In situ synthesis of carbon nanotubes for constructing highly conductive networks in lithium iron phosphate to enhance electrochemical performance

In this study, ferrocene was utilized as a catalyst precursor to synthesize the lithium iron phosphate (LiFePO₄)/carbon nanotube (CNTs) composite material via floating catalyst chemical vapor deposition (FCCVD). This approach enabled in-situ synthesis of CNTs on the surface of LiFePO₄ particles. In-situ-synthesized CNTs formed an efficient conductive network between lithium iron phosphate particles, improving their connectivity. Scanning electron microscopy (SEM) images clearly illustrate that LiFePO₄ particles were uniformly coated with a dense and continuous layer of CNTs. X-ray diffraction (XRD) analysis confirmed that the synthesis process did not induce decomposition or structural alterations in the LiFePO₄ crystal lattice. Raman spectroscopy revealed that the degree of graphitization of the synthesized CNTs depends on the gas ratio, with optimal graphitization achieved at an ethylene-to-hydrogen ratio of 1:20. Furthermore, this study systematically examined the effect of varying the CNTs coating amount on the electrochemical performance of electrode materials by designing CVD processes with different gas ratios. Results demonstrated that the LiFePO₄/CNTs composite cathodes prepared under an optimal ethylene-to-hydrogen ratio (1:20) exhibited a high specific capacity, achieving a discharge capacity of 165.8 mAhg⁻¹ at a 0.1 C rate, corresponding to 97 % of the theoretical capacity (170 mAhg⁻¹). After 100 cycles at a current density of 1 C, the discharge capacity of the lithium battery decreased from an initial value of 153 mAhg⁻¹ to 150 mAhg⁻¹ , with a capacity retention rate of 98 %, indicating excellent cycling stability. Cyclic voltammetry and electrochemical impedance spectroscopy further demonstrated that the electrochemical kinetics of the LiFePO₄/CNTs composite cathodes were significantly enhanced compared to those of the bare LiFePO₄ cathode.