Coordination polymer-derived Al3+-doped V2O3/C with rich oxygen vacancies for an advanced aqueous zinc-ion battery with ultrahigh rate capability

Abstract

The complex [Me₂NH₂]V₃O₇ was synthesized solvothermally, and possessed a 2D [V₃O₇]⁻ anionic layer with an interlayer [Me₂NH₂]⁺ cation. After cationic exchange and subsequent annealing, Al³⁺, Mn²⁺ or Zn²⁺-doped V₂O₃/C composites were obtained. Among them, oxygen-deficient Al³⁺-doped V₂O₃/C exhibits outstanding long-term cycling durability even with a high carbon content of 23.97 at%. The capacity retention is 94.7% after 1000 discharge/charge cycles at 5 A g⁻¹, which is superior to V₂O₃/C, Mn²⁺ and Zn²⁺-doped V₂O₃/C composites. Furthermore, Al³⁺-doped V₂O₃/C with oxygen vacancies displays excellent rate performance with 90.3% capacity retention when the current density is increased 50-fold, and can deliver an average specific capacity of 340, 360, 365, 356, 343 and 307 mA h g⁻¹ at 0.1, 0.2, 0.5, 1, 2 and 5 A g⁻¹, respectively, and the capacity returns to 375 mA h g⁻¹ at 0.1 A g⁻¹. A series of ex situ characterizations revealed that Al³⁺-doped V₂O₃/C completely transformed into Al³⁺-doped Zn₃(OH)₂V₂O₇·2H₂O during the 1^st charge process. However, the capacity of the sample far exceeds the theoretical capacity of Zn₃(OH)₂V₂O₇·2H₂O (224 mA h g⁻¹), which is associated with the doping of Al³⁺ and its dominant surface-controlled the capacitive behavior. It is also expected that the transformation occurs in the inner accessible sites of the nonporous V₂O₃, which are provided by its rich oxygen vacancies. Although DFT calculations indicate that the doping of Al³⁺ into Zn₃(OH)₂V₂O₇·2H₂O is energetically unfavorable, the present work provides a facile strategy for the preparation of Al³⁺-doped Zn₃(OH)₂V₂O₇·2H₂O. Furthermore, the doping of Al³⁺ can change the host framework of Zn₃(OH)₂V₂O₇·2H₂O, the positions, and the micro-environments of the inserted Zn²⁺, thus decreasing the binding energy and diffusion barrier of Zn²⁺.