Effects of Zr4+ Doping on the Electrochemical Characteristics of Li2FeP2O7/C in Lithium Ion Batteries

Abstract

Using splash combustion synthesis, Zr4+-doped Li2Fe1-xZrx/2P2O7/C (x = 0, 0.01, 0.02, 0.03, and 0.04) composites were successfully synthesized in order to increase the redox voltage and c-rate performance. X-ray diffraction (XRD) patterns indicated that the successfully obtained Li2Fe1-xZrx/2P2O7/C had a monoclinic structure. The results indicated that the zirconium atoms within the Zr4+-doped system do not change the lattice structure of Li2FeP2O7, but do enlarge the lattice volume. During the de-intercalation and intercalation of lithium ions, the doped zirconium atoms protect the Li2FeP2O7 structure from spontaneous structural rearrangement, which can lower the reaction potential. Among the various samples, Li2Fe0.97Zr0.015P2O7/C exhibited excellent rate and cycling performance. We investigated the electrochemical performance and lithium ionic diffusion coefficient by using three electrochemical perturbation methods: cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), and potentiostatic intermittent titration technique (PITT). Li2Fe0.97Zr0.015P2O7/C exhibited relatively good electrochemical performance in comparison with Li2FeP2O7/C. We further investigated the lithium ion diffusion behavior by using CV, GITT, and PITT. Li2Fe0.97Zr0.015P2O7/C demonstrated more rapid ionic diffusion than Li2FeP2O7/C did due to its higher diffusion coefficient value. Therefore, these ionic kinetic studies were helpful to understand the enhanced electrochemical performance.