Li Ion Diffusivity and Rate Performance of the LiFePO 4 Modified by Cr Doping

• Published in: Bulletin of the Korean Chemical Society 2011, 32(1), , pp.191-195
• Main Authors: Park, Chang-Kyoo, Park, Sung-Bin, Shin, Ho-Chul, Cho, Won-Il, Jang, Ho
• Format: Article
• Language: English
• Subjects: 화학
• ISSN: 0253-2964; 1229-5949
• DOI: 10.5012/bkcs.2011.32.1.191

This study reports the root cause of the improved rate performance of LiFePO_4 after Cr doping. By measuring the chemical diffusion coefficient of lithium (D_Li) using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the correlation between the electrochemical performance of LiFePO_4 and Li diffusion is acquired. The diffusion constants for LiFePO_4/C and LiFe_0.97Cr_0.03PO_4/C measured from CV are 2.48 × 10^‒15 and 4.02 × 10^‒15 cm^2 s^‒1,respectively, indicating significant increases in diffusivity after the modification. The difference in diffusivity is also confirmed by EIS and the DLi values obtained as a function of the lithium content in the cathode. These results suggest that Cr doping facilitates Li ion diffusion during the charge-discharge cycles. The low diffusivity of the LiFePO_4/C leads to the considerable capacity decline at high discharge rates, while high diffusivity of the LiFe_0.97Cr_0.03PO_4/C maintains the initial capacity, even at high C-rates. KCI Citation Count: 27