Targeted Surface Doping with Reversible Local Environment Improves Oxygen Stability at the Electrochemical Interfaces of Nickel-Rich Cathode Materials

Elemental doping represents a prominent strategy to improve interfacial chemistry in battery materials. Manipulating the dopant spatial distribution and understanding the dynamic evolution of the dopants at the atomic scale can inform better design of the doping chemistry for batteries. In this work, we create a targeted hierarchical distribution of Ti⁴⁺, a popular doping element for oxide cathode materials, in LiNi_0.8Mn_0.1Co_0.1O₂ primary particles. We apply multiscale synchrotron/electron spectroscopy and imaging techniques as well as theoretical calculations to investigate the dynamic evolution of the doping chemical environment. The Ti⁴⁺ dopant is fully incorporated into the TMO₆ octahedral coordination and is targeted to be enriched at the surface. Ti⁴⁺ in the TMO₆ octahedral coordination increases the TM-O bond length and reduces the covalency between (Ni, Mn, Co) and O. The excellent reversibility of Ti⁴⁺ chemical environment gives rise to superior oxygen reversibility at the cathode-electrolyte interphase and in the bulk particles, leading to improved stability in capacity, energy, and voltage. Our work directly probes the chemical environment of doping elements and helps rationalize the doping strategy for high-voltage layered cathodes.