The Star Daily reported on November 27 (Reporter Yu Jiaxin) that the popularity of solid state batteries continues to rise.

At the recent 2024 High-Performance Lithium Battery Annual Conference, Yu Dedelong, director of GGII, stated that GGII predicted last year that the shipment of solid state batteries would exceed 5GWh in 2024. However, data up to the third quarter indicates that by the end of this year, solid state batteries are expected to achieve a shipment volume exceeding 7GWh, with a goal of reaching 300GWh by 2030. Furthermore, full solid state batteries are expected to exceed GWh after 2028, and will surpass 100GWh around 2032.

Currently, as solid state batteries continue to develop, the reporter from Star Daily has noticed new changes in the lithium battery industry chain, while new application scenarios are accelerating the industrialization process.

From Liquid to Solid: Accelerated Iteration of Materials, Processes, and Equipment

Compared to liquid batteries, solid state batteries can be considered as replacing the electrolyte and separator in lithium-ion batteries with solid electrolytes, with the most significant change being the contact method of electrolytes and active materials changing from solid-liquid to solid-solid contact, resulting in a series of changes.

Xu Hangyu, general manager of Wei Lan New Energy R&D, stated that challenges for solid state batteries include maintaining stable interface contact under full life cycle conditions, as a single solid electrolyte material is difficult to meet the demands of full solid state batteries. Based on this, he believes that the development strategy of hybrid solid-liquid batteries compensates for the shortcomings of single electrolyte materials. "Currently, the company has achieved mass production of hybrid solid-liquid batteries based on oxide and polymer solid electrolytes, with products applied in areas such as low-altitude economics, new energy vehicles, and energy storage."

Under the influence of solid electrolytes, the development of cathode materials is also facing new changes.

Zhou Yuhuan, deputy chief engineer at Yibin Lithium Battery, stated that the main issues faced in the development of cathode materials for solid state batteries include interface stability, electrochemical stability, mechanical contact stability, and cost concerns. Therefore, the geometry and dimensions of cathode materials for solid state batteries should be personalized based on the form of the electrolyte used to ensure a close fit with the electrolyte. Cathode materials for solid state batteries need to be developed towards being denser, crack-free, and with zero strain. The surface coating of cathode materials requires more precise control, requiring uniform coating and controllable thickness, as well as the development of new coating processes suitable for industrial production.

In terms of battery technology, dry process technology has received widespread attention. Chen Yang, CTO of Huacai Technology, stated that the dry process electrode discards traditional liquid solvents, similar to the design concept of solid state batteries. With the empowerment of dry process technology, the manufacturing process of the electrode sheets for solid state batteries can be completely dry, eliminating the residual solvent molecules after drying in wet process technology. Additionally, using the fibrillation effect of adhesives to produce solid electrolyte films can enhance the performance of solid state batteries, with advantages including lower porosity and improved ionic conductivity; active materials and adhesives mixed into films without the need for drying, resulting in lower manufacturing costs; and higher compaction density, which is beneficial for resolving solid-solid interface issues.

Li Ning, the director of the Mannest Lithium Battery Coating Research Institute, also mentioned that at the material level, the dry method avoids the complex reactions caused by liquid media and allows for easier control of the interactions between materials. The dry method can operate in low-temperature environments and ensure a high-quality interface between sulfide electrolytes and electrode materials by optimizing parameters. In terms of process, operations such as mixing and rolling in the dry method are feasible in pilot line electrode production, enabling precise control over powder characteristics and process parameters, such as controlling the mixing ratio and rolling pressure, thus producing electrode sheets with suitable thickness and density.

New processes also require matching new equipment. Lu Qihui, the technology director of Liyuanheng Solid State Battery, stated that the company's dry coating equipment for electrodes can reduce raw material solvent costs by 11.5% compared to wet electrode processes, and reduce energy consumption by more than 46%, making it highly economical.

At the same time, it was mentioned that the key equipment for solid state batteries includes roll-to-roll hot composite dual-roller machines, electrode frame printing & stacking machines, and high-pressure formation equipment. Among them, the role of the electrode frame printing & stacking machine is to eliminate the separator in solid state batteries and require high-pressure formation, thus causing deformation at the edges of battery electrode sheets, which easily leads to internal short circuit issues. Printing resin onto the edges of electrodes forms a return frame, providing support and insulation under pressure.

Simultaneously, the high-pressure formation equipment can activate the battery materials and stabilize the battery performance after the initial charging and discharging process. Conventional battery formation or restraining pressure requirements range from 3 to 10 tons, while solid state battery formation or restraining pressure requirements range from 60 to 80 tons (10 MPa pressure per individual cell).

Compared to liquid batteries, the workshop environment for solid state batteries will also be more stringent, including stricter low dew point control, with the dew point at -50 degrees Celsius. Additionally, there is a need to enhance the toxic gas and explosion-proof design for sulfide and halide solid state battery equipment.

▍Fully solid state batteries still face multiple issues, with eVTOL manufacturers calling for breakthroughs at the material level.

Currently, industry insiders generally believe that solid state batteries are still in the early stages of development, mainly focusing on semi-solid state, while full solid state batteries still face many issues in terms of cost, processes, and safety production.

Regarding costs, GGII Director Yu Delong mentioned that the price of raw materials is high, with sulfide currently priced at 0.05 million yuan/kg, and the cost of full solid state is more than ten times that of liquid state.

At the same time, in terms of production line investment, looking at the 2GWh battery automation production line equipment that Jiangsu Xinjie intends to purchase from hymson laser technology group, the expected equipment procurement amount is about 0.4 billion yuan. Several industry insiders mentioned to the Star Daily that the investment amount for a solid state battery production line varies based on different product specifications; however, it is basically equivalent to double the previous investment for liquid battery production lines. Additionally, new solid state battery equipment, such as isostatic presses, costs hundreds of thousands of yuan, significantly increasing costs.

In terms of processes, full solid state batteries face challenges in mass production regarding dry process methods for cathodes and isostatic pressing techniques. Li Yuanheng's solid state battery technology director Lu Qihui stated that this includes challenges in continuous dry production of cathodes, difficulties in dry mixing technology and powder quantitative feed technology, which slows down manufacturing speed and leads to uneven distribution of electrode materials. The stability and lifespan of the roller systems are under challenge, with large particle lithium iron phosphate experiencing equipment jamming during film formation, issues of high-frequency vibration noises during film formation with small particles, and problems related to the fatigue lifespan of roller surfaces.

Regarding the isostatic pressing process, it was mentioned that extreme high pressures cause damage to the cells. High pressures of up to 500Mpa lead to appearance damage and internal short circuit issues in the cells; isostatic equipment has low production capacity and short lifespan, with a maximum batch output of only 48 pieces (for power soft pack batteries), and under 500 megapascals of pressure, the cylinder material reaches its yield limit, with each operation resulting in plastic deformation.

In terms of inherent safety, Mengwei Technology's Deputy General Manager Li Hongfei stated that the safety and failure mechanisms of solid state batteries require in-depth research. Existing experimental results indicate that solid state batteries do not equate to absolute safety; solid electrolytes can also experience thermal runaway, and their safety and mechanisms of thermal runaway need further in-depth study. In solid state lithium metal battery systems, when solid electrolyte materials are paired with metal lithium anodes, dendrites can grow along the interfaces, cracks, and gaps of the solid electrolyte, potentially causing short circuits and posing risks of thermal runaway.

In terms of application scenarios, currently, emerging markets such as the eVTOL field are receiving continuous attention.

On November 14 this year, ehang announced a major technological breakthrough in the high-energy solid state battery developed in collaboration with Xinjie Energy and the International Advanced Technology Application Promotion Center (Hefei) Low Altitude Economy Battery Energy Research Institute. The EH216-S equipped with this battery successfully completed a single uninterrupted flight test lasting 48 minutes and 10 seconds, suitable for different flight needs, with range times significantly improved by 60%-90%.

The president of Xinjie Energy, Sun Li, introduced at the High Engineering Lithium Battery Annual Conference that the company's solid state battery uses lithium metal anode and oxide ceramic solid electrolyte, which has undergone professional testing by several customers in the low-altitude flight field, including Ehang. The first solid state battery (greater than 450Wh/kg) 200MWh pilot line has been stably producing since the end of 2023, and plans are underway to build a 2GWh production line for solid state battery (greater than 450Wh/kg), which is expected to be put into production in Q2 2025, with a total investment of 1 billion yuan and land use of 70 acres.

However, Zhang Hong, vice president of Ehang, stated that if batteries as a whole are moving toward higher energy density, the current materials are insufficient. The best mature materials currently available for solid state batteries are high nickel level nine paired with third generation nano silicon carbon. This material system still faces bottlenecks if it is to achieve high rate capabilities. "In the future, we are also calling for the next generation of materials, such as those that can effectively enhance cell voltage. At present, there seems to be no particularly good new generation cathode material to match the low-altitude economy, and the composite lithium metal for the anode is also not mature yet."

Many manufacturers are seeking breakthroughs. Among them, Li Hongfei, deputy general manager of lithium metal battery manufacturer Mengwei Technology, believes that using lithium metal as an anode is an important way to improve battery energy density, utilizing the deposition and extraction of lithium for energy storage. Lithium metal theoretically has a capacity of 3860mAh/g, and also has a low electrode potential, making it the ultimate goal for the next generation of anode materials for batteries. He mentioned to the Star Daily that the company is currently collaborating with several eVTOL manufacturers on development.

Zhang Jin, the solid state battery research and development manager of Lishen Battery's basic R&D department, stated that the company selects active material with higher specific capacity, allowing the energy density of single cells to exceed 400Wh/kg, while using lithium metal type anodes can achieve energy densities greater than 500Wh/kg. Currently, the company has completed orders for three eVTOLs, with total sales nearing 100 million yuan.

However, overall, Zhang Hong, vice president of Ehang, also mentioned that battery safety itself requires a systematic approach to control. "If there are no particularly good methods at the system level, or if there is not enough good safety control at the overall machine level, we actually do not recommend using ternary. Currently, whether liquid or semi-solid, the safety of ternary materials still needs to be improved at the aviation-grade level. Therefore, we hope that at the system integration level, including intelligent control and overall machine design, everyone can work together and not put all the pressure on the battery."