High‐Valence‐Cation‐Induced Lattice Expansion for Activating Li ₂ S Cathode in All‐Solid‐State Lithium‐Sulfur Batteries

ABSTRACT The practical deployment of lithium sulfide (Li 2 S) cathodes in all‐solid‐state lithium‐sulfur batteries (ASSLSBs) is challenged by their poor innate conductivities and high activation barriers. Here, we demonstrate a lattice engineering strategy using Zr 4+ substitution to fundamentally activate Li 2 S. The introduced Zr 4 + expands the lattice, creating lithium vacancies that enhance ionic conductivity by two orders of magnitude. Simultaneously, Zr─S orbital hybridization narrows the bandgap for superior electronic conductivity and weakens Li─S bonds to lower the activation energy. This synergistic effect enables a highly reversible solid‐state sulfur conversion. As a result, our ASSLSB delivers an ultrahigh energy density of 996.2 Wh kg −1 based on the cathode with a record 65 wt.% electrode‐level Li 2 S content and maintains stability for over 100 cycles, far exceeding the conventional configuration of ∼40 wt.% loading. This strategy establishes a viable pathway toward practical high‐energy‐density ASSLSBs by fundamentally activating Li 2 S electrochemistry.