Bicycle battery pack with replaceable pouch cells

Abstract

This report covers the findings and considerations for the development of a reconfigurable bicycle battery pack with replaceable pouch cells.

On the path to net zero, electric vehicles will play a major role in the energy transition. As a result, battery demand is expected to rise significantly in the coming decade. To reduce the need for critical materials and prevent e-waste, it is essential to establish circular supply chains and implement effective end-of-life strategies.

Bicycle batteries consist of multiple cells, yet entire battery packs are often discarded when only a few cells fail, despite the remaining cells being perfectly reusable. One of the reasons is the excessive use of glue and solder in battery pack designs, which complicates both reuse and recycling.

In partnership with EAGLEBAT, this report explores the development of a battery pack that allows for the replacement of individual cells. Additionally, the design utilises pouch cells developed by EAGLEBAT instead of the conventional cylindrical cells typically used in bicycle batteries.

First, the context of battery design is explored, with a focus on existing bicycle batteries, their disassembly challenges, and their safety features. This phase also includes a comparison of pouch cells with other cell types, an introduction to EAGLEBAT’s pouch cell technology, and an evaluation of alternative joining techniques to replace soldering.

Second, boundaries are established to define the scope of the battery design. A vision for a reconfigurable system based on 12V modules is introduced, followed by the selection of a Battery Management System structure and an overview of the 12V module’s cell layout. Finally, design principles are formulated.

Third, ideation is started by dividing the design problem into sub-problems. Solutions for each sub-problem are generated and consequently compiled into a morphological chart. This chart, guided by design the design principles, serves as the basis for developing initial concepts. After evaluating these concepts, the focus shifts to the challenge of creating a durable, reversible tab connector. Three tab connector options are explored and through the DATUM method, the laser-welded flexible PCB tab connector is selected as the most suitable.

Ultimately, a final design concept is proposed as a demonstrator, integrating previous insights from the project. The laser-welded flexible PCB tab connector plays a central role in this design concept. The design is elaborated at cell, module, and battery pack levels, concluding with an evaluation of its overall performance.

The report then ends with a discussion of the project and with several recommendations toward the realisation of the design.