Calendar Ageing

Calendar ageing is a type of ageing that occurs in lithium-ion batteries over time, regardless of whether they are being used or not. It is caused by the gradual degradation of the battery's materials due to chemical reactions that occur over time. This type of ageing is different from cycle ageing, which occurs as a result of the battery being charged and discharged repeatedly.

Calendar ageing is an important issue to study because it can significantly impact the battery's performance and safety. As a battery ages, its capacity decreases and its internal resistance increases, which can lead to a reduction in its ability to deliver power. Additionally, calendar ageing can cause the battery to become less stable and more prone to safety issues, such as thermal runaway or short circuits.

There are several factors that can affect the rate of calendar ageing in lithium-ion batteries, including temperature, state of charge, and the composition of the battery's materials. By studying calendar ageing, researchers can develop strategies to extend the lifespan of lithium-ion batteries and improve their performance and safety.

How does it is measured?

It can be measured by monitoring changes in the capacity and resistance over time. One common method of measuring calendar ageing is to charge the battery to a certain level, keep it idle for certain amount of time, and then measure its capacity and internal resistance. Another method of measuring calendar ageing is to use electrochemical impedance spectroscopy (EIS), which involves applying a small AC voltage to the battery and measuring the resulting AC current over a range of frequencies. The impedance can then be calculated from the measurements, and changes in impedance over time can indicate changes in the battery's internal resistance and other properties. Measuring calendar ageing can be challenging, as it is a complex process that depends on many factors, such as temperature, state of charge, and the specific chemistry of the battery's materials. Additionally, accurate measurements require specialized equipment and expertise.

Nonetheless, studying calendar ageing is an important area of research in the field of lithium-ion batteries, as it can provide insights into battery performance and help inform strategies for extending battery life and improving safety.