Mitigating Concentration Polarization in Dry‐Processed Ultra‐Thick Cathodes Using a Low‐Viscosity Electrolyte With Soft Li + Solvation

ABSTRACT Dry‐processed high‐loading cathodes are essential for realizing high‐energy‐density lithium‐metal batteries because they increase areal capacity while minimizing inactive components. However, the dense and tortuous structure of dry‐processed ultra‐thick cathodes severely retards electrolyte penetration and Li + transport, aggravating concentration polarization, accelerating interfacial degradation, and causing rapid performance decay under high‐loading conditions. Herein, we report an electrolyte design strategy that simultaneously addresses cathode‐side Li + transport limitations and anode‐side Li + desolvation kinetics by introducing methyl ethanoate (ME) as a low‐viscosity and soft‐solvating solvent. Relative to the conventional EC‐based electrolyte, the ME‐based electrolyte facilitates electrolyte penetration into the ultra‐thick cathode framework and improves ionic conductivity owing to its lower viscosity. In addition, the weaker Li + ‐solvent coordination in MD‐E contributes to a higher Li + transference number and lower Li + desolvation energy. These combined features are expected to alleviate concentration polarization by promoting more homogeneous depth‐wise Li + transport during cycling and enabling more reversible Li plating/stripping at the Li‐metal anode. Laser‐induced breakdown spectroscopy further verifies that ME‐based electrolyte enables a much more uniform depth‐wise Li + distribution in the ultra‐thick cathode. As a result, Li||NCM622 pouch cells with an active material loading of 55 mg cm −2 achieved 81% capacity retention after 100 cycles at 0.3C.