Performance of Carbon/Polytetrafluoroethylene (PTFE) Air Cathodes from pH 0 to 14 for Li-Air Batteries

Abstract : The purpose of this project was to construct an inexpensive air cathode free of catalyst that is capable of functioning in both acidic and basic electrolytes. The performance of an uncatalyzed air cathode for use in a Li-Air battery was evaluated over the pH range from 0 to 14. This study was undertaken to determine if air cathodes constructed solely from carbon black and polytetrafluoroethylene (PTFE) can function at a sufficient rate in sulfate based electrolytes to be useful in Li-Air batteries. Layered cathodes were constructed with a hydrophobic wet-proofing layer and an active hydrophilic layer that utilizes a high surface area carbon black. Electrolytes were formulated using H2SO4, Na2SO4, and NaOH in various combinations giving pH values ranging from 0 to 14. Electrolytes were also formulated using H2SO4, Li2SO4, and LiOH in combination, and HCl, LiCl, and LiOH in combination giving electrolytes with pH values ranging from 0 to 14. The cathodes were discharged in a three electrode cell from 0.0 V to -0.6 V vs. a Ag/AgCl reference electrode. The cathode performed well and met the requirement that a current density of at least 1-2 mA/cm2 was maintained at -0.3 V vs. Ag/AgCl.