Constructing a High-Performance Aqueous Rechargeable Zinc-Ion Battery Cathode with Self-Assembled Mat-like Packing of Intertwined Ag(I) Pre-Inserted V<sub>3</sub>O<sub>7</sub>·H<sub>2</sub>O Microbelts with Reduced Graphene Oxide Core
P. Rangaswamy, Radha Nagaraj, Pranav Kulkarni, Hemanth Kumar Beere, Shrish Nath Upadhyay, R. Geetha Balakrishna, S.K. Nataraj, Srimanta Pakhira, Debasis Ghosh
Abstract
Orthorhombic crystal structure of the V3O7·H2O material has large interlayer spacing with an open tunnel, making it promising as an intercalation-based cathode for aqueous zinc-ion batteries. However, structural degradation and dissolution cause quick capacity fading for V3O7·H2O. We addressed this issue via a dual modification of the V3O7·H2O material by pre-intercalation with Ag(I) inside the layers (henceforth will be mentioned as AgxV3O7·H2O) and simultaneous in situ composite formation with reduced graphene oxide (rGO). Computationally, we showed that Ag(I) pre-intercalation in V3O7 facilitates the Zn2+ intercalation process by thermodynamically stabilizing the material with an intercalation energy of −34.3 eV. The AgxV3O7·H2O cathode showed ∼1.44-fold improved capacity (270 mA h g–1) with much improved rate capability, over the pristine V3O7·H2O. The specific capacity and cycle stability was further significantly improved in the graphene constructed conductive flexible architecture with hydrothermally assisted self-assembled packing of several intertwined AgxV3O7·H2O microbelt mats with rGO core (AgxV3O7·H2O@rGO). The AgxV3O7·H2O@rGO cathode enabled a reversible Zn2+ insertion/de-insertion process during charge/discharge (as observed in ex situ XRD study) and a significantly decreased (>27 times) charge transfer resistance over pristine V3O7·H2O to promote high specific capacity of 437 and 170 mA h g–1 at both low (100 mA g–1) and high (2000 mA g–1) current, respectively. The morphological analysis of the AgxV3O7·H2O@rGO before and after 1000 cycles reveals that, although the structural breakdown of the AgxV3O7·H2O is inevitable during repetitive cycling, the rGO support provides strong interaction with the AgxV3O7·H2O mat and buffers the structural strain, prevents the agglomeration of the active material, and slows down the structural dissolution at the interface. The synergistic interaction enabled ∼2.3-fold improved cycle stability over the pristine V3O7·H2O with only 0.028% capacity loss per cycle over 1000 cycles.