EGCG Polyphenol Polymer-derived Carbon:Preparation,Structure Regulation And Electrochemical Properties

In the context of energy crisis and carbon neutrality,how to develop and realize green and efficient energy storage and output has become imminent.Lithium-ion batteries are limited by low power output and low energy density of supercapacitors,which make them unable to meet the dual needs of human beings for high energy and high power.Therefore,it is urgent to develop an energy storage device that can overcome the above shortcomings.Lithium-ion hybrid capacitors with high energy/power density,composed of lithium-ion battery negative electrodes and supercapacitor positive electrodes,are theoretically considered to be promising alternatives to lithium-ion batteries and supercapacitors.The research on lithium-ion hybrid capacitors has made great progress in the past two decades.However,the scarcity and high cost of lithium resources have forced people to turn their attention to potassium,which is chemically similar with lithium,more abundant and cheaper.Generally,the energy/power density and long cycle life of potassium-ion hybrid capacitors are comparable to Li-ion hybrid capacitors.Unfortunately,Since the ionic size of K⁺is much larger than that of Li⁺,the slow kinetics and large strain of the material inside the K-ion hybrid capacitor are not conducive to the improvement of its electrochemical performance.In addition,due to the different electrochemical energy storage mechanisms of the positive and negative electrodes,the internal kinetics of the potassium-ion hybrid capacitor will inevitably be unbalanced,which further hinders its application in energy storage.Therefore,it is necessary to design and optimize the potassium ion anode and cathode materials and the whole device system to overcome the defects of potassium ion hybrid capacitors.In this paper,the cathode and anode materials were specially designed.Using EGCG as the organic precursor,a series of anode EGCG aldol condensation activated carbon materials and EGCG nanocarbon materials were prepared by different synthesis optimization strategies.The electrochemical performance of the material was evaluated,and the energy storage mechanism of EGCG carbon as the cathode of supercapacitor and the anode of K-ion battery was revealed by systematic characterization analysis.According to the electrochemical test results,EGCG aldol condensation activated carbon was used as the positive electrode,EGCG nanocarbon as the negative electrode,and organic electrolyte was used to assemble the potassium ion hybrid capacitor.The reaction kinetics of the device,a potassium-ion hybrid capacitor with high energy/power density was constructed,and the following results were obtained:（1）EGCG and glyoxal were used as organic precursor,using F₁₂₇ and P₁₂₃as soft templates,aldol condensation precursors were carbonized at high temperature and then activated by KOH etching to synthesize a series of porous carbon spheres with 0.5-4nm pore characteristics,the supercapacitor assembled in 6 M KOH aqueous electrolyte showed ultra-high charge storage capacity(287 F g^-1,1 A g^-1),excellent rate capability(201 F g^-1,50 A g^-1)and maintained an ultra-long cycle life of 93.7%after 20,000 cycles;the supercapacitor in[EMIM]BF₄ ionic liquid has outstanding specific capacitance(1 A g^-1,214.8 F g^-1),excellent rate capability(30 A g^-1,66.1%)and ultra-durable cycle life.（2）A series of EGCG nanocarbons were prepared by adjusting the concentration of EGCG and template and changing the carbonization temperature with EGCG as the organic body and calcium carbonate as the hard template.The carbonization mechanism of EGCG nanocarbons was analyzed by XRD and TG.With abundant pore structure,active sites,and"widened"carbon interlayer spacing,EGCa C₆₀₀ carbonized at 600°C is used as anode material for potassium-ion batteries.The SEI with a thickness of about 5 nm formed on the surface of EGCa C₆₀₀ uniformly and stably by the first discharge in EGCa C₆₀₀ improves the ionic conductance and reduces the interfacial impedance,the diffusion-capacitive hybrid energy storage mechanism dominated by the fast surface capacitance behavior and the extremely low K⁺diffusion The coefficients enhance the reaction kinetics.Therefore,it exhibits excellent reversible specific capacity(0.1 A g^-1,417 m A h g^-1),outstanding rate capability(20 A g^-1 with 138 m A h g^-1),and extraordinary cycle stability（stable more than 2000 laps）.（3）The key to optimizing the ionic hybrid capacitor is to make up for the dynamic imbalance as much as possible while improving the electrochemical capacity.Based on this,four potassium ion hybrid capacitors with different mass ratios of positive and negative electrodes were constructed by bridging the positive and negative electrode capacity ratios in a kinetically balanced manner,using AEGP₁F₁ as the positive electrode and EGCa C600 as the negative electrode.Among them,PIHC-1.5 with a mass ratio of positive and negative electrodes of 1.5:1 has an excellent upper limit of energy storage(150.7 Wh Kg^-1/877.3 W Kg^-1),outstanding power density(45.8 k W Kg^-1/61 Wh Kg^-1)and super long cycle life（20000 cycles keep 87.5%）.