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Although most of the world’s e-bikes are made in China, a lack of compulsory standards for batteries and chargers can result in tragedy

By Du Wei , Tian Ran Updated Jan.1

At midnight on September 20, a fire broke out in an apartment in Tongzhou District, southeast Beijing after an e-bike lithium battery explosion in a third-floor apartment. The fire burned quickly, engulfing the rented apartment above and killing five. The owner of the bike, a man surnamed Zhang, was arrested.  

From January to July this year, there were 6,462 electric bike fires nationwide, an average of over 900 accidents a month, taking a toll in injuries and lives. According to the Fire and Rescue Department of the Ministry of Emergency Management, 80 percent of the around 2,000 e-bike fires in China every year occur while batteries are charging, and most accidents are caused by lithium battery explosion. There are some 320 million e-bikes and e-scooters, one per 4.4 people in China.  

On May 10, an e-bike battery being transported in an elevator in a residential community in Chengdu, Sichuan Province, exploded, injuring five, including a 7-month-old baby who was left with lifealtering injuries. Beijing has regulations which say e-bikes and batteries should not be transported in residential elevators, but many residents ignore them. While more residential communities are providing e-bike charging stations outside, it requires signing up to an app and paying to charge. Many low-income workers prefer to charge at home, where it is cheaper. 
Ma Guilong, a retired Tsinghua University teacher and the first academic to study and promote e-bikes in China, told NewsChina that compared to lithium battery-powered electric cars, which require more complex technology and structure, e-bikes should not have so many safety issues. “The lithium battery pack for an e-bike is composed of dozens of serial-parallel batteries, but an electric vehicle battery pack has thousands of batteries, 100 times more [than an ebike].” With fewer batteries, pack capacity and voltage are lower, so they should be safer. Yet there are many more e-bike battery explosions than in electric vehicles, exposing a lack of mandatory standards for batteries and chargers. The safety of lithium batteries in e-bikes is not a technical or scientific problem, but a management problem.  

Lead or Lithium? 
There are two types of rechargeable batteries, lead-acid and lithium. Lithium batteries are lighter, have more storage capacity, and a longer life. Lead-acid batteries were the norm until the late 2010s, but in 2018, a new national standard for electric bikes was released, stipulating that the total weight of an e-bike including batteries should not exceed 55 kilograms. Since then, 35 percent of the 30 million new e-bikes produced nationwide use lithium batteries.  

Lu Jinlong, vice president of the China Cycling Association, said that before 2018, the number of e-bike explosions was much lower.  

Xue Yu, a manager at Light Electric Vehicle and Battery Product Quality Supervision and Inspection Center (CEVT), a government agency affiliated to the State Administration for Market Regulation in Wuxi, Jiangsu Province, said lithium batteries are more prone to accidents than lead-acid batteries, mainly due to the material and structure of the battery. Xue said lithium batteries have higher energy density than lead acid batteries, and lithium elements have more active chemistry than lead. Also, the electrolytes in a lithium battery – the liquid or paste which allows ions to move – burn easier than the dilute sulfuric acid electrolytes in lead acid batteries. Lead acid batteries can bulge or crack in an accident without causing further damage. Lithium batteries can combust because of thermal runaway, which happens when the heat produced inside a battery builds up and exceeds the amount of heat that is dissipated externally. If this occurs in a single battery, it affects adjacent batteries, which causes the runaway effect.  

Ma said the ultimate solution would be to develop a solid-state lithium battery, with the electrolytes in solid form too.  

“Now it’s easy for lithium batteries to expand and explode because the electrolytes are liquid,” Ma said. As a solid-state battery does not use a liquid electrolyte solution, it cannot combust and has no need of safety components, which makes it smaller. These batteries hold more charge and charge quicker as well. Development of a solid-state lithium battery, the holy grail of e-vehicles, is in the preliminary research stages, although a Harvard team led by Associate Professor of materials science Li Xin revealed in May 2021 that they have designed a solid-state battery which can last for the lifetime of a car, about 10- 15 years, and charge in 20 minutes, Nature reported.  

In the e-bike industry, most enterprises do not produce their own batteries, but buy custom batteries from manufacturers to assemble. Leading e-bike producers often work with lithium battery manufacturers including Phylion, Tianneng Group and Chilwee.  

According to Ma, some big manufacturers of automobile lithium batteries pack them with uniform voltage and internal resistance and sell them to auto factories, while selling lower-quality batteries with different internal resistance and uneven voltage to small, unlicensed factories. These factories connect batteries in parallel, pack them and then sell them to secondary markets such as repair shops and e-bike stores. If a battery pack is comprised of batteries of different voltages and internal resistance, it can cause accidents. Overcharging is responsible for most battery explosions, Ma said.  

“The way to form large-capacity batteries is to connect more than a dozen individual batteries in a series, and then combine them into a pack,” Ma said. “So if the configuration of the batteries is inconsistent, some batteries might be fully charged while others are not, and the battery pack continues to charge.” As a result, some batteries overcharge and heat up. The liquid electrolytes vaporize, increasing pressure which leads to an explosion.  

Ye Zhentao is technical head of CEVT and one of the drafters of the new national standard for electric vehicles. Because e-bikes and batteries are often sold separately in China, inferior batteries are often installed, Ye said. He added there is no special recycling system for waste lithium batteries or any special recycling outlets so far.  

Lu Jinlong said dozens of companies produce substandard lithium batteries in Dongguan, Guangdong Province with no safety guarantees. The price of these sub-standard batteries is normally 20-30 percent cheaper than leading brands. He suggests there should be compulsory national certification.  

Ma added that e-bike manufacturers should step up to ensure the consistency of battery panels. Violation of the regulations should lead to legal penalties.  

Battery Safety 
The Battery Management System (BMS) is an important safety component. It is an electronic circuit containing a chip, also known as the battery protective line or protective board. The BMS is usually installed at the end of a set of batteries and encased in the same box. Ma said that a BMS has three jobs: monitoring the voltage and current of each battery and the temperature of the battery pack. When a battery is fully charged, the BMS adjusts the current, and if it detects a problem, it should shut the current off.  

Xue said that although there are no mandatory regulations, lithium batteries should be equipped with a BMS for safety. In reality, prices for an e-bike BMS range from a couple of yuan up to dozens of yuan with different degrees of function and reliability. Substandard BMS may not function at all. Xue added that even if the battery has a BMS, if it is modified to have a high voltage and large capacity, the replacement BMS may not match with the batteries and thus may not function well.  

Another key safety issue lies in the chargers. Ma Guilong has consulted on preparing a national standard for “Technical Requirements for Electric Bicycle Chargers.” He emphasized that manufacturers of electric vehicle battery chargers should add a function to prevent thermal runaway while charging. Although the requirement is an official government guideline, it is just a recommended standard.  

According to Ye Zhentao, since this recommended standard was released in 2018, only a limited number of manufacturers followed it. In 2020, Jiangsu Market Supervision Administration randomly selected 50 batch es of chargers, and found only two were up to the national standard, despite many enterprises claiming they followed it.  

Due to the lack of enforcement, the National Standard Committee of the State Administration of Market Regulation started to establish a mandatory national standard for chargers, and Xue Yu was responsible for drafting it. The mandatory national standard was approved on September 28, and it is expected to be released by early 2022.  

Ma said that the most important thing for lithium battery chargers is that BMS and charger manufacturers need a communication mechanism to ensure products are safe and compatible. The BMS is equivalent to a “mediator” between a lithium battery and a charger, telling the charger exactly how to charge the battery under different conditions. Once the battery temperature is too high, the charger should stop charging immediately. The lithium battery pack should be equipped with a temperature sensor for BMS monitoring. This is the only way to solve the lithium battery combustion problem, and it should be included in the mandatory national standard.  

A property manager tests a smart surveillance system that alerts when e-bikes enter the elevator in a residential community, Haidian District, Beijing, May

Illegal Modification 
Under the implementation of the new national standard, Beijing Municipality set a three-year transition period to eliminate substandard e-bikes. In late September, Liu Gang, a takeaway delivery rider for takeout platform Ele.me, told NewsChina he spent 2,500 yuan (US$392) on a Luyuan brand e-bike with a BMS-rated voltage of 72V. Then at his request, the store changed the original factory speed limit of 25km/h to 50km/h, a common but illegal tweak known as “lifting” the speed limit.  

According to Beijing Management Rules on Non-motor Vehicles, modified e-bikes are banned in a regulation that took effect on November 1, meaning the maximum speed should be no more than 25 km/h and have a maximum weight of 55 kilograms, and all bikes should be licensed. Punishments for those caught with a non-standard e-bike range from a warning and fines to confiscation, although enforcement will be hard.  

Other provinces and regions are bringing similar rules, such as Hainan Province, which will ban modified bikes, ban owners from taking them in passenger elevators and mandate that batteries must be charged at communal points with built-in safety features. The rules go into effect from January 1, 2022.  

Ma Guilong said that although most cases of e-bike fires occur when charging, modified batteries can also cause fires. “People ride e-bikes in worse conditions than electric cars, on bumpy roads, often overloaded and exposed to harsh weather,” Lu Jinrong said.  

The new national standard does not fundamentally solve the two major problems of e-bike safety in driving and fire prevention. Ma Guilong suggested that all two-wheelers with manual speed control should be subject to traffic regulations. Once e-bikes are subject to speed limits, driving safety will improve.  

Globally, almost all e-bikes on the market are exported from China, and 70 to 80 percent use lithium batteries. But the e-bike accident rate is not as high as in China. This is because, on the one hand, maximum e-bike speeds are around 30km/h (20 mph) in the US and 25 km/h in the EU. It is also due to the high price of exported e-bikes, which in the US on average sell for between US$600-4,000, according to online blog site eBikesHQ.com. The most expensive models with carbon fiber frames sell for as much as US$14,00, the blog said. This means manufacturers can make enough profit to adopt better quality accessories. In China, the average price for an e-bike is around US$300, with lead acid battery bikes even cheaper.  

Ma said the domestic e-bike industry is still at a low level, and e-bike parts are mostly produced by small private household manufacturers. Enforced regulation means higher costs and prices which will have adverse effects on low-income consumers, who are major users of e-bikes. “It’s a government management strategy,” Ma said. “Despite the e-bike industry flourishing in recent years, the government prioritized electric cars instead.”  

Lu Jinlong sees the e-bike industry as no more than a basic industry, to which separate rules apply. Ma believes that e-bikes have advantages over electric cars in many aspects including space occupation, energy conservation, environmental protection and practicality. Yet in reality, local governments often attach more importance to and perceive lithium battery production, vehicle manufacturing and electric vehicles as high-tech industry. “But local governments often show less interest when talking about e-bikes,” Ma said.