How to evaluate a power battery? This is a big topic. This article puts aside some other factors such as cost manufacturing, and talks about performance evaluation only on the technical level. First of all, I want to talk about two misunderstandings first.
Do not leave the need for the entire vehicle to evaluate the battery separately.
First of all, I think that the first level of cognition is that there is no best power battery. Only the battery that is most suitable for one car, it is unfair to separately evaluate the quality of a power battery. The first step in evaluating is to figure out your needs. You can't figure out if you need vitamins or protein. How do you know if you are eating apples or eating fish?
In the more classic American manual "FreedomCAR", there is a term called BSF (BatterySizeFactor), which explains "for a specific battery or module design, it is the smallest integer that a single cell or module can meet all FreedomCAR performance and life goals. "In fact, it can be so simple to understand that it is a divisor that decomposes the overall requirements of the battery system into a single unit or module. How much this divisor depends on your system requirements and the actual level of your unit, such as a complete vehicle. The design requires that the pulse power requirement of the battery system under certain working conditions can reach 50kw. When you evaluate a 100-string battery pack, the dividend should be 100, and 500W should be for each unit under the working condition. The evaluation of the pulse capacity, and this dividend should also be used to decompose at the same time, and evaluate other series of other performance. This actually tells us that the first step in evaluating the power battery is to decompose the needs of the entire vehicle. This is also the first major misunderstanding we need.
Can't just talk about the overall performance of the battery in one aspect
It is often possible to see such news on the Internet. "The newly developed battery cell has a mass-to-mass ratio of 500Wh/kg, XXX kilometers, and has lost Tesla." "XX new graphene battery has a cycle life of 3,500 times." "XX car battery system only uses charging for 5 minutes, can run X hundred kilometers", thus boasting a breakthrough in its own battery technology, I think these are very one-sided, and can not justly evaluate whether the technology has really made a breakthrough, Let me give you an example. Please readers to judge the following people who are suitable for playing basketball?
Who is suitable for playing basketball?
A: A person who runs very fast, but has a height of only 170cm;
B: A person who is 2 meters tall, but who is weak and vulnerable to injury;
C: A person who is physically fit and will not be tired after running for 4 hours, but his height and speed are average;
It may be difficult for the reader to make a judgment. In fact, A is like a battery of the LTO system, which can be quickly charged and discharged quickly, but the low voltage determines that its specific energy is not high. B is like a lithium-rich cathode material battery, specific energy. It can be done very high, but its physical fitness and safety are difficult to guarantee. C is like a battery of LFP system. It is stable and durable, but its capabilities are not outstanding. Therefore, in practical applications, it is generally based on actual conditions. The use of the scene to select the right battery is like letting A go to the guard and let B go to the center. When it comes to this, I believe that readers will no longer think that Chinese basketball can compete because there is a person in China who is 2 meters tall. It’s all over the world.
Aside from the above two misunderstandings, we return to the essence of the power battery. The essence of the power battery is actually a vehicle-mounted chemical energy storage device. We know that chemical energy storage is only one kind of energy storage method. Others include physics. Energy storage, electromagnetic energy storage. Since the essence is an energy storage device, it is easy to understand, what should we focus on? How much energy can be stored in the first place, whether the stored energy will "slip away", that is, the ability to store energy; the second is necessary to store it, we should then pay attention to his ability to release energy, how can it be used? Finally, we should pay more attention to the energy control ability of this energy storage device. First, do we control it? Second, does it control itself in the complex environment of the car?
Energy storage capacity
How to evaluate the energy storage capacity of a power battery? I think it mainly lies in two aspects, the first is how much energy can be stored; the second is the stability of energy storage;
How much energy can the first store? In fact, the intuitive view is actually the capacity of a battery, but the capacity of this battery is not the capacity of a battery itself, but the energy that can be released during the whole life cycle of the battery is evaluated. In fact, the battery and life of Fresh have been taken. The batteries at the end of the period are all taken into account. But how much energy storage can release itself is actually how do you use this battery. If you still use 1C to fill up and check how many times a battery can be cycled, I think this has been totally out, first of all, this way There is no practical significance. Besides, I can compare the batteries of several different formulas horizontally. I don't think there is any other reference value, because just as evaluating the battery needs to decompose the whole vehicle first, the life of the battery should also be simulated. Working conditions, the whole car is difficult to appear 100% DOD1C continuous cycle, it is like you have not seen who opened the electric car has been moving forward at a constant speed, no brakes, no electricity, full charge, continue to open, open 10 years Investigate the life of the battery or the energy storage capacity of the whole life cycle. It must be meaningful to combine with the working conditions of the whole vehicle. How do you actually use it in your car? In what SOC interval? Is it a CD or a CS? How to charge when the electricity is used up, fast charge or slow charge, all the combined inspection is of practical significance.
The second is the stability of energy storage. In fact, when you look at how you don't use it, there is no loss in the energy. This is the so-called calendar life. Of course, the calendar life is not at all. It also requires you to use certain simple working conditions. At the same time, it should be carried out at different temperatures for the actual working conditions of different models. With the tracking of the state of the battery itself, the understanding of the calendar state of the battery is finally established. .
Energy release capacity
The ability to release the ability I think in one sentence is to examine how you can release your abilities under various working conditions.
This includes two levels of awareness. The first is in various working conditions, such as different temperatures, different SOCs, different life cycles, and second, how can it be put, how long it can be put, and how much can be put. Let's make the two levels of meaning orthogonal. In fact, you can roughly understand what kind of energy release capability this battery you are evaluating.
Energy control ability
The last one is the ability to control energy. I think it still has two meanings. First, how do we control it? Second, if it is attacked by itself, will it not be able to control itself;
The first thing to talk about is BMS, and the good control is actually the calibration of the battery. How to calibrate the SOC of this battery? In fact, this has always been a problem, but it is actually based on the calibration. The battery of different systems is actually different in calibration difficulty. For example, the SOC-OCV curve is actually a baseline. When we calculate online, we often need to make corrections on it. The calculation of the diffusion voltage and the establishment of the RC model, In fact, it is often related to the different systems of the battery, or the design of the power and energy type. The complexity of the different models of the system is also different. What is more, even if the temperature changes have different effects on the static voltage of the battery, of course, the control The difficulty will be different, so I think that the battery itself is not good control, but it has become one of the standards for evaluating a power battery;
The second is actually the design of the battery itself so that it can manage itself. In addition to the normal use of the vehicle, we also need to consider various extremes, such as acupuncture, extrusion, water immersion, fire, etc. Under these special extreme conditions, the battery can not "hold" itself so that there is no chain The heat is out of control. Of course, the verification of the whole system of the battery is far more than this. It will not be described here, but it is also a key point for us to consider.
In summary, we talked about two misunderstandings, and also talked about the essential judgment of the battery itself, including the storage, release and control of energy. Of course, here is a shallower chat, if the reader Friends are interested in going to see the classic FreedomCAR manual and the ECE_R100 standard developed by UN/WP29. Of course, if you have the opportunity, you will be willing to discuss the two classic materials with your readers.
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