Although fast charging is convenient for our daily lives, it also comes with certain risks. It may damage the battery and increase the risk of battery self ignition.

So, what is the so-called "overcharging"? In the industry, brand specific DC Charging station with power of 120 kW and above are generally defined as super fast charging.

In colloquial terms, a charging power of 1 kilowatt per hour can be understood as "1 hour charging 1 kWh", while a charging power of 60 kilowatt hours means "charging 60 kWh within 1 hour". Simply put, it's high-power, charging fiercely!

We can temporarily summarize the harm caused by this into two reasons:

1. Frequent fast charging accelerates the polarization of battery cells

During the charging process of lithium-ion batteries, the diffusion rate of lithium ions inside the electrode is relatively slow, while the diffusion rate of the electrolyte is faster. This diffusion process is mainly controlled by the diffusion inside the electrode. Due to the fact that the migration rate of lithium ions within the electrode particles is much slower than the electrochemical reaction rate occurring on the electrode surface, concentration polarization phenomenon occurs in the electrode, further increasing the degree of deviation of the potential difference between the positive and negative electrodes from the equilibrium potential.

When the charging current continues to be high, the concentration of lithium ions at the electrode will increase, exacerbating the polarization phenomenon. In this way, the terminal voltage of the battery cannot be directly proportional to the amount of electricity/energy charged. At the same time, high current charging can also lead to an increase in internal resistance, further exacerbating the Joule heating effect, and triggering a series of side reactions, such as electrolyte decomposition and gas production. These factors sharply increase the danger of batteries, have a negative impact on their safety, and the service life of non power batteries is bound to be significantly shortened.

2. Frequent fast charging may lead to cell crystallization.

During the charging process, our control over lithium ions is actually very weak. We can only guarantee that lithium ions will migrate to the negative electrode surface, but we cannot guarantee that lithium ions will be evenly distributed on the negative electrode surface. In lithium batteries, fast charging means that lithium ions quickly release and "swim" towards the negative electrode, which requires the negative electrode material to have fast lithium insertion ability. The anode materials used for rapid charging of lithium batteries include carbon materials, Lithium titanate and other new materials. For carbon materials, due to the similar intercalation potential and lithium precipitation potential, lithium ions are generally preferentially embedded in graphite under conventional charging. However, under fast charging or low temperature conditions, lithium ions may precipitate on the surface to form dendritic lithium (also known as crystallization). Dendritic lithium can penetrate the separator (SEI), causing secondary loss of Li+and reducing battery capacity. When the lithium crystal reaches a certain amount, it will grow from the negative electrode to the separator, causing a risk of battery short circuit. In severe cases, it can cause vehicle self ignition and irreparable consequences!

Another point to note is that most merchants usually emphasize fully charging 80% of the battery in a short period of time when promoting fast charging, rather than fully charging 100%. This is because in a fast charging state, the strength and internal resistance of the battery will sharply increase, making it impossible to maintain the original current and continue to be delivered to the battery, which will switch to slow charging. This is also why many companies usually only promote the time required to quickly charge the battery to 80%, without mentioning the time required to fully charge. Because the remaining 20% after fast charging reaches 80%, the charging time will be longer.

In addition, there is also the phenomenon of "virtual charging" that has been criticized by people for fast charging. Rapid charging can cause the battery to heat up, as during rapid charging, the internal temperature of the battery increases due to the action of high current, causing molecules to become more active, giving the illusion that the battery is fully charged. However, in reality, during the fast charging process, the actual amount of electricity charged into the battery is about 10% less than that during slow charging. This is why the so-called "virtual charge" phenomenon occurs.

To summarize, although fast charging is convenient for our daily lives, it also comes with certain risks. It may damage the battery and increase the risk of battery self ignition. Therefore, as car owners, we should carefully consider our own charging method and choose the correct charging method. In non emergency situations, try to use slow charging devices as much as possible. At the same time, as a manufacturer of Charging station, we should constantly improve the quality of Charging station, ensure that our fast charging equipment meets the quality standards, and produce products that can satisfy customers! Only in this way can we enjoy the convenience of fast charging while ensuring safety and user experience.

Issued by Alex, R&D, Jun. 8, 2023.

Disclaimer: This article only represents the author's personal view and has nothing to do with the website. This website is published for the purpose of transmitting more information, which does not mean to agree with its views or to confirm its description. The content of the article is for reference only. Please check the relevant contents by the reader.

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