At present, there are more and more articles promoting the fast charging of power batteries. Some manufacturers’ publicity is too much, and some experts also follow the trend and say that the charging of electric vehicles can be completed in 30 minutes and 15 minutes, which is even more ridiculous. , Said that the charging task can be completed within 5 minutes. The author expressed concern that these propaganda will be detrimental to the development of the industry. People who engage in engineering understand that "the principle is not feasible, and the engineering is impossible." The principle of lithium-ion batteries has told people that they cannot be charged quickly.
Vehicle batteries have positive and negative poles, and the ones that can charge the battery must be DC power supplies with positive and negative poles. What do you mean? The AC power of the grid cannot directly charge the vehicle battery.
But charging electric vehicles is 220V for civilian use, or 380V alternating current used in factories. Why is that? This is where engineers use the "AC to DC (AC/DC)" device to convert alternating current into direct current. For ordinary users, remember:
â‘ The power source for charging the car battery must be a DC power source, and an AC power source cannot directly charge the lithium-ion battery.
â‘¡Where is the DC power supply? At present, all electricity in the grid is alternating current. The direct current for charging electric vehicles is converted from an "alternating current to direct current (AC/DC)" device.
â‘¢ "Alternating current to direct current (AC/DC)" is a device that meets the standard requirements. If this device is installed in a car, the car and charging interface is an AC charging interface; if this device is installed under the car (ground), the car and charging interface is an AC and DC interface.
â‘£ AC/DC devices can be made into high-power on the ground (Note: the greater the power, the larger the volume and the heavier the mass; and the automobile has insulation requirements, volume and weight restrictions, so the vehicle-mounted AC Direct current (AC/DC) has low power.
The first level of "fast and slow" concept. The charging speed of the DC interface is faster than that of the AC charging interface. In principle, the charging speed of the DC interface is 3 hours to 4 hours, and the AC charging interface is 6 hours to 8 hours. (Note: The power grid can guarantee the supply, 220V for civilian use, or 380V AC for factory use)
The second level of "fast and slow" concept. At present, the theoretical charging speed of the DC interface is 3 hours to 4 hours, which is compared with 5 minutes of refueling for a petrol vehicle. Due to the limitation in 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 entire charging process is divided into sections.
The third level of "fast and slow" concept. The DC interface cannot charge quickly, which means that the entire process is 3% to 99%, and is fully charged; the DC interface can charge quickly, which basically refers to 20% to 80% of the entire space. This is part of the charge (discharge) curve of a lithium-ion battery. Some manufacturers have made some optimizations to this curve. In principle, there is no substantial innovation.
2. It is a comprehensive conclusion that the DC interface cannot be charged quickly, and it is a precondition for manyLet's look at an example of everyone's daily life. The wooden bucket is used to store water, and the tap is used to fill the empty wooden bucket with water. The barrel has a volume (similar to the amount of the car battery), and the maximum water output of the faucet is also certain (similar to the charging interface). analyse as below:
â‘ Add water to the barrel with a determined volume. If you want it fast, turn on the tap to the maximum.
â‘¡The water output of the faucet has been determined. If you want to add water quickly, you can make the barrel smaller.
â‘¢ Add water to the barrel whose volume has been determined, and the amount of water from 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:
â‘ The capacity of the on-board battery has been clarified. If you want to charge quickly, the physical approach is to add one (or two) more charging ports. Currently, this is the practice for 12-meter pure electric buses.
â‘¡The specifications of the charging interface are national standards (it has been clarified). If you want to charge quickly, the most basic approach is to make the car battery capacity smaller. This is the principle of lithium titanate charging faster than lithium iron phosphate.
3. In principle, lithium-ion batteries cannot be charged quicklyThe battery that can be charged quickly at present is lithium titanate, but the specific energy of lithium titanate batteries is too far from that of lithium iron phosphate and ternary batteries. In other words, the vehicle-mounted lithium titanate battery has a too short cruising range. Running the same mileage, the car lithium titanate battery is charged more times. The time of multiple fast charging on-board lithium titanate batteries is longer than that of a slow charging of lithium iron phosphate and ternary batteries. For users, there is no advantage. Can I change the battery? Nor does it work. Battery swapping also requires charging, which is technically more difficult and costly than charging.
The refueling speed of electric vehicles is too slow compared to that of fuel vehicles, which is an objective shortcoming. Everyone is trying to make up. How to do The author's point of view is that engineering technology (process) must find solutions with correct principles, and then integrate resources (conditions). Don't always try and try again with incorrect ideas in principle.
The best way is to increase the specific energy of the power battery, that is, with a slow charge, the mileage of a car can exceed the operating mileage of one day (two or three days). At present, the progress of power battery research and development has been faster than that of energy, and everyone’s mileage anxiety will slowly disappear.
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