Design And Energy Storage Mechanism Of Transition Metal-Based Electrodes/Multifunctional Electrolytes Based On Aqueous Electrochemical Energy Storage Devices

The demand for sustainable energy development is increasing due to the gradual depletion of fossil fuels and acute environmental issues.Developing efficient energy storage and conversion devices is an effective means to solve the energy crisis.Supercapacitors and zinc ion batteries have shown good prospects in many devices due to their advantages such as high energy storage efficiency,strong environmental adaptability,and low cost.However,there still exist some problems in electrode materials when used in practical applications,such as low capacity and unstable circulation.Furthermore,the side reactions in electrolytes caused by unfavorable metal ion solvent sheath structure also affect the normal operation of devices.Based on these,this thesis achieves significant improvement in energy storage capacity of electrodes through various interface control methods such as the construction of heterostructures,heteroatom doping,and surface modification.It also modifies the hydrogen bond network of aqueous electrolytes to inhibit dendrite growth and hydrogen evolution reactions,and improves cycle life in the charge and discharge process.The research in this thesis will provide some guidance for in-depth understanding of the relationship among electrode materials,electrolytes,and electrochemical performance.The specific content includes following four parts:1.Hierarchical porous ternary Co-Mn-Cu-S nanodisk arrays with high specific capacity and long cycle life were developed to improve the energy density of hybrid supercapacitors through the modification strategy of ion exchange/etching and vulcanization.The metal-organic framework was used as a self-sacrificing template to uniformly grow dimethylimidazole cobalt nanoarrays on nickel foam,followed by ion exchange/etching with bimetallic Mn/Cu solution,and then thioacetamide was added for solvothermal reaction.Finally,Co-Mn-Cu-S nanodisk arrays with hierarchical porous structures were grown in situ as electrode materials.A series of related tests show that the Co-Mn-Cu-S nanodisk arrays electrode has the best electrochemical performance due to the structural advantages of the Co-Mn-Cu-S ternary component and the synergistic effect.The Co-Mn-Cu-S nanodisk arrays electrode provides an ultra-high specific capacity of536.8 m Ah g^-1at a current density of 2 A g^-1.There is still 63%capacity retention at a high current density of 30 A g^-1,showing excellent rate performance.The assembled hybrid supercapacitor delivers an energy density of 63.8 Wh kg^-1at a power density of 743 W kg^-1when using the Co-Mn-Cu-S nanodisk arrays as the positive electrode and the nanoporous carbon material calcined from zeolitic imidazolate framework as the negative electrode.This work provides a new way to prepare electrode materials for high-performance multi-transition metal sulfide-based energy storage devices.2.A simple pre-intercalation strategy for electrochemical activation was proposed to synthesize Mn/K-Co-S nanoarrays with high specific capacitance as positive electrode materials for hybrid supercapacitors.Dimethylimidazole cobalt nanosheets were grown on nickel foam using metal-organic framework as a precursor,and then the material was electrochemically activated by a three-electrode system to introduce Mnand K,followed by solvothermal treatment with thioacetamide to obtain the final sample.The shift of characteristic peaks in X-ray diffraction pattern proves the successful introduction of Mnand K,which may change the original system of the material and provide more active sites,thereby improving the electrochemical performance of the final sample.Benefiting from the pre-intercalation of Mnand K,the Mn/K-Co-S sample provides a specific capacitance of 4100 F g^-1(569 m Ah g^-1)at a current density of 1 A g^-1,which is larger than most of the sulfides reported so far.The asymmetric supercapacitor device assembled with activated carbon has almost no capacity lose after 5000 cycles.3.The P-MnO_2-x@C hollow nanostructured composite was designed as an aqueous zinc ion cathode material to improve the mass transfer kinetics of zinc ion insertion/extraction.In this chapter,hollow carbon nanospheres were used as templates to grow manganese dioxide on the surface of carbon nanospheres.Hollow carbon spheres with ordered morphology and porous structure as the growth substrate can effectively ensure the uniform distribution of manganese dioxide nanosheets.The constructed heterojunction structure is conducive to the penetration of electrolyte.In addition,it increases the total contact area of the electrode-electrolyte interface and exposes more active sites,which can maximize the use of active components and accelerate ion diffusion kinetics.The synthesized hollow MnO₂@C nanospheres were then modified by surface phosphating to obtain P-MnO_2-x@C hollow nanostructured composites with oxygen defects.The introduction of symbiotic oxygen defects and phosphate ion intercalation not only improves the intrinsic electronic conductivity of MnO₂,but also expands its interlayer spacing.The P-MnO_2-x@C electrode delivers an ultra-high specific capacity of 562 m Ah g^-1at a current density of 0.2 A g^-1due to the synergistic effect,exceeding MnO₂@C without phosphating treatment(397 m Ah g^-1)and MnO₂without carbon spheres(258 m Ah g^-1).There is almost no attenuation after 1000 cycles at a high current density of 5 A g^-1,showing excellent cycle stability.4.Xylitol was reported as a novel nontoxic electrolyte additive in traditional zinc sulfate electrolytes for the highly durable dendrite-free stripping/plating of zinc metal anodes in zinc ion batteries.The abundant polar polyhydroxy groups in xylitol molecules have high electron density,endowing them with strong zinc affinity and effective ability to regulate water molecular activity.The introduction of this additive can destroy the tetrahedral structure of water,thereby reducing the binding degree of the original hydrogen bond.Both experimental studies and multiscale theoretical simulations unravel that a small amount of xylitol（100 m M）can not only modulate the interaction of Zn²⁺ions with water molecules and sulfate ions in the primary solvent shell through oriented reconstruction of hydrogen bonding to enhance ion migration and inhibit hydrogen evolution reaction,but also enables preferential adsorption on Zn slab to retard the deposition of Zn²⁺ions and block the two-dimensional diffusion of ions at the zinc-electrolyte interface,which can effectively improve the stripping/plating durability and ensure the stable operation of zinc ion batteries based on NaV₃O₈materials.