The "form dispute" of lithium battery cells has never stopped - cylindrical cells occupy half of the consumer electronics market with models such as 18650 and 21700, while square cells have become the mainstream of power batteries due to their high integration. The technological evolution of the two forms is essentially a precise response to the needs of different scenarios.
1 Cylindrical battery cells: inherent advantages of standardization and heat dissipation
The core competitiveness of cylindrical battery cells lies in high standardization. The standard size of 18650 battery cells with a diameter of 18mm and a length of 65mm makes it easy for automated production yield to exceed 95%, and the daily production capacity of a single production line can reach 500000 pieces. Tesla's 4680 battery cell has increased its energy density by 5 times by increasing its diameter to 46mm. At the same time, it adopts a stepless ear design, which shortens the current path and reduces heat generation by 40%. Combined with the bottom water-cooled plate, it can support 5C ultra fast charging (fully charged in 12 minutes).
The uniform heat dissipation brought by the circular structure is another major advantage. In laptops, the temperature difference of multi series parallel cylindrical battery packs can be controlled within 3 ℃, much lower than the 5 ℃ of square cells. A certain game originally used 21700 cylindrical battery cells. After running at full load for 4 consecutive hours, the battery temperature reached a maximum of 42 ℃, while the same configuration model using square battery cells reached 48 ℃. In the field of electric tools, cylindrical cells have better anti vibration performance. After 10G acceleration vibration testing, the capacity attenuation rate is 15% lower than that of square cells, making them the preferred choice for impact drills and angle grinders.
The modular combination of cylindrical cells has high flexibility. By using different series parallel connections, it is possible to quickly adapt to voltage requirements ranging from 1.5V to 1000V. A certain outdoor power brand uses 18650 battery cells and launches a series of products with capacities ranging from 500Wh to 3000Wh through a "building block" combination. The research and development cycle has been shortened to 3 months, saving 50% of time compared to square battery cell solutions.
2 Square shaped battery cells: advantages of space utilization and customization
Square battery cells excel in space utilization and customization capabilities. By adjusting the dimensions of length, width, and height, square battery cells can be adapted to different device cavities. A customized square battery cell from a certain mobile phone manufacturer has a thickness of only 3.5mm, reducing the weight of the body by 10% and increasing the capacity to 5000mAh. In the field of power batteries, the rigid shell of square cells can withstand greater compression, and the probability of short circuit in needle puncture testing is 25% lower than that of cylindrical cells. BYD's blade battery extends the length of square cells to 1.2 meters, and through array arrangement, the volume utilization rate is increased to 60%, which is 20 percentage points higher than traditional square cells.
The popularization of lamination technology has further upgraded the performance of square battery cells. Compared with traditional winding technology, the utilization rate of electrode plates in laminated square cells has been increased to 95%, and the capacity consistency error is controlled within 2%. CATL's CTP (non module) technology integrates square cells directly into battery packs, saving 20% of structural components and achieving an energy density of 290Wh/kg, which is 10% higher than the CTP solution for cylindrical cells. In the field of energy storage, square shaped batteries have an advantage in long cycle life. A certain 100Ah square lithium iron phosphate battery has a capacity retention rate of 80% after 10000 cycles, which is 15 percentage points higher than cylindrical batteries of the same specification.
3 Integration and differentiation: the future direction of technological roadmap
Two forms are moving towards "integrated innovation". The cylindrical battery cell adopts the stacking process of the square battery cell, and the 4680 battery cell uses stacked winding, with an additional 10% increase in energy density; The standardization concept of introducing cylindrical cells into square battery cells has been adopted. The "square cylindrical" battery cells launched by China Innovation Aviation retain the square shell while using circular pole cores, balancing heat dissipation and space efficiency. In the battery pack of SUV models, the volume utilization rate has been increased by 5%.
The differentiation of scenarios is becoming increasingly clear: in fields such as consumer electronics and power tools that require high standardization, cylindrical batteries are still the preferred choice, and 21700 batteries have already reached a market share of 70% in electric wrenches; In high-capacity scenarios such as new energy vehicles and energy storage, square cells dominate with their integration advantages, accounting for over 60% of global power batteries. In the future, with the development of CTC (Cell Integrated Chassis) technology, the two forms may further differentiate - cylindrical cells evolving towards high magnification miniaturization, and square cells breaking through towards large-scale and integrated structural components, ultimately continuing to deepen their respective expertise in their respective scenarios.