## 2 Materials and Methods  
Firstly, FePO\({}_{4}\)-2H\({}_{2}\)O, as the main precursor for LiFePO\({}_{4}\) synthesis, was prepared. FeCl\({}_{3}\)\(\cdot\)6H\({}_{2}\)O (Sigma Aldrich 98% Laborpharma LTD Almaty, Kazakhstan), (NH\({}_{4}\))\({}_{2}\)HPO\({}_{4}\)\(\cdot\)12H\({}_{2}\)O (Sigma Aldrich \(\geq\) 99.0%) and CH\({}_{3}\)COONa\(\cdot\)3H\({}_{2}\)O (\(\geq\)99.0%) solutions in a stoichiometric ratio were mixed together slowly dropwise and then stirred for several hours. Then, the sample was collected by filtration, washed several times with deionized water, and dried at 100 \({}^{\circ}\)C in air atmosphere for 12 h.  
LiFePO\({}_{4}\)/C was synthesized by the carbothermal reduction method from the following agents: LiAc\(\cdot\)2H\({}_{2}\)O (Sigma Aldrich \(\geq\) 99.0%), and as-synthesized FePO\({}_{4}\)\(\cdot\)2H\({}_{2}\)O and stearic acid (Sigma Aldrich 98%) as the reducing agent and carbon source, respectively [5]. Stearic acid (15% by weight of FePO\({}_{4}\)\(\cdot\)2H\({}_{2}\)O) was dissolved through stirring in 100 mL of ethanol at 60 \({}^{\circ}\)C. After complete dissolution, LiAc\(\cdot\)2H\({}_{2}\)O and FePO\({}_{4}\)\(\cdot\)2H\({}_{2}\)O (1:1 molar ratio) were added. The resulting mixture was heated at 90 \({}^{\circ}\)C to evaporate the solvent until a slurry was formed, which was dried in an oven at 100 \({}^{\circ}\)C in an air atmosphere for 12 h. The resulting mixture (powder) was calcined at 600 \({}^{\circ}\)C for 6 h in an argon atmosphere. X-ray diffraction (XRD) analysis of the synthesized sample was carried out on a DRON-3M diffractometer. Sampling modes were as follows: the voltage on the X-ray tube was 30 kV, the tube current was 30 mA, the pitch of the goniometer was 0.05\({}^{\circ}\) 2\(\theta\), and the time of the intensity measurement at the point was 1.0 s. Figure 2 shows the X-ray powder diffraction spectrum recorded under Bragg-Brentano geometry in diffraction angle ranging from 10\({}^{\circ}\) to 70\({}^{\circ}\) of the synthesized LiFePO\({}_{4}\) powder sample. All diffraction peaks are indexed to an orthorhombic crystal structure with the Pnma space group. The estimated lattice parameters are a = 10.412 A, b = 6.011 A, c = 4.696 A and V = 291.4 A\({}^{3}\), which are close to the corresponding constants of JCPDS (PDF No. 83-2092) data (Table 1) [13,14]. Figure 1: Scheme of LiFePO\({}_{4}\) oxidation in an aqueous medium at different pH. The Mossbauer spectrum of the sample was obtained on a MS 1104 Em spectrometer. The source was cobalt 57 in the chromium matrix, with an activity of 100 mCi (the temperature of the spectroscopy was 293 K). Mossbauer spectroscopy is very sensitive in terms of characterizing atoms with different valence states, as it provides a direct scrutiny of atomic information. Therefore, Mossbauer spectroscopy measurement was carried out to analyze the existence of Fe\({}^{3+}\)-containing species. Figure 3 shows the Mossbauer spectroscopy of the as-prepared LiFePO\({}_{4}\)/C. One symmetric doublet is dominant, with an isomer shift (IS) of 1.22 mm/s and quadrupole splitting (QS) of 2.94 mm/s, which is typical for octahedral Fe\({}^{2+}\) in LiFePO\({}_{4}\)--92% [15]. Another minor doublet was observed, which can be attributed to Fe\({}^{3+}\) with a typical IS value (0.32 mm/s) and QS of 0.86 mm/s--8%. The carbon content of the obtained synthesized LiFePO\({}_{4}\)/C (LFP/C) was determined using the gravimetric method, by dissolving a known mass of LFP/C in concentrated sulfuric acid, followed by carbon extraction from the sample. The results of the analysis showed the presence of 4% carbon. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Sample**} & \multicolumn{4}{c}{**Lattice Parameters**} \\ \cline{2-5}  & **a, Å** & **b, Å** & **c, Å** & **V, Å3** \\ \hline LiFePO\({}_{4}\) & 10.412 & 6.011 & 4.696 & 293.9 \\ \hline No. 83-2092 & 10.33 & 6.01 & 4.69 & 291 \\ \hline \end{tabular}
\end{table} 
Table 1: The lattice parameter values of the LiFePO\({}_{4}\)/C sample and standard data.