LiFeSO₄F can be synthesised in two different polymorphs, tavorite- and triplite-type, depending on the synthesis conditions¹. We have used a solvothermal route to synthesise the tavorite-type, which offers a decent energy storage capacity with an open crystal framework providing fast solid-state Li-ion transport². It’s functionality is strongly affected by surface modification. It shows minimal polarization during electrochemical cycling when coated with p-doped PEDOT³. This coating alleviates a kinetic barrier for its lithium insertion/extraction reactions⁴. The redox activity of this material has been studied with S and Fe K-edge X-ray Absorption Near Edge Spectroscopy (XANES) together with Raman and ⁵⁷Fe Mössbauer spectroscopies. The results indicated a stable p-doping of the PEDOT coating in the entire potential window for the electrochemical cycling. The iron-ligand electronic interaction increased during delithiation.

Fig. 1. Linear combination fit of S K-edge XANES spectrum for LiFeSO₄F-PEDOT conditioned at 2.5 V vs. Li⁺/Li.

Ref: 1. N. Recham et al. Nat. Mater. 9 (2010) 68–74. 2. R. Tripathi et al. Chem. Mater. 23 (2011) 2278–2284. 3. A. Sobkowiak, et al., Chem. Mater. 25 (2013) 3020–3029. A. Blidberg, et al. ChemElectroChem 4 (2017) 1896–1907.