Facile Magnetite Coating for Stable High-Voltage Cycling of Nickel-Rich Cathodes in Conventional Liquid and All-Solid-State Lithium-Ion Batteries.

The instability of Nickel (Ni)-rich cathodes at high voltage is a critical bottleneck toward developing superior lithium-ion batteries. This instability is driven by cathode-electrolyte side reactions, causing rapid degradation, and compromising the overall cycle life. In this study, a protective coating using dispersed "magnetite (FeO.Fe 2 O 3 )" nanoparticles is used to uniformly decorate the surface of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NMC 811) microparticles. The modified cathode delivers significant improvement in electrochemical performance at high voltage (≈4.6 V) by suppressing deleterious electrode-electrolyte interactions. A notably higher cycle stability, rate performance, and overall energy density is realized for the coated cathode in a conventional liquid electrolyte battery. When deployed in pellet-stacked solid-state cells with Li 6 PS 5 Cl as the electrolyte, the magnetite-coated NMC 811 showed strikingly superior cycling stability than its uncoated counterpart, proving the versatility of the chemistry. The facile surfactant-assisted coating process developed in this work, in conjunction with the affordability, abundance, and nontoxic nature of magnetite makes this a promising approach to realize commercially viable high voltage Ni-rich cathodes that exhibit stable performance in liquid as well as solid-state lithium-ion batteries.