minimum safety requirements. Testing assesses the
performance of cells, modules, and packs. Testing
conditions include battery abuse, transportation, handling,
storage, recycling, crash, intrusion of components in the
occupant compartment, and electric shock. New standards
for secondary battery use and recycling are also in
Although ESS packaging does not directly determine
cell performance in terms of energy and power, properly
designed frames and enclosures help to ensure efficient use
of space, protection against damage, and adequate thermal
management. All these factors ultimately affect power and
energy density, safety, and lifespan.
Designing battery enclosures, frames or trays depends on
many factors. Cell format and available packaging space
are among the top concerns. However, safety, compliance,
performance, and affordability are also major drivers. As EVs
improve, more advanced designs will not only account for the
immediate needs of a particular EV, but also allow for modularity,
interoperability, second life uses and recycling.
Figure 1 shows a typical design of an ESS for a light
EV, such as an e-bike, pedelec, or scooter. These typically
include an integrated electronic battery management system
and external connectors for in-situ charging or swapping.
Internally, the enclosure provides support and precise cell-placement with sub-millimeter features requiring precision
injection molding. Externally, the enclosure provides mechanical
interfacing, and protection against impact, dust, and intrusion.
In addition, this enclosure should be aesthetically pleasing,
ergonomic, and provide brand identification. To comply with
UL 2271, Batteries for Use In Light Electric Vehicle (LEV)
Applications, the enclosure should have a UL 94 flame class
rating of V- 2.
For such cell holders or enclosures, polycarbonate materials
designed for battery housing are typically specified. Materials
like these typically have a long track record in lithium-ion
battery packs with proven performance in IT, consumer
electronics, and medical devices.
Plug-in hybrid EVs and EVs feature a much larger ESS. They
are comprised of modules housed in large metal or composite
enclosures that centralize the battery management and thermal
management systems. Internal modules are still composed of
trays or frames that hold cells in place providing dimensional
stability and safe access to cooling media as needed.
Depending on the original equipment manufacturer (OEM)
preference, the cell format could be cylindrical (Figures 2 and
3), prismatic (Figure 5), or pouch (Figure 4). These concepts
may also be applicable to 48V mild hybrids.
For cylindrical cells, the use of injection molded
thermoplastics trays is necessary. This solution provides
the proper positioning and cooling given the cell geometry.
Because cylindrical cells act as pressure vessels, designers
are not concerned with swelling during charge and discharge
cycles. However, delivering cooling media to critical areas
becomes a challenge.
Figure 3 shows one such concept made entirely of plastics.
This concept eliminates the need to use separate conductive
metal conduits, positioning cooling channels directly on the
holding frame. The result is integrated functionality with a reduced
number of components, using less space at a lower cost. The
sealing between the frame with cooling channels and the lid may
be achieved by overmolding a self-adhesive liquid silicone.
Thermal simulations and tests conducted by materials experts
show that it is possible to achieve cooling performance targets
despite the lower conductivity of thermoplastics - by choosing
high-flow materials that allow thin walls to be molded. It may
be necessary to utilize a thermal interface material to ensure
direct contact between the cell and frame walls.
Similar solutions can also be achieved with pouch cells,
as shown in Figure 4. In this concept, the cooling channels
are molded into the thermoplastic and an aluminum sheet
is bonded with a self-adhesive silicone. In this design, the
complexity of the cooling channel is built into the injection
molded part without any extra cost.
Due to their geometry, pouch cells are easy to fit into tight
spaces, but packaging designs must also account for swelling
Figure 2. Design concept: