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The so-called memory effect in lithium-ion batteries, especially in the past, may have a negative impact on the storage capacity of batteries. The memory effect is triggered by the frequent partial discharging of the battery. This creates a premature voltage drop, causing the cell voltage to fall below the minimum requirement of the unit. Subsequently, the accumulator stores the charge level of the partial discharge as a “memory” and only provides a reduced capacity. Further partial discharges increase the effect.
Despite sufficient charge, the performance of the battery decreases. The device using the battery no longer functions for the usual length of time and the battery must be recharged much more frequently. If the lithium-ion battery memory effect is pronounced, the unit can even become unusable long before the end of its service life.
In our guide, you can read to what extent lithium-ion batteries are affected by the memory effect, what role the effect still plays in batteries today, and how it can be avoided.
Li-ion memory effect – which batteries are affected?
The problem of capacity loss due to this issue affects all battery types. However, the effect is most pronounced in nickel-cadmium batteries (NiCd) since, if the energy storage device is not completely discharged, crystals form on the cadmium cathode in the non-discharged area. These crystals reduce the conductivity of the material, resulting in a voltage drop. Thanks to technical developments, however, the memory effect in nickel-cadmium batteries is much lower today than in the past.
It was previously assumed that lithium-ion batteries would not be affected by the memory effect. However, researchers at the Paul Scherrer Institute in Switzerland and at Toyota’s Japanese research laboratory were able to observe the effect in lithium iron phosphate (LiFePo) batteries. This type of lithium-ion battery usually has a stable cell voltage with a flat charge and discharge curve. The researchers interpreted the anomalous voltage deviations that could be detected in tests as capacity changes that are very similar to the memory effect.
Memory effect and lithium-ion batteries – not as innovative as originally thought?
The discovery of the research group disproves the assumptions that lithium-ion batteries would not be affected by the memory effect. However, the voltage change is so small that it is only in the per thousandth range. This means that the effect is still very different from the loss of capacity in nickel-cadmium batteries. This is made possible by the construction of the lithium-ion batteries and the materials used.
In addition, tests done on the memory effect in lithium-ion batteries showed that the effect is only temporary and can be reversed with a waiting period between partial charging and complete discharging. Appropriate battery management systems that take this effect into account could automatically ensure that the capacity of lithium-ion batteries is maintained even in the case of frequent partial discharges.
In this way, intermediate charging is possible at any time, even if the battery is not completely discharged. In this way, vehicles powered by lithium-ion batteries, such as electric stacker trucks, do not have to be used until the battery is completely empty, but can be partially recharged during breaks in work or after the end of use. Furthermore, the service life of both nickel-cadmium and lithium-ion batteries can be extended with frequent partial discharges. It is recommended that the batteries are fully discharged once after approximately 50 partial discharge cycles. You can find more information about this in our guide on lithium-ion batteries.
Please note: The regulations mentioned above represent only a selection of the most important legal requirements. Please refer to the listed organisations and directives for more detailed information. If in any doubt, consult experts or contact the relevant regulatory authorities.
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