Lithium-ion batteries are classified by shape into square lithium batteries (such as commonly used mobile phone battery cells), cylindrical lithium batteries (such as 18650, 18500, etc.) and button lithium batteries; by outer casing material into aluminum-cased lithium batteries, steel-cased lithium batteries, and pouch batteries; and by positive electrode material into lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, and lithium polymer.
Currently, there are three main types of lithium battery packaging: cylindrical, prismatic, and pouch. Prismatic lithium batteries typically refer to aluminum or steel-cased prismatic batteries, which are very common in China. Prismatic batteries have a simpler structure than cylindrical batteries, which use high-strength stainless steel for the casing and include accessories such as explosion-proof safety valves. Therefore, the overall weight is lighter, resulting in a relatively higher energy density.
Structure of square lithium batteries
A typical square lithium battery mainly consists of: a top cover, a casing, a stack or winding of positive and negative electrode plates and a separator, insulating components, and safety components. The two components circled in red are safety structures: the NSD (Needle Penetration Safety Device) and the OSD (Overcharge Protection Device).
Needle puncture safety protection device. This involves adding a metal layer, such as a thin copper sheet, to the outermost part of the core. When a needle puncture occurs, the large local current generated at the puncture site is quickly reduced per unit area by the large copper sheet, thus preventing localized overheating at the puncture site and mitigating the occurrence of thermal runaway in the lithium battery.
Overcharge safety protection devices are now commonly found on many batteries. They are typically thin metal sheets used in conjunction with fuses. The fuse can be integrated into the positive current collector. When overcharged, the pressure generated inside the lithium battery causes the OSD (On-State Discharge Device) to trigger an internal short circuit, generating a large instantaneous current. This causes the fuse to melt and break the battery's internal current circuit.
The casing is generally made of steel or aluminum, but with the market's pursuit of energy density and the advancement of production technology, aluminum casing has gradually become the mainstream.
What are the advantages and disadvantages of square lithium batteries?
Advantages: Square lithium battery packaging has high reliability; high system energy efficiency; relatively light weight and high energy density; relatively simple structure and relatively convenient capacity expansion, making it an important option for increasing energy density by increasing the capacity of individual cells; large cell capacity results in a relatively simple system structure, making it possible to monitor each cell individually; another benefit of the simple system is relatively good stability.
The disadvantages are that, since square lithium batteries can be customized according to the size of the product, there are thousands of models on the market. Because there are so many models, it is difficult to standardize the process. The level of automation in production is not high, and the individual cells have large differences. In large-scale applications, the system life is much shorter than the individual cell life.
