Electric cars

Air-cooled batteries for electric cars explained

OWhile the inevitable tectonic shift of progression pits internal combustion engines against battery-electric drivetrains, the two struggling forms of automotive propulsion share a number of strikingly similar qualities.

Each requires careful management to get large amounts of power to the ground, and when engineers crack the code to unlock greater efficiency, bigger outputs are never far behind. That’s why it’s not hard to see the performance potential of the Mercedes-Benz EQXX concept, which is apparently a hypermiling electric vehicle that will be used by the German brand as a powertrain development tool for future electric models.

There’s no shortage of intriguing technological advancements with the EQXX, but what particularly interests us at MOTOR is the battery system and its unique form of cooling.

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Range, not outright power, was the ultimate goal of the EQXX, which Mercedes claims to have achieved by being able to drive the car 1,000km on a single charge.

It’s not just a vast battery either, with the unit slotted between the EQXX’s wheel arches having a capacity of 100kWh – fairly regular for modern EVs.

Demonstrating the link between efficiency and power, Mercedes has tasked its High Power Powertrains (HPP) – yes, the F1 engine division – with leading the charge on the EQXX.

Batteries, like combustion engines, must be cooled when operating. Traditionally, this is done with liquid.

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The dominant method of battery cooling is a “jacket” that wraps the entire unit and pumps liquid around it to keep temperatures in check.

More advanced units like those developed by Mercedes High Performance Powertrains for F1 and future AMG products pump coolant around the individual cells of a battery, rather than surrounding the entire unit as a whole.

You won’t find either system on the EQXX, which instead uses good fashionable airflow to stay cool. Yes, the circle is complete and air-cooled batteries are about to be all the rage.

The primary reason for using air instead of liquid to cool the battery is to minimize weight and, most importantly, to reduce the number of parasitic systems that divert energy from the vehicle’s propulsion activity.

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The way it works is via a shutter system in the vehicle’s subfloor, opening to allow airflow over a cooling plate for the battery and electric motor. The same system has a dual function of creating an air curtain that reduces overall aerodynamic drag, much like Peugeot’s 9X8 racer design that we featured in the October 2021 issue.

Mercedes admits the EQXX concept is a working prototype, so HPP engineers are still studying the practicality and long-term effects of a passively cooled battery.

“What we think is that each battery cell heats up, and if we know the cell well, we can control the temperature of the cell. A lot of resources go into that. We have to figure out what the best state of load,” says EQXX Powertrain Engineer Tim Wölfel.

A heat sink panel is also placed under the battery, helping to keep the unit cool, while, in what Mercedes considers a world first, active air vents have been integrated into the battery box itself. herself.

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The high-performance powertrains are also the brains behind the EQXX’s battery technology, bringing their performance-focused, motorsport-derived mindset to engineer the most efficient unit possible.

The EQXX’s battery, inverter and electronics unit are also the same as those developed by HPP for the Mercedes-AMG ONE hypercar.

Size and weight are the enemies of efficiency, something HPP knows well. To combat this, the EQXX battery does away with the usual design of packaging cells in separate enclosed modules, helping to reduce the physical dimensions of the unit. There are also clever developments in battery chemistry. Higher silicon content in the anodes means the cells can hold more energy than those found in more conventional batteries.

Sure, the EQXX isn’t a high-powered thriller, but the hunt for efficiency isn’t in vain for those who want more performance. With a weight of only 495 kg, the battery built by HPP has an energy density of more than 200 Wh/kg. More power, less weight. It is a recipe that we can follow.

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put it on ice

British company HPP has built one of the largest internal combustion engines ever – the 1.6-litre turbocharged V6 found in the back of Lewis Hamilton’s F1 car. Last year, the hybrid unit peaked at 756 kW.

lay me down gently

Linked to the EQXX’s battery, a single 150 kW electric motor is mounted on the rear axle. It is based on the same eATS unit found in the EQA and EQB. However, he also underwent the HPP treatment to maximize his effectiveness.

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captain planet

Air is not the only terrestrial element to play its part in the EQXX, the sun also helping thanks to the 117 solar panels installed on the roof. They supply a 12V system to power many auxiliary functions of the car, thus reducing the consumption of the 900V system.

There can only be one

US start-up Our Next Energy (ONE) has built a prototype battery for a Tesla Model S that exceeds the EQXX’s claimed total range by 200 kilometers. The company drove its car 1210 km as a proof of concept. To be fair to Mercedes, ONE had to use an oversized 203.8 kWh battery.

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