Jean-Yves Delétage

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.

Conductive adhesive joint for extreme temperature applications.

Abstract This work describes the thermo-mechanical behaviour of Polyimide Isotropic Conductive Adhesive (ICA) used on passive components assemblies in harsh thermal environment. Shear tests were carried out in an “Instron tensile” machine for thermo-mechanical characterization. The stress–strain curves have been used finite element models (FEM) parameterisation. Numerical modelling simulations have shown the most probable failure area, where accumulated strain in the adhesive is the highest. In addition, simulation results have been compared with results from aged assemblies. The comparative approach has permitted to evaluate the influence of the presence of voids in adhesive joints.

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.

Assessment of uni-axial mechanical stress on Trench IGBT under severe operating conditions: a 2D physically-based simulation approach

Power devices in their environmental application are submitted in addition to the electrical, thermal, radiation and other kinds of stresses to mechanical stress. In our study, we focuse in combination of electrical, thermal and mechanical stresses of a Trench Gate Punch Through Insulated Gate Bipolar Transistor during switching transients. With a 2D physically-based finite elements simulator, we can achieve electro-thermo-mechanical simulations. Two operating configurations have been analyzed: inductive switching and short circuit. Simulation results show that whereas the mechanical stress has low effect on the current tail during clamped inductive switching turn off and on the sustain voltage during unclamped inductive switching, the saturation current during short-circuit operating is strongly affected by external mechanical stress depending on its level, direction and nature (compressive or tensile).

Thermomechanical behaviour of adhesive jointed SMT components

This paper compares the efficiency of two thermosetting and one thermoplastic conductive adhesives for SMT assemblies. Their reliability is evaluated during accelerated life tests through electrical and mechanical measurements. The contact metallizations are taken into account. Finite element simulations confirm the experimental results, and a parametric study allows us to define some choice criteria for the physical properties of the adhesives.

Processing and characterization of a 100% low-temperature Ag-sintered three-dimensional structure

Due to RoHS restrictions, researches on lead-free packaging have increased over the past decade. Low Temperature Joining Techniques (such as silver sintering or Ni-Au Transient Liquid Phase Bonding) are particularly studied because they are processed below 300°C and the attaches obtained are reliable at high temperature. Silver paste sintering technique for die backside attach is now a well-known technology used in both industry and academic research. The objective of this work is to adapt the procedure related to conventional silver paste sintered assembly to produce a three-dimensional module. For such purpose, this paper presents some theoretical considerations on silver sintering in order to briefly introduce the technique. Then, sintering procedures for realizing both die backside attach and three-dimensional structure will be described. Experimental results (electrical and mechanical tests, cross-sections, thermal measurements) will be given and performances of the double-side structure will be compared to die backside attaches and with lead-free solder. This work demonstrates for the first time the feasibility of a 100% silver sintered three-dimensional module using silicon diodes and Ni-Au substrate. Mechanical properties of the two attach-packages are better than classical solders and the performances of each attach are similar to silver sintered die backside attach. These promising results open the way to the use of silicon devices for high power density assemblies because the dice will be cooled down on both sides. This technology just requires silver metallization on the two sides of the device and can be extended to new materials such SiC or GaN for high temperature applications.

Ageing quantification of supercapacitors during power cycling using online and periodic characterization tests

In this paper, a testing methodology for ageing quantification of supercapacitors (SC) for hybrid electric vehicles (HEV) applications is investigated. The accelerated ageing tests are based on power cycling and on the definition of a current profile that takes into account the high charge-discharge current levels of typical HEV functionalities. An online characterization method is used to follow the degradation of the cells performances in terms of evolution of capacitance and equivalent series resistance. The reproducibility of the measurements allows quantifying the impact of both the voltage and the temperature on the ageing for a significant number of cycles. Then, the regeneration phenomenon that appears during the power cycling stops is highlighted and its real impact on the cycle life is discussed. This database of experimental results will be used further to develop ageing laws that will be implemented in SC simulation models in order to optimize the sizing of the cells for a given HEV application.

Three-dimensional FEM simulations of thermomechanical stresses in 1.55 μm Laser modules

Abstract The purpose of this study is to present three-dimensional simulations using finite element method (FEM) of thermomechanical stresses and strains in 1550 nm Laser modules induced by Nd:YAG crystal Laser welds and thermal cycles on two main sub-assemblies: Laser submount and pigtail. Non-linear FEM computations, taking into account of experimental σ(e) measured curves, show that Laser welding process can induce high level of strains in columns of the Laser platform, bearing the Laser diode, responsible of an optical axis shift and a gradual drop of the optical power in relation with relaxation of accumulated stresses in the sub-assembly. In the case of thermal cycles, stresses can occur on elements sensitive to coefficient of thermal expansion mismatches such as solder joint between the Laser platform and thermoelectric cooler and as fiber glued into the pigtail leading to crack propagation with sudden drop of optical power. The main objective of the paper is to evaluate thermomechanical sensitivity and critical zones of the Laser module in order to improve mechanical stability after Laser weld and reach qualification standards requirements without failures. Experimental analyses were also conducted to correlate simulation results and monitor the output optical power of Laser modules after 500 thermal cycles (−40 °C/+85 °C VRT).