Mechanical Packaging and Material Selection 135 systems as it is the result of the electrical charge and can cause long-term reliability issues as the metal corrodes over time. Use of Plastics and Composites in Battery Design Some smaller battery systems may use plastic enclosures. These systems are more likely to use a plastic if the battery does not have major structural demands. In some of the hybrid and stop-/start-type automotive batteries, the enclosure only needs to enclose and protect the lithium-ion cells with minimum structural demands. Internal to even large battery pack, plastics and polymers are used in multiple areas.
For some of the larger automotive ESSs, a composite cover may be used in concert with a metal base. For instance, General Motors Chevrolet Volt uses a sheet molded composite made of a lightweight vinyl ester resin that contains haydite nanoclay filler and 40% glass fibers (Vink, 2012). In simpler terms, the cover for the Chevrolet Volt is made of fiber glass. The Volt and its sister vehicle the Ampera use lithium-ion pouch-type cells and so also use a plastic “end” and “repeating frames” to separate each of the cells in their systems.
These are injection molded plastic pieces made from BASF’s nylon 6/6 grade and Ultramid 1503-2F NAT, which is 33% glass filled and hydrolysis stabilized (LeGault, 2013). Another component that is frequently designed with plastics is the ICB. The ICB is often a plastic piece that integrates the cell interconnects, wiring harnesses for temperature and voltage monitoring, electronic monitoring circuitry, mechanical support for the cells, and cell vent management. Due to the amount of functions, this may take the form of an over-molded plastic piece with copper or nickel coated copper bus bars.
The GM Volt ICBs use DuPont’s Zytel 7335F grade of PA6 for the base and connector housing, and a 35% glass filled PA66 by Zytel for over molding the ICB (Vink, 2012). The other topic that should be considered in respect to plastics and polymers used in batteries is the flame retardant rating. Flame retardant ratings range from V0 to V2, the V stands for vertical flame rating but there are also horizontal flame ratings both of these sets of flame retardant ratings are based on the Underwriter’s Laboratory (UL) UL-94 standard (UL Prospector, 2014). It is important to ensure that the plastics used in your ESS design are nonflammable.
The reason for this is that in the event of a thermal runaway event of one or more lithium-ion cells you do not want to add more fuel to the combustion process. So if your plastics are V0 rated they will be less susceptible to the initial failure thereby making it easier to manage the cell failure. Sealed Enclosures ESS enclosure design must take into account the usage and installation location of the battery system. In virtually all battery systems, it is important to evaluate the international protection