Research On The Performance Of Hybrid Supercapacitors With High Specific Energy Nickel-based Compounds

Advanced electrical energy storage systems are urgently needed to link the rapid development of new energy resources and the mobile power applications of electrical vehicles,portable electronic devices,etc.Hybrid supercapacitors（HSCs）are actively studied due to they can possess the high power density of supercapacitors and high energy density of batteries.However,its energy density still cannot well meet the needs of practical applications.Therefore,improving the energy density of HSCs is particularly important for developing high-performance commercial HSC devices.Based on this,this article studies the high-performance battery-type electrode materials to improve the energy density of HSCs.High-performance amorphous nickel-based compounds were prepared by different methods,which improved the mismatch between the battery-type electrode and the capacitor-type electrode,thereby increasing the energy density of the HSCs.Simultaneously,a high-performance multi-metal Prussian blue analog material can be controllably synthesized,which has a wider voltage range in the aqueous electrolyte,thereby further increase the energy density of the HSCs.It is mainly divided into the following sections:（1）Amorphous nickel-based hydroxides with different cation substitutions have been synthesized by hydrolysis and conversion of the precursor in the presence of ethylene glycol,which provides a mild environment for the gradual hydrolysis of transition metal ions,giving rise to the formation of amorphous transition metal hydroxides.The amorphous hydroxides with rich grain boundaries and ion diffusion channels display significantly improved electrochemical performance than crystalline counterparts.In addition,the substitution of Ni ions by different transition metal ions further improves the charge storage performance of the amorphous hydroxides.The performance of NiCo–OH is better than that of the other amorphous nickel-based hydroxides.A hybrid supercapacitor based on amorphous NiCo–OH exhibits superior electrochemical performance with high specific power density,high specific energy density and ultralong cycling lifespan.（2）Based on the advantages of the electrochemical properties of amorphous structure and the challenge of the preparation of bimetallic amorphous compounds,a cation exchange reaction is utilized to prepare amorphous bimetal hydroxides for the first time.A cation exchange reaction can be conducted to exchange amorphous Ni（OH）₂ with Co²⁺,Mn²⁺,Cu²⁺and Zn²⁺to obtain a series of bimetal samples.The amorphous Ni–Co hydroxide delivers superior specific capacity,rate performance and cycling stability.A hybrid supercapacitor based on the prepared amorphous NiCo–OH shows both high specific energy and power performance,further confirming the outstanding performance of amorphous NiCo–OH.（3）A series of ultra-uniform transition metal ferrocyanates（MHCFs）or Prussian blue analogues were synthesized by using citrate as addictive,which found that citrate can control the nucleation and growth rate of MHCF.Therefore,a high crystallinity MHCFs with low Fe（CN）₆ vacancy and high alkali metal content were synthesized,which exhibited excellent sodium ion storage performance in both aqueous and organic electrolytes.This method is applicable to a wide range of MHCFs with different transition metals（e.g.,Co,Ni,Mn and Zn）.In the meantime,the effect of different transition metals on the Na ion storage performance of MHCFs has been investigated in aqueous electrolyte,and the transition metals in MHCFs can be used to tune the Na ion storage performance of MHCFs.The CoHCF nanocube sample displays higher performance than the MHCFs with other transition metals,which exhibits a specific capacity of 307 C g^–11 at1 A g^–1.The CoHCF nanocube sample also shows superior cycling stability with a stable cycling performance up to 12,000 cycles in aqueous electrolyte and 10,000 in the organic electrolyte.