Preparation And Potassium Storage Properties Of Porous Carbon Nanofiber Composites

The development of clean energy such as wind energy and solar energy and the popularization of new energy vehicles have promoted the development of energy storage devices.Due to the shortage of lithium and the soaring cost,the development of new energy storage system other than lithium-ion batteries has become an urgent need,and potassium-ion batteries emerged as a new star.The traditional anode material graphite used for PIBs has the problem of poor cycle and rate performance,so it is important to develop new anode materials.In this paper,carbon nanofibers were prepared by electrospinning,high temperature pyrolysis,melt diffusion and hydrothermal methods.The morphology,structure and electrochemical performance studies were studied,explored their potassium storage performance and mechanism.The main contents of the thesis are as follows:（1）In order to find the anode material that can accommodate the repeated insertion/removal of potassium ions,the precursor solution was prepared by polytetrafluoroethylene suspension（PTFE）,polyvinyl alcohol（PVA）and boric acid（BA）.Porous carbon nanofibers（PCNFs）were obtained by electrospinning,preoxidation and high temperature pyrolysis.The research results showed that PCNFs have a porous and cross-linked structure,and realized the doping of B,F,and O.The composition was mainly amorphous carbon,and the specific surface area were 672 m²g^-1.PCNFs exhibited a specific capacity of 240 m Ah g^-1at 100 m A g^-1,maintained178 m Ah g^-1after more than 6100 cycles at 1000 m A g^-1,and a high specific capacity of 185 m Ah g^-1was achieved at of 20 m A g^-1with high load of 12.6 mg cm^-2.Potassium Ion Hybrid Capacitor（PIHCs）with PCNFs as anode and AC as cathode was assembled and the corresponding electrochemical performance tests were carried out.PCNFs//AC PIHCs showed excellent performance,energy density was 87 Wh kg^-1,power density of 393 W kg^-1,and the capacity retention was 78%after more than4000 cycles.（2）In view of the low capacity of PCNFs,carbon-coated selenium-doping porous carbon nanofibers（C-Se@PCNFs）were synthesized by melt diffusion and carbon coating method.C-Se@PCNFs maintained the fibrous interconnected network structure and abundant pores.C-Se@PCNFs maintained a capacity of 295.4 m Ah g^-1after more than 100 cycles at 100 m A g^-1,and retained 221.2 m Ah g^-1after 1700cycles at 500 m A g^-1,revealed excellent cycle performance and rate capability.The pseudocapacitance contribution of C-Se@PCNFs will increase from 45.4%at 0.1 m V s^-1to 71.1%at 1.0 m V s^-1gradually by CV testing and corresponding analysis.（3）In view of the low capacity of PCNFs,poor conductivity and volume expansion of Mo Se₂,the carbon-coated molybdenum diselenide composite porous carbon nanofibers（C-Mo Se₂@PCNFs）was synthesized by hydrothermal and carbon coating methods.The porous and cross-linked structure of carbon nanofiber framework effectively enhanced the conductivity of Mo Se₂and solve the problem of volume change during charge and discharge.The specific capacity of C-Mo Se₂@PCNFs maintained 252 m Ah g^-1at 500 m A g^-1after 100 cycles.The potassium storage mechanism of C-Mo Se₂@PCNFs was analyzed by CV test and corresponding simple calculation.The results show that the C-Se@PCNFs is mainly controlled by the Faraday process due to the introduction of Mo Se₂,and the pseudocapacitive contribution rate gradually increases from 81.8%at 0.1 m V s^-1to92.9%at 1.0 m V s^-1.