Synergistic tuning of electrochemical surface area and surface Co3+ by oxygen plasma enhances the capacities of Co3O4 lithium–oxygen battery cathodes

Abstract

Modifying electrochemical surface area (ECSA) and surface chemistry are promising approaches to enhance the capacities of oxygen cathodes for lithium–oxygen (Li–O2) batteries. Although various chemical approaches have been successfully used to tune the cathode surface, versatile physical techniques including plasma etching etc. could be more effortless and effective than arduous chemical treatments. Herein, for the first time, we propose a facile oxygen plasma treatment to simultaneously etch and modify the surface of Co3O4 nanosheet arrays (NAs) cathode for Li–O2 batteries. The oxygen plasma not only etches Co3O4 nanosheets to enhance the ECSA but also lowers the oxygen vacancy concentration to enable a Co3+-rich surface. In addition, the NA architecture enables the full exposure of oxygen vacancies and surface Co3+ that function as the catalytically active sites. Thus, the synergistic effects of enhanced ECSA, modest oxygen vacancy and high surface Co3+ achieve a significantly enhanced reversible capacity of 3.45 mAh/cm2 for Co3O4 NAs. This work not only develops a promising high-capacity cathode for Li–O2 batteries, but also provides a facile physical method to simultaneously tune the nanostructure and surface chemistry of energy storage materials.