Preparation And Electrochemical Performances Of NiCo₂S₄-based Planar Flexible Solid-state Supercapacitors

Recently,manufacturing flexible,miniature,large-area and low-cost energy storage units has received great attention with the rapid development of flexible electronic devices.Supercapacitors not only feature high power density and fast charging/discharging rate,they are also easier to achieve miniaturization,integration,flexibility,and has gained prominence in the studies of micro energy storage devices.Among them,the all-solid-state interdigitated supercapacitor is attached to a flexible film substrate and has a planar two-dimensional structure,which is easier to integrate with other portable microelectronic systems,and helps to achieve higher integration and flexibility of flexible electronic devices.In general,the fabrication of interdigital architecture relying on photolithography,plasma etching and direct laser writing etc.involves complicated processes,high cost,and is not suitable for mass production.Also,the employment of electrode materials is usually confined to the traditional carbon and oxide materials,which may probably limit the performance enhancement.Therefore,it has become a new challenge to choose an efficient and low-cost research path in the preparation process and electrode materials to study the preparation of planar interdigital supercapacitors with high specific capacitance and high power density.Therefore,it has become a new challenge to choose an efficient and low-cost research path in the preparation process and electrode materials to study the preparation of planar interdigital supercapacitors with high specific capacitance and high power density.In this Dissertation,the nickel-cobalt bimetallic sulfide Ni Co₂S₄synthesized via a one-step sulfurizing process.The morphology and crystallinity of NCS were adjusted by adjusting the hydrothermal temperature.The NCS was prepared into ink,and the current collector and interdigitated structure electrodes were fabricated on the PET substrate with a simple shadow mask printing preparation technique,Finally,a flexible solid-state planar interdigital supercapacitor was assembled with gel electrolyte.In order to improve the conductivity and capacitive activity of electrode materials,subsequent attempts compounded with g-C₃N₄and activated carbon（AC）respectively.The results show that the composite material improves the conductivity,cycle rate and stability of NCS material,and further improves the specific capacitance of NCS.The prepared supercapacitor has high power density and energy density,and exhibits excellent mechanical stability and electrochemical stability.The main research results are as follows:（1）NCS nanocrystals were synthesized via a simple one-step sulfurizing process using Ni Cl₂·6H₂O and Co Cl₂·6H₂O as nickel and cobalt sources,and thiourea as vulcanizing agent.Experiments shows that single-phase NCS was obtained at 180°C,in spherical shape,about 10.7 nm.The specific capacitance of the electrode material is1401F/g at a current density of 1 A/g.Subsequent assembly into NCS-based planar interdigital solid-state supercapacitors,The device works under a voltage window of-0.45～0.6V and maintains the quasi-rectangular shapes even at 200 m V/s.The specific capacitance can reach 13.6 m F at a current of 0.35 m A/cm²,and a high energy density of2.1μWh/cm²is delivered at a power density of 0.189m W/cm².（2）NiCo₂S₄/g-C₃N₄nanocomposite material has been prepared via a one-step solvothermal process using nickel and cobalt nitrate hexahydrate as raw materials and thiourea as vulcanizing agent,in the present of pyrolysis g-C₃N₄.the Ni Co₂S₄particles with a size of～47 nm dispersedly grew on the g-C₃N₄nanoplates,The area specific capacitance of the nanocomposite electrode material is 9.1 F/cm²at a current density of 10m A/cm².Subsequent assembly into an all-solid-state interdigitated supercapacitor.The assembled supercapacitor can operate at the voltages of-0.2～0.6V and remained stable at scanning rate up to 500 m V/s,revealing good rate performance.The area specific capacitance of the device is 5.7 m F/cm²at a scanning rate of 20 m V/s,and it shows an energy density of 0.56 m Wh/cm³at the power density of 17.5 m W/cm³.（3）NiCo₂S₄/AC nanocomposite material has been prepared via a one-step solvothermal process using nickel and cobalt nitrate hexahydrate as raw materials and thiourea as vulcanizing agent,in the present of AC.the Ni Co₂S₄particles dispersedly grew on the AC nanoplates.The electrochemical test results showed that the introduction of AC significantly enhanced the electrochemical activity of NCS,and the equivalent series resistance of NCS/AC electrode is 1.2Ω.The area specific capacitance of the nanocomposite electrode material is 3.15 F/cm²at a current density of 10 m A/cm².The composite electrode is formulated into ink,and the interdigitated structure electrode is formed by the above process,Then the flexible,all-solid-state interdigital supercapacitor was obtained by coating a layer of gel electrolyte.The assembled supercapacitor can operate at the voltages of-0.2～0.6V and remained stable at scanning rate up to 200 m V/s,revealing good rate performance.The area specific capacitance of the device is 6.37m F/cm²at a current of 0.036 m A/cm²,and it shows an energy density of 0.56 m Wh/cm²at the power density of 11.5 m W/cm².