Synthesis Of Novel Pseudocapacitive Materials And Their Application In Flexible Supercapacitors

Supercapacitors?SCs?are an important kind of electrochemical energy storage devices,with their larger power density and longer cycling lifespan,they have found wide application in fields such as electric vehicles.As electronics moves towards being flexible and wearable,energy units have become the bottleneck of the performance increase of flexible electronic devices.Recently,SCs are found to possess great potential for this application.Our approach to the field of flexible SCs mainly focuses on the design and synthesis of electrode materials with high electrochemical performance.In this study,we synthesized a whole range of novel electrode materials,and fabricated asymmetrical flexible SCs based on these materials.The details are as follows:1)Porous hollow Co3O4 with rhombic dodecahedral structures have been prepared by the calcination of a precursor ZIF-67 synthesized via a very simple approach.The electrode exhibits a large specific capacitance of 1100 F g-1 and retained more than 95.1% of the specific capacitance after 6000 continuous charge-discharge cycles.The stable porous hollow rhombic dodecahedral structure provides an ideal platform on which the relationship between the chemical and physical properties and the materials structure could be systematically investigated.The unique structure of Co3O4 obtained in this work also holds promise for a broad range of applications such as electrochemical sensing and lithium ion batteries.2)Uniform manganese hexacyanoferrate hydrate nanocubes metal organic framework?MOF?has been prepared via a simple chemical precipitation method at room temperature.Due to both micro/mesopores of the Prussian blue analogue and nanocubic structures,the manganese hexacyanoferrate hydrate nanocubes allow the efficient charge transfer and mass transport for electrolyte solution and chemical species.Thus,the manganese hexa-cyanoferrate?MHCF?hydrate nanocube electrode shows a specific capacitance of 690 F g-1,a good rate capability and cycling stability.To further improve the electrochemical performance of the materials,NH4 F was added to the MHCF solution,resulting in a novel composite material-MHCF decorated with Mn Ox nano-flowers,which showed boosted capacitance.?1200 F g-1 vs 400 F g-1,10 A g-1?3)Cobalt-manganese-nickel oxalates micropolyhedrons are successfully synthesized by a simple room temperature chemical co-precipitation method.The material achieves a specific capacitance of990 F g-1?at current density of 0.6 A g-1?.A flexible solid-state asymmetric supercapacitor is built based on Co_0.5Mn_0.4Ni_0.1C₂O₄·n H2 O and reduced graphene oxide.The material was used as the electrode material along with reduced graphene oxide for asymmetric supercapacitor which showed a maximum volumetric specific capacitance of 0.46 m Wh cm-3 at the current density of 0.5 m A cm-24)Amorphous nickel pyrophosphate microstructures have been synthesized by calcination of the ammonium nickel phosphate hydrate microstructures in air at 350?C.A specific capacitance of1050.0 F g-1 is achieved?at the current density of 500 m A g-1?.Flexible solid-state electrochemical energy storage devices with amorphous nickel pyrophosphate microstructures and graphene nanosheets as positive and negative electrode materials have been successfully assembled.The device shows a maximum volumetric energy density of 0.50 m Wh cm-3?0.1 m A cm-2?and a long cycle life with little capacity decay even after 6000 cycles,with good mechanical flexibility.5)A flexible all-solid-state asymmetric micro-supercapacitor based on lamellar K₂Co₃?P₂O₇?₂·2H₂O)nanocrystal whiskers and graphene nanosheets has been fabricated by inkjet printing in a simple and cost-effective way.A facile method to synthesize lamellar K₂Co₃?P₂O₇?₂ 2H2 O nanocrystal whiskers under a mild hydrothermal condition is also established.The assembled micro-device exhibited a high specific capacitance?6.0 F cm-3?,good rate/flexibility stability and long-cycling stability?5000cycles?with a maximun energy density of 0.96 m Wh cm-3,demonstrating great promise for applications in flexible all-solid-state micro-supercapacitors.