Analysis of Chemical and Electrochemical Lithiation/Delithiation of a Lithium-Ion Cathode Material

Abstract

Redox targeting reactions between lithium-ion battery materials and redox shuttles have been proposed to design high energy density redox flow batteries. Designing these batteries would require a deeper understanding of the kinetics of redox targeting reactions and the phase transformation of the materials involved. In this study, the oxidation and reduction of lithium iron phosphate, LiFePO4, via chemical and electrochemical routes will be compared. Ultraviolet-visible spectroscopy was used as a technique to characterize the extent of chemical lithiation/delithiation during chemical redox of LiFePO4, while the electrochemical redox was characterized using battery coin cells. The kinetic parameters extracted using the Johnson–Mehl–Avrami–Erofeyev–Kolomogorov model suggested that chemical redox was slower than electrochemical redox within the experimental regimes. Calculated apparent activation energies suggested the limitations in the chemical redox rate were due to different processes than the electrochemical redox. In addition, asymmetry observed for oxidation and reduction of LiFePO4 materials will be discussed. As pairs of solid battery electroactive particles and soluble redox shuttles are designed, tools and analysis such as those in this study will be needed for interrogating and comparing electrochemical and chemical oxidation and reduction of the solid particles to understand and design these systems.