Progress of fast-charging 1.2V NiMH battery

　　If new energy vehicles want to truly achieve an experience close to that of traditional gasoline vehicles, shortening charging time, improving cruising range and charging convenience are unavoidable topics. Dr. Wang Shengwei, head of the fast charging project of Ningde Times New Energy Technology Co., Ltd. (CATL), said that the "superconducting electronic network" and "fast ion ring" technologies developed by CATL were combined to develop a set of lithium iron phosphate fast charging cores. Finally, it has 4C high-rate fast charging, which can complete 100% charging of pure electric buses in 15 minutes.

　　Recently, Wang Shengwei gave a speech analyzing the principles and characteristics of fast-charging 1.2V NiMH battery, and introduced CATL's maintenance plan and the progress of fast-charging 1.2V NiMH battery.

　　In principle, the bottleneck of fast charging of batteries is the negative electrode. Common chemical systems will produce by-products at the negative electrode during fast charging, which affects the cycle and stability of the battery core. Once the lithium ions are blocked in the negative electrode, it is very dangerous, but as long as the lithium ions enter the interior of the graphite, there will basically be no problem. Therefore, CATL developed "fast ion ring" technology to create a highway network on the surface and inside of graphite so that lithium ions can be quickly embedded anywhere in the graphite.

　　"It can achieve both lithium ion density and fast charging, which is like building a ring highway to alleviate traffic congestion. 'Fast ion ring' graphite has this mechanism. We have shipped hundreds of millions of mobile phones. It is reliable. Sex has been verified," Wang Shengwei introduced.

　　Is lithium iron phosphate suitable for fast charging?

　　Some people in the industry believe that lithium iron phosphate is not suitable for fast charging. In Wang Shengwei’s view, this problem has two sides. From a material perspective, the intrinsic conductivity of lithium iron phosphate materials is relatively low, only one percent of that of ternary materials. The conductivity of lithium iron phosphate materials needs to be optimized to meet the needs of fast charging.

　　Wang Shengwei said that after CATL's transformation, lithium iron phosphate is no longer the "original lithium iron phosphate" and is even better than ternary materials. On the positive electrode, CATL has developed "superconducting electronic network" technology, which enables lithium iron phosphate to have excellent electronic conductivity, up to 1,000 times that of ternary materials.

　　He pointed out that the current cycle performance of lithium iron phosphate fast-charging batteries is better than that of non-fast charging batteries. In principle, there is no contradiction between cycle performance and charging. So why are traditional batteries not good when used for fast charging cycles? The reason is that traditional batteries are not designed for fast charging. There will be by-products or side reactions during fast charging. When there are too many side reactions, the cycle will naturally deteriorate. Once the dynamic problem of fast charging is solved, its cycle will at least not get worse. At the same time, fast-charging batteries not only have higher kinetics, but also have lower energy density than non-fast-charging batteries. It is not surprising that the energy density is lower and there is more electrolyte, so the cycle becomes better. In fact, the lithium iron phosphate fast-charging battery they are currently developing can reach 10,000 cycles.

　　Ensure fast charging within "healthy charging range"

　　"After years of research at CATL, we believe that a healthy charging range is related to the irreversible reaction speed of charging. For a fixed chemical system, it will be affected by temperature and voltage. The speed of the irreversible reaction determines the battery's performance during the cycle. The speed of capacity fading and impedance increase, so the focus of our research is how to identify the speed of irreversible reaction. Fast charging within this "healthy charging range" can achieve fast charging without exposing the battery to the effects of fast charging. Damage, achieving both fast charging and long cycle time.”

　　Under low temperature conditions, CATL proposes two types of battery protection. One is charging in different temperature ranges, slow charging at low temperatures, and charging within the "healthy charging range" of the battery to better protect the battery. The second is to use a hydrothermal system to heat the battery core at low temperatures. When the battery core temperature reaches the requirement, the fast charging mode can be turned on to achieve "healthy" fast charging at low temperatures.

　　Similarly, the battery also needs to avoid the influence of high temperature, because it has its own redox reaction, and the higher the temperature, the more violent the reaction. In this regard, CATL's solution is to use a low-voltage system of 3.65V. The positive electrode has weak oxidation, few side reactions and is slow. In addition, there is water cooling to control the temperature to avoid high temperature conditions.

　　High energy density battery fast charging leads the world

　　In terms of "longer cruising range", CATL's technical plan is that the battery energy density should reach 300 watt-hours per kilogram before 2020. After 2025, there are plans to further increase the energy density. In terms of "shorter charging time", CATL is already developing a fast-charging battery with an energy density of 190Wh/kg and a full charge in 15 minutes. The battery is expected to have mass production capabilities in 2018, and its main application areas are passenger cars.

　　"For high-energy-density fast-charging batteries for small cars, we have technological reserve advantages, and domestic battery companies have the opportunity to lead Japan and South Korea." Wang Shengwei said, "In terms of charging speed alone, the chargers used in ordinary cars are basically It takes close to 50 minutes to charge to 80% for a product below 1C. Our product can charge to 80% in 12 minutes. The charging speed is a sharp contrast, even for fast-charging taxi users, it can be fully charged twice a day. It needs to be charged 700 times a year. According to the service life of a taxi of about 4 years, 2800 times of charging should be enough. The cycle life of our high-energy fast-charging battery is expected to be more than 3000 times, which should be able to meet the needs of passenger car applications. ”

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