Controlled Synthesis Of Three-dimensional Porous Carbon Matrix Composites And Their Applications In Potassium Ion Hybrid Capacitors

With the rapid development of modern portable electronics and electric vehicles,people have conducted in-depth research on the development of high-efficiency and low-cost new electrochemical energy storage systems（EES）.Thanks to the abundant reserves and cheap properties of potassium,potassium ion energy storage technology is considered to be a potential substitute for the current lithium-ion system.Potassium-ion hybrid capacitors（PICs）are a rapidly developing new type of capacitors that can provide high-power energy without sacrificing service life and are expected to become a substitute for potassium-ion battery PIBs.Battery-type anode is a key factor in achieving high energy density of PICs.The biggest challenge facing anode materials is the slow kinetics and severe volume expansion caused by the large ion size of K+.The appearance of layered porous carbon materials can effectively alleviate the above problems,and the porous structure provides sufficient interface area between the active site and the electrolyte,expands the interlayer spacing of the（002）crystal plane,and can also promote the electrolyte and ions.Transmission.In line with the purpose of green and simple synthesis,a series of three-dimensional porous carbon-based composite materials have been designed and successfully applied to a potassium ion hybrid capacitor（PICs）that can provide high energy density,power density and long life.The main conclusions are as follows（1）Using local pine leaves and graphene oxide as precursors,oxygen-doped activated carbon/graphene porous nanosheets（OAC/Gs）were successfully prepared by the hydrothermal-assisted-high-temperature carbonization activation method.GO not only acts as the carbon skeleton of OAC/G to induce the formation of a hierarchical-large mesoporous three-dimensional network carbon structure,but also introduces the doping of O elements through the reduction of GO,which enhances the electrochemical performance of the composite material and further expands the graphite layer spacing..Demonstrates excellent supercapacitor performance and potassium storage performance.OAC/G-5 has the best capacitance performance(317 F·g^-1@0.1 A·g^-1)and cycle performance(under 10A·g^-1 for 10000 cycles,the specific capacitance is only lost 2%).In addition,due to the large specific surface area(1538.2 m²·g^-1),a large amount of K ions can be adsorbed,and the increased interlayer spacing（0.41nm）and abundant mesoporous/microporous structure can serve as a fast K ion diffusion path.OAC/G-5 exhibits relatively high reversible capacity(318.5 m Ah·g^-1@25m A·g^-1),excellent rate performance and stable cycle life(93.2%@0.1A·g^-1,1000 cycles).The dual-carbon PIC battery assembled by OAC/G-5（negative）and PNAC（positive）has an ultra-high energy density of 156.67 Wh·kg^-1 and an excellent performance of 14.97k W·kg^-1 under a high voltage of 5V.Power density,and successfully provided energy for the"CUMT"circuit board composed of 52 LEDs.（2）Using urea as the pore former and nitrogen source,sodium nitrate as the molten salt template,and sodium alginate as the carbon precursor,a simple freeze-drying assisted carbonization method was developed to synthesize layered porous nitrogen-doped graphene-like carbon.Nanosheet LPNCs.The freeze-drying carbonization method developed in this research has the advantages of abundant raw materials and low cost,and the two functions of pore formation and nitrogen doping can be realized in one step.Thanks to the large specific surface area(2022 m²·g^-1)and high heteroatom doping（N:5.6 wt%）,the LPNC-700 electrode exhibits a high specific capacitance(207F·g^-1@0.1 A·g^-1),and has an outstanding cycle life.Similarly,the potassium storage capacity of LPNC-700 is very good(275 m A h·g^-1@0.05 A·g^-1).After 1000 cycles at 1A·g-1,there is still 94.5%capacity retention.Scientific analysis and first-principles calculations thoroughly discussed the K ion storage mechanism of LPNC-700.The assembled dual-carbon PIC has an ultra-high energy density of 78.75 Wh·kg^-1 and an excellent power density of 16.20 k W·kg^-1,and can successfully provide energy for small LED lights and watches.This experiment demonstrates molten salt.The carbon material prepared by the induction freeze-drying assisted carbonization method can be used as the feasibility of potassium ion hybrid capacitor electrode material.（3）Using cheap CMC-Na,（NH₄）₂HPO₄ and Na NO₃ as raw materials,the organic-inorganic hybrid aerogel precursor was prepared through improved bio-initiated mineralization under freezing conditions,through carbonization and removal of inorganic substances.Obtained by a large number of interconnected network porous carbon framework.Due to the synergistic effect of multi-stage porous structure,high specific surface area and N-P double doping,the prepared NPMCs material has excellent supercapacitance performance and K+storage performance at the same time.When NPMC-700 is used as the electrode material of the electric double layer capacitor,it has a specific capacitance as high as 318 F·g^-1 at 0.1 A·g^-1,and it still maintains 97.4%after 10000 times of charging and discharging at 10 A·g^-1 Capacitance:When used as the anode of a potassium half-cell,the reversible capacity of LPNC-700 is 275 m A h·g-1 at 0.05 A·g^-1.The cycle stability reaches 76.3%(1 A·g^-1 500 cycles).Dynamic mechanical analysis and DFT calculations show that expanded interlamellar spacing and sufficient active sites can accelerate the insertion/extraction of K⁺.The prepared PIC has an ultra-high energy density of 81.6 Wh·kg^-1 and an excellent power density of12.60 k W·kg^-1.The device can successfully provide energy for small LED lights and watches.The design of this chapter can effectively overcome the problems related to PICs and may stimulate the further development potential of other high-performance energy storage devices.The paper has 60 pictures,2 tables,and 141 references.