Low-energy Preparation Of Nickel Hydroxide Nanomaterials And Supercapacitor Application

Supercapacitors,as a new type of green and clean energy storage device,have attracted extensive attention due to their advantages such as high power density,extremely long cycle life and rapid charge-discharge property.The most important factor that determines supercapacitor's performance is electrode material.Nickel hydroxide,due to its high theoretical capacitance,low cost,non-toxic and environment-friendly characteristics,has been one of the candidates of electrode material.In this paper,two energy-saving preparation processes were used to synthesis Ni(OH)2 electrode,namely low-temperature hydrothermal method and microwave hydrothermal method.Besides,different hydrothermal temperature and microwave treatment time were adjusted to study the influence of different parameters on the microstructure and electrochemical properties of Ni(OH)2 electrodes under the two preparation processes.In addition,the electrode prepared by the above process and the activated carbon electrode were assembled to a supercapacitor device to evaluate the practical application capacity.First of all,a low-temperature hydrothermal method was developed and Ni(OH)2 electrodes were prepared using a glass bottle instead of autoclave under 100?.The performance characterizations of Ni(OH)2 electrodes were analyzed.The results of XRD,FT-IR and XPS showed that the Ni(OH)2 electrodes interlayered with nitrate and hydroxyl ion were successfully prepared at low temperature.SEM showed that all the Ni(OH)2 electrodes were uniformly covered on the substrate with interlaced nanosheets.The electrochemical properties of Ni(OH)2 electrodes prepared at different hydrothermal temperatures were tested,and the sample prepared at 95 degrees had the best performance.The Ni(OH)2-95 sample has good specific capacitance of 1759 F·g-1 at 1 A·g-1,and the specific capacitance retention rate was up to 85%after 5000 cycles,showing a comparable or better performance than other reports using high pressure hydrothermal method.On this basis,an asymmetric supercapacitor device was assembled with the negative electrode of commercial activated carbon,with a voltage window up to 1.6 V and an energy density of 44.5 Wh/kg at 0.4 kW/kg.When the power density was 4 kW/kg,the energy density was still 19 Wh/kg,indicating good performance and potential for practical application.Then Ni(OH)2 electrodes were prepared by microwave hydrothermal systhesis method of microwave irradiation treatment for 10 min to 20 min.And their properties were analyzed.The characterizations performance showed that the Ni(OH)2 electrodes synthesized by microwave hydrothermal method had interlaced nanosheet structure,and water molecules and nitrate ions were intercalated into the layer of Ni(OH)2.The electrochemical test indicates that Ni(OH)2-15 has the best performance,and the specific capacitance of Ni(OH)2-15 reaches 2516 F·g-1at 1 A·g-1.In addition,the maximum energy density of Ni(OH)2-15//AC is 66.7 wh/kg.It can be found that the performance of the sample irradiated 15 min was better than performance of the sample using hydrothermal method for more than 8 h,The results further proves that the electrode material of Ni(OH)2 nanosheet array prepared by microwave is not only flexible and fast,but also shows great potential in practical application.Finally,Ni(OH)2/NiOOH composite films were prepared by two-step method which adds a chemical bath deposition step on the basis of nickel hydroxide nanosheet array prepared by low-temperature hydrothermal method,and the properties of Ni(OH)2/NiOOH sample were analyzed.The 3D porous structure of the Ni(OH)2/NiOOH composite film with nanoflowers growing on the nanosheet was demonstrated by SEM.Electrochemical tests showed that Ni(OH)2/NiOOH sample had the highest specific capacitance of 3083 F·g-1 at 1 A·g-1,and also had the best rate capability(65%retention at 20 A·g-1)and cycling performance(80.5%retention at 10000 cycles).Futhermore.two electrodes were tested for Ni(OH)2/NiOOH//AC.The results suggested that the energy density of Ni(OH)2/NiOOH//AC was 52.2 wh/kg at 0.4 kw/kg,showing good performance.In addition,when the power density is 8 kW/kg,the energy density is still 29.3 Wh/kg.Compared with the previous work,the cycle performance and the rate capability of Ni(OH)2/NiOOH are significantly improved with an additional flexible step,which shows good practical application.