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 (α-MnO2 lg-bullet nH2O; n∼0.2-0.33), the heat-treated products (n∼0-0.1), as well as their more stable lithia-doped derivatives, α-[xLi2O]lg-bullet MnO2 (0 ≤ x ≤ 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 γ-MnO2 compounds and comparison with infrared data