Some Restatements on the Nature and Behavior of MnO2 for Li Batteries

Some aspects of the behavior of MnO 2 as a cathode for nonaqueous Li cells have been reconsidered. As found in the extensive investigation carried out at Sanyo's laboratories, the most active form is obtained by heating electrolytic MnO 2 in the range 350°–400°C. However, the basic support found in the present work for this behavior is quite different and excludes a γ‐β transition which, instead, has adverse effects on cathode performance. Indeed, β ‐ MnO 2 has been found to be as poor a cathode material in Li cells as in aqueous Zn / MnO 2 cells. In the disordered orthorhombic structure of EMD (substantially retained upon moderate heating), Li + is topochemically incorporated. This process causes structural alterations at relatively low Li + contents. The remarkably flat discharge curves suggest formation of a pseudo two‐phase compound. Reversibility is incomplete because of these features and only shows up in mild conditions.