CaF2-coated Li1.2Mn0.54Ni0.13Co0.13O2 as cathode materials for Li-ion batteries

Li-rich cathode material Li1.2Mn0.54Ni0.13Co0.13O2 is prepared by a sol-gel method and coated with CaF2 layer via a wet chemical process. The pristine and CaF2-coated samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). An amorphous nanolayer coating of CaF2 is obtained on the surface of layered pristine material. The CaF2-coated Li1.2Mn0.54Ni0.13Co0.13O2 material exhibits excellent electrochemical performance. The initial coulombic efficiency is enhanced to 89.6% with high initial discharge capacity of 277.3 mAh g−1 after CaF2 coating. Galvanostatic charge-discharge tests at 0.2 C display faster activation of Li2MnO3 phase and higher capacity retention of 91.2% after 80 cycles for CaF2-coated material. Meanwhile it also shows higher rate capability with the capacity of 141.5 mAh g−1 at the 3 C-rate and stable cyclic performance above 190 mAh g−1 after 100 cycles at the 1 C-rate. The analysis of dQ/dV plots and electrochemical impedance spectroscopy (EIS) indicates that the obvious improvement of CaF2 coating is mainly attributed to the accelerated phase transformation from layered phase to spinel phase and stable electrolyte/electrode interfacial structure due to the suppression of the electrolyte decomposition.