Electrochemical lithiation/delithiation kinetics and capacity of phosphate tungsten bronze and its chemically pre-lithiated derivatives in aqueous solutions
2016
Vujković, Milica | Nedić, Zoran | Tančić, Pavle | Aleksić, Obrad S. | Nikolić, Maria Vesna | Mioč, Ubavka | Mentus, Slavko
Monophosphate bronze (PW₈O₂₆, WPB) was synthesized by low-temperature (650 °C) heating of 12-tungstophosphoric acid (WPA). Its lithiated derivative with a low lithium content (Li₃-WPB) was synthesized by heating lithium salt of WPA at 650 °C. Its lithiated derivative with a high lithium content was synthesized by mechanochemical lithiation of Li₃WPB (Li ₙ -WPB) (n > 3), followed by heat treatment at 650 °C. X-ray powder diffraction analysis confirmed that the bronze structure changed with the increase of the incorporated lithium content. These bronzes were investigated from the aspect of lithiation/delithiation kinetics in an aqueous saturated LiNO₃ electrolyte solution. By cyclic voltammetry, both the kinetics of intercalation/deintercalation and the coulombic capacity were found to decrease with the increase of initial lithium content, in agreement with literature data for electrochemically lithiated tungstophosphate bronzes. Monoclinic lithium-free bronze PW₈O₂₆, as the most promising material, was subjected to a further detailed galvanostatic investigation coupled with the LiFe₀.₉₅V₀.₀₅PO₄/C composite as a cathode material in an aqueous battery. In comparison to its behavior in an organic electrolyte, a considerably lower initial capacity of the bronze electrode was measured. However, its cyclic stability was much better in an aqueous than in an organic electrolyte.
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