No abstract

A promising strategy to improve the rate performance of Li-ion batteries is to enhance and facilitate the insertion of Li ions into nanostructured oxides like TiO 2 . In this work, we present a systematic study of pentavalent-doped anatase TiO 2 materials for third-generation high-rate Li-ion batteries. Mesoporous niobium-doped anatase beads (Nb-doped TiO 2 ) with different Nb 5+ doping (n-type) concentrations (0.1, 1.0, and 10% at.) were synthesized via an improved template approach followed by hydrothermal treatment. The formation of intrinsic n-type defects and oxygen vacancies under RT conditions gives rise to a metallic-type conduction due to a shift of the Fermi energy level. The increase in the metallic character, confirmed by electrochemical impedance spectroscopy, enhances the performance of the anatase bead electrodes in terms of rate capability and provides higher capacities both at low and fast charging rates. The experimental data were supported by density functional theory (DFT) calculations showing how a different n-type doping can be correlated to the same electrochemical effect on the final device. The Nb-doped TiO 2 electrode materials exhibit an improved cycling stability at all the doping concentrations by overcoming the capacity fade shown in the case of pure TiO 2 beads. The 0.1% Nb-doped TiO 2 -based electrodes exhibit the highest reversible capacities of 180 mAh g −1 at 1C (330 mA g −1 ) after 500 cycles and 110 mAh g −1 at 10C (3300 mA g −1 ) after 1000 cycles. Our experimental and computational results highlight the possibility of using n-type doped TiO 2 materials as anodes in high-rate Li-ion batteries.

TiO2 is a promising material for high‐power battery and supercapacitor applications. However, in general TiO2 suffers from an initial irreversible capacity that limits its use in different applications. A combination of a microbead morphology, Nb‐doping, and the use of an ionic liquid electrolyte is shown to significantly decrease the irreversible capacity loss. A change in the electrochemical response in the first cycles indicates formation of a solid–electrolyte interphase (SEI) or a modification of the structure of the surface layer of the TiO2/Nb microbeads, which apparently stabilises the performance. The change in the response is manifested in an increased charge transfer resistance and the presence of two charge transfer contributions. During prolonged cycling the TiO2/Nb electrode shows an excellent stability over 5000 cycles. Ex situ analysis after cycling shows that the overall microbead morphology is intact and that there are no changes in the crystal structure. However, a decrease in the intensity of the XRD pattern can point to a decrease in size of the nanocrystals building up the microbeads or the formation of amorphous phases.

Compared to traditional electric double-layer capacitors, redoxenhanced electrochemical capacitors (redox-ECs) show increased energy density and steadier power output thanks to the use of redox-active electrolytes. The aim of this study is to understand the electrochemical mechanisms of the aqueous pentyl viologen/bromide dual redox system at the interface of an ordered mesoporous carbon (CMK-8) and improve the device performance. Cells with CMK-8 carbon electrodes were investigated in several configurations using different charging rates and potential windows. The pentyl viologen electrochemistry shows a mixed behavior between solution-based diffusion and adsorption phenomena, with the reversible formation of an adsorbed layer. The extension of the voltage window allows for full reduction of the viologen molecules during charge and a consequent increase in the specific discharge energy delivered by the cell. Investigation of the mechanism indicates that a 1.5 V charging voltage with a 0.5 A g −1 charging rate and fast discharge rate produces the best overall performance.

A combination of electrochemical and structural characterization techniques were used to study the lithiation in spray deposited amorphous mesoporous titania.