Study On Electrolyte Optimization For Enhancing The Stability Of Electrode Materials In Aqueous Zinc-Ion Batteries

With intrinsic safety,facile processing,resource availability,environmental benignity,and competitive energy density,aqueous zinc-ion batteries(AZIBs)have been prospected as a new generation of safe and economical energy storage devices.However,the practical application of AZIBs is mainly hampered by the limited operational lifetime,which is dominated by cathode material dissolution,Zn dendrite growth,corrosion,and hydrogen reaction.Aiming at the above issues,in this thesis,a series of functional electrolyte additives are developed to stabilize the electrodes,thereby improving the long-term cycling stability of AZIB s.The main research results are as follows:(1)Boosting the cyclability of organic cathode materials in AZIBs via high valent cation.Due to material dissolution issues,the capacity of 7,7,8,8-tetracyanoquinodimethane(TCNQ)tends to decay rapidly.In this chapter,high valent cation Al3+is introduced into aqueous electrolytes to improve the cyclability of the TCNQ-based cathode.The addition of Al3+would not only suppress the dissolution of TCNQ,but also optimize the storage mechanism.Both experimental and computational results reveal that the existence of Al3+can improve the feasibility and reversibility of the insertion/extraction process of multiple cations in TCNQ,which leads to synergistic improvement of both specific capacity and cycle life.(2)Regulating the deposition morphology of Zn metal anode via 1-butyl-3methylimidazolium(BMIm+)cation.Zn metal anode suffers from poor cycling stability and low Coulombic efficiency(CE),which inevitably deteriorate the electrochemical performance of cathode materials.Uncontrolled Zn dendrite growth restricts the battery lifespan directly.In this chapter,BMIm+is introduced into electrolytes to realize a dense and dendrite-free Zn deposition layer with a preferred(002)crystallographic orientation.Both experimental results and calculations unveil the selective adsorption of BMIm+on different crystal planes.As a result,the NH4V4O10‖Zn pouch cell using electrolytes with BMIm+exhibits prolonged cycling stability with a high capacity retention of 81.7%after 236 cycles at a current density of 0.4 A g-1.(3)Preventing interfacial side reactions via monosodium glutamate(MSG).Interfacial side reactions such as Zn corrosion and H2 evolution also compromise the CE and calendar life of AZIBs.In this chapter,MSG is introduced into electrolytes to reconstruct the Zn anode/electrolyte interface and suppress side reactions as well as Zn dendrite growth.Both experimental and calculations results confirm that the glutamate anions are preferentially adsorbed on the Zn surface via the chemical interaction between Zn and-COO-groups.The adsorbed anions can occupy the active sites for Zn corrosion and H2 evolution side reactions,as well as redistribute the zinc ion flux and promote[Zn(H2O)6]2+ desolvation.The bifunctional effect leads to high-efficiency dendrite-free Zn stripping/deposition.Thus,the MnO2‖Zn cell assembled with MSG can sustain a long cycle lifespan(800 h)at a current density of 0.5 C with a high capacity retention of 90%.(4)Tuning the solvation structure via amphiphile molecules.Fast charging-discharging at high current densities is necessary for next-generation batteries.To improve the stability of Zn metal anode under harsh test condition,nonylphenol ethoxylates(NPEO)is introduced into electrolytes to regulate the solvation structure of Zn2+.1H nuclear magnetic resonance spectroscopy analysis and molecular dynamics simulations reveal the formation of a solvation sheath of Zn2+with the co-participation of the NPEO molecules,water molecules,and salt anions.The bulky solvate structure with less coordinated water prevents Zn dendrite growth and water-induced side reactions.As a result,the Zn‖Zn symmetric cell with NPEO electrolyte additive achieves stable cyclic plating-stripping for more than 100 h at a high current density of 40 mA cm-2.Due to the better wettability of electrodes in electrolytes with NPEO,the NH4V4O10‖Zn cells exhibit a higher specific capacity and smaller cell polarization.