On the Role of Reaction Current Distribution to Attain Competitive Solid-State Batteries

Competitive solid-state batteries must allow for high areal loadings (> 5 mAh·cm^-2) and fast charging rates (> 2 C). Nevertheless, current academic research mainly focuses on systems with smaller loadings and lower C-rates. For established cell chemistries a focus shift is required when aiming toward practical application. Increasing the areal active material content and C-rates is often accompanied by charge transport limitations in the electrodes. In this work, the role of reaction current distribution in composite electrodes is highlighted as solid-state batteries advance toward higher areal loadings and charging rates. Using NCM-argyrodite composites as a case study, we revisit Newman's porous electrode theory in the context of solid-state batteries to rationalize composite electrode cycling performance. Further, operando high-energy X-ray diffraction is employed to track lithiation states of NCM across the electrode as a function of state of charge. The results reveal significant improvements in reaction current distribution, when employing faster conducting Li_5.5PS_4.5Cl_1.5 instead of conventional Li₆PS₅Cl, underscoring the need for fast lithium-ion conductors to enable competitive solid-state batteries. This work demonstrates the importance of precisely controlling electrode composition to balance ionic and electronic transport, ensuring homogeneous utilization of the active material and mitigating local strain and overcharging.