Modeling of electrical behavior of LiFePO4 cathode materials for lithium ion batteries

Abstract

In the present study, the electrical behavior of LiFePO4 cathode material is analyzed through the modeling of an equivalent electrical circuit, to infer its physicochemical characteristics. LiFePO4 has been synthesized using the hydrothermal route of synthesis with PVP K30 (Polyvinylpyrrolidone K30) as a surfactant. The X-ray diffraction (XRD) analysis of the as-prepared sample has been done to confirm the phosphor- olivine geometry of the LiFePO4 with orthorhombic lattice and pnma space group. Electrochemical characterizations of the sample have been done by analyzing the Cyclic voltammetry plot (CV) and the Electrochemical impedance spectroscopy (EIS) plots, generated by employing a three-electrode technique (CHI760E Electrochemical Workstation) with Ag/AgCl as a reference electrode in a 2 M NaOH aqueous electrolyte. The impedance spectroscopy was done in the frequency range of 0.1 Hz to 100 kHz and the EIS data from the impedance spectroscopy is employed to model an equivalent circuit that has been done using the CHI760E software which revels that the electrode is a finite length smooth-walled porous electrode. Thus, it can be concluded that the current generated in the as-prepared LiFePO4 electrode is mainly due to the charging-discharging of the double-layer capacitors at the electrode-electrolyte interface inside the pore walls and that the current due to faradic reactions are severely limited because of the diffusion related constraints of ions in the electrolyte inside the pore and the active materials of the LiFePO4 electrode. Overall the physicochemical properties of the as-synthesized LiFePO4 cathode are in tune with that of a smooth-walled porous electrode and is an efficient electrode material for lithium-ion batteries.