Unsaturated Ni/V centers and short Ni·V/Ni distances in nickel vanadate for high-performance zinc-ion battery

Abstract

Ni0.22V2O5(H2O)0.94 (NiVO) nanobelts were synthesized via a facile one-step hydrothermal method, which exhibited a 3D framework built by [Ni(H2O)6]2+ pillars connecting 2D V-O-V layers. Upon subsequent annealing, Ni0.22V2O5 (o-NiVO) nanobelts with a large d spacing of 9.2 Å were obtained. 3D rotation electron diffraction (cRED), Rietveld refinement and spherical aberration-corrected TEM reveal that o-NiVO displays a novel 3D framework. Annealing led to atom arrangement and partial Ni2+ ions entered into 2D V-O-V layer of o-NiVO with unsaturated Ni/V centers and short Ni ··· V (2.463 Å)/Ni ···Ni distances (2.401 Å), which can facilitate the electron transfer from O → Ni and improve the electron conductivity with a low Zn2+ migration barrier (0.64 eV) in o-NiVO, as evidenced by DFT calculations. Therefore, o-NiVO can deliver a high initial capacity of 445 mAh g−1 at 0.1 A g−1 with good rate capability and fast Zn2+ diffusion kinetics. Meanwhile, o-NiVO also possesses excellent long-term durability with capacity retention of 99.8 % over 1500 discharge/charge cycles. The fully discharged o-NiVO nanobelts was characterized by cRED, which disclosed the structural integrity of o-NiVO during the discharge process. A series of ex situ characterizations of the o-NiVO electrode reveal a co(de)intercalation mechanism of Zn2+/H+ along with partial phase transformation of o-NiVO → Zn3(OH)2V2O7(H2O)2.