Eric Woirgard

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.

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.

Thermomechanical modelling and reliability study of an IGBT module for an aeronautical application

In this paper, an IGBT (Insulated Gate Bipolar Transistor) module for an aeronautic application was investigated using non-linear Finite Element Analysis (FEA). Two failure modes were considered: brittle materials fracture and solder joint thermomechanical fatigue. The module reliability regarding these failure modes was evaluated over the 40000 flight cycles required for the application, under the real loading profile. Acceleration Factors (AF) were also computed with respect to Accelerated Thermal Cycling (ATC) used during the module design qualification and validation.

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.

Study of die attach technologies for high temperature power electronics: Silver sintering and gold-germanium alloy

Silver sintering joints and AuGe soldering are promising technologies for high temperature (>200 °C ambient) power electronics packaging. This paper presents the implementation of two silver-sintering processes with the one hand micrometer-scale silver particles, and on the other hand nano-meter-scale particles. Two substrates technologies have been investigated: A12O3 DBC and Si3N4 AMB. After the process optimization, tests vehicles have been assembled using both sintering processes, as well as a more classical high-temperature die attach technology: AuGe soldering. Multiple analyses have been performed, such as thermal resistance measurement, shear tests and micro-sections to follow the evolution of the joint during thermal cycling and high-temperature storage ageing.

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.

Parameters evolution of an ultracapacitor impedance model with ageing during power cycling tests

This paper deals with ageing evaluation of ultracapacitors (UC) during power cycling tests with high current levels. The quantification of ageing is made thanks to the monitoring of model parameters changes. The UC modeling uses a description of the main physical properties as porous nature of the electrodes. The model is defined by four main parameters which are identified thanks to specific characterization tests based on impedance spectroscopy. This model is validated for a new UC under different conditions of voltage and temperature. Then a power cycling methodology is applied. First, the specification of current profiles is made according to both power requirements in hybrid and electric vehicles applications and intrinsic properties of the UC. In order to have significant self heating, a current shape is chosen and used in a preliminary test allowing to verify that the thermal steady state is properly obtained. Then, the power cycling tests is started and the UC parameters changes are recorded thanks to periodic characterization tests. Finally, the results of the accelerated ageing are presented. They show two major effects that are opposed. The first one is the UC performances fading during power cycling tests and the second one is the performances recovery during the rest periods. The evolution of the impedance model parameters is presented and the link to physics is discussed.

Assessment of the Trench IGBT reliability: low temperature experimental characterization

The purpose of this study is an assessment of the Trench IGBT reliability at low temperature under static and dynamic operations by the aim of intensive measurements. The analysis of the Trench IGBT behaviour in these conditions is dedicated to the HEV applications. One question can be raised in case of the use of HEV in countries where during winter the temperature drops down -50°C or less: are Trench IGBT strongly affected by the low temperature environment? In this paper, we present experimental results under various test conditions (temperature, gate resistance, voltage and current) to give an understanding of the device behaviour by focusing on the device current and voltage waveforms and the power losses.