In order to understand the battery attenuation of electric vehicles, SAIC Roewe found two electric vehicles, a pure electric drive Roewe E50 and a plug-in hybrid Roewe E550. Among them, E50 meter mileage is 40,639 kilometers, and E550 meter mileage is 575,547 kilometers.
Both cars have been appraised by Nuo Nuo Taoche Consultant. Judging from the information such as the wear and tear in the car, the state of consumables, maintenance records and the data recorded by the on-board module, the mileage reliability of the car is extremely high.
Then, we removed the batteries of the two cars and sent them to the laboratory in Tsinghua University for testing to see what state the batteries were in.
Before publishing the experimental results, let's talk about two factors that lead to battery attenuation-internal resistance increase and battery management.
If you often read the test report of Nuo Nuo's self-operated cars, you should not be familiar with the word internal resistance. Internal resistance refers to the "resistance" of the battery when the battery is working.
In the list of consumables for self-operated vehicles, we will test the battery internal resistance of each self-operated vehicle. When the ordinary gasoline vehicle is started, the starter needs a very large current, and the lead-acid battery voltage of the vehicle is generally 12V. Because I=U/R, if the internal resistance r is too large, the current will be too low, making the vehicle unable to start.
The same is true for the batteries of electric vehicles. With the use of the battery, the internal resistance gradually increases, which leads to the decrease of the current that the battery can output, that is to say, the battery capacity decreases, thus affecting the cruising range of the car. The internal resistance is an important parameter to measure the performance of the battery, but the internal resistance has a great influence on the power battery because of the large current when the electric vehicle is working. At the same time, it is also influenced by many factors, such as the material of the battery itself, manufacturing technology and so on.
In addition to internal resistance, battery management is also a key factor affecting battery performance. If there is a good battery management, the battery performance attenuation can be greatly reduced. As we all know, the battery pack of electric vehicles is composed of many single batteries, such as the battery of Tesla Model S that we dismantled a long time ago. Its entire battery pack consists of more than 7,000 small batteries, so managing the consistency of each battery (small battery) becomes a key issue.
If all batteries can be discharged and charged synchronously, the battery can charge and discharge the most electricity at this time, but with the increase of battery use and charging times, the capacity of each battery and the remaining electricity in the battery will change.
Let's imagine a simple situation. A battery pack has only two batteries, and the capacity is the same. At this time, one battery has 50% power and the other battery has 80% power. Now put it together, and the battery with low power must be put first. If one battery in the whole battery pack is discharged, the other batteries can't be discharged, otherwise it is equivalent to charging the discharged battery. The same is true for charging. After one battery is fully charged, other batteries will not be charged. If you continue to charge, it will be overcharged, which may lead to high temperature, fire and other dangerous situations for a long time.
Speaking of battery temperature control and safety, I have to say that SAIC has done a very good job. Their engineers told me that SAIC's current battery safety technology has reached the L0 level. Once the heat is out of control, it will not spread outside the battery pack, and the whole battery pack will smoke at most, but it will not catch fire.
Let's talk about battery management. In fact, the capacity of the whole battery pack is just like the barrel effect, and the shortest wooden board determines the capacity of the whole barrel. In practical application, battery management is very complicated, because you have to face the situation that the battery capacity is different from the remaining power, so engineers will try their best to balance the battery power with hardware and software.
Knowing the two factors that affect battery attenuation, let's take a look at the experimental results.
The experimental method is to fully charge and discharge two groups of batteries to get the charging capacity and discharging capacity, and then get the battery capacity value through constant current discharge.
The Roewe E50 driven by pure electricity has a short mileage but a long car age. You may intuitively think that its battery should also have obvious attenuation. In fact, the battery capacity test result of E50 is 5 1Ah, and the capacity in the new state is 60Ah, which means that the battery capacity is 85% of that in the new state. For batteries, the range of 100% to 80% is normal attenuation, but 80% is a hurdle. If it is lower than 80%, the attenuation will accelerate sharply, which will affect the normal use.
Plug-in hybrid Roewe E550, its battery capacity test result is 34Ah, and the capacity in the new state is 40Ah, so its current battery capacity is also 85% of that in the new state. Although we are not sure how many times its battery has been charged and discharged during the 570,000-mile driving, as a powerful hybrid car, its battery should be in working condition for a long time, so I think such test results are enough to prove that its battery is excellent.
Finally, I would like to share with you some tips for prolonging the battery life of electric vehicles.
In fact, batteries are just like the human body. You should give it a very healthy working environment, including the temperature, neither too high nor too low. Do not use batteries violently, and try to reduce high-power charging and discharging; Don't charge the battery with very low power, just try to keep the battery in the range of 20%-90%.
In fact, through this experiment, we can see that the battery of electric vehicles has made great progress and is much more reliable and durable than we thought. In the future, developers will continue to make breakthroughs in manufacturing technology and battery materials, making the performance of batteries more and more powerful. By that time, the internal combustion engine may really have no meaning of existence.