Facile synthesis of CNTs@TiO2 composites by solvothermal reaction for high-rate and long-life lithium-ion batteries

Multi-walled carbon nanotubes (CNTs)@TiO2 composites with different contents of CNTs were prepared by employing solvothermal process using ethanol-glycerol mixture as solvent and subsequent calcination. The role of glycerol during solvothermal process was discussed and the microstructures of the as-prepared CNTs@TiO2 composites were characterized by scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. The results indicate glycerol is one of the solvothermal reactants and also play an important role for the coating of TiO2 particles on the surface of CNTs because of its high viscosity. Moreover, with the increasing of the content of CNTs in composites, the surface areas of composites increase and TiO2 layer becomes more uniform. Notably, CNTs@TiO2 composites with 42 wt% CNTs have a specific surface area of 265.7 m2 g−1, and exhibit excellent high-rate performance and cyclic stability. Their specific capacities at 1C, 2C, 5C, 10C, 20C, 30C and 40C are 248, 228, 225, 212, 200, 194 and 191 mAh·g−1, respectively. Even at 50C and 60C, their specific capacities are still as high as 187 and 184 mAh·g−1, respectively. Moreover, 90.1% of the reversible capacity is retained after 1000 cycles at 10C. The excellent performance can be ascribed to the electronic and ionic rapid conductive network formed by CNTs in composites and the synergistic contribution from pseudocapacitance.