High-Valence-Cation-Induced Lattice Expansion for Activating Li₂S Cathode in All-Solid-State Lithium-Sulfur Batteries

The practical deployment of lithium sulfide (Li₂S) 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 Zr⁴⁺ substitution to fundamentally activate Li₂S. 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 Li₂S 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 Li₂S electrochemistry.