Spectroscopic study of the proton dynamics in manganese dioxide electrode materials

Proton or lithium diffusion is a critical electrode process that occurs in manganese dioxide electrode materials during cycling of either aqueous (alkaline) or non-aqueous (lithium) batteries. The structural and electrochemical properties of a number of hydrated alpha-phase manganese dioxide compounds (a-MnO2.nH(2)O; n approximate to 0.2-0.33), the heat-treated products (n approximate to 0-0.1), as well as their more stable lithia-doped derivatives, alpha-[xLi(2)O].MnO2 (0 < x less than or equal to 0.25), have been investigated. Inelastic neutron scattering was used as a means to differentiate and interrogate the key proton or water interactions in these MnO2 structures. The neutron spectra reveal excitations associated with the hydrogen vibrations centered at 4, 13, 16, 26, 36, 65, 90, 110, 140, 200, 420, and 490 meV in the alpha-phase and 14, 24, 65, 84, 100, 202, and 425 meV in the lithia-doped derivatives. Band assignments were carried out by comparing these frequencies with those reported for structurally similar hydrated gamma-MnO2, compounds and by comparison with infrared data. (C) 1998 Elsevier Science B.V. All rights reserved.