What are the Differences Between Lithium-Ion Battery Packs and Polymer Lithium-Ion Batteries?

Lithium-ion battery packs and polymer lithium-ion batteries are two common types of lithium-based batteries, but they differ significantly in structure, materials, performance, and applications.

In terms of structure, a lithium-ion battery pack is typically composed of multiple cylindrical or prismatic lithium-ion cells connected in series or parallel, enclosed in a rigid metal or plastic case. The cells themselves have a hard shell, usually made of steel or aluminum, which protects the internal electrodes and electrolyte. The connection between cells is achieved through metal tabs or wires, and the entire pack is equipped with a protection circuit board to prevent overcharging, over-discharging, and short circuits. For example, the battery pack in an electric vehicle is often composed of hundreds or even thousands of 18650 cylindrical cells, which are grouped together to provide high voltage and large capacity.

Polymer lithium-ion batteries, also known as lithium polymer batteries, have a different structure. They use a polymer electrolyte instead of the liquid electrolyte used in traditional lithium-ion batteries. The electrolyte can be in the form of a gel or a solid film, which allows the battery to be made into thin, flexible, and various shapes. The outer casing of a polymer lithium-ion battery is usually a thin aluminum-plastic composite film, which is lightweight and has good sealing performance. Unlike lithium-ion battery packs, polymer lithium-ion batteries are often single cells, but they can also be combined into packs, but the process is simpler due to their flexible structure.

In terms of materials, the positive and negative electrode materials of lithium-ion battery packs and polymer lithium-ion batteries are basically the same, usually using lithium cobalt oxide, lithium iron phosphate, or lithium manganese oxide as the positive electrode, and graphite as the negative electrode. The main difference lies in the electrolyte: lithium-ion battery packs use liquid electrolytes (organic solvents containing lithium salts), while polymer lithium-ion batteries use polymer electrolytes (such as polyvinylidene fluoride-hexafluoropropylene copolymers).

In terms of performance, lithium-ion battery packs have the advantages of high energy density, high discharge current, and mature technology. They can provide stable power output and are suitable for high-power applications such as electric vehicles, power tools, and energy storage systems. However, they are relatively heavy and bulky due to the rigid casing and the need for multiple cells.

Polymer lithium-ion batteries have the advantages of light weight, thin thickness, and good flexibility. They can be made into ultra-thin batteries (as thin as 0.5mm) and can be bent to a certain extent, making them suitable for portable electronic devices such as smartphones, tablets, smart watches, and wearable devices. In addition, polymer lithium-ion batteries have better safety performance because the aluminum-plastic casing is not easy to burst when subjected to external forces, and the polymer electrolyte is less likely to leak. However, their energy density is slightly lower than that of high-performance lithium-ion battery packs, and their high-current discharge performance is not as good.

In terms of cost, lithium-ion battery packs are generally lower in cost for large-capacity applications due to mature production processes and the use of cylindrical cells with high production efficiency. Polymer lithium-ion batteries have higher production costs due to the complexity of the polymer electrolyte preparation process and the customization of shapes.

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