Lifetime of energy storage systems is a key factor that is extremely influenced by the operating conditions. For this reason, lithium-ion batteries (LiBs) and supercapacitors (SCs) were subjected to accelerated aging tests in several previous research in order analyze their lifespan. Lithium-ion capacitors (LiCs), which fall in between LiBs and SCs, are still considered as a novel technology. Their behavior during accelerated aging tests is not yet well studied in the literature. This paper focuses on studying the degradation of their properties during floating aging. Eighteen samples were tested under three different voltage values and two different temperatures over 12 months. Cells that were discharged to the minimum voltage showed a severe capacitance decrease that was much higher than the one of fully charged cells. The best storage voltage of LiCs was found to be 3 V, which is equivalent to a half charging state. The hybrid structure of LiCs was found to be the major cause of this change in behavior during aging at different voltages. Mechanisms that affect the electrodes and the internal composition of the cells in the diverse conditions were analyzed and predicted.

The integration of energy storage systems (ESSs) in contemporary applications highly depends on the performance of these devices. Supplying high power for a reasonable period of time is one of their main targets in several applications like backup systems and transport technologies. For this purpose, lithium-ion capacitors (LICs) would demonstrate better suitability than conventional ESSs for applications requiring a small installation space and a long lifetime. They are known for their energy density greater than that of supercapacitors and their power density greater than that of lithium-ion batteries. This paper explains the electrochemical processes that interfere in the storage of energy inside an LIC. The analysis of these phenomena was the tool for assessing the nonlinear capacitance evolution of the LIC with respect to its voltage. Several measurement techniques in the frequency and time domains were elaborated and compared in order to assess this nonlinear behavior of the LIC. Some of the measurement protocols contained constant voltage phases that had a significant effect on the variation of the capacitance. The novelty of this study concerns the introduction of a new measurement protocol that takes into account the particular characteristics of LICs. Their unique behavior is explained for the first time based on a physicochemical analysis.

Lithium-ion Capacitors (LiCs) that have intermediate properties between lithium-ion batteries and supercapacitors are still considered as a new technology whose aging is not well studied in the literature. This paper presents the results of accelerated aging tests applied on 12 samples of LiCs. Two high temperatures (60 °C and 70 °C) and two voltage values were used for aging acceleration for 20 months. The maximum and the minimum voltages (3.8 V and 2.2 V respectively) had different effects on capacitance fade. Cells aging at 2.2 V encountered extreme decrease of the capacitance. After storing them for only one month at 60 °C, they lost around 22% of their initial capacitance. For this reason, an aging model was developed for cells aging at the lowest voltage value to emphasize the huge decrease of the lifetime at this voltage condition. Moreover, two measurement tools of the capacitance were compared to find the optimal method for following the evolution of the aging process. It was proved that electrochemical impedance spectroscopy is the most accurate measurement technique that can reveal the actual level of degradation inside a LiC cell.

Lithium-Ion Capacitors (LICs) are a new technology of hybrid supercapacitors that aims to deliver relatively high energy and high power. Therefore, they are known for their constitution inspired from lithium-ion batteries and conventional supercapacitors. Due to their hybrid structure, they have a unique behavior during aging. This paper concerns the effects of high temperatures (60°C and 70°C) and two states of charge (fully charged and fully discharged) on the acceleration of aging of LICs. Fully charged and fully discharged cells were mounted at high temperatures and the evolution of their properties was monitored during 12 months. Electrochemical Impedance spectroscopy was the tool for regularly measuring their capacity. Results showed that fully discharged LICs encounter huge deterioration of performance. For example, at 60°C, a capacity decrease of 45 % was found. On another hand, fully charged cells lost around 12 % of their initial capacity Therefore, the state of charge that should be avoided when leaving LICs at rest is introduced for the first time in a paper. Moreover, based on the comparison of capacity decrease of fully discharged cells at different temperatures, the parameters of Arrhenius equation were analyzed. A physicochemical interpretation of the results was made according to the established results.

The capacitance of Lithium-ion Capacitors (LiCs) highly depends on their terminal voltage. Previous research found that it varies in a nonlinear manner with respect to the voltage. However, none of them modeled the capacitance evolution while considering the physicochemical phenomena that happen in a LiC cell. This paper focuses on developing a new capacitance model that is based on the Stern model of the electrochemical double layer capacitance. The model accounts for the asymmetric V-shape of the C(V) curve, which reflects the variation of the capacitance with respect to the voltage. The novelty of this study concerns the development of a model for LiCs that relies on the fundamental theory of Stern for the differential capacitance. The basic model of Stern is modified in order to account for the hybrid physicochemical structure of LiCs. Moreover, the model was applied to three aged cells to which accelerated calendar aging tests were applied at three voltage values: 2.2, 3 and 3.8 V. A drift of the voltage corresponding to the minimum capacitance was detected for the aged cells. This voltage is related to the neutral state of the positive electrode. The main cause of this phenomenon concerns the loss of lithium ions from the negative electrode of a LiC. In addition, capacitance values decreased after aging, showing an eventual blocking of the pores of the positive electrode. Therefore, the analysis of the C(V) curve was found to be an interesting tool for the interpretation of aging mechanisms.

This paper presents the design and simulation-based evaluation of a 225 kW grid-interactive bidirectional fast DC charger for electric vehicles operating in both grid-to-vehicle (G2V) and vehicle-to-grid (V2G) modes. The proposed charger is developed in MATLAB/Simscape and integrates a two-level PWM AC/DC converter, a bidirectional DC/DC stage, an LCL-filtered grid interface, a regulated 1000 V DC-link, and a lithium-ion battery pack operating under CC and CC–CV control. The battery model and supervisory state-of-charge signal are reused from a previously validated electro-thermal and EKF-based battery framework and are embedded here within a charger-level architecture to study the coupled behavior of the battery, converter, and grid interface. Under nominal operation, the charger achieves near-unity power factor and low grid-current total harmonic distortion of 0.55% in G2V mode and 0.26% in V2G mode. The study also examines charger behavior under bidirectional mode transitions and disturbed-grid conditions including source-harmonic injection, voltage sag, frequency deviation, and reactive-power command tests. The results show stable bidirectional operation, preserved DC-link regulation, and acceptable current quality under both nominal and non-ideal conditions, providing a charger-level simulation reference for future real-time and experimental validation.