A novel layered lithium niobium titanate as battery anode material: Crystal structure and charge-discharge properties

摘要

LiTi2NbO7 was synthesized from CsTi2NbO7 by direct Cs+/Li+ ion exchange and subsequent thermal decomposition of the hydrated form. Neutron powder diffraction data were collected at high-resolution (ILL, France) and analyzed by Rietveld refinements and Fourier difference techniques, revealing a layer-like crystal structure (orthorhombic Pbnm, a = 9.2476(6), b = 16.955(2), c = 3.7542(2) angstrom) partly similar to that of monoclinic LiTi3O7. Lithium is tetrahedrically coordinated and bridges adjacent layers of (Ti,Nb)O-6 octahedra. Nb atoms are strongly ordered in one of the three independent sites available for Ti/Nb, thus compensating for the unbalance of negative charge from the surrounding 0 atoms. Electrochemical measurements were performed on a LiTi2NbO7 electrode vs. Li/Li+ couple. Overlapping Ti4+/Ti3+ and Nb5+/Nb4+ redox processes occur around 1.4 V, with a specific charge of 245 mAh/g (about 2.8 electrons per f.u.) in the 230 to 1.15 V range. Charge-discharge cycling results show a reversible and stable specific capacity of 220 mAh/g at low current density, indicating that this material is a promising alternative to Li4Ti5O12 spinel for reversible anode applications in lithium batteries. (C) 2016 Elsevier B.V. All rights reserved.