Protective Nanosheet Coatings for Thiophosphate‐Based All‐Solid‐State Batteries

Superionic sulfide solid electrolytes (SEs) are of considerable interest forapplication in solid-state batteries, but suffer from limited stability. When incombination with state-of-the-art cathode active materials (CAMs), severedegradation at the CAM/SE interface occurs during electrochemical cycling.To improve upon the interfacial stability, inert coatings can be applied to theCAM particles, with the goal of preventing direct contact to the SE. In thisstudy, different methods of depositing coatings, including hexagonal boronnitride, tungsten sulfide and exfoliated ((CH3(CH2)3)4N)4Nb6O17,intheformof nanosheets onto the free surface of a Ni-rich LiNixCoyMnzO2(NCM) CAMare examined and compared with one another. While dry coating is shown toproduce relatively uniform coatings (good surface coverage), the secondaryparticle morphology of the NCM makes ball milling as a mechanicaldeposition method less attractive. In contrast, deposition from dispersions inorganic solvents yields protective coatings with a lower degree of surfacecoverage. The different materials are electrochemically tested in liquid- andsolid-electrolyte-based lithium-ion batteries. ... mehrA stabilizing effect fromnanosheet coating is only observed for the cells with lithium thiophosphate SE.