Flexible diamond fiber power high energy density zinc supercapacitors

Keywords: diamond, capacitor |2020-09-09 10:49:48| source: Energist

The research background of the increasing wearable intelligent electronic products promotes the sustainable development of flexible energy storage devices.With its advantages of good flexibility, small size, light weight and braid, fibrous supercapacitors are considered as ideal flexible energy storage devices.But low energy density limits its application...

The research background

The growing number of wearable intelligent electronic products promotes the sustainable development of flexible energy storage devices.With its advantages of good flexibility, small size, light weight and braid, fibrous supercapacitors are considered as ideal flexible energy storage devices.But low energy density is the main factor restricting its application.

Work is introduced

Recently, A flexible diamond fiber (a core-shell structure with carbon fiber as the core and boron-doped diamond wrapped by peripheral CVD deposition) was successfully prepared by Jiang Xin/Yang Nianjun research group of Siegen University, Germany.Because the composite material effectively combines the characteristics of carbon fiber and boron-doped diamond, the flexible fiber supercapacitor anode material can realize its excellent comprehensive performance.By combining with the characteristics of high energy storage, safety and low cost of zinc-ion hybrid capacitor, this paper constructs a high performance zinc-ion hybrid capacitor with the flexible diamond fiber as the positive electrode and the diamond fiber coated with zinc nano-sheet as the negative electrode.It is worth mentioning that the flexible diamond capacitor has high power density and high energy density both in terms of volume and mass calculation, and its performance does not change under different bending angles.This work opens up a prospect for the application of flexible diamond capacitors in wearable electronic devices.The article appears in Adv. Energy Mater.Suga, a doctoral candidate at The University of Siegen in Germany, was the first author.

The statement

An effective way to realize high energy density fibrous supercapacitors is to design and prepare new high performance fiber electrode materials.In recent years, boron-doped diamond as an SP3-carbon electrode material has attracted much attention due to its wide potential window, high chemical stability and environmental friendliness.However because of the boron doped diamond are deposited in the absence of a flexible hard substrate (such as silicon or metal substrate), or have been reported since the support diamond paper or network structure is flexible but its mechanical stability and ion limited, charge transport, therefore the diamond film flexible electronic devices (such as ah super capacitor) rare report.The diamond fiber designed in this paper is used as the positive electrode material of flexible fiber-like supercapacitor to realize the excellent performance of both diamond and flexible fiber.

Another way to increase the energy density of fibrous supercapacitors is to build hybrid capacitors.Because it can combine the energy storage mechanism of traditional supercapacitors with the Faraday process of batteries, high energy density and high power density can be realized simultaneously.Based on the advantages of high energy storage, safety and low cost, a flexible diamond zinc-ion hybrid capacitor is designed.The high pseudocapacitance of the flexible diamond capacitor comes from three aspects :(1) the hybrid energy storage mechanism of the zinc ion capacitor on the positive and negative poles;(2) Pseudocapacitance from the oxidation functional group on the surface of diamond fiber;(3) The oxygen reduction reaction between diamond fibers and dissolved oxygen in the electrolyte provides additional capacitance during the discharge process.

The prepared flexible diamond fiber is evenly covered with a dense boron-doped diamond film on the carbon fiber surface.The introduction of titanium carbide intermediate layer significantly improves the quality of diamond film grown on carbon fiber, and it also helps to reduce the resistance of charge transfer between electrolyte and diamond fiber electrode.        

FIG. 1. Material characterization of flexible diamond fibers.

The flexible diamond zn-ion hybrid capacitor has an energy density of 70.7WH kg-1 at a power density of 709.0W kg-1.Even at the high power density of 4395.3 W kg-1, the energy density can still be maintained at 16.2Wh kg-1.At a high power density of 4395.3w kg-1, the charging and discharging time of the whole capacitor is 25.7s.Both in terms of volume and mass, the flexible diamond capacitor exhibits a higher power density and energy density than other batteries and capacitors.Under the condition of high current density 10 A g-1, the specific capacitance is still 89.9% after 10 000 cycles.As a demonstration, the two FLEXIBLE diamond capacitors in series can supply 16 LED lamps to work continuously over 70s.It is worth noting that the total mass of the positive and negative electrodes is only 1.6 mg.

Figure 2. Electrochemical performance of flexible diamond capacitor

The diamond supercapacitor shows good flexibility.Under the bending deformation of 30°, 60° or even U bending, the electrochemical performance of the device is almost unchanged.Even after 1000 bending experiments of 60°, the specific volume was reduced by only 2.43%.

FIG. 3. Flexible testing of flexible diamond capacitors

conclusion

The flexible diamond fiber prepared by this work is a core-shell structure with carbon fiber as core and boron-doped diamond wrapped by CVD deposition on the surface.Thanks to the superior performance of carbon fiber and boron-doped diamond, the flexible diamond capacitor constructed by the material shows excellent performance, providing a broad prospect for the application of diamond in flexible electronic devices (such as wearable electronic devices).In addition, as a widely applicable strategy, the method of preparing flexible electrodes in this paper can provide a feasible scheme for the design and synthesis of flexible electronic device materials in the future. 
 

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