In our work we succeeded to isolate three pure polymorphs of Li2FeSiO4, which differ between them self in the FeO4 arrangements (orientation, Fe-O bond lenght, and distortion). These small differences do influence on the equilibrium potential measured during the first oxidation of Fe2+ into Fe3+ in all polymorphs of Li2FeSiO4. Starting structure has an influence on the kinetics of the thermodynamic stabilization. This is unique system which within the same composition shows the influence of the bond covalence on the electrochemical potential.
COBISS.SI-ID: 4600090
Polymorphism of Li2MnSiO4 was inspected by 6Li MAS NMR spectroscopy. The detected isotropic shifts and spinning-sideband patterns were successfully reproduced by first-principles calculations and offered an insight into structural differences among the polymorphs. The approach for predicting isotropic shifts was also tested on several other Li-containing paramagnetic structures.
COBISS.SI-ID: 4386074
This work reports the crystal structure of a new polymorph of Li2FeSiO4 (prepared by annealing under argon at 900°C and quenching to 25°C). Structure was determined by electron microscopy and X-ray and neutron powder diffraction. The crystal structure of Li2FeSiO4 quenched from 900°C is described in the space group Pmnb with lattice parameters a = 6.2836(1) ?, b = 10.6572(1) ?, c = 5.0386(1) ?. It differs from previously published structures obtained at lower temperatures on the respective orientations and alternate sequences of corner-sharing FeO4 and SiO4 tetrahedra.
COBISS.SI-ID: 4468250
Paper describes the in-situ study of Li2MnSiO4 and Li2FeSiO4 cathode materials with X-ray absorption spectroscopy. Local environment and oxidation state of Fe and Mn were simultaneously monitored during the electrochemical oxidation and reduction. In this work with the help of EXAFS analysis we discovered that deformations that occur during the reduction process are completely reversible in the case of Li2FeSiO4 and only partially in the case of Li2MnSiO4.This work confirmed anomalies observed from in-situ characterisation with X-ray diffraction spectroscopy.
COBISS.SI-ID: 1073915
The selected Li2Fe0.8Mn0.2SiO4 sample prepared by hydrothermal synthesis was electrochemically evaluated by the use of in-situ Mössbauer spectroscopy and in-situ X-ray absorption spectroscopy. Although sample showed high electrochemical activity in the formation cycles, only part of it can be connected with the change of oxidation states. The overall change of oxidation state did not exceed more than 0.8 electron per both transition metals. The prediction that the local environment around Mn in Li2FeSiO4 (when the Mn doping is low) can be stabilized during the oxidation has been confirmed.
COBISS.SI-ID: 1613051