The reason why dry-process separators are less used in the ternary lithium battery market is due to their thickness. Thinner separators allow more space in the battery to accommodate active materials, thereby increasing energy density. However, if the strength of dry-process separators decreases after they are made thinner, it will pose a safety hazard to the lithium battery.
However, with the improvement of technology and processes, dry-process separators are gradually transitioning to thinner profiles. The dry-process separators initially used in power batteries were 32μm, and then gradually evolved to 25μm, 24μm, and 22μm. Currently, the mainstream model is 20μm.
Industry insiders unanimously agree that the trend for dry-process separators in 2019 will be dominated by products with a thickness of less than 20μm. With the large-scale mature application of 16μm dry-process single-stretch (comparable to the current wet-process + coating thickness) products, coupled with their core cost advantage (cost is half that of wet-process separators), this is highly attractive to power battery companies.
However, the use of thinner separators not only tests the technical strength and mass production capacity of separator companies, but also the technical research and development and engineering capabilities of power battery companies.
An executive from a membrane manufacturing company stated that dry-process membranes consist of crystalline and amorphous regions, forming a fibrous structure. This fibrous material experiences stress reduction within the electrolyte, ultimately leading to membrane wrinkling. This problem is not very noticeable when the membrane is thicker, such as 20μm or more, but it becomes apparent quickly as the membrane is made thinner.
“Previously, no power battery company had used a 16μm single-layer dry-process separator. Some hidden problems would begin to be amplified as the separator became thinner, and separator wrinkling has become the most troublesome problem for battery companies using 16μm single-layer membranes,” the executive said.
Currently, a small number of domestic separator companies have the capacity for large-scale mass production of 16μm separator products and have entered the verification system of leading power battery companies with R&D capabilities.
The pressure of cost reduction further fueled the trend.
Traditionally, dry-process separators are considered suitable for lithium iron phosphate batteries, while wet-process separators are suitable for ternary lithium batteries. However, there is no strict distinction between the two technical approaches. For example, ternary lithium battery companies such as BAK Battery and Farasis Energy have always used dry-process separators, while companies such as BYD and Guoxuan High-Tech use wet-process separators for their lithium iron phosphate batteries.
“Each power battery company has different technologies and processes, and uses different material systems, mainly related to the company’s technology system and established practices. As the new energy vehicle industry is policy-driven, with subsidies being phased out and eventually withdrawn, it’s not impossible for battery companies to shift their material systems to meet the requirements of declining battery costs,” explained a chief engineer of a power battery company.
Faced with the significant reduction in subsidies, automakers have shifted away from their past approach of blindly pursuing energy density to obtain subsidies and have begun to adopt a fully market-oriented approach. Based on a comprehensive consideration of cost and performance, power battery companies are also actively cooperating with automakers' strategies.
In addition to switching some wet-process separators to dry-process separators to reduce costs, domestic substitution has also become an important strategy for power battery companies to reduce costs.
GGII (Gaogong Lithium Battery Research Institute) noted that the dry-process separators used by domestic ternary lithium battery manufacturers are mainly imported. In order to meet the cost reduction needs of domestic new energy vehicles, the dry-process separators for power batteries are gradually shifting to domestic production.
On January 28, Farasis Energy and Xingyuan Material signed a cooperation agreement, stipulating that the supply demand for lithium battery separator products in 2019 would be no less than 40 million square meters, with an annual procurement volume allowed to be adjusted within 20%. If the agreed supply volume is fully implemented, the contract value is estimated to be approximately RMB 102 million.
In addition, the increased demand for dry-process separators this year also stems from the booming energy storage market. Meanwhile, there has been a significant increase in demand for lithium iron phosphate batteries in niche markets such as A00-class vehicles, electric logistics vehicles, 48V mild hybrid systems, electric ride-hailing vehicles, and electric forklifts, which has also driven up the production volume of dry-process separators.
Wang Xiangdong, CTO of Zhongke Technology, said that thanks to the company's previous efforts in establishing and cultivating the energy storage market, the warming of the domestic and international energy storage market this year has brought considerable incremental benefits to the company's dry-process biaxially stretched diaphragm. Moreover, the collection and payment terms in this market are better than those in the power sector.
It is worth noting that while adding new wet-process capacity, leading domestic dry-process membrane manufacturers are still maintaining their expansion pace in dry-process capacity. This capacity expansion by these leading dry-process membrane manufacturers, along with large-scale manufacturing, will inevitably lead to further reductions in product costs.
In 2018, Xingyuan Material, leveraging its years of accumulated technical experience in the field of dry-process lithium-ion battery separators, planned and constructed eight new-generation dry-process lithium-ion battery separator production lines. Upon completion, this project will create an annual production capacity of 400 million square meters of dry-process lithium-ion battery separators. Data from GGII (Gaogong Industry Research Institute) shows that in 2018, China's lithium-ion battery separator shipments reached 2.02 billion square meters, a year-on-year increase of 39.7%. Among them, wet-process separator shipments reached 1.31 billion square meters, a year-on-year increase of 66.4%; dry-process separator shipments reached 706 million square meters, a year-on-year increase of 7.8%, with a growth rate far lower than that of wet-process separators.
With the new subsidy policy implemented in 2019, the drastic reduction in subsidies and the increased emphasis on product safety have forced the new energy vehicle and power battery industry chain to return to market-oriented thinking. As a result, low-cost, high-performance, and thin dry-process separators are expected to see a market "comeback".
According to GGII (Gaogong Lithium Battery Research Institute), the 20μm dry-process single-stretch separator currently used in large-scale power batteries is 18μm, while 18μm and 16μm are on the way to large-scale application. In 2018, the price of dry-process single-stretch separators decreased by more than 40% year-on-year, and this year the average price of some lower-end dry-process single-stretch separators has fallen below 1 yuan/square meter (wet-process separators are 1.8-2 yuan/square meter).
"Currently, the mainstream ternary lithium-ion batteries use wet-coated separators with a thickness of 12+4 (12μm base film + 4μm coating). The trend for dry-process single-stretch separators this year is below 20μm, and some power battery companies have already begun to use 18μm and 16μm products." The aforementioned person said that once 16μm products are used on a large scale, dry-process single-stretch separators will erode the wet-process separator market to some extent due to their cost advantage.
