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 (SCs) and their power density greater than that of Lithium-Ion Batteries (LIBs). This paper explains the electrochemical processes that interfere in the storage of energy inside a 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.Index Terms-Lithium-ion capacitor, nonlinear capacitance evolution, electrochemical impedance spectroscopy measurements, time domain measurements, energy storage system, constant voltage phase.

Lifetime of Energy Storage Systems (ESSs) 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 twenty 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 evolution of battery management systems has imposed the necessity of evaluating batteries equivalent circuit models. The advantage of this type of modeling is to accurately estimate the dynamic aspects of a battery. Circuit parameters are identified for the purpose of forecasting different battery states. This paper presents multiple circuit models described in the literature. Four types of batteries are studied: Nickel-Metal Hybrid, Lithium-Ion, Lead-acid and Lithium Polymer.

The expeditious development of electric vehicles and hybrid electric vehicles relies on using appropriate energy storage systems such as supercapacitors and lithium-ion batteries. The new technology that combines both conventional energy storage systems is the lithium-ion capacitor. The aim of this component is to fill the gaps between supercapacitor's low energy density and lithium-ion battery's low power density. This paper presents the main electrical characteristics, deduced from frequency domain measurements, of such a technology. The nonlinear capacitance evolution of a lithium-ion capacitor cell with respect to the voltage was analyzed based on its physicochemical properties. Moreover, the lithium-ion capacitor was modeled using a simple model derived from the frequency measurements.

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.

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