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 LiNi_0.5Mn_1.5O₄ (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.