Prescribing Functional Additives for Treating the Poor Performances of High-Voltage (5 V-class) LiNi0.5Mn1.5O4/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) LiNi0.5Mn1.5O4/MCMB (graphitic mesocarbon microbeads) Li-ion batteries at both room temperature and 50 degrees C. The high-voltage LiNi0.5Mn1.5O4/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 approximate to 90%, while the counterpart is only approximate to 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 degrees 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)-pentafluoro-cyclo-triphosphazene (PFPN) is introduced for reducing the flammability of the aforementioned binary functional additives containing electrolyte.