The transition to battery electric vehicles is underway—but key challenges remain
All around the world—and especially in Europe and China—the automobile industry is in the midst of a rapid transition from conventional gasoline-fueled vehicles to battery electric vehicles (BEVs). In BEVs, the gasoline engines in conventional vehicles are replaced by three primary modules: a motor, a battery, and an inverter.
Although BEVs are more energy-efficient than engine-powered vehicles, their batteries can store only limited quantities of energy, and thus the motors and batteries of BEVs must operate with high efficiency to ensure satisfactory performance. The temperature of these components tends to increase when in use, and strategies for offsetting these increases—to maintain each component within its optimal operating temperature range—are crucial for increasing energy efficiency and extending travel distances. Such strategies are known as a thermal management technology. Historically, thermal management systems for BEVs were typically implemented separately for each individual functional unit in isolation—one for the battery, another for the powertrain, and a third for the air conditioning, each operating independently from the others—but more recent vehicle designs have begun to address thermal management as a system-wide challenge demanding unified, comprehensive solutions.
Asahi Kasei offers both innovative material products and advanced technical support services to assist in developing the broad range of products required for ever-evolving thermal management systems.
Materials for valves with laser-welding and laser-marking characteristics 14G30
LEONA™ 14G30 polyamide resin
Asahi Kasei’s LEONA™ polyamide resin is an engineering plastics featuring high strength, high rigidity, high heat resistance, and outstanding chemical resistance. These materials may be further strengthened by reinforcing them with glass fibers or similar fillers, improving their strength, rigidity, durability, and dimensional stability.
As one example, LEONA™ 14G30 is a material with a proven track record of successful adoption for valves in thermal management systems. To help our customers take full advantage of the superior physical properties of this material—including its high strength, resistance to long-life coolants, and excellent laser-welding and laser-marking characteristics—Asahi Kasei offers extensive technical support services: our experienced engineers work together with customers to accelerate product development and achieve innovative solutions.
Materials for cooling-system pipes with excellent resistance to hydrolysis, calcium chloride, and long-life coolants (LLC)
Asahi Kasei offers a variety of materials and processing techniques for pipes used for various purposes. Pipes are typically made from metals (such as aluminum alloys) or from metals in combination with rubber materials. Replacing these metals with resin materials yields lighter-weight products at lower cost.
Below, we review some common techniques for forming materials into pipes.
Water-Injection Technology (WIT)
WIT is a specialized injection molding used to produce pipes and other hollow bodies. The technique begins by filling a mold with molten resin, as in conventional injection molding, but then a stream of water is injected through the center of the mold. Water injection is delayed until the resin near the outer pipe surface has cooled and solidified, while resin near the center of the pipe remains molten and is readily displaced by the water stream to yield a hollow pipe. Although this method is only recommended for relatively short pipes (on the order of 50 cm), it is capable of forming branched pipes and pipes with cross-sectional deformation or non-uniform diameters, making it a good choice for branched and curved pipes in cooling systems.
For WIT applications, Asahi Kasei recommends our LEONA™ 53G33 polyamide resin, which offers outstanding resistance to hydrolysis, calcium chloride, and long-life coolants, even compared to other
LEONA™ polyamide resins.
In this method, a resin material is heated beyond its melting point and extruded from a die to yield a contiguous body with a uniform cross-sectional shape.This technique is capable of producing tubes and pipes with small diameters and long lengths. In addition, the extruded bodies can be processed to yield complex configurations of interconnected pipes, with applications including cooling pipes for battery packs and interconnects between functional units such as radiators, battery packs, and motors.
Asahi Kasei is proud to offer two families of resin solutions for cooling line in EV water-cooled thermal-management systems:
1.For multilayer pipes, a combination of XYRON™ modified PPE resins for inner layers and LEONA™ polyamide 612 resins for outer layers. 2. For monolayer pipes, LEONA™ polyamide 612 resins.
Material for smaller, lighter cooling pumps BG230・ SG104
LEONA™ BG230 biomass plastic polyamide resin
LEONA™ BG230 polyamide resin is a material based on the biomass plastic PA610, which contains 60% plant-based polymers.
PA610 exhibits lower water absorption than PA66, ensuring good dimensional stability even when used in environments subject to water exposure. This material offers excellent chemical and calcium chloride resistance, and exhibits good laser-welding characteristics, making it a suitable choice for cooling pumps with reduced size and weight.
LEONA™ SG104 polyamide resin is an alloy grade made from semi-aromatic polyamide and polyamide 66.
This material exhibits low dimensional variation and degradation of physical properties upon water absorption. Its key features include high specific strength, attractive appearance, and excellent fluidity.Compared to polyphenylene sulfide (PPS), a material commonly used for these applications, LEONA™ SG104 generates less gas during injection molding and exhibits better moldability.
Engineering plastic foams help for thermal management systems
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
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 the world's first particle foam beads material to be certified as V-0, an extremely high level of flame resistance, under UL's flame Flame retardance for plastics and components, UL-94. Masu. Additionally, because it is a lightweight foam and has self-extinguishing properties, it is already being considered for use in parts surrounding EV battery packs.
For example, using SunForce™ beads for cell holders in vehicle-mounted battery packs offers the following advantages.
1．Improved safety: Use of foam materials with UL-94 V-0 flame retardance 2．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.)
Valuable technical assistance based on Asahi Kasei’s advanced simulation capabilities
For customers designing products based on Asahi Kasei’s engineering plastics, we offer a variety of technical support services based on our simulation capabilities.
For example, when attempting to replace metal with resin in parts such as valves, there are concerns about lack of strength and stiffness, and a decrease in strength of weld lines. In this case, we use simulation technology to examine the shape and gate position, and carry out design and performance predictions to minimize the effects of weld lines and prevent breakage and leakage during use.
Battery EV thermal management system related information
Three challenges in BEV
Thermal management is important for BEVs due to the following three issues.
Extending travel distance
The finite energy storage capacity of vehicle batteries imposes a limit on the total distance a vehicle can travel without recharging. Larger batteries can store more energy, but also weigh more and occupy more space, resulting in heavier vehicles with cramped interiors. Consequently, strategies for reducing power consumption are of primary importance. Aside from the challenges of improving the efficiency of motors and batteries, one major problem is the need for heaters to serve as heat sources. In contrast to gasoline vehicles, whose engines serve as major heat sources due to exhaust-gas emissions, electric vehicles have no intrinsic heat sources and must instead be equipped with external heating elements. For most BEVs, these take the form of Positive Temperature Coefficient (PTC) heaters, but recently some BEVs have instead made use of heat pumps to extract heat from the outside environment.
Reducing charging time
Another major challenge for BEV design is to accelerate the battery charging process. Rapid charging requires high power, resulting in heat generation due to electrical resistance. However, the lithium-ion batteries that constitute the heart of BEVs operate properly only within a narrow temperature range—roughly 0 to 45°C—and thus any excess heat generated by rapid charging must be efficiently removed by a well-controlled thermal management system. In particular, batteries operating outside their optimal temperature range tend to charge more slowly and degrade more rapidly. Techniques for cooling/heating batteries include both conventional air-cooling schemes and, more recently, liquid-cooling schemes involving coolant liquids circulating inside cooling plates.
Extending battery lifetime
The optimal operating temperature ranges described above are also relevant when considering battery lifetimes: ensuring that batteries remain within their optimal temperature range helps to extend their useful lifetime. Another relevant factor is the temperature distribution in and around the battery; a more uniform distribution leads to higher battery performance and a longer useful lifetime.
Thermal management systems and their key functional units
Vehicle thermal management systems comprise three functional units—an air conditioning, a battery, and a powertrain—and comprehensive control systems, capable of managing heat transfer among these components, are currently being developed. In this section, we describe the techniques and tools commonly used to heat and cool these units.
For heat sources, PTC heaters are one common and inexpensive choice, but heat pumps are an alternative option that can help reduce power consumption. The primary components of heat pumps are electrically actuated compressors, isolation valves, expansion valves, shutoff valves, water pumps, and temperature sensors, together with pipes to connect these functional units.
BEV batteries are accompanied by peripheral components—voltage sensors, current sensors, and a battery-management system (BMS), and are typically cooled (heated) via one of two strategies: air cooling or liquid cooling. The key features of these two approaches are as follows.
ーStrategies for cooling (heating) batteries
Air cooling：This approach is simple and inexpensive and boasts an extensive track record in practical application, but is capable of delivering only modest cooling performance. Air cooling schemes may be classified into three categories: natural air cooling, open-circuit forced air cooling, and closed-circuit forced air cooling; the latter two cases involve the installation of air-flow pathways driven by cooling fans and ducts.
Liquid cooling：The high cooling performance achievable with liquid coolants makes this the most promising strategy for cooling high-power batteries in the near future. Like air-cooling systems, liquid-cooling systems may be implemented in various ways; here we focus on one particular approach, in which coolant water is circulated within a cooling plate. This circulation, driven by an assembly of electric water pumps, chillers, expansion valves, and connecting pipes, is highly effective for cooling vehicle battery packs. In cold-weather conditions, PTC heaters are used to warm the circulating water. （Go here for details on “Extrusion-molding resin for cooling line in EV battery thermal management systems"）
There are also air cooling and water cooling for drive motors and inverters. For air cooling, attach heat radiation fins. Water cooling requires an electric pump, radiator, etc., but since it is connected to the battery system, the pipes and valves that connect the components tend to be complicated.