lithium 18650 battery

　　Improvement of lithium 18650 battery performance from high-power fast charging

　　Introduction to lithium 18650 battery performance improvement from the perspective of high-power fast charging - The benefits of high-power charging are that the frequency of use of charging piles is increased, their service capabilities are expanded, consumer satisfaction is improved, and profits can also be improved.

　　Charging speed, as the core performance indicator of power batteries, plays a crucial role in the experience of using electric vehicles.

　　Focusing on this, leading lithium 18650 battery companies are continuing to invest in this field. Taking the latest fast charging technology launched by CATL as an example, the battery state of charge (SOC) can be increased from 8% to 80% in 15 minutes.

　　Industry insiders said that the fast charging technology released by CATL is closely related to high-power DC charging.

　　High-power charging generally refers to the charging pile providing more than 150KW to charge the lithium 18650 battery with high current.

　　The benefits of high-power charging are that charging piles are used more frequently, their service capabilities are expanded, consumer satisfaction is increased, and profits can be improved.

　　At the same time, it can also achieve 400V high current or 800V low current charging, greatly reducing the range anxiety of new energy vehicles.

　　As for the technical difficulty of high-power charging, Gaogong Lithium Battery understands that it is mainly concentrated in power batteries.

　　The reason is that for charging piles, the technical difficulty of outputting high voltage and high current is much easier than improving the chemical performance of the battery.

　　From the perspective of power batteries, high-power charging mainly depends on the lithium evaporation window and thermal management of the battery cell.

　　Lithium precipitation is the deposition of lithium ions, and dendrites grow in preferred orientations, which can easily pierce the separator and cause short circuits in the battery core. Thermal management means that the charging current is large, the battery has internal resistance, generates a lot of heat, and the temperature rises, which needs to be controlled.

　　Judging from the current high-power charging mode, it is generally charged with constant current and high current, and then constant voltage and low current. On the one hand, the battery itself has a limit current. Once it is exceeded, fast charging, internal short circuit, thermal runaway and other phenomena are prone to occur.

　　On the other hand, the battery is equivalent to the series resistance of the capacitor, which is mainly physical resistance.

　　The physical resistance is only a few milliohms. If the voltage is slightly increased by a few volts, according to the circuit principle, the current will increase by hundreds of amperes. At this time, excessive current will breakdown the capacitor, causing the battery to lose its ability to store electricity.

　　The process of high-power charging, for example, is like battering noodles with water. Just starting constant current charging is equivalent to pouring water into the noodles.

　　Initially, because the flour structure is loose, the surface area in contact with water is large and it is easy to mix. As more water is injected, the mixture becomes more difficult to stir and becomes viscous, making it much more difficult to mix thoroughly.

　　Obviously adding water is equivalent to continuing to charge, which is overcharging. At this time, the electrochemical reactions of the positive and negative electrodes inside the battery will be greatly damaged, causing safety risks.

　　From a domestic perspective, the main battery companies that engage in high-power fast charging include CATL, BYD, Tianjin Lishen, Microvast Power and Yinlong New Energy.

　　Among them, companies whose product performance generally reaches 1C-2C include CATL, BYD and Tianjin Lishen. Those whose product performance reaches above 2C are mainly Micromacro Power and Yinlong New Energy. Most of the other companies are between 0.2C-1C.

　　In addition, Gaogong Lithium Battery learned from senior industry insiders that domestic high-power fast charging can achieve more than 10C, in other words, it can be fully charged in less than 6 minutes. But this kind of lithium 18650 battery may have a lower energy density and higher safety risks.

　　From a manufacturing perspective, under the limited space of battery packs installed in new energy vehicles, in order to achieve higher power fast charging, at least the migration rate and reaction embedding quantity of lithium ions must be accelerated.

　　The solution is generally carried out from two aspects: battery material system and material technology.

　　In terms of material systems, for example, the negative electrode uses silicon-carbon composite graphite, and the positive electrode uses high-nickel and multi-cobalt elements to improve high-power fast charging capabilities.

　　Regarding the high-nickel ternary cathode, nickel determines the energy density, cobalt affects the fast charging capability, and manganese or aluminum plays a stabilizing and balancing role. To a certain extent, the higher the cobalt content, the stronger the fast charging capability, but the energy density is relatively low.

　　In terms of material technology, methods such as carbon chemical coating, electrochemical corrosion, graphite modification, and material nanonization are commonly used to increase the contact surface area during lithium ion migration and store and capture more lithium ions. Higher performance separators are also used to accelerate the migration of lithium ions from the positive electrode and the rate at which the electrolyte passes through the separator.

　　Among them, for batteries, high-power fast charging and high energy density are often in a "contradictory" relationship. The reason is that fast charging requires a large specific surface area of the positive and negative electrodes for lithium ion migration. In addition, the electrodes themselves are limited in size and the coating thickness cannot be too thick, which can only reduce the battery energy density.

　　In addition, fast charging and high energy density can easily increase side reactions and cause lithium deposition, thereby shortening the cycle life and even causing safety hazards.

　　Therefore, to improve battery performance, we need to find a balance between high-power fast charging and high energy density, and choose accordingly. Fast charging cannot be achieved simply and crudely through high-power charging.

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