The calendar fade refers to the gradual performance deterioration that many battery types experience, even while they are not in use. Because of calendar fade, even a home energy storage system that has been used sparingly is likely to have undergone severe deterioration by the time its guarantee expires. Some battery types, such as zinc-bromide batteries, are immune to this issue.
All ageing processes that cause a battery cell to degrade without the aid of charge-discharge cycles are referred to as calendar ageing. It is a significant factor in many lithium-ion battery applications, such as in electric automobiles, because the working times are significantly shorter than the idle periods. In cycle ageing investigations, the degradation caused by calendar ageing can also be a major factor, particularly when cycle depths and current rates are low.
The calendar ageing of lithium-ion batteries is examined for 16 states of charge (SoCs) ranging from 0% to 100% at various temperatures. As per research, three different 18650 lithium-ion battery types with various cathode materials have been studied.
The very research shows that the pace of calendar ageing does not rise gradually with SoC. Instead, plateau zones are seen where the capacity fading is identical and cover SoC intervals of more than 20 to 30 percent of the cell capacity.
What causes capacity decline during calendar ageing?
A shift in the electrode balance is the primary source of the capacity decline, according to differential voltage investigations. The study also demonstrated the significant influence of the graphite electrode on calendar ageing.
Lower anode potentials have been found to be the primary cause of capacity fading during storage because they exacerbate electrolyte decrease and consequently encourage the formation of the solid electrolyte interphase.
Also Read: What is Capacity Factor (CF)?
The low anode potential promotes the loss of cyclable lithium in the high SoC regime, where the graphite anode is more than 50% lithiated, which in turn distorts the electrode balance. High cell potential appears to have little effect on ageing mechanisms such as transition-metal dissolution or electrolyte oxidation. Avoid high storage SoCs that have a low anode potential if you want your battery life to be as long as possible.