Hierarchy concomitant in situ stable iron(II)？carbon source manipulation using ferrocenecarboxylic acid for hydrothermal synthesis of LiFePO 4 as high-capacity battery cathode

摘要

Graphical abstractDisplay OmittedHighlights？Fe3+Impurities free LiFePO4has been synthesized via hydrothermal method using ferrocene carboxylic acid as an iron source.？Electron paramagnetic resonance spectroscopy has been used for determination of Fe3+concentration in LiFePO4.？The LiFePO4electrode demonstrates good electrochemical performance.AbstractThe iron precursor of lithium iron phosphate (LiFePO4) is highly prone to oxidation to Fe3+during the hydrothermal synthesis. The Fe3+impurities in LiFePO4restrict the conduction path of Li+ions in LiFePO4, which negatively affect the cell performance. In this paper, we report that ferrocenecarboxylic acid possessing an extremely stable Fe2+species and as carbon source has been used successfully to suppress Fe3+impurities in LiFePO4. The X-ray diffraction results reveal that Li2CO3first reacts with (NH4)2HPO4to form Li3PO4at low temperatures, which above 160°C further reacts with ferrocenecarboxylic acid to give LiFePO4. The infrared spectroscopy, nuclear magnetic resonance, mass spectrometry, and elemental analysis results show that the carbon sources during calcination of LiFePO4are derived from polymers through sequential [4+2] cycloaddition reactions of cyclopentadiene and 1,3-cyclopentadiene-1-carboxylic acid during decomposition of ferrocenecarboxylic acid. The electron paramagnetic resonance results show that the percentage of Fe3+in the synthesized LiFePO4is as low as 0.5 mol%. A plausible reaction mechanism for the hydrothermal synthesis of LiFePO4is also proposed. The as-synthesized LiFePO4shows an orthorhombic olivine with a discharge capacity of 158mAhg？1at a discharge rate of 0.1C. The cell also shows excellent C-rate and cycle-life performances.]]>