Ultrahigh rate capability and ultralong cycling stability of sodium-ion batteries enabled by wrinkled black titania nanosheets with abundant oxygen vacancies

Sodium-ion batteries (SIBs) have been considered as one of the promising alternatives for lithium-ion batteries, owning to the abundant reserve and low cost of sodium-related salts. However, SIBs usually suffer from the sluggish kinetics of Na⁺ and the serious volume expansion of anode materials, which inevitably restrict the performance of SIBs. Herein, electroconductive wrinkled anatase-phase black titanium oxide nanosheets with rich oxygen vacancies (OVs-TiO_2-x) was found to have an ultrafast Na⁺ insertion and extraction kinetics as anode material in SIBs. The wrinkled structure can significantly reduce the Na⁺ diffusion length, and the conductive networks formed by wrinkled OVs-TiO_2-x can boost the electron transfer during Na⁺ insertion and extraction processes. With the rapid Na⁺ insertion/extraction ability, wrinkled OVs-TiO_2-x delivers excellent sodium storage performance with high reversible capacity, ultra-high rate capability with the capacity reaches 91 mAh g⁻¹ even at 20,000 mA g⁻¹, and ultra-long cycling stability. These properties demonstrated the great potential of wrinkled OVs-TiO_2-x to serve as a realistic choice of anode materials in SIBs.