Ambient synthesis, characterization, and electrochemical activity of LiFePO4 nanomaterials derived from iron phosphate intermediates

Abstract

LiFePO 4 materials have become increasingly popular as a cathode material due to the many benefits they possess including thermal stability, durability, low cost, and long life span. Nevertheless, to broaden the general appeal of this material for practical electrochemical applications, it would be useful to develop a relatively mild, reasonably simple synthesis method of this cathode material. Herein, we describe a generalizable, 2-step methodology of sustainably synthesizing LiFePO 4 by incorporating a template-based, ambient, surfactantless, seedless, U-tube protocol in order to generate size and morphologically tailored, crystalline, phase-pure nanowires. The purity, composition, crystallinity, and intrinsic quality of these wires were systematically assessed using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), selected area electron diffraction (SAED), energy dispersive analysis of X-rays (EDAX), and high-resolution synchrotron XRD. From these techniques, we were able to determine that there is an absence of any obvious defects present in our wires, supporting the viability of our synthetic approach. Electrochemical analysis was also employed to assess their electrochemical activity. Although our nanowires do not contain any noticeable impurities, we attribute their less than optimal electrochemical rigor to differences in the chemical bonding between our LiFePO 4 nanowires and their bulk-like counterparts. Specifically, we demonstrate for the first time experimentally that the Fe-O3 chemical bond plays an important role in determining the overall conductivity of the material, an assertion which is further supported by recent "first-principles" calculations. Nonetheless, our ambient, solution-based synthesis technique is capable of generating highly crystalline and phase-pure energy-storage-relevant nanowires that can be tailored so as to fabricate different sized materials of reproducible, reliable morphology.

Synthesis of Iron Phosphate and Their Composites for Lithium/Sodium Ion Batteries

“…This confirms the amorphous structure of the porous FePO 4 in the composite . By studying the porous materials of lithium‐ion batteries, sodium ions can be thought to be inserted or adhered to the surface of porous FePO 4 , which is higher than in bulk materials …”

“…Copyright 2013, American Chemical Society. i) Reproduced with permission . Copyright 2015, Royal Society of Chemistry.…”

Crystal growth kinetics, microstructure and electrochemical properties of LiFePO4/carbon nanocomposites fabricated using a chelating structure phosphorus source

“…Actually, the electrical conductivity of the LFP/C composite (700 C, 150 min) according to the four-point DC method reaches 1.56 Â 10 À1 S cm À1 , which is nearly nine orders of magnitude higher than that of pristine LiFePO 4 (10 À9 -10 À10 S cm À1 ). 11,28,42 This clearly indicates that the electrical conductivity of the LFP/C composite is remarkably enhanced by the in situ grown carbon covering on the spherical LFP nanoparticles, which resulted from the effects of the inherent symmetrically distributed organic linking units and chelating function groups in BHMTPMPA.…”

“…Moreover, extra carbon sources or surfactants also need to be added to obtain the C-coating or nanosized LFP particles. 27,28 Recently, the organic phosphorous acid, bis(hexamethylene triamine penta (methylenephosphonic acid)) (BHMTPMPA), which is abundant, low-cost, and ecofriendly, was used to synthesize a wide range of inorganic materials with novel microstructures and properties. 29,30 BHMTPMPA, with the chemical formula C 17 H 44 O 15 N 3 P 5 , has a high phosphorus and carbon content and especially has some chelation functional groups in its molecule, as shown in Fig.…”

Effects of High Energy Milling on the Carboncoated Lithium Iron Phosphate Precursor Nature

“…LFP holds the desirable merits of abundant raw materials, non-toxicity, high thermal stability, suitable voltage of 3.4 V (vs Li + /Li) and theoretical capacity of 170 mA·h/g [3,4] . It meets both demands of high energy density and environmental friendliness and is an adequate cathode for power battery and stationary storage of electrical energy generated by renewable power [5,6,7] . However, the electronic conductivity of LFP ranges from 10 -9 to 10 -10 s/cm and the lithium-ion diffusion rate at 1.8×10 -14 cm 2 /s which is low and determine its poor electrochemical performance under high rates [8,9] .…”