Li-ion battery fast charging technology -Lithium - Ion Battery Equipment

Exploring the fast charging capability of lithium-ion batteries -Lithium - Ion Battery Equipment

When a new car is launched, of course I am talking about electric vehicles, there are often such introductions: "Quick charge, 80% charge in half an hour, 200 kilometers of battery life, completely solve your mileage anxiety!" Fast charging, commercial vehicles are used to improve equipment usage Efficiency, which passenger cars use to address range anxiety, is constantly approaching the time to add a tank of gas. There is a tendency to become standard. Today, let’s dig and dig the fast charging method together, and pass along the origin of the dig and dig method.(Lithium - Ion Battery Equipment)

How fast can the charging be called "fast charging"?

Our basic demands for charging:

1) Charge faster;

2) Do not affect the battery life;

3) Try to save money as much as possible, and charge as much power as possible into the battery as much as possible from the charger.

How fast can it be called fast charging? There is no standard literature that gives specific values. For the time being, we refer to the numerical threshold mentioned in the most well-known subsidy policy. The table below shows the subsidy standards for new energy buses in 2017. It can be seen that the entry-level of fast charging is 3C. In fact, in the subsidy standard for passenger cars, the requirement for fast charging is not mentioned. From the publicity materials of general passenger cars, it can be seen that people generally think that 80% charging in 30 minutes can be used as a gimmick for fast charging, and it is publicized, so let’s assume that the 1.6C of passenger cars can be entry-level fast charging. Charge reference value. According to this idea, 15 minutes of advertising is full of 80%, which is equivalent to 3.2C.

Where is the bottleneck of fast charging?

In the context of fast charging, relevant parties are divided into physical entities, including batteries, chargers, and power distribution facilities.

We discuss fast charging and directly think about whether there will be problems with the battery. In fact, before there is a problem with the battery, the first problem is the charger and the power distribution line. We mentioned Tesla's charging pile, which is called a super charging pile, and its power is 120kW. According to the parameters of Tesla Model S85D, 96s75p, 232.5Ah, and the highest 403V calculation, its 1.6C corresponds to a maximum demand power of 149.9kW. It can be seen from here that for long-range pure electric models, 1.6C or 80% full charge in 30 minutes has already constituted a test for the charging pile.

In the national standard, it is not allowed to directly set up charging stations in the original residential electricity network. The power consumption of one fast charging pile has already exceeded the power consumption of dozens of households. Therefore, charging stations all need to set up 10kV transformers separately, and not all distribution networks in a region have the margin to add more 10kV substations.

Then talk about the battery. Whether the battery can carry 1.6C or 3.2C charging requirements can be viewed from both macro and micro perspectives.

Macroscopic fast charging theory

The reason why the title of this section is called "Macroscopic Fast Charging Theory" is because the material properties, microstructure, electrolyte composition, additives, diaphragm properties, etc. For the content at the micro level, we temporarily put it aside and stand outside the battery to see the method of fast charging of lithium batteries.

There is an optimal charging current for lithium batteries

In 1972, American scientist J.A.Mas proposed that the battery has an optimal charging curve and his three laws during the charging process. It should be noted that this theory is proposed for lead-acid batteries, which defines the boundary conditions of the maximum acceptable charging current. It is the generation of a small amount of side reaction gas, obviously this condition is related to the specific reaction type.

But the idea that there is an optimal solution in the system is universal. Specific to lithium batteries, the boundary conditions that define their maximum acceptable current can be redefined. Based on the conclusions of some research literature, its optimal value is still a curve trend similar to Maas' law.

It is worth noting that the boundary conditions of the maximum acceptable charging current of lithium batteries, in addition to the factors of lithium battery cells, also need to consider system-level factors, such as different heat dissipation capabilities, the maximum acceptable charging current of the system is different. . Then we will continue the discussion on this basis for the time being.



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