PPy doped PEG conducting polymer films synthesized on LiFePO_4 particles

摘要

In this work, polyethyleneglycole (PEG) is introduced into polypyrrole (PPy) film coated on LiFePO_4 powder particles to promote the properties of cathode material for lithium-ion batteries. The enhancement of the electrochemical activity by the substitution of a carbon with electrochemically active polymer is investigated. Films of the PPy doped with the PEG were prepared by the chemical oxidative polymerization of pyrrole (Py) monomer. PEG has been added as an additive during polymerization process to improve mechanical and structural properties of the PPy in final PPy/PEG-LiFePO_4 cathode material. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvano-static charge/discharge measurements were employed to characterize the electrochemical properties of PPy/PEG-LiFePO_4 material. The electrochemical performance of PPy-LiFePO_4 electrodes was greatly improved by introduction of PEG into the PPy films. Charge/discharge measurements confirmed the increase in capacity when applying PEG in PPy. The morphology and particle sizes of the prepared cathode powder material were investigated by scanning electron microscopy (SEM) and particle size analysis (PSA). Distribution of PPy and PPy/PEG films onto the LiFePO_4 particles surface was studied by time of flight secondary ion mass spectrometry (TOF-SIMS). In addition to polymeric coating layer on the surface of PPy-LiFePO_4 composite particles, some PPy unequally distributed between the particles was found. The median diameter value is 4.92 μm for PPy-LiFePO_4 sample. TOF-SIMS measurements and SEM images confirmed that thickness of polypyrrole coating on LiFePO_4 particles is about 100nm.