Li6.3La3Zr1.65W0.35O12 (LLZO)-Li6PS5Cl (LPSC) composite electrolytes and all-solid-state cells containing LLZO-LPSC were fabricated by cold pressing at room temperature. The LPSC:LLZO ratio was varied, and the microstructure, ionic conductivity, and electrochemical performance of the corresponding composite electrolytes were investigated; the ionic conductivity of the composite electrolytes was three or four orders of magnitude higher than that of LLZO. The high conductivity of the composite electrolytes was attributed to the enhanced relative density and the rule of mixture for soft LPSC particles with high lithium-ion conductivity (~10−4 S·cm−1). The specific capacities of all-solid-state cells (ASSCs) consisting of a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and the composite electrolytes of LLZO:LPSC = 7:3 and 6:4 were 163 and 167 mAh·g−1, respectively, at 0.1 C and room temperature. Moreover, the charge–discharge curves of the ASSCs with the composite electrolytes revealed that a good interfacial contact was successfully formed between the NCM811 cathode and the LLZO-LPSC composite electrolyte.

Lithium argyrodite Li6PS5Cl powders are synthesized from Li2S, P2S5, and LiCl via wet milling and post-annealing at 500°C for 4 h. Organic solvents such as hexane, heptane, toluene, and xylene are used during the wet milling process. The phase evolution, powder morphology, and electrochemical properties of the wet-milled Li6PS5Cl powders and electrolytes are studied. Compared to dry milling, the processing time is significantly reduced via wet milling. The nature of the solvent does not affect the ionic conductivity significantly; however, the electronic conductivity changes noticeably. The study indicates that xylene and toluene can be used for the wet milling to synthesize Li6PS5Cl electrolyte powder with low electronic and comparable ionic conductivities. The all-solid-state cell with the xylene-processed Li6PS5Cl electrolyte exhibits the highest discharge capacity of 192.4 mAh·g−1 and a Coulombic efficiency of 81.3% for the first discharge cycle.

All‐solid‐state cells (ASSCs) typically operate at a specific pressure to ensure good contact between the solid electrolyte and the electrode‐active materials. However, establishing the ideal cell pressure is challenging because of the various cell structures, the mechanical characteristics of solid electrolytes, and the extent to which the volume of the electrodes changes during cycling. In this study, we propose a specially designed cell assembly that adjusts to the changes in volume that occur during cycling while maintaining a constant cell pressure. The evaluations indicate that the spring in the cell assembly effectively reduces the stress incurred from the volume expansion that occurs in the electrode during charging (lithiation) and the volume contraction that occurs during discharging (delithiation) while maintaining the prescribed cell pressure. The capacity fading—as a function of the cycle number—decreases when operating ASSCs comprising a cell assembly that include a spring, compared with those that exclude a spring. Focused ion beam–scanning electron microscope reveals no cracks and delamination in the LiNi0.8Co0.1Mn0.1O3 (NCM811) composite cathode of the ASSCs, operated at 25 MPa, with a spring‐equipped assembly. The Ag nanolayer that deposits on the Cu foil is an effective collector metal, forming a dense lithium plating layer on the Ag/Cu foil anode.

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