Kinetic and structural characteristics of niobium vanadium oxide electrodes for secondary lithium batteries

Abstract

Kinetic study of the insertion process of Li + ions into the crystal lattices of Nb 2− n V n O 5 ( n=0.50 and 0.70) was performed by using current pulse methods as well as an X-ray diffraction study of the structural changes of the oxide electrodes. The lithium insertion reaction of both oxides consists of two main steps. In the first step of Li x Nb 1.3V 0.7O 5 ( x=0∼1), the chemical diffusion coefficient D̃ of lithium was found to be on the order of 10 −11cm 2s, however in the second step ( x=1∼1.7) the D̃ value increased considerably to 10 −9∼10 −10cm 2s. On the other hand, for Li x Nb 1.5V 0.5O 5 ( x=0∼2) the D̃ value was mainly in the order of 10 −11 cm 2s. The self-diffusion coefficient D Li derived from the D̃ values was found to be on the order of 10 −12cm 2s in both oxides. Lithium was inserted in the crystal lattice while keeping the original crystal lattice arrangement. The largest unit cell volume (0.9409 nm 3) of Nb 1.3V 0.7O 5 among various Nb 2- n V n O 5 ( n=0.2∼0.8) and the increases in the cell volume and the crystallite size with lithium insertion may be related to higher diffusitivy of lithium in the crystal lattice of Li x Nb 1.3V 0.7O 5 ( x=1∼1.5).