Mercedes develops more flexible 800-volt battery technology

Mercedes-Benz is developing a new battery technology for electric cars in which a so-called power converter is intended to take over central tasks in the high-voltage architecture. The system is designed to provide a constant voltage of up to 800 volts regardless of the battery’s state of charge. At the same time, it could combine functions that today require separate components, including the conventional onboard charger.

Controlling cells more flexibly

At the core of the concept are programmable micro-converters that regulate energy flow at the level of individual battery cells or cell groups. Instead of permanently wiring many cells together in a fixed arrangement, individual units could be controlled, charged or integrated into the overall system as needed. This is intended to make the battery less rigid and shift more of the power electronics into the battery pack.

• The voltage is intended to remain constant at up to 800 volts, even when the state of charge changes.
• The converter modules tested so far reach up to 3 kW per module; depending on the configuration, more than 800 volts is also possible.
• Different cell groups could be charged and operated independently of one another.
• In theory, different cell chemistries in one battery pack would be conceivable, such as robust lower-cost cells together with particularly energy-dense cells.

The power converter is intended to handle both alternating-current and direct-current charging. This could eliminate the onboard charger commonly used today. Bidirectional energy transfer is also planned: the battery could not only take in electricity but, when needed, release it again, for example to external consumers or to the power grid. That would technically enable applications such as vehicle-to-load and vehicle-to-grid.

Benefits and unresolved hurdles

Mercedes associates several possible advantages with the approach: electric motors and charging electronics could be designed more easily around a stable high-voltage level, weaker cells or modules could be balanced or bypassed more precisely, and installation space as well as weight could be reduced if high-voltage components are eliminated or made smaller. However, the technology is not yet ready for series production. The many decentralized converters increase the complexity of the electronics and control software, while requirements also rise for semiconductors, cost control, long-term durability and thermal management inside the battery pack. When the power converter will be used in a production model remains open.