Ethylenediamine-Enabled Sustainable Synthesis of Mesoporous Nanostructured Li₂Fe^IISiO₄ Particles from Fe(III) Aqueous Solution for Li-Ion Battery Application

Abstract

Engineering of nanostructured lithium iron silicate (LFS) particles is pursued via a novel benign synthesis approach seeking to understand the crystalline particle formation process and its impact on energy storage capacity. Specifically, mesoporous Li 2 FeSiO 4 nanostructured particles are synthesized via a novel dual-step process involving organic-assisted hydrothermal precipitation from concentrated Fe(III) (1 mol/L) aqueous solution followed by reductive (5 vol % H 2 ) thermal transformation of the precipitate at 400 °C (LFS400) and 700 °C (LFS700). Scanning and transmission electron microscopy revealed the formation of secondary sub-micron-sized porous agglomerates of unitary primary nanocrystals (∼50 nm for LFS400 and ∼200 nm for LFS700). Both ethylene glycol and ethylenediamine are used as crystallization control additives. It is demonstrated that formation of LFS from Fe(III) precursor is made possible only by the action of ethylenediamine. The obtained LFS particles are found to be predominantly monoclinic as per X-ray diffraction and Rietveld refinement and bear an in situ formed N-doped carbon coating layer as characterized by X-ray photoelectron spectroscopy. TEM coupled with selected area electron diffraction (SAED) analysis confirmed the Rietveld refined XRD phase compositions. The reductive annealing-induced phase transformation sequence leading to LFS crystallization is characterized, and the enabling role of ethylenediamine is discussed. Initial galvanostatic charging−discharging and cyclic voltammetry measurements indicate the annealing temperature of LFS formation to influence the Li-ion storage profile as it shifts from two-phase reaction in LFS700 to solid solution in LFS400this being attributed to nanostructural changes.

In Situ TEM Investigation of Electron Irradiation Induced Metastable States in Lithium-Ion Battery Cathodes: Li2FeSiO4 versus LiFePO4

“…It is of interest to evaluate the effect of these metastable phases on the electrochemical performance of battery materials, such as the two-phase reaction in a LiFePO 4 cathode 7,8 and the solid-state reaction in Li 2 FeSiO 4 cathodes. 6,9 However, this conventional perspective on the structural evolution can be obscured, 10,11 if a size effect is considered, because the increasing specific surface area of the electrode materials enhances the surficial nonfaradic Li storage behavior, which always yields a sloped electrochemical curve during electrochemical cycles. With decreasing particle size, the side reactions and surface activity of the electrode materials increase during battery cycles or exposure to the air.…”

The recent progress of Li 2 FeSiO 4 as a poly‐anionic cathode material for lithium‐ion batteries

“…Wei et al took Fe(NO 3 ) 3 Á9H 2 O, CH 3 COOLi, and gaseous silica as raw materials and used organic solvents ethylene glycol (EG) and ethylenediamine (EN) as precursors to prepare intermediate precipitates by organically assisted hydrothermal precipitation method. 26 Then, after annealing and heat treatment, Li 2 FeSiO 4 nanoparticles with particle sizes of about 50 nm (annealed at 400 C) and 200 nm (annealed at 700 C) were obtained, which is respectively denoted as LFS400 and LFS700, with the corresponding mechanism diagram shown in Figure 11. The discharge capacity of modified Li 2 FeSiO 4 nanometer cathode material at C/10 ratio is 170 mAh/g, and the capacity retention rate is about 90% after several cycles, showing good cycling stability.…”

Fe‐Based Mesoporous Nanostructures for Electrochemical Conversion and Storage of Energy

“…Previous studies have indicated that lithium metal orthosilicates can provide higher capacity of up to 330 mA h g −1 which makes them potential options in LiB applications. The electrochemical performance of lithium metal orthosilicates is significantly influenced by the synthesis routes [96b] . Multiple lithium iron silicate synthesis routes have been reported, including solution and solid‐state synthesis methods, with their pros and cons.…”

“…This synthesis process was complicated due to the annealing process that requires higher temperature. To simplify the synthesis route and the reduction production cost of applying (Fe (II)) salt as the precursor, Wei et al [96b] . produced a mp‐C‐coated nanostructured lithium iron silicate based on Fe (III) salts with comparable capacity and stability to those derived from Fe(II) salts through a facile method.…”