Anodes Design And Electrolytes Modification For Aqueous Zinc-ion Batteries

Energy and the environment are closely intertwined with societal development and human survival.Aqueous batteries maintain a leading position in large-scale energy storage systems due to the virtue of environmental friendliness and high safety.Among the various types of aqueous batteries,aqueous zinc-ion batteries（ZIBs）have emerged as a promising technology due to their low potential（-0.762 V vs.SHE）and high theoretical capacity(820 m Ah g^-1).However,practical applications of zinc anode face tricky challenges.Zinc dendrities,formed by the uneven deposition of Zn²⁺,will pierce the separators and lead to short circuits,significantly impacting the performance of the cell.On the other hand,corrosion and hydrogen evolution reactions will irreversibly consume Zn and electrolyte,reducing the utilization of zinc and causing safety hazards such as battery swelling and electrolyte leakage.Therefore,inhibiting the growth of zinc dendrites and improving the stability of anode are importance for the practical application of zinc-ion batteries.In this paper,optimizing electrolytes,modifying interfacial layers and constructing current collectors were used to improve the interface properties of electrolyte/anode,so as to enhance the stability of zinc anode.The main research results are summarized as follows:（1）High-conductivity carbon material with abundant nitrogen functional groups（CN）was synthesized using a magnesium thermal reduction method and self-assembled on the surface of the zincanode by the Langmuir-Blodgett methode to inhibit the growth of zinc dendrites.CN with a stable electric field effectively restrains the accumulation of electric charge and provides a uniform surface electric field,inducing a uniform Zn deposition behavior.Meanwhile,the nitrogen content of CN is much higher than other N-doped carbon materials used to modify the surface of Zn anode.The increased number of active N sites（especially pyrrolic N）helps to effectively adsorb Zn²⁺,achieving uniform nucleation and a flat deposition.In addition,the large specific surface area of CN helps to enhance the wettability of the electrolyte,reduce the interface resistance,and improve the reaction kinetics.As results,the symmetrical cell exhibited a long-term reversible plating/stripping performance for more than 1300 h with an ultralow overpotential（24 m V）.Furthermore,the pouch cell also delivers an excellent electrochemical performance with discharge capacity of 116 m Ah g^-1 at 5 m A after cycles.（2）The silicon dioxide spheres rich in functional groups such as sulfonic acid were mixed with PVDF and coated on zinc foil as a hydrophobic protective layer,which effectively improved the stability of Zn anodes.The highly hydrophobic protective layer significantly suppresses the side reactions by isolating zinc from water molecules.Moreover,the functional groups within the protective layer can promote the Zn²⁺desolvation,facilitates Zn²⁺migration and improve zinc deposition kinetics.In addition,the spherical morphology of the material increases the surface of anode,helps to homogenize the Zn²⁺flux and reduce the local current density,which is conducive to uniform zinc deposition/stripping.Thus,the symmetrical cells exhibited stable cycling for 2000 cycles at 10 m A cm^-2 and 2 m A h cm^-2.Even at a high capacity of 10 m A h cm^-2,symmetrical cells also exhibited longer cycle life（300 h）.（3）To simultaneously address the issues of poor cycling stability and low zinc utilization,boron nitride was coated on copper foil as the current collector of Zn.The insulating BN layer,the upper layer of the anode,acts as the protective barrier of deposited zinc and accelerates the transmission of zinc ions.Besides,the zincophilic Cu substrate,the bottom layer of the anode,promotes dendrite-free Zn deposition.Under the synergistic effect of BN layer and substrate,sandwich-structured anode realizes 66.7%zinc utilization at 4 m Ah cm^-2.The full cells display high stability with an average fading of 0.06%per cycle for 600 cycles.（4）L-lysine was added to 2 M Zn SO₄solution as electrolyte for aqueous zinc-ion batteries to realize the simultaneous regulation of water molecules and zinc ions.L-lysine as the additive can regulates the p H value of the electrolyte and enhances the stability of the anode in the electrolyte.Furthermore,L-lysine effectively reduces the activity of water through strong interactions with H₂O,which can suppress the hydrogen evolution reactions.Additionally,the additive modifies the solvation structure of zinc ions,which is conducive to the transport of Zn²⁺.Thus,the symmetrical cells exhibited a long cycling life of 3000 hours at 1 m A cm^-2 and 1 m A h cm^-2.In summary,this thesis successfully constructed the Zn anode with strong stability and high reversibility by using the anode design and electrolyte modification strategy.Combined with experimental or theoretical calculation,the reasons for improving the performance of each method were systematically analyzed.The research findings provide new insights for the design and research strategies of anodes in future aqueous zinc-ion batteries.