Caractérisation électrochimique de matériaux à insertion de Li pour supercondensateurs hybrides à haute densité d'énergie

Les caractérisations électrochimiques effectuées sur différents matériaux à insertion de Li ont permis d'évaluer leurs performances de puissance. Il a ensuite été possible de concevoir des supercondensateurs hybrides à haute densité d'énergie grâce à i) l'augmentation de la capacité spécifique par l'utilisation d'un LiFePO4, ii) l'augmentation de la tension de fonctionnement en utilisant le Ti2C, un nouveau matériau obtenu par l'exfoliation d'une phase MAX, et iii) l'utilisation d'un matériau pseudocapacitif, le Nb2O5, permettant d'augmenter la densité d'énergie sans perte de puissance. Ce dernier cas a permis de mettre en évidence pour la première fois le phénomène de pseudo-intercalation comme une propriété intrinsèque du matériau. Ce processus de stockage de charges met en jeu l'intercalation du Li dans le volume des particules sans changement de phases et sans limitation par la diffusion, contrairement à la majorité des matériaux à insertion de Li. Ceci a alors permis d'atteindre des capacités élevées en des temps de charge/décharge de l'ordre de quelques secondes. Ces résultats montrent l'intérêt des matériaux faradiques pour concevoir des systèmes de puissance à haute densité d'énergie.Electrochemical characterizations of Li-ion insertion compounds were performed to assess their power performances. They were used to design hybrid supercapacitors with high energy density, by i) increasing the specific capacity by using a LiFePO4, ii) increasing the operating voltage by using Ti2C, a new compound obtained from exfoliation of a MAX phase, and iii) using a pseudocapacitive material, Nb2O5, that enables to achieve high energy with no power loss. In the latter, the pseudo-intercalation charge storage mechanism was characterized for the first time as an intrinsic property of the material. It involves Li insertion in the bulk in a one-phase system without diffusion limitation, unlike most battery materials. This phenomenon enabled to achieve high capacity values for short charge/discharge times, consistent with supercapacitors time constant. These results highlight the interest of faradic materials for designing high energy density power devices

Electrochemical Kinetic Study of LiFePO4 Using Cavity Microelectrode

Lithium cation insertion and extraction in LiFePO4 were electrochemically studied with a cavity microelectrode (CME). Cyclic voltammetry measurements were used to characterize the kinetics of the material. LiFePO4 was successfully cycled from 0.1 mV s–1 up to 1 V s–1 and is therefore a suitable material to be used in high power applications, such as asymmetric hybrid supercapacitors. Several kinetic behaviors were observed depending on the sweep rate. The LiFePO4 was found to follow different kinetics behaviors depending of the sweep rate. The charge storage mechanisms were investigated for Liþ extraction/insertion

MXene: a promising transition metal carbide anode for lithium-ion batteries

Herein we report on Li insertion into a new two-dimensional (2-D) layered Ti₂C-based material (MXene) with an oxidized surface, formed by etching Al from Ti₂AlC in HF at room temperature. Nitrogen sorption of treated powders showed desorption hysteresis consistent with the presence of slit-like pores. At 23 m² g-¹, the specific surface area was an order of magnitude higher than untreated Ti₂AlC. Cyclic voltammetry exhibited lithiation and delithiation peaks at 1.6 V and 2 V vs. Li+/Li, respectively. At C/25, the steady state capacity was 225 mAh g-¹; at 1C, it was 110 mAh g-¹ after 80 cycles; at 3C, it was 80 mAh g-¹ after 120 cycles; at 10C, it was 70 mAh g-¹ after 200 cycles. Since Ti₂C is a member of the MXene family - where M is an early transition metal and X is C and/or N - that to date includes Ti₃C₂, Ta₄C₃, TiNbC, and (V₀.₅,Cr₀.₅)₃C₂, our results suggest that MXenes are promising as anode materials for Li-ion batteries

Electrochemical Kinetics of Nanostructured Nb2O5 Electrodes

Pseudocapacitive charge storage is based on faradaic charge-transfer reactions occurring at the surface or near-surface of redox-active materials. This property is of great interest for electrochemical capacitors because of the substantially higher capacitance obtainable as compared to traditional double-layer electrode processes. While high levels of pseudocapacitance have been obtained with nanoscale materials, the development of practical electrode structures that exhibit pseudocapacitive properties has been challenging. The present paper shows that electrodes of Nb2O5 successfully retain the pseudocapacitive properties of the corresponding nanoscale materials. For charging times as fast as one minute, there is no indication of semi-infinite diffusion limitations and specific capacitances of 380 F g−1 and 0.46 F cm−2 are obtained in 40-μm thick electrodes at a mean discharge potential of 1.5 V vs Li+/Li. In-situ X-ray diffraction shows that the high specific capacitance and power capabilities of Nb2O5 electrodes can be attributed to fast Li+ intercalation within specific planes in the orthorhombic structure. This intercalation pseudocapacitance charge-storage mechanism is characterized as being an intrinsic property of Nb2O5 that facilitates the design of electrodes for capacitive storage devices. We demonstrate the efficacy of these electrodes in a hybrid electrochemical cell whose energy density and power density surpass that of commercial carbon-based devices

Design of Fe3–xO4 raspberry decorated graphene nanocomposites with high performances in lithium-ion battery

Fe3–xO4 raspberry shaped nanostructures/graphene nanocomposites were synthesized by a one-step polyol-solvothermal method to be tested as electrode materials for Li-ion battery (LIB). Indeed, Fe3–xO4 raspberry shaped nanostructures consist of original oriented aggregates of Fe3–xO4 magnetite nanocrystals, ensuring a low oxidation state of magnetite and a hollow and porous structure, which has been easily combined with graphene sheets. The resulting nanocomposite powder displays a very homogeneous spatial distribution of Fe3–xO4 nanostructures at the surface of the graphene sheets. These original nanostructures and their strong interaction with the graphene sheets resulted in very small capacity fading upon Li+ ion intercalation. Reversible capacity, as high as 660 mAh/g, makes this material promising for anode in Li-ion batteries application

Caractérisation électrochimique de matériaux à insertion de Li pour supercondensateurs hybrides à haute densité d'énergie

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Passenger flow forecasting framework based on vision transformer and inpainting: Application to a public transport system

TRISTAN XI, the 11th Triennial Symposium on Transportation Analysis, Balaclava, MAURICE, 19-/06/2022 - 25/06/2022Short-term forecasting is one of the most important challenges in intelligent transport systems (ITS). The demand information is crucial for transport operators in order to anticipate and optimize their service level and for travelers to have robust information. In addition, a good predictor can contribute to system resilience by predicting disrupted situations. In most forecasting models, the data collectors are based on regular time series and single stations of the urban area. This study considers trains as data collectors, i.e., sensors. Thus, we are not limited to single location sensors. Moreover, we have to deal with irregular time series

Understanding the Nanoscale Redox-Behavior of Iron-Anodes for Rechargeable Iron-Air Batteries

Iron-air cells provide a promising and resource-efficient alternative battery concept with superior area specific power density characteristics compared to state-of-the-art Li-air batteries and potentially superior energy density characteristics compared to present Li-ion batteries. Understanding charge-transfer reactions at the anode-electrolyte interface is the key to develop high-performance cells. By employing in-situ electrochemical atomic force microscopy (in-situ EC-AFM), in-depth insight into the electrochemically induced surface reaction processes on iron in concentrated alkaline electrolyte is obtained. The results highlight the formation and growth of the redox-layer on iron over the course of several oxidation/reduction cycles. By this means, a direct correlation between topography changes and the corresponding electrochemical reactions at the nanoscale could unambiguously be established. Here, the twofold character of the nanoparticulate redox-layer in terms of its passivating character and its contribution to the electrochemical reactions is elucidated. Furthermore, the evolution of single nanoparticles on the iron electrode surface is evaluated in unprecedented and artifact-free detail. Based on the dedicated topography analysis, a detailed structural model for the evolution of the redox-layer which is likewise elementary for corrosion science and battery research is derived

Simulation analysis of performances and yield rates on a lens module

A simulation platform is developed to analyze the tolerance ability of designed lens in the opto-mechanical system. The major task of lens designer is to find out the optimal parameters to meet the specification requirement. A real lens with decenter, tilt, and lens parameters’ variation could lower the performance of lens. The original parameters from the lens designer suffer certain probability distribution during manufacturing lenses so that the performance of assembly lens is always different from that of the optimal design. The proposal applies a variety of probability density functions of the manufacture to obtain the tolerance parameters used in simulation. Some macros of commercial optical software based on the Monte Carlo method are developed to simulate the lens manufacture tolerance and analyze the yield rate for mass production. With proper probability density functions of the manufacture, the tolerance can be estimated from the proposed algorithm