High Performance In-plane Micro-supercapacitors:Active Electrode Materials Design And Preparation Strategies

In-plane micro-supercapacitors（MSC）,which is a kind of emerging energy storage devices,have attracted intensive attention due to their intriguing merits involving high power density,large charge/discharge rate,excellent cycling stability,and fast frequency response.Moreover,they hold promising application potential for integration into microelectromechanical systems（MEMS）,such as miniaturized,wearable and portable electronic devices.With the rapid development of modern science and technology,the demand for the electrochemical performance of MSC is constantly increasing.At present,developing advanced in-plane MSCs with high energy density,remarkable rate capability,flexibility and integration capability,which is impeded by the limitation of highly-active electodematerials and complicated preparation prcocesses,is urgently desirable for the next generation electronic systems.However,this target still remains a great challenge.Herein,high-performance in-plane MSCs with wide application scopes have been achieved by developing active electrode mateirals,optimizing device structures and developing device fabrication strategies.The specific contents are as follows:（1）Core-shell-type one-dimensional（1D）conjugated microporous polymers（CMPs）were synthesized by layer-by-layer method and random method using single-walled carbon nanotubes（SWNTs）as structural-directing templates.The resulant CMPs possessed high specifc surface areas of up to 623 m² g^-1,and layered 1D CMP exhibited stronger electronic interactions between p-type CMPs and n-type CNTs than random 1D CMP.The CMPs were further used as precursors to prepare 1D ternary doped（B/N/S）porous carbons through direct pyrolysis.After that,in-plane MSCs were fabricated by ink-spraying process.The obtained MSC based on layered 1D porous carbon exhibited better capacitive performance with areal capacitance of 4.3 mF cm^-2than MSC based on random 1D porous.（2）A family of nano-sandwiched MHCF（Metal Hexacyanoferrate,M=Cu,Ni,Co,Fe）/graphene hybrid thin films（thickness of²μm）with interdigital patterns were concisely prepared through a step-by-step filtration method.According to varied intrinsic redox-active potential windows of these hybrid thin films,in-plane asymmetric MSCs（AMSCs）were manufactured using CuHCF/graphene as a positive electrode,and NiHCF/graphene,CoHCF/graphene,or FeHCF/graphene as a negative electrode.As-prepared AMSCs exhibited outstanding capacitive performance,offering high operating voltage windows of up to 1.8 V,superior areal capacitances of up to 19.84mF cm^-2,and ultra-high energy densities of up to 44.6 mW h cm^-3.Meanwhile,the resultant AMSC also exhibited long cycling stability（96.8%initial capacitance maintained after 5000 charge/discharge cycles）,excellent mechanical flexibility and integration capability.（3）The precise modification of[Fe（CN）₆]vacancies within the Prussian-blue network via coordination of pyridine units into Fe（III）was firstly achieved using an in-situ growth method.A series of pyridine-modified Prussian-blue（PBpy）thin films with rationally controlled nanoscale thicknesses（30 nm-150 nm）can be directly in-situ grown on the gold interdigital current collectors.As confirmed by experimental results and density functional theory calculation,the precise vacancy modification within Prussian-blue network improved film-forming property,hydrophilicity,and electrochemical activity of thin films.The resultant PBpy-based MSCs exhibited promising electrochemical performance,offering volumetric capacitances of up to 347F cm^-3 and superior volumetric energy densities of up to 12.1 mWh cm^-3.The achieved ultra-low RC time constant（τ₀）of 0.038 ms for PBpy-based MSCs was the best value among the state-of-the-art in-plane MSCs.Moreover,PBpy-based MSCs with remarkable mechanical flexibility can be highly desirable for portable and wearable appliances.（4）Highly flexible metal organic frameworks（MOF）（named Cu₃（BTC）₂）films（thickness of³μm）were directly grown on copper substrates by an efficient and simple epitaxial growth method.Functional organic molecules（TCNQ,BQ,PMDI）were doped into the pore structure of Cu3（BTC）2 for improving the conductivity of films.The experimental results demonstrated that the doping could make the guest of organic molecules interact with the host of Cu3（BTC）2 and regulated the band gap structures of Cu₃（BTC）₂.Thereby,the electrical conductivities of the Cu₃（BTC）₂ films were finally improved with a maximum enhancement of 41 times.The in-plane MSCs were fabricated by using doped Cu3（BTC）2 films with interdigitated pattern as positive electrodes and activated carbons as negative electrodes.The obtained MSCs exhibited excellent capacitive behavior with areal capacitances of up to 95.1 mF cm^-2,good flexibility and integration potential,showing broad application prospects.