Li+ Insertion in Nanostructured TiO2 for Energy Storage

Nanostructured materials possess unique physical-chemical characteristics and have attracted much attention, among others, in the field of energy conversion and storage devices, for the possibility to exploit both their bulk and surface properties, enabling enhanced electron and ion transport, fast diffusion of electrolytes, and consequently high efficiency in the electrochemical processes. In particular, titanium dioxide received great attention, both in the form of amorphous or crystalline material for these applications, due to the large variety of nanostructures in which it can be obtained. In this paper, a comparison of the performance of titanium dioxide prepared through the oxidation of Ti foils in hydrogen peroxide is reported. In particular, two thermal treatments have been compared. One, at 150 °C in Ar, which serves to remove the residual hydrogen peroxide, and the second, at 450 °C in air. The material, after the treatment at 150 °C, results to be not stoichiometric and amorphous, while the treatment at 450 °C provide TiO2 in the anatase form. It turns out that not-stoichiometric TiO2 results to be a highly stable material, being a promising candidate for applications as high power Li-ion batteries, while the anatase TiO2 shows lower cyclability, but it is still promising for energy-storage devices

Binder free and flexible asymmetric supercapacitor exploiting Mn3O4 and MoS2 nanoflakes on carbon fibers

Emerging technologies, such as portable electronics, have had a huge impact on societal norms, such as access to real time information. To perform these tasks, portable electronic devices need more and more accessories for the processing and dispensation of the data, resulting in higher demand for energy and power. To overcome this problem, a low cost high-performing flexible fiber shaped asymmetric supercapacitor was fabricated, exploiting 3D-spinel manganese oxide Mn3O4 as cathode and 2D molybdenum disulfide MoS2 as anode. These asymmetric supercapacitors with stretched operating voltage window of 1.8 V exhibit high specific capacitance and energy density, good rate capability and cyclic stability after 3000 cycles, with a capacitance retention of more than 80%. This device has also shown an excellent bending stability at different bending conditions

Monitoring hydration in lime-metakaolin composites using electrochemical impedance spectroscopy and nuclear magnetic resonance spectroscopy

This paper describes a study of the hydraulic reactions between metakaolin (MK) and air lime using electrochemical impedance spectroscopy (EIS) and nuclear magnetic resonance spectroscopy (NMR). Tests were carried out at 20, 25 and 30 degrees C on lime-MK pastes with 10:1 w/w ratio. Tests over 28 days allowed identification of relevant changes in the EIS signals and characterization of pastes using thermal analysis (TGA/DSC), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and uni-axial compressive tests. Tests over shorter periods of time (up to 42 h) allowed more detailed studies of the hydraulic phases formed at the very beginning of the reactions. Results of thermal analyses demonstrate formation of hydraulic compounds such as CSH, C(4)AH(13) and C(3)ASH(6) and show their evolution over time. MIP analysis demonstrates changes in pore size distribution related to the formation and trasformation of hydraulic phases. Variations of impedance response with time are shown to be associated with reaction kinetics. Changes in the NMR signal within the first 42 h of reaction are shown to be associated with the dissolution of calcium hydroxide in the pore solution. Overall, this paper demonstrates the importance of NMR in the study of hydraulic reactions in lime based materials and the ability of EIS to detect the formation of hydraulic compounds and the end of the calcium hydroxide dissolution process

Decoration of laser induced graphene with MXene and manganese oxide for fabrication of a hybrid supercapacitor

During the last years, Internet of Things has become a prominent topic of technical, social, and economic importance. One of the main consequences is the high demand for energy and power density from small energy storage devices. In this field the laser induced graphene (LIG) has become a promising material to produce flexible micro-supercapacitors. The issue with this material is that the performances are strongly restrained by its limited surface area and the relatively low conductivity. In this work we improve the performance of a LIG supercapacitor by decorating its surface through electrophoresis: one electrode will be decorated with metal nitrides and metal carbides (MXenes), the other with manganese oxide. These two materials have appreciable conductivity and pseudocapacitance. Electrochemical measurements have been carried out on the two electrodes separately. After a charge balancing, the device has been sealed in pouch and tested

Tunable all-solid-state wire-shaped high power device based on carbon nanotubes yarn

Energy storage devices integrated into textiles have emerged as a significant strategy for electronic applications. In this context, in the present paper novel flexible devices were developed, in which the control of both the electrode characteristics and the solid-electrolyte properties allows to build all-solid-state wire-shaped supercapacitors that can be integrated and waved. The proposed device was assembled using modified CNT yarns as electrodes and a blend of ionic liquid, Li salt and poly(ethylene glycol) acrylate to fabricate the solid-polymeric electrolyte. Excellent performance in terms of both electrochemical parameters and stability were obtained. These achievements are possible thanks to the coupling of asymmetric CNT yarns, following an optimization of the activation procedure together with the improvement of the polymeric electrolyte. The results show a capacitance as high as 1.8 mF/cm, energy density of 1.3 μWh/cm and a capacitance retention higher than 100% over 1200 cycles

Modeling of electrochemical capacitors under dynamical cycling

The electric responses of electrochemical capacitors produced with electrodes build up of reduced graphene oxide (rGO) deposited on Fluorine-doped tin oxide (FTO) coated glass have been experimentally investigated by cyclic voltammetry measurements. According to our experimental data, the parametric curve of the current in the circuit versus the external voltage is a continuous curve without discontinuity points respect to the inversion points of the external voltage. A few equivalent electric circuits able to reproduce the electric response of the capacitor are discussed. The dependence of the area delimited by the parametric cyclic voltammetry curve on the elements of the circuit is investigated. The possible evaluation of the effective capacitance of the capacitor by the numerical evaluation of the area delimited by the parametric curve is critically discussed and the limit of the procedure is underlined. A model based on the Poisson-Nernst-Planck theory with adsorbing electrodes is developed and used to fit the experimental voltammogram. The agreement between the theoretical model and the experimental data is good, indicating the importance of the adsorption phenomenon in the electric response of electrochemical capacitor to an external electric field