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As Kirin batteries, large cylindrical batteries, CTB batteries, sodium-ion batteries, semi-solid batteries and other products have been unveiled or put into application, power battery technology has shown a trend of contention among a hundred schools of thought.
The innovation of power battery technology is inseparable from material innovation and battery cell manufacturing technology innovation, so how is the power battery manufactured from the battery to the battery pack? This article will introduce the power lithium battery cell manufacturing process and the current innovation of power lithium battery technology in detail.
1. Battery cell manufacturing process
At present, power batteries are mainly lithium-ion batteries. According to different appearances, lithium-ion batteries can be divided into cylindrical cells, prismatic cells, and pouch cells.
Different battery cell manufacturing comparison
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Prismatic cell |
Pouch cell |
Cylindrical cell |
|
Aluminum housing is strong, safe and has good cycle life |
Aluminum-plastic film housing is prone to thermal runaway, but not prone to explosion |
The production process technology is mature, the battery cells are packaged and grouped flexibly |
|
Single cell has large capacity, fewer modules, and less risk in monitoring and management |
It is easy to cause flatulence, and the battery cell is bulging and deformed. After a long time of use, the battery life will drop precipitously |
There are many battery cell in the whole package, and the monitoring and management are difficult |
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Simple packaging and battery cell manufacturing process, high reliability |
The pouch case is weak and needs to be protected at the module level |
/ |
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The consistency of the battery cell is average |
Good cell consistency |
Good cell consistency |
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Energy density is average |
High energy density |
Single energy density is high |
The production process of lithium batteries is relatively complicated, and the main production process mainly covers the stirring and coating stage (front stage) of electrode production, the winding liquid injection stage (middle stage) of battery cell synthesis, and the packaging and testing stage (post stage) of chemical formation and packaging.
Lithium battery front stage production process
The lithium battery front stage production process is to prepare the lithium battery cathode and anode plates, including:
- Stir and homogenize the cathode and anode
- Coating and drying
- Roll pressing
- Cathode and anode cutting
Lithium battery middle stage production process
In the lithium battery manufacturing process, the middle process is mainly to complete the forming of the battery. At present, there are two main power lithium battery cell manufacturing processes: winding and lamination, and the corresponding battery structures are mainly cylindrical, prismatic, and pouch.
Cylindrical and prismatic batteries are mainly produced by winding battery cell manufacturing, while pouch batteries are mainly produced by laminated battery cell manufacturing. Since the winding battery cell manufacturing process can achieve high-speed production of cells through the speed, and the speed that the laminated battery cell manufacturing process can increase is limited, at present, many power lithium batteries companies such as top 10 lithium battery companies in the world mainly use the winding cell process.
The middle process of lithium battery includes:
- Sheet production and die cutting
- winding or lamination
- Shell and lug welding
- Liquid injection and injection port welding
- Sealing
- Packaging
Lithium battery post stage production process
The post-production process of lithium batteries mainly includes four processes: capacity separation, battery formation, testing, and packaging and storage.
Battery formation and capacity separation are the most important links in the back-end process, and the formed batteries are activated and tested. The main function of the formation process is to charge and activate the cells after liquid injection packaging. The capacity separation process is to test the battery capacity and other electrical performance parameters after the battery is activated and then classify it.
Formation and volume separation are performed by the formation machine and the volume separation machine, usually by an automated volume separation and formation system. The next thing to do is to screen capacity, internal resistance and voltage consistency, and conduct dozens of destructive tests such as impact and vibration puncture. Then carry out module and Pack packaging according to the needs of different car companies.
2. The development trend of battery cell manufacturing technology
① Cylindrical cell
In general, the development time of cylindrical cell is long and the technology is the most mature.
- Advantages: mature technology, low cost, stable and durable, high energy density of monomer, good consistency of monomer
- Disadvantages: small room for energy density increase, a large number of combinations require high BMS
Tesla took the lead in realizing the mass production of 4680 batteries, guiding the direction of the industry. Major battery manufacturers and auto brands pay more attention to the direction of large cylinders. It is expected that major battery manufacturers and some mainstream car companies will adopt 4680 battery solutions in 2024-2025.
Comparing the production process of 4680 and 21700, in terms of processing procedures, compared with 21700 battery, the 4680 battery has added the processes of tab die-cutting, flattening, laser welding collector plate, opening formation, and laser welding cover plate.
② Prismatic cell
Prismatic cell is a compromise solution at the moment, and square aluminum casings currently have an absolute advantage in the Chinese market.
- Advantages: high strength, small internal resistance, long life, high space utilization
- Disadvantages: difficult to unify the production process and difficult to dissipate heat
In March 2020, BYD launched the blade battery. It adopts a flat design for the prismatic battery cell manufacturing, reduces the thickness of the battery cell and increases the length, and adopts the CTP solution. Since then, major battery manufacturers have actively promoted the development of long and thin prismatic battery manufacturing. The flat and elongated battery cell manufacturing can increase the heat dissipation area between the cells and improve the safety of the lithium battery.
At the same time, it can be used as a structural part to realize CTP/CTC. The lithium battery cell manufacturing is developing in the direction of elongated cells. However, there are technical bottlenecks in the manufacturing and application of winding technology for flat and elongated battery cell manufacturing, which have poor internal structure stability and low space utilization. Naturally, elongated and elongated batteries are more suitable for lamination technology.
The main process difference between lamination and winding lies in the die-cutting process and the electrode forming process. In the die-cutting process, there are certain differences between the two battery cell manufacturing processes in terms of die-cutting methods, material shapes, tab spacing, and material punching. In the electrode assembly process, there are differences between the two battery cell manufacturing processes in terms of cutting judgment methods and the number of tabs.
Compared with winding batteries, the lamination process has greater advantages in energy density, internal structure stability, safety, and cycle life. In terms of disadvantages, the development time of the stacked battery cell manufacturing process is relatively short, the industry supporting maturity is not enough, there are shortcomings such as low equipment efficiency, high investment per GWh, and low yield rate of automated production.
Power battery companies are constantly breaking the constraints brought by the lamination battery cell manufacturing process, and continue to innovate and advance in improving production efficiency, yield, and product performance and quality.
③ Pouch cell
Pouch batteries belong to the most advanced echelon of technology, but the requirements for battery cell manufacturing are relatively high. When the current prismatic battery technology is gradually approaching the bottleneck period, the pouch battery with more mining potential and technical advantages will become a substitute.
- Advantages: high energy density, light weight
- Disadvantages: needs extra protection against battery damage and thermal runaway
The world's mainstream car companies have begun to increase the supply of pouch batteries, and many hot-selling models are also dominated by pouch batteries. In the industry's outlook on the future path of power batteries, solid-state batteries are the future direction of lithium batteries, and many battery manufacturers are actively investing in the research and development of solid-state and semi-solid batteries.
In the current market's technical cognition of solid-state batteries, there is a direction with high certainty, that is, pouch cells are the most suitable packaging method for solid-state batteries. Compared with the existing traditional lithium batteries, solid-state batteries have obvious advantages in three aspects: safety, performance, and cost. The pouch battery adopts the lamination battery cell manufacturing process.
Due to the weak flexibility of the oxide and sulfide electrolytes, the pouch battery using the lamination battery cell manufacturing process is the most suitable. Not only that, compared with cylindrical batteries and prismatic batteries, pouch batteries also have significant advantages in energy density. Due to the lack of flexibility due to the use of solid-state electrolytes, only stacked sheets can be used, so cylindrical packaging cannot be used, and the use of square packaging will weaken the energy density advantage of the battery.
Therefore, the industry believes that pouch packaging and solid-state batteries are the most suitable. Of course, there are always many uncertainties in the future. Whether the form of pouch batteries can usher in a leap in the era of solid-state batteries is still unclear. But for the battery manufacturers of the pouch battery production line, it also means that they are one step faster on the road to deploy semi-solid or solid-state batteries in advance.
Future industry development of power lithium battery
From the perspective of the medium-term development of lithium batteries, it is mainly through the iterative upgrade of the existing material system and structural innovation to promote the improvement of energy density and achieve efficiency and cost reduction:
Material iteration: Cathode and anode materials are the core factors that determine the energy density of power batteries, and the breakthrough of cathode materials is most likely to bring about a subversive improvement in the energy density of power batteries. In the short to medium term, cathode materials will still maintain the parallel pattern of lifepo4 battery and ternary battery, and technology iterations will be carried out on the basis of the current chemical system. High-nickel ternary still has adaptive value in the process of developing from semi-solid to all-solid, and has a broad prospect.
Structural innovation: Under the mature application of lithium battery material system, structural improvement and simplification are carried out in terms of battery cell manufacturing, modules, packaging methods, etc., to improve the system performance of the battery.
From the perspective of the long-term development of lithium batteries, it is a clear trend in the industry to continuously reduce the electrolyte content and develop towards solid-state batteries, but all-solid-state batteries still face relatively large technical challenges. From the point of view that the long-term development of lithium batteries will be restricted by the shortage of lithium resources, sodium-ion batteries have become an important alternative route, and will form a complementary pattern with lithium batteries after commercialization.
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