From Conductivity to Charging Rate: Thermal Regime Classification and Format Selection for Amorphous Li–P–S Solid‐State Batteries

The analytical conductivity design equation for amorphous Li–P–S solid electrolytes provides the material‐level foundation but does not address the device‐level question: at what C‐rate does thermal failure occur, and does cell format matter? This work closes the gap by introducing a single dimensionless thermal parameter that classifies every solid‐state cell into three regimes: Regime I (), where thermal constraints are negligible and prismatic format is preferred on packing grounds; Regime II (), where format selection depends on a wet‐fraction ratio exceeding 0.78; and Regime III (), where no format choice compensates for insufficient conductivity. Because depends on through Arrhenius scaling, room‐temperature () electrolytes with lie deep in Regime III above 1C, rendering the format debate moot until improves. A central result establishes that is an exact factorization identity within the adopted model, yielding closed‐form critical conductivity targets and the universal ratio independent of cell geometry. The three‐layer causal chain provides a complete, analytical bridge from material design to charging‐rate engineering. The analysis is steady‐state, omits explicit interfacial resistance, and uses an Arrhenius extrapolation from that is an optimistic upper bound at room temperature (a non‐Arrhenius/VFT correction would only lower ). We show explicitly that all of these caveats shift the quantitative thresholds but leave the structural identity and the direction of the Regime III diagnosis intact: each correction either reinforces or does not affect the central conclusion. The framework is therefore offered as a first‐pass diagnosis at the design stage, with each caveat mapped to a concrete future‐work direction for quantitative refinement.