Building an entropy-assisted enhanced surface on ultrahigh nickel cathodes to improve electrochemical stability.

Increasing the Ni content in Ni-rich cathodes to over 90% can further enhance the energy density and reduce costs. However, this aggravates the issue of lattice oxygen release due to the instability of the layered structure. In this work, an entropy-stabilized surface strategy is used to process ultrahigh nickel cathode LiNi_0.96Co_0.03Mn_0.01O₂ (NCM). Utilizing the low solid solubility of high-valent elements W, Mo and Nb in NCM, the simultaneous introduction of W, Mo and Nb ions will aggregate on the outer surface of NCM, which in turn forms a composite entropy assisted enhancement surface. This entropy assisted enhancement surface consists of a composite lithium compound coating and a high-entropy rock salt phase, which inhibits the loss of surface lattice oxygen and reduces the corrosion of cathode particles by electrolyte decomposition products. Furthermore, the formation of the entropy assisted enhancement surface retains the role of refined primary particles, thereby further enhancing the mechanical properties. NCM modified with composite entropy assisted enhancement surface (HE03) exhibits a capacity of 234.5 mAh g^-1 at 0.1C with a capacity retention of 96.7% after 100 cycles at 0.5C. This entropy-stabilizing strategy enables the ultrahigh nickel cathodes to display high specific capacity of and improved cycling stability, presenting a promising modification approach.