TiO₂ nanocrystals embedded in sulfur-doped porous carbon as high-performance and long-lasting anode materials for sodium-ion batteries

TiO₂ is now developed as a low-cost and high-safety anode material for sodium-ion batteries (SIBs), but its low sodium ion diffusion ability and poor electrical conductivity hinder its sodium-storage performance. In this work, TiO₂ nanocrystals embedded in sulfur-doped porous carbon (TSPC) were synthesized through the solvothermal synthesis of a metal-organic framework MIL-125(Ti) precursor and subsequent pyrolysis with inorganic sulfur powder under a nitrogen atmosphere. The inner TiO₂ nanocrystals enlarge the electrode/electrolyte interface and shorten the diffusion distance of sodium ions, while the sulfur-doped porous carbon enhances the electron transport ability, inhibits the aggregation of TiO₂ nanocrystals, and offers more reaction sites for sodium storage. Benefiting from the synergetic effects between TiO₂ nanocrystals and sulfur-doped porous carbon, when used as the anode material for SIBs, the TSPC demonstrates an ultrahigh specific capacity of 323 mA h g^-1 after 100 cycles at 50 mA g^-1 and extraordinary cycling stability with a capacity retention of 80.1% after 1500 cycles. The TSPC should be a promising anode material for high-performance SIBs.