Using UV-vis spectroscopy in conjunction with various electrochemical techniques, we have developed a new effective operando methodology for investigating the oxygen reduction reactions (ORRs) and their mechanisms in nonaqueous solutions. We can follow the in situ formation and presence of superoxide moieties during ORR as a function of solvent, cations, anions, and additives in the solution. Thus, using operando UV-vis spectroscopy, we found evidence for the formation of superoxide radical anions during oxygen reduction in LiTFSI/diglyme electrolyte solutions. Nitro blue tetrazolium (NBT) was used to indicate the presence of superoxide moieties based on its unique spectral response. Indeed, the spectral response of NBT containing solutions undergoing ORR could provide a direct indication for the level of association of the Li cations with the electrolyte anions.

© 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.

Improved efficiency and cyclability of cells containing LiBr demonstrate that the appropriate choice of electrolyte solution is the key to a successful Li–O 2 battery.

This work deals with core issues of Li–oxygen battery systems; intrinsic stability of polyether electrolyte solutions and the role of important redox mediators such as LiI/I 2 .

The stability of electrolyte solutions during lithium–oxygen cells operation is of great importance and interest. This is because oxides formed during reduction are strong nucleophiles which can initiate solvent decomposition. The highly polar amide based solvents have come to the fore as possible candidates for Li–O2 applications. They show typical cycling behavior as compared to other solvents; however, their stability toward lithium oxides is shrouded in doubt. The present study has focused on Li–O2 cells containing electrolyte solutions based on DMA/LiNO3. We have used various analytical tools, to explore the discharge–charge processes and related side reactions. The data obtained from FTIR, NMR, XPS, and EQCM all support a rational decomposition mechanism. The formation of various side products during the course the first discharge, leads to the conclusion that amide based solvents are not suitable for Li–O2 applications; however, electrolyte solution decomposition reduces the OER overpotential by forming oxidation mediators.

Polyether solvents are considered interesting and important candidates for Li?O2 battery systems. Discharge of Li?O2 battery systems forms Li oxides. Their mechanism of formation is complex. The stability of most relevant polar aprotic solvents toward these Li oxides is questionable. Specially high surface area carbon electrodes were developed for the present work. In this study, several spectroscopic tools and in situ measurements using electrochemical quartz crystal microbalance (EQCM) were employed to explore the discharge?charge processes and related side reactions in Li?O2 battery systems containing electrolyte solutions based on triglyme/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte solutions. The systematic mechanism of lithium oxides formation was monitored. A combination of Fourier transform infrared (FTIR), NMR, and matrix-assisted laser desorption/ionization (MALDI) measurements in conjunction with electrochemical studies demonstrated the intrinsic instability and incompatibility of polyether solvents for Li?air batteries.

Hierarchical activated carbon microfiber (ACM) and ACM/[small alpha]-MnO2 nanoparticle hybrid electrodes were fabricated for high performance rechargeable Li-O2 batteries. Various oxygen diffusion channels present in these air-cathodes were not blocked during the oxygen reduction reactions (ORR) in triglyme-LiTFSI (1 M) electrolyte solution. ACM and ACM/[small alpha]-MnO2 hybrid electrodes exhibited a maximum specific capacity of 4116 mA h gc-1 and 9000 mA h gc-1, respectively, in comparison to 2100 mA h gc-1 for conventional carbon composite air-electrodes. Energy densities of these electrodes were remarkably higher than those of sulfur cathodes and the most promising lithium insertion electrodes. In addition, ACM and ACM/[small alpha]-MnO2 hybrid electrodes exhibited lower charge voltages of 4.3 V and 3.75 V respectively compared to 4.5 V for conventional composite carbon electrodes. Moreover, these binder free electrodes demonstrated improved cycling performances in contrast to the carbon composite electrodes. The superior electrochemical performance of these binder free microfiber electrodes has been attributed to their extremely high surface area, hierarchical microstructure and efficient ORR catalysis by [small alpha]-MnO2 nanoparticles. The results showed herein demonstrate that the air-cathode architecture is a critical factor determining the electrochemical performance of rechargeable Li-O2 batteries. This study also demonstrates the instability of ether based electrolyte solutions during oxygen reduction reactions, which is a critical problem for Li-O2 batteries.