Dangers of Thermal Runaway: The Reaction Behind E-bike Battery Fires

Lithium-ion batteries have transformed the way we power everything from portable electronics to micromobility vehicles. They offer high energy density and rechargeable convenience at a relatively low cost. With the global market for e-bikes forecast to hit $120 Billion by 2030 - up from $37.47 billion in 2022 - these two-wheeled vehicles are here to stay. Micromobility growth is truly set to be massive: consider this figure doesn't even include the other types of battery powered vehicles on our streets such as scooters or hoverboards.

While rare, thermal runaway can happen anywhere and at any time.

While they offer a viable alternative to car travel and help reduce emissions, these battery powered vehicles aren't without risk. A quick Google search will show a potentially deadly phenomenon known as thermal runaway is to being discussed everywhere from Wired to Reddit. This process - marked by rapid and uncontrolled temperature escalation within the battery - is no joke.

What is thermal runaway in e-bikes?

At its core, thermal runaway in lithium-ion batteries begins when a triggering event causes one or multiple battery cells to deteriorate. This event may stem from an internal fault within the battery, such as a manufacturing defect or damage to the cell's internal structure resulting in a short circuit. This is why it's suggested to replace a battery after a drop or a crash. Similarly factors like overcharging or exposure to extreme temperatures can also serve as catalysts for thermal runaway. It can be easy to forget but a bike battery is storing an immense amount of energy. A 350Wh e-bike battery could charge your smartphone around 32 times. Release that amount of energy quickly and the impact can be catastrophic.

A simplified example of how the heat from one cell can rapidly impact those adjacent to it.

E-bike battery fires are of particular concern because of the concept of thermal propagation. This is where the heat generated by one battery cell experiencing thermal runaway can swiftly spread to adjacent cells

within the battery pack. This is otherwise known as a chain reaction.

Once initiated, thermal runaway triggers a chain of exothermic (heat-releasing) reactions within the battery cell, leading to the production of heat and the release of volatile gases. As pressure builds within the battery and its cells, its internal structure begins to deteriorate, ultimately resulting in the venting of highly flammable vapor. Heat + pressure + flammable gases = prime conditions for fires and explosions.

In response to this hazards, governments around the world are increasingly imposing safety measures aimed at preventing and mitigating lithium-ion battery fires. Major cities such as New York and London have passed their own rules, and even the U.S. federal government recently managed to actually do something, passing the EBIKE Act. We expect this to be just the start for legislation, with European countries expected to codify laws on safe battery storage in the coming years.

Understanding the intricacies of thermal runaway in lithium-ion batteries is crucial for establishing effective safety measures and averting catastrophic incidents. By prioritizing safety and adhering to best practices, we can harness the benefits of lithium-ion technology while minimizing the associated risks to individuals and the environment.

At PowerShelter, our lockers are designed to minimize the impact of e-bike battery fires and offer time for emergency services to respond. If you'd like to understand how we address this growing issue please get in touch with us today.