Design And Preparation Of Self-supporting Porous Carbon-based Composite Materials And Research On The Performance Of Compressible Supercapacitor

During practical applications,flexible electronic devices are inevitably subjected to deformation by varying degrees of external forces.However,conventional energy storage systems for such devices may malfunction due to mechanical fracture under high strain,leading to serious safety hazards like toxic electrolyte leakage,device fire or even explosion.To address these challenges,there is an urgent imperative to develop flexible energy storage devices that can withstand external deformation without significant performance degradation.Supercapacitors represent one of the most promising candidates for flexible energy storage systems.Nitrogen-doped carbon foams（NCF）possessing low density,high porosity and a large specific surface area are deemed as optimal materials for constructing compressible supercapacitors.However,despite current research progress,the development of compressible supercapacitors with both mechanical and electrochemical properties remains a significant challenge.This paper provides a review of the research progress on flexible compressible supercapacitors and introduces the current status of compressible electrode materials.The modification of free-standing 3D carbon foams by spinel oxides,self-catalytic nitrogen-doped carbon nanotubes（NCNTs）and conducting polymers is explored,which in turn enhances their mechanical and electrochemical properties.The application of these composite electrode materials in compressible supercapacitors is also investigated in depth as follows:（1）Three-dimensional NCF is being explored for fabrication of a compressible supercapacitor with pseudocapacitive spinel.Zn Fe₂O₄ nanosheets grown on highly compressible NCF substrates can deliver significant pseudocapacitance at negative potentials.By combining it with Ni Co₂O₄/NCF cathode,an all-pseudocapacitive asymmetric supercapacitor device was assembled.The composite electrodes combine the superior electrochemical and mechanical performances with maximum compressive strain of 80%and durability（up to 500 cycle strains at 60%strain）.The asymmetric supercapacitor demonstrates an energy density of 11.84 Wh kg^–1(0.39 m Wh cm^–3)at 300 W kg^–1(10 m W cm^–3),with 96.5%capacitance retention after 15,000 charge–discharge cycles at the compressive strain of 60%.（2）To address the problem that the mechanical strength of the composites prepared in the previous work was reduced,this work presents a strategy for integrating mechanical compressibility and excellent electrochemical properties into a single device.We demonstrate a compressible and high-performance supercapacitor based on NCF with hierarchical carbon nanotubes.Hierarchically structured Fe₃C@NCNTs/NCF and Ni@NCNTs/NCF have been synthesized via a simple and universal self-catalytic strategy.The hierarchical structural features of NCNTs serve as a cushion when the composite is subjected to an external force,exhibiting excellent mechanical properties with a maximum compressive strain of 80%and fatigue resistance of 1,000 cycles.Moreover,the different electroactive potentials of the transition-metal species in the composites provide the assembly with a maximum operating voltage of 1.4 V,which shows a maximum energy density of 10.74 Wh kg^–1 at the power density of 179.2 W kg^–1,and retains 88.4%of the original capacitance after 20,000 charge–discharge cycles,even at a strain of 80%.（3）A deformable and electrochemically stable PEDOT is proposed as a"Polymer Chainmail"for compressible electrodes.The effect of doping PEDOT with anions of different volumes and charges on the performance of PEDOT and its intrinsic mechanism were investigated by density flooding theory calculations,and the in-situ chemical oxidation polymerization method was used as a theoretical guide to prepare PF₆^–doped PEDOT-coated nitrogen-doped carbon foam composites（PEDOT–PF₆^–/NCF）,which significantly improved the mechanical properties,multiplicative properties(81.1%at 20 m A cm^–3),and cycling stability（95.9%of the initial capacity after 20,000 cycles）of the composite.The symmetrical supercapacitor assembled on the basis of PEDOT–PF₆^–/NCF composite reached a maximum energy density of 28.3 Wh kg^–1(power density of 128 W kg^–1),and when the power density reached 2,560 W kg^–1,the energy density could still be maintained at 16.5 Wh kg^–1 after 4,000cycles of charge and discharge,maintaining more than 85%of the initial capacity.