Investigation On Design And Electrochemical Properties Of Novel Energy Storage Devices Based On Porous Carbon Fabric

The global climatic issues and energy crisis caused by the excessive consumption of fossil fuels have seriously impeded society’s rapid development.New energy storage technologies play a critical role in alleviating the above issues.Among them,aqueous energy storage devices with high safety attributes,high power characteristics,durability,and low-cost stand out among many energy storage technologies and have attracted considerable attention from researchers.However,current aqueous electrochemical energy storage devices（AEESDs）still have multiple issues,including low energy density,poor cycling stability,low Coulombic efficiency due to gas evolution competition reaction,and inadequate low-temperature energy storage performance due to aqueous electrolyte condensation,which have severely limited the commercial application of AEESDs.In the dissertation,the conductivity and capacitance properties of the carbon fabric are enhanced by increasing the degree of graphitization and nitrogen-doped surface modification,and it is successfully applied to the ultra-low-temperature symmetric supercapacitor（SSC）and Zn ion hybrid supercapacitor（ZHSC）,and the construction of novel all-manganese and chromium-based AEESD with high stability is explored.The correlation between the energy storage characteristics of AEESDs and the electrochemical energy storage mechanism is thoroughly investigated,and the structure of the storage devices has been optimized to realize the design of high-performance AEESDs.The research results are summarized as follows:（1）Two pieces of PCFs with high specific surface area（SSA）,high electrical conductivity,and good flexibility were successfully prepared by two activation techniques at high temperatures.（i）N-doped porous carbon fabric（NPCF）with abundant surface defects and high SSA(162.2 m² g^-1)was achieved by a two-step sequential process of KOH high-temperature activation and NaN₃ hydrothermal treatment;（ii）porous graphitized carbon fabric（PGCF）with high SSA(331.7 m² g^-1)and high degree of graphitization was prepared using K₂FeO₄ high-temperature activation process.Based on the analysis of comparative electrochemical performance,PGCF was found to have a superior energy storage capability.Meanwhile,the directly assembled SSC based on 37wt%H₂SO₄ electrolyte and PGCF electrodes achieves an energy density of up to 0.73 mWh cm^-2 and a power density of up to 31.75 mW cm^-2 at room temperature,and maintains an areal capacity output of up to 0.51 mAh cm^-2 at-60°C,while exhibiting excellent cycling stability.（2）Based on the redox chemistry of Mn²⁺,a novel all-Mn energy storage device（AMnESD）is designed with PCF as the collector.In 3 M Mn SO₄+0.5 M（NH₄）₂SO₄aqueous electrolyte,the negative electrode of the PCF reduces Mn²⁺in the electrolyte to form Mn metal,while the positive electrode oxidizes Mn²⁺to form amorphous MnO₂ on the surface of the PCF,resulting in the in-situ construction of the AMnESD.The device assembled by PGCFs can provide an areal capacity of 1.50 mAh cm^-2,with a maximum energy density of 1.1 mWh cm^-2 as well as a maximum power density of 9.70 mW cm^-2.Meanwhile,it is confirmed that（NH₄）₂SO₄ can significantly improve the cycling stability of AMnESDs,which enables AMnESDs to achieve a capacity retention rate of 93.5%after 40,000 cycles.By investigating the energy storage mechanism of its positive and negative electrodes,the influence of the stable pseudocapacitance mechanism and the deposition/stripping mechanism on the high cycle stability performance of AMnESD can be determined.（3）Metallic Zn has a low theoretical reduction potential and a high overpotential of hydrogen evolution reaction,which makes it more potential as an anode material for AEESDs.ZHSC devices can be assembled by pre-depositing Zn on PCF and using the PCF as the positive electrode.By introducing a high-performance LiCl+Zn Cl₂ hybrid electrolyte,the efficient Zn plating/stripping reaction on the PCF substrate is realized,and the synergistic effect of the porous substrate and electrolyte is confirmed to inhibit the formation of Zn dendrites.The assembled ZHSC exhibits the highest areal capacity of2.37 mAh cm^-2,the highest energy density of 2.02 mWh cm^-2,and the highest power density of 11.47 mW cm^-2 at room temperature.In addition,due to the superior ionic conductivity of the hybrid electrolyte at low temperatures,the ZHSC can still deliver a maximum areal capacity of 1.15 mAh cm^-2 and an energy density of 0.87 mWh cm^-2 at-60°C.（4）The Cr metal also has a favorable theoretical reduction potential,and due to its three-electron reaction characteristics and low relative atomic mass,its theoretical specific capacity and volume capacity can reach 1546 mAh g^-1 and 11,118 mAh cm^-3,respectively,which has the characteristics of an excellent anode for AEESDs.The assembly of flexible Cr ion supercapacitors is investigated by depositing the Cr negative electrode on the PGCF surface,and it is confirmed that Cr has high plating/stripping efficiency as well as good stability in 18 M LiCl+0.5 M CrCl₃ electrolyte.The electrochemical performance of the novel flexible AEESD in a wide low-temperature range（-40～25℃）is further investigated.At 25℃,it achieves the highest areal capacity of 1.76 mAh cm^-2,the maximum energy density of 1.47 mWh cm^-2,and the highest power density of 9.95 mW cm^-2,and still exhibits superior electrochemical performance at-40°C.This work provides a solid foundation for the development and application of next-generation energy storage devices.