Electrolyte Interfacial Reactivity Regulation Of Nickel-cobalt-based Compounds And Study On Performance Of Hybrid Supercapacitors

Hybrid supercapacitors deliver the both advantages from the batteries and electric double-layer capacitors,which have been widely investigated owing to their merits of high-power and high-energy densities combined with long-term cycling stability.However,the slow ion diffusion and low structure stability of battery material limits the electrochemical performance of hybrid supercapacitors,and therefore,high-performance battery materials should be exploited for advanced hybrid supercapacitors.Here,the performance of hybrid supercapacitor is improved by tuning the structure and constructing composites of battery materials,which can increase the electrochemical activity of the battery electrode/electrolyte interface.The main contents are as follows:Firstly,nickel-cobalt selenides with hierarchical structures have been synthesized by low temperature selenization method,and the hierarchical structure improves the reactivity of electrode material/electrolyte interface.The hydroxide precursors can react with selenium vapor to form selenide,which leads to the recrystallization of the sample,and the produces show a hierarchical structure which is constituted by nanoparticles and nanosheets.By tuning the Ni to Co ratios,the optimal charge storage performance of selenides can be obtained,and the Ni-Co selenide with a Ni to Co ratio of 4:2 shows the best electrochemical performance.The Ni_0.67Co_0.33Se₂ shows excellent performance in terms of specific capacity and cycling performance.The hybrid supercapacitor based on Ni_0.67Co_0.33Se₂ also shows both high specific energy and specific power performances.Secondly,Mn doped NiCo₂S₄ double-shell hollow nanowire arrays have been synthesized by an anion exchange reaction,and improved electrochemical reaction activity of the NiCo₂S₄ electrode/electrolyte interface can be enhanced by such hierarchical structure.In addition,the doping effect of Mn in NiCo₂S₄ is also investigated,and it is found that the Mn constitution slow down the external diffusion of transition metal ions during the anion exchange reaction,forming the double-shell hollow structure in the nanowire array.The special double-shell hollow nanowire structure of NiCoMn-S endows the electrode with better performance in terms of high specific capacity,superior rate performance and stable cycling stability.More importantly,the NiCoMn-S based hybrid devices assembled with reduced graphene oxide(RGO)have high energy density and power performances.Lastly,graphene composited nickel-cobalt oxide(Ni_mCo_1-mO/RGO) ultrathin nanosheets have been prepared by a simple water bath method and excellent supercapacitor performance can be achieved.The graphene composited nickel-cobalt oxide presents an ultrathin nanosheet structure,which optimizes the interface performance between the electrode material and the electrolyte.In addition,oxygen vacancy can be introduced into the oxides in the annealing process,and the electrical conductivity and active site of can be both improved to enhance the electrochemical performance.In the meantime,the hybrid supercapacitors based on Ni_0.5Co_0.5O/RGO show both high specific energy and specific power,indicating the attractive potential of the composite as electroactive material for hybrid supercapacitor.