Optimal Interconnection for Prismatic Battery Systems in Electric Vehicles

Jun 16, 2020

Thermal Management

In a previous blog, we examined the current collector busbars for the cylindrical cell in electric vehicles. Many of the electrical, mechanical and thermal requirements are also applicable to prismatic cells. However, the manner in which a battery pack in the vehicle is designed depends on the OEM´s preference. Building a battery system with fewer large prismatic cells, similar to what was used in the BMW i3, decreases the overall system complexity. Additionally, it opens the possibility of using a modular design, comparative to the new modular electric drive matrix (MEB) platform from Volkswagen. The MEB battery module platform is designed to accommodate any form of prismatic or pouch cells. However, large and more complex battery systems, like those applied by Tesla using a cylindrical cell, yield better pack density and overall enhance system reliability in the instance of a single cell failure.

The major design difference in the current collector busbar for the cylindrical cells has the interconnector directly joined onto the cell housing. Whereas, pouch and prismatic cells have individual externally located connector tabs (electrical lugs) which are joined to the interconnector. However, in modern designs individual connector tabs are being replaced by a single current collector busbar, particularly for the usage of cylindrical cell connection.

To connect the prismatic cells manufacturers typically use high thickness aluminum conductors, compared to the cylindrical cell due to the cell´s higher Ah capacity. As a benefit, the Aluminum in the current collector busbar offers large weight and cost savings.

The connection of prismatic cells in one assembly involves a similar joining process to cylindrical and pouch cells between current collector tabs or busbars and electrode foil(s) between the collector tab and the battery terminal. Ultrasonic and laser welding are most commonly used for joining current collector tabs and busbars with electrode foil and case sealing. Generally, the positive and negative terminals of large prismatic cells use mechanical nuts and bolts assembly.

Currently there is an existing design which due to complexity is able to integrate a flexible printed circuit (FPC) for sensing and control of battery cells on top of the collector busbar. This design typically accommodates voltage and temperature sensing lines for the Battery Management Systems (BMS).

Overall, we must be mindful considering the electrical cell connection is an essential element of the battery pack design and the selection of the current collector busbar for the battery cell is not always as simple. If you have any design questions or require assistance for the optimization of your design using current collector busbars for your application, Rogers’ PES experts are available to help. Please contact us, if you have any questions.

Support

Power Electronics Solutions

Find local representatives for personalized support.