Single‐Particle Performances and Properties of LiFePO4 Nanocrystals for Li‐Ion Batteries

It has been recently reported that the solution diffusion, efficiency porosity, and electrode thickness can dominate the high rate performance in the 3D‐printed and traditional LiMn_0.21Fe_0.79PO₄ electrodes for Li‐ions batteries. Here, the intrinsic properties and performances of the single‐particle (SP) of LiFePO₄ are investigated by developing the SP electrode and creating the SP‐model, which will share deep insight on how to further improve the performance of the electrode and related materials. The SP electrode is generated by fully scattering and distributing LiFePO₄ nanoparticles to contact with the conductive network of carbon nanotube or conductive carbon to demonstrate the sharpest cyclic voltammetry peak and related SP‐model is developed, by which it is found that the interfacial rate constant in aqueous electrolyte is one order of magnitude higher, accounting for the excellent rate performance in aqueous electrolyte for LiFePO₄. For the first time it has been proposed that the insight of pre‐exponential factor of interface kinetic Arrhenius equation is related to desolvation/solvation process. Thus, this much higher interfacial rate constant in aqueous electrolyte shall be attributed to the much larger pre‐exponential factor of interface kinetic Arrhenius equation, because the desolvation process is much easier for Li‐ions jumping from aqueous electrolyte to the Janus solid–liquid interface of LiFePO₄.     

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) 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.