Research shows that driving range and charging duration are among the most significant barriers to purchasing an electric vehicle. Charging to 80% in 30 minutes does not seem to be satisfying for many potential customers. To make driving e-vehicles more convenient and to reduce users' range anxiety, improving energy storage for long-distance travel is one of the highest priorities in EV traction battery development.
For the vehicle manufacturer, the battery’s high cost from 35% to 45% of the total vehicle is significant. Especially since most OEMs depend on external partners for battery development. Cell development and production occur at suppliers who almost without exception come from East Asia, primarily China, South Korea and Japan. The OEMs are usually only involved in development and production at the battery module and pack level. Here, local partners with modern development and test centers are important. This resource makes the OEM more agile and allows them to focus on their innovations regarding this vital part of the e-vehicle.
The world is continuously changing. To see today's developments in context, it is often interesting to take a look into the past. Battery-powered vehicles are by no means a new invention.
Michael Faraday laid the foundation for electric vehicles in 1821 when he developed the first rudimentary electric motor. The first electric vehicles were built as early as the late 1830s, although they were not yet convenient. This changed in the 1870s with the invention of the rechargeable lead battery. As a result, the electric vehicle achieved a respectable 38% market share in the USA, for example, which it lost again very quickly from 1910 onwards. The range problem remained - and the nationwide supply of cheap gasoline was now guaranteed.
A revival of electric propulsion in individual traffic did not take place until the 1990s. Triggered by rising oil prices and greater environmental awareness, some manufacturers began to develop electric cars or hybrids. The best-known representative of this period is probably the Toyota Prius, which was first sold in 1997. This development was accelerated by a more powerful battery technology. First, the heavy lead-acid batteries were replaced by nickel-metal hydride (NiMH) and later by even more powerful lithium-ion batteries. The latter were first used commercially by Sony in 1991 and are now state of the art in almost all vehicles with traction batteries. Whereby there is no single "the" lithium-ion battery solution. There are different technologies in use here, which have specific advantages and disadvantages.
Common to all lithium-ion batteries is the fact that the eponymous Li+ ions move from the positive to the negative electrode during discharge. The material of the negative electrode in vehicle batteries is mainly graphite, a rare alternative is lithium titanate.
The distinction between lithium-ion batteries is usually made based on the material of the positive electrode. Three variants are particularly relevant here for electric vehicles. The related NCA (lithium nickel cobalt aluminum oxide) and NMC (lithium nickel manganese cobalt oxide) electrodes are the most commonly used cells in the automotive sector today. NCA cells are relatively inexpensive and have a very high energy density, the main criticism being their dubious safety, as they react early and very violently in the event of overvoltage or overtemperature. NMC cells are more and generally have a longer service life, but they are also more expensive.
LFP cells (lithium iron [Fe] phosphate) still have a relatively small market share in the passenger car sector. However, it is a promising technology in development. LFP cells are considered very safe, have the longest lifetime of all Li-ion technologies, and are highly resilient in charge and discharge rates. On the other hand, they are very costly and have an energy density that does not yet reach the level of NCA / NMC cells.
The decreasing acquisition costs of an electric vehicle, primarily due to the battery’s decreasing cost, make EVs more attractive for the final customer. At the same time, combustion engines are becoming more and more expensive for OEMs due to increasing environmental regulations, which makes it necessary to include hybrid and electric vehicles in the portfolio. Electric vehicles and hybrids have long since broken out of their niche existence and will face a sharp increase in market share over the next few years. By mid-20´s, an electric vehicle is expected to be comparable with a combustion engine vehicle, not only regarding its purchase price, but also in terms of total cost of ownership. In the future, automotive industry players and decision makers will have to prove a strong expertise in order to meet the market's expectations with the new technology.
Increasing the range has always been one of the main focuses of battery development. In addition to further chemical development at the cell level, the battery management system (BMS) has particular potential in this area. By closely monitoring the cells, they can be optimally loaded, allowing more capacity for the same service life. This may sound simple at first, however, reality proves it is highly complex in its practical implementation, because only a few parameters can actually be measured on the battery. Important information such as the exact state of charge (SOC) or the state of health (SOH) can only be determined indirectly using complex calculation models. These are the subject of ongoing research and development, and must be adapted and validated again for each cell type in elaborate tests.
The BMS also plays an important role when it comes to fast charging capability. Innovative charging methods such as pulse charging can noticeably shorten charging times in certain operating states without sacrificing service life. The current state-of-the-art is a maximum of 150kW (Audi e-tron) or up to 180kW for short periods (Porsche Taycan). In the future, up to 350kW will be possible. Charging to 80% might, therefore, take less than 15m, even with large batteries.
With these enormous charging capacities, the thermal management of the battery is also becoming an increasingly important factor. The power must be reliably dissipated in order to enable a constantly high charge / discharge performance and to guarantee the service life and safety of the battery. On the other hand, the battery must be heated quickly and effectively in winter to keep the range losses at cold temperatures within limits. Intelligent thermal management systems can have an extreme impact on the overall efficiency of the battery, especially in winter. Since, in contrast to the combustion engine, there is hardly any usable energy loss, an intelligent interconnection of the thermal systems for the battery, electric machine, power electronics and passenger compartment makes sense.
According to experts, the lithium-ion battery with its current technology has not yet reached the end of its development, but there are limits to the energy densities of battery solutions currently on the market. At present, specific energies of about 230Wh/kg are possible. Experts forecast a maximum increase to 300Wh/kg to 350Wh/kg for current technologies. For even more powerful batteries, the technology at cell level must be changed more profoundly. Numerous companies and institutions are working at high speed on this today. Some promising technologies can be found already, and many of them have proven to work on a laboratory scale.
Solid-state batteries are one example. With these, it can be possible to reach up to 500Wh/kg. In this case, a different conductor, which consists of solid powder rather than liquid, makes it possible. The powder is much more voltage stable than the liquid electrolytes currently used. This technological update opens up new possibilities. It allows the use of new electrode materials and raises the cell voltage from the previously possible 3.6-3.8V to up to 5V. The ultimate outcome is generation of a higher energy density. Tests have been carried out with promising results for this technology, however a major challenge still lies in the economical series production.
Additionally to the profound knowledge of the drivetrain, hofer powertrain as a system supplier has built up extensive, strong know-how around battery technologies in recent years. Battery analysis, battery testing and battery development have grown into important areas of competence and business goals at hofer powertrain's Nürtingen location.
Thanks to the most modern test facilities, combined with the knowledge and persistency of our battery experts, we have the possibility to analyze battery concepts in house. Our competencies reach beyond identification of potentials and implementation. We provide a complete battery development process from conceptualization, design and simulation, testing and validation to series production, if desired, with a clear requirements analysis in advance.
“Never stand still” is what hofer powertrain lives by. Cooperations with universities and professors bring lively exchanges, new perspectives and constantly challenge us. We make sure that research findings are implemented quickly and efficiently for our customers.
In this light, the modular battery design kit hofer powertrain ULTEVATE was developed. Thanks to the modular design of standardized VDA battery modules, practically all requirements regarding size, installation space and capacity can be met. Furthermore, smaller quantities can be produced at reasonable costs. The interchangeability of the VDA modules and the cooperation of hofer powertrain with different cell manufacturers ensure the greatest flexibility in the selection of cells. Individual design preferences between high power or high energy batteries can be considered, and special requirements, regarding safety, can be fulfilled. The specially developed battery management system guarantees state-of-the-art battery control and efficient integration of the thermal management into the overall vehicle in line with the most individual requirements.
The result is batteries that can be charged to 80% in only 12 minutes. This powerful high-energy battery has a capacity of 86.5kWh and is good for ranges of more than 500km. With a constant discharge power of 430kW (up to 690kW for short periods), it hardly sets any limits for the drive power of the electric motors, even in luxury class vehicles. Furthermore, within the scope of a research project, it proved possible, to build batteries which can be charged to 80% of their capacity in only 5 minutes and to 100% in 8 minutes.
Such technological progress is made possible by our extensive testing landscape. Starting with cell characterization, through typical electrical and thermal tests of battery modules and battery packs to endurance runs, the complete spectrum of development can be mapped. Validation and certification in compliance with all current standards (LV124, ISO26262, UN38.3 among others) can also be carried out while running environmental tests and abuse tests under appropriate safety measures.
For specific requirements we design individual testing procedures supporting you with a cost- and time efficient approach towards the completion of your project.
Exciting times for batteries are ahead and by delivering the solutions of tomorrow today, we are as well.
Come along and join us on our journey towards the future of battery solutions!
