Detailed analysis of the safety of electric bicycle batteries and charging
Fire accidents related to electric bicycles are still a prominent problem in vehicle fires. In electric bicycle fire accidents, there are mainly potential safety hazards in the design and manufacture of vehicles and batteries, including the physical protection of batteries and battery packs, the design of battery management systems, and the safety performance of batteries themselves. This is also something that the production end of electric bicycles can really solve.
Table of Contents
Application of lithium ion batteries in electric bicycle
In addition to electric bicycles, lithium-ion batteries have been well applied in the field of electric vehicles, and Chinese-made lithium-ion batteries have occupied most of the global market. Data show that by the end of 2021, China’s power battery production capacity will account for about 70% of the world’s total, and among the world’s top 10 lithium battery manufacturers, China will occupy six seats.
As for electric bicycles with Chinese characteristics, in addition to lithium batteries, they also include lead-acid batteries that have been used for a long time. Lead-acid batteries have been widely used in electric bicycles, and their main advantages are low cost, safety and stability, high current discharge and high and low temperature discharge performance. The application of lead-acid batteries in electric bicycles is very mature. It is the main force of electric bicycle batteries, and the market size is close to 50 billion RMB. However, lead-acid batteries have lower energy density and are heavier for the same battery capacity.
The main advantage of lithium-ion batteries is that they have high energy density, are lighter than lead-acid batteries, and have a longer service life. The new national standard imposes strict restrictions on the weight of electric bicycles. As a result, lithium-ion batteries, which were not favored in the field of electric bicycles, have been rapidly applied. At the same time, lithium-ion batteries have the characteristics of short charging time, which meets the needs of consumers for fast charging.
However, the cost of lithium-ion batteries is relatively high, and their safety performance is worse than that of lead-acid batteries, which has laid a hidden danger for the large-scale application of electric bicycles. Divided by different technical routes, lithium-ion batteries for electric bicycles mainly include lithium iron phosphate, lithium manganate and ternary lithium batteries.
Electric bicycle lithium batteries comparison
The biggest advantage of lithium iron phosphate battery is its good safety, which is mainly reflected in its high self-ignition temperature. The lithium iron phosphate battery has a long cycle life, and can be charged and discharged more than 2,000 times under normal application conditions, but its low-temperature performance is poor, and the power loss is severe in winter, and the mileage is significantly shortened. In addition, compared lfp vs nmc, the energy density is lower than that of ternary lithium batteries.
Under the same battery energy, the volume and weight are about twice that of ternary lithium batteries, so the application ratio in electric bicycles is relatively small. The advantage of ternary lithium battery lies in its high energy density, which is an upstart in the field of electric bicycles. Contrary to lithium iron phosphate batteries, the cycle performance of lithium manganate batteries is not good.
Generally, the capacity has decayed to less than 80% when charging and discharging 700 to 800 times. Its high temperature performance is not good, and its cycle life will be significantly reduced if it is left for a long time at a temperature above 45 degrees, but its low temperature performance is good, and its safety performance is similar to that of lithium iron phosphate batteries. Now there are new technologies that can improve the high-temperature performance and cycle performance of lithium manganese oxide batteries, and are currently being accelerated in electric bicycles.
Although the performance is very different, the above three lithium-ion batteries have one thing in common. Charging at low temperatures is slow and not safe enough. The heat-resistant temperature of the separator used in lithium ions is generally between 140-180 degrees Celsius. If this temperature is exceeded, the polymer material will change from a glass state to a fluid state, resulting in direct contact between the cathode and anode, violent discharge, and fire or explosion.
From charging piles to battery swap station
One way to solve the safety problem of electric bicycles is to manage the risk of accidents and reduce the cost of accidents. In recent years, outdoor public charging and battery swap piles have gradually become a rigid demand. To realize the centralized and isolated charging of vehicles or batteries, one can use technical measures to protect the batteries, and two, it can reduce the damage to life and property in the event of an accident.
When the battery is charging, the voltage is high, which is when the electric bicycle has a high risk of catching fire. Charging outdoors can largely protect the user’s life safety. However, experts in the industry believe that the current construction of outdoor charging piles and cabinets is not enough. More importantly, the charging facilities are simple and lack the function of monitoring battery data. Many lithium battery cabinets are set up in the downstairs of high-density residents, some are close to fire sources, some have exposed wires, and some of the batteries are very old and still in use.
There are no industry standards and regulatory measures to standardize construction and operation, resulting in a high risk of accidents in outdoor charging areas. Is there a more convenient, smart and safe charging method? The motorcycle battery replacement has recently received widespread attention. Compared with the traditional charging mode, it manages the battery in a unified manner, and makes charging safer through data monitoring. At the same time, battery swapping saves the user’s time, which is equivalent to extending the battery life.
The battery is placed in a relatively airtight and constant temperature battery swap station compartment for charging. The compartment has a built-in fire monitoring device, fire extinguisher and automatic power-off switch. It can be safely charged to a certain extent in low temperature or thunderstorm weather, and the constant temperature system can avoid the lithium dendrite problem caused by low temperature charging.
The battery swap station is equipped with a digital monitoring system, and the real-time monitoring of the rechargeable battery can effectively avoid overcharging. Generally speaking, the charging environment of the battery swap stations currently on the market is better than that of ordinary charging piles.
Detailed analysis of the safety of electric bicycle batteries and charging
Fire accidents related to electric bicycles are still a prominent problem in vehicle fires. In electric bicycle fire accidents, there are mainly potential safety hazards in the design and manufacture of vehicles and batteries, including the physical protection of batteries and battery packs, the design of battery management systems, and the safety performance of batteries themselves. This is also something that the production end of electric bicycles can really solve.
Application of lithium ion batteries in electric bicycle
In addition to electric bicycles, lithium-ion batteries have been well applied in the field of electric vehicles, and Chinese-made lithium-ion batteries have occupied most of the global market. Data show that by the end of 2021, China’s power battery production capacity will account for about 70% of the world’s total, and among the world’s top 10 lithium battery manufacturers, China will occupy six seats.
As for electric bicycles with Chinese characteristics, in addition to lithium batteries, they also include lead-acid batteries that have been used for a long time. Lead-acid batteries have been widely used in electric bicycles, and their main advantages are low cost, safety and stability, high current discharge and high and low temperature discharge performance. The application of lead-acid batteries in electric bicycles is very mature. It is the main force of electric bicycle batteries, and the market size is close to 50 billion RMB. However, lead-acid batteries have lower energy density and are heavier for the same battery capacity.
The main advantage of lithium-ion batteries is that they have high energy density, are lighter than lead-acid batteries, and have a longer service life. The new national standard imposes strict restrictions on the weight of electric bicycles. As a result, lithium-ion batteries, which were not favored in the field of electric bicycles, have been rapidly applied. At the same time, lithium-ion batteries have the characteristics of short charging time, which meets the needs of consumers for fast charging.
However, the cost of lithium-ion batteries is relatively high, and their safety performance is worse than that of lead-acid batteries, which has laid a hidden danger for the large-scale application of electric bicycles. Divided by different technical routes, lithium-ion batteries for electric bicycles mainly include lithium iron phosphate, lithium manganate and ternary lithium batteries.
Electric bicycle lithium batteries comparison
The biggest advantage of lithium iron phosphate battery is its good safety, which is mainly reflected in its high self-ignition temperature. The lithium iron phosphate battery has a long cycle life, and can be charged and discharged more than 2,000 times under normal application conditions, but its low-temperature performance is poor, and the power loss is severe in winter, and the mileage is significantly shortened. In addition, compared lfp vs nmc, the energy density is lower than that of ternary lithium batteries.
Under the same battery energy, the volume and weight are about twice that of ternary lithium batteries, so the application ratio in electric bicycles is relatively small. The advantage of ternary lithium battery lies in its high energy density, which is an upstart in the field of electric bicycles. Contrary to lithium iron phosphate batteries, the cycle performance of lithium manganate batteries is not good.
Generally, the capacity has decayed to less than 80% when charging and discharging 700 to 800 times. Its high temperature performance is not good, and its cycle life will be significantly reduced if it is left for a long time at a temperature above 45 degrees, but its low temperature performance is good, and its safety performance is similar to that of lithium iron phosphate batteries. Now there are new technologies that can improve the high-temperature performance and cycle performance of lithium manganese oxide batteries, and are currently being accelerated in electric bicycles.
Although the performance is very different, the above three lithium-ion batteries have one thing in common. Charging at low temperatures is slow and not safe enough. The heat-resistant temperature of the separator used in lithium ions is generally between 140-180 degrees Celsius. If this temperature is exceeded, the polymer material will change from a glass state to a fluid state, resulting in direct contact between the cathode and anode, violent discharge, and fire or explosion.
From charging piles to battery swap station
One way to solve the safety problem of electric bicycles is to manage the risk of accidents and reduce the cost of accidents. In recent years, outdoor public charging and battery swap piles have gradually become a rigid demand. To realize the centralized and isolated charging of vehicles or batteries, one can use technical measures to protect the batteries, and two, it can reduce the damage to life and property in the event of an accident.
When the battery is charging, the voltage is high, which is when the electric bicycle has a high risk of catching fire. Charging outdoors can largely protect the user’s life safety. However, experts in the industry believe that the current construction of outdoor charging piles and cabinets is not enough. More importantly, the charging facilities are simple and lack the function of monitoring battery data. Many lithium battery cabinets are set up in the downstairs of high-density residents, some are close to fire sources, some have exposed wires, and some of the batteries are very old and still in use.
There are no industry standards and regulatory measures to standardize construction and operation, resulting in a high risk of accidents in outdoor charging areas. Is there a more convenient, smart and safe charging method? The motorcycle battery replacement has recently received widespread attention. Compared with the traditional charging mode, it manages the battery in a unified manner, and makes charging safer through data monitoring. At the same time, battery swapping saves the user’s time, which is equivalent to extending the battery life.
The battery is placed in a relatively airtight and constant temperature battery swap station compartment for charging. The compartment has a built-in fire monitoring device, fire extinguisher and automatic power-off switch. It can be safely charged to a certain extent in low temperature or thunderstorm weather, and the constant temperature system can avoid the lithium dendrite problem caused by low temperature charging.
The battery swap station is equipped with a digital monitoring system, and the real-time monitoring of the rechargeable battery can effectively avoid overcharging. Generally speaking, the charging environment of the battery swap stations currently on the market is better than that of ordinary charging piles.