Synergistic Effect of Fluorinated Solvents for Improving High Voltage Performance of LiNi_0.5Mn_1.5O₄ Cathode

Abstract

A "dual-fluorinated" electrolyte consisting of fluoroethylene carbonate (FEC), 1H,1H,5H-Perfluoropentyl-1,1,2,2-tetrafluoroethylether (F-EAE) was investigated for 5V-class LiNi 0.5 Mn 1.5 O 4 (LNMO)-based batteries. It is found that the synergistic effect of two fluorinated solvents brings about high oxidation durability of exceeding 5 V (vs Li + /Li), and then excellent cycle performance with the capacity retention of ∼92% after 200 cycles at the cutoff voltage of 5 V, far beyond conventional carbonate-based electrolyte and another "mono-fluorinated" electrolyte merely with F-EAE. The SEM, TEM and XPS test reveal that a uniform and F/Pcontained surface film exists in the cycled LNMO cathode in the "dual-fluorinated" electrolyte, possibly derived from the interactivity of two fluorinated solvents under the high voltage environment. It is further stressed that that the suitable interface modification on the cathode is another important factor for the long-term and stable cycling at 5 V operation besides the oxidationresistivity of the electrolyte self.

Synergy of an In Situ-Polymerized Electrolyte and a Li3N–LiF-Reinforced Interface Enables Long-Term Operation of Li-Metal Batteries

“…Among the cells with GPEs, the EIS plots show the relatively low Li + transport resistance in an electrode/electrolyte interphase for that with FEC/LiNO 3 –GPE. Before and after the galvanostatic cycling, the respective interfacial charge transfer resistance is 215.6 and 22.06 Ω, suggesting a fast transport of Li + ions across the electrode/electrolyte interface …”

“…Before and after the galvanostatic cycling, the respective interfacial charge transfer resistance is 215.6 and 22.06 Ω, suggesting a fast transport of Li + ions across the electrode/ electrolyte interface. 50…”

Stabilizing Commercial LiMn2O4 Cathode by Constructing Protective Saccharin Coating

“…On the contrary, the integral area of Mn–O peak in P-LMO accounts for 2.9% of the total area, and that in 1.0S-LMO accounts for 3.8%, denoting that the SAC coating could indeed ameliorate the stability of LMO during cycling by inhibiting the oxidation and decomposition of the electrolyte on the electrode surface. Furthermore, from the P 2p spectra in Figure b, the Li x PO y F z content (20.6%) in 1.0S-LMO is lower than that in P-LMO (37.9%), meaning that the reaction of LMO with the trace water in the electrolyte was greatly suppressed by the SAC coating. , The F 1s spectra give similar information (Figure c); i.e., the F content in Li x PO y F z of 1.0S-LMO (46.3%) is lower than that of P-LMO (60.2%). , The reaction between LMO and the trace water could be expressed as follows: , LiPF 6 + normalH 2 normalO → HF + Li x PF y + Li x PF y normalO z LiMn 2 normalO 4 + HF → LiF + Li 1 − x Mn 2 O 4 − y + normalH 2 normalO …”

Improved electrochemical performance of a LiCoO2/MCMB cell by regulating fluorinated electrolytes

“…This facilitates Li + intercalation in the LCO particle, allowing for faster and more efficient charge transfer reaction. 28 As for EET, it offers higher interfacial resistance than EE no matter before or after precycling, suggesting that the employment of single fluorinated ether merely leads to unsuccessful cathodic interface modification.…”