Insight into the channel ion distribution and influence on the lithium insertion properties of hexatitanates A_2Ti_6O_(13) (A = Na, Li, H) as candidates for anode materials in lithium-ion batteries

摘要

Li_2Ti_6O_(13) and H_2Ti _6O_(13) were easily synthesized from Na_2Ti _6O_(13) by successive Na~+-Li~+-H ~+ ion exchange. The crystal structures of Na_2Ti _6O_(13), Li_2Ti_6O_(13) and H_2Ti_6O_(13) were investigated using neutron powder diffraction. Monovalent A+ cations (Na, Li and H) have been located using difference Fourier analysis. Although monoclinic lattice parameters (space group C2/m) of the three titanates remain almost unchanged with retention of the basic [Ti_6O_(13) ~(2-)] network, monovalent Na, Li and H cations occupy different sites in the tunnel space. By comparing the structural details concerning the A~+ oxygen coordination, i.e. NaO_8 square prismatic coordination, LiO_4 square planar coordination and covalently bond H atoms, with results from ~(23)Na, ~7Li and ~1H NMR spectroscopy we were able to obtain a more detailed insight into the respective local distortions and anharmonic motions. We were able to show that the site that the A~+ cation occupies in the hexatitanate channel structure strongly influences the lithium insertion properties of these compounds and therefore their usefulness as electrode materials for energy storage.