Study On The Modified Preparation And Storage Of Sodium And Potassium Of Metaplexis Japonica Fluffs Derived Carbon Tubes

Recently,lithium-ion batteries（LIBs）have been widely used in electronic equipment,electric vehicles,and power grid energy storage,but the excessive consumption of lithium resources and rising costs seriously restrict its development.Resource-rich sodium-ion and potassium-ion batteries are the most promising low-cost alternative and complementary products for conventional LIBs.However,the larger ionic radius of sodium and potassium ions makes graphite no longer suitable for the development of LIBs anode materials.Because biomass is undoubtedly the richest,greenest,and most inexhaustible resource on the earth.And its derived carbon is also structurally diverse and has been widely developed in the field of energy storage in recent years.Therefore,this dissertation based on metaplexis japonica fluffs derived carbon constructs anode materials of sodium and potassium ion battery with high capacity and good circulation stability by means of activation,N doping and CO₂ etching holes.And assembling the sodium and potassium ion hybrid capacitors investigate the practical application performance of electrode materials.With metaplexis japonica fluff as the carbon source,urea as the N source and etching agent,the N doped carbon tubes（N-MJ）decorated with graphene-like structures of carbon sheets are prepared through a step of carbonization method.Thanks to its structural advantages and high N content（11.08%）,N-MJ exhibits excellent electrochemical properties in sodium-ion half batteries:it can provides high reversible capacity of 390.9 m Ah g^-1 after 50 cycles at 50 m A g^-1;N-MJ still deliver 251.8 m Ah g^-1after 1600 cycles at 200 m A g^-1and the capacity retention rate of 93.3%is maintained;at a high current density of 1 A g^-1,the capacity of the N-MJ increased from 193.1 to 208.1 m Ah g^-1 after 2650 cycles and the retention of is up to 107.8%.Kinetic analysis shows that good sodium storage performance is due to the larger contribution of surface capacitance.In addition,N-MJ matching with commercial activated carbon to assemble sodium ion hybrid ion capacitors can provide a maximum energy density of 111.4Wh kg^-1and power density of 2455.2 W kg^-1as well as a capacity retention rate of 100%after5000 cycles at 1 A g^-1.A flexible free-standing electrode（FSF-PCTs）consisting of porous carbon tubes is designed by softening,filtering,carbonizing and CO₂ etching holes in four steps,which can be applied simultaneously to the anode and cathode electrode of potassium ion hybrid capacitors.In addition,the FSF-PCTs electrode has a 3D interconnected conductive skeleton and a rich ion transmission channel,which is not only conducive to shortening the diffusion mass transfer distance of ions but also accelerating the infiltration of the electrolyte.Therefore,the electrode shows high reversible capacity and great cycle stability in the potassium ion half battery test of both anode and cathode electrode.When FSF-PCTs act as anode materials（test voltage range of 0.01-3 V）,it can demonstrate a high reversible capacity of 300 m Ah g^-1 after 100 cycles at50 m A g^-1,and 100%capacity retention of FSF-PCTs is obtained after 500 cycles at 0.2 A g^-1.When FSF-PCTs act as cathode materials（test voltage range is 1.5-4 V）,the reversible capacity is 104.3 m Ah g^-1 and the capacity retention rate is as high as 99.4%at 500 m A g^-1 after 500cycles.FSF-PCTs still provide a high specific capacity of 62.3 m Ah g^-1(94.6 m Ah g^-1)after2200（1000）cycles at a high current density of 3 A g^-1(1 A g^-1).In addition,the free-standing symmetrical potassium-ion capacitors are assembled adopting FSF-PCTs as both anode and cathode materials.It can provide a maximum power energy density of 117.8 Wh kg^-1 and a power density of 8109.9 W kg^-1.And the hybrid capacitor also demonstrates a high reversible energy of 46.7 Wh kg^-1and maintains a capacity retention rate of 80%after 2200 cycles at 3 A g^-1.