Acceleration of Processes on Positive Electrode of Lithium–Oxygen Battery: Electrocatalyst or Redox Mediator?

Abstract

The approaches to increasing the efficiency of lithium–oxygen battery (LOB), which are based on the use of PtCo/carbon nanotubes (CNT) catalyst and iodine-containing liquid-phase mediator, are compared. It is found that, when 1 M LiClO4/DMSO electrolyte is used, the 20PtCo/CNT catalyst provides an increase of the capacity of a Swagelok LOB model in the complete discharge to a voltage of 2 V as compared to the CNT-based LOB. During the cycling of LOB with each of the materials, the charging voltage increases to 4.5 V. This leads not only to an increase in the rate of electrochemical oxidation of lithium peroxide, but also to an acceleration of corrosion of the electrolyte and active material. In the presence of iodine compounds in the electrolyte, Li2O2 is oxidized by the chemical mechanism, which reduces the charging voltage. In the 0.05 M LiI + 1 M LiClO4/DMSO electrolyte, 85 successive cycles were obtained at a capacity of 500 mA h/gС in the LOB discharging stage and a final charging voltage of not more than 3.8 V. When scaling the LOB to the size of the positive electrode (5 × 5 cm2), the complete discharge capacity close to this characteristic of Swagelok model (as calculated for the geometric electrode surface area) was reached. An introduction of iodine-containing additive into the electrolyte enabled us to obtain up to 100 cycles at a capacity of 300 mA h/gC. The results of the work show that the use of iodine-based redox mediator is more effective from the viewpoint of stability of characteristics of LOB of this type as compared with the use of the platinum-containing catalyst.