Poly(ethylene glycol) grafted multi-walled carbon nanotubes/LiFePO ₄ composite cathodes for lithium ion batteries

Poly(ethylene glycol) (PEG) grafted multi-walled carbon nanotubes (MWCNTs-g-PEG or MP) were synthesized and used to modify LiFePO₄ as cathodes for lithium-ion batteries (LIBs). The effects of different molecular weights of PEG grafted on MWCNTs and different mass fractions of MP on the properties of LiFePO₄/MP composite cathodes were evaluated by their morphology, charge-discharge tests, electrochemical impedance spectroscopy, electrical and thermal conductivities. Their electrochemical behaviors at ambient temperature and low temperature, high rate capability and cycling performance were observed in the presence of the MP additives. The lithium ions diffusion in the LiFePO₄/MP composite electrodes was almost 2 orders of magnitude higher than that in the LiFePO₄/acetylene black (AB) electrode when the conductive additive content was 5 wt.%. Thermal studies of LiFePO₄/MP were also examined by the heat-pole method, which showed higher thermal conductivity of the cathode in cases of MP being incorporated into LiFePO₄ particles than LiFePO₄ cathodes with AB or MWCNTs additives. These results suggest that MP is a promising conductive additive to increase the electrochemical performances, thermal transport and safety of LiFePO₄ cathodes for LIBs.