1. Definition of cylindrical lithium battery
Cylindrical lithium battery is a kind of lithium ion battery, its shape is cylindrical, so it is called cylindrical lithium battery. The structure of a typical cylindrical battery includes: casing, cap, cathode, anode, separator, electrolyte, PTC element, gasket, safety valve, etc. Generally, the battery shell is the anode of the battery, the cap is the cathode of the battery, and the battery shell is made of nickel-plated steel plate.
They are able to supply stable power with a flat discharge voltage and a high reliability. Last but not least, their low self-discharge is impressive. The usage of our Li-Ion batteries requires a safety unit.
2. The Development History of Cylindrical Lithium Batteries
Since Tesla’s Battery Day in September 2020 introduced the 4680 large cylindrical cells, these cells have once again become a focal point in the battery industry. In addition to Tesla, leading battery manufacturers in China have also begun investing in the mass industrialization of large cylindrical cells.
According to data presented by Tesla, the 4680 large cylindrical lithium battery increases energy density by five times compared to the 21700 cylindrical cells, enhances mileage by 16%, and reduces costs by 14%. Its technical appeal is highly significant. However, during the rapid development of China’s new energy vehicle industry, first-tier brands such as CATL and BYD primarily focused on the technical path of prismatic cells. Currently, the industrialization of power batteries largely revolves around prismatic batteries, with Tesla even sourcing prismatic batteries with a capacity of about 161Ah in China for use in one of its models.
From a technical standpoint, both approaches have their own merits and advantages. In a complex battery system, although the battery itself represents the highest cost, safety and cost performance must also be taken into consideration. Focusing solely on one aspect of the battery is insufficient. For instance, Tesla has successfully industrialized and applied cylindrical cells such as the 18650 and 21700 in electric vehicles with energy capacities exceeding 70 kWh through advanced management system design. This demonstrates how advanced management techniques can optimize the overall performance of the battery system.
3. Relative advantages of cylindrical lithium batteries
Advantages of small capacity flexibility
Due to the size and process limitations of cylindrical cells, the capacity of a single cell is typically small. For example, the 18650 ternary battery has a capacity of 3.5Ah, the 32700 lithium iron phosphate battery 6Ah, the 33140 lithium iron phosphate battery 15Ah, and the 34190 lithium iron phosphate battery 20Ah. Outside the realms of electric vehicles and large-scale energy storage markets, in other applications such as automated guided vehicles (AGVs), portable energy storage devices, and home energy storage systems, the capacity of single-module batteries is usually not very large. In practical applications, the large-capacity prismatic cells designed for automobiles and large-scale energy storage do not always align precisely with market demands in terms of size and capacity.
Small-capacity cylindrical lithium batteries can be connected in parallel to meet the capacity requirements of battery modules for specific market needs. For instance, lithium batteries with configurations like 24V60Ah and 48V30Ah, which are commonly used in AGV vehicles, can be achieved by combining cylindrical cells such as 32700, 33140, or 34190 in parallel to form the required 60Ah or 30Ah modules. Moreover, cylindrical cells allow for greater flexibility in space structure design, enabling adaptation to the requirements of various models.
Cost advantage
Among all lithium-ion batteries produced globally by lithium battery manufacturers, cylindrical lithium batteries have the highest degree of process standardization and are the earliest to achieve commercialization. Their assembly efficiency is significantly higher than that of prismatic batteries and pouch batteries. The winding process of cylindrical batteries has reached a production rate of 200 parts per minute (PPM) with advancements in automation. Although the efficiency of producing large cylindrical lithium batteries is slightly lower than that of traditional 18650 or 21700 cylindrical cells, it is still much higher than the efficiency of stacking or winding processes used for prismatic and pouch cells, which is generally around 10 PPM.
The small capacity of cylindrical lithium batteries is attributed to the fact that the coated strip-shaped continuous electrode sheet is cut into smaller strip-shaped electrode pieces. This miniaturization enhances the material utilization rate of the electrode sheets. Under identical screening standards and automation levels, the material utilization rate of cylindrical cells is typically 3–5% higher than that of prismatic cells.
The heat dissipation effect is obvious
Lithium-ion battery fires are primarily caused by thermal runaway, and controlling the spread of thermal runaway is a critical factor in ensuring battery system safety. Among various structures, the cylindrical design is the most effective in addressing thermal runaway, whereas square and pouch structures are largely unable to resolve this issue. The relatively low capacity of individual cylindrical cells results in less energy being released during thermal runaway, in contrast to the higher-energy, large-capacity square or pouch cells. Additionally, with continuous advancements in material safety, the heat released during thermal runaway has been significantly reduced, further enhancing the safety of cylindrical battery systems.
The curved surface design of cylindrical lithium batteries inherently limits heat transfer between cells, which positively impacts the containment of thermal runaway. In contrast, square and pouch batteries face significant challenges in this regard. Moreover, with the adoption of the full-tab process, heat transfer in cylindrical cells is concentrated more on the upper and lower end caps, further reducing heat transfer across the curved surfaces.
The above points provide an analysis and reflection on the performance of lithium batteries with different structural designs in various application scenarios. While the focus here is on the advantages of cylindrical lithium batteries, it is important to acknowledge that cylindrical cells also have limitations in certain applications. At the same time, it is necessary to objectively recognize the unique advantages that square and pouch cells possess.
4. Common Cylindrical Lithium Battery Models
With the development of lithium battery technology, there are more types of cylindrical lithium batteries. Cylindrical lithium batteries are categorized into lithium cobalt oxide, lithium manganese oxide, and ternary materials. These three material systems each have distinct advantages. Let us explore the models and specifications of cylindrical lithium batteries. Cylindrical lithium batteries are typically identified by five digits. Counting from the left, the first and second digits represent the battery’s diameter, the third and fourth digits represent the battery’s height, and the fifth digit indicates the shape. There are many types of cylindrical lithium batteries, with the more common ones being 10440, 14500, 16340, 18650, 21700, 26650, 32650, and others.
– 10440 Battery
The 10440 battery is a cylindrical lithium battery with a diameter of 10mm and a height of 44mm. It has the same size as what is commonly referred to as the AAA battery. Its capacity is generally small, typically a few hundred mAh, and it is primarily used in mini electronic products such as flashlights, mini stereos, and megaphones.
– 14500 Battery
The 14500 battery is a cylindrical lithium battery with a diameter of 14mm and a height of 50mm. This battery corresponds in size to the AA battery. It is generally rated at 3.7V or 3.2V, with a nominal capacity slightly larger than that of the 10440 battery, usually around 1600mAh. It has excellent discharge performance and is mainly used in consumer electronics, including wireless audio devices, electric toys, and digital cameras.
– 16340 Battery
The 16340 battery is a cylindrical lithium battery with a diameter of 16mm and a height of 34mm. Due to its shorter height and relatively small capacity, it is commonly used in high-intensity flashlights, LED flashlights, headlights, laser lights, and other lighting fixtures.
– 18650 Battery
The 18650 battery is a lithium-ion battery with a diameter of 18mm and a height of 65mm. Its key feature is its high energy density, nearly reaching 170 Wh/kg. This makes it a cost-effective battery option. The 18650 battery is a mature lithium-ion battery with stable performance across all aspects. It is widely used in applications requiring a battery capacity of approximately 10 kWh, such as mobile phones, notebook computers, and other small electronic devices.
– 21700 Battery
The 21700 battery is a cylindrical lithium battery with a diameter of 21mm and a height of 70mm. Its larger size allows for improved energy density at both the cell and system levels, making its volumetric energy density significantly higher than that of the 18650 battery. It is widely utilized in digital devices, electric vehicles, balance scooters, solar-powered lithium-ion streetlights, LED lights, and power tools.
– 26650 Battery
The 26650 battery is a cylindrical lithium battery with a diameter of 26mm and a height of 65mm. It has a nominal voltage of 3.2V and a nominal capacity of 3200mAh. This type of cylindrical lithium battery features excellent capacity and high consistency, making it a growing trend to replace 18650 batteries. It is increasingly favored in many power lithium battery applications.
