Improved electrochemical performance of Li(Ni_0.6Co_0.2Mn_0.2)O₂ at high charging cut-off voltage with Li_1.4Al_0.4Ti_1.6(PO₄)₃ surface coating

Li(Ni_0.6Co_0.2Mn_0.2)O₂ has been surface-modified by the lithium-ion conductor Li_1.4Al_0.4Ti_1.6(PO₄)₃ via a facile mechanical fusion method. The annealing temperature during coating process shows a strong impact on the surface morphology and chemical composition of Li(Ni_0.6Co_0.2Mn_0.2)O₂. The 600-℃ annealed material exhibits the best cyclic stability at high charging cut-off voltage of 4.5 V (versus Li⁺/Li) with the capacity retention of 90.9% after 100 cycles, which is much higher than that of bare material (79%). Moreover, the rate capability and thermal stability are also improved by Li_1.4Al_0.4Ti_1.6(PO₄)₃ coating. The enhanced performance can be attributed to the improved stability of interface between Li(Ni_0.6Co_0.2Mn_0.2)O₂ and electrolyte by Li_1.4Al_0.4Ti_1.6(PO₄)₃ modification. The results of this work provide a possible method to design reliable cathode materials to achieve high energy density and long cycle life.