Interfacial Regulation And Performance Study On Zinc Metal Anode For Aqueous Zinc Ion Batteries

In the aqueous electrolyte,zinc metal anode has a low redox potential(-0.76 V vs.SHE)and a high theoretical capacity(820 mAh g-1,5851 mAh cm-3),which facilitates the improvement of power density and energy density of aqueous ion batteries.However,the uneven deposition leading to dendrites and the side reactions leading to irreversible by-products at the interface between zinc metal anode and aqueous electrolyte,can result in the decrease in battery capacity,shorting cycle life,and even short circuit or open circuit.Therefore,zinc metal anode with high stability is essential to improve the electrochemical performance of aqueous zinc ion batteries.In this dissertation,we focus on the modulation of the surface interface between zinc metal anode and aqueous electrolyte,to enhance the stability of zinc metal anode by in-situ/ex-situ constructing protective layers on the surface of zinc metal.And they apply to zinc‖oxide aqueous full cells.The main work is as follows:1.Uniform diffusion of zinc ions is achieved by ex-situ constructing an inorganic solid electrolyte layer on the surface of zinc metal.In this work,diffusion barrier energy of Zn2+in several phosphate lattices is compared by the current peak of cyclic voltammetric and density functional theory calculations.And a fast ionic conductor-NTP is selected and uniformly coated on the zinc anode surface.XPS,exsitu XRD and HRTEM are further explored to verify the process of Zn2+diffusion in the lattice of NTP.The results show that the NTP protective layer with high ionic conductivity and low electronic conductivity can effectively homogenize the diffusion of Zn2+on the zinc anode surface and inhibit the formation of Zn dendrites.Meanwhile,the protective layer effectively hinders the occurrence of side reactions and ultimately improves the reversibility of Zn deposition.Ten thousand cycles of NTP@Zn‖MnO2 aqueous full cell at 10 C is achieved,and the specific capacity is still 105 mAh g-1 after cycling with a decay rate of only 0.004%per cycle.2.The aqueous ZnSO4 electrolyte is modulated with the glycerol additive to insitu produce a tight basic zinc sulfate layer on the Zn surface.In this work,glycerol increases the viscosity of the aqueous electrolyte,decreases the diffusion rate of zinc ions and regulates the solvation component around zinc ions;Raman spectra shows that glycerol also decreases the free water percentage of the aqueous solvent which in turn regulates the growth rate of basic zinc sulfate,inducing its flat growth into micron-sized sheets.And basic zinc sulfate can suppress corrosion side reactions and promote uniform zinc deposition.The Zn-Cu half-cell with zinc ion plating/stripping can achieve 5000 reversible cycles;the Zn symmetric cell can cycle for 2400 h;the Zn‖VO2 full cell exhibits a high energy density of 240 Wh kg-1 and a discharge capacity of 192 mAh g-1 after 1000 cycles.3.A composite organosilicon based polymer/inorganic zinc salt protective layer with a thickness of only 3.26 μm is in-situ constructed on the Zn surface by the SiO-Zn through the reaction of silane coupling agent with Zn.Moreover,different reaction activation energy between different crystalline surfaces of Zn and H+is exploited to achieve a selective orientation of the zinc {001} crystalline surface.This work demonstrates the zinc metal surface crystallographic reconstruction by electron backscatter diffraction and XRD combining with theoretical calculations.XPS and infrared absorption spectroscopy characterization show that the protective layer has Si-O groups guiding the diffusion of zinc ions.Optical microscopy,SEM and other characterizations show that the zinc ions uniformly deposite and smoothly grow.Various corrosion resistance tests and differential electrochemical mass spectrometry show the dense protective layer can effectively inhibit hydrogen precipitation.The electrochemical performance study shows that the capacity retention of Zn‖MnO2 button cell reaches 96.3%after 1600 cycles at 5 C,and the pouch cell still has a specific capacity of 122 mAh g-1 after 200 cycles.4.The highly utilizable zinc powder anode(Zn-GC)is achieved by graphenecoated zinc powder of indium shell modification combined with carbon nanotube composite.SEM shows Zn-GC has high porosity.Electrochemical tests indicate ZnGC has more nucleation sites than zinc foil.And the electric potential indicates a strong negative potential on the graphene surface,which has a strong adsorption effect to Zn2+;SEM and TEM prove that the 3D conductive network formed by carbon nanotubes is beneficial to mitigate the large volume change effect during deep charging/discharging.These advantages facilitate deep deposition and stripping of Zn-GC electrodes.Large Zn powder particle size and surface indium shell passivation layer modification facilitate the suppression of corrosion side reactions.Finally,the full depth of charge of Zn-GC electrode can reach 60%;Zn-GC‖MnO2 full cell achieves no significant capacity decay after 400 cycles.