Intergranular Shielding for Ultrafine-Grained Mo-Doped Ni-Rich Li[Ni0.96 Co0.04 ]O2 Cathode for Li-Ion Batteries with High Energy Density and Long Life.

ABSTRACT

Deploying Ni-enriched (Ni≥95 %) layered cathodes for high energy-density lithium-ion batteries (LIBs) requires resolving a series of technical challenges. Among them, the structural weaknesses of the cathode, vigorous reactivity of the labile Ni4+ ion species, gas evolution and associated cell swelling, and thermal instability issues are critical obstacles that must be solved. Herein, we propose an intuitive strategy that can effectively ameliorate the degradation of an extremely high-Ni-layered cathode, the construction of ultrafine-scale microstructure and subsequent intergranular shielding of grains. The formation of ultrafine grains in the Ni-enriched Li[Ni0.96 Co0.04 ]O2 (NC96) cathode, achieved by impeding particle coarsening during cathode calcination, noticeably improved the mechanical durability and electrochemical performance of the cathode. However, the buildup of the strain-resistant microstructure in Mo-doped NC96 concurrently increased the cathode-electrolyte contact area at the secondary particle surface, which adversely accelerated parasitic reactions with the electrolyte. The intergranular protection of the refined microstructure resolved the remaining chemical instability of the Mo-doped NC96 cathode by forming an F-induced coating layer, effectively alleviating structural degradation and gas generation, thereby extending the battery's lifespan. The proposed strategies synergistically improved the structural and chemical durability of the NC96 cathode, satisfying the energy density, life cycle performance, and safety requirements for next-generation LIBs.