The Enhanced Electrochemical Performance of Li_1.2Ni_0.2Mn_0.6O₂ through Coating MnF₂ Nano Protective Layer

While Li-rich layered materials are one of the most promising next-generation cathode materials for Li-ion batteries, they still face some challenges, such as large irreversible capacity, bad cycling performance, and inferior rate capability. In this work, MnF₂ nanolayers are successfully coated on Li_1.2Ni_0.2Mn_0.6O₂ (LNMO) samples. There is a great progress in the electrochemical performance of LNMO after coating MnF₂ nanolayers. The pristine LNMO shows a discharge capacity of only 269.4 mAhg⁻¹, and after coating, MF-1.5 (coating weight percent of 1.5%) the sample exhibits a high initial discharge capacity of 296.8 mAhg⁻¹. Furthermore, the MF-2.5 sample displays improved capacity retention of 85% after 100 cycles at 0.5 C. In terms of rate capability, MF-1.5 retains 141.7 mAhg⁻¹ of capacity at 5 C compared with pristine LNMO, which is only 70.4 mAhg⁻¹. The enhanced electrochemical performance of MnF₂-coated samples is attributed to the conversion reaction of the MnF₂ layer, which limits the electrode–electrolyte side reaction and decreases the dissolution of transition metal ions in the electrolyte. In addition, there is spinel phase formation after coating the MnF₂ nanolayer, which promotes Li-ion transfer and further restrains the transformation of structure on the surface of the material.