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What is the recoverable memory effect of Ni-MH batteries

by:dcfpower     2021-04-01
Unlike lithium batteries, when sealed nickel-metal hydride batteries (MH-Ni) repeat incomplete charge-discharge cycles, the battery exhibits a recoverable voltage drop and capacity reduction. For example, the battery is fully discharged and charged once, and then partially discharged to 1.15V and charged several times, during which the voltage and capacity gradually decrease, and then the complete discharge is performed. The voltage at this time is lower than the voltage at which the battery is initially fully discharged. When the battery is discharged to the initial termination voltage, the full battery capacity is not released. This phenomenon is called voltage drop. Because the battery seems to memorize a lower capacity, it is sometimes called the memory effect.' But after several full charge and discharge cycles, the battery can recover its full capacity, that is, MH-Ni batteries have a slight but recoverable memory effect.' . In recent years, you may often hear people say 'Ni-Cd and Ni-MH batteries are difficult to use because they have a memory effect' or 'When a battery starts to have a memory effect, it is time to replace it.' The memory effect of the battery does occur in some rechargeable batteries, and the performance is a phenomenon that the capacity of the rechargeable battery decreases. People use this term more and more widely to describe similar situations, but in fact it is not a permanent phenomenon. However, many users don't seem to really understand its meaning, so we explain it here. More professionally, the battery memory effect refers to the reversible failure of the battery. The memory effect refers to the fact that it will automatically maintain this specific tendency after being subjected to a specific work cycle for a long time. Pouch batteries have no memory effect. Sintered batteries have a memory effect. For example, after a long period of shallow discharge cycle, the battery will show obvious capacity loss or voltage drop when it is deep discharged. So let's talk about the elimination method of the memory effect, which is to make the battery fully charged by the normal charging method, which is usually completed by the overcharge method. After the battery is fully charged, it is discharged with a large current to the final voltage, and then discharged at a small current to a fully discharged state, and then charged with a constant current of 0.1C5A for more than 20h to ensure that the positive and negative electrodes of the battery are fully charged, and then discharged as usual To a fully discharged state. Through multiple charge and discharge cycles, the memory effect can be eliminated. The reason for the voltage drop is that only part of the active material participates in the discharge and charge during the shallow charge or partial discharge process; the physical properties of the active material that does not participate in the cycle have changed, and the internal resistance of the battery has also increased. Subsequent full charge and discharge cycles can restore the active material to its original state. The degree of voltage drop and capacity loss depends on the depth of discharge. This phenomenon is very obvious when the discharge reaches a higher end voltage. When the final voltage is 1.15-1.10V, this loss is small. If the termination voltage is lower than 1.1V, there will be no significant voltage drop and capacity reduction in the subsequent discharge process. The memory effect is also related to the discharge rate. For a specific discharge termination voltage, the higher the discharge rate, the smaller the depth of discharge, and the less active materials that participate in the cycle, so the capacity loss increases. u003c/pu003e
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