The essential role of effective cooling in e-mobility
Cooling solutions secure performance and longevity in e-vehicles. Li-ion battery operating temperature plays a decisive role in functionality and especially lifespan in high-performance batteries. Keeping to a constant temperature profile is essential in ensuring long-term performance in EV batteries and stationary energy storage modules. Like people, Li-ion batteries have a definite comfort zone when it comes to temperature – they feel at their best in temperatures between 20 and 30°C, and achieve their maximum electrical performance and durability in this temperature range. Temperatures that are too low or too high will affect performance. The liquid inside the battery (electrolyte, acid or conductive paste) becomes viscous and carries less charge when temperatures drop. Apart from that, sub-zero temperatures cause issues in the electrochemical reaction at the electrodes, which are usually made of graphite and transition metals. The result is a significant drop in performance and range. Cell oxidation rates increase at temperatures above 30°C, leading to more rapid battery deterioration – and on to declining performance and diminishing capacity. Operation at over 40°C may even cause permanent damage. EV manufacturers usually install liquid cooling systems to keep operating temperatures constant within the optimum range. The advantage of liquid cooling systems is that they carry off relatively large amounts of heat at uniform rates. Systems of this type are closely matched to the batteries. Li-ion batteries in electric vehicles are often equipped with cylindrical, prismatic or pouch cells surrounded by channels for the cooling fluid to circulate from the cooling system. Hardly any auxiliary power is required in contrast to air cooling; this makes the process highly energy-efficient. Each battery cell is usually equipped with a sensor to measure voltage, capacity and temperature within the cell for monitoring using a battery management system. This battery management system communicates with the cooling system, which then adjusts to situational requirements. Pioneer in customised liquid cooling Based in Sassenberg near Münster, Germany, Technotrans was one of the first manufacturers of liquid-based battery and charging cable cooling systems on the market. Together with Siemens, the company launched a prestigious project in Qatar towards integrating a bespoke cooling solution in e-trams without overhead lines as early as in 2011. The company also developed a system to ensure constant operating temperatures in hybrid energy storage systems consisting of capacitors (supercaps) and Li-Ion batteries even under extremely challenging ambient temperatures of above 50°C in some cases as well as high humidity and sand ingress. In addition, it developed an especially lightweight system to keep the total weight of the tram down. Energy storage cooling systems from Technotrans ride along in trams and regional trains in Europe Asia and the Americas, and cool inverter stations for rail and bus projects worldwide. Other fields of application include electric buses, trucks and vehicles in seaports and airports. Demands may have increased with time, but the development process has remained largely the same for the system manufacturer – designing batteries and the corresponding cooling system is a very precise process highly dependent on customer specifications, in which a variety of factors play a key role. For example, battery power and cooling requirements are based on regular fixed routes that e-buses run in public transport. Not only distances, but also gradients need to be included in these specific route profiles. An e-bus that has to deal with heavy gradients such as while crossing bridges needs more power at this point – and therefore also more cooling power – than on a route that remains flat. Problems arise when battery performance and capacity begin to diminish early due to temperature. Operators can no longer run the intended routes with the issue eventually being passed onto the battery manufacturer, which cannot fulfill its guarantee of usually five years and has to provide a replacement. High-power charging – advanced fast-charging stations Not only high-performance batteries but expansion in the charging infrastructure will be essential if electric vehicles are to develop into the transportation of choice in the long term. Many vehicle manufacturers have been investing in high-power charging (HPC) to allow a full charge in a matter of minutes. Charging cables need to transfer large amounts of power at around 300 to 400 kW in an extremely short time for HPC to work. This causes significant heating from electrical resistance within the cable depending on cable length, cross-section area and conductivity in the wire cores. The copper cores are surrounded by liquid-bearing tubes for cooling. The cooling unit is usually integrated into the charging station and uses active and passive cooled charge cable cooling modules, which means either a compressor or ambient air, depending on requirements. Manufacturers attach great importance to sleek, space-saving designs in modern charging stations, which also poses a challenge when developing the components. Cooling system manufacturers are often left out of the loop in this part of the design process, only to be involved much later when installation space and requirements have already been specified; Technotrans has to dimension its cooling systems accordingly. The company will sometimes use a split design to overcome physical boundaries. Apart from that, the company’s experts develop decentralised cooling systems for entire charging centres with centralised cooling systems serving a number of charging stations. E-mobility still a major growth market E-mobility is set to form the heart of a resource-efficient urban infrastructure, especially in Europe. Many cities are investing in e-buses, so their share in public transport is increasing accordingly. The same applies to regional railways that need to cover long distances in contrast to trams. This reflects in an increased requirement for efficient cooling systems at Technotrans, which means increased technical challenges as virtually every project comes with its own peculiarities. As an example, the company develops cooling systems for automated guided vehicles (AGVs) to be used in harbours. These AGVs are not only subjected to extreme environmental conditions such as sea air and saltwater, but also heavy pressure and vibration from loaded freight, such as containers. The company integrated a cooling system for a series
Charging in record time
A superior technology ensures high power charging in the most convenient and safe way. Super-charged in 15 minutes – how HUBER+SUHNER is accelerating the electric vehicle market Electric vehicles are increasingly becoming the car of choice as more people become environmentally conscious. The sale of electrical vehicles in the US increased by 81% in 2018, with a growing number of charging stations being installed across the US to meet this demand. According to J.P. Morgan, by 2025 electric vehicles are expected to make up a total 30% of all vehicle sales, contributing to a rise of 8.4 million electric vehicles on the road. Yet, when consumers think of purchasing an electric vehicle, one of the biggest concerns is where they will be able to power up, as well as how long it will take. No one wants to be stood by the roadside for hours waiting for their vehicle to charge to continue a journey. However, purchasing a low-emission, fuel-efficient vehicle does not mean consumers have to compromise on performance or convenience. Currently, charging times are often lengthy and disruptive for everyday life as many charging spots offer average outputs of 7-50kW, with a full charge taking up to three hours. When compared to the wait time of eight hours when electric vehicles were first launched, this is progress – but there is still some way to go before the ultimate aim of making charging as quick and easy as filling up with fuel is achieved. Reducing charging time As a result of this, and discussions with various Automotive OEM’s, HUBER+SUHNER, a Swiss-based manufacturer of components and systems for electrical and optical connectivity, has developed an innovative power cable solution to enhance electrical charging stations and reduce charging time. In order to achieve this, higher power must be transmitted through cables for charging electric vehicles. The standard solution would be to just increase the cross section of the cable, but this would lead to a very bulky cable making handling difficult for the majority of consumers. Therefore, to reduce weight and increase flexibility, a cooled cable solution was developed. This solution ensures easy handling at the charging station and can draw up to 500A/1000V, enabling new generation EV cars to charge in just 10-15 minutes to 80% state of charge. Dubbed the RADOX® HPC, the system has been developed to be flexible, easy to handle and lightweight, enabling even higher ratings to ensure it is future-proof. The upward compatible and customisable system helps the utility provider to be prepared for future needs and, as a result, secure vital investments. As providing a solution with 500A in public use is new, safety and reliability were given the highest priority in the development phase. Additionally, the product is approved in accordance with European and American standards. Accelerating the electric vehicle market To enable a successful market introduction of the new generation of EV cars, an HPC infrastructure is required. With the ability to charge an electric vehicle in less than 15 minutes from a convenient station and enough power to last for hundreds of kilometres, we believe it now makes sense for motorists to switch to electric cars as their favoured method of transport. The state-of-the-art infrastructure will not only make lives easier and safer, but with the addition of more charging points with the RADOX® HPC system implemented around the world, charging an electric car away from home is now simple and convenient. The product is already in serial production, with various roll-out programmes currently running in the US and Europe. We hope Asia will also follow soon. To bring more advanced and adaptable electrical cars successfully into the market, a solid network of charging stations is also required. Along with the existing standard charging points for electric cars at home, work and in car parks, a new generation of high-power charging points along main travel routes are being implemented to ensure drivers are not restricted, with experts suggesting that the worldwide number of public charging points will increase to approximately 40 million in 2030. HUBER+SUHNER is currently playing an integral role in the development of these stations by supplying the cooled cables to Electrify America. Electrify America is a Volkswagen subsidiary set up as part of the diesel emissions test settlement to develop a network of electric charging stations across the U.S. In the next two years, Electrify America will install a highway network of ultra-fast Direct Current Fast Charge stations. This will include building new sites which will connect regional destinations and filling in existing routes as station utilization of the highway network increases. This project will continue to see HUBER+SUHNER play a vital role in developing the infrastructure needed to make electric vehicles a reality for consumers across America. With projects such as this one, we are confident consumers will continue to increasingly choose electric vehicles, meeting and even exceeding the ambitions of the electric vehicle market. By Max Göldi, Market Manager at HUBER+SUHNER
e-mobility
Thermal Management- Challenges for electric vehicles
Wolfgang Hofer The change to electric powertrains and the increasing importance of autonomous driving imply a variety of new challenges. Thermal management or rather thermal connectivity and cooling of electrical components have an important role to play. While there is a large number of Thermal Interface Materials, the most common solution for the automotive sector are the Gap Filler Liquids (GFL) and the Soft Therm Pads, both of which can be individually customized. According to the latest calculations by the Federal Ministry of Environment, Germany will significantly miss the self-imposed climate target of reducing CO2 emissions by more than 40% by 2020. In contrast to the trend of other sectors, greenhouse gas emissions from the transport sector recorded a slight increase compared to the referenced year 1990 and are responsible for one fifth of Germany’s total emissions. Improved vehicle efficiency could not compensate conflictual factors such as increasing traffic and engine performance. The Federal Government’s new climate protection plan envisages a 40-42% reduction in greenhouse gas for the transport sector by 2030, just a small component to meet the 2 ° C target of the Paris climate agreement. Alternative drive systems are essential in order to meet the target of 95 g CO2/km on average for cars. If these values are exceeded, car manufacturers face massive fines. This pricing mechanism has a positive impact on low-emission cars. A global rethink has to take place in the automotive industry. Thermal Interface Materials According to forecasts by leading German automobile manufacturers, all top sellers will also be available as an electric car by 2030 at the latest, an extremely ambitious goal. Aspects like a continuous increasing power density or higher heat flow per area (W/m2) and “high power charging” leads to increased component temperature and consequently to a reduced lifetime in the application. Efficient thermal cooling of electrical components by connecting of the heat source to heat sink, while at the same time having an electrically insulating effect, is therefore a prerequisite for the high-quality standards from the automotive sector. This connection and the levelling of appropriate component tolerances, gaps or air inclusions can be realized individually by the wide range of Thermal Interface Materials, depending on the requirements for thermal conductivity (W/mK) and desired temperature difference ∆T. Thermal Management for e-mobility The change to electric drive systems as well as the increasing importance of autonomous driving imply completely new applications and challenges in the field of “Thermal Management.” The functional relationship between the operating temperature of a battery stack and its maximum achievable number of cycles has been sufficiently proven, which can be quantified extremely precisely by the following rule of thumb: “A reduction in operating temperature by 10°C doubles the lifetime of the battery cells” The net reach of an electric car is also noticeably dependent on the operating temperature of the battery and thus also indirectly on the present thermal cooling. In addition to the concept for thermal connectivity of the energy source, the “car of tomorrow” also requires solutions for electrical components in the areas of LED, sensor technology, on-board network and inverter, one of the core elements of the electric powertrain. Gap Filler Liquids For high volumes in particular, two-component GFL are an efficient and cost-oriented solution. For this purpose, the two components of the ceramic filled silicone elastomers are blended by a mixing tube and can be directly applied to the component (e.g. metal housing) by a dispensing system. In the next step, the electronic components (e.g. IGBTs, capacitors, etc.) are attached under slight pressure to the still uncured mass, thus creating an even distribution of the mass and consequently a defined thickness as well as reproducible electrical and thermal parameters. The cross-linking or curing of the mass takes place under room temperature and lasts about an hour, but can be customized at the customer’s request. Primarily the GFL with lower thermal conductivity has a high self-adhesion, which can be very useful for the assembly. Nevertheless, in case of a disassembly the GFL of KERAFOL can be removed again, a property that is not always customary in the market. Table 1: Properties of Gap Filler Liquids Gap Filler Liquids Basic Material Silicone Thermal Conductivity (W/mK) 1,8 – 4,5 Breakdown Voltage (kV/mm) 12 – 20 Viscosity (Pas) 45 – 90 Application Temperature (°C) -40 up to +200 Hardness (Shore 00) 45 – 70 Compared to systems based on polyurethane or epoxy, silicon-containing GFL can absorb and compensate vibrations much better, an effect that is favoured by the high softness of the GFL. In addition, the low viscosity of the GFL allows for a simple workability and has a gentle effect on the dispensing system, a thesis that has been confirmed by leading plant manufacturers such as ViscoTec, bdtronic or Scheugenpflug. Soft Therm Gap Pads For many thermal connections in the field of e-mobility, classic thermal conducting tapes and pads are still “state of the art.” Especially cross-linked silicone-based elastomers, better known as Soft Therm Gap Pads, can play a crucial role in thermal cooling (power range up to 6 W/mK) of electronic components due to their variety of specifically adjustable properties. Table 2: Properties of Softtherm Pads Soft Therm Gap Pads Basic Material Silicone Thermal Conductivity (W/mK) 1,0 – 6,0 Breakdown Voltage (kV/mm) 2 – 16 Compression (%) up to 40 Application Temperature (°C) -60 up to +250 Hardness (Shore 00) 10 – 75 Due to the high flexibility and enormous mechanical resistance of the Soft Therm Pads, large gap dimensions as well as high component tolerances can be compensated. In addition to individual solutions, such as one-sided adhesive coating for component fixation or fibreglass reinforcement to increase mechanical stability, two-layer films (required by specific regulations) can also be of great added value to the customer. KERAFOL is meeting these customer-specific requirements for many years and finds the right solution for every application, regardless of which of the “Thermal Interface Materials” is the best solution from a technical and monetary point of view. Wolfgang Hofer https://www.kerafol.com/en/
