Electronics believes that it is very important to correctly understand and use lithium batteries for electric vehicles

Since electric vehicles entered every family in 2010, after 10 years of development, they have gradually completed the transition from lead-acid batteries to lithium battery packs. In 2012, electric bicycles using lithium batteries began to appear. The common specifications are voltage 36V/48V and capacity 8Ah-12Ah. If an electric bicycle with pedals uses a 48V12Ah lithium battery, the battery life can reach 50 kilometers. Basically, it can meet the short-distance travel needs of families. Electronics will now explain some of the relevant knowledge of lithium batteries, so that we can buy lithium batteries for electric bicycles, and we can better maintain the batteries during use, so that they can last longer. 1. Charge and discharge rate Bicycle batteries have no special requirements for charging. The common charge rate is between 0.1C-0.3C. Ordinary lithium batteries can do it, but the discharge rate is slightly higher, and at least 1C is required. The pressure is not great for the battery factory. But there is still a kind of electric motorcycle that adopts the shape of a scooter, and the speed can even exceed 100km/h. The battery requirements of this kind of car are raised to 2C-3C, so if you assemble this high-performance electric car yourself, Make a good calculation when purchasing a battery. Manufacturers often don’t have to worry about the batteries they match. There are generally three types of batteries: lithium iron phosphate batteries, ternary lithium batteries, and power ternary batteries. Their highest discharge rates are: 2C, 1.5C, and 10C. You can also increase the current corresponding to 1C discharge by increasing the capacity of the battery pack. However, in general, the high discharge rate lithium battery performs better in terms of power, because the performance of the higher rate power ternary lithium battery's instantaneous discharge current is always stronger than that of the ordinary ternary lithium battery. 2. The number of charge and discharge cycles The life of lithium iron phosphate battery is about 2000 times, the ternary lithium battery is about 800 times, and the power ternary lithium battery is about 800 times. However, because electric bicycles are often not single batteries, the barrel effect causes capacity failures after grouping, and the service life after grouping is usually 4/1 to 2/1 of that of a single unit. Of course, the life of lithium batteries is also related to usage habits. The energy density of lithium iron phosphate is 40% lower than that of a ternary lithium battery. The lithium iron phosphate battery of the same energy has a large volume and a heavy weight. The advantage is that it has a large number of cycles and is easy to maintain. For example, the conditions just mentioned are still the conditions just mentioned. When the ternary lithium battery is fully charged for 3 months, the battery capacity decays to 60% of the initial value, but the lithium iron phosphate can maintain 90% in the face of such harsh storage conditions, although it is also lost, but Far less serious than ternary lithium battery. This reason is related to the fact that most of the energy of lithium iron phosphate (more than 85%) is concentrated on the 3.2V voltage. Although the cut-off voltage for charging of this battery is 3.6V, the energy stored in the range from 3.6V to 3.2V is not enough. To 1% of the total energy, even after being fully charged, the voltage will drop to 3.2V after a few minutes. So lithium iron phosphate automatically maintains low voltage stress. It is not easy to form a passivation film. This reason is also one of the reasons why the life of lithium iron phosphate batteries is longer than that of ternary lithium. 3. The internal resistance of the battery. Regarding the internal resistance, you can find relevant information on Baidu. Internal resistance is the standard basis for all battery life assessments. As the battery is used, the corresponding resistance of the battery will become larger and larger. Under normal circumstances, when the battery fails, we can determine whether the single cell of the battery can be reused again by the internal resistance of the battery. Fourth, the issue of battery consistency is more important. At present, there are roughly two types of single batteries used in electric bicycles: 1. Small single batteries, that is, 18650 batteries, with a capacity of 2.2Ah-2.6Ah, and the number of battery cells in each group is 200. -500 pcs. 2. Large single battery, the capacity is generally between 20Ah-40Ah, and the number of battery cells in each group is 15-30. Let's take the 72V40Ah battery pack as an example. If a small single battery is used, 20 strings and 19 parallels are required, with a total of 380 18650 batteries. Every 20 batteries are connected end to end. The voltage difference of 19 battery packs must be within 0.02V for charging and discharging at any time. It sounds very demanding, but in fact it is not as difficult as imagined, because the process of 18650 battery has been Very mature, the consistency of the same batch of batteries is quite good. Consistency usually describes that the voltage and internal resistance of a batch of batteries are infinitely close. If the voltage deviation is too large, the answer will cause the battery composition to be unbalanced. Unbalanced batteries will not be able to be used normally after the battery pack is charged several times. Discovered the risk of fire and explosion. When the consistency deviation of the internal resistance is too large, it will directly affect the service life of the battery. The combination of large monomers may become the mainstream way in the future. More convenient maintenance is becoming more and more important. If 20Ah large single cells are used, 20 series and 2 parallels are required, and a total of 40 large cells are required. As long as these 40 cells are synchronized, there is no problem. In general, the large cells are consistent after being grouped. The chance of problems on the Internet is even smaller. There are also disadvantages. If it is a large lithium iron phosphate battery, the consistency will be much worse than that of a ternary lithium battery. Therefore, the battery pack needs to add an automatic equalization circuit to determine which battery needs to be at the end of each charge. Charge it separately for a while to solve the weakness of poor consistency of lithium iron phosphate. The issue of consistency has risen to a very important position here, but it has not yet reached its extreme. Disclaimer: The articles published on this site are all from the Internet and do not represent the views of this site. If there is any infringement, please contact to delete WeChat: Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact delete A: The charger manufacturer analyzes the trade-off factors of the charge management of nickel and lithium batteries.