Synthesis Of Composite Nickel Hydroxide And Its Pseudo-capacitance Properties

With the rapid development of wearable and portable electronic devices,flexible,lightweight and environmentally friendly flexible energy storage devices require higher energy density and storage rate of energy storage elements.In this paper,a new nickel hydroxide pseudocapacitor material with high specific capacitance,super high rate performance and long cycle life is designed and fabricated,aiming at the low power density and poor cycle performance of secondary batteries and the low energy density of traditional double-layer capacitors.The main research contents of this paper are as follows:(1)In this paper,a layer of uniform Ni(OH)2 nanosheet array is synthesized on the surface of nickel Foam by complexation precipitation method,and Ni foam@Ni(OH)2 composite material was formed.The morphology and crystal form of the composite are characterized by SEM and XRD.CV,constant current charge-discharge,Tafel and AC impedance are used to test the samples.The results of electrochemical tests show that the optimum Ni(OH)2 load of the composite is 0.4 mg cm-2,and its specific capacitance is 2410.6 F g-1,and the specific capacitance is still 1911.7 F g-1 at a super current density of 200 A g-1.After 50,000 cycles,the specific capacitance maintained 98.6%(100 A g-1)of its maximum specific capacitance,indicating that the composite has the advantages of high specific capacitance,good rate performance and long cycle life.(2)A Ni Foam@Ni(OH)2 composite is synthesized by in-situ growth method in order to improve the shortcomings of low utilization of raw materials,uneven distribution and easy to fall off of nickel hydroxide.The specific capacitance of the composite is up to 2422.1 F g-1(10 A g-1).Moreover,the composite has excellent rate performance and cycle stability.2301.4 F g-1 can still be obtained at a super high current of 200 A g-1.After 100,000 cycles,the capacity maintains 97.2%(100 A g-1)of the initial capacity.Moreover,the sample has good flexibility.After 100 bendings,its capacity retention rate is 93.6%.(3)In order to further improve the specific capacitance of the material,other metal ions(expressed as M)is added into the main body of Ni(OH)2 by double complexation precipitation method to prepare nickel base double hydroxides with good electrochemical properties and stable structure of a-Ni(OH)2.SEM,XRD and electrochemical measurements show that the nickel base layered double hydroxides doped with Mn,A1 and In elements have a stable structure of a-Ni(OH)2.However,the structure of NiIn-LDHs is solid spherical,which is not conducive to the diffusion of electrolytes and ion transport,resulting in the specific capacitance of NiIn-LDHs is lower than that of pure nickel hydroxide.The electrochemical properties of Ni-Mn dihydroxides and NiAl-LDHs are better than that of pure Ni(OH)2 because of their excellent 3D spherical structure of nano-sheet stacking.In order to obtain more excellent Ni/M LDHs,the synthesis conditions of Ni-Mn dihydroxides and NiAl-LDHs are further optimized.(4)Ni-Mn dihydroxides material is synthesized by controlled complex precipitation crystallization.SEM and XRD show that the material is a 3D spherical structure of a-Ni(OH)2 with nano-sheet accumulation.The electrochemical tests show that the optimum Mn content of Ni-Mn dihydroxides is 10%.The specific capacitance of the sample can reach 2735.8 F g-1(1 A g-1),and the specific capacitance of the material is up to 1146.2 F g-1 even at 100 A g-1.After 10,000 cycles,the capacity retention rate of the material is 95.6%(10 A g-1).(5)NiAl-LDHs is prepared by the double complexation-precipitation method.SEM and XRD show that the material is a spherical structure of a-Ni(OH)2 with three-dimensional nano-flakes.XRD and XPS are used to test the sample under different charge and discharge conditions.It is verified that the conversion reaction between a-Ni(OH)2 and ?-NiOOH is a stable and reversible process.The results of electrochemical and XRD measurements show that the optimum content of A1 is 18%.The specific capacitance of the sample can reach 2761.2 F g-1(1 A g-1)which is much higher than that of pure Ni(OH)2.Moreover,the NiAl-LDHs has high rate charge-discharge performance and excellent cycle stability.The NiAl-LDHs can still give a specific capacitance up to 2216.8 F g-1 at 20 A g-1.The specific capacitance of the NiAl-LDHs keeps 97.8%of the initial capacitance after 5000 cycles(10 A g-1).(6)Ni Foam@NiAl-LDHs composites are prepared by the in-situ growth method to improve the electrochemical properties of NiAl-LDHs materials.SEM and XRD show that the NiAl-LDHs nanosheet arrays are uniformly prepared on the surface of the nickel foam,and NiAl-LDHs nanoplates are stable for the structure of the ?-Ni(OH)2.The electrochemical tests show that the composite has a high specific capacitance(3088.8 F g-1 at 10 A g-1).Moreover,the composite has excellent rate performance and can still reach 2768.9 F g-1 at a super high current of 200 A g-1.After 70,000 cycles,the capacity retention rate is 98.2%(100 A g-1),which indicates that the material has excellent cycling performance.