Why can't lithium-ion batteries be recharged quickly?

At present, there are more and more articles promoting the quick charging of power batteries. Some manufacturers' propaganda has gone too far. Some experts also follow the trend and say that the charging of electric cars can be completed in 30 minutes or 15 minutes. These publicity is adverse to the development of the industry. Engineering people understand, "the principle doesn't make sense, neither does the engineering work". Lithium ion battery principle has told people that the battery cannot be charged quickly.

One, what is fast, slow charge?

Car batteries are positive and negative, can charge the battery, there must be a positive and negative dc power supply. What do you mean? The alternating current of the power grid cannot be directly charged to the car battery.

But when it comes to charging electric cars, it's all 220V ac for domestic use, or 380V ac for factory use. Why is that? This is an "AC to DC" (AC/DC) device used by engineers to convert alternating current into direct current. Remember for the average user:

(1) the car battery charging power supply, must be dc power supply, ac power supply is not "directly" to the lithium ion battery charging.

Where is the dc power supply? At present, all electricity in the power grid is alternating current. The direct current used to charge electric cars is converted through an "AC to DC" (AC/DC) device.

"AC to DC (AC/DC)" is a device, is in line with the standard requirements of the product. If this device is installed in the car, the car and the charging interface is ac charging interface; If this device is installed under the car (ground), the car and the charging interface is the ac/dc interface.

(4) AC to DC (AC/DC) device in the ground can be made of high power (note: the greater the power, the larger the volume, the heavier the quality; But the automobile has the insulation request, has the volume, the weight limit, therefore the vehicle-mounted alternating current to direct current (AC/DC) is the power small.

The first level is the concept of "fast and slow". The charging speed of dc interface is faster than that of ac charging interface. In principle, the dc charging speed is three to four hours, and the ac charging speed is six to eight hours. (note: the power grid can guarantee the supply of 220V alternating current for civil use or 380V for factory use.)

The second level is the concept of "fast and slow". The current theoretical charging speed of the dc connector is three to four hours, compared with five minutes of refueling for oil-fueled vehicles. Due to the theoretical limitations, some experts have proposed the concept of "30 minutes (or 15 minutes) charging to 80%", and there is still 20% space, charging time is ignored. In other words, the whole process of charging is segmented.

The third level is the concept of "fast and slow". Dc interface can not be fast power, which means 3% to 99% of the whole process, fully charged; Dc ports can charge very quickly, basically 20 to 80 percent of the space. This is part of the charging (discharging) curve of a lithium-ion battery. Some manufacturers have done some optimization on this curve. In principle, there is no substantial innovation.

Second, the dc interface can not be charged quickly is a comprehensive conclusion, can be charged quickly is a lot of preconditions

Let's start with an example of your daily life. Bucket, is used to store water, tap to empty bucket water. The barrel has a volume (similar to the amount of electricity of the car battery), and the maximum water output of the faucet is also certain (similar to the charging port). The analysis is as follows:

To the volume has been determined to add water barrel, if you want to quickly, you can turn the tap to the maximum.

(2) faucet output determined, if you want to add water quickly, you can make the bucket volume smaller.

(3) to the volume has been determined to add water barrel, tap water also determined, add water will have an average (rated) speed. The average speed comes with a maximum speed and a minimum speed.

Logic analysis of quick charging of power battery:

(1) car battery capacity has been clear, if you want to charge quickly, the physical approach is to add 1 (or 2) charging interface, the current 12 meters pure electric bus, is this approach.

(2) the specification of the charging interface is the national standard (has been clear), if you want to charge quickly, the basic approach is to make the car battery capacity is small, lithium titanate charge faster than lithium iron phosphate charge, is this principle.

Three, lithium ion battery principle can not be charged quickly

At present, lithium titanate battery can be charged quickly, but the specific energy of lithium titanate battery is far from that of lithium iron phosphate and ternary battery. In other words, the range of the on-board lithium titanate battery is too short. The same mileage, car lithium titanate battery charge times are also more. The time of the on-board lithium titanate battery with multiple quick charge is longer than that of the lithium iron phosphate battery and ternary battery with one slow charge, which has no advantages for users. Is it ok to change the electricity? Also not line. Changing electricity also requires charging, which is technically more difficult and costly than charging.

The electric vehicle electric energy supplement, is slower than the fuel oil vehicle refueling speed, is an objective short board. People are trying to make up for it. How to do? The author's point of view, engineering technology (process) must find the principle is correct program, and then integrate good resources (conditions), do not always use the principle is not correct idea, to try, try again.

The best way to increase the power of the battery than the energy, that is, a slow charge, a car mileage can be more than a day (two days, three days) operating mileage. At present, the development progress of power battery is faster than that of energy research and development.

The page contains the contents of the machine translation.