Mercedes wants to move its EVs' brakes to the middle of the chassis

Since the dawn of things with wheels, stopping power has been provided by brakes. Those brakes are traditionally discs or drums and are placed at each corner of the car, providing all four wheels with individual stopping power.

Mercedes wants to change that tradition. The invention of EV motors and regenerative braking has mostly removed the need to use regular brakes other than in emergencies. So what if we took those regular brakes, and moved them somewhere where they'd still be usable but would also improve the car?

Mid-mounted brakes would improve drivability and be more environmentally friendly
The Mercedes R&D center in Sindelfingen, Germany thinks the best place for them would be in the middle of the car. The brake discs would be contained within aluminum housings inside the same electric drive unit as the motor, transmission, and differential. A pan at the bottom of each housing would collect any brake dust and material from the pads and discs, thus eliminating a prevalent environmental pollutant. These traditional brakes would be intended to last the life of the vehicle. 

Beyond the environmental impact, mid-mounted brakes would shift weight away from the car's corners, potentially improving ride quality and enabling more aerodynamic, fully enclosed wheels. Think something similar to the Salt Flats racers.

Brake discs would squeeze the pads instead of the other way around
It gets even more interesting though. Whereas in a traditional disc braking system you have pads that squeeze a singular disc to stop the car, Mercedes's "in-drive brakes" would instead have two brake discs squeezing a spinning, two-sided, circular brake pad attached to the driveshaft.

Cooling such technology remains a challenge for engineers
What prompted such a significant change to the traditional braking system? Cooling. Both of the stationary brake discs will have coolant running through them to help dissipate the heat created by heavy braking. The last challenge is what heat exchanger to run the hot coolant through. In a regular cooling system, the coolant flows from the engine to the radiator where it is cooled down and returned to the engine.

Mercedes is considering using the battery and motor's cooling circuit for this purpose, given that it is the biggest and thus the most effective, but those components' operating temperatures would cause a problem. A lithium-ion battery is usually around 85 degrees Fahrenheit while electric motors operate at around 175 degrees Fahrenheit. Disc brakes can reach upwards of 300 degrees Fahrenheit, so running that temperature coolant into the powertrain could overheat those components.

Final thoughts
The technology is still in its testing phases so it is nowhere near close to being production-ready. I'll be the skeptic here and say that overcomplicating something that isn't broken and has worked for so many decades is just not worth it. 

Weight savings can be achieved in other ways and re-creating the brake system would not only be complicated, but it might increase the vehicles' MSRP until the technology is standardized. The last thing we need today is even more expensive cars.