Colossal-dielectric cathode interface engineering enables interfacial stability in dry-processed Li₆PS₅Cl solid-state batteries

Dry-processed electrolytes have emerged as a leading direction for the commercialization of solid-state batteries, enabling the fabrication of rigid Li₆PS₅Cl (LPSC) into flexible electrolyte membranes while maintaining a high ionic conductivity on the order of 10^-3 S cm^-1. However, the practical application of this approach remains severely constrained by the intrinsic instability of LPSC, which renders it incompatible with conventional wet processed cathodes and leads to undesirable side reactions at the cathode interface. Herein, a colossal-dielectric cathode interfacial engineering strategy induced by calcium copper titanate (CCTO) is proposed. This approach fundamentally achieves interfacial isolation between LPSC electrolyte, cathode active materials, and conductive carbon, which effectively suppresses the detrimental interfacial reactions and parasitic processes triggered by their direct contact, and consequently prevents the anomalous capacity originating from interfacial parasitic oxidation (ACIPO) behavior that commonly plagues conventionally dry processed electrolyte based cells. Thereby, the high-voltage tolerance of dry-processed LPSC electrolyte membranes on the cathode side is markedly enhanced. Meanwhile, the colossal-dielectric effect together with the anchoring interaction toward TFSI^- effectively regulates the lithium-ion coordination environment at the cathode interface. As a result, the electrochemical stability window of the system is fundamentally extended to 4.62 V while preserving a high ionic conductivity of 1.44 mS cm^-1. Benefiting from this improvement, full cells coupling an LiFePO₄ (LFP) cathode with a lithium-metal anode exhibit outstanding cycling stability, delivering 89.2% capacity retention after 1100 cycles at 1C and room temperature. Moreover, NCM811/Li cells operated up to 4.4 V maintain stable cycling over 150 cycles. Small-format pouch cells further demonstrate remarkable mechanical robustness under bending, folding, and puncture conditions, highlighting an alternative and initially feasible pathway toward the practical commercialization of dry-processed solid-state electrolytes. To our knowledge, this work pioneers the integration of colossal dielectric CCTO into solid-state electrolytes (SSE).