Fast charge storage kinetics by surface engineering for Ni-rich layered oxide cathodes

Abstract

A Ni-rich (Ni content ≥ 80%) layered oxide (NRLO) cathode is a promising candidate for boosting the energy density of Li-ion batteries due to its high discharge voltage and capacities over 200 mA h g⁻¹. However, hindrance to Li transport due to limited Li-vacant sites, NiO-like rock-salt structures and resistant surface Li residuals restricts its practical electrochemical performances. Herein, controlled water treatment was applied to modify the surface crystal structure and chemical environment of LiNi_0.83Co_0.11Mn_0.06O₂ (NCM83), which improved Li transport kinetics within NCM83 lattices and across cathode/electrolyte interfaces. Li–H₂O interactions during water treatment caused chemical de-lithiation at the NCM83 surface and induced Li migration from the bulk to the surface of NCM83, facilitating the construction of Li-vacant layered structures at the NCM83 surface after a heat treatment in an oxygen-rich environment. dQ/dV vs. V curves revealed that surface Li vacancies promoted Li migrations in the NCM83 lattice at a low state of charge (SOC), improving the reversibility of the H1 phase transformation of NCM83 and hence boosting the reversible capacity. Additionally, the concurrent removal of Li residuals on the NCM83 surface by water treatment also ameliorated Li transport across cathode/electrolyte interfaces and prevented side reactions induced by Li₂CO₃ decomposition, enhancing the rate performance and cycling stability of NCM83. NCM83 with Li-vacant surface layered structures and the lowest Li residual content displayed a high 1st cycle reversible capacity of 212.8 mA h g⁻¹ (coulombic efficiency of 94.9%) and capacity retention of 89.4% over 100 cycles.