Lithium batteries cannot be charged quickly in principle
At present, there are more and more articles promoting the fast charging of power batteries. Some manufacturers have gone too far. Some experts also follow the trend and say that the charging of electric vehicles can be completed in 30 minutes and 15 minutes. What's more ridiculous is that the charging task can be completed in 5 minutes. The author expressed concern that these publicity will be unfavorable to the development of the industry. People engaged in engineering understand that "it is impossible in principle and impossible in engineering". The principle of lithium-ion battery has told people that it can not be charged quickly.
1、 What is fast and slow charging?
Vehicle batteries have positive and negative poles. If they can charge the battery, they must be DC power supply with positive and negative poles. what do you mean? The AC of the power grid cannot directly charge the vehicle battery.
However, charging electric vehicles is 220V for civil use or 380V AC for factory use. Why? This is the "AC / DC" device used by engineers to change AC into DC. For ordinary users, remember:
① The power supply for vehicle battery charging must be DC power supply, and AC power supply cannot "directly" charge lithium-ion battery.
② Where is the DC power supply? At present, the electricity in the power grid is AC. The direct current for charging electric vehicles is converted through the "AC / DC" device.
③ "Alternating current to direct current (AC / DC)" is a device, which meets the standard requirements. If the device is installed on the vehicle, the vehicle and charging interface is the AC charging interface; If the device is installed under the vehicle (ground), the vehicle and charging interface is AC / DC interface.
④ AC / DC devices can be made into high-power devices on the ground (Note: the larger the power, the larger the volume and the heavier the mass; while automobiles have insulation requirements and volume and weight restrictions, so the on-board AC / DC devices have low power.
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 charging speed of DC interface is 3 hours to 4 hours, and that of AC charging interface is 6 hours to 8 hours. (Note: the power grid can provide 220V for civil use or 380V AC for factory use)
The second level is the concept of "fast and slow". At present, the charging speed of DC interface in theory is 3 hours to 4 hours, compared with 5 minutes for fuel vehicles. Due to the limitation of principle, some experts put forward the concept of "charging to 80% in 30 minutes (or 15)", there is still 20% space, and the charging time is ignored. In other words, the whole process of charging is segmented.
The third level is the concept of "fast and slow". The DC interface cannot be powered fast, which means that 3% to 99% of the whole process is completely full; The DC interface can charge quickly, which basically refers to 20% to 80% of the whole space. This is part of the charge (discharge) curve of lithium ion battery. Some manufacturers have optimized this curve. In principle, there is no substantial innovation.
2、 It is a comprehensive conclusion that the DC interface cannot be charged quickly, and many preconditions are that it can be charged quickly
Let's take a look at an example of your daily life. Wooden bucket is used to store water. The faucet adds water to the empty bucket. The wooden bucket has a volume (similar to the amount of vehicle battery), and the maximum water output of the faucet is also certain (similar to the charging interface). The analysis is as follows:
① To add water to the bucket whose volume has been determined, if you want to be fast, you can turn the faucet to the maximum.
② The water output of the faucet is determined. If you want to add water quickly, you can reduce the volume of the barrel.
③ To add water to a wooden bucket with a determined volume, the water output of the faucet is also determined, and there is an average (rated) speed for adding water. The average speed comes from the fastest speed and the lowest speed.
Logic analysis of fast charging of power battery:
① The on-board battery capacity has been defined. If you want to charge quickly, the physical method is to add one (or two) charging interfaces. At present, it is a 12 meter pure electric bus.
② The specification of the charging interface is the national standard (already defined). If you want to charge quickly, the basic method is to reduce the capacity of the on-board battery. The charging of lithium titanate is faster than that of lithium iron phosphate.
3、 Lithium ion batteries cannot be charged quickly in principle
At present, lithium titanate can be quickly charged, 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 lithium titanate battery on vehicle is too short. Running the same mileage, the on-board lithium titanate battery also charges more times. The time of multiple fast charging on-board lithium titanate battery is longer than that of one slow charging lithium iron phosphate and ternary battery, which has no advantage for users. Can I change the power? Neither. Changing electricity also requires charging. Technically, changing electricity is more difficult and costly than charging.
Electric energy supplement of electric vehicles is too slow to refuel than fuel vehicles, which is an objective short board. Everyone is trying to make up. What to do? From the author's point of view, engineering technology (process) must find a scheme whose principle is correct, and then integrate resources (conditions). Don't always try and try again with incorrect ideas in principle.
The best way is to improve the specific energy of the power battery, that is, one-time slow charging, and the vehicle's one-time mileage can exceed the operating mileage of one day (two or three days). At present, the research and development progress of power battery is faster than that of energy. Everyone's mileage anxiety will slowly disappear.
