Abstract
The disposal of LiFePO4 (LFP) cathode material through oxidation in an air atmosphere is explained by its high chemical activity and high surface area (especially for nanoparticles). In this article, new methods for the determination of the degree of iron oxidation in LFP (oxidation degree) are taken into consideration, specifically those which do not require complicated hardware support. The proposed methods are based on electrochemical oxidation (coulometric method) and chemical oxidation (chemical oxidation in alkaline and acidic solutions). As an arbitration method for analyzing the iron state, the method of Mössbauer spectroscopy (being the most proven and reliable method) was chosen. With respect to the proposed methods for determination of the oxidation degree, the most reliable and quick approach is the titrimetric method (oxidation in an acidic medium), which is in good correlation with Mossbauer spectroscopy. The coulometric method is also able to determine the material oxidation degree (with some approximation), but it requires a number of conditions in order to eliminate errors.
Highlights
Lithium ion batteries are suitable power sources for newly developed mobile devices because of their superior electrochemical characteristics in comparison with classical batteries (Ni-Cd, Ni-MH)
Insoluble carbon remains as a precipitate which can be filtered out, dried, and gravimetrically determined
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 Fe2+ in LiFePO4 —92% [15]
Summary
Lithium ion batteries are suitable power sources for newly developed mobile devices (cellphones, laptops, cameras, etc.) because of their superior electrochemical characteristics in comparison with classical batteries (Ni-Cd, Ni-MH). The following reaction (1) describes the LiFePO4 cathode material’s behavior in a lithium-ion battery: LiFePO4 − xe− (1 − x )LiFePO4 + xFePO4 + xLi+ This process in the forward direction can be carried out chemically in solution, using the Ox-Red reaction. For the dissolution of lithium iron phosphate, a mixture of sulfuric (50%) and hydrochloric (50%) acids (1:1) is used while heating and stirring the solution Under these conditions, insoluble carbon remains as a precipitate which can be filtered out, dried, and gravimetrically determined. The obtained transport parameters will characterize the cathode material itself directly, and not the total characteristics of the composite electrode (binder, electroconductive additive, active material) Such transport parameters (summary) are obtained through different electrochemical methods (GITT, PITT, EIS) [8,9].
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