Factors of self-discharge of nickel-hydrogen battery and improvement methods

When the battery is not connected to the external circuit, the battery capacity loss caused by the internal spontaneous reaction is the self-discharge of the battery. Among all the power battery types, the nickel-hydrogen battery has the largest self-discharge, and the ordinary nickel-hydrogen battery reaches the self-discharge rate of 30%.

There are three main factors affecting the self-discharge of nickel-metal hydride batteries:

1. Temperature influence: Under normal circumstances, the higher the temperature, the greater the self-discharge; on the contrary, the lower the temperature, the smaller the self-discharge;

2. It is related to the battery charge. Generally, the fuller the nickel-metal hydride battery is charged, the higher the self-discharge rate. Here is the average value. When the higher battery capacity drops to a lower capacity, the self-discharge rate of other batteries with the same lower capacity is the same;

3. The impact of storage conditions. Nickel-metal hydride batteries in a conductor environment may generate micro-current, speeding up the self-discharge process of the battery, and the instantaneous high current passing by accidental causes may even cause a short circuit.

The self-discharge of the battery will cause capacity loss. Most of this loss is reversible. It can be supplemented by the charging behavior. The terrible is the over-discharge caused. The over-discharge is actually the storage and work of the battery in the case of a small amount of charged or unpowered. The way, it often appears as a low voltage or zero voltage of the battery, thus forming an irreversible loss of partial capacity.

Reducing self-discharge is an important part of improving the performance of Ni-MH batteries. For the cause of self-discharge, we can improve from the following aspects:

1. Temperature environment: According to the IEC standardized nickel-hydrogen battery, the storage temperature is preferably 20±5°C; and the working temperature is generally 0~40°C;

2, the battery should be charged storage, because the self-discharge rate of ordinary nickel-hydrogen battery is as high as 30%, so try to make the battery store at 80% capacity, at least 40% of the electricity, because the battery is self-discharge at 40% capacity The rate will be much smaller. If the capacity is not enough, it is easy to make the NiMH battery in the over-discharge because it has forgotten the power supply;

3, the storage environment should be clean and tidy, in order to prevent the dust containing conductive material to make the battery self-discharge faster.

From the mechanism, the size of the self-discharge is related to the dissolution of the positive electrode material in the electrolyte and its instability after heating, which is easy to self-decompose. Therefore, the self-discharge of the nickel-hydrogen battery is determined by its structure, but it is controlled. Self-discharge in the reversible range can be achieved by the user's correct use, in addition to the above three aspects of improvement measures, it is necessary to charge in time to supplement the power loss caused by self-discharge, so that self-discharge will not cause irreversible reaction.

There are some low self-discharge nickel-metal hydride batteries on the market, which are expensive, but can still maintain 80% capacity after one year, so the number of times of charging can be significantly reduced.

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