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| The cathode material of "lithium" is the key to change the fate of ele |
| Release time:2022-12-30 15:10:06| Viewed： |
The cathode material of "lithium" is the key to change the fate of electric vehicles!
The charging is too slow, the battery life is not enough, and the virtual electricity anxiety is the obstacle that every person who wants to own a pure electric car can't get around. If one day new energy vehicles have two super capabilities, namely, fast charging and endurance awesome, new energy vehicles and even the huge energy storage market will usher in another spring. Recently, the Shanxi Institute of Coal and Chemical Industry, Chinese Academy of Sciences has received good news that the 709 research group of the Institute has successfully achieved a new breakthrough in lithium battery cathode materials after six years of research.
The third generation technology of lithium battery cathode materials
Among the heavy traffic, the proportion of pure electric vehicles is getting higher and higher. The global lithium battery industry benefits from the rapid development of automobile electrification, driving the demand for lithium battery cathode materials to grow rapidly. In 2011, China's lithium battery cathode material industry entered a rapid development period. Most domestic enterprises have achieved import substitution in the field of lithium battery cathode materials. In the first half of the year, the shipment of anode materials reached 332000 tons, of which 85% was man-made graphite.
In 2016, Chen Chengmeng, the 709 Research Group of Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences, with the support of provincial funds, tried to explore the technical route of anthracite to produce artificial spherical graphite. After five years, they mastered the basic theoretical knowledge and engineering experience of coal based artificial graphite, laying the foundation for the rapid development and application of coal based anode materials in lithium batteries.
The most criticized problems of lithium batteries are slow charging and poor endurance, which are related to cathode materials, diaphragms and electrolytes. However, compared with anode materials, anode materials are the main factor and need to be broken through. The traditional artificial graphite is the second generation of commercial anode materials. It is made of petroleum coke or needle coke through a series of processes such as coating granulation, carbonization, and graphitization.
Compared with the first generation natural graphite and other materials, it is a very ideal choice with good cycle performance, excellent high and low temperature performance, high safety and mature process. However, its indicators are close to the theoretical limit, and there is very limited room for improvement in the future.
The more mature the technical route is, the narrower the future will be. The characteristics of artificial graphite made of needle coke and petroleum coke determine its upper limit. For this reason, lithium battery manufacturers have been looking for the third generation technology. 709 groups of coal based fast charging cathode materials developed can exceed this theoretical value. The unique structure makes fast charging and fast discharging of lithium batteries a reality. This scientific and technological achievement has met the necessary conditions for entering the industrial demonstration line from the laboratory.
In 2021, Chen Chengmeng's research group gave full play to the advantages of the research and development of new coal based materials, pioneered a new way to use anthracite to make artificial graphite cathode materials for lithium batteries, abandoned the traditional methods of using needle coke and petroleum coke to make cathode materials at home and abroad, completed the complete technology research and development of coal based fast charging cathode materials, and built the first domestic tonnage test demonstration line.
Break through the congestion at the "tunnel" entrance
To achieve fast charging, the lithium battery must be able to carry large current. If the charging process is considered as a "tunnel" for a car to drive into the expressway, the lithium ion is driven on the old expressway of traditional artificial graphite. Due to its small layer spacing, it is easy to form congestion at the "tunnel" entrance. Excess lithium ions will form "lithium dendrites" on the negative electrode surface, which will seriously affect the driving speed of the ions, and even easily lead to "safety accidents".
Researcher Sun Guohua, a member of the research team, told us: "In the process of high temperature heat treatment of traditional artificial graphite materials, the molecules will be rearranged and combined, and the spacing of microcrystalline layers will be reduced; coal based artificial graphite is relatively hard, with micropores, and the spacing of microcrystalline layers is appropriate, which is the natural advantage of anthracite. This is conducive to the insertion of lithium ions, without causing significant expansion of the structure, and has good rapid charge discharge performance. The mesopores and through holes on the material surface are like expanded 'tunnels', It will not cause lithium ion congestion, so it speeds up the charging and discharging process. "
Not only the embedding speed has been improved, but also the capacity of the cathode material has been expanded. "Traditional needle coke and petroleum coke series artificial graphite are like a book, regular graphite is like paper, and a layer of lithium ion can be embedded in the middle; while coal based artificial graphite is like scattered paper, each piece of paper can be embedded with lithium ion on both sides, and the pores between different pieces can also store lithium ion, so the capacity is larger." Sun Guohua vividly described the structure of coal based artificial graphite.
After evaluation, the initial storage capacity of the coal based fast charging cathode material developed by the research group has exceeded the theoretical specific capacity of 372 milliampere hours per gram (mAh/g), and can also meet the requirements of fast charging at 5C. For the first time, the specific capacity can reach 365-375mAh/g, which is 5% - 10% higher than the current market fast charging products. Under the same large magnification, the capacity retention rate is 10% - 20% higher than the market products, which can shorten the charging time to less than 20 minutes, and the price of anthracite less than 3000 yuan/ton has increased more than 20 times.
Seek the industrialization path of innovative achievements
Compared with other fields, it takes 10-20 years to form a solid technical route, and it takes less than 6 years for the 709 research group to complete a breakthrough, which stems from their three major advantages - solid basic theory, engineering experience, and a complete innovation chain.
"This organizational ability is the pain point of many scientific and technological achievements, but it is also the strength of our research group," said Li Xiaoming, a member of the research group and the technical director of carbon based new materials. Coal is composed of complex organic matter and more than 120 kinds of minerals. The composition is complex and changeable. The primary engineering problem faced by all new coal based materials is the purification of raw materials - mastering efficient and low-cost ash and impurity removal technology. The traditional coal washing technology only needs to control the ash content at 8-11wt%. Coal based fast charging cathode materials need to control the ash content index at a very low level, and there is no precedent for solid-liquid separation, efficient deashing technology, etc. If the raw materials are impure, there is no basis for research. If the raw materials do not pass the standard, it will make it difficult to control the quality of materials, shorten the service life of equipment, and cause safety accidents such as "fire explosion". Chen Chengmeng's team has broken through this technology after six months of technical research. After extreme crushing to the micron level, coal with ash content less than 2wt% can even be obtained.
Another key technology is coal graphitization, which requires heat treatment of coal at a high temperature of 3000 ℃ and continuous operation for 50-100 hours. During this period, team members collected 20 kinds of anthracite from Shanxi, Yunnan, Henan, Beijing and other places, and repeatedly tested them for hundreds of times. Run upstream, run downstream, enter enterprises, enter exhibitions... Even though coal based artificial graphite has great advantages in performance, how can it win the favor of the market as an exotic "species" entering the new market?
709 research group has its own unique method. According to their previous experience, it is difficult to impress customers with a mature material in their eyes, no matter how extravagant the presentation is. "The anode material can only show its advantages by placing it on the lithium battery. We bought the anode material and diaphragm to make our own lithium battery. Whether it is debugging or testing, the first-hand data can always be quickly mastered, and the customer's recognition is also high. In addition, we have also made theoretical exploration in the field of self-made diaphragm," Li Xiaoming said, "The scientists of the research group spent a lot of energy to keep in close contact with leading lithium battery enterprises and leading anode material enterprises, understand the most cutting-edge downstream needs, and improve targeted indicators."
"Exploring and studying the development path of coal raw materials and low carbon materials is in line with the national layout, and hopes to give electric vehicles greater confidence through the new generation of cathode material technology." Chen Chengmeng said.
At present, with the rapid expansion of the lithium battery market scale and the rapid change of the industry technology, leading enterprises in the industry are closely laying out the next generation of cathode materials. The 709 research group has also put the industrialization of this innovative achievement on the agenda. |
