What is in a NIMH battery?

Compared with lead-acid batteries, nickel-based batteries have relatively higher voltage, higher capacity and longer cycle life. However, with the emergence and development of lithium ion battery,  when we compare li-ion vs ni-mh battery, nickel-based battery is obviously at a disadvantage in energy density and other aspects. In addition, NimH battery has memory effect, which seriously affects the available energy in the cycle process.

Although the memory effect of NimH battery can be minimized to some extent by regular charge and discharge, their high self-discharge rate is another stumbling block.In this article we will mainly introduce the NimH battery.

The material of NimH battery

The anode material of nickel metal hydride battery (NimH battery)is NiOH, and cathode material of NimH battery is hydrogen absorption alloy. Electrolyte usually is the solution of water and potassium hydroxide contains a small amount of NiOH which is about 30%. And the separator of the NimH battery uses porous vinylon non-woven fabric or nylon non-woven fabric.

The characteristic of NimH battery

Self-discharge characteristics:

It refers to the phenomenon of self-consumption of capacity of the NimH battery under the condition of sufficient power without load. Self-discharge characteristics are mainly affected by the temperature. The higher the temperature, the more the capacity self-consumption of the NimH battery when it in idle.

Long-term storage characteristic:

Mainly refers to the power recovery ability of NimH battery . After a long period of storage (e.g., one year), the capacity of NimH battery may be lower than the pre-storage capacity, but after several charging and discharging cycles, the capacity can be renew to the pre-storage capacity.

Cycle life characteristic:

Cycle life of NimH battery is affected by charge and discharge system, temperature and usage. According to IEC standards, the charge cycle of NimH battery is a full charge and discharge cycle. Multiple charge cycles constitute the cycle life, charge and discharge cycle of NimH battery can be more than 500 times.

Safety characteristic:

The safety performance of NimH battery is better than other battery, which is related to the used material , but also has an inseparable relationship with its structure. In the process of use, if the improper usage cause overcharge, over discharge, and short circuit. It will promote the internal pressure of NimH battery , then a recoverable safety valve will be opened and reduce the internal pressure, so the battery explosion can be prevented.

How to charge the NimH battery? Especially for the first time

1. In normal circumstances,the new NimHbattery has very little power, so it needs to be charged first and then used. However, if the delivery time is short and the battery is sufficient, it is recommended to use it before charging. New NimH battery generally need to be charged and discharged for 3-4 times, and the charging time can be slightly longer for best(of course, not too long).In this way, the battery can be activated and its performance can be maximized.

1. Although the memory effect of NimHbattery is small, it is best to carry out a complete charge and discharge cycle every time. And we should charge it a one-time full. Do not charge for a while and then charge again, so that we cankeep the stable charge cycle , which helps to reduce the memory effect of the battery and extend the life of the NimH battery.
2. When charging, pay attention to the heat dissipation around the charger. Keep the NimH battery clean when not in use, especially the contacts at both ends, and gently wipe it with a soft dry cloth if necessary. If it not used for a long time, please remove the NimH battery from the battery compartment and place it in a dry environment.
3. NimH battery will enter a “dormant” state after several months of storage, and their battery life will be greatly reduced. If the NimHbattery has been placed for a long time, it is recommended to charge it with slow charge first. NimHbattery that you will not use for a long time should be removed from the appliance and then fully charged before storage. Otherwise, when you try to use them again after a long time, you will find that the batteries have been broken because of excessive discharge. The best condition for the preservation of NimH battery is about 80% charged, because NimH battery has a large self-discharge (about 10-15% a month). For example, if the battery leave the factory without electricity, and the battery not be used for a long time(not sold), the self-discharge phenomenon of NimH battery can cause the over discharge. It will damage the battery. So a new NimH battery is full charged when it leave the factory (at least 80-90%).

The application of NimH battery

The NimH battery, which comes in both cylindrical and square form, was initially widely used in mobile power devices and has since been found to have significant advantages in hybrid electric vehicles. NimH battery typically have an energy density of 30-80Wh/kg, and the ratio of energy and power is about twice that of lead-acid batteries.

The first mass-produced electric vehicles were powered by NimH battery. However, with the emergence of lithium ion battery with high energy density, the market share of NimH battery in the electrification field is becoming smaller and smaller. So far NimH battery still hold a significant place in the field of hybrid electric vehicles, with more than 7 million Toyota Prius hybrid electric vehicles (using NimH battery) sold worldwide. In addition to the automotive field, with the development of fixed power supply and communication power supply, NimH battery partly replace lead-acid battery and occupy a certain market share.Although the price of lead-acid battery is lower than NimH battery and far lower than lithium battery, but at the aspect of performance, lithium ion battery is better than NimH battery and far better than lead-acid battery. So for the comprehensive consideration of cost and performance , NimH battery has a certain space for development.