The performance of lithium-ion battery separators directly affects battery capacity, cycle life, and safety. The numerous characteristics required of lithium-ion battery separators place specific demands on their manufacturing processes, which include raw material formulation and rapid formulation adjustment, micropore preparation technology, and the independent design of complete sets of equipment.
Lithium-ion battery separators are generally classified into dry-process and wet-process separators according to their manufacturing process. Therefore, separator products are also divided into two categories: dry-process separators and wet-process separators. Below, we'll explore the differences between dry-process and wet-process lithium-ion battery separators, and which type is better.
I. Differences between dry-process and wet-process separators for lithium batteries
1. Dry-process membranes require less fixed asset investment than wet-process membranes due to their simpler process; however, controlling parameters such as temperature is more difficult with dry-process membranes, while wet-process membranes have a simpler process.
2. Dry-process membranes can be made into three-layer membranes, while wet-process membranes can only be made into single-layer membranes;
3. Dry-process and wet-process diaphragms differ not only in their processing technology but also in the raw materials they use.
4. The raw materials used in dry-process membranes are those with good flowability and low molecular weight, so the high temperature can only reach 135 degrees Celsius.
5. It shrinks (<5%) when heated, making it unsuitable for high-power, high-capacity batteries; wet-process separators use non-flowing, high-molecular-weight raw materials, and their thermal shut-off temperature can reach 180 degrees Celsius. The company's "Separion" ceramic inorganic separator can reach 200 degrees Celsius, ensuring the safety of high-power batteries;
6. In the production of general lithium batteries, dry-process separators have advantages, such as lower cost, less pollution, and more uniform pores; for high-power batteries, wet-process separators have advantages, mainly in terms of safety and less thermal shrinkage.
II. Which is better for lithium-ion batteries: dry-process or wet-process separators?
1. Comparison in terms of product strength
In terms of product performance, wet-process separators are superior to dry-process separators in terms of thickness uniformity, mechanical properties (tensile strength, puncture resistance), air permeability, and physicochemical properties (wetness, chemical stability, safety). These properties facilitate electrolyte absorption and retention, improve battery charge/discharge and cycle life, making them suitable for high-capacity batteries. Overall, wet-process separators offer superior performance compared to dry-process separators.
2. Comparison of diaphragm performance
In terms of product performance, wet-process membranes have certain advantages in mechanical properties, air permeability, and physicochemical properties compared to dry-process membranes. By coating the base membrane with adhesives such as ceramic alumina, PVDF, and aramid, the thermal stability of the membrane can be significantly improved, the high-temperature shrinkage rate can be reduced, and the exposure of the electrode sheets caused by the large shrinkage of the membrane can be avoided, thus making up for the shortcomings in thermal stability. The product performance has been fully comparable to that of dry-process membranes.
In recent years, wet-process separators have gradually become the mainstream technology for power batteries, and the current supply of wet-process separators is insufficient to meet demand. With newly built wet-process production lines in China gradually coming online and ramping up production, the proportion of wet-process separator production has increased again, far exceeding that of other separator types.
