Effect of MgO and Ta2O5 co-coatings on electrochemical performance of high-voltage spinel LiNi0.5Mn1.5O4 cathode material

High-voltage spinel LiNi0.5Mn1.5O4 (LNMO) athode material is subject to capacity degradation, particularly at elevated temperatures, which limits its practical applications. In this study, MgO and Ta2O5 co-coatings of LiNi0.5Mn1.5O4 are prepared, and their electrochemical performances at 25 °C and 55 °C are investigated using a combination of analytical techniques. The results reveal that the bare and co-coated LNMO half-cells exhibit a relative stable capacity retention and coulombic efficiency at 25 °C. However, at 55 °C, the bare LNMO half-cell only exhibits a capacity retention of 62.9% after 100 cycles, when compared with 88.2% of the co-coated LNMO half-cell. Detailed structural examinations suggested that the MgO and Ta2O5 co-coatings may stabilize the surface structure of LNMO while retaining a bulk structure similar to that of the bare LNMO. The improvement of the electrochemical cycling performance is attributed to the combined effects of the MgO and Ta2O5 co-coatings, i.e., MgO acted as an HF scavenger and Ta2O5 acted as an HF barrier, and they mitigate the Mn dissolution and side reactions caused by HF. These combined effects lead to a better cycling performance for co-coated LNMO than that of MgO-coated or Ta2O5-coated LNMO at 55 °C.