Overcome high-nickel ternary materials for battery life

Lithium battery production

Scanning electron micrograph of NCM ternary material

"How many kilometers can this car run?" "How long does it take to charge a battery?" "Is the battery safe?"

Recently, in a new energy vehicle 4S store in Beijing, a family who came to buy a car surrounded Liu Li, a sales manager, and kept asking questions he cared about. "Now when people buy new energy vehicles, the most frequently asked questions are about the cruising range, charging time, and whether it is good for charging in winter." Liu Li said.

Power lithium batteries have become the benchmark for comparing the performance of electric vehicles. However, many people do not know that the key to determining the performance of lithium batteries is the cathode material.

"The cathode material is the most critical raw material for power lithium batteries. Its performance directly determines the main performance indicators of lithium batteries, accounting for more than 30% of the total cost." Chen Chen, deputy general manager of Beijing Dangsheng Material Technology Co., Ltd. Yan Bin told reporters.

For a long time, the lack of high-performance cathode materials has been the "pain point" for the development of China's new energy vehicles and its power lithium battery industry. As the founder of the technology of a listed company focusing on the research and development of lithium battery cathode materials in China, Chen Yanbin led the R & D team to develop and mass-produce automotive lithium battery cathode materials in China in 2014. It has high specific capacity, long cycle life and high pressure The four performance advantages of high solid density and excellent low temperature performance, the corresponding power battery cell energy density reaches 230Wh / kg, the cycle life reaches 4000 times, and the low temperature charge and discharge performance advantages are also very prominent, which has become a high-end electric vehicle power at home and abroad The first choice of cathode materials for lithium batteries. In the 2017 Beijing Science and Technology Awards, the project won the second prize.

High nickel type and high energy, long life of electric vehicles

It is understood that the commercially available lithium battery cathode materials include lithium cobalt oxide, lithium manganate, lithium iron phosphate, and NCM (nickel cobalt manganese) ternary materials. In the early development of domestic electric vehicles, power batteries were dominated by batteries using lithium iron phosphate cathode materials. Although the battery made of this cathode material has a better cycle life, the energy density is relatively low, which results in a relatively short cruising range for electric vehicles. .

"Energy density, cycle life, high temperature storage stability, low temperature characteristics, safety, and cost are several key indicators of power lithium batteries." Chen Yanbin said.

As the demand for long cruising range of passenger cars becomes more and more urgent, it is necessary to develop higher energy density cathode materials for lithium batteries.

"High-nickel ternary materials can significantly increase the energy density of lithium batteries, and the amount of electricity that can be stored in a unit volume or unit weight battery is more, so it has gradually become the mainstream of the passenger car power battery market." Chen Yanbin said from the technology From a perspective, the main performance indicators such as energy density, output characteristics, cycle life, storage stability, and safety of ternary materials are relatively balanced, so it is the mainstream direction of cathode materials for power batteries in the future.

Compared with the conventional ternary materials NCM111 and NCM523, NCM622 has a higher specific capacity, and the energy density of the battery made by it can reach more than 230Wh / kg.

"NCM811 and NCA with higher nickel content have high energy density, but are difficult to prepare, high in production cost, and have a high safety risk. Currently, they are mainly used in small-sized cylindrical batteries (below 5Ah), and are used in large square batteries and aluminum-plastic Film flexible packaging batteries (above 50Ah) still face many technical challenges. "Chen Yanbin said," NCM622 is therefore the current and even the first choice of high-end large-scale power battery cathode materials. "

Relevant information shows that in 2018, Volkswagen and BMW used high-nickel NCM622 in the selection of their supporting power batteries, and will adopt ternary materials with higher nickel content in the future. Among the power battery companies, including Panasonic, LG, SK, Samsung and other international companies are marching into high-nickel ternary material power lithium batteries.

In the domestic market, whether it is mainstream electric vehicle companies such as BAIC New Energy, BYD, Geely, Zotye, etc., or mainstream power battery companies such as Ningde Times, Funen, Carnegie, Jiewei Power, etc., are increasing high-nickel ternary batteries. Development and application.

"From the perspective of future market trends, the energy density of battery cells should reach 280Wh / kg or even more than 300Wh / kg, so the application of high nickel ternary materials will become a long-term mainstream trend." Chen Yanbin said.

Break through bottlenecks and master key technologies

However, the development of NCM622 materials is not easy.

"To make high energy density ternary materials, it is easy to increase the energy density by increasing the nickelization or increasing the working voltage, but its cycle life and high temperature storage characteristics will be poor, and its safety risks are also increasing. The technical difficulty to solve these problems is very difficult. "Chen Yanbin said.

At present, only a few technology-leading companies in the world have carried out the development of power lithium battery high-nickel ternary NCM622, and now there are only three or five mass production. The NCM622 material developed by most domestic companies has a high content of alkaline impurities, poor cycle performance, and poor thermal storage stability, and cannot be used for the production of high-end power lithium batteries.

"For ternary materials, a big problem is that the" islands "generated by the breakage and pulverization of aggregate particles cannot participate in the charge and discharge process, and more side reactions will occur in the new crack interface. Will lead to a decline in the overall performance of lithium batteries. To have a stable particle structure and excellent comprehensive performance, it is necessary to start the whole process system design from the precursor. "Chen Yanbin said.

Chen Yanbin led the R & D team and systematically developed many key technologies for the preparation of high nickel materials, including precursor precipitation technology, sintering process, doping technology, surface (boundary) surface modification technology, and enhanced the phase structure, surface and interior of the particles The stability of the interface has greatly improved the cycle life, storage performance and safety of the material.

Through continuous improvement of key process technologies, Chen Yanbin led the team to overcome many key problems in the industry of high-nickel ternary material products, and established a set of industry-leading product design and its clean and efficient manufacturing technology.

Firstly, a high-density spherical precursor of a certain specification is synthesized by a continuous method of sulfate system. The obtained precursor has a specific particle size distribution, good sphericity, crystallinity, internal structure and particle strength, which is conducive to the preparation of ternary with excellent comprehensive performance material.

Further, the precursor and lithium carbonate are rapidly mixed through a high-efficiency mixing device, and high-temperature sintering is performed under a certain sintering temperature curve and atmospheric conditions, so that the lithium salt and the precursor fully contact and completely react. The sintered material is crushed and classified to prepare micron-level ultra-fine powder, and then subjected to the synergistic modification treatment of the surface (boundary) surface of multiple elements and phases, which greatly improves the stability of the material and effectively suppresses the electrolyte Side reactions such as oxidative decomposition of the surface of the positive electrode and erosion and dissolution of the positive electrode material achieve the purpose of improving the structural stability and chemical stability of the material, and finally prepare the NCM622 material with excellent comprehensive performance.

For enterprises, only the industrialization of laboratory research results can realize their commercial value. Dangsheng Technology's R & D team took the lead in designing and establishing a fully-automatic large-capacity, fully-enclosed precursor clean and efficient production line and cathode material production line through continuous optimization and improvement of preparation process technology and equipment.

"This is the first large-capacity, automated, non-breakpoint, fully enclosed precursor production line and positive electrode material production line in China. The equipment process uses a three-dimensional layout to maximize the use of gravity to reduce logistics costs and labor; lye, washing water It realizes the use of cascades and greatly reduces the unit consumption of production; the single-line production capacity of the sintering furnace has doubled compared with the original, and the energy consumption and labor of the unit product have been greatly reduced. "Chen Yanbin said.

Engineering industrialization, achievement transformation promotes development

China's lithium battery cathode material industry has only been more than ten years from the beginning to now. In terms of the preparation technology of lithium battery cathode materials, the technical level of the entire industry is not high.

The high energy density NCM622 cathode material developed by the project team has a practical battery charge and discharge life of more than 4,000 times at room temperature, which is much higher than the international counterparts ’2,200 times. Successful research and development and export to the international high-end lithium battery market, and large-scale application in high-end electric vehicles.

The industrialization of this technology not only meets the market demand for high-end lithium battery materials, but also promotes the development of domestic lithium battery cathode material technology from traditional manufacturing to clean, efficient, automated and intelligent. At present, Dangsheng Technology has the top ten international lithium battery customers. It is one of the two suppliers to provide high-quality lithium battery cathode materials to high-end lithium battery companies in China, Japan, and South Korea, which has contributed to the improvement of the industry's overall level. Demonstration leading role.

The research and development process of the project is also a microcosm of the technological innovation of Beijing's high-tech enterprises in recent years. Under the guidance of Beijing's "10 + 3" high-end and sophisticated industrial development policy, these technological enterprises are closely integrated with the new situation of capital development and new industrial development. The trend is to take technological innovation as the core of the development strategy, continuously enhance the innovation ability and core competitiveness, and contribute an important force to Beijing's construction of a national technology innovation center with global influence. (Reporter stated)

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