Deciphering the Performance Enhancement, Cell Failure Mechanism, and Amelioration Strategy of Sodium Storage in Metal Chalcogenides‐Based Anodes

Abstract Transition metal chalcogenides (TMCs) emerge as promising anode materials for sodium‐ion batteries (SIBs), heralding a new era of energy storage solutions. Despite their potential, the mechanisms underlying their performance enhancement and susceptibility to failure in ether‐based electrolytes remain elusive. This study delves into these aspects, employing CoS₂ electrodes as a case in point to elucidate the phenomena. The investigation reveals that CoS₂ undergoes a unique irreversible and progressive solid–liquid–solid phase transition from its native state to sodium polysulfides (NaPSs), and ultimately to a Cu_1.8S/Co composite, accompanied by a gradual morphological transformation from microspheres to a stable 3D porous architecture. This reconstructed 3D porous structure is pivotal for its exceptional Na⁺ diffusion kinetics and resilience to cycling‐induced stress, being the main reason for ultrastable cycling and ultrahigh rate capability. Nonetheless, the CoS₂ electrode suffers from an inevitable cycle life termination due to the microshort‐circuit induced by Na metal corrosion and separator degradation. Through a comparative analysis of various TMCs, a predictive framework linking electrode longevity is established to electrode potential and Gibbs free energy. Finally, the cell failure issue is significantly mitigated at a material level (graphene encapsulation) and cell level (polypropylene membrane incorporation) by alleviating the NaPSs shuttling and microshort‐circuit.