Into the 21st century, coal and oil and other traditional non-renewable energy shortages, and traditional non-renewable energy sources lead to serious environmental pollution prompted the development of renewable, clean, efficient new energy system has been urgent.
Renewable new energy mainly includes solar energy, wind energy, tidal energy, water energy and geothermal energy, etc. Although these renewable energy resources are abundant and the development cost is relatively low, but at the same time, because of its own intermittent and fluctuating characteristics, it is difficult to be integrated into the power grid use. In order to store and reuse these renewable energy sources when they are in surplus, large-scale development of energy storage technology is essential.
Are lithium-ion batteries safe?
The current energy storage technology is mainly divided into three categories: physical energy storage, chemical energy storage and electromagnetic energy storage. Among them, chemical energy storage mainly includes liquid current batteries, storage batteries, supercapacitors and so on. Battery has become the most mature and reliable energy storage technology due to its advantages of stable voltage, safety and reliability, low price, wide range of application, abundant raw materials and high recycling rate.
According to the different materials used, the battery can be divided into lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries and so on. Among them, lithium-ion batteries are developing rapidly due to many advantages such as high energy density, high output voltage, long service life, low self-discharge rate, etc. They have been widely used in the fields of renewable energy, smart grids, distributed power generation, microgrid systems, new energy vehicles, industrial energy saving, emergency power supply, home energy storage, warehousing, logistics, etc.
With the mass electric bikes and application of lithium-ion batteries, fires and even explosions of varying degrees have occurred at home and abroad in the fields of energy storage, warehousing, and logistics. New energy fire accidents are sudden, combustion fire spreads rapidly, lasts for a long time, and the accident is potentially dangerous, accompanied by toxic gas release and explosion hazards, and the risk of re-ignition is high. Once the lithium-ion battery pack burns, it is difficult to extinguish and easy to cause secondary disasters.
What are the classifications of lithium-ion batteries?
Lithium-ion battery according to the cathode material classification mainly includes lithium cobalt acid battery, lithium manganese acid battery, nickel-cobalt-manganese ternary lithium battery, lithium iron phosphate battery and so on. At present, the most commonly used lithium iron phosphate batteries in energy storage stations, a few countries use nickel-cobalt-manganese ternary lithium batteries, commonly used power batteries are nickel-cobalt-manganese ternary lithium batteries and lithium iron phosphate batteries.
The structure of lithium-ion battery generally consists of positive electrode, negative electrode, diaphragm and electrolyte, in addition to binder, conductive agent, collector and encapsulation materials and other components of the battery. Lithium-ion battery diaphragm, electrolyte and other materials are flammable or combustible materials, easy to be thermally decomposed, and the resulting gas products are easy to burn, which leads to thermal runaway.
With the development of electric vehicles, people's electric vehicle range requirements are getting higher and higher, requiring faster and faster battery charging speed, which makes the battery in the active material content increases, activity enhancement, but also disguised as an increase in the fire risk of lithium-ion batteries; the increase in battery energy density also increases the potential for lithium-ion batteries to release energy.
Why do lithium-ion batteries catch fire?
The main reason for lithium-ion battery fire is the battery thermal runaway, when the battery thermal runaway can make the battery temperature rapidly rise to 400 degrees Celsius to 1000 degrees Celsius, and then fire, explosion and other accidents. The main reasons for thermal runaway of lithium-ion batteries can be roughly divided into mechanical abuse, electrical abuse, their own defects and high temperature environment.
Mechanical abuse includes types such as collision, extrusion and puncture. During the use and storage and transportation of lithium-ion batteries, due to extrusion, collision, puncture and other external forces, the battery cell or battery pack may be deformed, resulting in battery diaphragm damage and internal short circuit, and ultimately lead to fire. In mechanical abuse, puncture damage is the most serious, which refers to the sharp conductor piercing the battery body, resulting in a direct short circuit of the positive and negative electrodes. The puncture causes the battery to short-circuit at the puncture point, and the short-circuit area generates a large amount of heat due to the short-circuit and forms a localized hot zone, when the temperature of the hot zone exceeds the critical point, it will trigger thermal runaway, and smoke, fire or even explosion will occur. Collision, extrusion and puncture similar, are caused by a local short circuit may cause thermal runaway. The difference is that collision and extrusion are only probabilistic internal short circuits. In contrast, the generation of heat during the puncture process is more intense and has a higher probability of triggering thermal runaway.
Electrical abuse mainly includes overcharging, overdischarging and short-circuiting types, which are mainly caused by improper use of batteries. When the battery is overcharged, the positive pole voltage gradually rises, and the lithium removal process becomes difficult, which leads to a sharp increase in the internal resistance of the battery, thus generating a large amount of Joule heat, while the positive pole oxygen release sends out a large amount of heat, and the negative pole also reacts exothermically with the electrolyte after the temperature rises. When a series of exothermic reactions lead to the internal temperature of the battery rises to a certain level, thermal runaway will occur. When the battery is charging, lithium ions are deposited on the surface of the negative electrode to form lithium dendrites, which are prone to puncture the diaphragm, causing a short circuit at the positive and negative electrodes. When the battery is over-discharged, the voltage of the battery decreases, which may lead to the dissolution of the copper foil of the negative electrode, accelerating the failure of the battery. Short circuit includes two types of external and internal short circuit; external short circuit refers to the direct conduction between the positive and negative electrodes of lithium-ion batteries without passing through the load, when the external short circuit occurs, the heat generated by the battery can not be effectively dispersed, and the temperature of the battery will rise, and the high temperature triggers thermal runaway.
Self-defects mainly include burrs, impurities, process defects, inconsistency and other types. In the process of battery production, there are metal burrs around the battery pole piece or metal particles mixed in the pole piece, and under certain conditions, the burrs or metal particles pierce the isolation film causing an internal short circuit. Battery modules or battery packs require lithium-ion monomers to maintain good consistency during production and use. When there are production process defects or battery management system management defects, it will cause lithium-ion monomer inconsistency, which will lead to battery module or battery pack overall use of the process of battery monomer overcharging and self-discharge between monomers, accelerating the aging of the battery monomer, battery performance degradation, and ultimately triggered thermal runaway.
High-temperature environments include thermal shock, poor heat dissipation and other types. Batteries subject to external heat as well as internal heat generation and battery cooling system failure will form a high temperature environment. High-temperature environment will accelerate the aging of lithium-ion battery, battery performance degradation, resulting in the use of the process of battery heat increase, a vicious cycle, and ultimately triggered thermal runaway. Excessive temperature may also directly decompose the battery diaphragm material, forming an internal short circuit, which in turn triggers thermal runaway. In order to solve the problem of thermal runaway of lithium-ion batteries, we can improve the intrinsic safety of lithium-ion batteries and strengthen the external protection of two aspects. From the point of view of current research hotspots, to improve the intrinsic safety of lithium-ion batteries is mainly focused on the development of high thermal stability, can reduce or eliminate the formation of needle-like metal crystals of the anode and anode materials, the development of high temperature resistance, mechanical resistance of new diaphragms, the development of flame-retardant electrolyte, the development of low heat production of solid-state batteries and so on. Strengthen the external protection of the main optimization of the battery manufacturing process, strict control of the battery factory testing; set the battery monitoring and protection devices, and constantly improve the battery management system management level; set the battery cooling system, enhance its heat dissipation capabilities.
How to buy lithium-ion batteries?
For consumers, in order to avoid lithium-ion battery safety incidents, should do the following points:
First, when purchasing lithium-ion batteries and related products, you should choose products from regular manufacturers and use a charger that matches the voltage and current of the battery;
Secondly, when charging lithium-ion batteries and related products, they should be charged correctly according to the instructions, to avoid charging time is too long;
Third, in the preservation, movement, use of lithium-ion batteries and related products, should try to avoid the battery by bumping, extrusion and other strong external forces;
Fourth, avoid storing and using lithium-ion batteries and related products in high temperature and other environments;
Fifth, do not disassemble or dissect the battery;
Sixth, do not privately change the electrical wiring in the electric bicycle, private replacement of large-capacity batteries, which can easily lead to wire overload, short circuit.
Lithium-ion battery fire how to extinguish?
Regarding the extinguishing of lithium-ion battery fire, energy storage stations use more fire extinguishing media for heptafluoropropane, perfluorohexanone, fine water mist, vehicle-mounted fire extinguishing devices use more fire extinguishing media for dry powder and aerosols. The above extinguishing media are only effective for the initial fire of lithium-ion batteries, and in addition to water can not prevent lithium-ion batteries from re-igniting. Extinguish lithium-ion battery fire water demand, fighting time is long, will produce water pollution, generally used for the final stage of disposal can not be extinguished.
When encountering a lithium-ion battery fire, you should first wear personal protective equipment and respiratory protection equipment, and then begin to extinguish the fire.
For pure electric vehicle fires, note that in addition to treating or rescuing trapped people when you can work in close proximity, fire extinguishing and disposal should be kept 5 meters away. When extinguishing the fire, first cut off the power supply, and then in the upwind place to implement the fire, to avoid inhaling toxic smoke. Strictly prohibit the fire-fighting and rescue process on the vehicle structure and electrical components such as cutting, prying, etc., to avoid electric shock and make the battery thermal runaway expansion. Control the fire is the main part of the battery pack to continue to cool down, reduce the risk of combustion and explosion. Monitor the battery temperature in real time to prevent heat spread and re-ignition. Before the battery power is fully discharged, the vehicle wreckage should be placed in the open air and keep a reasonable safety distance from the surrounding. Vehicle wreckage should be under 24-hour monitoring and arrange professional personnel to handle it.
For storage stations and other storage of lithium-ion battery fire, fire extinguishing should be the first study of the fire, when the fire accident is in the early stages of non-explosion, it is strictly prohibited to the battery pack direct injection of water to cool the periphery around the periphery of the main control, depending on the circumstances of the extinguishing; when the lithium-ion batteries have been in a large-scale combustion or explosion, a large number of water cooling to extinguish the fire and prevent the accident from expanding. Disposal process to maintain a safe distance from the lithium-ion battery and do a good job of anti-electrocution protection, can not blindly open or break open the closed lithium-ion battery storage room on fire, to prevent explosion or explosion. Necessary on-site detection, smoke removal, explosion suppression operations can be implemented, the use of drones and other equipment to carry out firefighting, reducing personnel safety risks.
With the progress of technology, the research and development of new high-energy density, good safety lithium-ion batteries, battery management system management level, accurate, efficient, applicable, safe lithium-ion battery fire prevention and control technology and equipment research and development and application of lithium-ion battery safety will be the future development trend of lithium-ion battery safety.