Olivier Briat

Comparison between changes of ultracapacitors model parameters during calendar life and power cycling ageing tests

This paper deals with the performances fading of ultracapacitors under calendar life and power cycling tests. The used impedance model is analytical and based on physical quantities as double layer capacitance, specific area and electrolyte conductivity but also on elementary electrodes dispersion. This model is validated in frequency domain using the initial state of the tested ultracapacitor. Then, the two types of tests are presented and specified. A periodic characterization based on impedance spectroscopy is done in order to quantify the impedance changes during ageing tests. The obtained results confirm that impedance real part is increasing and the capacitance is decreasing during the two ageing tests, nevertheless the way they change is different. Indeed the impedance real part increase is independent of the frequency in calendar life test while, in power cycling test, this increase is accentuated at low frequencies. This difference will be explained thanks to impedance model parameters evolution. This study confirms that the two ageing tests affect differently the ultracapacitor performances.

Improved Supercapacitor Floating Ageing Interpretation Through Multipore Impedance Model Parameters Evolution

Like any electric energy storage system, supercapacitors have a limited lifetime. Indeed, they degrade with time because of parasitic reactions between electrodes and electrolyte. Porous electrodes are complex structures and pores have size dispersion because of manufacturing processes. This paper proposes to study the specific impact of supercapacitor floating ageing on different pore sizes using a multipore model. The multipore model is an equivalent electrical circuit model, capable of representing impedance behavior of supercapacitor in full range of its operating frequencies and classifying different sized pores by their impedance parameters. This paper first presents a link between pore sizes and impedance parameters of the modeling circuit. Then, floating ageing experiments are carried out using three samples from two different manufacturers. Multipore model impedance parameters evolution is monitored and discussed. Finally, a new representation of ageing processes is proposed by pore size and for different ageing phases.

Ageing monitoring of lithium-ion cell during power cycling tests

Abstract In this paper, the ageing monitoring of lithium-ion cell during power cycling tests is investigated. First of all, the results of a time-domain characterization method have been used to identify the main factors of ageing. Then, a methodology that takes benefits of a periodic characterization protocol based on impedance spectroscopy measurements is proposed. The obtained results are presented and discussed for different values of State-of-Charge (SoC), temperature and number of cycles. In a second part of this study, we have focused on how to take into account the ageing in a simulation model. This model is based on an equivalent electric circuit. The main ageing mechanisms and the influencing factors are highlighted and described using time-domain and frequency-domain measurements. Then, by focusing on the parameters evolution of the proposed model with ageing, it was confirmed that the growth of the solid electrolyte interface is the most influent phenomenon in the performances fading.

Contribution of calendar ageing modes in the performances degradation of supercapacitors during power cycling

Due to their high specific power and their long cycle life, supercapacitors (SC) are very interesting devices for on-board energy applications such as hybrid-electric vehicles. However, in order to ensure optimal performances during the whole vehicle lifetime, the reliability of the SC must be quantified. Thus, accelerated ageing modes based on both calendar life tests and power cycling tests have been investigated and the performances degradation of the SC was quantified using periodic characterization tests based on impedance spectroscopy measurements. Hence, the aim of this paper is to determine the contribution of calendar ageing modes in the performances fading of supercapacitors during power cycling. The degradation of the performances was quantified through the monitoring of the parameters for a SC impedance model. Then, the results of calendar life tests were used to define an equivalent acceleration factor for power cycling by considering the impact of the voltage and the temperature individually. The obtained results confirm that the evolution of model parameters during power cycling corresponds to an equivalent calendar ageing, leading to a global approach for the study of the supercapacitors ageing.

How supercapacitors reach end of life criteria during calendar life and power cycling tests

Abstract In this paper, a testing methodology for ageing quantification of supercapacitors (SC) for Hybrid Electric Vehicles (HEV) applications is investigated. In order to ensure optimal performances during the whole vehicle lifetime, the reliability of the SC must be quantified. Thus, accelerated ageing modes based on both calendar life tests and power cycling tests have been investigated and the performances degradation of the SC is quantified using periodic and online characterization for different test conditions. Hence, we discuss the end-of-test criteria using a new representation based on the evolution of the capacitance loss with the increase of the equivalent series resistance.

Prediction of supercapacitors floating ageing with surface electrode interface based ageing law

Supercapacitors (SC) are power devices used as transitory energy sources for peak power applications such as braking energy recovering in hybrid transports. They are subject to electrochemical ageing processes which affect their performances and reliability. Consequently, the main influence factors on SC ageing kinetic are temperature and voltage. Some ageing law based on experiment results have already been produced (for instance the Eyring law) but are not precisely related to physical considerations. In this article, we propose to use an ageing law which links ageing kinetic with the growth of an interface layer between the electrodes surface and electrolyte, called here SEI (Solid Electrode Interface) layer. In order to have a representative sample, 81 commercial supercapacitors coming from 3 different manufacturers will be tested through floating ageing tests at different voltage and temperature constraints. All presented components are manufactured with the most widespread SC technology (double layer SC using activated carbon for electrode and acetonitrile). The fitting of SC experimental ageing results and SEI ageing law is achieved. Then the effect of temperature and voltage on SEI ageing law parameters is performed.

Lithium-ion cell modeling from impedance spectroscopy for EV applications

Investigation dealing with lithium batteries modeling has a growing importance in researches on energy storage for hybrid and electric vehicles. This is especially due to the ever-increase of the applications variability of this kind of battery and the high performances required in severe complex applications. In this paper, we present a model for a 100 Ah high-energy-density Lithium-ion Polymer cell, based on impedance spectroscopy measurements. This model, based on an equivalent-circuit approach, is characterized by its simplicity. At the same time it takes into account several important phenomena that occur into the lithium cell, such as the dependence of a part of the internal resistance and the open-circuit voltage on the state of charge.

Ageing assessment of supercapacitors during calendar life and power cycling tests

Supercapacitors, also known as ultracapacitors, are commonly based on porous activated carbon electrodes and electrostatic charge storage mechanisms. Carbon electrodes are supposed to be chemically and electrochemically inert and the electrostatic nature of the charge storage mechanism is highly reversible. These properties should assure that supercapacitors have an infinite shelf life. But in practice, supercapacitor cells exhibit performances fading when they are used for months.

Power cycling tests for accelerated ageing of ultracapacitors

In this paper, a test methodology is presented and evaluated in order to quantify the lifetime of ultracapacitors in case of active power cycling. The test profiles are specified for taking into account both the high charge-discharge levels and the periodicity of typical HEV applications. Before cycling, preliminary tests have been done with Maxwell BCap 2600F devices and have proved that pulsed current profiles can be predetermined in order to induce a given self-heating. Then, during power cycling, periodic characterization tests have been done in order to follow the evolution of cell parameters. The results at 25,000 cycles illustrate that impedance real part and capacitance are significant parameters for ageing quantification. Furthermore, the trend of these results shows that the self-heating acts as an accelerating factor for ageing.

Electro-thermal model of lithium-ion batteries for electrified vehicles applications

Lithium batteries are key solutions for sustainable energies storage and particularly interesting for green transportation. Vehicle manufacturers are making a clear transition to a more efficient and ecofriendly transport. In fact, Battery Management Systems (BMS) are crucial for a safe and optimized use of these energy storage systems. This article presents an accurate dynamic electro-thermal model for lithium batteries, designed for high power applications. The model has been implemented using MATLAB (Simulink) and parameters were obtained from experiments. Most parameters depend on current, temperature, and Battery State of Charge (SOC). The accuracy of this model is tested under different operating conditions (static and dynamic current profiles) and simulations are in agreement with experimental results, even after twenty hours of test.