Exploring the Origin of the Superior Electrochemical Performance of Hydrothermally Prepared Li-Rich Lithium Iron Phosphate Li_1+δFe_1−δPO₄

Abstract

Li-rich lithium iron phosphate Li 1+δ Fe 1−δ PO 4 (Lirich LFP) prepared by the solvothermal method via the Li 3 PO 4 precursor demonstrates excellent electrochemical characteristics such as C-rate capability (140 mAh g −1 at 10 C charge for the Li 1.04 Fe 0.96 PO 4 /C material) and low voltage hysteresis between lithiation and delithiation (14 mV at C/300 rate for the same sample). Phase transformations and evolution of the Fe cations coordination environment during Li + (de)intercalation are studied in operando regime by means of synchrotron X-ray powder diffraction (SXPD) and 57 Fe Mossbauer spectroscopy (MS). The presence of a certain amount of Li + in the M2 position in the crystal structure of the as-prepared Li-rich LFPs leads to an additional component in the MS spectra corresponding to ferric ions in the M2 position with distorted second coordination sphere. Evolution of the MS spectra during charge/discharge reveals the clear relationship between the relative fraction of this component and the mechanism of Li + (de)intercalation. Extended single-phase regions with large Li + nonstoichiometry in the triphylite and heterosite phases of Li 1.04−x Fe 0.96 PO 4 observed by means of SXPD appear due to Li − Fe defects existing in the as-prepared Li-rich LFPs and acting as a "diluting" agent, which prevents two-phase transition. Increased thermodynamic stability of the intermediate Li 1+δ−x Fe 1−δ PO 4 solid solutions was also shown by DFT calculations. These features can be regarded as an additional merit of Li-rich LFPs, rendering them promising cathodes for high-power Li-ion batteries.

A Li-rich strategy towards advanced Mn-doped triphylite cathodes for Li-ion batteries

“…Thus we may conclude that additional Li ions at the M2 site could be a significant factor affecting the solid solution propagation upon Li de/intercalation in the material. A supportive confirmation of our hypothesis is provided by Drozhzhin et al ., 17 where it was speculated that additional Li at the M2 site in Li-rich LFP prevents nucleation of the heterosite phase thus increasing the contribution of the solid solution mechanism to the overall process. It seems that the same effect is reasonable for the Mn-containing Li-rich LFMP system.…”

Comparative Study of the Thermal Stability of Electrode Materials for Li-Ion and Na-Ion Batteries

“…Detailed synthetic routes as well as the structural and electrochemical properties of these materials are presented in the corresponding papers − and are not given in this work. To analyze the thermal stability of the materials in the charged state, all of the electrodes were charged up to (or down to) their typical operation potentials at C/10 current densities in lithium or sodium half-cells.…”

Effect of Polymer Binders with Single-Walled Carbon Nanotubes on the Electrochemical and Physicochemical Properties of the LiFePO4 Cathode

“…Lithium iron phosphate was synthesized from LiOH·H 2 O, FeSO 4 ·7H 2 O, phosphoric acid, and ascorbic acid (Sigma-Aldrich) via a solvothermal route as has been elaborated by us earlier . Briefly, H 3 PO 4 was added to LiOH solution (molar ratio 1:3) to form the Li 3 PO 4 precipitate.…”

“…O, phosphoric acid, and ascorbic acid (Sigma-Aldrich) via a solvothermal route as has been elaborated by us earlier. 33 Briefly, H 3 PO 4 was added to LiOH solution (molar ratio 1:3) to form the Li 3 PO 4 precipitate. Iron(II) sulfate in an appropriate molar ratio and ascorbic acid were dissolved separately and mixed with Li 3 PO 4 -contained solution.…”