Self discharge of Ni MH battery

Self discharge of Ni MH battery

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

There are three main factors affecting the self discharge of nimh batteries.

Ⅰ. Temperature: generally, the higher the temperature, the greater the self discharge; conversely, the lower the temperature, the smaller the self discharge.

Ⅱ.  It is related to the charge of the battery. Usually, the full charge of nimh battery is higher, and the self discharge rate is also higher ( The average value ). When the higher battery capacity falls to a lower capacity, it has the same self discharge rate with other batteries with the same low capacity.

Ⅲ. Influence of storage conditions. Ni MH battery is in a conductor environment, which may generate micro current and accelerate the self discharge process of the battery. The instantaneous large current caused by an accidental cause may even cause a short circuit.

Reducing self discharge is an important part of improving the performance of Ni MH battery. Aiming at the cause of self discharge, it can be improved from the following aspects:

Ⅰ. Temperature environment: according to the regulations of IEC, the storage temperature of nimh battery is 20±5℃, and its working temperature is generally 0~40℃ centigrade;

Ⅱ. The battery should be charged for storage because the self discharge rate of the ordinary Ni MH battery is up to 30%, so that the battery can be stored at a capacity of 80%, at least 40% of the electricity, because the self discharge rate of the battery in 40% capacity will be much smaller. If the capacity is not enough, it is easy to forget the power supply and make the nimh battery over discharge;

Ⅲ. The storage environment should be clean and neat, so as to prevent dust from containing conductor material and make the battery self discharge faster.

In mechanism, the self discharge is related to the dissolution of the cathode material in the electrolyte and the instability of the material after it is heated, and the self decomposition is related to it. Therefore, the self discharge of the Ni MH battery is unavoidable by its structure, but the control of the self discharge can be achieved through the correct use of the user in the reversible range. In addition to the improvement measures of the three aspects mentioned above, it should be filled in time. The electric charge is added to self discharge, so that the self discharge will not happen irreversible.

There are some low self discharge nimh batteries in the market. The cost is high, but it can still maintain 80% capacity after a year, so the number of charging can be significantly reduced.