Prescribing Functional Additives for Treating the Poor Performances of High-Voltage (5 V-class) LiNi_0.5Mn_1.5O₄/MCMB Li-Ion Batteries

In this paper, tris(trimethylsilyl) phosphite (TMSP) and 1,3-propanediolcyclic sulfate (PCS) are unprecedentedly prescribed as binary functional additives for treating the poor performances of high-voltage (5 V-class) LiNi_0.5Mn_1.5O₄/MCMB (graphitic mesocarbon microbeads) Li-ion batteries at both room temperature and 50 °C. The high-voltage LiNi_0.5Mn_1.5O₄/MCMB cell with binary functional additives shows a preponderant discharge capacity retention of 79.5% after 500 cycles at 0.5 C rate at room temperature. By increasing the current intensity from 0.2 to 5 C rate, the discharge capacity retention of the high-voltage cell with binary functional additives is ≈90%, while the counterpart is only ≈55%. By characterizations, it is rationally demonstrated that the binary functional additives decompose and participate in the modification of solid–electrolyte interface layers (both electrodes), which are more conductive, protective, and resistant to electrolyte oxidative/reductive decompositions (accompanying active-Li⁺ consuming parasitic reactions) due to synergistic effects. Specifically, the TMSP additive can stabilize LiPF₆ salt and scavenge erosive hydrofluoric acid. More encouragingly, at 50 °C, the high-voltage cell with binary functional additives holds an ultrahigh discharge capacity retention of 79.5% after 200 cycles at 1 C rate. Moreover, a third designed self-extinguishing flame-retardant additive of (ethoxy)-penta-fluoro-cyclo-triphosphazene (PFPN) is introduced for reducing the flammability of the aforementioned binary functional additives containing electrolyte.