-based electrolyte to Li anode, the assembled Li–O2 battery delivers a reduced charge overpotential and a robust cyclability over 250 cycles. This study provides a promising strategy for electrolyte design towards next-generation high-performance Li–O2 batteries.