Lithium-ion insertion in a V6O13 cathode

Abstract: The transition metal oxide V6O13 is a promising cathode material for high-capacity lithium-polymer batteries in conjunction with a lithium-metal anode. The electro-chemical behaviour of V6O13 has its origin in the ability of the vanadium ions to change their-oxidation states, combined with the open nature of its crystal structure which allows lithium ions to diffuse through it. When incorporated into the cathode, the material passes through a series of lithiated phases as the battery is discharged. Inthis thesis, structure-property relationships of these lithiated phases have been studied. The techniques used have been in situ X-ray powder diffraction and single-crystal X-ray diffraction on electrochemically lithiated samples, in combination with electrochemical cycling.Five different lithiated phases were identified : LixV6O13 for x = 0.5, 1.0, 2.0, 3.0 and 6.0 at potentials 2.78, 2.68, 2.52, 2.45 and 2.00V vs. Li/Li+, respectively. The structures of the x = 0, 2.0 and 3.0 phases have been investigated using single-crystal techniques; deformation electron density refinement has been performed for the x=0 and 2.0 phases. The reduction (from V5+ to V4+) of one of the threeindependent vanadium atoms (V2) in the asymmetric unit can be identified with some degree of certainty as Li2V6O13 is formed. On this basis, a proposal is made for the complete sequence of vanadium oxidation-state changes for the entire lithium insertion process.