Construction And Electrochemical Properties Of Fiber-based Lithium Ion Capacitors

We report the fabrication of a novel way all fibers-based Li-ion capacitor(LIC)from flexible phenolic-based mesoporous carbon nanofibers and PAN/lignin-based carbon nanofibers materials by using electrospinning technique and simple thermal treatment.Accordingly,utilization of pre-lithiated PAN/lignin-based carbon nanofibers and phenolic-base mesoporous carbon nanofibers as negative and positive electrodes,respectively.Assemble into lithium-ion capacitor.Prior to the LIC assembly,both the phenolic-base mesoporous carbon nanofibers and PAN/lignin-based carbon nanofibers electrodes were tested with Li in a half-cell configuration to determine the charge balance between positive and negative electrodes.The anode and cathode materials on morphology and structure of carbon nanofibers were investigated intensively,and their electrochemical properties as positive and negative electrodes for LIC without a binder or current collector were systemically studied for the first time.Firstly,a type of one-dimensional mesoporous carbon nanofibers has been prepared via the electrospinning technique and thermal treatment by using resol as the carbon source and triblock copolymer Pluronic F127 as the template.The effects of the PF/F127 mass ratios varying from 1/0,2/1 to 1/1 on morphology and structure of carbon nanofibers are systematically studied.The obtained MCNFs-2 shows a mesoporous structure with ultra-high specific surface area of 1444.26 m2 g-1 providing numerous electroactive sites to accommodate more charges.As a result,the MCNFs-2 hybrid electrode exhibits high specific capacitance(139.6 F g-1 at 0.05 A g-1)and rate of performance in a 6 M KOH aqueous solution.Next,A type of renewable lignin-based carbonized nanofibers has been fabricated via electrospinning technique and thermal treatment,using lignin with polyacrylonitrile(PAN)as the carbon source and N,N-dimethylformamide(DMF)as the solvent.The ratio of polyacrylonitrile to lignin was optimized.The composite carbon nanofibers PL-5/5 obtained excellent rate performance and long cycle stability.Through the modification of PL-5/5 to obtained PL-MCNFs.And,the PL-MCNFs anode exhibited a large reversible capacity of 384.4 mAh g-1 at 20.0 mA g-1 and maintain 177.7 mAh g-1 at 1.0 A g-1 after 400 cycles.Even at a fast(91 s)charge and discharge condition,the PL-MCNFs showed a good discharge capacity of 127.7 mAh g-1.Eventually,we successfully fabricated all fibers-based LIC by using pre-lithiated PAN/lignin-based carbon nanofibers and phenolic-base mesoporous carbon nanofibers as negative and positive electrodes without a binder or current collector.The energy density and power density were calculated based on the total mass of active materials on both the cathode and the anode.This novel all fibers-based LIC produces an energy density of 72.62 Wh kg-1 at a power density of 97.62 W kg-1 and retains an energy density of 33.05 Wh kg-1 with high power density of 11.89 kW kg-1.Furthermore,a energy density 58.47 Wh kg-1 is obtained from the LIC at a 0.5 A g-1 current density,along with 91.94%capacitance retention,even after 2100 cycles.