High ionic conducting lithium fluoride rich solid electrolyte interphase induced by polysulfide for carbon-based dual ion batteries

Abstract

Carbon-based dual ion batteries (DIBs) promise a high working voltage, ease of production, low cost and low environmental impact, yet they suffer from poor electrochemical performances ascribed predominantly to electrolyte decomposition, consequently impacting the stability of solid electrolyte interphase (SEI) formation in the negative electrode. Herein, we report a facile pre-formation of lithium fluoride (LiF)-rich SEI derived from lithium polysulfide (LiPS) added lithium bis(trifluoromethane)sulfonimide (LiTFSI)-based electrolyte. A pre-formed lithium sulfide (Li2S) as the inner passivation layer effectively facilitates the growth of LiF on carbon anode, which greatly enhances the ionic conductivity of SEI and prevents the formation of Li dendrites. The designed electrolyte consisting of 3.4 M LiTFSI in the mixture of ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) (1:1 by vol.) with the addition of 0.1 M LiPS achieves excellent compatibility with activated carbon, delivered an initial specific capacity of 408 mAh g−1 with coulombic efficiency ∼100% at 1 A g−1 over 150 cycles. With an in-depth analysis of compositions and the distribution of decomposition products at the interface, the critical impact of Li2S on SEI formation is revealed. DIB full cells assembled using the carbon anodes with a pre-formed SEI layer delivered an initial discharge capacity of 57.2 mAh g−1 and average voltage of 4.35 V. The above-mentioned findings shed new light on SEI pre-forming technique for high-performance DIB based on the rational design of electrolytes.