Preparation And Supercapacitor Performances Of Nickel-aluminium Layered Double Hydroxide And Itscomposites

Supercapacitors have attracted considerable attentions due to their high power density,high charge/discharge rates,and long cycle life performance.They are considered as one of the most promising electrochemical energy storage devices.In this study,a simple urea-assistant-strategy was developed to synthesize ultrathin Ni-Al LDH nanosheets.Based on this,Cu₂O@Ni-Al LDH core-shell structure composite and Ni-Al LDH/3DG self-supporting structure were designed and prepared,and explored their electrochemical performance as supercapacitor electrode materials.The main works are follows:1.Ultra-thin Ni-Al LDH nanosheets with high surface area,were successfully prepared by urea-assisted hydrothermal method,which showed excellent electrochemical performance.In the voltage range of 0-0.55 V,the specific capacity was 1933 F·g^-11 at the current density of 2 A·g^-1,and the reversible capacity still reached 1665 F·g^-1 at the current density of 30 A·g^-1.The discharge capacity can still be recovered to 433 F·g^-1 after 3000cycles.After calcined at 400°C,the cycle performance of the Ni-Al LDO was tested in a voltage range of 0-0.5 V.The initial discharge capacity was 662.57 F·g^-1,and the discharge capacity could still remain at 325.71 F·g^-11 after 2,500 cycles at a current density of 2 A·g^-1.The main reasons of superior electrochemical performance are shown as follows:on the one hand,layered double hydroxides are capable of anion exchange between layers,which are conducive to ion transfer;on the other hand,the large lateral size and ultrathin thickness of two-dimensional ultrathin structures endow them with ultrahigh specific surface area,making them highly favorable for surface active applications.2.Cu2O was used as a template to prepare core-shell Cu2O@Ni-Al LDH by solvothermal method,and the composite material electrochemical performance was explored as supercapacitor anode material.The initial capacities of Cu₂O@LDH-2,Cu₂O@LDH-1 and Cu₂O are 250 F·g^-1,305 F·g^-1 and 194.5 F·g^-1,respectively.However,the discharge capacity of Cu₂O@LDH-2 could still remain at 1019 F·g^-11 after 12,000 cycles,and the discharge capacity of Cu₂O@LDH-1 decreases to 457 F·g^-1 from 525 F·g^-1,which may be due to the poor Ni-Al LDH and result in poor cycling stability.The discharge capacity of Cu₂O was maintained at 264 F·g^-1 after 12,000 cycles.It was proved that the composites have better cycle performance compared with the pure Cu₂O cube.This is mainly attributable to the fact that the Cu2O@Ni-Al LDH core-shell structure not only increases the contact area between the electrode material and the electrolyte,but also facilitates the charge transfer,effectively prevents the deposition of the two-dimensional Ni-Al LDH,and the volumetric expansion of the Cu₂O cube was alleviated during the process.3.The Ni-Al LDH nanosheets were directly grown on the three-dimensional graphene foam network through simple hydrothermal method,and showed excellent electrochemical performance as a binder-free electrode material.In the initial stage,the maximum discharge capacity was 561.86 F·g^-11 at a current density of 5 A·g^-1,and the discharge capacity was maintained at about 615 F·g^-1 and the Coulomb efficiency was above 90%after 4500 cycles.Ni-Al LDH/3DG composites exhibit excellent cycling stability as supercapacitor electrode materials.