Lithium batteries refer to cylindrical lithium batteries, typically the 18560 type. Cylindrical lithium batteries are extensively studied and represent one of the most widely discussed battery types in technical literature. They consist primarily of a positive electrode, a negative electrode, a separator, positive and negative current collectors, a valve, an overcurrent protection device, insulating components, and a casing.
　　The battery casing has historically been predominantly made of steel, but aluminum casings now dominate. Lithium‑cobalt oxide, lithium‑manganese oxide, and ternary‑material batteries are available. Each of these chemistries has its own distinct characteristics, and such batteries are widely used in applications including laptops, digital cameras, lighting devices, children’s toys, power tools, and portable energy systems. This paper jointly examines several key technical aspects of cylindrical batteries.
　　Taking power batteries as an example, the 18560 cylindrical cell is the most extensively studied and technologically debated battery type. It primarily consists of a positive electrode separator, a negative electrode separator, the positive and negative electrodes, current collectors, a safety valve, an overcurrent protector, insulating components, and a casing. In the past, steel casings were more common; today, aluminum casings predominate. The internal safety valve, such as the PTC device shown in the figure, plays a critical role in ensuring safe operation.
　　Lithium‑battery single‑cell overcurrent protectors vary in design among manufacturers; prices differ based on safety requirements, and custom solutions are available. Currently, the most commonly used safety protection devices include PTC temperature‑coefficient fuses and fusible‑type fuses. When the current through a PTC device exceeds its rated value, the resistor heats up, causing its temperature to rise and further increasing its resistance. Once the temperature surpasses a certain threshold, the PTC’s resistance rises sharply, effectively isolating the faulty cell from the rest of the circuit and preventing further thermal runaway.