They are all “lithium batteries”, so why can power banks be brought on planes, but electric bicycles always have accidents?

In recent years, fires caused by electric bicycle batteries have become a common topic in media reports. In response to this problem, many regions have begun to take strict measures, explicitly prohibiting the charging of electric bicycles and their batteries indoors, in order to avoid potential safety risks.

Data shows that in 2022, a total of 18,000 electric bicycle fires were reported nationwide, up 23.4% from 2021; in 2023, the number rose to 21,000, up 17.4% from 2022. Electric bicycle fire accidents have increased year by year, while there are very few reports of fire accidents involving small electrical appliances such as power banks and mobile phones. This raises a question: Why are electric vehicles so prone to accidents when they are all "lithium batteries", while compliant power banks can be brought on planes?

Image: AI generated

In fact, although electric bicycle batteries and small lithium battery devices we use in daily life (such as mobile phones and power banks) may be similar in materials, they are essentially different in design, usage conditions, safety characteristics, etc. These differences have a significant impact on their performance and safety, so let's talk about them in detail.

Capacity gap

The first is that the differences in design and size are significant. The capacity of e-bike batteries is much larger than that of mobile phones and power banks, and is usually measured in kilowatt-hours (kWh) or ampere-hours (Ah), while the latter are usually measured in milliampere-hours (mAh).

The battery of an electric bicycle needs to provide enough energy to support the vehicle's long-distance travel, while the battery in a mobile phone and a power bank only needs to meet the power needs of daily electronic devices. In order to meet the large capacity and high power requirements of electric bicycles, its battery is composed of dozens or even hundreds of cells, and has a management and balancing system to ensure the uniform charging and discharging of each cell, while mobile phones and power banks usually contain only a few cells and have a relatively simple structure.

Electric bicycle batteries have more cells and a more complex system, which means there are more possible points of failure. It also means that once a fire occurs, the electric bicycle battery will burn more vigorously and faster because it has more "fuel", ultimately causing greater harm.

An electric car that was charging in the stairwell suddenly caught fire and exploded three times in the short 15 seconds of the video!

Working and charging environments are different

During use, electric bicycles will encounter various extreme environmental conditions, such as high temperature, low temperature, humidity changes, vibration and impact, etc. These factors may aggravate battery aging and loss, thereby increasing safety risks.

In contrast, mobile phones and power banks are usually properly stored in a milder environment and are rarely bumped or vibrated during use, so the safety risks are relatively small.

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At the same time, people's usage habits of electric bicycle batteries, mobile phones and power banks are also different. Electric bicycle batteries often need to be charged regularly at high power for a long time, and sometimes charging is carried out without proper supervision. Some accident cases show that chargers will connect multiple sockets in series or use long wires to charge, which increases the risk of safety accidents.

In comparison, the charging power of mobile phones and power banks is usually smaller (even with flash charging technology, the power is usually not as high as that of electric vehicles), and charging behavior is more frequent and dispersed. In addition, users are more dependent on and pay more attention to these devices, so they tend to be more cautious during use and are less likely to encounter risks.

In summary, although electric bicycle batteries and small lithium battery devices are similar in basic materials, their performance, safety characteristics and safety requirements are quite different due to their essential differences in design concepts, usage scenarios and safety requirements. This makes us understand why we have to be strict with electric bicycle batteries, but are relatively relaxed about mobile phones and power banks.

So how can we make electric bicycle batteries safer?

Safety protection is no small matter

Considering that once an electric bicycle battery fails, it may cause serious consequences, the electric bicycle battery system contains more levels and higher-intensity safety protection measures, such as overcharge protection, over-discharge protection, short-circuit protection, thermal protection, etc.

At the same time, many big brands of electric bicycles are equipped with battery management systems (BMS) to monitor various parameters of the battery in real time and take measures to ensure safety when necessary. Although mobile phones and power banks also have a certain degree of battery management functions, these functions are relatively simple and their main purpose is to extend battery life and improve efficiency.

In fact, my country has made significant progress in the regulation of electric bicycles, especially through the implementation of laws and regulations such as GB17761-2018 "Safety Technical Specifications for Electric Bicycles" and CNCA-C11-16:2021 "Compulsory Product Certification Implementation Rules for Electric Bicycles", which provide electric bicycle manufacturers with clear production specifications and safety standards.

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These specifications not only set out the production requirements for electric bicycles, but also strengthen the supervision of electric bicycles through measures such as 3C certification to ensure that only certified products can enter the market. These measures have greatly improved the safety performance of newly produced electric bicycles and helped reduce safety accidents caused by product quality problems. The vast majority of electric vehicle fire accidents today are caused by electric bicycles that do not meet standards, private modifications, especially battery modifications, and improper charging methods. I believe that with the implementation of new standards, the elimination of old products, and the improvement of public safety awareness, electric bicycles will also be safer.

Planning and production

Author: Zhang Yan, PhD candidate jointly trained by Institute of Process Engineering, Chinese Academy of Sciences and University of Surrey, UK

Audit丨Shao Hanqi Engineer of Zhejiang Zhongke Lide New Materials Co., Ltd.

Planning丨Ding Zong

Editor: Ding Zong

Proofread by Xu Lailinlin