Synchronously Consolidating Li, Se, S, and C for Robust Li–SeS Batteries

S-redox involving solvated polysulfides is accompanied by volumetric change and structural decay of the S-based cathodes. Here, we propose a synchronous construction strategy for consolidating Li, Se, S, and C elements within a composite cathode via a paradigm reaction of 8Li+2Se+CS₂ = 2Li₄SeS+C. The obtained composite features crystalline Li₄SeS encapsulated in a carbon nanocage (Li₄SeS@C), exhibiting ultrahigh electrical conductivity, ultralow activation barrier, and excellent structural integrity, accordingly enabling large specific capacity (615 mAh g^-1) and high capacity retention (87.3% after 350 cycles) at 10 A g^-1. TOF-SIMS demonstrates its superior volumetric efficiency to a similar derivative SeS@C (2Se+CS₂ = 2SeS+C), and DFT reveals its lower activation barrier than Li₂S@C and Li₂Se@C. This consolidation design significantly improves the electrochemical performance of S-based cathodes, and the paradigm reaction guarantees structural diversity and flexibility. Moreover, employing a synchronous construction mechanism to maximize the synergistic effect between element consolidation and carbon encapsulation opens up a new approach for developing robust S or chalcogenide cathodes.