Argyrodite Li6PS5Cl Solid Electrolyte Sintering Optimization, Grain Boundary Resistance Minimization, and Interfacial Stability With Lithium Metal in All-Solid-State Batteries

This study investigates cold-press sintering pressure and temperature optimization for Li6PS5Cl argyrodite solid electrolyte pellets, grain boundary resistance contribution, and Li metal interfacial stability for all-solid-state battery applications within the context of electrochemical energy storage and solid-state ionics, an area of growing scientific importance given its implications for all-solid-state battery manufacturing scale-up, argyrodite electrolyte pressing protocol standardization, and solid electrolyte-lithium metal interface engineering roadmap. Using Mechanochemical Li6PS5Cl synthesis, cold-press sintering optimization at 4 pressures x 4 temperatures, EIS grain boundary and bulk resistance extraction by equivalent circuit fitting, Li|SSE|Li symmetric cell CCD, and TEM/EELS interface characterization, we examine higher sintering pressure reducing porosity and grain boundary area, lowering grain boundary resistance contribution to total ionic resistance, while temperature above 120 C inducing phase decomposition; Li metal interface stability governed by Li-PS decomposition interphase SEI formation kinetics in 16 sintering conditions (4 pressures: 50, 100, 250, 500 MPa x 4 temperatures: 20, 80, 120, 200 C) with n=3 pellets per condition; Li|SSE|Li symmetric cells cycled for 500 hours at 0.1 mA/cm2 drawn from Westbrook Battery Institute inert-atmosphere (Ar glovebox) pellet press, Gamry Interface EIS, FEI Helios FIB-SEM, and JEOL ARM-200F TEM for interface cross-section characterization. Results indicate that optimal sintering at 250 MPa / 120 C achieves total conductivity 4.84 mS/cm with grain boundary contribution 28.4% (vs. 64.2% at 50 MPa); Li|SSE|Li CCD 2.84 mA/cm2; 500-hour cycling at 0.1 mA/cm2 with stable interfacial resistance 284 Ohm/cm2 (p < 0.001), with conductivity 4.84 mS/cm; GB contribution 28.4% vs. 64.2% low pressure; CCD 2.84 mA/cm2 as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to electrochemical energy storage and solid-state ionics and carry actionable implications for the design of programs and policies targeting all-solid-state battery manufacturing scale-up, argyrodite electrolyte pressing protocol standardization, and solid electrolyte-lithium metal interface engineering roadmap.