Pinecone-like hierarchical anatase TiO2 bonded with carbon enabling ultrahigh cycling rates for sodium storage

Hierarchical anatase TiO2 homogeneously tuned by using carbon through Ti-C bonds has been designed, exploiting carbon quantum dots as uniform carbon additives and functionalization inducers for structure tailoring and surface modification. The fabricated pinecone-like structure constructed by ultrafine subunits presents a highly increased surface area (202.4 m2 g(-1)) and abundant mesopores. Surface bonded carbon significantly boosts its electronic conductivity derived from both the conductive carbon and accompanied oxygen vacancies. When utilized in sodium-ion batteries, it delivers a high reversible specific capacity of 264.1 mA h g(-1) at a rate of 0.1C (33.6 mA g(-1)) and still maintains 108.2 mA h g(-1) even after 2000 cycles at 10C with a retention of 94.7% outstandingly. Notably, its Na+ intercalation pseudocapacitive behavior is enhanced by the modulated TiO2/ carbon interfaces, facilitating a fast (de-) sodiation process. Combining the elaborate hierarchical structure with the unique surface composition, synergetic merits are noticed when the promoted kinetics, improved electronic conductivity, increased electrolyte penetration areas and shortened Na+ diffusion length are achieved simultaneously, giving rise to remarkable high-rate capabilities and long- term cyclability.