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

Chang Lin Liu,Yang Liu,Xing Liu,Yun Gong

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 1st 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+.