The effects that electrolyte and air cathode formulation have on discharge capacity, rate capability, and the rechargeability of the lithium/oxygen organic electrolyte cell were characterized. To characterize the effects of cell formulation on the discharge reaction, we used techniques including static and dynamic gas consumption measurements and scanning electron microscopy. It was found that electrolyte formulation has the largest effect on discharge capacity and rate capability. Electrode processing is also important in determining discharge capacity at low rate. The Brunauer-Emmett-Teller surface area of the carbon black used to prepare the air electrode is not a significant factor in determining discharge capacity. The discharge product was found to depend on both discharge rate and electrolyte formulation. This is understood in terms of the concentration of oxygen in the electrolyte during discharge.

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.

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The practical operation of a lithium/oxygen organic electrolyte battery depends on a significant amount of dissolved oxygen transporting through the organic electrolyte permeating the carbon black cathode before its reduction occurs. The rate of oxygen transport directly influences rate capability and discharge capacity. The organic electrolyte can be tailored to maximize the transport of oxygen while still retaining the ability to form a stable solid electrolyte interface with the lithium anode, chemical stability towards the discharge products normalLi2normalO2 and normalLi2O , and oxidative stability to over 3V . We investigated an ether-based electrolyte containing four different electrolyte salts to determine how electrolyte properties such as oxygen solubility, dynamic viscosity, and conductivity change with each electrolyte salt, and how this directly affects rate capability and discharge capacity. The results indicate that discharge capacity at 0.5mA∕cm2 is determined by dynamic viscosity alone for these electrolytes, while discharge capacity at 0.2 and 0.05mA∕cm2 shows no correlation with either oxygen solubility, dynamic viscosity, or conductivity. Our results demonstrate that a substantial improvement in rate capability can be achieved by optimizing electrolyte viscosity.

Electrochemical cells utilizing graphite intercalation compounds at both electrodes have been proposed as an energy storage technology where the electrolyte salt is split and stored in the electrodes on charge and reformed on discharge. The anion intercalation compounds of graphite proposed as cathodes in these systems have been studied in electrolytes that are resistant to oxidation at 5 V but that are incompatible with graphite anodes. Recent work has demonstrated that electrolytes based on monofluoroethylene carbonate (FEC) and ethylmethyl carbonate (EMC) have superior oxidative stability on graphite cathodes over previously studied electrolytes and form a stable solid electrolyte interphase (SEI) on graphite anodes that allow for full dual-graphite cells to be evaluated for energy storage applications. There is still a limited understanding as to structure of the anion intercalate formed in these electrolyte systems and the effect of solvent cointercalation on cathode performance. This effort was undertaken using a number of in situ techniques to better characterize the fully intercalated composition as well as to investigate the process of solvent cointercalation. It was shown that a series of stages based on the C 24 PF 6 composition are formed until, upon reaching full charge, the structure approaches a C 20 PF 6 stage I composition with PF 6 − anion in close contact with the graphite layers and 0.7 molecules of cointercalated solvent. For the first time, we have shown that solvent molecules move with anion during the intercalation/deintercalation process while analysis of fully intercalated crystals demonstrated that there is an unusually strong preference for EMC over FEC to cointercalate in this anion intercalation compound.

Lithium/air batteries have the potential to substantially outperform the best battery system nowadays on the market. Oxygen reduction reaction (ORR) at the cathode in an aprotic organic lithium electrolyte is well-known to limit the discharge rate and capacity of the lithium/air batteries. In this study, the discharge characteristics of Li/air cells with cathodes made of different carbon materials were examined. The results showed that the ORR kinetics in the lithium/air batteries can be drastically improved by using an effective catalyst, achieving higher discharge voltage and rate. The discharge capacity of the lithium/air battery was found to be correlated to the cathode pore volume, to which the mesopore volume of the carbon material has a large contribution. An ORR mechanistic model involving a reaction product deactivating the catalytic sites on the carbon surface is proposed to explain the experimental results.