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.