The structure and advantages and disadvantages of square lithium battery

Lithium-ion batteries are divided into square lithium batteries (such as commonly used mobile phone battery cells), cylindrical lithium batteries (such as 18650, 18500, etc.) and button lithium batteries according to their appearance; lithium batteries are divided into aluminum shell lithium batteries, steel Shell lithium battery, soft pack battery; according to the positive electrode material, it can be divided into lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, and lithium polymer.

At present, there are three main packaging forms of mainstream lithium batteries, namely cylinder, square and soft package. Rectangular lithium batteries usually refer to aluminum or steel prismatic batteries, and the penetration rate of prismatic batteries is very high in China. The structure of the square battery is relatively simple, unlike the cylindrical battery, which uses high-strength stainless steel as the shell and accessories such as explosion-proof safety valves, so the overall accessories are light in weight and relatively high in energy density.

The structure of a square lithium battery

The main components of a typical prismatic lithium battery include: a top cover, a casing, a positive plate, a negative plate, a stack or winding of separators, insulating parts, safety components, etc. Among them, the two in the red circle are safety structures, NSD acupuncture safety device; OSD overcharge protection device.

Acupuncture safety device. This is to add a metal layer, such as copper foil, to the outside of the core. When acupuncture occurs, the local high current generated at the acupuncture site quickly reduces the current per unit area through the large-area copper sheet, which can prevent the local overheating of the acupuncture site and slow down the thermal runaway of the lithium battery.

Overcharge safety protection device, this safety design can be seen on many batteries at present. Generally, it is a thin metal sheet, which is used in conjunction with the fuse. The fuse can be designed on the positive current collector. When the lithium battery is overcharged, the internal pressure will cause the OSD to trigger an internal short circuit and generate an instantaneous high current, which will cause the fuse to fuse and cut off the internal current loop of the battery. .

Shells are generally steel or aluminum shells. With the market’s pursuit of energy density and the progress of production technology, aluminum shells have gradually become the mainstream.

What are the advantages and disadvantages of square lithium batteries?

Advantages, the packaging reliability of the square lithium battery is high; the energy efficiency of the system is high; the relative weight is light, the energy density is high; the structure is relatively simple, and the expansion is relatively convenient. It is currently an important option to increase the energy density by increasing the capacity of the monomer; If the system is large, the system structure is relatively simple, which makes it possible to monitor the monomers one by one; another advantage brought by the simplicity of the system is that the stability is relatively good.

Disadvantages, since the square lithium battery can be customized according to the size of the product, there are thousands of models on the market, but because of too many models, it is difficult to unify the process; the level of production automation is not high, and the differences in monomers are relatively large. Large, in large-scale applications, there is a problem that the life of the system is much lower than that of the monomer.