Breaking the Conductivity–Stability Trade-Off in Na ₃ SbS ₄ Solid Electrolytes via Synergistic Codoping with As and Se

Sulfide solid electrolytes for all-solid-state sodium batteries are inherently constrained by the strong coupling among ionic conductivity, interfacial stability, and environmental tolerance, which remains insufficiently addressed by conventional single-element doping strategies. The lack of a unified design principle to regulate these interdependent properties has hindered their practical deployment. Herein, we propose a coregulation paradigm that simultaneously engineers the anion and cation sublattices to decouple these coupled limitations in Na 3 SbS 4 -based electrolytes. By cointroducing As and Se, a cubic glass-ceramic Na 3 Sb 0.75 As 0.25 S 3.8 Se 0.2 is constructed, where lattice topology, bonding covalency, and defect landscape are cooperatively modulated. This dual-site regulation not only expands the Na + migration framework through a more polarizable Se-substituted anion network, but also reinforces structural robustness and interfacial compatibility via enhanced covalent interactions associated with As incorporation. Importantly, such synergistic modulation suppresses grain boundary resistance and enables quasi-continuous ion transport across the electrolyte, representing a transition from grain boundary-limited to bulk-dominated conduction behavior. As a result, the optimized electrolyte achieves a high ionic conductivity of 1.83 mS/cm with a low activation energy of 0.198 eV, along with a high critical current density of 1.405 mA/cm 2 and prolonged stable cycling over 400 h against Na metal. Beyond the specific material system, this work establishes a generalizable coregulation strategy for simultaneously tuning transport kinetics and interfacial chemistry in sulfide electrolytes, providing a conceptual framework for overcoming long-standing trade-offs in solid-state ionics.