Advances in Electrochemical Models for Predicting the Cycling Performance of Traction Batteries: Experimental Study on Ni-MH and Simulation Développement de modèles électrochimiques de batteries de traction pour la prédiction de performances : étude expérimentale de batteries NiMH et simulations

Rigorous electrochemical models to simulate the cycling performance of batteries have been successfully developed and reported in the literature. They constitute a very promising approach for State-of-Charge (SoC) estimation based on the physics of the cell with regards to other methods since SoC is an internal parameter of these physical models. However, the computational time needed to solve electrochemical battery models for online applications requires to develop a simplified physics-based battery model. In this work, our goal is to present and validate an advanced 0D-electrochemical model of a Ni-MH cell, as an example. This lumped-parameter model will be used to design an extended Kalman filter to predict the SoC of a Ni-MH pack. It is presented, followed by an extensive experimental study conducted on Ni-MH cells to better understand the mechanisms of physico-chemical phenomena occurring at both electrodes and support the model development. The last part of the paper focuses on the evaluation of the model with regards to experimental results obtained on Ni-MH sealed cells but also on the related commercial HEV battery pack. Des modèles électrochimiques fins permettant de simuler le comportement de batteries ont été développés avec succès et reportés dans la littérature. Ils constituent une alternative aux méthodes classiques pour estimer l’état de charge (SoC pour State of Charge) des batteries, cette variable étant ici un paramètre interne du modèle physique. Cependant, pour les applications embarquées, il est nécessaire de développer des modèles simplifiés sur la base de ces modèles physiques afin de diminuer le temps de calcul nécessaire à la résolution des équations. Ici, nous présenterons à titre d’exemple un modèle électrochimique 0D avancé d’un accumulateur NiMH et sa validation. Ce modèle à paramètres concentrés sera utilisé pour réaliser un filtre de Kalman qui permettra la prédiction de l’état de charge d’un pack complet. Une étude expérimentale d’accumulateurs NiMH permettra de mieux comprendre les mécanismes physico-chimiques ayant lieu à chaque électrode et ainsi d’alimenter le modèle physique en informations. La dernière partie de cet article sera consacrée à la validation du modèle par comparaison à des données expérimentales obtenues sur cellule individuelle mais également sur un pack batterie NiMH commercial complet

Self-healing coatings: An alternative route for anticorrosion protection

International audiencePolymer coating systems are classically applied on a metal surface to provide a dense barrier against the corrosive species. Cathodic protection is used for many applications in addition to coatings to protect the metal structures from corrosive attack when the coating is damaged. However, the current demand will increase with the disbonded areas. Moreover, the reactions that take place at the cathode can cause a progressive enlargement of the unbonded area. Self-healing coatings are considered as an alternative route for efficient anticorrosion protection while maintaining a low demand in cathodic protection. Such coatings typically incorporate micro- or nanocapsules that contain film-formers and repair the coating damage when the coating is scratched. Self-healing systems have been developed for metal structures under cathodic protection using specific-film-formers sensitive to the electrical field and pH encountered in the vicinity of a default on a coated structure under cathodic protection. The present paper describes the principle of this novel self-healing concept and discusses the healing efficiency on the basis of laboratory results. Electrochemical impedance spectroscopy was used to evaluate the performance of the barrier efficiency and continuous current demand monitoring assessed the ability of specific-film-formers to provide self-healing and repair defects generated in the coating to the metal

Durability of Syntactic Foams for Deep Offshore Insulation: Modelling of Water Uptake under Representative Ageing Conditions in Order to Predict the Evolution of Buoyancy and Thermal Conductivity

Three different syntactic foams were aged under various conditions of both temperature (from 4°C to 130°C) and pressure (from 1 bar to 300 bar) in renewed sea water. Some functional properties were measured during aging. First, the link between water uptake and both buoyancy and thermal conductivity evolutions was established for each syntactic material under any ageing conditions. Then a finite element model was developed in order to compute water uptake in the materials. The model, based on the description of three hydration mechanisms, each mechanism being linked to a part of the microstructure of the foam, gives a satisfactory agreement with experimental results for all aging conditions and specimen sizes. The model was finally used to simulate the evolution of some functional properties that would experience a structure immersed in real conditions over 20 years. Furthermore, the thickness of the insulation material affected by water ingress after 20 years of aging can be estimated, and this value can be used at the time of design as a sacrificial thickness

Hot wet aging of glass syntactic foam coatings monitored by impedance spectroscopy

International audienceThis paper examined both short and long term behaviors of glass-epoxy syntactic foam coatings containing various types of microspheres while exposed to hot deionized water. Electrochemical impedance spectroscopy (EIS) was used to monitor in situ the water uptake of the coating in complement to gravimetry but also to investigate the degradation phenomenon occurring after the matrix had reached saturation (monitoring over 420 days). Diffusion properties were discussed from capacitance measurements in comparison to classical gravimetric data. In addition, attention was paid to the increase of ionic conductivity suggesting the creation of water paths through the material and/or the occurrence of ionic extraction from the microsphere glass due to water leaching. Possible degradation mechanisms were discussed from the modeling of the results obtained by in situ monitoring. The interest of EIS for the investigation of composite coating aging was highlighted

OS05-3-3 Experimental study of the hydrostatic compression behaviour of syntactic foams by X-ray microtomography

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