| Flexible supercapacitors as important energy storage units are crucial for intelligent wearable electronic devices.However,many non-electrochemically active components in electrode design are included in the fabrication of flexible supercapacitors,such as binder,conductive additives and current collectors,causing more dead weight and volume in the device.Therefore,it is still challenging to realize high gravimetric and volumetric energy density performance at the device level.In addition,interfacial separation occurs between the active material and the substrate,leading to electrode failure by conventional coating of the electrode to increase the loading and thickness of the active materials.The longer distance of electron transfer and larger resistance of ion transport seriously affect the electrochemical performance of the electrode.Therefore,developing the flexible and lightweight electrode design strategy and optimizing the loading conditions of electrode materials are of great significance in improving the practical energy density of flexible supercapacitors.In this paper,graphite paper（GP）was chosen as flexible substrate because of its excellent conductivity and inexpensive cost.GP with a density of 1 g cm-3and a thickness of 25μm shows the advantages of thinness and lightness compared with other various flexible substrates.Three-dimensional carbon nanowire network（CNW）was in-situ grown on GP surface by constant current electrodeposition and carbonization process.Polyaniline（PANI）was further loaded on CNW by chemical oxidation to obtain PANI coated three-dimensional carbon nanowire network flexible electrode（CNW@PANI/GP）with high proportion of active material.We investigated the effects of carbonization temperatures and chemical oxidation parameters on electrochemical performance of CNW@PANI/GP flexible electrodes.The results show that polypyrrole nanowires polymerized on GP substrate with a current density of 1.5 m A cm-2and a deposition time of 2400 s can generate the appropriate network morphology.Three-dimensional CNW electrodes with a thickness of 10μm and high graphitic-N ratio obtained at 900℃can achieve area-specific capacitance of 82.9 m F cm-2,at a current density of 0.5 m A cm-2.The optimal electrochemical performance of CNW@PANI/GP flexible electrode was acquired by polymerization at aniline concentration of 0.9 M,which exhibits area-specific capacitance of 1117.26 m F cm-2,at a current density of 0.5 m A cm-2.Furthermore,we assembled a flexible solid-state supercapacitor based on CNW@PANI/GP electrodes to evaluate its specific capacitance and energy density from whole device level,and tested the electrochemical stability of the device under different bending states as well as cycling performance.The total thickness and mass of CNW@PANI/GP based flexible supercapacitor are 148μm and 83.6 mg,respectively.The whole device can achieve maximum area-specific capacitance of292.9 m F cm-2,indicate a high mass-specific capacitance of 22.4 F g-1and a volumetric specific capacitance of 19.8 F cm-3,superior to other reported flexible supercapacitors,corresponding the maximum gravimetric energy density of 1.99 Wh kg-1and volumetric energy density of 1.76 m Wh cm-3,respectively.The flexible device has no significant capacitance loss at any bending angles,and shows a capacitance retention rate of 79.1%after 1000 cycles.The results show that CNW@PANI/GP flexible electrodes can be obtained without any binder and conductive additives.The thin and light GP substrate reduces the mass and volume percentage of inactive components in the flexible electrode,resulting in high specific capacitance and energy density at the CNW@PANI/GP flexible device level.The CNW@PANI/GP flexible electrodes with simple preparation process have broad application prospects,which provides ideas for designing lightweight flexible supercapacitors and enhancing practical energy density of the devices. |
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