Surface engineering of argyrodite-Li₆PS₅Cl solid electrolytes with a polyborosiloxane copolymer for all-solid-state batteries

The development of robust solid electrolytes is a key challenge for realizing all-solid-state batteries (ASSBs) to replace commercial lithium-ion batteries (LIBs), which are currently used in various energy-storage applications. Argyrodite-Li₆PS₅Cl (LPSCl), a class of sulfide solid electrolytes, has been highlighted as the most practical candidate due to its high ionic conductivity (∼10⁻³ S cm⁻¹) and mechanical ductility. However, its vulnerability to moisture and structural instability at the interfaces with commercial cathode materials remain open problems. To overcome these limitations, we propose the design and synthesis of polyborosiloxane (PBS), a structural derivative of polydimethylsiloxane, synthesized using boric acid as a functional coating layer to enhance the atmospheric and interfacial stabilities of LPSCl solid electrolytes. The distinctive physicochemical properties of the PBS copolymer are essential for suppressing the evolution of H₂S through effective molecular absorption under humid conditions while simultaneously minimizing direct contact of LPSCl with moisture. Moreover, it is effective in mitigating the formation of a space-charge layer at the interfaces with commercial cathode materials, leading to a strong enhancement in the cycling stability and durability of ASSBs.