Reducing the Weight of EV Batteries with Specialty Thermoplastics

September 18, 2024

Somasekhar Bobba

Weight reduction in EV battery components is an important factor in optimizing battery energy density, which in turn is critical to extending vehicle range and boosting power and performance. Although traditional metals such as steel and aluminum are widely used in EV batteries, the ongoing push for higher energy density is opening new opportunities for thermoplastic resins, compounds, and composites.

The main advantage of these materials vs. metals is their inherent lighter weight – particularly in the case of lower-density polymers. Thermoplastics can be 30-50 percent lighter than metals. They also increase design freedom, which permits further weight-out through part consolidation and thin walls.

Of course, to successfully replace metals altogether, or to augment them in hybrid, multi-material components, thermoplastics must provide much more than lighter weight. Each component of an EV battery requires specific performance properties, such as flame retardance (FR), electromagnetic interference shielding, electrical insulation and dimensional stability.

Some of these requirements are becoming more stringent as battery technology advances. For instance, UL94 V0 FR requirements for some components are trending down to 1.0 mm and below. These are significantly thinner gauges than those previously specified. Likewise, wall thicknesses are decreasing from 1.5 mm to 1.0 mm or less as system designers seek to maximize energy density by shrinking the battery footprint.

Specialty thermoplastics well suited for diverse battery components

Leading thermoplastics suppliers are developing new products that can meet stricter EV battery requirements while delivering performance comparable to that of metals, plus weight, design and processing advantages.

What follows are some EV battery components that can benefit from specialized thermoplastic materials.

Battery module enclosures

Depending on the design, battery modules require suitable enclosures to protect cells and electrical components from damage, unwanted contact and exposure. These enclosures may also reduce fire propagation in the event of thermal runaway. They must be mechanically robust and appropriately flame retardant to pass applicable safety tests.

Battery module insulation

The industry is transitioning to higher-voltage EV batteries (600-800 volts) to help shorten vehicle charging times, extend range and improve energy management. Higher voltages can pose a greater risk of short circuits and fire propagation. Next-generation thin insulation films can help protect EV battery modules from these exposures while saving valuable space in the battery pack.

Cylindrical cell retainers

Major EV manufacturers already use cylindrical cells, and others are considering using them. This technology is cost-efficient and mature, making it easy to manufacture. For optimal function, retainers that hold the cells in place require excellent impact resistance under a wide range of temperatures of-60-100 Celsius (140-212 Fahrenheit) and FR and tracking resistance. An emerging trend is transparency to enable UV curing of the glues used to attach the parts of the retainer structure.

Battery pack covers, housings and trays

Some battery packs are becoming larger to meet consumer demands for greater power and range. Regardless of size, battery enclosures and other protective components must deliver excellent impact resistance for safety.

Busbars

EV battery busbars connect hundreds or thousands of cells and distribute electric current throughout vehicle subsystems. These connectors must be durable, able to withstand high vibration levels from vehicle operation, and rigid enough to maintain the integrity of the battery module assembly. Electrically, busbars must handle large amounts of current from the cells and voltage levels of up to 5.0V per cell.

Rocker panel structures

Reinforced rocker panel structures absorb energy during a crash, protecting the battery from intrusion and shock. Conventional steel or aluminum rocker panel structures are typically heavy and require several secondary steps to attach to the vehicle frame.

Thermoplastics can replace or augment metal in several different rocker panel designs, including all-plastic versions, multi-material over-molded designs and modular options. All three are based on injection-molded thermoplastic honeycomb cores that offer light weight, good energy absorption, a high performance-to-weight ratio and ease of manufacturing. Testing has shown that these rocker panel solutions can be up to 40 percent lighter than steel/aluminum solutions, with similar crushing behavior for energy absorption.

Wireless battery management systems

Battery management technology, required on vehicles with lithium-ion batteries, monitors each cell for safe operation based on specified voltage and temperature ranges. Battery management systems can be centralized or distributed and wired or wireless.

Thermally conductive composites can be used because they are electrically insulative and are formulated with non-brominated/non-chlorinated FR additives. They are also radio frequency (RF) transparent to help permit wireless communication.

Lighter weight and much more

The EV battery sector is growing rapidly and constantly adapting to emerging regulatory requirements, which are focused primarily on safety. Despite these changes, a common theme persists: the need for additional lightweighting to boost range, load capacity and power. One proven approach to cutting battery pack weight is adopting thermoplastics to replace or augment heavier metals, and expand design options with thin walls, space-saving geometries and part consolidation. Specialty thermoplastics can deliver equivalent performance to metals while adding significant value to a wide range of battery pack components.

Somasekhar Bobba is the global technical manager of automotive at SABIC.

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