Research On Preparation And Properties Of Li₄Ti₅O₁₂/G Composites For Supercapacitors

Supercapacitor is a new type of energy storage element between batteries andtraditional capacitors, which has the advantage of high specific energy for batteriesand high power density for capacitors.Anode materials for asymmetric supercapacitor have a series of properties, suchas low operating voltage, high energy density, stable cycling performance andhigh current charge-discharge capability, etc. Spinel structure Li4Ti5O12has exertedgood prospects as anode materials for supercapacitor with the advantage of highLi-ion diffusion coefficient, stable cycling performance, no passivation film formedand high safety. However, spinel structure Li4Ti5O12is a type of semi-insulatingmaterial with the shortcomings of low electronic conductivity and Li+diffusion rate,which limits its application. Lamellar structure graphene can enhance the electronicconductivity of the material as good for the soaking of electrolytes and the Li+intercalation and deintercalation, which is helpful for improving the energy and powerdensity of the composites.In this paper, sol-gel method was adopted to prepare Li4Ti5O12nano-material,and Li4Ti5O12/G composite was synthesized via presintering and chemical reductionmethod. X-ray diffraction(XRD) and scanning electron microscope(SEM) were usedto analyze the morphology and structure of the synthetic materials; Cyclicvoltammetry(CV), constant current charge-discharge tests and electrochemicalimpedance spectroscopy(EIS) were available for the electrochemistry properties ofthe assembled button batteries and asymmetric supercapacitors.1. Synthesized precursor by sol-gel and prepared Li4Ti5O12by segmentedcalcination. And Research on the effects of molar ratio of lithium titanium, calcination time on the product, optimized the preparation process, prepared a small particle size,good degree of crystallinity Li4Ti5O12nanoparticles. Electrochemical test pure phaseLi4Ti5O12, results showed that the initial capacity density was145mAh·g-1at a currentdensity of17.5mA·g-1The pure Li4Ti5O12has good electrochemical reversibility, thelow electron conductivity.2. Prepared Li4Ti5O12/G composites by adding graphene oxide (GO) in so-gelsystem, the pre-calcination and chemical reduction method. when adding grapheneoxide (GO) in so-gel system, the composite material contains a large amount of TiO2,does not reach the purposes of the graphene doping because of lower capacity densityof the composite. Prepared Li4Ti5O12/G composites by the pre-calcination andchemical reduction method, XRD, SEM analysis showed that the product formedLi4Ti5O12, and formed conductive networks. Study on electrochemical properties ofcomposite materials, thecapacity density was155mAh·g-1,160mAh·g-1, respectively,at a current density of17.5mA·g-1. And discharge platform of composites is smooth,polarization potential is small, cycling performance is better. The reason iscrystallinity of the material increased, the particle sizes reduce, forming conductivenetworks, so that composites have excellent electrochemical properties.3. Li4Ti5O12/G composite electrodes by the pre-calcination and chemicalreduction method, and Li4Ti5O12/AC composite electrodes with the AC assembledasymmetric supercapacitor respectively, charge and discharge electrochemical test,results showed that, at the current density2mA·g-1, the energy density of capacitorsreach on83Wh·kg-1, description AC//Li4Ti5O12/G asymmetric supercapacitor hasexcellent charge-discharge performance. For AC//Li4Ti5O12/G/AC asymmetricsupercapacitor, when Li4Ti5O12content is30%, the energy density and power densityof the capacitor is relatively high.