Special performance requirements, for example in high-performance applications, require an optimal battery design with regard to electrical and thermal behavior. In 2019, the BMZ Group developed several particularly high-performance battery modules with cylindrical cells in various designs. So far, the focus has been on the 18650 format, but the technical findings can also be applied to the new 21700 format.

The battery design with laser-welded cell connectors made of copper optimizes the performance considerably compared to steel or nickel connectors by reducing thermal losses. With the help of the powerful cooling unit, BMZ has succeeded in achieving temperature control of the battery cells via the cell poles. The cooling unit has been optimized to operate the battery cells continuously under maximum load. The advantages of the cylindrical cells can be used optimally with this concept. In addition to the classic rectangular module designs, circular and trapezoidal module designs were also developed. The electrical and thermal properties were validated in theory and practice.

The results from the development show that the battery modules with a high gravimetric energy density greater than 200 Wh/kg including the cooling unit and the suitable cell selection can emit a load of more than 10 C, i.e. in this case an output of more than 100 W per round cell in the 18650 format - a considerable value for the repetitive power requirement. The maximum operating temperature in the load profile with active cooling unit is around 70 to 80 °C. Contrary to expectations, long service lives were achieved with high loads. During the service life investigation, various scenarios could be mapped on the test stand. The cells proved to be extremely resilient and long-term stable when the active temperature control takes place via the cooling unit. In everyday operation with average user driving scenarios, much higher lifetimes can be expected, since the user does not usually operate the battery systems continuously under maximum load.

The comparative measurements of the different module designs were particularly remarkable. The circular and trapezoidal module designs were able to achieve approx. 95% of the reference performance of the classic rectangular module design with the same basic conditions and temperatures. In the future, completely new battery system forms are conceivable. BMZ is looking towards future partnerships and developments for high-performance applications.