MnPO4‐coated Li(Ni0.4Co0.2Mn0.4)O2 for lithium(‐ion) batteries with outstanding cycling stability and enhanced lithiation kinetics

Abstract

Herein, the successful synthesis of MnPO4-coated LiNi0.4Co0.2Mn0.4O2 (MP-NCM) as a lithium battery cathode material is reported. The MnPO4 coating acts as an ideal protective layer, physically preventing the contact between the NCM active material and the electrolyte and, thus, stabilizing the electrode/electrolyte interface and preventing detrimental side reactions. Additionally, the coating enhances the lithium de-/intercalation kinetics in terms of the apparent lithium-ion diffusion coefficient. As a result, MP-NCM-based electrodes reveal greatly enhanced C-rate capability and cycling stability—even under exertive conditions like extended operational potential windows, elevated temperature, and higher active material mass loadings. This superior electrochemical behavior of MP-NCM compared to as-synthesized NCM is attributed to the superior stability of the electrode/electrolyte interface and structural integrity when applying a MnPO4 coating. Employing an ionic liquid as an alternative, intrinsically safer electrolyte system allows for outstanding cycling stabilities in a lithium-metal battery configuration with a capacity retention of well above 85% after 2000 cycles. Similarly, the implementation in a lithium-ion cell including a graphite anode provides stable cycling for more than 2000 cycles and an energy and power density of, respectively, 376 Wh kg−1 and 1841 W kg−1 on the active material level.