Two in one: The use of hexagonal copper sulfide (CuS) nanoparticles as a bifunctional high-performance cathode and as a reinforced electrolyte additive for an all-solid-state lithium battery

•Hexagonal CuS nanoparticles are used as bifunctional cathode/electrolyte additives.•PEO with (1 wt%) CuS filler improves ionic conductivity/Li+ transfer coefficient.•PEO with (1 %wt) CuS filler exhibits 200x Li stripping/plating without dendrites. All Solid-State Batteries (ASSBs) based on solid polymer electrolytes (SPEs) have improved safety, energy, and power densities than conventional liquid electrolyte-based Lithium-ion batteries (LIBs). However, two significant obstacles still need to be addressed, including the low ionic conductivities and the low interfacial contact between ASSB components. This study involves the fabrication of hexagonal CuS nanoparticles by a one-step hydrothermal method and uses them for both cathode and solid electrolyte formulation functions. The reasonable ionic conductivity of 4.68 × 10−4 S.cm−1 at 60℃ and the instant transport number of 0.86 of the designed CuS filler-incorporated solid electrolyte offered great promise for ASSBs applications. In particular, the CuS filler-incorporated solid electrolyte exhibited ceaseless and prompt Li-ion transportation kinetics and delivered a dendrite resistance capability over 200 cycles of stripping/plating of Li. In addition, the Li metal solid-state battery is also verified using CuS as the cathode and SPE electrolyte (PEO/LiTFSI/CuS SPE) system. It offers an initial discharge capacity of up to 695 mAh/g and keeps an average capacity of ∼ 365 mAh/g after 50 cycles at a current density of 0.5C. Thus, this study introduced a simple but effective solution to mitigate the dendrite problems associated with solid polymer electrolytes by using CuS as a durable inactive filler.