What is the impact of new energy electric vehicle fast charging on vehicles?

The charging pile is actually equivalent to the tanker in the gas station. The popularization of new energy vehicles has enabled charging piles to gradually enter people's lives. According to people's actual situation, new energy owners use fast charging, slow charging and flying lines as the main charging methods. First of all, the flying line is a highly unadvisable and most dangerous charging method, and the slow charging time is long, especially for owners who do not have a personal charging pile. The time, energy and money of the slow charging method are too much, and the fast charging method is harmful. The rumors of the battery have been circulating in the way of charging in a fast and slow way.

With the continuous accumulation of electric vehicle users, the basic charging problem is gradually exposed. The charging equipment and the enterprise do not communicate with each other. The owner must not only grasp the position of the charging pile, but also understand the brand and payment method of the charging pile.

How lithium batteries work

To discuss the impact of DC charging on the battery, first understand the electric car battery.

Most of the electric vehicles on the market today are lithium-ion batteries. The batteries have two poles: the positive electrode is a lithium compound and the negative electrode is graphite.

During charging, lithium ions (Li+) are formed on the positive electrode of the battery, and the generated lithium ions (Li+) move from the positive electrode to the negative electrode through the electrolyte, while the graphite of the negative electrode is a layered structure having micropores, and lithium ions reaching the negative electrode. (Li+) is embedded in the micropores of the carbon layer. The more lithium ions (Li+) are embedded, the higher the charging capacity; during discharge (that is, the process we use the battery), the lithium ions embedded in the carbon layer of the negative electrode (Li+ When it is taken out and moved back to the positive electrode, the more lithium ions (Li+) that return to the positive electrode, the higher the discharge capacity. What we usually call battery capacity refers to the discharge capacity. Therefore, in the ideal state, during the charging and discharging process of the lithium battery, the lithium ion (Li+) is actually moved from the positive electrode to the negative electrode to the positive electrode, as long as the chemical structure of the positive and negative materials does not substantially change, and the reversibility of the battery charge and discharge. Very good, lithium ion (Li +) batteries can guarantee long-term circulation.

Fast charging is mainly to ensure that lithium ions (Li+) are quickly embedded from the positive electrode and quickly embedded in the negative electrode, which does not cause deposition of lithium ions (Li+). However, when the current is increased, a semi-permeable membrane (SEI film) on the surface of the electrode negative electrode (graphite) has a certain degree of cracking, so that the electrode material and the electrolyte react with each other. In addition, the increase in temperature is accompanied by some side reactions such as decomposition of the electrolyte and deposition of deposits on the electrodes, resulting in a decrease in reversibility and a decrease in battery capacity.

The effect of fast charge on the battery

When the electric vehicle is charging, the battery management system BMS of the electric vehicle estimates the state of charge of the power battery pack (StateofCharge), and automatically adjusts the charging current according to the condition of the battery pack to ensure that the SOC is maintained within a reasonable range. Internally, damage to the battery due to overcharging or overdischarging is prevented, so there is no need to worry too much about damage to the battery by fast charging.

In fact, the lithium ion in the battery is like a swinging swing. When there is no external factor such as friction and gravity, the swing will continue to swing from side to side because the energy is conserved. But as long as there is an external factor, perhaps the swing of lithium ions will not be as high as before. This factor has always existed, and the swing may stop someday.

Therefore, whether the battery pack of the electric vehicle will be overcharged or overdischarged depends largely on the management level of the BMS system. Therefore, whether consumers or car companies pursue high battery life, not only increase battery capacity, but also improve the management and upgrade of battery management system BMS.

How to reduce damage to the battery by charging fast and slow

If you don't have confidence in the battery management system BMS, and you have the conditions to build your own charging pile, then it is best to use AC slow charging as the main, and DC fast charge to supplement the electricity. Because the AC slow charging input is AC, and then the car charger converts to DC power to charge the battery pack, the relative input power is small, and the chance of overcharging is small.

At present, in the charging pile market, some DC charging piles are equipped with an overcharge active protection function. It actively detects the state of charge of the battery pack and intelligently optimizes the charging curve. When the charging post detects that the battery pack is about to be fully charged, the charging post will automatically reduce the output current and enter the turbulent slow charging phase; when the charging post detects that the battery pack has reached a certain value (such as when the battery pack reaches 97%) ), and after trickle charging for more than a certain period of time (such as 10 minutes), the charging post will actively disconnect the charging to prevent the battery pack from overcharging. If you use this charging pile with anti-overcharge function, you don't need to worry about this problem.

Although the charging mode and the payment method are different when the user is charging with the charging post, alternating charging between different charging piles basically does not adversely affect the battery. As mentioned above, in theory, the charging effect of different charging piles on electric vehicles is basically the same, and the quality of charging is determined by the management level of its own battery management system.

The promotion time of electric vehicles is still short, and neither the use of vehicles nor the corresponding charging facilities have kept up with the development needs. As the saying goes, if you want to build a road ahead of the road, if you want to develop electric vehicles and achieve the goals of "Made in China 2025" and "13th Five-Year Plan", the development of charging piles must be at the forefront.

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