Three-dimensional hierarchically porous micro sponge-ball comprising anatase TiO2 nanodots and nitrogen-doped graphitic carbon as anodes for ultra-stable lithium-ion batteries

Abstract

Hierarchically porous three-dimensional micro sponge-balls comprising highly conductive nitrogen-doped graphitic carbon (NGC) and anatase-type TiO2 nanodots (TiO2@NGC MSB) are synthesized using spray pyrolysis technique followed by heat treatment. The as-sprayed powders obtained after spray pyrolysis consist of polystyrene (PS) nanobeads-derived macropores and anatase TiO2 nanodots embedded in an amorphous carbon (AC)-NGC carbon matrix (TiO2@NGC-AC MSB). The subsequent heat treatment of the as-sprayed powders at 300 °C resulted in the formation of additional micropores by selective removal of the AC into gaseous products to form TiO2@NGC MSB. The obtained hierarchically porous and highly conductive architecture guarantees effective electrolyte infiltration inside the electrode, enhanced Li-ion diffusion, and faster charge transfer during the redox reactions. Benefited from the structural merits, the TiO2@NGC MSB anode exhibits remarkable electrochemical performance compared to those of TiO2@NGC-AC MSB and filled-type TiO2 anodes. A reasonable discharge capacity of 105 mA h g−1 at a high current density of 10.0 A g−1 and exceptional cycling performance (219 mA h g−1 with 0.0006 % decay rate after 2000 cycles at 2.0 A g−1 and 160 mA h g−1 with 0.003 % decay rate after 5000 cycles at 3.0 A g−1) are obtained.