Interphase stability is a critical requirement for achieving long-term performance and safety in advanced battery systems, particularly in all-solid-state batteries where electrode - electrolyte interfaces often limit cell stability and cycling life. We demonstrate that a mixed ionic - electronic conducting interfacial layer formed on the surface of the high-nickel cathode material NMC811 effectively modulates interfacial charge-transfer kinetics and mitigates interfacial degradation. This engineered layer helps to preserve the structural integrity of the cathode and enables stable electrochemical cycling even under pressure-free conditions, addressing one of the key challenges in the development of practical solid-state batteries.
A complementary approach is explored for metallic lithium anodes, where interfacial instability often leads to dendrite formation and rapid performance decay. A multi-component protective coating composed of modified cellulose, a single-ion conducting polymer, and lithium nitrate is introduced to stabilize the lithium surface.  The coating promotes uniform lithium-ion transport, suppresses the formation of high-surface-area lithium and dendrites, and significantly improves Coulombic efficiency and cycling stability.