Structural and Electronic Changes in Li₂FeP₂O₇ during Electrochemical Cycling

Structural and electrochemical properties of the Li2FeP2O7/C composite prepared using soluble methylcellulose

“…The right trigonal-bipyramidal surrounding enabled a greater deviation of the charge symmetry around the Fe nucleus than the oblique trigonal-bipyramidal arrangement. Therefore, the Fe2 doublet had larger quadrupole splitting, which is similar to the findings of Blidberg et al [27]. The greater isomer shift of the Fe2 doublet was a consequence of a larger 3d population.…”

Neutron Pair Distribution Function Study of FePO4 and LiFePO4

“…For the alternative explanation, computational studies have shown that Li–Fe antisite defects are the most energetically favorable instrinsic defects within LiFePO 4 , ,− with a formation energy ranging from 0.51–0.55 , to 0.74 eV. , Such defects are a significant hindrance to the widespread use of LiMPO 4 (M = Fe, Co, Ni, and Mn)-based cathode materials in rechargeable batteries, where the disappointing electrochemical properties shown by materials synthesized by hydrothermal methods at relatively low temperatures have been attributed to the formation of Li–M antisite defects in which the M cation blocks the Li + diffusion channels in the [010] directions. − As a consequence, the Li + are forced to hop across channels, which have a higher energy barrier. , The concentration of antisite defects under ambient conditions is typically also rather low (of the order of a few %), making it difficult to probe them experimentally. ,,,− Diffraction studies of LiFePO 4 and LiFe 1– x Mn x PO 4 have shown the presence of an antisite disorder, with the former study observing changes in the lattice parameters and site occupancies in samples quenched from high temperatures. Additional evidence has been provided by scanning tunneling electron microscopy, and a combined nuclear magnetic resonance and Monte Carlo simulation study concluded that although the concentration of such defects on LiFePO 4 was only ∼0.5%, around 80% of the diffusion channels contains such defects and the capacity fading in LiCoPO 4 -based batteries has been attributed to the formation of antisite defects during battery discharge. , Finally, other polyanionic iron-based compounds also show a propensity toward forming Li–Fe antisite defects during lithium extraction . Thus, the factors which influence and, ideally, restrict the formation of such antisite defects, are a key issue for the successful future use of LiMPO 4 -based cathodes in future lithium battery technologies.…”

Similarity between the redox potentials of 3d transition-metal ions in polyanionic insertion materials and aqueous solutions

“…LiMPO 4 F contains monatomic F À , [25][26][27][28] while LiMP 2 O 7 contains the diphosphate anion (P 2 O 7 ) 4À . [28][29][30] In this study, three polyanionic materials characterised by simple structures composed of only the MO 6 octahedron and PO 4 3À or SO 4 2À tetrahedron, namely, the olivine, NASICON-type, and MOXO 4 -type structures, were selected. Fig.…”