Regularities of processes occurring on a MnO2 electrode in the course of its electrochemical treatment in aprotic organic solutions of rare earth salts by cathodic intercalation

• E.S. Guseva

Yuri Gagarin State Technical University of Saratov, Engels University of Technology (branch), ul. Politekhnicheskaya 77, Saratov, Saratov Region, 410054 Russian Federation

Abstract: Extensive fundamental studies of the kinetics of processes on solid metallic electrodes under cathodic treatment in solutions of alkali, alkali earth, and rare earth salts show the necessity of studying the factors determining the electrode history by removing undesirable effects on the course of the process in order to provide full control of the experiment [1, 2]. This is especially important at the initial stage of the electrochemical intercalation process due to interaction between the metal cation in the solution and the electrode surface being studied. Comprehensive studies of the effect of the potential, duration of cathodic polarization, temperature, and solution composition on the kinetics of electrolytic alloying by cathodic intercalation show that finding the regularities of electrochemical metal intercalation into electrodes is based on analysis of the results of the semigraphical processing of potentiostatic plots. The study is aimed at enhancement of the electrochemical characteristics of lithium-ion batteries with the LiLaAl/LaMnO₂ system by modification of a MnO₂ electrode with lanthanum. This favors the formation of additional vacancies for movement of lithium ions within the cathode material. This is aimed at solving the problem of enhancement of the electrode stability in the charge–discharge processes, a natural corrosion destruction process due to dissolution of a small amount of manganese ions from the spinel surface followed by their transportation to the anode, which, in its turn, results in anode surface deactivation. The presumable mechanism of dissolution of manganese ions includes disproportionation by the scheme: 2Mn³⁺→Mn²⁺+Mn⁴⁺. A critical problem is to choose an anode characterized by corrosion resistance to an electrolyte in the course of cycling. Inhibition of anodic processes on a lithium anode in the case of active interaction with the electrolyte leads to a decrease in the battery lifetime due to the electrode embrittlement and promotes short circuiting and battery failures later on. The chosen intermetallic compounds based on the LaLiAl anode favor corrosion inhibition in an aprotic electrolyte solution in the course of cycling and stability of the electrode morphology. The work also considers a proof of the fact that modification of the studied manganese dioxide electrode occurs as a result of electrochemical cathodic intercalation. It involves a shift in the electrode potential towards more negative values as a result of the process and points to significant changes in the electrode crystalline structure. Secondary ion mass spectrometry analysis shows a high electrochemical activity of rare earth adatoms and their intense propagation inside the manganese dioxide electrode. It is found that the percentage of the electrode material components changes due to chemical transitions in the studied electrode structure and changes in the stoichiometry of the phases that are formed.

Keywords: rare earths, lanthanum, electrochemical modification, intercalation, lithiation, manganese dioxide, lithium, anode corrosion resistance

Int. J. Corros. Scale Inhib., 2020, 9, no. 1, 257-264 PDF (493 K)
doi: 10.17675/2305-6894-2020-9-1-16

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