Preparation And Zinc Ion Storage Mechanism Study Of Boron Doped Vanadium Oxide/Mn₃AlC Cathodes

The rapid consumption of traditional energy has caused the energy crisis in the world,forcing people to use renewable energy sources such as solar energy and wind energy.However,its discontinuity,instability and uncontrollable power generation are difficult to use directly.The energy storage system as a medium that regulates power output and improves power grid to withstand renewable energy capabilities can be used to effectively transform and reliably store these intermittent power sources.In various energy storage systems,aqueous zinc ion batteries have great application potential due to the variety of cathode materials,abundant resources and high theoretical specific capacity of zinc metal(5855 m Ah cm^-3and 820 m Ah g^-1).In aqueous zinc ion batteries,the performance of batteries largely depends on the choice of cathode materials.The vanadium/manganese base electrode has great application prospect due to its advantages of diverse lattice structure,rich resources and high theoretical specific capacity.Therefore,we first use VO₂（B）as the research object to improve the electrochemical properties through the doping strategy of light boron element,and study the zinc storage mechanism.Then,the reverse perovskite structure Mn₃AlC was used to explore the zinc storage properties and mechanism.The details are as follows:（1）A series of VO₂（B）is prepared by one-step hydrothermal method,which is used as the cathode material of aqueous zinc ion battery.Firstly,X-ray photoelectron spectroscopy and inductively coupled plasma spectrometer analysis show that boron is successfully doped in VO₂（B）.The doping amount of boron has saturation limit characteristics.The X-ray diffraction results further indicate that the（110）crystal plane peak of the doped sample has shifted towards a small angle,which is due to the formation of boron oxygen bonds with adjacent oxygen at the gap position,resulting in an increase in crystal plane spacing.The analysis of transmission electron microscope data shows that the lattice spacing of the（110）crystal is increased by 0.012 nm after doping with 2 at.%boron,which is consistent with the results of X-ray diffraction analysis.Electrochemical property characterization found the best doping ratio is 2 at.%boron-doped VO₂（B）at a voltage window of 0.2-1.4 V.At the current density of 0.1 A g^-1,the first discharge specific capacity of the battery of 281.7 m Ah g^-1is much higher than that the pure VO₂（B）.The research on zinc storage mechanism shows that VO₂（B）introduced by boron have a pseudocapacitance reversible Zn²⁺intercalation/de-intercalation mechanism.（2）The commercial Mn₃AlC was used as the cathode material for the first time to study its electrochemical properties and zinc storage mechanism.X-ray diffraction and transmission electron microscope analysis shows that Mn₃AlC material has antiperovskite structure.Scanning electron microscope analysis further shows that its microstructure is composed of micron particles and presents irregular blocks.Electrochemical properties were characterized at a voltage window of 0.8-1.8 V.The first discharge specific capacity at the current density of 0.1 A g^-1was 229.4 m Ah g^-1,where two voltage platforms appeared during the first charge.The study on the mechanism of zinc storage found that the two voltage platforms that appeared in the charging process correspond to the dissolution of manganese ions and the oxidation of manganese ions toδ-MnO₂,respectively.During the subsequent discharge process,the MnOOH was obtained via in-situ conversion reaction due to the proton insertion inδ-MnO₂.