Improvement of electrochemical and electrical properties of LiFePO4 coated with citric acid

Abstract

LiFePO 4 was synthesized using hydrothermal method and coated with different amounts of citric acid as carbon source. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), surface area measurement-Brunauer-Emmett-Teller (BET), discharge capability, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results show that the quality and thickness of the carbon coating on the surface of LiFePO 4 particles are very important. The optimum carbon content (about 30 wt%) can lead to a more uniform carbon distribution. Electrochemical results show that the samples containing 20 wt%, 30 wt%, 40 wt%, and 50 wt% carbon deliver a discharge capacity of 105, 167, 151, and 112 mAhÁg -1 , respectively, at the rate of 0.1C. The increase of carbon content leads to the decrease of discharge capacity of LiFePO 4 /C, owing to the fact that excess carbon delays the diffusion of Li ? through the carbon layers during charge/discharge procedure. The LiFePO 4 /C with low carbon content exhibits poor electrochemical performance because of its low electrical conductivity. Therefore, the amount of carbon must be optimized in order to achieve excellent electrochemical performance of LiFePO 4 /C for its application in a lithium ion battery.

Encapsulation of LiFePO4Nanoparticles into 3D Interpenetrating Ordered Mesoporous Carbon as a High-Performance Cathode for Lithium-Ion Batteries Exceeding Theoretical Capacity

“…65 On the other hand, the LF/C@CMK-8-0.3 sample with a lower content of carbon exhibited poor electrochemical performance due to poor electronic conductivity. 36 Therefore, the LF/C@CMK-8-0.5 sample with the optimum carbon content delivered the highest capacity in comparison to the LF/C@CMK-8-0.3 and LF/C@ CMK-8-0.7 samples.…”

“…The higher percentage of carbon lengthened the Li + -ion diffusion through the carbon layers during charge–discharge and reduced the diffusion coefficient resulting in the decrease in the capacity . On the other hand, the LF/C@CMK-8-0.3 sample with a lower content of carbon exhibited poor electrochemical performance due to poor electronic conductivity . Therefore, the LF/C@CMK-8-0.5 sample with the optimum carbon content delivered the highest capacity in comparison to the LF/C@CMK-8-0.3 and LF/C@CMK-8-0.7 samples.…”

“…Moreover, carbon can act as a reducing agent to prohibit the formation of ferric impurities during the calcination process . With the help of carbon coating on the LiFePO 4 particles, researchers are able to reduce the charge transfer resistance and achieve capacity value close to its theoretical capacity at lower current rates. − However, the high rate capability and cycling stability of the LiFePO 4 /C composite are still needed to be improved.…”