Focus on the textile world: from batteries to artificial turf

Potential applications of battery systems

This development is being accompanied by an increase in demand for technical textiles, especially nonwovens and their diverse applications – such as functioning as separators in battery systems.

Requirements placed on separators

The task of the separator is to separate the cathode and anode in batteries (the negative and the positive electrodes in accumulators) both electrically as well as physically and to absorb an electrolyte. This barrier is important for insulating the poles and preventing short-circuits in the batteries, while absorption of the electrolyte is a prerequisite for the ion flow.

The requirements placed on the separator are:

Nonwovens on their way to the electrotechnical industry

Meeting these numerous requirements constitutes a major challenge for separators. Possible battery separators include microporous polymer membranes, inorganic composite membranes, and nonwovens. Price is a further important criterion in the selection of a suitable separator. In this emerging industry, constant pressure on prices, the ever more economical production of nonwovens, diversity in the choice of raw materials, and the high number of possible variations are all sharply increasing demand for nonwovens.

Separators that have to remain stable over many charge/discharge cycles are made of higher-quality materials than those used in inexpensive, disposable batteries. Today's battery industry is now inconceivable without powerful separators and thus without nonwovens.

Battery production primarily uses carded nonwovens, wetlaid nonwovens, meltblown fabrics and spunbond fabrics as separators. These are usually still needled or hydroentangled to obtain certain properties, e.g. a larger surface by means of felting. Depending on the respective manufacturing process and field of application, nonwovens are subsequently further equipped in order to generate additional special effects: Hydrophilization (increase in fluid intake capability) and ceramic equipment are just two options for increasing the efficiency of a battery.

Separators for rechargeable or secondary batteries

In lead-acid batteries, materials are used which withstand the highly acidic and oxidative conditions. Extruded or sintered separators made of polyethylene, sintered PVC or mats made from microfiber fleece are used here. For nickel-cadmium batteries in the strongly alkaline milieu of potash, separators made of polyamide and polyethylene/polypropylene combinations are predominantly used. Here, nonwovens are almost exclusively in use today.

The conditions for nickel-metal hydride batteries are the same as for nickel-cadmium batteries, except that the battery separator also has to be able to reduce self-discharge. This is achieved through functionalization of the nonwoven surface by means of chemical treatment, e.g. surface treatment with acrylic acid or sulfonation.

Separators for non-rechargeable or primary batteries

With non-rechargeable Li batteries or Li-primary batteries, either nonwovens or microporous films are used. In non-rechargeable alkaline manganese batteries, nonwovens are mainly used as separators in a mixture of polyvinyl alcohol microfibers (PVA) and cellulose. Similarly, laminates made from nonwoven fabrics and membranes such as cellophane are also utilized.

The ideal needle for diverse applications

Depending on the requirements placed on nonwovens as battery separators, Groz-Beckert offers numerous opportunities to achieve the required properties or optimize the separator through utilization of the right needle. Due to the high process stability of Groz-Beckert products and the resulting continuously high level of quality, effects can be generated in the manufacturing process that are just as continuous and reproducible. This is reflected directly in the separator's performance in the battery.

The choice of suitable needle type depends on the raw material used, the fiber fineness, and the desired effect. Here Groz-Beckert, with its many years of experience in the nonwovens sector and numerous exclusive needle types, can make application recommendations. The GEBECON®, EcoStar and CrossSTAR® needles are just a few of the needle types that have proven themselves in separator production.

A common needle-machine configuration in the nonwoven line for producing battery separators often consists of pre-needling followed by the needling process itself.

In pre-needling, conical needles with a barb distance of 4.80 mm and the RF barb shape are often used. Conical needles with these specifications combine a high needling effect with defined and gentle fiber transportation. Groz-Beckert felting needles with a conical working part differ from standard working-part needles because of their much higher stability.

When using very fine fibers, microfibers or ceramic fibers, the HL barb is recommended for the pre-needling phase, since it is very gentle on the fibers and minimizes breakage and elongation. GEBECON® needles are also suitable for pre-needling, especially in the needling of fine fibers and microfibers, since they reduce the risk of needle breakage to a minimum.

In the main needling process itself, standard felting needles with a C barb distance and RF barb shape are mostly used. These guarantee effective compaction while providing the opportunity to precisely adjust the pore size and the resulting permeability.

During the main needling process, with EcoStar and CrossSTAR® needles, certain effects (porosity, pore size, permeability, hydrophilization, etc.) can be influenced in the product.