Versatility of MnO2 for lithium battery applications

Abstract

Manganese dioxide has for many years found widespread use as a cathode material in aqueous Leclanche, zinc chloride and alkaline cells and, more recently, in nonaqueous lithium cells. However, despite the large number of polymorphic structures that exist in the manganese dioxide family, the battery industry has used gamma-MnO2 exclusively as the positive electrode in these cells. With the advent of rechargeable lithium battery technology, research efforts have demonstrated that other MnO2 structures, when processed in the correct way, provide attractive electrochemical properties for lithium cells. In this paper, some recent advances that have been made in MnO2 materials technology are discussed, for example, in the development of alpha-MnO2, layered-MnO2, spinel-related Li2O.yMnO2 (y > = 2.5) and ramsdellite-MnO2 materials. An attempt has been made to clarify issues relating to the structural features of 'CDMO'-type materials that are prepared by the reaction of gamma-MnO2 with LiNO3 (or LiOH) at 300-400°C. Significant progress has been made in synthesising high-purity MnO2 materials and in understanding the structural features that account for their electrochemical properties in Li cells. Although more information about their long-term cycling performance is still required, it seems that alpha-MnO2, spinel-related Li2O .yMnO2 (y > = 2.5) and stabilised gamma-MnO2, (CDMO) electrodes offer particular promise for 3V rechargeable Li batteries.