Preparation Of Nickel Cobalt Layered Double Hydroxide And Its Application In Micro Energy Storage Devices

The rapid development of miniaturized,wearable electronics has led to higher requirements for planar miniaturized electrochemical energy storage systems with high performance,high safety,long life,and integrability.For example,in terms of the shape,size,mechanical properties,stimulus response capability,and environmental adaptability of the device,it is required to achieve design,self-healing,integration,and miniaturization.Compared with traditional energy storage devices with a diaphragm sandwich structure,the planar interdigitated structure has significant advantages such as short ion transmission distance,long cycle life and excellent power density.As a micro-unit that can be integrated in a large number of planes,it has become the main energy supply object for microelectronic devices.In addition,the planar interdigitated energy storage device has a convenient and space-saving connection method as well as a flexible shape and size design,which can greatly improve the output voltage and the energy density of the energy storage device.High conductivity and a large number of charge storage reaction sites are key features of high-performance energy storage materials.Layered double hydroxides（LDHs）,commonly known as hydrotalcites,are layered structures composed of multiple positively charged metal layers and anions that balance charges in the middle.Among them,nickel-cobalt layered double hydroxide（Ni Co-LDH）is widely used as an energy storage material due to its strong electrochemical activity,high theoretical specific capacity,adjustable layered structure,and simple synthesis process.However,the poor conductivity of the material itself and the microstructure that is difficult to maintain during the long-term cycle make the charge storage capacity of energy storage devices still have a lot of room for improvement.Based on this,this thesis improves the conductivity and structural stability of Ni Co-LDH through interface regulation,and prepares an in-plane interdigitated,integrable micro energy storage device.The following are the main research findings:（1）Using ITO NWs and polypyrrole（PPy）to improve the conductivity and microstructural stability of Ni Co-LDH through interfacial modulation,a high-performance in-plane interdigitated asymmetric micro-supercapacitor was prepared.First,the three-dimensional ITO NWs conductive network was prepared by chemical vapor deposition（CVD）as the current collector of the active material.The conductive network greatly increased the loading of the active material and accelerated the rapid charge transfer.Ni Co-LDH nanosheets were successfully grown on ITO NWs by electrodeposition.In order to prevent the agglomeration and shedding of Ni Co-LDH nanosheets and keep the microstructure stable,a layer of PPy was coated on the composite electrode obtained above by electropolymerization.The coating of PPy provides an additional electron transport path in addition to ITO NWs,and as an outer shell,it can also prevent the large expansion and contraction of the Ni Co-LDH structure during the charge storage process,thereby improving the cycle stability of Ni Co-LDH.The"water-in-salt"（9.2 M Na Cl O₄·H₂O）electrolyte was selected to expand the electrochemical stability window,the obtained PPy@Ni Co-LDH@ITO NWs electrodes have a wide voltage range from 0 to 1.3 V,a maximum areal capacitance of598 m F cm^-2 at a scan rate of 5 m V s^-1,and a capacitance retention rate of 83%after10000 charge-discharge cycles,demonstrating the composite electrode has excellent long-term cycle stability.Benefit from the Ni Co-LDH layered structure coated with PPy grown on ITO NWs and the WIS electrolyte with a wide voltage window,The assembled positive electrode PPy@Ni Co-LDH@ITO NWs//negative electrode PPy@Fe OOH@ITO NWs asymmetric MSCs have an operating voltage range of 0～2.5V and a maximum areal capacitance of 63.04 m F cm^-2,and it provides a high volume energy density of 32.2 m Wh cm^-3 when the power density is 294.1 m W cm^-3.In addition,the series-parallel lighting test further proves the good consistency of the device.（2）Laser etching technology assisted synthesis of membrane-free aqueous high-safety Zn//Ni Co-LDH@ITO NWs@CC planar micro-zinc batteries.Based on manually manipulated carbon cloth（CC）and zinc foil（Zn）,the conductivity and microstructural stability of Ni Co-LDH was improved by using ITO NWs grown on CC（ITO NWs@CC）as current collectors through interfacial regulation.Afterwards,the ITO NWs@CC and Zn were respectively etched into two independent fingers of the same size by laser etching.Ni Co-LDH was electrodeposited on the ITO NWs@CC finger to obtain the cathode Ni Co-LDH@ITO NWs@CC,with Zn as the anode,and assembled into Zn//Ni Co-LDH@ITO NWs@CC MBs on the glass slide with the aid of AB glue,conductive gel and CC wire.The three-dimensional ITO NWs@CC conductive network can increase the loading of active materials,facilitate the fast transfer of charges,and buffer the large expansion and contraction of active materials during long cycling,thereby improving the performance and lifetime of ZMBs.The aqueous ZMBs provided an areal capacity of 0.56 m Ah cm^-2(453.5 m Ah g^-1),achieved a maximum energy density of 798.4μWh cm^-2(649.9 Wh kg^-1)and a power density of4.1 m W cm^-2(3.29 W kg^-1),exhibiting satisfactory rate performance(63.8%capacity retention from 1 m A cm^-2 to 3 m A cm^-2)and excellent cycling stability(101%capacity retention after 1000 cycles at 1 m A cm^-2).In addition,the series-parallel and lighting tests of ZMBs illustrate the consistency of the devices.Therefore,the synthesis of fast and simple planar interdigitated ZMBs provides a reference for the next generation of high-performance,green-friendly and scalable planar micro-energy storage systems.