CATL/Guoxuan power 23A batteryfast charging path analysis

　　As we all know, one of the sales pain points of new energy vehicles is the long charging time.

　　Especially when subsidies are declining and market sales are declining, developing 23A batteryfast charging technology to shorten charging time and improve driving experience is crucial to developing the new energy vehicle market.

　　However, when the 23A batteryis fast-charged, if the negative electrode does not have the ability to insert lithium at a high speed, lithium dendrites and lithium precipitation will occur, which will lead to irreversible attenuation of 23A batterycapacity and shortened service life.

　　In addition, the 23A batteryheats up quickly, generates a lot of heat, and is prone to short circuit and fire. In terms of electrolyte, it needs high conductivity, does not react with the positive and negative electrodes, can resist high temperatures, is flame retardant, and prevents overcharging.

　　From the perspective of charging strategies, there are three main methods: constant current, constant voltage, and staged charging.

　　Constant current and constant voltage charging have low cost and simple system circuit, but the time is too long and the efficiency is not high. If the current or voltage becomes larger, the duration can be shortened, but the 23A batterylife will be shortened. The staged charging method cannot be unified at all due to the different 23A batterydesigns of each manufacturer.

　　From the perspective of 23A batteryresearch and development, the current common negative electrode material is still graphite. However, during the charging process, the negative electrode graphite is sensitive to the electrolyte, has strong directionality, and has low lithium insertion properties.

　　If the negative electrode graphite is changed to silicon carbon, a research and development director of a soft pack 23A batterycompany told Gao Gong Lithium 23A batterythat Tesla's current fast-charging 23A batteryis graphite compounded with 5% silicon oxide.

　　In China, the silicon content of the 23A batterynegative electrode has not exceeded 5%. The reason is that when the silicon carbon negative electrode is charged, the material expands greatly and the 23A batteryattenuates seriously, making it difficult to be commercially applied in large quantities. For large quantities, the silicon content must reach at least 10%-20%.

　　In addition, the executive also said that the 23A batterycharging speed depends on the mass transfer speed of the positive and negative electrode matrices. The charging end uses high voltage and high power, and the charging strategy is only an external optimization. To fundamentally solve the problem of slow charging, we must reform the positive and negative material systems of the battery.

　　At the same time, a senior technical engineer from an OEM said that the fast charging methods for 23A batterymaterials such as ternary, lithium iron phosphate, lithium manganate, and lithium titanate are roughly similar. They all use constant current (large current) for fast charging first, and then constant current. Charge slowly (reduce current) until finally fully charged.

　　Regarding the difficulties of fast charging, he believes that the main focus is on how to control temperature rise side reactions, lithium deposition in the negative electrode, capacity fading during charging, and charging strategies suitable for 23A batterySOC and other parameters.

　　According to Gaogong Lithium Battery, in terms of 23A batteryfast charging, domestic 23A batterycompanies include CATL, BYD, Hefei Guoxuan, Microvast Power, Wanxiang 123 and many other companies participating in research and development.

　　Among them, the typical representative that focuses on improving the performance of the 23A batteryitself is CATL, and the representative that focuses on 23A batterycharging optimization strategies is Hefei Guoxuan.

　　Ningde era: super 23A batteryfast charging

　　In terms of fast charging, CATL mainly focuses on research on 23A batterymaterial systems. By breaking through the inherent bottleneck of the 23A batteryelectrochemical system, super fast charging technology that takes into account safety and high energy density has been developed.

　　In principle, when charging, as shown in Figure 1, the lithium ions in the positive electrode of the 23A batterymove to the negative electrode through the electrolyte. The graphite used as the negative electrode has a layered structure and has many micropores for the insertion of lithium ions reaching the negative electrode. The more lithium ions embedded, the higher the charging capacity.

　　Figure 1 23A batterycharging diagram

　　During fast charging, lithium ions must be accelerated and instantly embedded into the negative electrode. This requires the negative electrode to quickly receive lithium ions. When batteries with ordinary material systems are fast-charged, by-products will appear in the negative electrode, such as lithium dendrites, which will reduce the cycle life and stability of the 23A batterycells.

　　Figure 2 CATL fast charging technology

　　As shown in Figure 2, CATL’s fast charging technology can increase the 23A batterystate of charge (SOC) from 8% to 80% in 15 minutes. Its innovation is still the fast ion ring and "super electronic network".

　　The fast ion ring creates a high-speed channel on the surface of the graphite anode, allowing lithium ions to quickly embed into any position of the graphite, greatly increasing the embedding speed of lithium ions in the graphite anode. And it is necessary to ensure that during fast charging, high energy density characteristics can be taken into account, and no by-products will appear in the negative electrode, which will affect the cycle life and stability of the 23A batterycore.

　　"Superelectronic network" is used to modify the cathode material. Specifically, it is combined with the design and deployment of the crystal orientation coefficients of the positive and negative electrodes of lithium batteries to optimize the dynamic properties of the electrolyte and positive and negative electrodes, so that the chemical system and 23A batterydesign parameters can be optimally matched.

　　Of course, in order to ensure the safety and reliability of fast charging cores, CATL's technology can calculate the "healthy charging range" under different temperatures and SOC states.

　　Then, the charging current is kept within the "healthy charging range", which can achieve fast charging without damaging the 23A batteryby fast charging, achieving fast charging, long cycle, and safety and reliability.

　　Hefei Guoxuan: Charging strategy optimization

　　Hefei Guoxuan's invention patent is a lithium-ion charging strategy optimization method for fast 23A batterycharging, as shown in Figure 3, which is mainly implemented in three stages.

　　In the first stage, multiple batteries are charged at different charging rates and discharged at the same discharge rate. Cycle multiple times, and determine the lithium-elimination charging rate C2 based on the final 23A batterycapacity retention rate and whether there is lithium precipitation on the negative electrode of the battery.

　　In the second stage, the batteries are charged to different SOC states at the lithium-elimination charging rate C2, and then discharged at the same lithium-elimination discharge rate. Loop multiple times. According to whether there is lithium precipitation in the negative electrode of the final battery, the SOC1 without lithium precipitation at the lithium precipitation charging rate C2 is determined.

　　In the third stage, charge to 90% SOC at a rate lower than the lithium evaporation charging rate C2, then charge to 95% SOC at 0.2C, and then fully charge at 0.1C. Finally, cycle through multiple discharges, and determine the charging rate C3 without lithium precipitation under high voltage based on whether there is lithium precipitation on the negative electrode of the battery.

　　This patent of Hefei Guoxuan determines the best charging strategy by measuring the maximum continuous rate allowed for 23A batterycharging and the corresponding cut-off SOC.

　　The advantage of this method is to ensure 23A batterycycle performance and reduce actual charging time. It can also be used to benchmark 23A batterycharging performance from different manufacturers, which is beneficial to improving 23A batterydesign and manufacturing levels.

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