Charge 500 kilometers for five minutes - burning? explosion? You don't know what's going on!

The concept of “low-carbon travel and green living” has penetrated into every aspect of people’s lives, and new energy vehicles have also become more and more popular. Xiao Bian went out and interviewed several electric car owners. Apart from getting to the point where they chose electric cars, they also found that they were all puzzled about charging, especially the fast charge.

Why is the fast charge mode only used once a day? How to wait for an hour or two for fast charging? Faster charging and more battery life will be reduced faster? Will it explode?

Here, Xiao Bian answers questions for everyone and talks about those things.

What is fast charge?

There will be slowness inevitably. The concept of fast charging is relative to slow charging. The speed of electric vehicle charging is closely related to charger power, battery charging characteristics and temperature. The average owner himself is charged in the form of a slow charge when he is charged at home. It takes 6 to 8 hours to fully charge. Fast charge is generally high-power DC charging. By increasing the current, half an hour can charge 80% of the battery capacity and speed up the charging time.

When it comes to this, everyone is having problems again. Since half an hour will be able to charge 80% of the electricity, why is it still a matter of an hour or more before it is fully charged?

In fact, this is a bottleneck encountered by current battery technology. Currently, most of the electric vehicles in the market are lithium-ion batteries. The principle of fast charging is to ensure that lithium ions are rapidly embedded from the positive electrode and then quickly inserted into the negative electrode. This process is divided into three phases, namely, constant current pre-charging, high current constant current charging, and constant voltage charging.

When the lithium battery is precharged in the first stage, its state is already relatively stable, so in the second stage, the charging current can be appropriately increased. After the power exceeds 80%, in order to protect the safety of the battery, the charging current must be reduced, so it will take longer to charge 100% of the time. In addition, when the temperature in winter is low, the battery requires less charging current and the charging time becomes longer.

Fast charge on the battery

After introducing the principle of fast charging, I believe we have a preliminary understanding of this, then it will not affect the battery capacity of the battery, or even an explosion?

In fact, when the current increases, a semi-permeable membrane (SEI membrane) on the surface of the electrode negative electrode (graphite) will have a certain degree of rupture, so that the electrode material and the electrolyte react with each other. In addition, the temperature rise will be accompanied by some side reactions, such as electrolyte decomposition, deposits on the electrode, to a certain extent, will cause the battery capacity to slowly decrease. However, this is not the only factor that affects the battery capacity. When a typical power battery is manufactured and charged and discharged every time, either fast charge or slow charge will cause the battery capacity to attenuate.

In addition, when it comes to fast charging will not cause an explosion, it is actually related to the battery overcharge problem. Whether the battery pack of an electric vehicle will be overcharged or overcharged depends largely on the management level of the BMS system. Therefore, whether consumers or car companies pursue high endurance, not only increase the battery capacity, but also improve the management and upgrade of the battery management system BMS.

When the electric vehicle is charged, the battery management system BMS of the electric vehicle will estimate the state of charge of the power battery pack, and automatically adjust the size of the charging current according to the status of the battery pack to prevent damage to the battery due to overcharging and overdischarging. And some charging stations will also stipulate that the car can only be charged once a day, so there is no need to worry too much about the impact of fast charging on the battery.

Fast charge instead of slow charge?

Since we say that as long as a safe standard is followed, fast charging is not as scary as it should have been. Will quick charge completely replace slow charge?

In fact, this involves a cost issue. Fast charging will use large currents and power. So many cars must be charged quickly, and it is still difficult for power supply companies to achieve such a power supply. In addition, fast charging also requires some ancillary equipment, such as the conversion of alternating current direct current, so the cost will increase.

Slow charge of the charging current and power are relatively small, the impact on the battery life is relatively small, and the low cost of electricity when charging low cost, it is to meet the general owners of commuting cars, night home charging application scenarios. Therefore, Xiao Bian thinks that this mode of slow charging will not be replaced, but it will develop in synergy with the fast charge or even power exchange mode.

In any case, the promotion time of electric vehicles is still short. Both the use of vehicles and the corresponding charging technologies have not kept pace with the development needs. I believe that with the development of technology, like some car owners mentioned why the fast charge still takes an hour or two and will be solved slowly. The idea of ​​charging 500 kilometers for 5 minutes will eventually become a reality.