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Through coupled experimental analysis and computational techniques, we uncover the origin of anodic stability for a range of nonaqueous zinc electrolytes. By examination of electrochemical, structural, and transport properties of nonaqueous zinc electrolytes with varying concentrations, it is demonstrated that the acetonitrile-Zn(TFSI)2, acetonitrile-Zn(CF3SO3)2, and propylene carbonate-Zn(TFSI)2 electrolytes can not only support highly reversible Zn deposition behavior on a Zn metal anode (≥99% of Coulombic efficiency) but also provide high anodic stability (up to ∼3.8 V vs Zn/Zn(2+)). The predicted anodic stability from DFT calculations is well in accordance with experimental results, and elucidates that the solvents play an important role in anodic stability of most electrolytes. Molecular dynamics (MD) simulations were used to understand the solvation structure (e.g., ion solvation and ionic association) and its effect on dynamics and transport properties (e.g., diffusion coefficient and ionic conductivity) of the electrolytes. The combination of these techniques provides unprecedented insight into the origin of the electrochemical, structural, and transport properties in nonaqueous zinc electrolytes.

From dictating the redox potential of electrolyte solvents to shaping the stability of solid-electrolyte interfaces, solvation plays a critical role in the electrochemistry of electrolytes.

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A series of electrolyte formulations containing fluorinated cyclic carbonates and fluorinated linear carbonates with LiPF 6 has been evaluated as electrolyte solvents for high-voltage Li-ion batteries. The anodic stability of the new electrolytes on fully charged spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode was examined by electrochemical floating tests. The effects of fluorine substitution on the cyclic and linear carbonate, ratio of cyclic vs. linear carbonate, and LiPF 6 concentration on the electrolyte oxidation stability were investigated. Based on this study, the floating test proved to be an effective tool for identification of stable electrolyte materials. have been proposed. Because of the large number of candidates for high-voltage electrolyte solvents, screening the voltage stability of each solvent would be very labor-intensive. Traditional methods of measuring the oxidation potential of organic solvents usually involves linear/cyclic voltammetry using an inert electrode such as platinum and glassy carbon. However, such measurements are in many cases misleading, because interactions of these organic solvents with actual electrode materials are usually more complicated and may happen at a much lower potential due to the catalytic effect of the cathode material lowering the kinetic barrier of oxidation. Unfortunately, using active cathode material to run voltammetry measurement has a drawback in that the material itself is redox active and can interfere with the observation of electrolyte oxidation. Thus, developing a fast and effective method to screen the voltage stability of electrolyte solvents on actual cathode materials is of vital importance. Herein, we report a method using constant potential electrolysis with a slightly overcharged LNMO cathode as the working electrode, abbreviated as an "electrochemical floating test", where the cell potential is allowed to "float" at different values to evaluate the voltage stability of the electrolyte. For an ideal electrolyte with no impurities and no oxidation at the working electrode, the only current observed when a potential is applied is the capacitance current, which should decline to zero when the equilibrium is reached. However, in reality, the electrolytes are oxidized, and the current intensity measured corresponds to the severity of oxidation. As a result, the leakage currents of each electrolyte at different potentials can be compared to produce a voltage stability profile of a given solvent. The effect of different ratios of mixed solvents and lithium salt concentrations can also be probed. * Electrochemical Society Active Member.z E-mail: zzhang@anl.gov Materials and MethodsTheoretical calculations.-The Gaussian 09 code was used for all calculations.14 Oxidation and reduction potentials were calculated by optimizing the geometries of the neutral and ionic species at the B3LYP/6-31G * level, followed by frequency calculations to determine gas-phase free energies. Solvation effects were taken into account by using a single-point B3LYP/6-31+G * PCM...

Triethlylphosphite (TEP) and tris(2,2,2-trifluoroethyl) phosphite (TTFP) have been evaluated as electrolyte additives for high-voltage Li-ion battery cells using a Ni-rich layered cathode material LiNi0.5Co0.2Mn0.3O2 (NCM523) and the conventional carbonate electrolyte. The repeated charge/discharge cycling for cells containing 1 wt % of these additives was performed using an NCM523/graphite full cell operated at the voltage window from 3.0-4.6 V. During the initial charge process, these additives decompose on the cathode surface at a lower oxidation potential than the baseline electrolyte. Impedance spectroscopy and post-test analyses indicate the formation of protective coatings by both additives on the cathode surface that prevent oxidative breakdown of the electrolyte. However, only TTFP containing cells demonstrate the improved capacity retention and Coulombic efficiency. For TEP, the protective coating is also formed, but low Li(+) ion mobility through the interphase layer results in inferior performance. These observations are rationalized through the inhibition of electrocatalytic centers present on the cathode surface and the formation of organophosphate deposits isolating the cathode surface from the electrolyte. The difference between the two phosphites clearly originates in the different properties of the resulting phosphate coatings, which may be in Li(+) ion conductivity through such materials.

New fluorinated sulfones were synthesized and evaluated in high voltage lithium-ion batteries using a LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode.

Battery safety is critical for many applications including portable electronics, hybrid and electric vehicles, and grid storage. For lithium ion batteries, the conventional polymer based separator is unstable at 120 °C and above. In this research, we have developed a pure aluminum oxide nanowire based separator; this separator does not contain any polymer additives or binders; additionally, it is a bendable ceramic. The physical and electrochemical properties of the separator are investigated. The separator has a pore size of about 100 nm, and it shows excellent electrochemical properties under both room and high temperatures. At room temperature, the ceramic separator shows a higher rate capability compared to the conventional Celgard 2500 separator and life cycle performance does not show any degradation. At 120 °C, the cell with the ceramic separator showed a much better cycle performance than the conventional Celgard 2500 separator. Therefore, we believe that this research is really an exciting scientific breakthrough for ceramic separators and lithium ion batteries and could be potentially used in the next generation lithium ion batteries requiring high safety and reliability.