What is the reason for the fast charging of the power battery?

In the stage of the power battery to 350 wh / kg target sprint, some people have proposed a higher power battery "fast charge" target, from the original 1 hour fast charge target value, step by step to 30 points, 20 minutes, 15 minutes, Up to now, it has been proposed to fill the 80% target for 5 minutes. Some experts have already put forward the argument that high-power fast charging is an inevitable trend in the future development of electric vehicles. The author has questioned this for the following reasons:

First, the origin of fast filling

In China, pure electric vehicles originated from urban buses. In the beginning, when everyone was obsessed with developing hybrid buses, Chongqing Hengtong Bus Factory teamed up with Weihong Battery to develop pure electric buses using lithium titanate batteries. Yes, the lithium titanate charging rate is higher (3 c or more), so the Chongqing bus company has a so-called "fast charge" battery bus. Explain in technical terms, if the charging rate is 3 c, 12 m pure electric bus, it can be fully charged in 15 minutes. This is already very ideal for urban public transport.

The actual situation is that Chongqing Hengtong Bus Factory develops a “fast charge” bus with lithium titanate battery, and each charge can maintain a round trip operating distance (about 30 kilometers), it is necessary to go to the charging station to make up Electricity, the actual product is to charge a bus at the same time with two guns.

Here to the layman, a concept, lithium titanate battery is not high energy, and high cost. The development of pure electric mainly requires higher power than energy requirements, and lithium titanate batteries do not meet this requirement. As a result, the next lithium titanate battery bus was excluded from the new policy of new energy vehicle subsidies from 2013 to 2015.

What is a lithium titanate battery? Under the premise that the negative electrode material of the power battery is unchanged, the carbon negative electrode is replaced by a lithium titanate material, and as a result, the specific energy is lowered, the charging rate is improved, and the safety is much better. However, reducing the "specific energy" is not the development direction of battery technology and the trend of technological progress. Therefore, lithium titanate fast charging technology gradually faded out of the actual product promotion, so there is a concept of compound lithium fast charging, began to replace the lithium titanate fast charge.

Second, what is fast charging, how to express fast charging technology?

At present, the fuel car arrives at the gas station. Under the support of the prior art, taking the passenger car as an example, it can be basically completed in 5 minutes. Starting a pure electric passenger car (taxi) for more than 3 hours on a single charge, compared to the fuel car refueling "5" minutes, 3 hours charging technology, there is no way to convince the taxi driver to use a pure electric passenger car. In fact, the passenger car is charged with 220 AC power for 7-8 hours, so the pure electric passenger car production plant has special fast-charging technology for passenger cars, which is 30% full. Charging technology.

Why is it 80%, not 100%? At present, the power battery takes a long time to fully charge the battery. Mainly there is 20% battery capacity, the ability to accept charging is very limited, it must be "Trickle" charging mode. In other words, the external charging power is no longer large, and it is useless. This is the bottleneck of “fast charging technology”.

Third, the grid company has been disapproving of the charging mode of electric vehicles.

Grid companies have been actively promoting the best "changing" mode for electric vehicles. State Grid, China Southern Power Grid is an advocate of “changing” electricity mode and an active participant. A charging station for electric buses was built in Qingdao, and a taxi charging station was built in Xinxiang, Henan. At present, Beiqi New Energy and Changan Automobile have also responded positively to the “changing” mode. But based on specific models, there is no universal significance for specific operators.

The electric vehicle project determines that the electric vehicle charging mode is a universal mode or a mainstream mode. However, the charging efficiency is too low, which is also a common question. How to solve it?

1 For electric vehicles, for example, for a pure electric bus of 10 meters or more, it is a more practical method to use a double "gun" DC charging;

2 pairs of 4 m, 5 m city freight cars, double "mouth" charging is equipped with AC charging port and DC charging port, which is also in line with market requirements;

3 For pure electric rental cars, with a dedicated charging station, it is also explored in practice;

4 private passenger cars, AC charging at home; in the public charging station, DC fast charging can be used to make up the electricity, there is nothing wrong with it.

Fourth, high-power fast charge is just a charging method

1 The accelerated development of new energy vehicles, high-power fast charging, can greatly reduce the charging time of electric vehicles, which is for public charging stations.

2 Electric vehicle "fast charge" refers to the charging technology that the battery is charged from 0% to 80% for less than 30 minutes. Can't be faster, 30 minutes of charging, which is 2 c charging rate. If you want to increase it to 10 minutes, that is, the 6 c charging rate, the geometry of the matching guns and cables can't bear it, and people can't stand it;

3 China's application of pure bus is 350 kW charging pile, and 120 kW charging pile is used in a pure electric passenger car, which is very scientific and economical;

4 high-power fast charge, will inevitably lead to many problems such as battery heating, safety isolation, charging station construction, power supply, and other infrastructure facilities.

Fifth, blindly advocating high-power fast charging technology is unscientific

Some experts have suggested that "if the charging time is shortened to 3-5 minutes, then the electric car has the ability to compete with the traditional fuel car." The author believes that this is misleading, blindly advocating high-power fast charging technology, is unscientific. The reasons are as follows:

1 car charging methods are diversified. Fuel car fueling must go to the public fuel-saving station to refuel. The charging of electric vehicles can be dispersed, space can be exchanged, and it is not necessary to promote the need to charge to a public charging station;

2 High-power charging must require existing grid support, and more stringent requirements are imposed on the safety of the grid;

3 high-power DC fast charging (voltage is higher than 1000 v, the current is higher than 350 years), the whole vehicle voltage platform will be required to increase to more than 1000 v, and it is inevitable to increase the high-voltage protection level of the whole vehicle;

4 high-power DC fast charging (voltage is higher than 1000 v, the current is higher than 350 years), it is inevitable to improve the thermal management technology of the power battery and the whole vehicle and increase its cost.

In a word, different functions and non-use vehicles, the corresponding charging method will be the basic trend.

The page contains the contents of the machine translation.