Conformal Li₂HfO₃/HfO₂ Nanoparticle Coatings on Layered Ni-Rich Oxide Cathodes for Stabilizing Interfaces in All-Solid-State Batteries

Solid-state batteries (SSBs) are a promising next-generation energy-storage solution to complement or replace current battery technologies in the wave of automotive electrification. Especially SSBs using sulfide solid electrolytes (SEs) hold great potential; however, (electro)chemical instability when in contact with layered oxide cathode active materials (CAMs) remains an obstacle to further implementation. SE degradation occurring during cycling adversely affects the ion/electron transport and may possibly cause mechanical failure. In the present work, a protective surface coating composed of Li 2 HfO 3 and HfO 2 nanoparticles (NPs) was produced on the secondary particles of a high-capacity LiNi 0.85 Co 0.1 Mn 0.05 O 2 (NCM85) CAM to mitigate side reactions and enable robust interfacial charge transfer. HfO 2 NPs dispersed in solution served both as a coating material and as a precursor to react with residual lithium during post-deposition annealing. The Li 2 HfO 3 /HfO 2 -coated NCM85 showed much improved cycling performance over uncoated CAM in all-inorganic SSB cells with Li 6 PS 5 Cl SE and Li 4 Ti 5 O 12 anode. Thorough characterization using a series of techniques helped to elucidate the role that the coating plays in stabilizing interfaces and preserving structural integrity of the cathode.