No abstract

The structure of the transition metal oxide V6O13, a potential cathode material in lithium-polymer batteries, has been studied at 95 K using single-crystal X-ray diffraction (XRD). A phase transition has been determined by differential scanning calorimetry (DSC) measurements to occur at 153 K, with a heat of transition of -1.98 kJ mol(-1). In this low-temperature phase, the V and O atoms move by up to 0.21 A out of the mirror plane they occupy in the room-temperature structure. It is concluded that the earlier reported space group P2(1)/a [Kawada et al. (1978). Acta Cryst. B34, 1037-1039] is incorrect and that a more appropriate choice of space group is Pc.

Resonant soft x-ray emission ͑SXE͒ spectroscopy was used to study the electronic structure of Li x V 6 O 13 battery cathodes. We observe that the V 3d-bands of V 6 O 13 exhibit a rather rigid behavior. Upon lithiation, electrons enter the top of the valence band and add intensity to the corresponding part of the V L-emission spectrum without significantly distorting the lower lying bands. We perform ab initio calculations which are in good agreement with the experimental results. Moreover, we find that lithiation leads to an overall decrease of the V 3d-O 2p hybridization. In contrast to x-ray diffraction, it is possible to study charge transfer effects in Li-batteries with SXE spectroscopy over the entire lithiation range.

Changes in the electronic structure of V6O13 on lithium-ion insertion into battery cathodes were studied by soft x-ray absorption (SXA) spectroscopy and resonant soft x-ray emission (SXE) spectroscopy. SXA and resonant SXE spectra were recorded ex situ for cycled battery cathodes discharged to different potentials corresponding closely to distinct lithiated stages (LixV6O13,x=0,1,…,6). Large systematic changes were observed in the vanadium and oxygen x-ray spectra, reflecting the effects of electrochemical reduction associated with the Li-ion insertion. Spectral shape analysis indicates that a large fraction of the vanadium ions have been reduced to V3+ ions for the highest degree of lithiation, x=6. Nevertheless, further lithiation may be possible, in view of the linear development of the vanadium and oxygen bands on charge uptake.

The structures of Li3V6O13 and Li(3+delta)V6O13, delta approximately 0.3, have been determined by single-crystal X-ray diffraction. Both compounds have the space group C2/m, with very similar cell parameters. In Li3V6O13, the Li atoms are found in the Wyckoff positions 4(i) and 2(b) with multiplicities of four and two, respectively. Since Li3V6O13 exhibits no superstructure reflections, it is concluded that Li3V6O13 contains one disordered lithium ion in an otherwise ordered centrosymmetric structure. On inserting more lithium into the structure, the Li(3+delta)V6O13 phase is formed with the homogeneity range 0 < delta < 1. It is concluded that the site for the extra inserted lithium ion is closely coupled to the position of the disordered lithium ion in Li3V6O13. A mechanism for this behaviour and for the further formation of the Li6V6O13 end-phase in the LixV6O13 system is proposed.