Factors controlling the stability of O3-and P2-type layered MnO2 structures and spinel transition tendency in Li secondary batteries

Cathode properties of two layered manganese dioxides (A(x)MnO(2+delta). yH(2)O, 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 KNO3, LiOH, and MnO at 800 and 1050 degrees C, respectively. The 800 degrees C-prepared MnO2 has a trigonal R(3) over bar m space group with an O3-type oxide-packing pattern, whereas the 1050 degrees C 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 degrees C material. Due to the higher mobility of pillaring cations in the 800 degrees C 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 to the spinel-related phases. By contrast, as the 1050 degrees C material has rather immobile pillaring cations and its oxide-packing pattern (P2-type) is far different from that of the spinel phases, this cathode shows better cycling performance, with its structural integrity bring well maintained. (C) 2000 The Electrochemical Society. S0013-4651(99)06-148-0. All rights reserved.