This year's fire accident has exceeded 6,000! Why is electric bicycles frequently exploded?

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

In the early morning of September 20, a fire that occurred in a unit of happiness in Tongzhou District, Beijing, and finally caused a five-level death in the 5th floor. The culprit of the accident is the electric bicycle battery of a tenant on the third floor. On the night, the husband who leased the family took the lithium-ion battery of the electric car to charge, and then triggered this deadly fire.

From January to July this year, the electric bicycle fire in the country has reached 6462, and the average accident has more than 900 accidents. 80% of electric bicycle fire occurs when charging, most accidents cause the lithium ion battery. At the moment, the national electric bicycle has a total number of 320 million, which is equivalent to an average of 4.

4 people. Tsinghua University retired teacher, Ma Gui Long, known as "my country Electric Bicycle", said to "my country News Week", compared to electric vehicles with lithium-ion batteries, electric bicycles should not be found at the safety of lithium-ion battery safety. question.

"The lithium-ion battery pack of electric bicycles is only in parallel, and the electric car battery has several thousand sections, and the difference is one hundred times.". The less the number of batteries, the lower the battery pack, the lower the voltage, the easier the battery is safe.

However, in practice, the number of electric bicycles is higher than that in electric vehicles. Behind the safety of the electric bicycle lithium-ion battery, the exposure is the lack of mandatory standards such as the battery, charger, and the current situation in low-level development. Electric vehicle lithium-ion battery safety, not technical issues, is not scientific issues, essentially management issues.

Battery cat greasy electric bike battery is generally divided into two-lead-acid batteries and lithium-ion batteries. Simply put, lithium-ion batteries are lighter than lead-acid batteries, higher than energy (measuring battery energy density), longer life. The lithium ion battery can be different depending on the battery positive electrode material, divided into three-dimensional lithium ion battery, lithium manganate ion battery, lithium iron ion battery.

The so-called superconducting graphene battery in the market is now used as a pampina to improve the battery conductivity. However, since the added graphene performance and poor characteristics, the content is too small, and the performance of the battery cannot be fundamentally changed. The biggest advantage of lithium-ion batteries is lightweight than lead-acid batteries.

Also 48 volts, 12 security, a set of lead-acid batteries can reach around 16 kg, while the lithium ion battery is about 4 kg. But lithium-ion battery is more expensive. Common 48 volts, 24-time lead-acid battery price is approximately 350 yuan, and the three-yuan lithium-ion battery is about 600 yuan, and the price of lithium iron phosphate is substantially 900 yuan.

In China, the lead-acid battery manufacturer of electric vehicles is important is Chaoyi and Tianneng in Changxing County, Zhejiang Province. The market share of the two companies account for 70%, and the leading company of the lithium-ion battery market is Suzhou Xingheng. Heaven.

In 2018, the new national standard of electric bicycles announced that the weight of the vehicle included in the battery is allowed to exceed 55 kilograms. This provision makes the lithium-ion battery to seize the market of lead-acid batteries. In recent years, vehicles with lithium-ion batteries have been 35% in the entire 300 million electric vehicles nationwide.

The ratio of the proportion of lithium-ion battery electric vehicles has risen from 3% before the new national standard to rise to about 15%. At the moment, the eve of the majority of the transition period of more than the high-definition car is in the country, and the demand for the old or buy new car. However, the charging safety issues of electric vehicles lithium-ion batteries have not been resolved.

In the impression of the vice chairman of my country's Bicycle Association, Lu Jinlong, the honorary chairman of the Jiangsu Bicycle Electric Automobile Association, before the 2018 new national standard promulgated, the probability of the electric vehicle in the explosion incident is much lower than the present. Wuxi City Inspection and Testation Research Institute / National Light Electric Automotive and Battery Product Quality Supervision and Inspection Center Minister, researcher-level high-rise, Xue Yu explained that lithium-ion batteries are more prone to safety accidents more than lead-acid batteries. This is important to be determined by the material and structure of the battery.

The energy density of lithium ion battery is higher than lead acid batteries, and the chemical properties of lithium elements are more active than lead, and the electrolyte in the lithium ion battery is also more fun to combust to the dilute sulfuric acid electrolyte of lead-acid batteries. The lead-acid battery is in the event of an accident, and there will be a more intense reaction. The lithium ion battery will occur due to small internal resistance, the separator is thin, and the thermal out of control is blocked.

Similarly, the energy density of the ternary lithium ion battery is higher than the other, constitutes the three elements of the battery positive electrode, cobalt, and manganese is also high, so that the safety is not as good as the lithium iron phosphate ion battery. However, due to the highest energy density, the three-dimensional lithium-ion battery in the electric vehicle lithium-ion battery market has reached more than 50%. At the moment, some manufacturers have launched sodium batteries and sodium chemical properties without lighter, relatively safer, but energy density does not have lithium-ion batteries.

Ma Gui Long said that the final solution for lithium-ion battery safety is to produce solid lithium-ion batteries, that is, electrolyte is solid state. "The current lithium-ion battery is expanding, exploding because the electrolyte is liquid. Solid lithium-ion batteries are also difficulties in overcoming the world, how to combine solid electrolytes and positive negatives is the bottom difficulty.

But this technology route wants to succeed, go to the market, still needs time. In the past two years, due to the frequent accident, the electric bicycle manufacturer began to use more safety factors, and the price of lithium iron phosphate ion batteries is higher. But in the new energy electric vehicle field, the ternary lithium-ion battery is still mainstream.

In the electric bicycle industry, most of the vehicle will not produce batteries themselves, but directly customize the battery manufacturers, purchase batteries or purchase individual batteries and assemble. The head company usually works with Star Heng, Tianneng, Super Wei and other manufacturers, supplies battery. Ma Guilong said that some of the large factories producing a car lithium-ion battery will pack the battery, the internal resistance, and the group is equipped to the automobile vehicle factory, and the internal resistance, the voltage is uneven, and it is not completed.

Battery is sold to some small plants without lithium-ion battery production. These small plants are directly connected to the battery, packaged, becomes a battery pack, and then sold to some small brand electric vehicles, such as maintenance points, sales stores and other secondary markets. Such a battery between the battery is very large, which will lead to frequent accidents.

Ma Guilong said that the core of the battery in the battery is over charge. The way to form a large-capacity battery is to connect more than 10 individual batteries, and then in parallel. If there is a poor battery, there will be a battery that has soon being filled, and the other batteries have not "full".

The charger will continue to charge all of these batteries on this and "do not know". In this way, the filled battery will contain an electrolyte in the battery, and the pressure is increased, an explosion occurs in the battery. Ye Zhentao is a person in charge of the national light electric vehicle and battery product quality supervision and inspection center (CEVT) technology, is also one of the drafter of the new national standard of electric vehicles.

He pointed out that in the past two years, the first new energy vehicle battery in which it put into use begins to enter the large-scale replacement. In 2018, new energy vehicles retired lithium-ion batteries can reach 11 billion watts. In this process, there will be some retired phase-out batteries, through some small manufacturers, flow into electric bicycle fields.

"Some surfaces look at a good battery, which may have expired, there is a risk of risk failure, if you don't test it together, there will be a big danger". In the sales model of electric bicycles, the whole cars and batteries can be sold separately. When the electric bicycle is shipped at the electric bicycle, it will support the battery.

Some small companies only sell the car shelf, and the battery installation is performed by the sales point. Such sales models will make some inferior batteries through the network, after sell, install it on the electric bicycle. Such a battery flow chain is particularly obvious in the takeaway car experience.

Liu Gang is hungry and a soldier in Beijing, in 2017, so far, it has changed at least two electric vehicles and three electric vehicle batteries. Liu Gang said that when the takeae member is in purchase, it often has bought the battery. He has ride a 500 yuan Jidi second-hand electric car.

It is a large-capacity battery of 72V, 65AH Heng. It takes nearly 3,000 yuan to buy from the Internet, and the life will reach more than 100 kilometers. Pursue high speeds, long mileage is taken from the work needs, 72V has exceeded the rated voltage of the battery 48V specified by the new national standard.

Before and after 2019, he bought two groups of 72V, 20AH near the community, spent more than 3,000 yuan. The one is still used normally, and the other is not used for nearly a year. "At that time, it was new, and it may be an old battery.

". On both sides of Zhao Deng Road, Xicheng District, Beijing, there are more than ten electric bicycle stores. Some of these stores, in front of them, they do not contain batteries or exceeded electric vehicles.

The important buyers of this type of electric car are takeago. Ye Zhentao said that the domestic waste lithium ion battery has not yet established a special recycling system and set up a special recycling outlet. In the new national standard, the time period is issued, and it is found that the phenomenon of electric vehicles is eliminated by the electric vehicle.

Therefore, the new national standard has not specified, in turn, this also shows that these batteries have not been detected and flowing directly. market. Lu Jinlong said that there are dozens of production of hundreds of companies producing miscellaneous lithium-ion batteries in Dongguan, Guangdong, and the batteries produced have no security.

"It is definitely necessary", and the price is more cheaper than the big brand of 20% to 30%. He suggested that from the national level, manufacturers with lithium-ion batteries in the production of electric vehicles should be enforced. Ma Guilong said that in order to solve the problem of electric car safety, it must be determined, and the lithium-ion battery entering the field of electric bicycle must have a threshold.

The electric vehicle vehicle factory is filtered after the remaining battery, and it is not allowed to flow into the manufacturer of electric bicycle batteries. Engaged in electric bicycle battery manufacturers to have testing, reasonable group with battery capacity and qualifications to ensure battery distribution. Violators should bear strict legal responsibility.

He also said that now some well-known electric bicycle vehicle companies have played the propaganda slogan of "automotive-level lithium electricity", its true meaning, nothing more than electric vehicles, the battery gauge, this should be a basic requirement for electric bicycle batteries. After the electric bicycle battery safety accident, it reflects the lack of relevant management. Automotive lithium battery has strict mandatory access standards.

In contrast, Ye Zhentao said that "lithium-ion battery" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" GB / T36972-2018 are only a recommended standard. "Some companies have standard projects in some standards, and only specify the projects that can be detected. Or formulate company standards, avoid strict projects in implementing standards.

"There is a" overchaout "in the standard, that is, after removing the battery protection device, it is overcharged for 90 minutes. According to the standard, after the battery is over, you can't explode, fire. After charging, the protection device is installed, the battery can also use it normally.

"But according to I know, after the organism test, some products directly fire or exploded in the test. "Battery Management System and Charger Battery Management System (BMS) is an important defense line of guarding battery security. This is an electronic circuit containing a chip, also known as a protection line or protector of a battery.

The BMS lead is connected to the battery of the battery, and the use of the management battery. Electric Vehicle BMS is usually mounted on the end of a set of batteries, and the outer casing is re-encapsulated. Ma Gui Long explained that BMS has three uses: First, monitor the voltage at a high voltage, current size and battery pack temperature of each battery charge.

When a battery is charged, the BMS adjusts the current from bypass, discharge, and a certain battery monomer voltage is too low, and the battery monomer discharge voltage is equalized by adjustment. Furthermore, when the battery pack is detected, the charging current is cut off. BMS is only in a lithium-ion battery, lead-acid batteries are not easy to explode without mating BMS.

Xue Yu said, although there is no mandatory provision, the lithium-ion battery is equipped with BMS for safety considerations. In reality, the price difference between electric bicycle BMS is large, cheap, more than a dozen dollars to twenty or thirty dollars, etc. Accordingly, the function of electric car BMS, reliability is also different.

BMS with poor quality may be mounted, what is not affordable. In contrast, the BMS of the electric car can make more precise management of thousands of batteries, and the cost is also greatly improved, the price is 20,000 yuan. Xue Yu said that when the electric car lithium-ion battery is factory factory, there is a BMS that is originally supported.

If the battery is changed to high voltage, large capacity, the BMS that may be replaced and the battery is not supported, and the protection is not protected. For electric bicycles, the BMS of more than a dozen dollars can play effective protection, technology is not difficult, but the cost of cost. The charger is also an important ring.

Before and after 2016, a 22-year-old to Beijing Girl took a super-brand electric vehicle lead-acid battery to charge home. In the middle of the night, the charger has been filled with the battery, and the short circuit has occurred. After the fire, the girl will burn.

Charger producers, Chaoyou is arrived, Ma Gui Long as an expert witnesses. In the past few years, Ma Guilong has participated in the preparation of "Electric Bicycle Charger Technical Requirements" national standard, in the discussion, he strongly urges electric vehicle lead-acid battery charger manufacturers new charger to prevent thermal out-of control. This will add a number of yuan to the manufacturer, once attached to individual manufacturers, but ultimately under the efforts of everyone, the relevant provisions are written to the document.

However, "Electric Bicycle Charger Technical Requirements" GB / T36944 is a standard standard. Ye Zhentao said, after this standard, only a few companies executed, 2020 Jiangsu Provincial Market Supervision Administration took out 50 batches of charger, only 2 implementation of this recommended national standard; some companies express the implementation of the company's standards or similar standards Some security items are below GB / T36944 standard. Due to the insufficient national standard of recommendability, the State Maritorian Committee of the State Market Supervision and Management has set up the mandatory national standard of charger, and Xue Yu is responsible for drafting.

On the afternoon of September 28, this mandatory national standard was approved, and it is expected to be announced at the end of this year. Ma Guirong said that the most important thing about the lithium-ion battery charger is the communication between the BMS and charger builds each other, and implements the communication. BMS is equivalent to "mediation" between lithium-ion batteries and chargers.

Just like the doctor is the same as the patient, BMS is to charge the battery by taking the monitoring of the battery. Once the battery temperature is found, the charger should stop charging immediately. Temperature sensors are installed in the lithium ion battery pack for BMS monitoring.

This is the only way to solve the combustion of lithium ion batteries, which should be included in the mandatory national standard. The so-called a brand battery must match a factory charger, which is actually a bundle of commercial interests. Domestic electric two-wheeled car (including light-saving, electric motorcycle, exceeding standard electric vehicle) lead-acid battery charger manufacturers present a significant production company and region concentration.

The first-level market is 25 million annual sales volume, of which 70% of Zipper, Nanjing, Nanjing, Nanjing. Take 48V, 20AH specification charger as an example, the charger cost of the first-level market is about 25 yuan. The second-level market is important by the more than 70 companies in Qin Zai Town, Tianchang City, Anhui Province.

The market share accounts for 70% of the secondary market. The charger quality is lower than the first level, and the annual sales volume is about 100 million. Only charger cost is 18 yuan.

Lithium-ion battery charger is important in Wuxi Triple, Shenzhen Madi Rui and other manufacturers. Compared to the lead-acid battery charger, the lithium-ion battery charger market is still in its infancy, there is no big company, many small plants still have many production irregularities. "my country News Week" searched on the e-commerce platform, the price of lithium-ion battery charger with self-stop function is over 60 yuan, a brand has overheating, overcharge, overcurrent protection lithium-ion battery charger price 159 yuan.

Ye Zhentao said that from the analysis of supervision and spot check data, the network platform is unqualified, of which the charger unqualified rate is as high as 80%. Ma Guilong said that resolving the safety of lithium-ion batteries, it is necessary to take a lithium-ion battery, BMS, and charger, to prevent inferior lithium battery and charger from flowing into the market, otherwise, it can only be a boots. If it is just from the angle of battery pack and charger, the new cost of manufacturers will be two or 30 yuan.

"Will not exceed 50 yuan, consumers have new costs will not exceed 100 yuan. "The" grassroots industry "new country standard is not attached to the attention, Beijing has established three years of transition for exceeding the standard car. From November 1st, the super-standard cars that configure the temporary yellow card will be eliminated, and the roads on the road will be "compliance" white cards.

Before the National Day, Liu Gang found an electric car shop, selling his Yadi electric car with an old new 200 yuan, and spent 2500 yuan to buy an ingredient 72V green source electric vehicle, and in the store maintenance personnel, The electric vehicle originally set to 25km / h is changed to 50km / h, which is called release speed in the line. Regardless of the motor speed, the speed displayed on the electric vehicle dashboard still does not exceed the maximum limit of the new national standard 25km / h. Ma Guilong said that although most electric car fire accidents occur, but privately modified high-voltage, large-capacity batteries, will also bring fire safety hidden dangers.

The high voltage is high speed. When the electric vehicle is driving at a high speed, it means that the discharge current increases, the battery temperature is increased, and the possibility of new battery burning. The load will also have a large current, and another large possibility of knocking during the driving process of electric vehicles is a short acceptance of the battery positive and negative electrode.

Lu Jinlong said that in fact, the requirements of the electric bicycle lithium-ion battery should be higher than that of the automatic lithium battery. "The use environment of electric bike is more bad, bumps, weight, exposure, cold, and cars rarely face this situation, the safety of its batteries and various equipment is also better. "But at the same time, electric vehicles have limited economic capabilities, more sensitive to prices," buy cars will not care for thousands of pieces, electric bicycles may be worth 200 yuan, consumers can't accept it.

"This is also an important reason for many miscellaneous electric car batteries. Ma Guilong said that in accordance with the speed, weigh the electric bicycle into electric bicycles, electric light motorcycles, electric motorcycles, this is just a way to manage. The new national standard does not fundamentally solve the two major problems of traffic safety and fire safety of electric bicycles.

Ma Gui Long suggested that all hands should be included in the motor vehicle management. Once according to the motor vehicle management, electric vehicle riding speed is specified in the section, this can better protect traffic safety, and the management of its production and sales can also be seen from the motor vehicle. As for the vehicles used by the takeaway, special standards should be formulated, selecting qualified electric vehicle manufacturers, making corresponding standards, battery can meet the vocational needs of foreign sellers, from the takeaway small brother to join the company to change to the company Purchase vehicle.

Such takeover cars can be converted from disorder to standardization. Ye Zhentao said that the takeaway platform should also establish a regular check to ensure vehicle safety. Foreign electric bicycles are almost from my country's exports, and 70% of the lithium-ion batteries are used.

But foreign electric bicycle accident rate is not so high in China. This is because on the one hand, the electric bicycle is more electricity to power in foreign countries, and the speed will not be higher than 30km / h. On the other hand, since the export electric bicycle prices can be sold to 8,000 yuan to 10,000 yuan, manufacturers also have enough profit space to adopt quality accessories.

For example, electric bicycles exported abroad have installed BMS, and battery matching consistency is also better. Ma Guilong said that the development of the entire electric bicycle industry in China is still at a low level, and the manufacturer of electric auto parts is basically an individual. There are thousands of fireworks in the country, only dozens of dozens of good doing well.

But if supervision is strengthened, it means that the cost and price increase may result in damage to the low-income person in its consumer group. This involves the issue of government management strategy. In recent years, the electric bicycle industry has flourished, but the government departments have much higher emphasis on electric vehicles than electric bicycles.

"As for electric bicycles, it is a grassroots industry, and there is a certain difference in policies. Lu Jinlong said. Ma Guilong believes that whether it is a footprint, energy saving and environmental protection, or practicality, electric bicycles have a very superiority of electric cars.

However, in many local governments, it is high-tech to do a lithium-ion battery. It is not a high-tech. "As for electric bicycles, everyone is not interested in".

(文 刘 刘 为).

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