Three-dimensional porous pitch-derived carbon coated Si nanoparticles-CNT composite microsphere with superior electrochemical performance for lithium ion batteries

Although silicon has attracted attention as a promising anode material for lithium ion batteries due to its high theoretical capacity and relatively low discharge potential, the issue of large volume expansion and contraction during its de-/alloying reaction with Li has resulted in the development of nanostructured electrode design and coating methods using suitable carbon sources to improve the stability of the electrode. Pitch is regarded as an attractive carbon coating source owing to its mesophase characteristics, high mechanical strength, and electrical conductivity. In this study, three-dimensional porous pitch-derived carbon coated Si nanoparticles-carbon nanotube (Si-CNT@PC) composite microspheres were successfully synthesized by spray pyrolysis and a following pitch infiltration process. Uniformly distributed Si nanoparticles, acid-treated multiwall CNTs, and polystyrene (PS) nanobeads enabled the formation of porous structured Si-CNT composite microspheres by spray pyrolysis. Uniform infiltration of pitch dissolved in tetrahydrofuran followed by a carbonization process resulted in Si-CNT@PC microspheres. The uniquely structured Si-CNT@PC microspheres exhibited superior electrochemical properties compared with Si-CNT microspheres not coated with carbon. The synergetic effects of carbon-coated Si nanoparticles, macroporous structure formed by decomposition of PS nanobeads, and the CNT backbone resulted in excellent lithium-ion storage performance of Si-CNT@PC microspheres. The discharge capacities of Si-CNT and Si-CNT@PC at a current density of 1 A g⁻¹ for the 200th cycle were 51 and 1209 mA h g⁻¹, respectively.