The effects of O2 pressure on Li-O2 secondary battery discharge capacity and rate capability

The nonaqueous lithium-oxygen (Li-O2) battery is investigated in a contained, high pressure O2 system. Increasing the O2 pressure from 1 atm to 10 atm of O2 increased the discharge potential by 10% when discharged at 100 μA cm−2 from 2.65 V to 2.77 V. In addition, the cell discharge capacity increased from 1400 mAh gC−1 at 1 atm of O2 to 2100 mAh gC−1 at 10 atm at 100 μA cm−2. The discharge capacity of the 1 atm O2 cell decreased to 100 mAh gC−1 at 1000 μA cm−2, while at 10 atm of O2 it retained one third of the 100 μA cm−2 capacity at 2100 μA cm−2 and two thirds the 1 atm/100 μA cm−2 capacity at 500 μA cm−2. This increase in capacity results from a more efficient utilization of the carbon electrode surface at higher pressures. As seen by SEM, the thickness of the discharge product layer was much greater when discharged under higher pressures, indicating more O2 reached the active carbon surfaces and was reduced. In addition, at high pressure the electrode surface was more evenly used, having fewer areas with little or no discharge products.