Colloidal Crystal Templating to Produce Hierarchically Porous LiFePO₄ Electrode Materials for High Power Lithium Ion Batteries

Abstract

Porous LiFePO 4 has been prepared via a solution-based templating technique. Beads of poly (methyl methacrylate) were synthesized with diameters of 100, 140, and 270 nm and used to form colloidal crystal templates to produce LiFePO 4 , which featured pores spanning from 10 to 100 nm. The use of colloidal crystal templates allowed an examination of the effects of pore size on the electrochemical properties. The templated LiFePO 4 samples were fully characterized using SEM, TEM, XRD, Rietveld analysis, and nitrogen sorption prior to electrochemical testing. The materials with the largest pores, around 100 nm diameter, gave the best discharge capacities, with 160 mA h g -1 at 0.1C and 115 mA h g -1 at 5C being achieved. This compares with a theoretical discharge capacity of 170 mA h g -1 .

Highly ordered LiFePO4 cathode material for Li-ion batteries templated by surfactant-modified polystyrene colloidal crystals

“…The space group of LiFePO 4 was identified as Pmna with a crystal size of 78.1 nm and the lattice parameters are determined and listed in Table 1. The parameter values and crystal structure agree very well with the results described in the literature [18,[26][27][28]. The reference peaks are used to simulate the fit in order to evaluate the lattice parameter and crystal size using the software TOPAS v4.2.…”

“…It was found to be 7.71 m 2 g −1 which was much lower than that for LiFePO 4 [29]. It is known that the amount of carbon in LiFePO 4 /C composite affects greatly the surface area of LiFePO 4 ; the higher the amount of carbon the lower the surface area [18]. This could be attributed, among other things, to the fact that the carbon content in the composite interferes in the 3D porous network and blocks some of the paths hence isolating large surfaces from the accessible total surface area of LiFePO 4 .…”

“…Recently, Doherty et al [18] synthesized 3DOM LiFePO 4 using a polymethyl methacrylate (PMMA) colloidal template and Lu et al [19] using a copolymer of poly(styrene-methyl methacrylateacrylic acid). The use of PMMA as a colloidal templates was a natural choice due to its hydrophilicity that allows for the infiltration of LiFePO 4 aqueous precursor (CH 3 COOLi, Fe(NO 3 ) 3 , H 3 PO 4 ) solution into its interstitial voids by interacting with the ionic acrylate groups of the polymer.…”

A colloidoscope of colloid-based porous materials and their uses

“…One of the primary reasons hierarchical CBPM are used as electrodes is their high surface area, with a higher active area for a given volume of material. High surface area allows for easy access to active materials in batteries 75,421,423,426,[428][429][430][431] and fuel cells, 432,433 improving energy density. It also leads to higher dye loading, and thus increased light absorption and higher rates, in dye-sensitized solar cells.…”

“…341,458 Much like for catalysis, the macroporous structure of CBPM provides for easier diffusion to the active surface; in electrodes, fast ion diffusion means faster charging and reaction rates. 430 Ordered, inverse structures have been particularly well investigated as a means of controlling ion transport, for example in Li-ion batteries, 26,428,466 Li-air batteries, 431 dye-sensitized solar cells (DSSC), 450 and fuel cells. 432,433 These colloid-templated structures have also been used as separators in batteries 184 and fuel cells 434 due to their ability to control ion diffusion.…”