TiO₂and Graphene/Ni（OH）₂Electrode Materials For Energy Storage

With the development of the times and social progress, the traditional fossil energy is gradually failing and increasing the burden on the environment. Energy issues have become one of the problems human has to face. As two kinds of electrochemical energy storage devices of the most active research fields, lithium ion batteries and supercapacitors show excellent power density, cycle reversibility, and is considered to the most competitive energy storage devices.Pure and carbon-coated TiO2of which theoretical capacity is335mAh/g used for lithium ion battery anode materials were successfully synthesized via the spray drying process followed by post-calcination, wherein titanium isopropoxide(TTIP) was employed as the Ti organic source, oxalic acid as the inhibitor of TTIP hydrolysis and polyvinyl alcohol(PVA) as the carbon source. Thermogravimetric diagram and differential thermal analysis(TG-DTA), X-ray diffraction(XRD), energy dispersive X-ray spectroscope-scanning electron microscope(EDX-SEM), transmission electron microscope(TEM) and electrochemical tests were used to characterize the morphology, microstructure and capacitance performance of the prepared samples.Measurement results demonstrate that micrometer-level, smooth, dispersed, well spherical, typically anatase TiO2particles were successfully prepared after calcined between350and500℃. After calcining for4h at400℃, the sample appears a relatively optimal electrochemical performance. At0.5,1,2,5and10C current densities, its initial discharge specific capacity is175.7,161.5,149.9,120.8and90.6mAh/g, respectively, and charge-discharge efficiency is82.2,85.1,88.9and90.8%, respectively. After10wt.%PVA carbon coating TiO2, surface modification relieves the polarization and improves the cycle performance at large current densities. Comparing with uncoated sample, at10C current density after250cycles, the specific capacitance is improved from75.8to93.2mAh/g and capacitance retention is improved from75.8to82.9%at room temperature; the specific capacitance is improved from66.6to79.8mAh/g at0℃and from77.6to82.8mAh/g at40℃.The rGONS(reduced Graphene Oxide Nanosheets)/Ni(OH)2composites with excellent supercapacitive performance were successfully prepared by a facile hydrothermal route. Homogeneous graphene oxide dispersion solvent, NiCl2·6H2O, precipitant ammonia and reducing agent ascorbic acid were used as initial materials. Prepared samples were characterized by XRD, SEM, fourier transform infrared spectroscopy(FT-IR) and electrochemical tests to characterize the morphology, microstructure and capacitance performance.Measurement results demonstrate that the addition of graphene has greatly increased the specific capacitance of pure Ni(OH)2. Ascorbic acid can not only effectively reduce GO(Graphene Oxide) to rGONS which can eliminate the conductivity of functional groups on the GO surface, but also take advantage of electrostatic and coordination iteraction of functional groups to attract the metal ions, making the composites more closely and improving the electrochemical performance. By three groups of comparing experiments, the optimized hydrothermal synthesis conditions are:the addition of NiCl2-6HbO is4mmol and retention time is4h at140℃. At various current densities, the sample can still keep excellent specific capacitance. In lmol/L KOH solution, specific capacitances of827.6,754.7,533.2and389.7F/g is obtained at current densities of0.5,1,5and10A/g, respectively.