Adaptive Stress Response in 2D Graphene@Se Composite toward Ultra‐Stable All‐Solid‐State Lithium‐Selenium Batteries

Abstract All‐solid‐state lithium‐selenium batteries (ASSLSeBs) offer high energy density and improved safety for next‐generation energy storage. Still, selenium cathodes suffer from large volume changes during cycling, leading to mechanical stress and rapid capacity fade. To address this, a stress‐adaptive 2D graphene@Se composite cathode is developed, where small Se nanoparticles are anchored onto acid‐treated expanded graphite (AcEG) to enhance charge transport and alleviate stress. Mechanical characterization confirms that the composite effectively mitigates Li‐ion‐induced strain. As a result, ASSLSeBs with this cathode achieve exceptional cycling stability with ultrahigh capacity retention after 4000 cycles at 2 C and stable performance for over 400 cycles even under high active‐material loading. Furthermore, an all‐solid‐state Li‐Se pouch cell with a record energy density of 376.8 Wh kg⁻¹ is demonstrated, the highest reported for ASSLSeBs. This work presents a strategy for designing stress‐adaptive cathodes, enabling ultra‐stable ASSLSeBs for practical applications.