Li-ion Cells are getting better, not cheaper.
That’s why it all comes down to a smart Battery Pack and Application. Guru’s or Engineers? There are a lot of guru’s and prophecies about energy storage and battery technology in particular. Publications are often single sided news by emphasizing the benefits of new energy storage technology and not the disadvantages like high costs, time to market and the chance it will never reach the market anyhow. There are some facts however. The Li-ion technology is currently the dominant technology and, indeed, on a structural bases there will be periods of shortage of cells. We also know that cell suppliers are still making very little money. But, next to that, the current (Asian) Cell suppliers are executing their roadmaps step by step and continuously improving the performance of Cells, but at a constant cost per Wh. The world needs engineers to utilise that value, not guru’s. Unlock the value of Li-ion Cells The current most effective way forward to make electric mobility more affordable can be found in the application to unlock the value of the Li-ion to its full extent. The key to this lies in the advanced cell management that orchestrates the interdependency of ranges of cells within a Battery Pack, and an accurate integration in the driveline of the Vehicle. This implies a full understanding of the customer en design requirements of the application with sufficient granularity. Cell suppliers may be knowledgeable on the Cell side but are generally too big to deal with and lack the capability to tailor solutions. Advanced Batteries Concepts The Advanced Battery Department of Cleantron a Dutch company based on the outskirts of Amsterdam specialises in exploring and developing battery concepts that go beyond the usual tracks, with battery concepts that are based on proven cell technology, utilising the results of extensive research. The results of Cleantron research, Li-ion cell algorithms driving electronic (impedance based) BMS solutions, package designs with integrated thermal management and new collaborations of cell chemistries, are the major building blocks for Advanced Battery Concepts. The Impedance based BMS This next generation Battery Management (BMS) makes use of impedance, instead of only current, voltage and temperature, which is the traditional approach. Impedance of a battery cell corresponds directly to the internal state of the cell, and thus paints an accurate picture of what is going on inside the cell. This can be used to deduce cell parameters. This can determine SoC, internal temperature and SoH values with a higher precision than a traditional approach. Based on this more accurate data, the BMS can optimise the operating strategy to fully suit the battery cell, which enables an extension of battery cell lifetime, and simultaneously a similar or improved battery cell performance. “We have a strong commitment to quality. Our fully automated production facility in the Netherlands really sets us apart from our competitors, who may not always be as precise when it comes to testing”, explains Maurice van Giezen, co-founder and Director at Cleantron. “Lithium battery packs are complex and potentially hazardous. So safety is a top priority for us.” Range & Acceleration, overcoming the waterbed effect The waterbed-effect of Batteries that offer either high specific power (for i.e. acceleration) or high specific energy (for i.e. range) is a central theme for electric mobility and therefore for the Advanced Battery Department of Cleantron. van Giezen went on to say “We have many years of experience with portable exchangeable 48V battery modules (“battery swapping”) for instance in electric scooters and industrial AGV’s ; now, after years of research, we have developed a low voltage and high voltage battery system for light electric vehicle & automotive applications that overcomes the waterbed effect. The new system offers the required C- rates for acceleration & speed on the one hand, and works with lightweight exchangeable battery modules with high specific energy for the range, on the other hand” One size fits all? “It goes without saying that there is no such thing as a standard solution; “one size fits all” is another way of saying that it is suboptimal: too expensive, not good enough or both. In the market sector of electric mobility the requirements for personal mobility are different then for urban logistics. That is why Cleantron refers to the system as an Advanced Battery Concept. It needs to be engineered into an optimal solution that works and keeps on working”. van Giezen continued “So, based on this Cleantron can develop tailored battery systems that unlock the value resulting in the lowest TCO without compromising on quality and lifetime. Unlocking the true value of Li-ion Cells will unlock the value of electric mobility”, he concluded. About Cleantron Cleantron is a specialist supplier of advanced battery packs, serving the market sectors of Industry 4.0, Light Electric Vehicles; Low Voltage as well as High Voltage. Cleantron is a dutch, privately owned, company, located in Nieuw Vennep, 10 minutes with a Tesla taxi from Amsterdam Schiphol Airport. The ISO9001 certified company has 6 automated production lines. Because Cleantron has developed her own battery pack production machines, the strategy is clearly systems for pure electric and plug-in hybrid vehiclesthat everything that Cleantron develops and engineers is eventually supposed to be produced within Cleantron. For years the company runs an research & innovation program in close collaboration with Eindhoven University of Technology (former Philips country) resulting in, among other things, impedance based BMS solutions. In 2017, by introducing CAM (Cleantron Automotive Module) Cleantron presented herself also to the Automotive Industry. In 2020 Cleantron will open in the Netherlands the CAC; the Cleantron Automotive Centre, where automotive niche series (urban delivery, motorsport, defence and luxury applications) will be produced. with the CAC Cleantron also serves Automotive OEM Advanced Engineering with prototypes for mainstream automotive applications As well as the production and Head Quarters in the Netherlands, Cleantron has offices in Munich, Paris and Thaizou (China).
ASICS for Battery Management Systems
Lithium-ion battery packs are becoming increasing commonplace in a wide range of applications including automotive, marine, aerospace, rail and energy storage. However, whilst there have been many advances in lithium-ion cell chemistries in recent years, the design of the Battery Management System (BMS) that ensures the performance and safety of the pack has remained broadly the same. A typical BMS consists of a wiring harness that measures the voltage of each parallel string of cells, i.e. cells connected positive-to-positive, negative-to-negative. Additionally, a number of temperature probes, such as thermocouples, will be present in the pack, but these will typically cover a large number of cells each. In a centralised BMS, all sense wires are directly connected to a master board, which checks for cells that are exceeding their maximum or minimum specified voltage or temperature and takes action to resolve the issue, for example by reducing the charge/discharge current or activating a cooling system. In a decentralised BMS, slave boards perform some calculations before sending data back to the master board. However, such systems are far from optimised for lithium-ion battery packs. To explain the limitations of a conventional BMS, let’s analyse the BMS used on the world’s best-selling electric car. The Nissan LEAF has 192 cells in its battery pack, arranged 96 in series, 2 in parallel. With its conventional wired setup, the BMS master board only has access to 96 voltage readings, a maximum of 4 temperature readings and no cell-level current readings. If a cell in a parallel pairing starts to fail, the master board will have no indication of irregularities in current flow between the two cells, and any increase in temperature could take a considerable amount of time to reach the nearest temperature sensor. As a result, individual cells could undergo sub-optimal or abuse conditions and the vehicle would be completely unaware of the onset of cell failure until the cell is in a more advanced state of degradation. A conventional BMS also has limitations when packs are being prepared for second life applications. When a module is disconnected from a battery pack, all data that is indicative of the State of Health of the module is lost. Furthermore, unless there are no parallel cells in the module, the BMS had no access to cell-level State of Health data to begin with. This results in labour- and time-intensive characterisation of modules in order to grade them for second life applications. The expensive and bulky wiring harness is most likely disposed of in the process. Some manufacturers have attempted to reduce this expense by daisy-chaining voltage sense data, but this risks communications from a large portion of the battery pack being lost should a single connection fail. There is a clear need for the ability to measure cell-level data in battery pack, even on parallel cells; communicate that data to the master board in a simple, secure and inexpensive manner; and retain State of Health data with the cell throughout its lifespan. Based in Edinburgh, UK Dukosi a company which is leading the next generation of battery management has wiped the slate clean and built upon its sensor-on-a-chip expertise to deliver a completely new and fit-for-purpose solution to battery management. Their ASIC (Application Specific Integrated Circuit) can be embedded into a cell at the point of manufacture or attached to the top of an existing cell, where it will wirelessly relay raw cell data such as voltage and temperature, and calculated data such as State of Charge and State of Health, to the master board via a single proprietary near-field RF antenna. This eliminates 95% of the wiring harness and provides a breadth and depth of valuable data that was previously unavailable with a conventional BMS. Returning to the Nissan LEAF example, a BMS based on the Dukosi cell monitoring system would give the master board access to all 192 voltage measurements, 192 temperature measurements, and 192 current, State of Charge and State of Health measurements. Additionally, the solution provides an on-cell event log that details the conditions that the cell has been subjected to during its working life. This gives the BMS full knowledge of the health and performance capabilities of every cell in the pack, improving the performance and lifespan of the pack and facilitating predictive rather than reactive maintenance, thus improving the availability of the vehicle. Each cell communicates its data back to the BMS master board via a single RF antenna, ensuring that every cell in the pack remains in contact with the master board even in the event of a single cell failure, unlike other communications protocols such as daisy chains. When a cell is removed from the pack, the cell-powered ASIC stays with the cell, as does all of the valuable data contained within it. This data can be accessed via an RFID reader within seconds, vastly decreasing the time taken to grade cells for second life applications and greatly increasing the throughput and safety of battery reuse and recycling facilities. Another key advantage of the Dukosi system over a conventional BMS is that it is chemistry-agnostic and therefore intrinsically future-proof. Many vehicles have lifespans of several decades, but battery technology in 10, 20- or 30-years’ time will not be the same as battery technology today. Many upcoming cell chemistries have different cell voltages, meaning that the number of cells in series in a replacement battery pack for the vehicle would be different from its original pack, and potentially not a multiple of 8 or 12 as per the inputs on many conventional wired master and slave boards. A conventional BMS master board could not cope with this change, resulting in the need to completely retrofit the electronics within the vehicle, which is time-consuming and expensive. However, the Dukosi system is not limited to a specific number of voltage inputs and can handle any number of cells in series, so the master board would merely require a quick over-the-air software update to configure it for the new cutting-edge cell
High voltage battery systems – Driving the transformation
The entire global auto industry is on the brink of a profound technological transformation. Networked or “connected” vehicles, ranging from electrically powered (electrified) and fully automated to autonomous vehicles, as well as new mobility concepts (shared), are ushering in a significant transformation of the auto industry – from changing priorities in customer use to new vehicle functions and technologies, as well as new supplier and value creation structures. The automakers (OEMs) are not only rising to meet the challenge of these new technologies but are also expanding their business models and activities to accommodate new mobility platforms and produce lines, as well as vehicle operation. Indeed, this will present a range of new opportunities for the supplier industry as well – from development service providers to system suppliers and contract manufacturers – as an important innovation and value creation partner for the OEMs. Stricter regulations on CO2 and NOx emissions are driving the accelerated transformation of traditional combustion engine vehicles to electric vehicles. Although the specific emissions controls and targets vary from region to region (Europe, USA, China, etc.), they are united on one point: fleet consumption targets will be drastically tightened and/or sales targets for electric vehicles will be set by regulators – with billions in penalties to be paid for the failure to achieve targets. The new EU target calling for a reduction of CO2 fleet emissions by -37.5% (passenger vehicles) by 2030 will already require a dramatic shift, and thus a further acceleration of the transformation towards electromobility. All analysts are accordingly expecting rapid growth in the market for electric vehicles. This market is primarily spread across China and Europe and, trailing slightly, also North America. Nonetheless, considerable uncertainty remains – very often the plans made yesterday are already obsolete by today because of the far more ambitious volume scenarios that are needed. As a 2025 milestone, all German OEMs are aiming for a target share of around 25% of worldwide sales for purely battery-electric vehicles, with significantly higher market shares likely in certain key electromobility markets. New battery electric vehicle platforms and architectures are creating the basis for the substantial expansion of the product line that is needed – to new sub-brands and entirely new model families, such as the derivatives portfolio under the Mercedes Benz sub-brand “EQ” or the I.D. product facility at Volkswagen. In the future, plug-in hybrids will also be offered in all premium vehicle series, which will have to meet battery-electric distances of up to 100 km (62 m). For this reason, virtually all automakers have defined high-voltage battery systems as core competencies and in-house services and are building up appropriate development and production capacities. All development service providers and suppliers in the market for vehicle battery systems are accordingly competing first and foremost with the in-house resources of the automakers. Nonetheless, the needs of OEMs are increasing sharply all along the value creation chain, from product development to process development to production and assembly of battery cells, modules, and packs – at a volume that is also putting pressure on new service providers and suppliers in the EV battery market; the business models and spectrum of the competition are correspondingly diverse. While in the passenger vehicle segment, OEMs tend to acquire development services and/or order production of battery systems in addition on account of their greater in-house value creation, in the van and bus segment it is mainly complete packages that are developed and produced under one roof as a system solution that are desirable; and for that reason system suppliers will be used here that in the future offer “complete” module solutions “off the shelf” in order to then offer the pack integration and assembly. It is also likely that the OEMs will not only scale their module solutions as a platform solution in the company but will also help external clients as a “3rd party business” – with the goal of achieving additional scaling effects not only in the battery but also in the entire electric drive train. Volkswagen, for example, has announced that it will also open the MEB electric platform to third parties. The OEMs are thus also becoming relevant actors in a market for battery modules that in the future will become ever more competitive. At the same time, a substantial market is also opening up for testing service, i.e. contract testing (testing as a service), mainly focused on (battery) systems and their integration in the electric power train – a market that, together with development service providers, is also being served by large test providers like TÜV and SGS. Nonetheless, the testing of battery cells, modules, and packs requires substantial investments in order to master the wide range of performance, lifecycle and safety tests. These investments are increasingly expected by the development and testing service providers, since the OEMs only invest in-house for basic needs – in contrast to the combustion engine, where huge motor testing facilities for development were built in the 1990s and 2000s. With the substantial growth in the number of new battery programs at all the OEMs, a service market is emerging around the prototype construction of high-voltage battery systems. In the coming years, the “Contract Manufacturer” business model will also persist, with the supplier as a partner in industrializing a previously developed battery system and producing under contract for the OEM. New business models dealing with after sales solutions for battery systems will likely also have to be developed: battery systems that are no longer produced in series production will still have to be available after End-of-Production (EOP) for replacement parts supply – new service business models are emerging that produce such battery systems in smaller volumes and on a highly flexible basis, including in combination with cell upgrades and appropriate development service. Playing a significant role as system suppliers are the established battery cell producers from Japan, South Korea and China, which are increasingly also offering battery modules and packs; for example, CATL, LG Chem, Panasonic, Samsung SDL,
FORMULATIONS FOR MATERIAL SELECTION FOR BATTERY PACK DESIGNS
The Cell, the Battery and Battery Management societies are facing numerous challenges. These challenges span many different disciplines, technologies and applications. Experience indicates that many battery pack and battery management designers and manufacturers overlook the key challenges of material selection for assembly, placement and chemical and thermal protection. This is to be expected as information available, classically only concentrates on key characteristics like Thermal Conductivity. Although these key characteristics are considerably important, they do not always deliver the desired need or result. Before going into details about the material selection, we first investigate the generic characteristics of the main chemistries involved. In Table 1 we see for example that Silicones are soft, Epoxies rigid and Polyurethanes somewhere in the middle. Plus, the reparability; adhesion where the more adhesion the more difficult it is to remove. In Table 2, we highlight the typical characteristics that are influenced when modifying chemistries to meet certain functional challenges. Table1 Table2 When selecting a material it is taken that ease of processing is inevitable and that technical properties remain unchanged and in many cases it may be so. However how does this material fit within the existing processing environment? How easy is it to integrate and scale-up and will this have an effect on the technical properties? Using the simple formula Processability, can help to achieve the desired technical properties without compromise. First material flow, the thixotropic properties of the material; how easy it will spread. The mix ratio, an important criteria for the equipment suppliers. 1:1 mix ratio is considered desirable but could create other bottle-necks typically if fillers are present in both A & B components, resulting in higher equipment costs and maintenance. Reactivity range, the speed at which the material will for example begin to gel. A potential major bottle-neck and a common misperception “what is used for prototyping is not always best suited for mass-production”. These characteristics are off-set by Thermal conductivity, namely solid contents or filler type and volume. Also the viscosity ratio is always important especially for dispensing and equipment suppliers. A major consideration for battery pack design is thermal conductivity; how to remove the heat from the cells or modules. This should never be confused with Thermal propagation or runaway. However, Thermal conductivity does play a key role in heat dissipation. In simple terms, thermal conductivity is the heat path between two points. It is the transfer of this heat from point A. (i.e., a cell or module) to point B. (i.e., the cooling plate or channel). The main concern of thermal conductivity alone is it only refers to the heat transfer and the link or path and the bulk material value. The reliable dissipation of heat and excess heat is essential for the stability and longevity of the system. For heat dissipation to be optimised Density, Wettability and Compressibility are all key factors. Here we should also include adhesion, in many cases a critical component for thermal conductivity but also a growing concern as battery packs become integral to the vehicle structural integrity and face greater mechanical stress. These characteristics are off-set by the layer thickness and here we can also add substrate type and mechanical stress. E-mobility vehicle development strives to increase range while reducing total weight. The system weight is therefore of critical importance in battery development and yet surprisingly material density is sometime overlooked. Thermal conductive Gapfill materials are the largest contributor to weight. For every 1Ltr of 3.5W·mk material, with a typical density of between 3 to 3.5g/cm3, adds approximately 3.5kg of weight. Considering a modest size battery pack employs more than 5Ltrs of Gapfill material, this adds 15 to 20kg of unwanted weight. We can discuss low density materials, employing exotic filler types but cost is currently unrealistic. Some of these fillers increase the viscosity or changes thixotropic or more drastically the hydrophilic behaviour. Using materials with higher adhesion and better flowability it is possible to improve heat dissipation and reduce weight by employing lower thermal conductive (density) materials. Taking these considerations a step further, base material chemistries can be compared. Graph 1 represents key functionalities required. From the top clockwise: Thermal Conductivity from Low 1W·mk up to currently 3.5W·mk and possibly higher. Mechanical Adaptability from Low to high, elastomeric, hardness, dampening and cycling behaviour. Flame Retardant properties from weak to good. Capability vrs Permanent operating temperature. Temperature stability from low to high. Long term thermal stability and cycling behaviour Adhesion from weak to good. Chemistry, substrates, environment. Impregnation from weak to good. Application and environment where the material will be employed. Insulation properties from Low to high. Dielectric strength, breakdown voltage. Reactivity Range from narrow to wide. Versatility to adjust the gelation speed. As the graph shows, Silicone has excellent Thermal Conductivity, good insulation properties, UL and a high permanent operating temperature. For Polyurethane, due to the thixotropic behaviour of the material with large filler content, Thermal conductivity is lower and the natural temperature boundary of the chemistry, a lower Thermal stability. However for Mechanical strength (namely adhesion) and the reactivity time, the speed the material can or not gel, Polyurethane has more range capability. Critical for designs requiring mechanical reliability. In Graph 2, the same data for Silicone versus Epoxy. For battery pack designs due to the potential rigidness or crack potential, epoxy is not considered. For applications such as motors, then epoxy is of interest, especially impregnation and adhesion properties. WEVO Chemie GMBH is a family owned, independent company headquartered in the German automotive manufacturing hub, Stuttgart. Their global presence supports the major electrical and electronic societies. Since producing their first polyurethane-based electrical casting resins in 1978, the company has continued to develop and supply a range of solutions for OEM’s and Tiers in the automotive, home, engineering and energy sectors. They have taken the lead as a supplier of encapsulation solutions for automotive sensors and in 2007 supplied their first resin solution for an EV battery system, which is still running today. Author: Terence Kearns and Jochen
