Novel state-of-health diagnostic method for Li-ion battery in service

International audienceHighlights • Two modules of 66 cells were aged with two cycling protocols corresponding to the EV cycling of electric school bus demonstrator. • Free charge/discharge signals were used to determine the quasi-EIS (QEIS) spectra during ageing. • These QEIS spectra were fitted with an equivalent circuit model. • The fitted parameters were used to develop a diagnostic tool to estimate the SoH of a battery. • This tool shows good accuracy in the estimation of SoH (2 % uncertainty) for both types of ageing studied. Abstract The development of improved State-of-Health (SoH) diagnostic methods is a current research topic for battery-powered applications. For instance, the current rapid development of Electric Vehicles (EV) creates a strong demand for an accurate and reliable on-board SoH indicator during operation. Such an indicator is a key parameter required to optimize battery energy management and to track the degradation of the system performance. The electrochemical impedance spectrum (EIS) of an electrochemical system is a powerful lab-based diagnostic technique, usually measured using a frequency response analyzer. In this paper, we present an innovative diagnostic technique based on analysis of free voltage and current signals to give a so called " quasi-electrochemical impedance spectrum " (QEIS) and demonstrate its application on a Li-ion battery during a real EV duty cycle. It is worth noting that in our technique no additional signal is applied to the cell, since the current flowing into cells during use on-board is directly processed in the data treatment step. Commercial batteries (1.4 Ah cylindrical LiFePO 4 /graphite cell) were selected in this study to validate the diagnostic method in the framework of an applied case study related to an electric school bus demonstrator. In order to study the capability of QEIS measurements as a diagnostic tool for SoH of Li-ion cells, a test procedure including ageing phases has been defined to characterise Li-ion cells before and during ageing. Voltage and current signals were treated by Fast Fourier Transform (FFT) in order to determine the QEIS spectra of Li-ion cells under study. Then, SoH prediction algorithms have been obtained from a mathematical analysis of the impedance parameters sensitive to SoH

Innovative Pipe Coating Material and Process for High Temperature Fields

To date, the high temperatures (above 140°C) met in some fields in, e. g. , the North Sea, impose the development of innovative corrosion protecting coatings. Thermostable products have been developed from combining a high-Tg thermoplastic and epoxyamine monomers (the latter reducing the viscosity of the former to allow processing) which, together with the associated coating process solve these services innovatively. Details of the subtleties of material choice and behavior, process engineering and how environmental issues are met are presented. Data from various long term ageing tests performed on these thermostable materials, including filled formulations, are discussed. Durability tests against sea water over 12000 hours at 160°C are followed by desorption and dynamic mechanical analysis to assess whether any irreversible degradation has occurred. Carbon steel adhesion measurements are carried out in the view of coating applications as well as in situ Tg values evaluated by impedance spectroscopy. Plasticization effect of water is discussed. In addition, impedance spectra also indicate the quality of corrosion resistance achieved under accelerated ageing conditions

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

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

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

Experimental study of the compression behaviour of syntactic foams by in situ X-ray tomography

International audienceSyntactic foams (hollow glass microspheres embedded in a polymeric matrix) are being used increasingly for thermal insulation purpose in ultra-deep water. A better understanding of the damage mechanisms of these materials under such a hydrostatic loading condition would be useful in determining actual material limits, improving phenomenological modeling and developing novel formulations in the future. To achieve this goal, a study based on X-ray microtomography was performed on various syntactic foam materials (epoxy/PP/PU matrix). Spatial resolution of (0.7 µm)3 and in situ non-destructive scanning allowed unique qualitative and quantitative analysis of the composite microstructure during stepwise confined compression testing in the dry state. It is shown that in the three materials, the thickness of the spheres is rather constant while their diameter is strongly distributed. The adherence is strong between PU and glass and rather weak between both PP and epoxy and glass. In the two foams where the matrix is more compliant (PU and PP), damage is homogeneously distributed and affects mainly the larger spheres, while in the stiff and strong epoxy material, damage is localized in bands

Advances in Electrochemical Models for Predicting the Cycling Performance of Traction Batteries: Experimental Study on Ni-MH and Simulation

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