The oxygen transport properties of several organic electrolytes were characterized through measurements of oxygen solubility and electrolyte viscosity. Oxygen diffusion coefficients were calculated from electrolyte viscosities using the Stokes-Einstein relation. Oxygen solubility, electrolyte viscosity, and oxygen partial pressure were all directly correlated to discharge capacity and rate capability. Substantial improvement in cell performance was achieved through electrolyte optimization and increased oxygen partial pressure. The concentration of oxygen in the electrode under discharge was calculated using a semi-infinite medium model with simultaneous diffusion and reaction. The model was used to explain the dependence of cell performance on oxygen transport in organic electrolyte.

The oxidative stability and initial oxidation-induced decomposition reactions of common electrolyte solvents for batteries and electrical double layer capacitors were investigated using quantum chemistry (QC) calculations. The investigated electrolytes consisted of linear (DMC, EMC) and cyclic carbonate (EC, PC, VC), sulfone (TMS), sulfonate, and alkyl phosphate solvents paired with BF4 –, PF6 –, bis­(fluorosulfonyl)­imide (FSI–), difluoro-(oxalato)­borate (DFOB–), dicyanotriazolate (DCTA–), and B­(CN)4 – anions. Most QC calculations were performed using the M05-2X, LC-ωPBE density functional and compared with the G4MP2 results where feasible. The calculated oxidation potentials were compared with previous and new experimental data. The intrinsic oxidation potential of most solvent molecules was found to be higher than experimental values for electrolytes even after the solvation contribution was included in the QC calculations via a polarized continuum model. The presence of BF4 –, PF6 –, B­(CN)4 –, and FSI– anions near the solvents was found to significantly decrease the oxidative stability of many solvents due to the spontaneous or low barrier (for FSI–) H- and F-abstraction reaction that followed the initial electron removal step. Such spontaneous H-abstraction reactions were not observed for the solvent complexes with DCTA– or DFOB– anions or for VC/anion, TMP/PF6 – complexes. Spontaneous H-transfer reactions were also found for dimers of the oxidized carbonates (EC, DMC), alkyl phosphates (TMP), while low barrier H-transfer was found for dimers of sulfones (TMS and EMS). These reactions resulted in a significant decrease of the dimer oxidation potential compared to the oxidation potential of the isolated solvent molecules. The presence of anions or an explicitly included solvent molecule next to the oxidized solvent molecules also reduced the barriers for the oxidation-induced decomposition reaction and often changed the decomposition products. When a Li+ cation polarized the solvent in the EC n /LiBF4 and EC n /LiPF6 complexes, the complex oxidation potential was 0.3–0.6 eV higher than the oxidation potential of EC n /BF4 – and EC n /PF6 –.

No abstract

No abstract

This paper describes a study of room temperature lithium cells employing solutions of LiBCl4 in POCl3 and LiAlCl4 in SOCl2  as electrolytes and polytetrafluoroethylene (Teflon)‐bonded carbon black electrodes as cathodes. A novel feature of these cells is that during discharge the solvents, i.e., POCl3 and SOCl2 , are electrochemically reduced and behave as soluble cathodes. Sealed prototype cells were fabricated using a polyethylene‐polyester laminated bag container. Based on total cell weight, a prototype cell yielded an experimental energy density of 244 W‐hr/lb for a 57‐hr discharge rate (20 mA constant current; 1 mA/cm2 current density). The performance of these cells is also compared with the performance of prototype lithium‐organic electrolyte‐graphite monofluoride and lithium‐inorganic electrolyte‐tetracarbon monofluoride cells.