Laser‐Induced Graphene Assisting Self‐Conversion Reaction for Sulfur‐Free Aqueous Cu‐S Battery

In aqueous/nonaqueous metal‐sulfur batteries, sulfur‐based redox couple exhibits significant challenges mainly due to its low electrochemical kinetics, potential shuttle effect, and large volume change. Although massive researches have been conducted to optimize or replace metal anode and cathode composite, major challenges caused by the dependency on sulfur‐based redox couple still remain. In this study, a novel redox couple of CuS/Cu2S, which provides the same theoretical capacity (based on conventional S/S2− redox couple) by changing the valence of ion charge carrier, is proposed. For achieving high reversibility, commercially viable laser‐induced graphene (LIG) is fabricated and used for the first time in aqueous metal‐sulfur batteries. By virtue of the synergism between novel redox couple and LIG, aqueous CuS/Cu2S battery delivers a highly reversible capacity of 1654.9 mAh g−1 in the initial cycle and retains 91.2% with 1509.5 mAh g−1 after 328 cycles. When being cycled at 2.8 A g−1, its reversible capacity still retains 92.1% after 410 cycles. This study provides a new choice by using a sulfur‐free redox couple from screening thermodynamic parameters and analyzes the functional mechanism of LIG by density functional theory, aiming to innovate the energy storage mechanism of aqueous metal‐sulfur batteries. S‐free self‐conversion is introduced to avoid defects from a S‐based cathode by adopting CuS/Cu2S redox couple to fully undertake energy storage tasks, and laser‐induced graphene as polar carbon material is first applied in the metal‐sulfur system for efficient electrochemical process and excellent kinetic properties.