Lithium diffusion in Li3V2(PO4)3-based electrodes: a joint analysis of electrochemical impedance, cyclic voltammetry, pulse chronoamperometry, and chronopotentiometry data

Abstract

In order to establish the mechanism and to determine the parameters of lithium transport in electrodes based on lithium-vanadium phosphate (Li3V2(PO4)3), the kinetic model was designed and experimentally tested for joint analysis of electrochemical impedance (EIS), cyclic voltammetry (CV), pulse chronoamperometry (PITT), and chronopotentiometry (GITT) data. It comprises the stages of sequential lithium-ion transfer in the surface layer and the bulk of electrode material’s particles, including accumulation of lithium in the bulk. Transfer processes at both sites are of diffusion nature and differ significantly, both by temporal (characteristic time, τ) and kinetic (diffusion coefficient, D) constants. PITT data analysis provided the following D values for the predominantly lithiated and delithiated forms of the intercalation material: 10−9 and 3 × 10−10 cm2 s−1, respectively, for transfer in the bulk and 10−12 cm2 s−1 for transfer in the thin surface layer of material’s particles. D values extracted from GITT data are in consistency with those obtained from PITT: 3.5–5.8 × 10−10 and 0.9–5 × 10−10 cm2 s−1 (for the current and currentless mode, respectively). The D values obtained from EIS data were 5.5 × 10−10 cm2 s−1 for lithiated (at a potential of 3.5 V) and 2.3 × 10−9 cm2 s−1 for delithiated (at a potential 4.1 V) forms. CV evaluation gave close results: 3 × 10−11 cm2 s−1 for anodic and 3.4 × 10−11 cm2 s−1 for cathodic processes, respectively. The use of complex experimental measurement procedure for combined application of the EIS, PITT, and GITT methods allowed to obtain thermodynamic E,c dependence of Li3V2(PO4)3 electrode, which is not affected by polarization and heterogeneity of lithium concentration in the intercalate.