Preparation Of Hollow Carbon Nanofibers By Electrospinning And Electrochemical Properties In Lithium-Ion Batteries

Flexible smart wearable devices and flexible smart phones are inevitably become the direction of future science and technology.Therefore,flexible lithium-ion batteries have become the most basic and core requirements of a new generation of flexible products,so low-cost,flexible,high energy density and cycle performance have been developed.Good flexible electrode materials are critical.In this paper,high carbon content polyimide?PI?is selected as the carbon matrix material,and the flexible hollow carbon nanofiber?HCNF?is prepared by electrospinning method,which is used as the negative electrode of lithium ion battery,and in order to further improve the electrical properties of the electrode,A flexible composite electrode was prepared by hydrothermal loading of MnO2.Firstly,the optimum process parameters of polyimide nanofibers were determined by morphology analysis,chemical structure analysis,mechanical property test and thermogravimetric analysis.When the concentration of polyamic acid?PAA?is 15wt%,the spinning voltage is 15kV,the injection rate is 0.6mL/h,the receiving distance is 15cm,and the linear speed of the drum is 2.4m/s,the electrospinning is the most stable and the fiber is continuous,smooth and uniform.Secondly,polyimide-based hollow carbon nanofibers with uniform cavities were prepared for the first time by using poly?propylene carbonate??PPC?as a porogen.Hollow carbon nanofibers have a high specific surface area which can provide more active sites for the insertion of lithium ions?Li⁺?,and store electrolyte to shorten the Li⁺transmission distance and reduces the internal resistance.That contributes to the improvement of electrochemical performance.It was found that when the PPC concentration was 20wt%and the flow rate was0.2mL/h,the hollow carbon nanofibers?HCNF-0.2?had uniform hollow structure,large cavity and maximum specific surface area of 500.5m²/g,which to increase by 65%compared to solid fiber?301.1m²/g?.At a current density of 0.1A/g,the specific capacity is 337.0mAh/g,which is 55%higher than that of solid fiber?217.7mAh/g?.Even at a large current density of 1A/g,the reversible specific capacityremains at 220.1mAh/g.Finally,the flexible composite electrode?MHCNF-0.2?can be prepared by hydrothermal method,which can uniformLy and environmentally load MnO₂ on HCNF-0.2.MnO₂ helps to increase the energy density of the electrode,while the three dimensional conductive network of HCNF-0.2 can improve the conductivity of MnO₂ and alleviate volume expansion.It has been tested that the specific capacity of the composite electrode MHCNF-0.2 is 427.1mAh/g at a current density of 0.1A/g,which is 27%higher than that of HCNF-0.2?337.0mAh/g?,and the volume specific capacity is doubled.The energy density is increased by 84%.Even at a large current density of 1A/g,the reversible specific capacity is maintained at 245.4mAh/g,and still has good cycle stability and rate performance.