Antioxidation Mechanism of Highly Concentrated Electrolytes at High Voltage

Abstract

It has been researched that highly concentrated electrolytes (HCEs) can solve the problem of the excessive decomposition of dilute electrolytes at a high voltage, but the mechanism is not clear. In this work, the antioxidation mechanism of HCE at a high voltage was investigated by in situ electrochemical tests and theoretical calculations from the perspective of the solvation structure and physicochemical property. The results indicate that compared with the dilute electrolyte, the change of solvation structures in HCE makes more PF6 – anions easier to be oxidized prior to the dimethyl carbonate solvents, resulting in a more stable cathode–electrolyte interphase (CEI) film. First, the lower oxidation potential of the solvation structure with more PF6 – anions inhibits the side effects of the electrolyte effectively. Second, the CEI film, consisted of LiF and Li x PO y F z generated from the oxidation of PF6 – and Li3PO4 generated from the hydrolysis of LiPF6 via the soluble PO2F2 – intermediate, can reduce the interface impedance and improve the conductivity. Intriguingly, the high viscosity of HCEs and the hydrolysis of LiPF6 are proven to play a positive role in enhancing the interfacial stability of the electrolyte/electrode at a high voltage. This study builds a deep understanding of the bulk and interface properties of HCEs and provides theoretical support for their large-scale application in high-voltage battery materials.

Improving Compatibility between Trimethyl Phosphate and Graphite Anodes by Preconstructing a Stable Solid Electrolyte Interphase Film

“…In addition, the graphite has separated from the copper foil current collector in cross-sectional characterization, caused by the cointercalation of Li + -TMP into graphite. We find, quite interestingly, the graphite surface is dense in Li|1.5 M without TMP|graphite (Figure c,d), which helps to effectively inhibit the negative side reactions . This indicates that the SEI film derived from DFOB – is a feasible strategy to improve the interfacial stability.…”

“…We find, quite interestingly, the graphite surface is dense in Li|1.5 M without TMP|graphite (Figure 5c,d), which helps to effectively inhibit the negative side reactions. 30 This indicates that the SEI film derived from DFOB − is a feasible strategy to improve the interfacial stability. The SEM image of the reassembled Li|0.7 M with 40%TMP|graphite@SEI cell in Figure 5e,f, as expected, shows a similar SEI film with the one in the Li|1.5 M without TMP|graphite cell, which is much thinner and denser than that in the Li|0.7 M with 40%TMP|graphite cell.…”

Improve the Electrochemical Performance of Na2Ti3O7 Nanorod through Pitch Coating

“…As shown in the O 1s spectrum in Figure c, five peaks are observed at 529.5, 530.5.2, 531.1, 532.1, and 533.1 eV, which are fitted by O–Ti–O, Ti–O, C–O–Ti, and O in chemisorbed water H 2 O and O in hydroxyl OH – . − The O 1s peak at 534.9 eV is generally ascribed to the Na–O bond as well as the oxygen bond associated with carbonaceous materials . Also, the C 1s spectra in Figure d can be fitted to the peaks at 283.5, 284.4, 285.2, 285.7, 286.6, and 288.9 eV, corresponding to C–O–Ti, C–C, CC, C–O, CO, and O–CO bonds, respectively . In summary, both C 1s and O 1s confirm the existence of a C–O–Ti bond in the Na 2 Ti 3 O 7 @C composite electrode.…”

High‐Voltage Electrolyte Chemistry for Lithium Batteries

“…As the salt concentration increases, the oxidation potential of the anion decreases, and more inorganic interfacial films are formed on the cathode interface. [ 89 ] In addition, high‐concentration electrolytes are flame retardant better than conventional electrolytes, which meets safety requirements. [ 90 ] By increasing the concentration of LiFSI to 10 m , Fan et al not only achieved high Coulombic efficiency of stripping/intercalating lithium on the Cu electrode, but also successfully maintained the capacity of 86% of the original capacity on the 4.6 V NCM622 || Li‐battery after 100 cycles.…”