Factors Controlling the Stability of O3− and P2-Type Layered MnO[sub 2] Structures and Spinel Transition Tendency in Li Secondary Batteries

Cathode properties of two layered manganese dioxides (AxMnO21d?yH2O, where A is the pillaring alkali cations) having different crystal structures were compared in 3 V Li secondary batteries. The materials were prepared from the mixture of KNO 3, LiOH, and MnO at 800 and 10508C, respectively. The 8008C-prepared MnO2 has a trigonal R3m space group with an O3-type oxide-packing pattern, whereas the 10508C material has an orthorhombic Cmcm symmetry with a P2-type oxide-packing pattern. The gallery space where the pillaring cations and water molecules reside is wider in the case of the 800 8C material. Due to the higher mobility of pillaring cations in the 800 8C material and similarity in the oxide-packing pattern (O3-type) to the spinel phases, the pillaring cations are easily leached out during cell cycling, which ultimately leads to a lattice collapse and structural transition t o the spinel-related phases. By contrast, as the 1050 8C material has rather immobile pillaring cations and its oxide-packing pattern (P2type) is far different from that of the spinel phases, this cathode shows better cycling performance, with its structural integri ty being well maintained.