Charging piles are actually equivalent to the gas pumps in gas stations. The popularization of new energy vehicles has gradually brought charging piles into people's lives. According to people's actual situation, new energy car owners use fast charging, slow charging and flying wires as the main charging methods. First of all, fly-by-wire is the most unpromoted and dangerous charging method, while slow charging takes a long time, especially for owners who do not have private charging piles, the time, energy and money pressure of the slow charging method is too great, while the fast charging method has rumors of damaging the battery, and rumors have been circulating to charge in a combination of fast and slow charging.
With the accumulation of electric vehicle users, basic charging problems are gradually exposed. Charging equipment and companies do not interoperate with each other, and owners must not only master the location of charging piles, but also understand the brand and payment method of charging piles.
The working principle of lithium battery
To discuss the impact of DC charging on batteries, it is important to first understand electric vehicle batteries.
Most electric vehicles on the market today are lithium-ion batteries, which have two poles: the positive pole is a lithium compound, and the negative pole is graphite.
When charging, lithium ion (Li+) is generated on the positive electrode of the battery, and the generated lithium ion (Li+) moves from the positive electrode to the negative electrode through the electrolyte, while the graphite of the negative electrode is a microporous layer structure, and the lithium ion (Li+) that reaches the negative electrode is embedded in the microporous carbon layer, and the more lithium ion (Li+) embedded, the higher the charging capacity; when discharging (i.e. the process we use the battery), the lithium ion (Li+) embedded in the negative electrode The more lithium ions (Li+) embedded in the carbon layer come out and move back to the positive electrode, the more lithium ions (Li+) return to the positive electrode, the higher the discharge capacity. What we usually call battery capacity refers to the discharge capacity. Therefore, ideally, the charge and discharge process of lithium battery is actually the movement of lithium ion (Li+) from the positive electrode → negative electrode → positive electrode, as long as the chemical structure of the positive and negative electrode materials basically does not change, the reversibility of battery charge and discharge is good, lithium ion (Li+) battery can ensure a long time cycle.
Fast charging mainly ensures that lithium ions (Li+) are quickly embedded from the positive electrode and quickly embedded in the negative electrode, which cannot cause deposition of lithium ions (Li+). However, when the current increases, a layer of semi-permeable film (SEI film) on the surface of the negative electrode (graphite) will break down to a certain extent, causing the electrode material and electrolyte to react with each other. In addition, the increase in temperature will be accompanied by some side reactions, such as electrolyte decomposition and deposits on the electrode, leading to a reduction in reversibility and a slow decrease in battery capacity.
The effect of fast charging on the battery
When charging an electric vehicle, the battery management system BMS on the electric vehicle will estimate the State of Charge (i.e. remaining battery power) of the power pack and automatically adjust the size of the charging current according to the condition of the battery pack to ensure that the SOC is maintained within a reasonable range to prevent damage to the battery due to overcharging or overdischarging, so there is no need to worry too much about the damage to the battery from fast charging.
In fact, the lithium ion in the battery is like a swinging swing, when there is no friction, gravity and other external factors, because of the conservation of energy, the swing will always be swinging from side to side. But as long as there is an external factor, perhaps the lithium ion swing, will not swing as high as before, this factor has always existed, the swing may someday stop.
Therefore, whether the battery pack of electric vehicles will be overcharged or overdischarged depends largely on the management level of the BMS system. So both consumers and car companies in pursuit of high range, not only to increase the battery capacity, but also to improve the management and upgrade of the battery management system BMS.
How to reduce the damage to the battery through fast and slow charging
If you do not have confidence in the battery management system BMS, and have the conditions to build their own charging pile, it is best to AC slow charging as the main, DC fast charging complementary. Because the input of AC slow charging is AC power, and then converted by the vehicle charger to DC power to charge the battery pack, the relative input power is small, and the chance of overcharging is very small.
At present, in the charging pile market, some DC charging piles come with an active overcharge protection function. It will actively detect the charging status of the battery pack and intelligently optimize the charging curve. When the charging pile detects that the battery pack is about to be full, the charging pile will automatically reduce the output current and enter the trickle charge stage; when the charging pile detects that the battery pack power has reached a certain value (such as when the battery pack power reaches 97%) and the trickle charge exceeds a certain time (such as 10 minutes), the charging pile will actively disconnect the charge to prevent the battery pack from overcharging. You don't need to worry about this problem if you use this kind of charging post with anti-overcharge function.
Although users charge and pay differently when using the charging piles, alternating between different piles is basically not going to have an adverse effect on the battery. As mentioned above, in theory, the charging effect of different charging piles for electric vehicles is basically the same, and their charging quality is determined by the management level of their own battery management system.
The promotion of electric vehicles is still short, both the use of vehicles and the corresponding charging facilities have not kept up with the development needs. As the saying goes, if you want to get rich first, you have to build a road. If you want to develop electric vehicles and achieve the "Made in China 2025" and "13th Five-Year Plan" goals, the development of charging piles must be in the front.
