All-solid-state battery research and development is "forced to speed up"

Amid the high attention and hype in the market, CATL, as the global leader in power batteries, cannot avoid talking about solid-state batteries.

Recently, Wu Kai, chief scientist of CATL, said at CIBF that if the technology and manufacturing maturity are used as the evaluation system (scored on a scale of 1-9), CATL's all-solid-state battery research and development is currently at a level of 4 points. Wu Kai said that CATL's goal is to reach a level of 7-8 points by 2027. "In 2027, CATL's all-solid-state battery has great opportunities for small-scale production, but due to factors such as cost, large-scale production is not yet possible."

In fact, before this, Zeng Yuqun, chairman of CATL, had expressed his views on all-solid-state batteries twice. In March this year, when accepting an institutional survey, Zeng Yuqun, chairman of CATL, said that the implementation of cutting-edge technology must go through three routes, namely the technical route, the product route, and the commodity route. First, see whether it is technically feasible and can be connected; second, after it becomes a product, whether the safety, reliability, consistency, and quality can be guaranteed during the production and manufacturing process; third, whether it can be sold, because it may not be sold if it is too expensive.

01

Interest in all-solid-state batteries grows

There are three technical routes for solid-state batteries, namely the oxide route, the sulfide route, and the polymer route. "There are still many basic scientific problems to be solved, such as the order of magnitude difference between the ion diffusion rate in most solid electrolytes and liquid electrolytes, and the difficulty in maintaining good contact at the solid-solid interface. After breaking through these scientific and technological problems, there will still be problems with industrialization," said Zeng Yuqun.

In the same month, Zeng Yuqun also pointed out in an interview with the Financial Times that the solid-state batteries for electric vehicles touted by Japanese automakers and others are still several years away from commercialization. The technology is not perfect enough, lacks durability, and still has safety issues (such as the consequences of batteries rupturing in car accidents).

It can be seen that Wu Kai’s statement on all-solid-state batteries last month was CATL’s third public statement on the industrialization of all-solid-state batteries this year.

Since the beginning of this year, the attention and heated discussion on all-solid-state batteries have spread from foreign countries to China. For foreign companies, they hope to achieve a curve overtaking through all-solid-state batteries and catch up with China's advantages in the field of power batteries; for domestic companies, how to consolidate and lead the industry and technology advantages in the field of power batteries is also of great importance to the government and leading companies.

The reason why all-solid-state batteries have become the core route that domestic and foreign companies are betting on is that they can significantly increase energy density under the premise of ultra-high safety guarantees, thereby achieving ultimate performance, meeting the application needs of more scenarios, and subverting the existing battery system.

In the global competition for all-solid-state batteries, CATL also had to say, "The company (CATL) attaches great importance to solid-state batteries and has been planning for many years, and has recently increased a lot of investment."

It should be pointed out that CATL is still relatively calm on the timetable for the industrialization of all-solid-state batteries.

Wu Kai believes that to realize the industrialization of all-solid-state batteries, four major problems still need to be solved, including solid-solid interface, application of lithium metal negative electrode, instability of sulfide electrolyte in air and high synthesis cost, and all-solid-state battery production process.

In fact, none of the above four problems can be well solved at present.

Taking the solid-solid interface problem as an example, the solid-solid interface contact between the positive electrode material and the electrolyte is insufficient, which hinders ion transmission; the negative electrode expands greatly in volume during the charging and discharging process, resulting in dynamic damage to the solid-solid interface, which is difficult to repair and continuously deteriorates the solid-solid interface... These all seriously affect the cycle life and rate performance of all-solid batteries.

In order for all-solid-state batteries to achieve the high energy density goals of 500Wh/kg and 1000Wh/L, lithium metal must be used as the negative electrode of the battery based on current technology, but lithium metal has two problems: huge volume expansion and dendrite growth. In addition, all-solid-state lithium metal batteries have another bottleneck that needs to be broken through, which is the increase in the number of battery cycles. According to Ouyang Minggao, an academician of the Chinese Academy of Sciences, the current 500Wh/kg lithium metal battery has a cycle life of only about dozens of times, and a lot of work needs to be done. In addition, in terms of fast charging and safety, because the melting point of lithium metal is only 180 degrees Celsius, these all need to be tackled.

It can be seen that the research and development and mass production of all-solid-state batteries is a very arduous and complex project. CATL has accumulated more than ten years of research and development experience in solid-state batteries. It has currently established an all-solid-state battery research and development team of nearly 1,000 people and has also made some progress and experience. Wu Kai said that from the perspective of the technical maturity and manufacturing maturity of all-solid-state batteries, it is expected to gradually enter the mature stage in the next three years and truly start the mass production process.

02

The semi-solid route is necessary and meaningful

Compared with foreign companies that directly bet on all-solid-state batteries, domestic companies are currently focusing on semi-solid (solid-liquid hybrid) products, with a complete industrial chain, and are trying to install them in vehicles. Industry insiders believe that the reason for this situation is that China has mature technology in liquid battery technology, a very complete industrial chain, and a variety of downstream application scenarios.

Ouyang Minggao believes that as a transitional technology route, it is necessary and meaningful for China to develop semi-solid-state batteries.

In fact, semi-solid-state batteries have been widely promoted in the country in recent years with remarkable results.

Currently, many companies including EVE Energy, Farasis Energy, Lishen Battery, Qingtao Energy, Weilan New Energy, Zhengli New Energy, BYD Battery, Guoxuan High-tech, Ganfeng Lithium Battery, etc. have pushed semi-solid-state batteries into the industrialization stage.

Recently, BAK Battery revealed that the company expects to be able to deliver semi-solid batteries in July this year. It is reported that BAK's semi-solid lithium battery adopts a composite system of polymer + oxide, and through solid electrolyte blending and in-situ curing technology, a semi-solid battery with an electrolyte content of less than 10% is formed. "The energy density under this technical route can reach more than 350Wh/kg, showing the characteristics of high energy, high safety, low expansion, low internal resistance, and wide temperature range."

According to BAK Battery, the company is continuously optimizing the semi-solid system, and the current energy density can reach 360Wh/kg. At the same time, BAK Battery is planning to apply metal lithium negative electrodes to the semi-solid battery system, and plans to increase the energy density to 450Wh/kg by the end of 2024.

Last month, Zhengli New Energy released a dual semi-solid-state large cylindrical battery with ultra-long battery life. It is reported that Zhengli New Energy has developed solid electrolyte surface modification technology and solid electrolyte composite diaphragm technology for ultra-high nickel positive electrode materials. Thanks to this, the failure starting temperature of the large cylindrical battery cell has increased by 10°C, and the maximum failure temperature has decreased by 150°C. In terms of power performance improvement, the low-temperature power at -20°C has increased by 20%.

It is reported that the Zhengli New Energy 46 series large cylindrical battery cells use an ultra-high nickel positive electrode + high silicon negative electrode material system, which makes the power battery system energy density exceed 245Wh/kg, and the whole pack capacity is up to 170kWh, supporting pure electric MPV models, and a full-charge range of more than 1,000 kilometers.

Recently, EVE Energy revealed that the company's solid-liquid mixed semi-solid system has completed some product development. Based on a 50Ah soft-pack semi-solid battery, it can achieve an energy density of 330Wh/Kg and a cycle life of more than 2,000 times.

Qingtao Energy's semi-solid battery consists of a composite positive electrode, a composite negative electrode, an electrolyte and an electrolyte separator. It still has a liquid injection process, and the liquid ratio is about 5%-15%. This year, it will be installed on Zhiji L6 and put on the market for sale.

According to Farasis Energy, its first generation of semi-solid-state batteries have been successfully mass-produced and installed on vehicles; the next generation of semi-solid-state products are ready for mass production, have higher energy density, and are suitable for emerging fields such as passenger cars and low-altitude flights.