Programmable Solid Electrolyte Interphase Enables Simultaneous Optimization of Electrochemical Performance and Self-Discharge of Lithium Sulfur Batteries under Practical Conditions

Abstract

The development of lithium–sulfur batteries is impeded by their suboptimal electrochemical performance and significant self-discharge under practical conditions, especially at high sulfur-to-host ratios and low electrolyte-to-sulfur ratios. Under these conditions, improving electrochemical performance necessitates accelerating the polysulfides conversion, while reducing self-discharge entails inhibiting the same conversion (disproportionation reaction, a key contributor to self-discharge). Herein, to address this challenging contradiction, an imprisoning strategy is designed that utilizes programmable solid electrolyte interphase (SEI) layers formed only on the outer surface of TiO_2−x coated hollow carbon spheres (TiO_2−x@C). TiO_2−x@C is chosen primarily because that it supports regulated SEI growth upon simple voltage control, leveraging the different SEI formation potential on TiO_2−x and C, and its conductivity and catalytic property ensure high sulfur reaction kinetics. This strategy functions effectively even under practical conditions. The exposed internal surface provides abundant effective sites and the outer SEI (as a dense barrier) prevents polysulfides from migrating out of spheres, improving the electrochemical performance. These soluble polysulfides, being confined within spheres, easily reach saturation concentrations during storage, inhibiting disproportionation reaction. Consequently, SEI wrapped TiO_2−x@C/sulfur cathodes exhibit both high electrochemical performance and low self-discharge. This work is a new attempt to achieve above simultaneous optimization without performance compromise.