Increasing the efficiency of carbon coating on olivine-structured cathodes by choosing a carbon precursor

Abstract

• LiFe 0.5 Mn 0.5 PO 4 /C is obtained by mechanochemically assisted solid-state synthesis. • Carbon black, citric acid and polyvinylpyrrolidon are used as carbon precursors. • Carbon coating formation is studied using FTIR spectroscopy of adsorbed probe molecules. • The properties of carbon coating are studied by Raman spectroscopy, MSCP and EIS. Carbon-coated LiFe 0.5 Mn 0.5 PO 4 (C-LFMP) cathode materials were obtained by two-step mechanochemically assisted solid-state synthesis. After mechanical activation and heat treatment of the reagent mixture at 400 °C, the pre-prepared carbon-free LFMP-400 was obtained, which was then ball milled with three different carbon precursors: carbon black (CB), citric acid (CA) and polyvinylpyrrolidon (PVP) and subsequently annealed at 700 °C. FTIR spectroscopy of adsorbed probe molecules (pyridine) was used to detect the presence of Brønsted acid centers on the surface of LFMP-400. The mechanism of their interaction with functional groups of carbon precursors during joint ball milling and heating up to 700 °C was investigated using FTIR spectroscopy. The properties of carbon coatings were studied by Raman spectroscopy, standard contact porosimetry, and electrochemical impedance spectroscopy, and their effect on electrochemistry of the C-LFMP composites was studied by galvanostatic cycling. It is shown that the LFMP/PVP composite is characterized by higher capacity and better high-rate capability due to the formation of well-graphitized carbon coating tightly bound to the surface of LFMP and having an optimal porous structure.