The characteristics of LiFePO₄/copper nanoparticles/carbon nanotubes composites used as lithium ion battery cathode

Copper nanoparticles and carbon nanotubes (CNTs) have been used to form a LiFePO₄/Cu nanoparticle/CNT (LFP/Cu/CNT) composites and applied as an active material in lithium ion battery cathode. The composites were prepared by mixing commercial LFP powders with a variation of copper nanoparticles and or CNT compositions in a vacuum mixer. The mixture was then applied onto an aluminium foil as a cathode current collector. For the characterization, X-ray diffraction (XRD) was used to confirm the phase, grain size and the presence of the impurities, whereas the morphology of the surface was characterized by using field emission scanning electron microscope equipped with energy dispersive X-ray spectroscopy (FESEM/EDX). The electrical conductivity of this cathode material was tested by using electrochemical impedance spectroscopy (EIS). XRD results showed that the composite has single phase LFP form and that the presence of copper nanoparticles and CNT were not detected in the crystal structure. Morphology and distribution of CNT and copper nanoparticle analysed using FE-SEM/EDX showed mixed materials in the variation of copper nanoparticles and CNTs with homogenous and even distribution of particle size in the range 100-300 nm. The electrical conductivity of LFP increased with the addition of copper nanoparticles at a certain level with 1-order of magnitude, whereas almost 3-order of magnitude with the addition of both copper nanoparticles and CNTs. The addition of CNTs alone, however, is more effective in increasing the conductivity as compared to the addition of copper nanoparticles due to the inevitable formation of secondary phase revealed by the EIS diagrams.