Preparation and characterisation of LiFePO₄ ceramic powders via dissolution method

Various LiFePO₄ (LFP) powders with natural ironstone as a base material were prepared using the dissolution method. They were synthesised using different (a) calcination temperatures, (b) milling times, and (c) Cu doping concentrations. X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) were conducted to determine the purity, grain and crystallite morphology, and crystalline and local structure of the phases formed, respectively. According to the XRD data, LFP can be produced using the aforementioned variations, and no other phases were found. The TEM images showed that the LFP size can be reduced from 200 nm to 60 nm by milling. The SEM images confirmed the nanometric characteristics of the milled powder and also the effect of calcination temperature on growing the particle sizes. The EDX analysis further reinforced that the samples’ atomic fractions were relatively compatible with LFP to explain the synthesised products’ purity. Analysis of the Fe K-edge XANES data showed that the samples’ oxidation number of Fe for all samples was 2+ with 6 coordination numbers, which corresponded to the oxidation and coordination number of Fe in LFP. The EXAFS Fe K-edge analysis demonstrated that slightly increasing the temperature increased the distance between the absorbing Fe atom and its nearest neighbouring atom but milling reduced it. The XAS analyses, therefore, confirm that all synthesised samples contain only LFP. A preliminary electro-chemistry test showed that these materials are promising candidates for cathodes in LFP-based batteries.