Material Solutions in Electric Vehicle Batteries
Overview
For EVs and other eMobility applications, batteries are critical not just for function but for market adoption. Continued EV market growth, therefore, depends on the development of batteries that are safer, more reliable, faster-charging, and that provide greater charge range. These factors make the battery and battery compartment arguably the most integral part of EV design and development. Several factors, however, threaten battery function and performance. These include harsh and unpredictable environments, noise, vibration, shock, thermal runaway, overheating, dust and fluid contamination, electromagnetic interference, and other risks. Battery compartments also require collision impact solutions to enhance consumer safety and reduce warranty expenses. Engineered material solutions can help mitigate these factors. Developed correctly, they can improve battery performance for better range, safety, and reliability. This paper addresses current trends and projections for the EV market and explores material science design challenges for EVs, focusing on batteries. It will aid engineers in understanding the role of material applications to improve system development and foster design creativity.
Electric Vehicle Market Trends and Projections
Types of excitation forces can come in many forms. Many products contain rotating motors, fans, gears, etc. in which the unbalance of rotating components or misalignment of drive shafts result in unwanted excitation forces. These are discrete in nature, usually containing a prominent peak at the fundamental rotational speed plus harmonic multiples of this tone. With an operating fan, for example, there will also be disturbances created at multiples of the fundamental rotational speed times the number of fan blades.
Other factors such as bearing loads, or load fluctuations (often electrically driven) can create additional excitation inputs. Operating behavior of reciprocating motion of components, especially when it results in hard impact between parts, can result in both forced excitation at the reciprocating frequency as well as an impact transient that will input energy over a broad frequency range. Both the level and frequency range of the force level is affected by the mass of the components involved as well as the hardness between contact points (i.e. metal on metal contact will result in energy distributed over a very wide frequency range). Rapid start/stop motion of components during normal operating conditions can also be a source of transient loads that tend to self-excite the structure.
An example of this is the read/write operation of a typical hard disk drive that undergoes rapid rotary actuation of the arm assembly as it moves from track to track over the disk media during normal read/write operations. Each hard start & stop action is like a miniature impact hammer hitting the structure and energizing all its internal resonances. This is problematic to the extent that there is not sufficient damping in the system to quickly dissipate this unwanted motion of the read/write head. Ultimately, off-track errors can occur slowing down the performance of the device.
Elaborating on this example further, a typical hard disk drive is subject to a collection of excitation sources: the rotating spindle motor that spins disk platters to 7500 or 10000 RPM, the rotary actuated voice coil motor that pivots the arm actuator assembly, the bearing effects of either the arm pivot or spindle bearing that create unwanted disturbances, and the air induced excitation from turbulent airflow from the spinning disks pushing air over the arm / suspension components. The goal is to control these excitation forces at the source level through various design choices. For example, a significant improvement in idle noise created by the drive was achieved once the drive industry changed to more precise fluid dynamic bearings. Better quality components manufactured to higher quality standards reduced variation by tightening component tolerances further helping to reduce excitation levels. Air induced vibration is a by-product of the high speed drives made today, but even this source can be controlled through the use of air straightening devices that help to minimize turbulent air flow, thus reducing this source of broadband excitation to the disk platters and actuator.
In general, strategies for minimizing excitation source levels involve such things as use of light weight components to reduce force levels, minimizing unbalance and misalignment between components, and more precise manufacturing methods that remove unwanted variation. The reduction of reciprocating loads can be achieved by reducing the mass of moving components or the use of inertial counter balances. For geared components, selection of high contact ratios (>2.0), proper lubrication, selection of gear materials, tooth profile and surface finish, and shaft alignment are all factors influencing good gear design and operation. Other methods involve the modification of the actual operating profile whereby sacrifices in speed or power are made for the benefit of better NVH characteristics (i.e. “quiet mode” of a cooling fan that runs at a slower speed often actively controlled to control cooling demand, or an automotive air conditioner that takes longer to cool because of less powerful components, or a hard drive that decelerates slowly to a stop minimizing excitation levels at the expense of longer seek times).
Key Engineering Challenges for EV and Emobility Batteries
The average age of vehicles on U.S. roadways is 12.1 years, up from less than ten years in 2001. Cars are driven longer and perhaps harder than ever before and need to stand up to years upon years of abuse from environmental factors such as rain, UV light, ice and road salt, stop-and-go traffic, poorly maintained roads, and more.
Compounding these factors are the vehicles themselves. They’re far more complex than ever before, loaded with expensive computerized electronics, sensors, and other equipment.
Challenge: Thermal Protection
EVs have an entirely different set of cooling needs than ICE vehicles, with a completely different system design. To ensure safety and promote consumer adoption, EV and battery manufacturers have strict requirements to prevent and manage thermal runaway, a unique challenge to lithium-ion batteries. Battery manufacturers rely on mica, ceramic fibers, other materials, and smart system design to prevent these thermal runaway events.
Challenge: Electrical Shortages
Applying insulative layers can prevent spark voltage between critical internal components, preventing electrical shortages or fires.
Boyd offers adhesive tape products, including multilayer stack configurations with tight tolerance control that prevent shorting in flexible, printed circuits and other high voltage components such as lithium-ion cell subassemblies. Combining electrically insulating double coated tapes with compression pads and other materials creates multi-functional solutions that prevent electrical shortages and absorb road vibration or collision impact energy. Single-coated insulating tapes applied to liquid cooling system components, such as aluminum cold plates and other metal structures, add electrical performance to thermal systems.
Challenge: Dust and Fluid Contamination
Sealing the battery pack protects lithium-ion cells against liquid, gas, and dust particle intrusion — contaminants that could cause catastrophic failure or shorten battery life. Seals should optimize performance and provide waterproofing while considering compression set and force deflection, assembly efficiency, noise/vibration/harshness (NVH), and other mechanical factors.
Display seals and bonding solutions are not in the battery pack but are still crucial to the consumer driving experience. Boyd’s are engineered with innovative pressure-sensitive adhesives and acrylic foams to protect the display assembly through its lifetime. Their ultra tight tolerances can achieve “zero-gap” performance, offering unbeatable protection against dust and liquid contamination. We design these solutions for simplified customer assembly, design-for-manufacturing (DFM) throughput, and material optimization.
Our portfolio of seals and gaskets includes hundreds of foams, polymers, adhesives, and other options. We combine this material expertise with DFM mass production capabilities to deliver customized designs that exceed your high-performance operating conditions for battery pack and display assembly contamination protection.
Challenge: Shock and Collision
Battery packs must be protected against collision impact, harsh road conditions, and temperature extremes. The placement of rugged and resilient compression pads, layered between lithium-ion cells, compensates for swelling forces due to charge cycling. When placed around the battery module, these pads serve as an impact protection barrier by absorbing mechanical energy from collision impact, extreme road conditions, and extended vibration for enhanced consumer safety and reduced warranty costs.
Boyd offers a range of closed and open-cell foams. These provide varying performance characteristics to meet the needs of a broad spectrum of temperature and environmental exposure applications. Foams can be combined with single- and double-coated tapes that incorporate dielectric films for electrical insulation in EV batteries.
These foam solutions reduce your total cost of ownership by solving technical challenges while promoting easy assembly and efficient installation.
Challenge: Thermal Management
With EV design and functionality evolving to heavily incorporate advanced electronics, EV engineers are turning to traditional electronic system thermal management market leaders for thermal system innovation.
EV battery designers look to maintain homogenous temperatures across battery cells. They must do this while enabling faster charge/discharge cycles, reducing battery overheating, isolating catastrophic battery events when they happen — or better yet, preventing those events from ever happening. Boyd’s complex material assemblies integrate lithium-ion battery cell-to-cell cooling with impact-absorbing and heat/flame isolating solutions to address the primary mechanical, thermal, and environmental factors that prevent thermal runaway.
Thermal interface materials (TIMs) facilitate heat transfer between the liquid cooling system’s cold plate and battery module, reducing thermal resistance to maximize thermal system efficiency. They help minimize the resistance of heat flow into, through, and out of an interface. Drawing heat away from sensitive components promotes greater power density and efficiency.
Boyd’s manufacturing capabilities combine raw materials from multiple vendors to create optimized multilayer stack-ups of material configurations, helping engineers achieve greater design flexibility. These materials can be combined with flame retardant adhesives that enable composites and materials to meet UL® 94 V-0 and other flame retardancy requirements, along with single-and double-coated tapes with easyrelease liners and filmic layers with strong dielectric properties.
Our liquid aluminum cold plates provide Robust Structural Support (RSS) and high-efficiency cooling for today’s highest performing battery modules and packs. Their low profile and light weight create extra design space for more powerful batteries and more reliable vehicles with greater range.
Challenge: Electromagnetic Interference
Seams and openings provide avenues for rogue energy waves to enter or exit a device, causing electromagnetic interference (EMI). EMI shielding reduces electronic malfunction susceptibility and improves battery performance, safety and reliability by blocking or absorbing these unwanted waves. Generally, this shielding first deflects electromagnetic waves with reflective surfaces. This heats the shield, making moderate electrical and thermal conductivity essential characteristics of an EMI/RFI shield.
Boyd’s LectroShield metal foils, conductive foams, elastomers, and adhesives are designed to manage interference energy. The outcome is improved reliability and efficiency.
Boyd’s EV Battery Protection Material Solutions
Brazed liquid cold plates – A cold plate transfers heat from surfaces with high heat loads to the fluid in a liquid cooling system. The performance of the cold plate is critical to the overall effectiveness of the liquid system.
Seals and gaskets – Seals and gaskets protect the battery module and cells against contamination from liquids, gases, and particles for longer battery life, improved safety, and reduced warranty costs.
Compression pads – Rugged and resilient compression pads protect batteries against collision impact, harsh road conditions, and temperature extremes. Pads are layered between cells to compensate for swelling forces or placed around the module as an impact protection barrier.
EMI shielding – Shielding reduces electronic malfunction susceptibility and improves battery performance by blocking unwanted electromagnetic waves, increasing battery performance.
Electrical insulation and cell wrapping – Insulation and wrapping prevent spark voltage between internal critical components that can lead to device shorting or fire.
Thermal interface materials (TIMs) – TIMs facilitate heat transfer between the cold plate and battery module while minimizing the resistance of heat flow into, through, and out of an interface. Designed specifically to keep batteries within their optimum temperature ranges, especially in unpredictable environments, TIMs reduce draw from battery power required for cooling and heating systems.
Dielectric adhesives for busbars – Dielectrics protect flexible printed circuits in battery assemblies, helping extend their lifetimes.
Multilayer thermal runaway protection – Complex cooling and impact absorption protection layers meet strict requirements to prevent thermal runaway.
Battery housing seals and collision protection – Robust seals, gaskets, and damper pads are designed to withstand and absorb variable force and mechanical energy from extreme road conditions, sudden impact, or prolonged vibration, minimizing the detrimental effect on the battery and reducing warranty costs.
Have questions? We’re ready to help!