About the service life and discharge characteristics of lithium iron phosphate battery

lithium iron phosphate battery (hereinafter referred to as lithium iron battery) as a kind of iron battery has been widely concerned by friends in the industry (some people say that lithium iron battery is actually a kind of lithium ion battery). As far as iron batteries are concerned, they can be divided into high-iron batteries and lithium-iron batteries. Today, we take the lithium-iron battery model STL18650 as an example to illustrate the discharge characteristics and life of lithium-iron batteries.

The discharge characteristics of the STL18650 lithium-iron battery (capacity 1100mAh) at different discharge rates are shown in Figure 2. The minimum discharge rate is 0.5 C and the maximum discharge rate is 10 C. Five different discharge rates form a set of discharge curves. It can be seen from Fig. 1 that no matter which kind of discharge rate, the voltage during discharge is very flat (that is, the discharge voltage is stable and remains basically unchanged), and the curve is bent downward only when the discharge voltage is terminated. The downward bending occurs only after the discharge amount reaches 800mAh. In the discharge rate range of 0.5 to 10 C, the output voltage mostly changes in the range of 2.7 to 3.2 V. This shows that the battery has good discharge characteristics.

The discharge curve of the STL18650 with a capacity of 1000mAh under different temperature conditions (from -20 to +40 °C) is shown in Fig. 2. If the discharge capacity is 100% at 23 ° C, the discharge capacity at 0 ° C is reduced to 78%, and at -20 ° C to 65%, and at +40 ° C, the discharge capacity is slightly greater than 100%.

The STL18650 lithium iron battery can work at -20 ° C, but the output energy is reduced by about 35%.

The charge and discharge cycle life curve of STL18650 is shown in Figure 4. The charge and discharge cycle conditions were: charging at a 1 C charge rate, discharging at a 2 C discharge rate, and 570 charge and discharge cycles. It can be seen from the characteristic curve of Fig. 3 that the discharge capacity has not changed after 570 charge and discharge cycles, indicating that the battery has a high life.

Over discharge to zero voltage test

The STL18650 (1100mAh) lithium-iron power battery was used for over- discharge to zero voltage test. Test conditions: A piece of 1100mAh STL 18650battery was charged at a charging rate of 0.5 C, and then discharged at a discharge rate of 1.0 C until the battery voltage was 0 C. The batteries placed in 0V are divided into two groups: one group is stored for 7 days, and the other group is stored for 30 days; after the storage expires, it is filled with a charging rate of 0.5 C, and then discharged with 1.0 C. Finally, compare the differences between the two zero voltage storage periods.

The result of the test is that the battery has no leakage after 7 days of zero voltage storage, and the performance is good, the capacity is 100%; after 30 days of storage, there is no leakage, the performance is good, the capacity is 98%; after 30 days of storage, the battery is further charged and discharged for 3 times. The capacity is restored to 100%.

This test shows that even if the battery is over-discharged (even to 0V) and stored for a certain period of time, the battery will not leak or be damaged. This is a characteristic that other types of lithium-ion batteries do not have.

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