How to measure Lifepo4 battery performance?

There are several important indicators to measure Lifepo4 battery performance:

1、 Charge and discharge ratio: the higher the better

"C" is a special symbol to describe the charge and discharge current of the battery. 1C discharge represents the current to discharge the battery from full charge to empty within 1 hour. If the capacity of each battery used in BYD e6 electric vehicle is 200AH, the 1C discharge current of this battery is 200A. If a battery is discharged at a high rate, it usually releases less energy than the low rate.

2、 Number of charge-discharge cycles: more is better

The number of charge and discharge cycles is 500 times, which is a common value for lithium batteries. The number of charge and discharge cycles for lithium batteries made of different materials varies from 300 to 3000 times. Winston Battery, CALB Battery, CATL Battery, Sinopoly Battery, Headway Battery and so on. The specific meaning of this value may vary slightly from factory to factory, which can be roughly understood as follows: according to the charging and discharging rate specified by the manufacturer (such as 1C discharge, 0.3C charge; each time from 0% to 100%, according to this cycle), after 500 cycles, the battery capacity remains at the initial 80%. The charge and discharge times have too much to do with usage habits. Let's give a few examples.

① Influence of charge-discharge intensity on cycle number

Factory notes: each time from 0% to 100%, 1C to 0.3C, the capacity will decay to 80% after 500 times. This is the most severe test cycle, but it can be less stringent:

If each cycle of power is between 25% and 75%, the capacity will be reduced to 80% after 2000 times of discharging at 1C and charging at 0.3C

If each cycle of power is 50% - 100%, 1C discharge, 0.3 charge, the capacity will decay to 80% after 1800 times

② Influence of shallow filling and shallow lowering on service life

Factory notes: each time from 0% to 100%, 1C to 0.3C, the capacity decays to 80% after 500 times, which is the most severe test cycle, or not so strict:

Each power cycle is between 25% - 75%, with 1C discharge and 0.3C charge. After 2000 times, the capacity decreases to 80%

Each power cycle is 50% - 100%, 1C discharge, 0.3 charge, and the capacity decays to 80% after 1800 times

From the above two examples, it can be seen that the smaller the rate of charge and discharge, the better the service life; Shallow charging and shallow discharging are also conducive to the improvement of service life.

3、 Internal resistance: the smaller the better

This parameter changes with the load, temperature and other factors at any time. As the battery life decreases, the internal resistance also gradually increases. The smaller the internal resistance, the higher the rate of charge and discharge. The internal resistance of the 18650 battery is about 50m Ω, and that of the power 18650 battery is about 15m Ω. If you want to know how large the internal resistance is, you need to use special equipment to measure it, but the ordinary multimeter can not.

4、 Battery consistency

The higher the consistency of the capacity, internal resistance and charge-discharge curve of the battery produced by the same material and process, the better. It is very important that the battery can form a battery pack on a large scale. The larger the battery pack is, the higher the consistency requirement is.

Article source: https://article-realm.com/article/Finance/33939-How-to-measure-Lifepo4-battery-performance.html