With environmental regulations and exhaust-gas restrictions growing stricter in Europe and elsewhere—and efforts to restrict CO2 emissions expanding around the world—different nations and regions have different regulations and policies regarding electric vehicles and other emerging vehicle technologies such as hybrid and fuel-cell vehicles.
Although CO2 emissions from automobiles are already regulated at strict levels, in the future we will see increasingly stringent emission standards that will not be achievable through improvements in engine efficiency alone.
The no.1 challenge in EV (electric vehicle) batteries is to increase their energy density. By increasing the energy density, the range of the vehicle can be extended without sacrificing space or weight. With over a decade of experience making advanced engineering plastics for automobile batteries, Asahi Kasei is ready to meet your production needs.
for EV batteries
What is XYRON™?
XYRON™ is polymer alloy combining polyphenylene ether (PPE) with other resins. Asahi Kasei’s The XYRON™ family, which Asahi Kasei has been producing since 1979, boasts an extensive track record—occupying a key role in the history of engineering plastics—and today encompasses an extensive lineup of polymer alloys.
XYRON™ materials offer multiple excellent physical properties. In addition to their outstanding heat resistance, they boast flame retardance, electrical insulation property, good dimensional stability, and hydrolysis resistance, as well as low specific gravity. These polymer alloys combine the advantages of PPE with the specialized properties of various other plastics to yield unique functional properties.
XYRON™ resins have a high oxygen index (a measure of the volume of oxygen required for burning), making them highly flame retardant. In the figure below, a flammability test was conducted using the burner and flame used in UL's flammability test. Under unique conditions, XYRON™ was able to confirm the high flame retardancy.
Case studies: Applications of XYRON™ for EV batteries
Inter-cell spacer：XYRON™ 340Z resin, T series
For inter-cell spacers, the insulating components placed between battery cells, Asahi Kasei recommends our XYRON™ 340Z resin, which features excellent tracking resistance, hydrolysis resistance, acid and alkaline resistance, and long-term stability of physical properties—or our XYRON™ T series of PP/PPE alloys, which feature all of these properties plus excellent oil and chemical resistance. These materials are well-suited to fabrication of thin-walled components, helping to shrink product footprints and reduce weight. Their excellent creep resistance and (non-halogen) flame retardance also improve vehicle safety.
When insulating protective covers for conducting elements carrying high currents at high voltages must be lightweight and exhibit good dimensional stability, we recommend XYRON™ TF701, TA720, X9110, which are well-suite to fabrication of thin-walled components and boast electrical insulation and heat resistance. We also offer oil-resistant grades for easier handling.
XYRON™ 644Z is used for connectors in automotive battery systems. Resin materials must be highly reliable to comply with the stringent automotive OEM standards demanded by LV214 and USCAR. XYRON™ 644Zoffers outstanding flame retardance (UL 94 V-0, 5VA), long-term stability of physical properties (UL746B RTI 125°C), tracking resistance (CTI PLC=2), weather resistance (UL746C f1), and other excellent features.
These superior properties have earned XYRON™ 644Z an extensive track record of use in junction boxes for solar-power generation systems and other similar applications. （Click here to learn more about solar-power generation.） The same features have also led to XYRON™ 644Z being chosen by a large Chinese battery manufacturer for use in automotive battery connectors.
Peripheral components for fuel cell stacks：XYRON™ 500H
XYRON™ 500H for the peripheral components of fuel cell stacks. Asahi Kasei recommends This material features low elution (of ions, oligomers, and other species) and excellent resistance to heat, water, and acid, and their physical properties exhibit minimal degradation upon long-term immersion in liquids.
Nickel metal hydride battery cell case：Flame-retardant XYRON™ grades
XYRON™ grades for NiMH battery-case components are lower in weight than the metals conventionally used for battery cases, and Asahi Kasei has developed these materials to feature the properties required for battery-cases applications:Flame-retardant low weight (low specific gravity), alkali resistance, gas-barrier strength, and resistance to metal degradation.
Also, as part of Asahi Kasei’s lineup of ”Contribution through Business Activities” products, these products help to reduce CO2 when in use.
Polyamide resins feature excellent heat resistance, strength, and rigidity
What is LEONA™?
Asahi Kasei’s LEONA™ polyamide resins are engineering plastics featuring excellent strength, rigidity, heat resistance, and chemical resistance.
These materials may be reinforced with fillers such as glass fibers to improve strength, rigidity, durability, and dimensional stability.
Case studies: Applications of LEONA™ for EV batteries
Battery end plate： LEONA™ SN Series
For battery end plates—positioned at either end of a battery module to compress and hold in place a stack of battery cells—Asahi Kasei recommends our LEONA™ SN series of resin grades. These materials offer good moldability, feature high strength, high rigidity, good electrical properties (CTI), and good heat resistance.
Bus bar cover：LEONA™ SN11B
When insulating protective covers for conducting elements carrying high currents at high voltages must have high strength and long-term stability of physical properties (RTI compliance), Asahi Kasei recommends LEONA™ SN11B, which is well-suited to fabrication of thin-walled components, offers high strength against dielectric breakdown, and features excellent tracking resistance (CTI 600V), flame retardance (UL 94 V-0), and long-term heat resistance (RTI).
Flame-retardant PA66 has expanded its range of applications, primarily in the E&E and automotive domains. Recent years have witnessed growing demands to eliminate materials containing halogens and red phosphorus, both to reduce environmental impact and to improve worker safety.
To support these environmental and worker-safety initiatives, Asahi Kasei embarked on a program to develop new LEONA™ grades using flame retardants without halogens or red phosphorus. This program is now nearing completion.
Engineering plastic foams help to reduce weight and improve thermal insulation for EV batteries
What is SunForce™?
SunForce™ is Asahi Kasei’s family of XYRON™-based foam materials that combine the unique lightweight and thermal-insulation characteristics of foams with superior properties—far beyond the capabilities of conventional foams—as a result of the use of modified polyphenylene ether (m-PPE) ingredients. These properties include excellent flame retardance (UL-94 V-0), dimensional precision, and suitability for fabricating thin-walled components.
The foamy structure of SunForce™ beads means that this material contains less resin than solid materials—and, as a consequence, fewer pathways for heat to flow through the material, ensuring low thermal conductivity and high thermal insulation.
Case studies: Applications of SunForce™ materials for EV batteries
SunForce™ beads facilitate thermal management for EV batteries.The superior thermal-insulation properties of
The superior thermal-insulation properties of SunForce™ beads facilitate thermal management for EV batteries.
A well-known property of batteries is that their output falls dramatically at low temperatures. To avoid this behavior, various strategies have been devised for electric and high-output hybrid vehicles, involving heaters and other mechanisms, for keeping batteries at sufficiently high temperatures.
Asahi Kasei recommends insulating vehicle batteries with
SunForce™ beads. This prevents batteries from releasing heat and cooling while the vehicle is at rest, preserving the battery’s high output power for hours with no need for a heater.
When heaters are present, the insulation provided by SunForce™ beads minimizes external thermal loss.
SunForce™beads also reduce the power used to cool batteries while driving by reducing the influx of external heat through the vehicle chassis. This improves heat-exchange efficiency and maximizes battery performance.
Also, SunForce™ materials are foams that may be used wherever flame-retardant behavior is required.
SunForce™ is a foam-bead material to achieve compliance with the V-0 level of the UL-94 flame-retardant standard for plastic components, indicating an extremely high level of flame retardance.
SunForce™ materials are lightweight foams with self-extinguishing behavior for fires, and have been adopted or are under consideration for an increasing variety of peripheral components of EV battery packs.
For example, using SunForce™ beads for cell holders in vehicle-mounted battery packs offers the following advantages.
Improved safety: Use of foam materials with UL-94 V-0 flame retardance
Weight reduction: SunForce™ foams can reduce weight compared to injection-molded resin materials. (The specific gravity of 10x foam grades is 0.1 kg/L.)
LENCEN™ (c-GFRTP) is a continuous glass fiber reinforced thermoplastic formed by stacking layers of a continuous glass fiber textile with polyamide-66 (PA66) films.
We intend to propose this material as a material which may provide collision safety and weight reduction because it has tensile strength and impact properties equal to or greater than those of metals, and may also contribute to improved reliability and fuel efficiency.
Proposal to EV battery cases
Battery cases in electric vehicles are typically made from metals such as steel or aluminum. The goal of reducing component weight to extend vehicle travel distance suggests the possibility of switching to resin materials, but typical resins cannot offer the required thermal resistance; also, cost reduction is a perennial issue.
1．Lightweight: Specific gravity approximately 1/4 that of steel.(Specific gravity: LENCEN™ 1.9 Steel 7.9 Aluminum 2.7）
2．Heat-resistant: No holes appeared in burning tests after 30 minutes at 1000°C.
3．Cost-effective: Cost reduction can be possible through integration or reduction of components ・Upper cover: Potential reduction in need for anti-rust paint and thermal insulation. ・Lower case: Potential reduction in need for undercover.
Automakers today are developing and deploying a variety of electric-vehicle technologies to achieve greater fuel efficiency. In addition to these developments, many countries and regions are indicating plans to regulate internal-combustion engines (ICEs), the key components of gasoline- and diesel-powered vehicles, giving all the more reason to expect an increasingly prominent role for electric vehicles in the coming years.
The world’s strictest vehicle regulations are found in the European Union, which has announced policy revisions that would effectively ban production of ICEs after 2035. This ban would include hybrid and plug-in hybrid electric vehicles (HEVs and PHEVs), which incorporate both ICEs and electric motors. Consequently, European automakers are racing to develop battery electric vehicles (BEVs) as quickly as possible.
Elsewhere in the world, a recent executive order in the U.S. calls for BEVs, PHEVs, and fuel-cell electric vehicles (FCEVs) to account for 50% of all new vehicle sales by 2030. In China, the China Society of Automotive Engineers has announced that, by the year 2035, it would be desirable if 50% of vehicles were new-energy vehicles (NEVs, a category encompassing BEVs, PHEVs, and FCEVs), with the remaining 50% represented by vehicles with lower fuel efficiency (HEVs). Finally, Japan has established that, by 2035, electric vehicles (HEVs, PHEVs, BEVs, and FCEVs) will account for 100% of new vehicle purchases, including Japan’s “K-car” light vehicles (information current as of February 2022).
The new components of electric vehicles
Three critical components of electric vehicles are the motor, the battery, and the inverter.
In conventional ICEs, gasoline from a fuel tank is supplied to an engine, which generates a rotational force (torque) that is modified by the vehicle’s transmission and transmitted to the tires to induce motion. In BEVs, in contrast, the engine and fuel tank are replaced respectively by a motor and a battery, and electrical energy supplied by the battery is mediated by the inverter—which controls the current, voltage, and frequency—and used to drive the motor or various electrical components. HEVs and PHEVs incorporate both ICEs and battery-powered electric motors as mechanisms to induce motion; the difference between the two is that PHEVs, unlike HEVs, allow the battery to be charged from an external source. The failure of HEVs to allow external charging means that these vehicles are primarily powered by the engine, with the motor only a secondary driving source (although some vehicles are able to exploit other mechanisms such as energy regeneration through braking). In PHEVs, which allow external battery charging, this relationship can be reversed: the motor may furnish the primary source of power, with the engine playing a secondary role.
In general, ICE-powered vehicles in motion tend to emit significant quantities of CO2, while CO2 emissions from BEVs in motion are minimal. However, it is important to consider each vehicle’s total environmental impact, including factors such as CO2 emissions during the production of vehicle batteries and, beyond the vehicles themselves, the distribution of energy sources responsible for powering the electrical grid in various nations and regions.
This perspective has led to growing adoption of an environmental-impact analysis technique known as life-cycle assessment (LCA). LCA is a comprehensive approach that seeks to quantify the environmental impact of automobiles at every stage in their life cycle, from resource identification and extraction through vehicle discarding and recycling. As the LCA mindset grows in acceptance, increasing attention will be paid to the ease and efficiency of reusing resources—and to frameworks for facilitating this reuse—not only at the manufacturing stage but also when vehicles are discarded and recycled. For batteries, in particular, a variety of research initiatives and practical tests are currently underway to explore manufacturing-related CO2 emissions and effective utilization of precious resources.
Types and structures of electric-vehicle batteries
Let us now take a closer look at one of the most important components of electric vehicles: the battery.
Although batteries come in many varieties, the most common type of secondary battery in widespread use today is the lithium-ion battery, which has been extensively studied and adopted in electric vehicles for the two primary advantages it offers: high energy density and high storage capacity, allowing battery sizes to be reduced while still supplying copious quantities of energy. On the other hand, the high energy density for lithium-ion batteries also ensures that safety precautions are essential for working with these devices, and a variety of strict safety regulations and protocols governing their use have been established and put into effect.
For lithium-ion batteries, the smallest structural element is known as the cell. Cells come in three shapes: cylindrical, prismatic, or laminate (also known as pouch).
Cylindrical cells As their name suggests, these cells have the same circular-cylinder shapes as common disposable batteries. These batteries are formed by stacking three layers of material—a positive electrode, a negative electrode, and a separator—then rolling into a cylinder and inserting into a cylindrical metal case together with an electrolyte fluid. In comparison to cells of other shapes, cylindrical cells are particularly suitable for mass production and are considered relatively inexpensive. On the other hand, the shape of cylindrical cells ensures that these cells cannot be packed together in large numbers without significant gaps arising between cells, resulting in inefficient use of space.
Prismatic cells These cells involve positive electrode, negative electrode, and separator layers rolled together, and packaged with electrolyte fluid into a rectangular metal case, whose shape is responsible for the main advantages of these cells: high mechanical strength and high energy density per unit volume.
Laminate (pouch) cells In these cells, the metallic cases used for cylindrical and prismatic cells are replaced by laminate-film packages. The internal electrolyte may be a liquid electrolyte, as in typical metal-case cells, or a polymer-like substance consisting of electrolyte fluid enclosed in a gel. Manufacturing and quality control are challenging for these cells, but they offer the advantages of reduced spatial footprint and considerable shape flexibility.
As these descriptions indicate, each type of cell has its own distinct characteristics, and the choice of cell type for a given application must take into account design guidelines, manufacturing methods, and the purpose for which the cell will be used, among other considerations.
In particular, batteries intended to serve as large energy sources for applications such as electric vehicles must be realized in the form of modules, consisting of multiple cells packaged together into a frame or tray to constitute a single large battery. In this case, the electrodes of multiple cells must be interconnected; for cylindrical or prismatic cells this is achieved using a metallic slab known as a bus bar.
For increased capacity, multiple modules may be joined together by a battery management system (BMS)— equipped with sensors for monitoring voltage, current, and temperature —and packaged with a cooling system (involving cold air blowers or pipes circulating chilled water), with additional components such as wire-harness connectors to interconnect various subsystems, to form a complete battery system known as a pack. Such packs are assembled from a variety of materials and in a variety of shapes to meet the specifications of automakers (regarding mass, capacity, shape, etc.) with added protection to insulate battery units from damage due to shock or vibration. Only after careful system design to satisfy safety requirements and other performance criteria are battery packs ready to be installed in electric vehicles.