Iodine-containing additive engineering for rejuvenating inactive lithium and constructing highly stable lithium metal anodes

Abstract

Inactive (‘dead’) lithium and conventional fragile solid-electrolyte interphase (SEI) usually cause performance degradation and safety hazards in Li-metal batteries. Recovering inactive lithium and constructing stable SEI are urgently required to enhance the capacity and lifespan of lithium metal batteries. Herein, we have designed a novel dual-additives electrolyte containing an I3−/I− redox couple for reviving the inactive lithium, and caffeic acid (CA) that can be anion-polymerised to modulate the composition and improve stability of the SEI. It’s found that the generated I3−/I− redox couple can turn the inactive Li2O into soluble Li+, and prompt the formation of SEI composed of inorganic LiI, Li3N and organic RCOOLi with high stability. Density functional theory (DFT) calculations indicate that the diffusion potential barrier of Li+ is significantly lower on the LiI-rich SEI interface, which can not only accelerate the transport of Li+ at the interface, but also effectively prevent I3− from attacking Li metal. Benefiting from this elaborate dual-additives electrolyte design, the symmetrical-cells present a superior electrochemical performance, i.e., high critical current density up to 10 mA cm−2, ultra-long lifespan over 7000 h at 1 mA cm−2, and over 2500 cycles under harsh conditions of high temperature (50 °C) and high current density (5 mA cm−2). In addition, as a proof of concept for practical applications of Li-metal batteries, Li|LiFePO4 full cell delivers excellent cycle stability and rate performance with low hysteresis voltage at a high cathode loading of 17.4 mg cm−2.