Large PK between wet separator and dry separator materials for power lithium ion batteries

Power lithium ion battery wet separator PK dry separator material. Diaphragm is the core of lithium ion battery preparation, and lithium ion battery separators are generally divided into dry process and wet process according to the process. Therefore, membrane products are also divided into dry process and wet process separators. The many characteristics that lithium ion battery separators need to possess pose special requirements for their processing processes, including raw material formulation and rapid formula adjustment, microporous preparation technology, and independent design of complete equipment. Let's take a look today, which is better, wet diaphragm or dry diaphragm.

Here is an analysis of wet and dry method manufacturing of membranes: these are two methods of manufacturing membranes.

Wet method refers to the method of stretching the membrane using solvents and plasticizers, and then forming micropores in the membrane through solvent evaporation (to allow lithium ions to pass through). Because there is solvent evaporation during the process, it is called wet method. The drying method is to only stretch the crystallized film to form micropores in the membrane. Because the crystallized film is a dry article, it is called the dry method.

Comparison of differences between wet and dry separators for power lithium ion batteries

1. Due to the simple process, the investment in fixed assets in the dry method is smaller than that in the wet method; However, it is difficult to control the temperature and other indicators of the dry process, and the wet process is simpler;

2. The dry method can make three layers of film, while the wet method can only make a single layer of film; (The advantage of three-layer films is that the thermal sealing temperature is 135 degrees, but the thermal stability temperature is 160 degrees, which can guard against thermal inertia and has a space safety of 25 degrees.)

3. In addition to different production processes, dry and wet processes also use different raw materials. The raw materials used in the dry process have good fluidity and low molecular weight, so the high temperature can only reach 135 degrees Celsius, which can contract when heated. Therefore, the safety is not suitable for making high-power and high-capacity batteries; The wet process uses non flowing, high molecular weight raw materials, and the thermal sealing temperature can reach 180 degrees, ensuring the safety of high-power lithium ion batteries;

4. In processing ordinary lithium ion batteries, the dry method has advantages such as low cost, less pollution, and more average pore size; Wet method has advantages in high-power batteries, mainly due to its low safety and thermal shrinkage.

Market status of wet and dry separators for power lithium ion batteries

The separator is used to separate the positive and negative electrodes of the battery to prevent short circuits and allow lithium ions to pass through. Diaphragm is one of the materials for lithium ion batteries, accounting for up to 15-20% of the cost of the battery core. According to the process, lithium electric separators can be divided into dry method and wet method. The advantages of wet method over dry method lie in the higher average pore size and permeability, as well as the thinner thickness. Dry process separators are mainly used in large lithium iron phosphate power batteries, while wet process separators are more widely used in ternary batteries that focus on energy density. Wet diaphragm can greatly improve reliability and high temperature resistance through ceramic coating. We expect that as the permeability of the ternary battery increases, the wet membrane will gradually replace the dry membrane.

In recent years, with the heating up of the power battery market, wet coated membranes have become increasingly popular in China. Even in the industry, there is a view that the future power battery membrane market will inevitably be wet coated membranes. On the contrary, those who support the dry method believe that domestic enterprises are just following the trend of Japan and South Korea. In fact, wet coating membranes have some weaknesses, which can easily lead to potential safety hazards for power batteries after long-term use. The dry method double pull coating membrane is the appropriate choice.

Judging from the market trend and the newly invested processing lines of membrane enterprises, wet coating membranes are currently in the ascendant. It is reported that there are qualitative differences between dry double pulling and dry single pulling, and there are not many enterprises with dry double pulling technology. The market demand for dry double pulling coated membranes is also rapidly increasing.

It is estimated that with the explosive growth of new energy vehicles, there will be a demand for 470 million m2 of battery separators, and the demand will reach 3.7 billion m2 in the next five years. Based on the lithium membrane unit price of 3 yuan/m2, the power lithium battery separators will generate a market space of more than 10 billion yuan.

In 2015, the production of lithium ion battery separators in China was 628 million square meters, a year-on-year increase of 49.5%. From a breakdown perspective, the shipment of dry process separators was 390 million square meters, a year-on-year increase of 33.1%; The shipment of wet membrane was 238 million square meters, a year-on-year increase of 90.5%. The growth rate of wet process separators is far higher than that of dry process separators. Firstly, the demand is growing rapidly. In 2015, power battery companies represented by BYD began to shift to wet process separators; The second reason is that the proportion of ternary power batteries has increased, driving the sales of wet coating membranes to increase.

In the past two years, with the increase in the production capacity of domestic diaphragms, the market competition for medium and low end products has become increasingly fierce. In addition, under the impact of new production capacity, the price of domestic diaphragms has experienced a rapid decline. According to the statistics of Gaogong Lithium Battery, in 2016, 2010 μ The average price of dry membrane is 7.5 yuan/square meter, compared to 3.5 yuan/square meter in 2015; Domestic in 2010 16 μ The average market price of wet membrane is 9.5 yuan/square meter, compared to 4 yuan/square meter in 2015, with a decline of more than 50%. The sharp decline in membrane prices is mainly due to the rapid expansion of domestic low-end product production capacity and the low price competition strategy occupying the market; In addition, the downstream battery and battery cell industries also have overcapacity at the mid and low end, as well as disorderly competition, which also provides a market for low end and low price separators.

The separators in lithium-ion batteries play a crucial role in improving performance, but the processing processes for battery separators are diverse and very complex, including dry and wet manufacturing. The technology for lithium ion battery separators is currently mature, and both dry and wet manufacturing of battery separators can well meet the needs of different categories of products.