Electrochemical Stability Windows of Sulfone-Based Electrolyte System for Lithium Metal Batteries: Insight from MD-Assisted DFT Calculation

Lithium metal batteries using lithium metal as the anode are attractive for a next-generation energy storage device due to their high theoretical energy density. Nevertheless, electrolytes with wider electrochemical stability windows are also necessary for realizing a high voltage. Despite its advantageous characteristics, including excellent oxidation stability and low flammability, there is a general lack of understanding of the handling of a sulfone-based electrolyte, and thus, there exists a demand for a framework that can accurately estimate the stability of the electrolyte system. Here, we examine the solvation structures and electrochemical stability of electrolyte systems with dimethyl sulfone and lithium-bis­(fluoromethanesulfonyl)­imide as the solvent and salt, respectively. Based on this case, strategies are provided, including the level of theory and generation of configurations that can effectively reduce the calculation cost, while maintaining the reliability of the calculated electrochemical stability window. Consequently, a computational framework combining molecular dynamics and first-principles calculation is proposed that achieves high efficiency and accuracy of the calculations. A key perspective on the electrolyte design of high-performance lithium metal batteries is outlined with the development of a detailed understanding of the explicit description of the solvent environment

Probing Local pH Change during Electrode Oxidation of TEMPO Derivative: Implication of Redox-Induced Acidity Alternation by Imidazolium-Linker Functional Groups

The chemical degradation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-based aqueous energy storage and catalytic systems is pH sensitive. Herein, we voltammetrically monitor the local pH (pHlocal) at a Pt ultramicroelectrode (UME) upon electro-oxidation of imidazolium-linker functionalized TEMPO and show that its decrease is associated with the greater acidity of the cationic (oxidized) rather than radical (reduced) form of TEMPO. The protons that drive the decrease in pH arise from hydrolysis of the conjugated imidazolium-linker functional group of 4-[2-(N-methylimidazolium)acetoxy]-2,2,6,6-tetramethylpiperidine-1-oxyl chloride (MIMAcO-T), which was studied in comparison with 4-hydroxyl-TEMPO (4-OH-T). Voltammetric hysteresis is observed during the electrode oxidation of 4-OH-T and MIMAcO-T at a Pt UME in an unbuffered aqueous solution. The hysteresis arises from the pH-dependent formation and dissolution of Pt oxides, which interact with pHlocal in the vicinity of the UME. We find that electrogenerated MIMAcO-T+ significantly influences pHlocal, whereas 4-OH-T+ does not. Finite element analysis reveals that the thermodynamic and kinetic acid–base properties of MIMAcO-T+ are much more favorable than those of its reduced counterpart. Imidazolium-linker functionalized TEMPO molecules comprising different linking groups were also investigated. Reduced TEMPO molecules with carbonyl linkers behave as weak acids, whereas those with alkyl ether linkers do not. However, oxidized TEMPO+ molecules with alkyl ether linkers exhibit more facile acid–base kinetics than those with carbonyl ones. Density functional theory calculations confirm that OH– adduct formation on the imidazolium-linker functional group of TEMPO is responsible for the difference in the acid–base properties of the reduced and oxidized forms

Unveiling the Impact of Fe Incorporation on Intrinsic Performance of Reconstructed Water Oxidation Electrocatalyst

Because of the salient impact on the performance of oxygen evolution reaction (OER), the surface dynamics of precatalysts accompanying the surface oxidation and dissolution of catalytic components demands immense research attention. Accordingly, the change in the structural integrity under high current density generally results in inconsistent OER performances. To address this challenge, here, we present the intricate design of precatalysts, strategically followed by reconstruction treatment in the presence of Fe under water oxidation condition, which significantly enhances the OER activity and long-term stability. Notably, the surface tailored heterointerface structures (Fe-doped NiOOH/CoOOH) obtained through the reconstruction of a precatalyst (Ni­(OH)2/Co9S8) with the incorporation of Fe, are abundantly enriched with electrochemically accessible high valence active sites. This results in remarkable OER activity (400 mA cm–2 at 345 mV). Density functional theory (DFT) calculations indicate that Fe-incorporated electrocatalysts give optimal binding energies of OER intermediates and show substantially reduced overpotential compared to Fe-undoped electrocatalysts