Akademik Veri Yönetim Sistemi
4th International EV Charge Show Conference, İstanbul, Türkiye, 12 - 14 Kasım 2025, ss.57-58, (Özet Bildiri)
Calendar aging refers to the time-dependent degradation of lithium-ion batteries that occurs even without cycling. In electric vehicles (EVs), it critically affects the State of Health (SoH), which quantifies remaining capacity and performance. Calendar aging reduces SoH by decreasing capacity and increasing internal resistance, leading to lower driving range and peak power, and negatively impacting EV performance [1], [2]. The rate of degradation strongly depends on storage conditions, with elevated temperatures and high SOC accelerating parasitic reactions such as SEI growth and electrolyte decomposition [2], [3]. SoH deterioration also reduces vehicle residual value and may require earlier battery replacement. Accurate SoH assessment, considering both calendar and cycle aging, is essential for warranty, maintenance, and lifetime cost estimation [3], [4]. Modern BMS incorporate SoH models accounting for calendar aging to predict degradation, optimize charging, and enhance battery longevity [4]. Calendar ageing in Li-ion batteries refers to the irreversible performance degradation that occurs over time while the cell is at rest, without cycling. It is driven mainly by storage temperature, SOC, and duration, and involves side reactions such as SEI growth, electrolyte decomposition, and gas formation, leading to increased internal resistance and reduced capacity [5–7]. For the calendar ageing experiments, commercial 2800 mAh (Aspilsan) and 2500mAh (Samsung) 18650 lithium-ion cells were first charged to 4.2 V using a constant-current–constant-voltage (CC–CV) protocol at a rate of 1C. After charging, the cells were placed into a temperature-controlled oven and stored at 50 °C for one week. At the end of the storage interval, the cells were removed from the oven and allowed to cool to ambient temperature for 24h. Subsequently, electrochemical impedance spectroscopy (EIS) and energy throughput (Wh) measurements were carried out to characterize degradation effects. In addition, open-circuit voltage (OCV), internal resistance (R_int), charge/discharge capacity (Ah), and peak power capability were recorded. The cells were then recharged to 4.2 V at 1C using the same CC–CV protocol, followed by another one-week storage interval under identical conditions. This sequence of full charging → storage at 100% SOC → characterization was repeated in order to impose calendar ageing at 100% SOC, enabling the study of time- and temperature-dependent degradation under high-SOC stress, while providing quantitative data for SoH prediction. During the storage period, flammable gas formation due to electrolyte decomposition or cell venting was monitored and recorded using Hydrogen (H₂), Carbon monoxide (CO), carbon dioxide (CO₂), and Volatile organic compounds (VOC) sensors. These sensors ensure early detection of unsafe conditions during high-SOC, high-temperature calendar ageing experiments.The results demonstrate that high-SOC calendar ageing significantly impacts 18650 Li-ion cell SoH, emphasizing the need for optimized storage and monitoring strategies to ensure reliable performance and longevity in electric vehicle applications.