New electrocatalyst for Li/Air cathode batteries : MnO2 via hydrothermal method

Since the first announcement in 1996 by Abraham, Li/air batteries have attracted the attention because of their high specific capacity (up to 1800mAh·g-1), thanks to the positive pole reaction based on the reduction of O2, that can be directly provided by the air without the necessity to upload the chemical reagent in the battery. At the same time, secondary Li/air cells suffer serious limitations under recharging conditions, because the “combustion” products, Li2O2 and/or Li2O, can clog the carbon-based cathode pores, thus reducing the performance and lifetime of the batteries. It is well accepted that their complete removal during the charge cycle is hard to accomplish without an appropriate catalyst. The use of electrolytic MnO2 has been proved to be rather effective, but the overall performance of the modified cathode material is still inadequate to guarantee the expected long life cycles to the new Li/air batteries. In this context we present a new composite material based on ordered mesoporous carbon cathode modified with MnO2 electrocatalytic nanopowders prepared by an hydrothermal method, based on the oxidation of Mn2+ by ammonium peroxodisulphate. The syntheses were carried out for 24 h at different temperatures (60, 90, and 120 °C) also in the presence of dopant species. The results are discussed in term of cyclic voltammetry experiments performed by hosting the new composite powders in cavity microelectrodes, and in term of laboratory Li/Air battery life cycles.