## 3 Results and Discussion
### Chemical Oxidation in Alkaline Solution  
By using the chemical delithiation reaction in an alkaline aqueous medium, it is also possible to determine the oxidation degree of the material by establishing the consumed amount of oxidant or obtained oxidation product (lithium cation). Hydrogen peroxide was chosen as the oxidizing agent, because it does not form insoluble compounds during its reduction and is stable in alkaline medium over time.  
The reaction of complete oxidation (chemical delithiation) without the material dissolution can be expressed by the following Equation (2):  
\[2\text{LiFePO}_{4}+\text{H}_{2}\text{O}_{2}\to 2\text{FePO}_{4}+2\text{Li}^{+}+2 \text{OH}^{-} \tag{2}\]  
By determining the precise amount of extracted (deintercalated) lithium in the liquid phase upon the complete oxidation process, the oxidation degree can be assessed by (\(w(\text{Ox})=\frac{m\left(\text{Li}^{+}_{\text{2d}}\right)}{m\left(\text{Li}^ {+}_{\text{2 IFFO4}}\right)}\)).  
To carry out the chemical oxidation of LiFePO4, a covered glass cell was used. A platinum and a pH glass electrode (relative to the silver-chloride reference electrode) were installed to measure the Ox-Red potential and the pH of the solution, respectively. The lithium concentration in the solution was determined using a lithium-selective electrode; the response time was three seconds. All measurements were carried out using a universal ionometer I-160 MI with automatic data recording (Figure 6).  
LiFePO4/C powder of known mass was added to the alkalized solution (\(V\) = 100 mL) of hydrogen peroxide. The amount of hydrogen peroxide was 100 times higher relatively to LFP/C. To alkalize the solution to a pH equal to 10, several drops of concentrated NH4 OH solution were added. The oxidation process was carried out with constant mixing to distribute the powder evenly throughout the entire solution volume.  
Figure 5: Electrochemical characteristics of synthesized material: (**a**) the second charge/discharge curve at 0.1 C; (**b**) cycling at different C rate.  
Figure 7 shows the degree of delithiation dependence versus time at different temperatures. The chemical oxidation process is fully realized at all temperatures and the delithiation degree is close to 100% (29 \({}^{\circ}\)C-2000 s, 40 \({}^{\circ}\)C-1300 s, 50 \({}^{\circ}\)C-800 s). Despite that, in our case, the delithiation degree equals 99.8%, which is much higher than the value determined by Mossbauer spectroscopy. According to the results of Mossbauer spectroscopy, the oxidation percentage of LiFePO\({}_{4}\)/C should not be higher than 92%. However, in this case we measured the total amount of lithium that can be extracted from 92% LiFePO\({}_{4}\) and from 8% impurities (since the Li:Fe ratio was 1:1 in the synthesis). Unlike the coulometric method, chemical oxidation in alkaline solution provides mistaken results. Probably, the results were influenced by the indirect determination of divalent iron ions, along with the lithium ions from the solution.  
Chemical oxidation without material dissolution can serve as a method for determining the transport parameters of the chemical delithiation process, such as diffusion coefficient and activation energy [11; 12; 13].