In situ self-catalyzed formation of carbon nanotube wrapped and amorphous nanocarbon shell coated LiFePO4 microclew for high-power lithium ion batteries

Abstract

A novel in situ self-catalyzed synthetic strategy is explored to prepare graphitic carbon nanotubes (CNTs) wrapped and amorphous nanocarbon shells coated LiFePO4 microclews (LiFePO4@C@CNT) at one-step. The formation mechanism of CNTs entangled LiFePO4@C microclews is investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the in situ intergrowths of CNTs and LiFePO4@C could be realized by the catalytic effect of Fe3C nanoparticles based on the tip-growth mechanism. The as-prepared LiFePO4@C@CNT-5 composite with a low carbon content of 5 wt%, an optimum composition of graphitic CNTs and amorphous carbon shells (ID/IG = 0.9), a specific surface area of 83 m2 g−1 and an electronic/ionic conductivity of 0.68 S cm−1/2.1 × 10−12 cm2 s−1 delivers a stable discharge capacity of 158.2 mAh g−1 at 0.1 C, outstanding rate capability of 136.1 mAh g−1 at 1 C and remarkable long-term cycling stability of 129.6 mAh g−1 after 1000 cycles at 1 C, indicating a promising application in high-power lithium-ion batteries. The combined good electronic-ionic conductivity of twisted carbon nanotubes and porous nanocarbon shells and robust mechanical stability of geometrically confined LiFePO4 particles within dual nanocarbon matrices contribute to the excellent electrochemical performance of LiFePO4@C@CNT.