Use of Ce to Reinforce the Interface of Ni-Rich LiNi _0.8 Co _0.1 Mn _0.1 O ₂ Cathode Materials for Lithium-Ion Batteries under High Operating Voltage

Nickel-rich cathode materials are among the most promising cathode materials for high-energy lithium-ion batteries. However, their structural and thermodynamic stability, cycle and rate performances still need to be further improved. In this study, the rare earth element Ce is employed to reinforce the interface of Ni-rich cathode materials both internally and externally. High-valence Ce ⁴⁺ can easily cause the oxidization of Ni ²⁺ to Ni ³⁺ when doped into the material owing to its strong oxidation performance, thus reducing Li ⁺ /Ni ²⁺ mixing. In addition, the inert Ce ³⁺ ions in transition metal slabs with strong Ce−O bonds can maintain the layered structure at high delithiation state. Furthermore, when the calcination temperature during synthesis is above 500 °C, a CeO ₂ coating layer will form, which can protect the electrode from erosion by the electrolyte and alleviate the increasing resistance during cycling. The modified Ni-rich materials fabricated with an erosion-resistant CeO ₂ layer outside and stronger Ce−O bonds inside with reduced Li ⁺ /Ni ²⁺ mixing exhibit excellent electrochemical properties, especially at high operating voltages, for example, the 50th capacity retention at 0.2 C within 2.75–4.5 V is improved from 89.8 % to 99.2 % after the modification.