18650 battery

　　Is it true or false that 18650 battery can be charged in 5 minutes?

　　At present, most new energy vehicles use 18650 battery, but in actual operation, new energy vehicles often catch fire due to lithium battery consistency and safety issues.

　　Regarding the relevant technical issues of 18650 battery, the reporter interviewed He Xiangming, director of the Lithium-ion Battery Laboratory of the Nuclear Research Institute of Tsinghua University.

　　Strengthening battery technology and manufacturing level

　　Reporter: What do you think of the widespread battery consistency problem?

　　He Xiangming: Mobile phone batteries are all used in single blocks, but now whether it is large-scale energy storage or electric vehicles, many batteries need to be connected together. Taking Tesla as an example, thousands of 18650 batteries are connected in series and parallel, which will bring consistency problems, and the current and voltage will be uneven in actual distribution. This will bring two major hazards. One is that the system life is greatly reduced; the other is that it causes the battery to heat up and there are safety hazards.

　　Reporter: How to ensure the consistency of the battery and prevent problems from occurring?

　　He Xiangming: The general practice is to screen the battery through a series of parameters such as capacity and voltage, but these screening processes are currently more complicated, and the effects are limited. There are also many problems, some of which are caused by measurement errors.

　　At present, the measurement error of the equipment is mostly around 1%. In fact, to meet the battery consistency requirements, the error must be less than 1%. From a manufacturing perspective, the fully automated manufacturing project has reduced human factors due to the fixed equipment accuracy and measurement parameters, and has made great improvements in improving consistency.

　　We are also thinking about other ways to solve the consistency problem, and thus proposed the idea of using series charging and discharging for consistency screening. Specifically, all batteries produced from the factory are first screened for consistency, then connected in series, and then charged and discharged, so that equipment errors can be avoided.

　　Reporter: New energy vehicle battery fire incidents are often reported in the newspapers, further highlighting the safety issues of 18650 battery. How to ensure battery safety?

　　He Xiangming: Battery safety accidents are probabilistic events. The current testing standards cannot completely eliminate battery safety issues. 18650 battery are flammable, have high energy density, have positive and negative electrodes, and heat during use will cause thermal runaway problems. At present, we are strengthening technical research on battery body technology, and the safety of batteries can be guaranteed in about 5-10 years.

　　Battery safety is closely related to the manufacturing level. For example, if dust in the air falls on the diaphragm, it is invisible to the naked eye, but it has a great impact on battery performance. Battery safety is closely related to the management and manufacturing levels of the battery factory. To improve the safety and reliability of the battery, it is necessary to gradually improve in all aspects and run through all aspects of production management.

　　10-15 minutes fast charging is more realistic

　　Reporter: Japan and South Korea are ahead of China in lithium battery technology. Benefiting from the outbreak of domestic new energy vehicles, China is also catching up in 18650 battery, and this gap is gradually narrowing.

　　He Xiangming: In the field of 18650 battery, the United States ranks first in terms of innovation ability; Japan ranks first in terms of quality level; South Korea ranks first in terms of manufacturing level. But China's comprehensive ability is the strongest, and it is leading in terms of comprehensive competitiveness and cost-effectiveness of 18650 battery. Therefore, China, Japan, South Korea and the United States are indispensable to the lithium battery industry.

　　Reporter: There are many reports on electric vehicle fast charging technology now. Is 5-minute fast charging feasible?

　　He Xiangming: Lithium battery fast charging is promising, but the hype on the Internet that it can be fully charged in 5 minutes is a false proposition. We think 10-15 minutes is a more realistic goal. For example, a car with 50 kWh of electricity needs a 50-kilowatt charging pile for one hour; a 500-kilowatt charging pile is needed to fully charge in 6 minutes. If the voltage of a 500-kilowatt charging pile is 220 volts, the current is more than 2,000 amperes, which is impossible. It will not be allowed in the community, which involves the capacity expansion of the community infrastructure. In addition, fast charging has great hidden dangers to the life and safety of the battery.

　　In terms of fast charging, we are also making some technical reserves and independently developed a negative electrode material that can greatly shorten the charging time. It is still in the laboratory stage.

　　Energy density should not be used as an indicator alone

　　Reporter: The country plans to achieve a battery cell energy density of 300 watt-hours per kilogram by 2020. It is understood that the research and development teams of CATL, Tianjin Lishen, and Guoxuan High-tech have basically achieved the research and development of 300 watt-hours/kilogram power batteries. The goal of 300 watt-hours does not seem to be a challenge.

　　He Xiangming: The 300 watt-hour target is not a problem purely from a technical point of view, but as a product for large-scale application, the battery will eventually be used in new energy vehicles. We cannot only consider the charge and discharge capacity, but also the safety and reliability. We also need to continuously verify in practice, and we must absolutely pass the test in terms of reliability.

　　The state has issued new energy vehicle subsidy standards, set a threshold for subsidies, and stipulated that the subsidy should be guided by battery energy density. The original intention is good.

　　But there are also certain side effects. First of all, the cost has pushed up the manufacturing cost of batteries, leading to an increase in corporate costs. On the other hand, companies need to move forward with heavy burdens to meet technical indicators.

　　In comparison, foreign countries pay more attention to the reliability and safety of batteries in the development of batteries, on the premise of meeting a certain energy density.

　　Reporter: We see that many new technologies are emerging now. Some experts believe that the energy density of 18650 battery is constantly approaching the ceiling. What do you think of this?

　　He Xiangming: Lithium battery technology is determined by materials. It is an electrochemistry that is constantly evolving from materials. The progress of 18650 battery is not achieved overnight, nor is there progress every two or three days. It is a process of crawling slowly like a snail.

　　Nowadays, it is often said that many new technologies have made progress in one way or another, but technological breakthroughs require a long period of accumulation. The development of any industry is a steady process, and laboratory breakthroughs often take a long time to transform into real productivity.

　　In addition, any battery technology has a ceiling. The market is the best test for whether the technology is good or bad - user choice and investment trends. At present, most new energy vehicles are driven by 18650 battery.

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