Electrochemical and TOF-SIMS investigations of PPy/PEG-modified LiFePO4 composite electrodes for Li-ion batteries

The role of polyethylene glycol (PEG) in mixed polypyrrole (PPy) polymer blend for new cathode material used in Li-ion battery has been studied. The films of PPy containing PEG were prepared by chemical oxidative polymerization of pyrrole (Py) monomer. PEG has been applied as an additive during polymerization process to improve mechanical and structural properties of PPy in final PPy/PEGaLiFePO4 cathode material aiming also better electronic conductivity. The electrochemical behavior of the samples was examined by galvanostatic charge/discharge technique and cyclic voltammetry (CV). It was found that PPy/PEG blend polymer decreases the contact resistance and improves the Li+ intercalation/deintercalation during cycling. Charge/discharge measurements confirmed the increase in capacity when applying PEG in PPy. Time of flight secondary ion mass spectrometry (TOF-SIMS) analysis confirmed supporting effect of PEG in PPy predominantly for mixed polymer mechanical stability (important at charging cycles). Distribution of PPy, PEG and Li+ fragments within blended polymer films were monitored by measuring the intensities of different secondary ions, applying SIMS.