© 2017 American Chemical Society. In this study, we present a new aprotic solvent, 2,4-dimethoxy-2,4-dimethylpentan-3-one (DMDMP), which is designed to resist nucleophilic attack and hydrogen abstraction by reduced oxygen species. Li-O 2 cells using DMDMP solutions were successfully cycled. By various analytical measurements, we showed that even after prolonged cycling only a negligible amount of DMDMP was degraded. We suggest that the observed capacity fading of the Li-O 2 DMDMP-based cells was due to instability of the lithium anode during cycling. The stability toward oxygen species makes DMDMP an excellent solvent candidate for many kinds of electrochemical systems which involve oxygen reduction and assorted evaluation reactions.

During the last two decades, we have observed a dramatic increase in the electrification of many technologies. What has enabled this transition to take place was the com-mercialization of Li-ion batteries in the early nineties. Mobile technologies such as cellular phones, laptops, and medical devices make these batteries crucial for our contemporary life-style. Like any other electrochemical cell, the Li-ion batteries are restricted to the thermodynamic limitations of the mate-rials. It might be that the energy density of the most advance Li-ion battery is still too low for demanding technologies such as a full electric vehicle. To really convince future customers to switch from the internal combustion engine, new batteries and chemistry need to be developed. Non-aqueous metal-ox-ygen batteries—such as lithium–oxygen, sodium–oxygen, magnesium–oxygen, and potassium–oxygen—offer high ca-pacity and high operation voltages. Also, by using suitable polar aprotic solvents, the oxygen reduction process that oc-curs during discharge can be reversed by applying an external potential during the charge process. Thus, in theory, these batteries could be electrically recharged a number of times. However, there are many scientific and technical challenges that need to be addressed. The current review highlights recent scientific insights related to these promising batteries. Nevertheless, the reader will note that many conclusions are applicable in other kinds of batteries as well.

Chemically prepared manganese dioxide (CMD), which is traditionally used as a cathode material for Li-ion batteries, was tested and characterized for the first time as a positive electrode material for hybrid supercapacitors with two different aqueous electrolyte solutions (6 M KOH and 0.5 M K2SO4). The CMD electrodes exhibit distinct electrochemical characteristics that depend on the electrolyte solution used. The CMD electrodes show higher specific capacitance in the basic electrolyte solution, 137 F/g, at a current density of 0.1 A/g. Asymmetric supercapacitors comprising CMD positive electrodes and activated carbon negative electrodes were fabricated and tested within an electrochemical window wider than the thermodynamic voltage limitation for aqueous solutions. The asymmetric supercapacitors based on KOH and K2SO4 showed very good electrochemical stability during more than 7000 charge-discharge cycles and reasonable energy and power density. The electrochemical performance of CMD/AC asymmetric supercapacitors, their easy assembly, and their low cost make these super capacitors promising as practical energy-storage devices.

Diglyme (G2) is the highly preferred solvent choice over other types of glymes for achieving longer cycling performance of Li–O 2 cells.

In this paper we present a comprehensive structural, chemical and electrochemical characterization of monoclinic Li0.33MnO2as a positive electrode material for aqueous high-voltage hybrid supercapacitors. The monoclinic Li0.33MnO2, which is traditionally used as cathode material for lithium ion batteries, was synthesized through a simple thermal solid-state synthesis. The monoclinic Li0.33MnO2electrode exhibits a wide operational potential window ranging between −1.25 and 1.25 V vs SCE, which enables it to serve as either a negative or a positive electrode. In addition, this electrode material exhibits a high specific capacity of 140 mAh g−1at a low current density of 0.1 A g−1, and 76 mAh g−1at high current density of 1 A g−1in this range of potentials. Hybrid supercapacitors composed of Li0.33MnO2positive electrode and activated carbon (AC) negative electrode were fabricated. They exhibit outstanding electrochemical performance in terms of operational potential window, cycleability, and energy and power density. The Li0.33MnO2/AC hybrid capacitor has an energy density of 13.5 Wh kg−1at power density of 100 W kg−1, which is twice than that of MnO2/AC and AC/AC supercapacitors, and an energy density of 7 Wh kg−1at 1000 W kg−1, which is seven times higher than that of AC/AC capacitors at this power density. Furthermore, this hybrid capacitor presents an excellent cycle life with 80% specific capacitance retention after 12,000 cycles to 2 V. The electrochemical charge storage mechanism of the monoclinic Li0.33MnO2was investigated by cyclic voltammetry and X-ray diffraction.