Porous manganese oxide generated from lithiation/delithiation with improved electrochemical oxidation for supercapacitors

Abstract

For manganese oxides with low manganese oxidation states, such as MnO or Mn₃O₄, the electrochemical oxidation during potential cycling is critical to achieve high supercapacitor performance. In this work, dense Mn₃O₄ thin films are prepared by pulsed laser deposition. An electrochemical lithiation/delithiation process is applied to the Mn₃O₄ thin film, which leads to a nanoporous structure of the film and greatly increases the porosity of the film. The nanoporous MnO_x thin film electrode exhibits significantly improved supercapacitive performance compared to the as-prepared Mn₃O₄ thin film electrode. After 1000 cyclic voltammetric scans in 1 M Na₂SO₄ electrolyte between 0 and 1 V, only part of the surface of the as-prepared Mn₃O₄ thin film transforms into a MnO₂ porous structure while the complete film of the nanoporous MnO_x transforms into a MnO₂ porous structure. It is believed that the nanoporous structure, which facilitates the electrolyte penetration, leads to the completion of electrochemical oxidation through the film during the potential cycling, resulting in promising supercapacitive performance of the film.