What is the impact of fast charging on EV Batteries?
Publish：Sino Energy Corporation Time：2017-03-30
[lithium engineering comprehensive report]
Charging pile is equivalent to the gas station refueling machine. The popularization of new energy vehicles, charging pile gradually into people‘s lives.
According to the actual situation of the people, the new energy vehicle owners to fast charge, slow charge and fly line as the main charging mode. The first line is the way of charging does not fly, advocate the most dangerous, and slow charging time is long, especially there is no private charging piles owners, slow charging mode time, energy and money pressure is too large, rumors and fast charge mode and battery damage, there has been spread to combine with the filling speed charging.
With the accumulation of electric vehicle charging users, basic problems are gradually exposed, between charging equipment and enterprise interoperability, owners should not only grasp the charging pile location, but also understand the charging pile brand and payment.
Working principle of lithium battery
To discuss the impact of DC charging on the battery, we must first understand the electric car battery.
At present, most of the electric vehicles on the market are lithium ion batteries, the battery has two poles: the cathode is a lithium compound, the negative electrode for graphite.
When charging, a lithium ion battery anode (Li+) generation, lithium ion generation (Li+) through the electrolyte from the anode to cathode and anode movement, the graphite is a layered structure with micropores, reach the lithium ion anode (Li+) embedded into the microporous carbon layer, intercalation of lithium ions (Li+) more, the higher the charge capacity; discharge (in the process that we use the battery), lithium ions in the cathode layer of carbon (Li+) release and movement back to the cathode, back to the cathode of lithium ion battery (Li+) more and more high discharge capacity. We usually refer to the battery capacity refers to the discharge capacity.
Therefore, under ideal conditions, the charge and discharge process of lithium battery, the lithium ion (Li+) from the cathode, anode and cathode movement, as long as the chemical structure of the anode and cathode materials does not change, reversible battery charging and discharging well, lithium ion battery (Li+) can ensure long time cycle.
Fast charging is mainly to ensure that the lithium ion (Li+) is quickly inserted from the anode and quickly embedded in the anode, can not cause the deposition of lithium ion (Li+). But in the current increases, the negative electrode (graphite) on the surface of a semipermeable membrane (SEI membrane) will have a certain degree of rupture, the electrode material and the electrolyte interactions. In addition, the temperature rise will be accompanied by a number of side reactions, such as electrolyte decomposition, the resulting sediment on the electrode, resulting in reduced reversibility, the battery capacity will be gradually reduced.
The effect of fast charge on battery
Electric vehicle charging, electric vehicle battery management system BMS estimation of power battery state of charge (State of Charge, namely the remaining battery power), automatically adjust the size of the charge current according to battery pack, ensure that SOC is maintained at a reasonable range, to prevent the overcharge or overdischarge of battery injury, therefore not unduly worried about the damage of fast charging battery.
In fact, the lithium-ion battery is like a swing swing, when there is no friction, gravity and other external factors, because the energy conservation, the swing will swing around. However, as long as there is an external factor, perhaps the swing of lithium ion, not as high as before, this factor has always existed, the swing may one day stop.
Therefore, the battery pack of electric vehicles will be over charge or over discharge, largely depends on the management level of BMS system. So whether consumers or car companies to pursue high endurance, not only to increase the battery capacity, but also to improve the management and upgrading of the battery management system BMS.
How to reduce the damage to the battery
If you do not have confidence in the battery management system BMS, and the conditions of self charging pile, it is best to exchange the slow charge based, DC fast charging and supplemented by electricity. Because the AC slow charge input is alternating current, and then by the car charger into direct current to charge the battery pack, the relative input power is small, the opportunity is too small.
Currently, in the charging pile market, some of the DC charging pile comes with over charge protection function. It will take the initiative to the battery pack to detect the state of charge, and intelligently optimize the charging curve. When the charging pile detects battery pack forthcoming about full, charging pile will automatically reduce the output current into the trickle slow filling stage; when the charging pile detects the battery pack power has reached a certain value (such as the battery pack charge reached 97%), and the trickle charge over a certain period of time (e.g. 10 minutes), then charging pile will take the initiative to open the charge, the battery pack to prevent overcharge. Such as the use of this anti overcharge charging pile, there is no need to worry about this problem.
Although the user in charge of charging pile, charging and payment methods are different, but the alternate charging between different charging piles, basically not adversely affect the battery. As mentioned above, the charging effect of different charging piles is basically the same, and the charging quality is decided by the management level of the battery management system.
Electric vehicle promotion time is short, whether it is the use of the vehicle or the corresponding charging facilities have not kept up with the development needs. As the saying goes, to the rich first build roads, electric vehicles to develop, implement "2025 China manufacturing" and "13th Five-Year", the development of charging pile must be at the forefront.
