Enhancing the electrochemical performance of high-voltage LiNi0.5Mn1.5O4 batteries with a multifunctional inorganic MgHPO4 electrolyte additive

The instability of the electrode/electrolyte interface and the metal-ions dissolution of high-voltage LiNi0.5Mn1.5O4 (LNMO) material lead to significant degradation of cycling performance, thereby limiting the large-scale application of LNMO-based batteries. Here, inorganic Mg/Ca/Sr-contained phosphates (MgHPO4, CaHPO4, and SrHPO4) are used individually as functional additives of standard electrolytes to enhance the cycling performance of LNMO. Combined with theoretical calculations, a series of electrochemical measurements and characteristics corroborate that the MgHPO4 is the optimal additive and can preferentially undergo oxidation and reduction decomposition over carbonate solvents. Electrochemical results reveal that the LNMO/Li half-cell containing the MgHPO4 additive shows a capacity retention of 91.9% after 500 cycles at 5 C, higher than that obtained with STD (76.5%). In addition, the LNMO/graphite (Gr) full-cell with MgHPO4 additive increases the capacity retention from 70.8 to 78.0% after 100 cycles at 0.5 C. The addition of MgHPO4 allows a thin, uniform, and conductive cathode-electrolyte interphase (CEI) and solid-electrolyte interphase (SEI) film to be formed on the LNMO cathode and graphite anodes. Furthermore, the preferential reduction of MgHPO4 inhibits the lithium dendritic growth and enables the formation of a more stable SEI on the Li anode. Besides, the MgHPO4 additive serves as a scavenger of detrimental HF, thus suppressing the Ni/Mn ions dissolution and improving the structural stability of LNMO. This study provides a cost-effective strategy involving the use of an inorganic additive for improving the electrochemical performance of high-voltage lithium-ion batteries.