Safety and battery life shall be considered for -Lithium - Ion Battery Equipment

Safety and battery life shall be considered for fast charging -Lithium - Ion Battery Equipment

On September 27, the No. 1 Electric Network held the eighth open class. The theme of this open class is "Is the era of charging for five minutes and driving for two hours coming?", In this open class, representatives of vehicle manufacturers, battery enterprises, charging operators and other enterprises as well as industry experts were invited to discuss the necessity and progress of rapid charging development, and whether there is market space in the future. Huang Xuejie, a researcher from the Institute of Physics of the Chinese Academy of Sciences, introduced the obstacles encountered by rapid charging from the perspective of the working principle of batteries, as well as various factors that need to be taken into account in the development of rapid charging. The following is based on Huang Xuejie's speech transcripts.

The working principle of lithium battery mainly depends on the lithium ion moving back and forth between the positive and negative poles. Charging is a process of moving lithium ion from the positive pole to the negative pole. It is a fast process for lithium ion to go out of the material and a slow process for lithium ion to enter the material. For graphite materials, when lithium ions come out, they are more than 100 times slower than when they go in, and the speed is two orders of magnitude slower. It is easier to discharge, but harder to charge. Therefore, some enterprises claim that "by improving the positive pole, the battery can be charged as much as possible in five minutes", which is totally untrustworthy, because charging is not the the final say of the positive pole, but the the final say of the negative pole.(Lithium - Ion Battery Equipment)

Today's battery material systems, including graphite as the anode material, and other carbon materials, recently want to add silicon oxide, as well as lithium carbonate for fast charging, actually have different characteristics. When a large amount of lithium ions are charged, they first diffuse through the electrolyte, which makes charging at low temperatures problematic. Because at low temperatures, the power of the electrolyte is not enough, and the diffusion speed of the ions is not enough. Fast charging at low temperatures will become more difficult.

There are two problems when the battery cannot be charged. It is a problem that lithium ions cannot be transported in the electrolyte. However, after lithium ions are transported from the electrolyte to the electrode interface, the entrance door is too small for lithium ions to enter. After they enter, the room is too crowded and crowded at the door is more dangerous. Stacking at the door will lead to short circuit. The lower the temperature, the greater the problem.

Consumers have a demand for fast charging. If the charging power of a normal car is increased, the time will be shortened accordingly. It is not a great thing to be able to fully charge in a few minutes, but whether this fast charging is meaningful within an hour or even half an hour depends on whether the battery and charging infrastructure can meet the requirements, which involves safety issues.

In addition to safety issues, fast charging and charging modes will affect the battery life. Setting the upper voltage limit of the battery higher will reduce the battery life. During fast charging, higher temperature can achieve the effect, but also at the expense of battery life. This may not be obvious at the beginning of using the vehicle, but the impact on the battery will be more obvious when the vehicle is used later.

The battery life is also related to the depth of charging and discharging. For example, a cell phone battery stops when it is charged to 90% and starts charging when it is more than 20%, which is much longer than that of others when it is fully charged every time. It is charged only when it is turned off every time. Therefore, for lithium batteries, it is better in the middle.

As an example of fast charging, the National Laboratory of the United States used Nissan Leaf to do experiments under different charging conditions and at different temperatures. The main experiment is the difference between 50 kilowatt DC charging and 33 kilowatt AC charging. Through the experiment, it is found that if the temperature can keep the battery temperature better, the voltage can be controlled better, and the influence is not too big. There are two conditions for a reasonable fast charging. One is that the temperature can be controlled, and the other is that the voltage can not be increased, which should be done within the voltage range.

To sum up, rapid charging should not only care about speed, but also about safety and battery life. Battery life is closely related to the depth of battery charging and discharging. Reasonable charging and reasonable fast charging can achieve no impact on the battery, but rapid charging at a high rate will have an impact on the battery.



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