Lithium batteries have completely changed every field from consumer electronics to electric vehicles, and separators play a crucial role in their performance and safety.

Battery separator is one of the materials used in lithium batteries

  The battery separator, anode electrode material, cathode electrode material, and electrolyte are the most important lithium-ion battery materials, accounting for approximately 4% of the total cost of lithium-ion battery materials. The lithium battery separator has a large number of tortuous and interconnected micropores, which can ensure the free passage of battery electrolyte ions and form a charging and discharging circuit. Its main function is to isolate the anode and cathode electrodes, preventing battery short circuits.

  At the same time, ensure that lithium ions pass through the microporous channels normally during charging and discharging, ensuring the normal operation of the battery. The performance of the battery separator determines the key characteristics of lithium-ion batteries, such as internal resistance, capacity, cycling performance, and charge discharge current density.

  At present, the commercialized lithium battery separators mainly include polyethylene (PE) separators, polypropylene (PP) separators, and PE and PP composite multilayer microporous membranes. PE battery separator has high strength and a wide processing range. PP membranes have high porosity, breathability, and mechanical properties. Ordinary 3C batteries mainly use single-layer PE separator or single-layer PP battery separator.

  Power batteries generally use PE/PP double-layer battery separators, PP/PP double-layer separators, or PP/PE/PP three-layer separators. However, polyolefin membranes have very obvious drawbacks, such as thermal stability and insufficient wettability of electrolytes, which makes the coating and modification of polyolefin membranes a trend direction.

Production process of battery separator

  The production process of battery separators is mainly divided into two categories: wet method and dry method. The production process of lithium-ion battery separators includes raw material formula and rapid formula adjustment, microporous preparation technology, and independent design of complete equipment. Among them, microporous preparation technology is the core of lithium-ion battery separator preparation process, which can be divided into dry stretching and wet stretching according to the type of process.

  Dry separators have high safety and low cost, and are often used in large lithium iron phosphate power batteries. Due to its thin thickness and high porosity, wet diaphragm has a higher uniformity of pore size and higher permeability. Compared with dry separators, it has certain advantages in mechanical performance, breathability, and physicochemical properties, so it is more widely used in ternary batteries that focus on energy density.

  Membrane coating is the process of mixing and stirring aluminum oxide, binder, and deionized water on the original lithium-ion battery separator to form a slurry. Micro gravure extrusion coating is used to create one or two layers of ceramic surface on the substrate diaphragm. The ceramic separator increases the mechanical strength of the original membrane, making the battery exhibit excellent performance in high temperature resistance, puncture resistance, thinning, and other aspects.

  Will not affect breathability, ensuring the flow of lithium ions, thereby improving safety. The coating process can not only enhance the thermal stability of the battery separator, improve its mechanical strength, but also prevent the large area contact between the anode and cathode electrodes caused by the contraction of the battery separator. It can also improve the puncture resistance of the separator and prevent lithium dendrites from piercing the separator and causing short circuits in the battery under long-term cycling conditions.

  The coating process is beneficial for enhancing the liquid retention and wettability of the battery separator, thereby extending the cycle life of the battery. Coating materials can be divided into inorganic materials and organic materials. Inorganic materials mainly include ceramics, while organic materials mainly include PVDF and aramid. Generally speaking, ceramics are relatively inexpensive and are mostly used for power batteries, while aramid is more expensive and mainly used for consumer electronics products.