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.

In this work, we synthesized nano-particles (20-80 nm) of Li 2MnO3 using the self-combustion reaction and studied the electrochemical activity of electrodes prepared from this nano-material at 30, 45, and 60 C. It was shown that the first Li-extraction from nano-Li 2MnO3 occurs at much lower potentials (by 180-360 mV) in comparison with micron-sized Li2MnO3 electrodes. This can be associated with the higher surface-to-volume ratio, much shorter the diffusion path and the increased surface concentration of the electrochemically active sites. On the basis of magnetic susceptibility studies of nano-Li 2MnO3 we proposed a model of disordered surface layer, containing Mn3+ or Mn2+ ions, both at low spin state, at the surface of these nano-particles. From the results of structural analysis (by X-ray and electron diffraction and vibrational Raman spectroscopy) of galvanostatically cycled nano-Li2MnO3 electrodes in Li-cells we came to a conclusion of partial transition of layered LiMO 2 to spinel-type ordering. ?? 2013 Elsevier Ltd. All rights reserved.