Preparation Of Heteroatom Doped Porous Carbon And Its Application In Hybrid Capacitors

The development of smart power grids and other stationary and municipal renewable energy storage applications depends heavily on large-scale energy storage technologies.Lithium-ion batteries are commercially available in various energy systems,but their development is limited by the scarcity of lithium resources.Potassium metal has similar properties to lithium and holds the promise of being the next generation of energy storage applications.For example,potassium-ion hybrid capacitors（PIHCs）combine the benefits of energy density rechargeable batteries with high power density capacitors,offering a wide range of development prospects.The electrode material is key to the energy density of the capacitor,however,the large size of K⁺leads to slow kinetics and volume expansion during charge and discharge.The porous carbon as well as defect engineering can effectively solve these problems,thus increasing the reserve space and fast diffusion kinetics of K⁺.By using defect engineering and heteroatom doping,several porous architectures have been created and used to potassium ion hybrid capacitors,with the following main elements and results:（1）The nitrogen doping was able to increase the active sites,which was beneficial to improve its electrochemical properties as an energy storage material,exhibiting excellent supercapacitance and potassium storage properties.When the current density is 0.5 A g^-1,the specific capacitance of HPNC-700 reaches a maximum of 286 F g^-1.The capacity is still 98.9%after 10,000 cycles at 10 A g^-1.To characterize the potassium storage performance of HPNC-700,the discharge and charge capacities of HPNC-700 were 554.2 m Ah g^-1and 2179.1 m Ah g^-1at 0.05 A g^-1,respectively.The HPNC-700//PC-700 potassium ion capacitor has a capacity of116.5 Wh kg^-1energy density and 19 k W kg^-1power density at a voltage window of3.8 V.It has a capacity retention rate of 92.5%after 1000 cycles and can power the"CUMT"panel.（2）The controlled preparation of honeycomb boron and nitrogen co-doped porous carbon was accomplished using inexpensive CMC-Na,H₃BO₃,and KNO₃as basic materials.Due to the huge specific surface area(2582 m²g^-1)and rich porous structure,BNHC-650 exhibited high specific capacitance(389 F g^-1@0.2 A g^-1),and can charge and discharge 10000 times at a high current of 10 A g^-1,while still maintaining a specific capacity of 98.2%.Testing the potassium storage performance of BNHC-650,the reversible charging capacity of BNHC-650 can reach 249 m Ah g^-1at 0.05 A g^-1,and it can cycle for 200 cycles.By using DFT calculations and kinetic analysis,the potassium storage mechanism of BNHC-650 can be analyzed.The doping of heteroatoms can provide more storage sites for potassium ions and improve electrochemical performance.At a voltage window of 4.2V,the potassium ion capacitor BNHC-650//PC-700 has an energy density of 233.3 Wh kg^-1and a power density of 16.8 k W kg^-1.The capacity retention rate reaches 92.5%after 1000cycles,and it also supplies power for the watch.（3）The N/S co-doped porous carbon materials with abundant carbon defects were synthesized by freeze-drying and high-temperature carbonisation using inexpensive sodium polyacrylate,sodium thiosulphate and sodium nitrate as raw materials,and the prepared electrode materials have excellent supercapacitance performance and K⁺storage performance at the same time thanks to the abundant specific surface area and pore defects.At 1 A g^-1,NSC-700 possesses a specific capacity of 193.7 F g^-1and can be charged and discharged 10,000 times at a high current of 10A g^-1while still maintaining a specific capacity of 98.2%at 144.6 F g^-1.The potassium storage performance of NSC-700 is also excellent,as the initial charge/discharge capacity of the first cycle is 441.6 m Ah g^-1and 1672.4 m Ah g^-1respectively at a current density of 0.05 A g^-1when NSC-700 is utilized as the negative electrode of the potassium ion half-cell.And after 200 cycles,the NSC-700still exhibits a reversible capacity of 274.8 m Ah g^-1.Using DFT calculations and kinetic analysis of the potassium storage mechanism of the nitrogen-sulphur double-doped carbon,the doped porous carbon with a stable structure and high defect concentration favours potassium storage.The potassium ion capacitor NSC-700//PC-700 has a power density of 12 k W kg^-1and an energy density of 141.2 Wh kg^-1.At a voltage window of 4 V,the gadget can illuminate a"CUMT"panel.The design of this chapter offers additional possibilities for future investigations into low-cost,high-performance electrode materials.This dissertation has 112 references,45 illustrations,and 4 tables.