| Layered double hydroxides（LDH）,as electrode materials for supercapacitors,have high specific capacity,high charge discharge voltage,good rate performance,and cycling stability,making them one of the current research hotspots in new energy materials.The electrochemical performance of LDH is closely related to its chemical composition and microstructure.Transition metals nickel and cobalt have shown good performance in various electrode materials.This article constructs a three-dimensional structure of nickel cobalt LDH by regulating the preparation reaction process of nickel cobalt LDH precursors,exploring the relationship between its morphology,chemical composition,and electrochemical performance,and preparing high-performance supercapacitor electrode materials.NiCo-LDH electrode materials are prepared using a hydrothermal method to explore the effects of different Ni/Co ratios on the micro-morphology of the materials.It is found that the introduction of cobalt source can induce the transition of NiCo-LDH morphology from solid spherical to three-dimensional sea urchin-like structure,and the burr of sea urchin-like NiCo-LDH increases with the increase of cobalt source.This three-dimensional sea urchin-like structure can provide a larger volume expansion space and expose more electrochemically active sites.In the three-electrode test system,the specific capacity of NiCo-LDH with three-dimensional sea urchin structure reaches 224.56 m Ah g-1 at a current density of 1 A g-1,and its discharge specific capacity reaches 169.44 m Ah g-1even at a current density as high as 10 A g-1.The assembly of an asymmetric supercapacitor with an activated carbon cathode（NiCo-LDH//AC）shows a significant increase in specific capacity of 41.46 Wh kg-1 and a decrease in specific capacity of169.44 m Ah g-1,respectively.The asymmetric supercapacitor（NiCo-LDH//AC）assemble with an active carbon negative electrode exhibits high energy and power densities of 41.46Wh kg-1 and 1750 W kg-1,with a capacity retention rate of 81.17%after 5000 cycles.Using hexamethylenetetramine as a base source and a structure-directing agent,flower-like NiCo-LDH is prepared.In order to enhance the electrical conductivity of the material,rGO is coated on its surface using electrostatic self-assembly technology,which ensures the rapid ion/electron transport of NiCo-LDH during charge/discharge due to the unique three-dimensional structure and good electronic conductivity properties.In the three-electrode test system,the discharge specific capacity of flower-like NiCo-LDH/rGO can still reach 180.58 m Ah g-1 at a current density of 10 A g-1,indicating its excellent high-current discharge characteristics.The asymmetric supercapacitor（NiCo-LDH//CNT@rGO）assemble with homemade CNT@rGO composite gel has an energy density of 56.30 Wh kg-1 at 108.26 W kg-1 power density.The capacity retention was also89.5%after 10,000 cycles at a current density of 10 A g-1.The hollow nanocage-structured NiCo-LDH is prepared by the self-sacrificial template method using ZIF-67 as a template.Its unique hollow structure not only provides more active sites for electrochemical reactions,but also is more favorable for electrolyte transport.In the three-electrode test system,the specific capacities of NiCo-LDH with the hollow nanocage structure were 466.14,427,413.67,385,347.8,and 314.99 m Ah g-1 at 1,2,4,6,8,and 10 A g-1 current density,respectively,indicating that its excellent multiplicity performance.An asymmetric supercapacitor（NiCo-LDH//AC）is assembled with an activated carbon negative electrode,and its discharge specific capacities were119.7,123.7,110.32,106.03,100.97,and 96.3 F g-1 when the current densities were 1,2,4,6,8,and 10 A g-1,respectively.The NiCo-LDH//AC device was cycled at 10 A g-1current density for 3000 cycles with 67.33%capacity retention.Based on the above study,flower-like NiCoAl-LDH with typical hydrotalcite phase is prepared by introducing Al element,and NiCo Al-OH with more active sites and containing cationic vacancies was further obtained by alkali etching.It is found that the alkali treatment did not destroy the original morphology of NiCo Al-LDH,while the introduction of cationic vacancies further increased the electrochemical reaction active sites.In the three-electrode test system,the NiCo Al-OH electrode has a specific capacity of 259.46 m Ah g-1 at a current density of 1 A g-1,and its capacity retention rate is 94.13%after 10,000 cycles,which demonstrates superior cycling stability.The asymmetric supercapacitor（NiCo Al-OH//AC）was assembled with activated carbon with an energy density of 68.54 Wh kg-1 at a power density of 256.07 W kg-1. |
