Ultrafine TiO₂ Nanoparticles Confined in N‐Doped Porous Carbon Networks as Anodes of High‐Performance Sodium‐Ion Batteries

TiO 2 ‐based nanocomposites with rationally designed size, structure, and composition are highly desirable for Na‐ion storage. In this work, various TiO 2 /N‐doped porous carbon nanocomposites (TiO 2 /NC) have been fabricated by directly carbonizing NH 2 ‐MIL‐125(Ti) at different temperatures. These TiO 2 /NC nanocomposites exhibit unique structure features, such as ultrafine TiO 2 nanoparticles, micro‐mesoporous structure, and N‐doped carbon coating, which can shorten the Na‐ion diffusion distance, enhance the electronic conductivity, and prevent nano‐sized TiO 2 from aggregation. When applied as sodium‐ion battery anodes, TiO 2 /NC‐600 exhibits the best sodium storage properties among the TiO 2 /NC nanocomposites produced at different carbonization temperatures. Correlations between electrochemical properties and size/structure/composition of the TiO 2 /NC nanocomposites are disclosed. TiO 2 /NC‐600 delivers a high reversible capacity of 190 mA h g −1 for up to 500 cycles at 1 C (1 C=335 mA g −1 ), an ultrahigh capacity of 76 mA h g −1 at a high rate of 20 C, and an excellent long‐term cycling stability with a capacity of 159 mA h g −1 retained after 2500 cycles at 5 C. The outstanding sodium storage performance of TiO 2 /NC‐600 is attributed to an appropriate crystalline structure, particle size, and high nitrogen‐doping content.