Lithium–Oxygen Power Source: the Influence of Positive Electrode Thickness on the Overall Discharge Characteristics

Characteristic feature of the discharge process of lithium–oxygen battery cathode with non-aqueous electrolyte is the blockade of pores in the positive electrode by lithium peroxide (Li2O2), an insoluble in the electrolyte and non-conductive substance. Lithium peroxide blocks cathode pores and thus hinders the oxygen entering therein. This complicates, in its turn, further behavior of the reaction. The goal of this work is to understand the following problems: (1) why is the acceptable thickness of the positive-electrode active layer extremely low, and (2) what is the reason of the lowering of specific capacity with the increasing of the active layer thickness. The main properties of the lithium—oxygen battery discharge—the current density, discharge time, specific capacity and the constant of oxygen consumption k*—were calculated using a digital simulation method. It was shown that the necessity of usage of low discharge current density is caused by the small thickness of the cathode region adjacent to the boundary with gaseous phase, in which the formation of Li2O2 occurs. An increase in the cathode thickness induces a decrease in the current density, which, in its turn, leads to increase in parameter k and decrease in the discharge capacity.