Study On The Preparation Of Nickel And Cobalt Compounds And Their Energy Storage Performance

Hybrid supercapacitors are being actively pursued because they combine the advantages from both supercapacitors and batteries for high-power and high-energy performance.However,the low rate performance or cycling stability of battery materials cause a mismatch with the capacitor electrode and this is still a big challenge for the practical application of hybrid supercapacitors.Therefore,exploring electroactive materials with high rate and cycling performances is gaining increasing focus and becoming particularly important for hybrid supercapacitors.Based on the synergistic effect of multi-metal ions and the electrochemical regulation effect of coordination anions,this thesis designed a serious of high-performance nickel-cobalt bimetallic compounds,aiming to further improve the specific capacity,rate performance and cycle stability of nickel-cobalt compounds.Based on these,we concentrated on synthesis and preparation of binary nickel-cobalt hydroxides,sulfides and selenides,which are mainly divided into the following several parts:?1?Amorphous hydroxides with different metal compositions have been investigated because they have abundant active sites and ion diffusion channels owing to their disordered structure.A precursor conversion method was developed to synthesize ultra-uniform nanospheres containing different Ni to Co ratios,which exhibits ultra-high electrochemical activity.At the same time,amorphous hydroxides with high electrochemical activity,rate performance and cycling performance were successfully achieved by adjusting the nickel and cobalt components.As a result,the Ni_0.67Co_0.33?OH?₂exhibits the best specific capacity of 833 C/g at 1 A/g and retains 65%of capacity value at50 A/g.A hybrid supercapacitor based on the amorphous Ni_0.67Co_0.33?OH?₂ was assembled,which shows superior electrochemical performances include high specific power capability,high specific energy density and ultralong cycling lifespan.?2?Porous M₃S₄?M=Ni,Co?samples with different Ni to Co ratios have been synthesized by anion exchange-based precursor conversion method.Wherein,the anions exchange causes outer motion and recombination of transition metal ions with S^2-,giving rise to a porous microstructure enriched with electroactive edge sites.The synergy between Ni and Co results in superior electrochemical activity for high specific capacity performance.The M₃S₄ phase contributes to low charge transfer resistance for better rate performance.As a result,the Ni₂CoS₄ exhibits the best specific capacity of 768 C/g at 1A/g and retains 59%of capacity value at 50 A/g.In addition,the Ni₂CoS₄ is also used as the cathode materials to assemble hybrid supercapacitor with reduced graphene oxide?RGO?,and the resulting hybrid supercapacitor device demonstrates both high energy and power densities.?3?Hierarchical Ni_0.5Co_0.5Se₂ containing a hollow inner structure,with a 3D sea-urchin-like overall morphology and very porous nanowires,was first synthesized by a low-temperature selenization method.Benefiting from such a hierarchical structure,the Ni_0.5Co_0.5Se₂ demonstrates a much improved specific area to provide more electroactive sites and a self-supporting 3D structure to make good contact with the electrolyte.As a result,the hierarchical Ni_0.5Co_0.5Se₂ exhibits a higher specific capacity of 524 C/g at 1 A/g and excellent cycling stability of 91%capacity retention after 3500 cycles.In addition,Ni_0.5Co_0.5Se₂//reduced graphene oxide?RGO?hybrid supercapacitor achieves a high specific energy,an ultrahigh specific power and an outstanding cycling stability,further confirming the superior performance of hierarchical Ni_0.5Co_0.5Se₂.