With a range of 1000km, the Mercedes Vision EQXX concept car looks to the future of battery technology
Never a company to rest on its laurels, Mercedes-Benz has spent just 18 months of highly focused development on the Vision EQXX, the result of a mission to break through technological barriers across the board and to lift energy efficiency to new heights.
To achieve this, development engineers needed to rethink the fundamentals from the ground up. This includes advances across all elements of its electric drivetrain as well as the use of lightweight engineering and sustainable materials. Complete with a barrage of innovative and intelligent efficiency measures, including advanced software, the Vision EQXX pushes the boundaries of efficiency.
According to Mercedes, the result is the most efficient Mercedes-Benz ever built with an energy consumption figure of less than 10 kWh per 100 kilometres and a range of more than 1,000 kilometres on a single charge using a battery that would fit even into a compact vehicle.
High Energy Density Battery
When designing the Vision EQXX, rather than simply increasing the size of the battery, Mercedes-Benz and battery experts from partner company HPP, developed a completely new battery pack achieving a remarkable energy density of close to 400 Wh/l (Watt-Hours per litre of volume). This figure is what made it possible to fit a battery pack with just under 100 kWh of usable energy into the compact dimensions of the vehicle.
According to Adam Allsopp, the Advanced Technology Director of HPP, this was like fitting the energy of earlier EQS models into the vehicle dimensions of a compact car.
“The battery has almost the same amount of energy but is half the size and 30% lighter. The battery management system and power electronics have been designed with an absolute focus on reducing losses. In achieving this efficiency milestone, we learnt a lot that will flow into future development programmes,” he says.
The substantial increase in energy density comes in part from significant progress in the chemistry of the anodes. Their higher silicon content and advanced composition mean they can hold considerably more energy than commonly used anodes. Another feature that contributed to this is the high level of integration in the battery pack. This platform created more room for cells and helped reduce the overall weight. The separate compartment for the electrical and electronic (EE) components, called the OneBox, likewise made more room for cells, with added benefits for installation and removal. The OneBox also incorporates novel safety devices with energy efficient operations that consume significantly less energy than the equivalent component in a production EV.
The battery development team also decided to experiment with an unusually high voltage. Increasing the voltage to more than 900V proved an extremely useful research tool for the development of the power electronics. The team was able to gather a great deal of valuable data and is currently assessing the potential benefits and implications for future projects.
Weighing around 495Kg, including the OneBox, the battery also draws energy evenly from the cells while the car is driving – in effect, giving it greater stamina.
The testing phase made extensive us of Software in the Loop (SiL) systems, which kept the subsequent commissioning phase with the real hardware extremely short, enabling Mercedes to drive large-scale tests early on in the project. Using this approach, the team was able to install the drive unit, flash the software and get the wheels turning on the VISION EQXX within the space of just two hours and contributed to the overall short development duration of the vehicle.
The VISION EQXX also has an advanced thermal-management system, which preserves thermal energy whilst also significantly reducing cooling drag. Both contribute to maximum efficiency.
It uses a “cooling-on-demand” concept, which provides for optimal cooling based on the prevailing circumstances. The exceptional efficiency of the electric drive unit means it generates only minimal waste heat. This helped keep the thermal management system extremely small and lightweight. The carefully engineered interaction of aero-shutters, coolant valves and water pumps ensures the electric drive unit, comprising the power electronics, electric motor and transmission, maintains the most efficient temperature balance at minimum energy cost. Technically, this system is a combination of an innovative air-flow management system and a cooling plate.
The cooling plate is installed in the vehicle floor, enabling it to take advantage of the air flowing along the underside of the Vision EQXX. This is the most aerodynamically efficient way of keeping the electric drive unit cool under normal conditions, allowing the vehicle to gain about 20km of range in the most aerodynamic mode.
Only when the weather is hot or the driving style is lively does the cooling system ramp up a notch. Shutters that are normally closed at the front of the Vision EQXX open when things heat up, and send extra cooling air along a system of air guides. The inlets for these air guides are cleverly located along the front bumper’s highest-pressure zone. Conversely, the outlets are in low-pressure zones along the top of the bonnet.
The beauty of this “cooling-on-demand” approach is that when the shutters are open, it adds only seven points (0.007) to the drag coefficient. If cooling is required when the vehicle is at a standstill, a backup cooling fan kicks in.
For cabin warmth, a heat pump takes energy generated by the drive system and from the ambient air outside to keep the cabin at the right temperature. Mercedes factored this into the overall search for efficiency and the heat pump is considered a major boost for battery range in colder parts of the world.
It recovers waste heat from the drivetrain and has an external heat exchanger that draws heat from the ambient air. Not available in previous Mercedes-Benz heat pumps, this feature increases the operating temperature range. This is especially handy for heating up the cabin quickly and is highly effective at lower temperatures.
On a regular long-distance drive, a typical electric vehicle dedicates almost two-thirds of its battery capacity to cutting its way through the air ahead, such is the importance of aerodynamics.
A huge amount of work went into integrating the painstaking passive and active aerodynamic features into the external form of the Vision EQXX. The team of engineers and designers used advanced digital modelling techniques to reach a compromise that reduces drag while retaining the Mercedes-Benz design identity.
“It usually takes around a year to finalise the form,” says head of aerodynamics at Mercedes-Benz Teddy Woll. “We had less than half of that for the VISION EQXX. Lean, agile processes and mature digital tools make collaborative work far easier, with faster decision-making and more nimble compromises. We also needed fewer models and less time in the wind tunnel. The result is a very slippery drag coefficient of just 0.17.”