Fast charging - a new breakthrough for rechargeable battery 18650 3.7v

　　Different battery material systems have different advantages and disadvantages. New battery material systems emerge one after another, and there is a trend of "the younger generation surpassing the older generation". Especially after the ban on ternary materials on electric buses was lifted, the system has received more and more calls. As the backbone of the current battery material system, does the lithium iron phosphate material system have other killer features to ensure its independence in the market when its energy density is getting closer and closer to the upper limit? The prospects of lithium iron phosphate battery materials are highly valued.

　　The "danger" and "opportunity" of lithium iron phosphate

　　The positive electrode materials of lithium-ion batteries mainly include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, ternary materials, etc. In terms of working principle, lithium iron phosphate is also a lithium ion embedding/de-embedding process, which is the same as lithium cobalt oxide, lithium manganese oxide, etc. Lithium iron phosphate is often compared with ternary lithium batteries, and the two often become the focus of controversy in the industry.

　　Both materials will decompose at a certain temperature. The ternary material will decompose at about 200 degrees Celsius, while the lithium iron phosphate material will decompose at about 800 degrees Celsius. This means that the ternary material is more likely to become the "claws" of fire accidents. To achieve the same level of safety as lithium iron phosphate, the ternary battery has higher requirements for technology and process.

　　However, the energy density of lithium iron phosphate is lower than that of ternary batteries. The energy density of lithium iron phosphate battery monomer is about 145Wh/kg. In contrast, the energy density of ternary batteries is higher, and the energy density of ternary lithium battery monomer is about 220Wh/kg. Therefore, given the material characteristics of lithium iron phosphate, the industry has frequently reported that the energy density of rechargeable battery 18650 3.7v has limited room for improvement and may be replaced by other battery systems in the future.

　　At a time when intellectual property rights are increasingly valued, lithium iron phosphate is inferior to ternary, which has constrained the development of rechargeable battery 18650 3.7v. The earliest patent application for lithium iron phosphate was obtained by FXMITTERMAIER&SOEHNEOHG (DE) on June 25, 1993, and the application results were announced on August 19 of the same year. The basic patent of lithium iron phosphate is owned by the University of Texas, and the carbon coating patent is applied for by Canadians. These two basic patents are difficult to bypass. The statistics of global patents in the automotive nickel-cobalt-manganese ternary lithium battery industry by industry organizations in 2017 show that whether it is the patent layout of other countries or the awareness of technical innovation protection in China, the technical research and development of manganese-cobalt-nickel ternary lithium batteries are the technical hotspots at the time, and the number of patent applications for nickel-cobalt-manganese ternary lithium batteries in my country is far ahead in the world. Therefore, in terms of patents, lithium iron phosphate is not as good as ternary batteries.

　　In terms of energy density, the ceiling of lithium iron phosphate is slightly lower, and there is not much room for development, but it opens a window in terms of charging speed that users care about. Fast charging is a technical path that must be overcome in the development of new energy vehicles. It has obvious effects on alleviating range anxiety and reducing charging time. Therefore, fast charging has become the focus of car companies and battery companies, and has also become a highlight of the future application of rechargeable battery 18650 3.7v.

　　In addition, in the subsidy adjustment plan for new energy vehicles released at the end of December 2016, the three levels of fast charging rates of "3C-5C, 5C-15C, 15C+" can obtain subsidies of 0.8 times, 1 times, and 1.4 times respectively. Encouraged by this policy, enterprises taking the lithium iron phosphate technology route have increased their research and development efforts in fast charging, and fast charging has made rechargeable battery 18650 3.7v achieve new breakthroughs.

　　The core of fast charging technology is to accelerate the speed of lithium ion movement between positive and negative electrodes through the design of chemical systems without affecting the life and safety of the battery cells. Many fast charging technologies are optimized around this point. CATL and Watma are representative of the research and development of lithium iron phosphate battery fast charging.

　　CATL's lithium iron phosphate fast charging technology is relatively mature. In terms of the positive electrode, CATL has developed the "super electron network" technology. On the basis of ensuring the safety and reliability of the fast charging battery system, the electrons of lithium iron phosphate have excellent conductivity, which can reach 1,000 times that of ternary materials. In terms of negative electrode, CATL uses the "fast ion ring" technology to create a circle of "highway" on the graphite surface, which accelerates the embedding of lithium ions in the graphite layer, and the charging rate can reach 4C~5C, and can ensure the energy density of the system level above 70Wh/kg, and achieve a cycle life of 10,000 times. In addition, in order to adapt fast charging to different working environments, CATL has also specially developed a thermal management system to ensure fast charging in low and high temperature environments.

　　Huang Shilin, president of CATL, said that CATL will develop more sophisticated battery fast charging technology, and deploy professional centralized charging stations according to charging needs to meet the market's demand for long-distance driving and short-time charging. It is understood that CATL will gradually improve battery energy density and improve the cruising range of electric vehicles. It will launch new technologies before the end of 2017 and strive to produce battery products that can be charged in 10 minutes and have a cruising range of 300 kilometers.

　　After investigating Watma and consulting relevant information, Battery China.com learned that Watma is a staunch supporter of the lithium iron phosphate material system, and it has been working hard on lithium iron phosphate fast charging. For the positive electrode, Watma uses lithium iron phosphate materials with smaller particle sizes. The common lithium iron phosphate particles in the market are between 300 and 600nm, while Watma only uses lithium iron phosphate materials with a particle size of 100 to 300nm, which makes lithium ions move faster and can achieve higher current rates for charging and discharging. For the negative electrode, Watma also uses artificial graphite with smaller particle sizes for carbon coating - small particle sizes are conducive to the detachment and embedding of lithium ions; carbon coating can optimize and improve the cycle life of the battery, and the microporous carbon structure is conducive to the adsorption of the electrolyte, thereby improving the cycle life.

　　In terms of safety protection measures, Watma batteries use a cylindrical structure, and are equipped with a vent pipe device and a pull-off opening device outside the conventional safety device. The vent pipe device can ensure the balance of internal air pressure and prevent the risk of battery explosion caused by excessive local air pressure in the battery cell; and the pull-off opening device will produce gas to disconnect the circuit when the battery is overcharged, overcurrent, or overheated, stopping the electrochemical reaction inside the battery to prevent the occurrence of explosion.

　　rechargeable battery 18650 3.7v have been playing a leading role in battery systems in recent years. Although the theoretical energy density has limited room for improvement and will eventually be replaced by other battery materials, lithium iron phosphate has found a new breakthrough point and challenged other battery material systems in terms of fast charging. It is foreseeable that in the future, lithium iron phosphate can go further with its fast charging "one trick".

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