Nickel-cadmium and nickel-metal hydride rechargeable batteries can lose charge over time due to a memory effect where they “remember” how full they were when they were last charged. This is caused by a number of chemical processes, with cadmium being the main issue in nickel-cadmium batteries. If the batteries are charged for too long or not completely drained, the cadmium crystals on the anode can grow up to 100 microns and shorten the battery’s lifespan. To prevent this, it is recommended to periodically drain nickel-based batteries completely. Nickel-metal hydride batteries perform somewhat better in this regard.
FAW: The Memory Effect of Nickel-based Rechargeable Batteries
Nickel cadmium and nickel metal hydride rechargeable batteries have been popular for decades due to their ability to be recharged hundreds of times. However, many users have experienced a frustrating phenomenon known as the memory effect. This is when a battery seems to “remember” its previous charge level, causing it to lose capacity over time. In this article, we will explore what the memory effect is and what causes it, as well as how to prevent it.
WHAT is the Memory Effect?
The memory effect is a phenomenon where nickel-based rechargeable batteries, such as nickel cadmium (NiCd) and nickel metal hydride (NiMH), appear to lose their maximum capacity. The reason for this is that these batteries are designed to remember their previous charge levels, and if not discharged completely before recharging, they will only recharge to the previous level. Thus, over time, the battery appears to have less and less capacity, as it never charges to its full potential.
What Causes the Memory Effect?
The memory effect is caused by several chemical processes, but the primary culprit is the cadmium used in NiCd batteries. Cadmium is a highly toxic metal and is well-known for its negative impact on the environment. When a new NiCd battery is manufactured, the cadmium crystals on the anode are tiny, about one micron in size. However, over time and with repeated charging, these crystals can grow to be as large as 100 microns, limiting the battery’s capacity.
This is why NiMH batteries suffer less from the memory effect. NiMH batteries do not contain cadmium and have a more complex chemistry. The nickel-based electrodes in NiMH batteries use metal hydride instead of cadmium. The metal hydride acts as a sponge that absorbs hydrogen during charge, which then releases the hydrogen during discharge; as a result, the active material does not suffer from crystal growth, and the battery has a longer life span.
How to Prevent the Memory Effect?
The best way to prevent the memory effect is to follow a few simple guidelines. Firstly, ensure that you fully discharge your nickel-based batteries before recharging them. This practice will help to break down any large crystal formations and keep the battery capacity at its maximum. Secondly, avoid leaving nickel-based batteries unused for long periods as this can cause dendrite growth, which can lead to short circuits and reduced capacity. If you must store them, make sure they are stored at a moderate temperature, around 20°C/68°F, and periodically charge and discharge them.
Thirdly, consider investing in NiMH batteries rather than NiCd batteries. NiMH batteries do not contain cadmium, making them safer for the environment, and their complex chemistry reduces the likelihood of crystal growth. They also typically have a longer lifespan than NiCd batteries.
The memory effect can be frustrating for those who use nickel-based rechargeable batteries regularly. However, the good news is that it is preventable. By discharging your batteries fully before recharge, storing them correctly, and considering NiMH batteries as an alternative to NiCad, you can help to extend their lifespan and keep their capacity at its maximum.
Remember, nickel-based batteries are handy and convenient, but they require care and maintenance to avoid the memory effect. Follow these simple guidelines, and you can prevent battery capacity loss and save money in the long run.