At present, most of the new energy vehicles use lithium batteries, but in actual operation, due to lithium battery consistency and safety issues, new energy vehicle fires often occur.
Regarding the related technical problems of lithium batteries, the reporter interviewed the chief of lithium ion battery laboratory of the Institute of Nuclear Physics of Tsinghua University.
Enhanced battery technology, manufacturing level
China Energy News: How do you see the prevalence of battery consistency problems?
He Xiangming: The mobile phone batteries are used in a single piece, but nowadays, whether large-scale energy storage or electric vehicles, many batteries need to be connected together. Take Tesla as an example, thousands of 18650 battery strings are connected in parallel. Consistency problems, current and voltage in the actual distribution will appear uneven. This will bring two major hazards, one is a substantial decline in system life; second is to cause the battery to heat, there are security risks.
China Energy News: How to ensure battery consistency and prevent problems?
He Xiangming: Everyone's common practice is to screen the batteries through a series of parameters, such as capacity and voltage. However, these screening processes are currently more complicated, and their 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 about 1%. In fact, to meet the battery consistency requirements, the error is less than 1%. From the manufacturing point of view, the fully automated manufacturing engineering due to equipment accuracy, the measurement parameters are fixed, reducing the man-made Factors, have greatly improved the improvement of consistency.
We are also thinking about other methods to solve the consistency problem, and we have proposed the idea of using the series charge and discharge for consistency screening. Specifically, we must first screen all the consistency of the battery produced from the factory, and then connect them in series, and then charge and discharge. This avoids equipment errors.
China Energy News: The incident of new energy vehicle battery is often seen in newspapers, further highlighting the safety issues of lithium batteries. How to ensure battery safety?
He Xiangming: Battery safety accidents are probable events. The current testing standards cannot completely eliminate battery safety issues. Lithium batteries are flammable materials. They have high energy densities. They have a positive electrode and a negative electrode. Heating during use can cause thermal runaway. Problem. At present, technical research on battery technology is strengthened to ensure the safety of the battery within 5-10 years.
Battery safety is closely related to the level of manufacturing, such as dust in the air. If it falls on the diaphragm, it is invisible to human eyes, but this has a great impact on battery performance. Battery safety and battery factory management , The level of manufacturing is closely related. To improve the safety and reliability of batteries, we must gradually increase in all aspects, to run through all aspects of production management.
10-15 minutes fast charge more realistic
China Energy News: Japan and South Korea lead China in lithium technology, benefit from the outbreak of domestic new energy vehicles, China is also catching up with lithium, and this gap is gradually narrowing.
He Xiangming: In the field of lithium power, it is the first in the United States in terms of innovation capabilities; Japan ranks first in terms of quality; and Korea ranks first in terms of manufacturing. However, China’s overall capability is the strongest. In the comprehensive competitiveness of lithium batteries, the cost performance is Leading. So China, Japan, Korea, and the United States are indispensable for the lithium battery industry.
China Energy News: There are many reports on fast charging technology for electric vehicles. Is it possible to use a 5-minute fast charge?
He Xiangming: Lithium fast charge is promising, but like 5 minutes of online hype, it is a false proposition. We think 10-15 minutes is a more realistic goal. For example, a car with 50 kWh is charged for 1 hour. To charge a 50-kilowatt charging pile; for a full charge of six minutes, a 500-kilowatt charging pile, a 500-kilowatt charging pile, and if it is a voltage of 220 volts, the current is more than 2000 amps. This is not possible. Will make use of, this involves the expansion of residential infrastructure. In addition, the fast charge on the battery life, safety has a great hidden danger.
In terms of fast charging, we are also making some technical reserves. We have independently developed a negative electrode material that can greatly reduce the charging time. It is still in the laboratory stage.
Instead of simply using energy density as an indicator
China Energy News: The state plans to have a battery cell energy density of 300 watt-hours per kilogram by 2020. It is understood that Ningde Times, Tianjin Lishen, and Guoxuan Hi-Tech Corporation R&D team have basically realized a 300-watt-hour/kg power battery. R&D. The 300-watt goal seems to be no longer a challenge.
He Xiangming: The goal of 300 watt-hours is purely technically not a problem. However, as a large-scale application product, batteries are ultimately used in new energy vehicles. It is not possible to consider only charge and discharge capacity, but also to consider safety and reliability. Need to continue to verify in practice, in the absolute ability to pass the reliability.
The state introduced a subsidy standard for new energy vehicles, set a threshold for subsidies, and stipulated the guideline of battery energy density. The intention is good.
However, there are certain side effects. Firstly, the cost of the battery is pushed up and the cost of the enterprise is increased. On the other hand, the company needs to work hard to meet the technical requirements.
In comparison, in the development of batteries in foreign countries, under the premise of meeting certain energy density, more attention is paid to the reliability and safety of batteries.
China Energy News: We see that many new technologies are emerging. Some experts think that the lithium energy density is constantly approaching the ceiling. What do you think about this?
He Xiangming: Lithium-ion technology is determined by materials. It is an electrochemical system that evolves continuously from materials. Lithium-electricity advancement does not happen overnight. It is not a process that takes place in three days and two. It is a process that crawls like a snail.
It is often said that there are many new technologies that have achieved this or that kind of progress, but breakthroughs in technological advancement require long-term accumulation. The development of any industry is a steady development process, and laboratory breakthroughs often require a long process to become reality. productive forces.
In addition, any battery technology has a ceiling, technology is good or bad, the market is the best detection - the user choice and investment trends, now the vast majority of new energy vehicles are lithium batteries to drive.
