Interfacial Stabilization of Li_1.3Al_0.3Ti_1.7(PO₄)₃ Solid Electrolytes Enabled by a Sulfone-Based Crystalline Organic...

NASICON-structured Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) solid electrolyte (SE) exhibits satisfactory ionic conductivity and robust mechanical strength, but it suffers from interfacial instability against lithium metal anodes due to Ti⁴⁺ reduction, which limits its application in solid-state lithium metal batteries (SSLMBs). Herein, we developed a sulfone-based crystalline organic interlayer (COI) composed of dimethyl sulfone and lithium bis(trifluoromethanesulfonyl)imide at an optimized molar ratio of 8:2, and applied it to LATP pellet surfaces via a melt-casting process. The standalone COI exhibits a room-temperature ionic conductivity of 0.67 mS cm^-1. The resulting LATP@COI composite shows an ionic conductivity of 0.78 mS cm^-1 and a critical current density of 1.5 mA cm^-2. Li|LATP@COI|Li symmetric cells deliver stable cycling for over 700 h at 0.1 mA cm^-2. Full cells using LiFePO₄ and LiNi_0.5Co_0.2Mn_0.3O₂ cathode with the lithium metal anode retain 93.1% and 92.3% of their initial capacities after 200 cycles, respectively, while maintaining excellent rate capability up to 2 C and operable discharge down to -40 °C. This COI provides a practical interfacial-engineering strategy to overcome the intrinsic limitations of LATP SEs for SSLMBs.