Preparation Of Pueraria-Derived Carbon And Study Of Energy Storage Properties

Energy is vital to human development,energy consumption and production dependent on fossil fuel combustion will have a serious impact on the world economy and ecology.In the context of"double carbon",there is a growing demand for environmentally friendly,high-performance renewable energy storage devices.Supercapacitors are well known in the field of energy storage devices for their high power density,fast charge and discharge rates and long cycle life.However,they are limited by the unreasonable pore structure and low comparative area of the electrode materials,resulting in their low specific capacity and energy density.In addition,potassium ion hybrid capacitors are a class of hybrid energy storage devices that can theoretically combine the respective advantages of supercapacitors and ion batteries with high energy density and power density,but the large size of K⁺causes severe volume expansion when conventional anode materials such as graphite are used for K⁺storage,resulting in poor kinetics with low capacity.In this thesis,capacitive and battery type materials were designed and prepared based on pueraria-derived hydrothermal carbon microspheres and nitrogen-doped porous carbon,respectively.The influence law of synthesis conditions on the structure of porous carbon materials is investigated with the help of systematic characterization,revealing the intrinsic connection between their structural characteristics and electrochemical properties,elucidating the energy storage mechanism of porous carbon as capacitive and battery-type materials.It provided a valuable reference for the optimization and development of potassium ion hybrid capacitors.The specific results obtained are as follows:（1）A series of porous carbon microspheres were prepared by simple hydrothermal pre-carbonization supplemented with KOH activation strategy using biomass pueraria powder as carbon source.Among them,the sample GFHC-4K with a mass ratio of alkali to carbon of 4 showed excellent performance in the three-electrode system test due to the layered porous structure of both microporous/mesoporous,ultra-high specific surface area(2846 m²g^-1)and extremely large pore volume(V_total=1.310 cm³g^-1).Next,symmetric supercapacitors were constructed using 6M KOH and1-ethyl-3-methylimidazolium tetrafluoroborate（EMIMBF₄）ionic liquids as electrolytes,respectively.When 6M KOH was used as the electrolyte,it exhibited super high specific capacity(0.5 A g^-1,293 F g^-1)and excellent multiplicative performance(30 A g^-1,169 F g^-1),and the capacity retention rate was as high as 90.3%after 20,000 cycles.When EMIMBF₄is used as the electrolyte,it has a specific capacity of 181 F g^-1at 0.5 A g^-1and can still maintain a specific capacity of 123 F g^-1at 5 A g^-1,and can output an ultimate energy density of 76.6 Wh kg^-1and an ultimate power density of 10.2 k W kg^-1.（2）The porous carbon materials with wide layer spacing（4.09（?））,high nitrogen doping（13.7%）and mesoporous/macropore were obtained by paste mixing,freeze-drying and carbonization using graphite phase C₃N₄as nitrogen source and porogenic agent and pueraria powder as carbon source.The effects of the mixing ratio of graphitic phase C₃N₄and pueraria powder on the specific surface area and pore structure of porous carbon materials was systematically investigated.When used as the negative electrode of potassium ion batteries,the sample of GFNPC-1 with a mass ratio of 1:1 exhibited considerable potassium storage capacity(0.1 A g^-1,330 m Ah g^-1),outstanding multiplicity performance(5 A g^-1,140 m Ah g^-1)and long-lasting cycling stability(High specific capacity of 196 m Ah g^-1even after 1,000 cycles of 2 A g^-1,with 88%capacity retention).（3）Potassium ion hybrid capacitors with asymmetric dual carbon based electrodes were assembled using Pueraria powder biomass based porous carbon microspheres and Pueraria/g-C₃N₄porous carbon materials as positive and negative electrode materials.Using GFHC-4K as the capacitive positive electrode and GFNPC-1 as the battery type negative electrode,the mass ratio of the active material of the positive and negative electrode materials was adjusted to successfully improve the capacity difference and the kinetic imbalance of the positive and negative electrodes.The potassium ion hybrid capacitor PIHC-1.5 with a mass ratio of 1.5:1 exhibited an ultimate energy/power density of 107 Wh kg^-1/8.2 k W kg^-1and excellent cycling stability.