Alpha manganese dioxide for lithium batteries: A structural and electrochemical study

A highly crystalline α-MnO2 phase has been synthesised by acid treatment of Li2MnO3. A neutron-diffraction study has shown that the stoichiometry of this phase is A0.36Mn0.91O2 (or MnO2·0.2A2O) where A refers predominantly to H+ ions and a very minor concentration of Li+ ions. Heat-treatment at 300°C leaves a virtually anhydrous α-MnO2 product. The absence of any foreign cation such as K+, Na+ or Rb+ within the channels of the structure has raised the possibility of utilizing the α-MnO2 framework as a high performance electrode for secondary lithium cells. Preliminary electrochemical data indicate that capacities in excess of 200 mAh/g are achievable from these α-MnO2 electrodes in room-temperature lithium cells. Cyclic voltammograms show that lithium is inserted into α-MnO2 in a two-step process and that this process is reversible.