Silica-mediated Formation Of Nickel Sulfide/CNT Films Composites For Versatile Energy Storage

The performance of electrode materials is a key factor determining the efficiency of electrochemical energy storage.Therefore,the preparation of electrode materials with high flexibility and electrochemical activity is the primary goal to promote their application in the field of energy storage.In this work,a generalized principle to utilize silicon oxide as the intermediate is reported to design and fabricat a flexible,conductive and high-performance nickel sulfide/carbon nanotube?NS/CNT?composite film by two-step hydrothermal method.By controlling parameters of hydrothermal reaction,the regulation mechanism of phase change and microtopography in each step is studied,and the application of products in various fields of electrochemical energy storage is explored.Adjusting the hydrothermal reaction time,the conversion mechanism of nickel nitrate and SiO₂/CNT film to form Ni-silicate/CNT film is studied.When the reaction time is 12 h,the two-dimensional pleated Ni-silicate sheets uniformly filled in the three-dimensional network formed by CNT,which gives the Ni-silicate/CNT film excellent electrochemical performance.When used as the electrode of Li-ion batteries,Ni-silicate/CNT-12 achieved a very high first discharge specific capacity(1798.0 mAh g^-1at 0.05 A g^-1),outstanding rate performance(over 44.2%reversible specific capacity retention at 3 A g^-1).When used in supercapacitors and Na-ion batteries,it also delivered excellent cycling stability and cycle stability.The NS/CNT composite film was then synthesized by hydrothermal reaction using the above-prepared Ni-silicate/CNT-12 film as a raw material.The result shows that different phases and compositions of NS can be effectively regulated by simply adjusting the amount of added Na₂S.With the increase of Na₂S concentration,the products gradually change in the order of Ni₃S₂,NiS and Ni₃S₄.When the Na₂S concentration was increased to 2.1 g L^-1,NS/CNT-2 possesses the best electrochemical performance,compared to other samples.When used in supercapacitors,NS/CNT-2achieved a very high specific capacitance(2699.7 F g^-1@10 A g^-1),outstanding rate performance at extremely high rates(1519.7 F g^-1@250 A g^-1),and excellent stability.When used for storing Li and Na ions as a battery anode material,it also delivered excellent cycling stability with high capacity and initial coulombic efficiency.Finally,Effect of using SrCl₂?6H₂O-SrCO₃ and CNT as composite nucleating agent on the energy storage properties in the induced crystallization nucleation process of MgCl₂?6H₂O-CaCl₂?6H₂O were investigated.It is suggested that the addition of CNT can reduce system supercooling degree?SSD?,which decreases with increased CNT.When the composite nucleating agents consisting SrCl₂?6H₂O-SrCO₃ and CNT were introduced SSD can be further decreased when the composite nucleating agents consisting SrCl₂?6H₂O-SrCO₃ and CNT were introduced because of the good thermal conductivity and high phase change latent heat.SSD decreased to a minimum of 0.6?when the ratio of CNT,SrCO₃ and SrCl₂?6H2O was optimized as 0.25 wt.%?1 wt.%and 3 wt.%,respectively.