Quasi-one-dimensional polaronic states due to the preferential reduction in the Li_1 xV₃O₈insertion electrode

Abstract

The structural and electronic properties of the Li1+xV3O8 insertion electrode, where 0 ≤ x < 0.4, have been explored by means of x-ray four-circle diffraction and through measurements of electrical resistivity, thermoelectric power, magnetization and electron paramagnetic resonance. Detailed structure refinements for x = 0.06 and 0.29 reveal the preferential and partial reduction of V ions which may give rise to low-dimensional electronic properties. The composition with x = 0 exhibits a quasi-one-dimensional polaronic transport in the localized states of band tails due to the slight deficiency of oxygen atoms. For x > 0.1 with nearly stoichiometric oxygen atoms, small polarons exist without carrier-creation energy at high temperatures, while at low temperatures the conduction may be of variable-range hopping (VRH) type. For x > 0.2, one-dimensional magnetic properties appear due to sizable exchange couplings and order–disorder effects of additional Li ions may lead to significant change of transport properties. For the intermediate composition 0 < x ≤ 0.1, strong randomness of the Li doping and the congenital oxygen deficiency cause VRH states even at high temperatures.

Calculations of the thermodynamic and kinetic properties of Li1+xV3O8Jiang1, Falk2 2012Phys. Rev. B364430View full textAdd to dashboardCite

“…Since this material is empirically observed to be a semiconductor over the entire concentration range, we need to choose a large enough value of U such that all structures become semiconducting. The experimental measurement of Li1V3O8 single crystal 62 indicates a small bandgap of approximately 0.1eV, which is smaller than the value predicted by either DFT or DFT+U calculations for Li1V3O8 where the band gap is approximately 1.0eV. However, for higher values of lithiation, Li1+xV3O8, we can technically open a small gap within the 3d band with appropriate U for each configuration.…”

“…The electron donated from lithium intercalates into toptactic compound to form an electron polaron which hops from one transition metal ion to another. In particular, M Onoda 62 found small polorans mainly exist on the V(2) and V(3) sites due to preferential reduction. In another study, Florent Boucher 64 also showed a preferential reduction sequence V(3)>V( 2)>V( 1) upon lithiation from XPS data.…”

“…Onoda et al62 found highly anisotropic resistivity in Li1+xV3O8 and significant difference in energy gaps calculated from temperature dependent resistivity and thermoelectric power measurements, which suggests small polaron motion. This small polaron transport is commonly found in many other semiconducting compounds, e.g.…”

Influence of adsorbed polar molecules on the electronic transport in a composite material Li1.1V3O8–PMMA for lithium batteries

“…Charge carriers are small polarons which move along vanadium chains parallel to the b-axis. 36 Noteworthily, Onoda et al have obtained the same activation energy by dc-conductivity measurements on a Li 1.1 V 3 O 8 single crystal. Nevertheless the s p value obtained here is 110 times lower than that measured along the b-axis in a Li 1.1 V 3 O 8 single crystal.…”

“…31,32 A great deal of interest has been focused on the structural characterization and cyclability of this compound. [33][34][35] Onoda and Amemiya 36 have shown that Li 1.1 V 3 O 8 exhibits a quasi-one dimensional polaronic transport along vanadium chains (from V IV to V V ) parallel to the b-axis. The lithium self-diffusion coefficient D Li of about 5.6 Â 10 À12 to 9 Â 10 À12 cm 2 s À1 at RT was previously determined by 7 Li NMR.…”