Carbon coating and oxygen vacancies render superior Li-ion storage of crystalline Ta₂O₅ by enhanced pseudocapacitance

Tantalum pentoxide (Ta₂O₅) possesses enormous potentials as high-performance anodes for lithium-ion batteries owing to its high specific capacity and abundant sources. Herein, various crystalline Ta₂O₅ nanomaterials were fabricated by annealing the precursors of (NH₄)₂Ta₂O₃F₆ mesocrystals or polydopamine coated (NH₄)₂Ta₂O₃F₆ composites in Ar or air atmospheres, which were synthesized with a hydrothermal process and followed the in-situ coating of polydopamine in aqueous solution. Particularly, the products obtained in Ar possess abundant oxygen vacancies. When evaluated as anodes for LIBs, Ta₂O₅@C-Ar with carbon coating and oxygen vacancies exhibits superior lithium storage properties including remarkably high reversible capacity, high rate capability (166 mAh g⁻¹ at 2 A g⁻¹), and excellent cyclic stability (up to 1000 cycles at 1 A g⁻¹ with 0.02% capacity fading per cycle), in comparison with Ta₂O₅-Ar and Ta₂O₅-Air electrodes. Kinetics analysis based on cyclic voltammograms (CVs) discloses that the higher lithium storage capacity and superior rate capability of Ta₂O₅@C-Ar are primarily attributed to fast surface capacitive kinetics, which stem from large active surface area, ultrasmall Ta₂O₅ nanosheets with conductive carbon layer, and abundant oxygen vacancies. This strategy of constructing electrode materials with conductive carbon coating and oxygen vacancies provides a promising avenue for engineering advanced anodes with high specific capacity and excellent rate capability.