Separation Anxiety

By Karen McIntyre, Editor | February 29, 2012

Valued as much for its growth potential as its ability to fetch a competitive price, the battery separator market has been a hot investment area in recent years.

Estimates as to what the size of the battery separator market is vary but experts agree that this market for nonwovens will rise thanks to growth in the electric cars market as well as in the personal electronics segment. This has prompted investment in the category by several key players in recent years. Companies like Ahlstrom and DuPont have invested in porous membrane technology that they think will enjoy decent growth as the electric vehicle markets continue to grow.

Tonnage growth is not the only factor influencing investment in the area. While battery separators represented only 3% of the durable applications in North America last year, they comprised 11% of sales, according to INDA, showing that the price per square meter of these applications is significantly higher than other durable applications like construction of automotive materials.

Nonwovens have been used in nickle cell batteries for several decades where they have needed to meet harsh conditions like high temperatures. Companies like Freudenberg, Japan Vilene and Hollingsworth & Vose have met these demands with homogeneous drylaid and wetlaid technologies. Meanwhile,in more recents years, more attention is being paid to lithium batteries which are findinga place in portable electronics and hybrid and electric automobiles. Nonwovens makers are meeting the demands of this market with porous membrane structures that also handle extreme conditions and can contribute to faster charging and improved battery life.

Got a nickel?
Freudenberg Nonwovens has been active in the separator business for more than 40 years. Starting with separators for alkali manganese batteries, the company—together with its affiliate Japan Vilene Company (JVC)—are now global market leaders for separators for the Nickel chemistry (NiMH and NiCd).

While earlier separators based on drylaid carding technology, the demand for increased performance has made a more homogenous wetlaid process more attractive. “The combination of being able to use finer fibers, greaterhomogeneity, better control over key properties like pore size and by developing special surface treatments, has ensured Freudenberg meets or exceeds the demands of the industry,” explains Ruediger Finke, manager of battery separators.

The chemistry of nickel cells requires the nonwoven separators to survive in harsh conditions: the internal battery environment is both alkaline (30-40% potassium hydroxide solution) and highly oxidizing. Under harsh use, the battery can also reach high temperatures which puts further stress on the nonwoven. NiCd and NiMH cells have different performance characteristics, which are influenced strongly by the nonwoven separator and therefore each chemistry needs its own design of nonwoven.

For the NiCd batteries, Freudenberg offers wetlaid products based upon polyamide nonwovens: Typically between 30-70 gsm in weight and 90-210 micron in thickness. To aid the construction of the battery, the company offers an additional surface finish which helps speed up the electrolyte filling step.
Meanwhile, the NiMH chemistry has greater flexibility and is used to produce both high capacity and high drain batteries. As such the range of nonwovens and surface treatments used is larger. For standard NiMH batteries, wetlaid nonwovens based upon polyolefin materials with surface treatments to improve the performance are often favored. In applications needing higher performance, products can be made from spunlaced or meltblown materials—depending on the batteries’ needs—and usually receive surface treatments to improve the batteries performance. The two main surface treatments are fluorination which plays no part in the battery chemistry but helps maximize the discharge characteristics and the cycle life or grafting (chemical bonding of poly-acrylic acid to the fiber surface), which is an active chemistry and increases the charge retention of the battery, and further improves the cycle life and discharge characteristics. The combination of meltblown materials and grafting are finding use in very demanding application, like HEV and aerospace.

Another surface treatment for higher performance is the sulfonation, which is offered by Freudenberg affiliate Japan Vilene Company.

The demand for more energy efficient cars and the reduction in CO2 emissions, are currently a key market drivers. While Freudenberg has supplied nonwoven separators used in HEV, the company has developed a special polyester nonwoven as a pasting paper replacement for the traditional lead-acid battery. This helps extend the life of batteries used in cars with the automatic stop/start function.

Lithium’s rise
In 2010, the global market for separators for Nickel batteries was around 38 million square meters but the advent of the Lithium batteries has limited the growth of nickel-based cells, Finke admits More recently, the growth has been further impacted by the high cost of the“rare earth elements which are used extensively in NiMH batteries. This resulted in a negative growth in the NiMH batteries of around 20% and a growth in NiCd batteries as manufacturers moved production back to NiCd to offset lithium cost increases. Another portion of the NiMH batteries changed to the lithium ion battery. Longer term, there is a big potential for NiMH batteries for HEVs, a proven and safe technology for those cars, but againNiMH is in competition with Lithium.

As it continues to strengthen its ability to offer the marketplace high performance and functional fabrics, Ahlstrom is one of the companies betting on Lithium. In December, the Finnish nonwovens producer, who has recently been focusing more on business-to-business industrial markets, purchased a stake in Porous Power Technologies, LLC, a Colorado-based company developing technology for lithium-ion battery separators. Ahlstrom had previously partnered with Porous Power by providing the nonwovens component of the membrane technology used in battery separators.

The resulting product is a highly interesting membrane, says Laura Raitio, executive vice president of Ahlstrom’s business and energy business. Using Symmetrix technology, the product aids in faster charging and provides safety aspects like an ability to hold up under extremely hot and extremely cold temperatures.

“Everything we are hearing from this market is that it is growing strongly and will continue to until at least 2020, Raitio explains. “The transaction will be very beneficial because it will give us access to the membrane technology and it’s a good fit to our existing business.”

Ahlstrom had been working with Porous Power for some time, supplying a nonwoven component to the porous membrane product. As an owner of the company,Ahlstrom, together with Porous Power, will be offering a new generation of separator solutions for safer batteries and capacitors in electric-drive vehicles, e-bikes, portable electronics and utility-grade storage products. Porous Power’s current separator products are already being evaluated by battery manufacturers around the world. The products for electric vehicles will be commercially available in larger scale at a later date. Among the benefits of the Porous Products product is its ability to hold up well in extremely hot and cold temperatures. It’s extreme porosity helps aid in charging speeds and can be offered at an attractive price point.

DuPont is hoping to capitalize on this growth in lithium battery separators—which the company predicts will reach $7.5 billion by 2020—through a recent investment in Chesterfield County, VA. The company is building a new site to exclusively make Energain battery separators from a technology once known as Hybrid Membrane Technology. Previously made at DuPont sites in Wilmington, DE and Korea, this nanofiber-based polymeric battery separator can increase power 15-30%, increase battery life by up to 20% and improve battery separator safely by providing stability at high temperatures. With more battery power, drivers can travel farther on a single charge and accelerate more quickly and safety. It is made using a proprietary spinning process that creates continuous filaments with diameters between 200 and 1000 nanometers. They can exhibit stability and low shrinkage in high temperatures and are highly saturable in electrolyte liquids.

Beyondhybrid and electric vehicle batteries, the technology is also being targeted for batteries in renewable energy, grid applications, specialty consumer applications including laptops, cell phones and power tools as well as in a range of liquid filtration applications for biopharmaceutical, microelectronics and the bood and beverage industries.

“This launch and our investment in a new production facility are important steps in our strategy to expand DuPont’s role in energy storage,” says Thomas Powell, president of DuPont Protection Technologies. “What sets DuPont apart is our integrated science and proven results for better, safer and more sustainable performance.”

Calling Energain a breakthrough platform technology, Powell adds that he expects to translate improvementsseen in automotive battery applications to deliver equal or better battery performance in specialty consumer electronics, where reliable, faster and longer lasting battery power are essential.

Freudenberg is also tailoring its battery separators products to meet the needs of the lithium battery cell. “This requires a very thin and stable wetlaid PET nonwoven and a novel coating technology of inorganic particles, both of which are being developed in-house,” Finke says, adding that he expects nonwovens technology to continue to dominate the rechargeable battery market.

“The ability to vary the thickness, weight, pore size, surface treatment and to tailor the nonwoven to the needs of the battery manufacture has proved a winning formulation,” he says. “Technologies that work in primary (disposable) cells such as cellulose/paper do not survive the environments found in rechargeable batteries.”

Related Application:

Related Technology: