Now it is unquestionable that battery is the most core and key particle of the electro mobiles. Battery not only affects the functions and endurance of cars but also the life and safety. Therefore it is necessary for both automobile companies and battery plants to test the battery thoroughly for truly understanding battery and well using it. As for people who begin to know the battery testing, they may be confused with various testing terms, standards and methods. So first we begin to analyze the purpose of battery testing and then to know how battery testing is conducted gradually.
(1) Know its features (start with the battery itself): we need to know the capacity, internal resistance, voltage characteristics, ratio characteristics, temperature characteristics, cycle life, energy density and any other important parameters of battery to testify whether the battery reaches the original design goals and to better manage and control the battery during application.
(2) Evaluate its ability to meet the demands (start with application scenarios): this kind of tests could be understood that starting with application requirements to find out what should it be met. And through battery testing the battery is testified whether it reaches the standard or not. For instance, automobile companies will design the cold cranking of battery testing according to the driving scenarios in the low temperatures, and design the energy efficiency testing according to power consumption indicators as well as design the power formance testing according to scenarios of vehicle climbing or acceleration and so on. Additionally automobile companies will design tests of overcharge, discharge, short circuit, over-temperature and squeeze the puncture out of consideration of vehicle safety.
So when we start to know a new testing project, we need to consider that the purpose of this testing is to know the battery or to evaluate its ability in the application scenarios. When you get to know this, you can further know the contents of battery testing.
1. Capacity Test
Capacity test is to measure the battery's available capacity including its energies in different environments and temperatures by static volumetric method. Though different companies has different standards on the SCT test, the general mentality is similar. For instance, fully charge the battery at 25 degrees under the battery manufacturer's rules, fully dispose it and discharge with 1C rate until the voltage gets to 2.5 V, then record the released capacity that is the energy. It could be tested for continuous three times to get mean value for accuracy.
2. Mixed Pulse Power Performance Test
HPPC test is to test battery's characters like the rate functions, open-circuit voltage, internal resistance and so on. The system of HPPC is to discharge impulsively for 10 seconds, let it stand for 40 seconds, and charge impulsively for 10 seconds under some certain SOC purpose. This way could lead to the DCIR of charge and discharge of this SOC position. It should be noted that different test methods of battery may lead to certain difference of DCIR.
3. Rate Capacity Test
Rate capacity test sets different rate of charge and discharge according to power characters(energy type or rate type). For example, if you choose to charge with 0.5C constant current flow, you can discharge with 0.2C, 0 5C, 1C or 2C rate, which provides you with discharge curve in different rate of battery and its constant current flow curve.
4. Self-discharge Test
Discharge test of battery is to ensure the capacity loss after the scheduled shelving time. Specific testing methods has many types. For example, capacity recovery is one of the ways to test the self-discharge. This test is that shelve the battery for 28 days at normal temperature, and then discharge and record the capacity retention. At last do the normal SCT to get the present practical capacity. Calculate the rate of capacity retention to get the self-discharge characters. In real situation methods of high-temperature accelerating and OCV judgement are used to shorten the period of self-discharge test.