Carbon sphere-based hierarchical architecture for electrode materials: the role of copolymer composition and pyrolysis temperature

We have developed a general methodology to realize surface coating and encapsulation of electrode materials in hierarchical graphite-like carbon matrix and studied how the composition of the copolymer (as the precursor of the graphite-like carbon) and pyrolysis temperature affect the performance of the electrode material. The typical anode material, anatase TiO₂, has been used as an example to have encapsulated and distributed the TiO₂ nanoparticles in the poly (acrylonitrile-co-styrene) matrix to form hybrid spheres (HSs) Then, the HSs are converted to TiO₂/carbon anode materials after appropriate pyrolysis. The copolymers with different ratios of acrylonitrile to styrene from 3:7 to 5:5 have been synthesized, and the pyrolysis is performed in the temperature range from 550 to 850 °C. It is found that both the composition of the copolymer and the pyrolysis temperature can strongly affect the performances of the final TiO₂/C anode materials. A proper design optimization is necessary to obtain the electrode materials with the desired performance. Under the optimized conditions, the capacity of the cell with the synthesized TiO₂/C as the anode and Li as the reference has reached above 200 mAh g⁻¹ at a current density of 500 mA g⁻¹ and stays stably around 170 mAh g⁻¹ after 1000 cycles.