MOF-Derived MnV2O4/C Microparticles with Graphene Coating Anchored on Graphite Sheets: Oxygen Defect Engaged High Performance Aqueous Zinc-Ion Battery

By annealing [Mn(phen)H 2 O][V 2 O 6 ] (phen = 1,10-phenanthroline) in the presence of graphite template, MnV 2 O 4 /C microparticles are obtained, in which MnV 2 O 4 particles with one-layer or few-layer coating of graphene are anchored on the graphite sheets. The optimal sample, MnV 2 O 4 (p)/C-700 with a high carbon content (35.3 at. %) can deliver a large specific capacity of 410 mAh g −1 at 0.1 A g −1 with a high capacity retention of 94.3% over 1000 discharge/charge cycles at 20 A g −1 as cathode in zinc-ion battery. Ex situ X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectra, as well as elemental mappings and X-ray photoelectron spectroscopy of MnV 2 O 4 (p)/C-700 discern the partial phase transformation mechanism of MnV 2 O 4 →Zn 3 (OH) 2 V 2 O 7 (H 2 O) 2 during discharge/charge process. It is because the rich oxygen defects of MnV 2 O 4 can improve electrical conductivity, favor the electron transfer from V→Mn/O, thus facilitate the binding of Zn 2+ , and the captured Zn 2+ cannot be extracted, as evidenced by density functional theory calculations. Furthermore, it is found that O-deficiency can capture the water shell from the hydrated Zn 2+ , then the dehydrated Zn 2+ is easy to insert into MnV 2 O 4 with lower migration barrier of Zn 2+ (0.84 eV), leading to the structural reversibility of MnV 2 O 4 in cycling test.