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

Abstract

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.