9V carbon battery fire hazard and related research progress

　　Lithium-ion Battery relies on the movement of lithium ions between the positive and negative electrodes to complete charging and discharging. It is a high-performance rechargeable battery. Lithium-ion battery is different from "9V carbon battery"

　　(LithiumBattery), the latter’s positive electrode material is manganese dioxide or thionyl chloride, and the negative electrode is lithium. After the battery is assembled, it stores electrical energy without charging. During the charge and discharge cycle, lithium crystals are easily formed and cause an internal short circuit in the battery. Charging is generally prohibited, so lithium-ion batteries should not be referred to as "lithium batteries" for short.

　　The original idea of using lithium for discharge originated from the American inventor Edison in the 19th century. He proposed that Li+MnO2=LiMnO2 is the redox reaction of discharge. However, due to the very active chemical properties of lithium and the very high requirements for processing, storage, and use, lithium has not been used for a long time. In the 1980s, Bell Labs successfully trial-produced the first usable lithium-ion graphite electrode rechargeable battery. In 1991, Sony released the first commercial lithium-ion battery. Since then, lithium-ion battery technology has developed rapidly. Due to its high energy density (mass and volume are more than 50% less than nickel-cadmium or nickel-hydrogen batteries with the same capacity, energy density is 540~720KJ/Kg) and high open circuit voltage (single operating voltage 3.3 ~4.2V, equivalent to three nickel-cadmium or nickel-metal hydride batteries connected in series), high output power (300~1500/Kg), pollution-free (does not contain harmful heavy metals such as cadmium, lead, mercury), high cycle life, no With the advantages of memory effect, fast charging, and wide operating temperature range (-20~60℃), it is widely used in consumer electronics, specialty products, special products and other fields. With the rapid development of electric vehicle technology, lithium-ion batteries have become an important source of power for electric vehicles and hybrid vehicles. It is predicted that the current lithium-ion battery market is expanding by 20% every year. The global market size of lithium-ion batteries in 2011 was US$8 billion and will reach US$18 billion in 2020.

　　2. Overview of lithium-ion battery fires

　　With the widespread use of lithium-ion batteries, their fire hazards have gradually emerged. There have been many influential fire accidents at home and abroad, which have triggered large-scale recalls of related products.

　　2.1 Fires in the use and transportation of lithium-ion batteries

　　In 2006, a DC-8 cargo plane of a U.S. express company made an emergency landing at the airport because the lithium-ion battery used in transporting laptops caught fire. The fire in the cargo plane continued for 4 hours, most of the cargo was burned, and three crew members were injured.

　　In 2010, a Boeing 747 cargo plane of the company crashed in Dubai due to a fire caused by a lithium-ion battery being loaded. For this reason, the U.S. Federal Special Administration (FAA) has repeatedly issued warnings about potential safety hazards during the air transportation of lithium-ion batteries, and the international civil aviation industry has also put forward strict restrictions on the transportation of lithium-ion batteries.

　　2.2 Fires in the field of lithium-ion battery recycling

　　The fire at a lithium-ion battery recycling warehouse in Trail, Canada, on November 7, 2009, was the largest fire accident of this type to date. The warehouse where the fire broke out is located on the banks of the Columbia River in southern British Columbia, with a construction area of 6,500 square meters. It belongs to TOXCO Inc., headquartered in Anaheim, California, USA. In August 2009, the company received a special subsidy of US$9.5 million from the U.S. Department of Energy to develop lithium-ion battery recycling and processing technology.

　　At the time of the fire, there were a large number of lithium batteries and lithium-ion batteries waiting for recycling in the warehouse, including small mobile phone and laptop batteries, as well as high-power batteries used in electric vehicles. After the fire broke out, it quickly entered a stage of violent burning, and the local government launched a regional emergency linkage mechanism. Due to the fierceness of the fire and the fear that lithium would react with water to form lithium hydroxide and hydrogen, which would make the burning more violent, the firefighters did not spray a large amount of water, but only controlled the fire on the periphery to prevent it from spreading. The fire was not completely extinguished until the afternoon of the next day, causing some damage to the local environment. The cause of the fire has not been determined, but it is estimated that the lithium batteries stored in the warehouse were short-circuited and overheated and burned at high temperatures.

　　2.3 The fire hazard of automotive lithium-ion batteries has attracted great attention

　　As an important part of promoting the development of new energy, various countries attach great importance to electric vehicle and hybrid vehicle technology. It is expected that the number of electric vehicles in the United States will reach 1 million in 2015, and China's production and sales of electric vehicles will also reach 500,000 by then. Lithium-ion batteries are the most widely used form of energy for electric vehicles. In recent years, many electric vehicle fires related to lithium-ion batteries have occurred at home and abroad.

　　On January 7, 2010, a certain brand of "dual-electric" hybrid pure electric bus with supercapacitor and lithium-ion battery in the garage of Urumqi City Public Transport Company overheated and caught fire due to a faulty lithium iron phosphate battery. (The car was put into storage and out of service due to cold weather on December 23, 2009, and caught fire after being parked for 15 days).

　　On April 11, 2011, a fire broke out in an electric taxi in Hangzhou while driving. On July 18, 2011, a pure electric bus in Shanghai spontaneously ignited. The reasons were all due to overheating failure of the lithium iron phosphate battery.

　　Since May 2011, the fire hazard of lithium-ion batteries for electric vehicles produced by a certain American automobile company has attracted great attention from the international automobile industry and the fire protection community.

　　The company's world's first plug-in gasoline-electric hybrid vehicle using lithium iron phosphate batteries has passed four frontal and side crash tests from the U.S. National Highway Traffic Safety Administration (NHTSA) and received a five-star safety rating. However, Three weeks later, on June 6, a crash test prototype caught fire in the warehouse. The fire started in the battery compartment. Disassembly and inspection found that the battery compartment was penetrated by the transverse rigid member under the driver's seat during the collision, causing damage to the lithium-ion battery coolant circulation system, leakage, and a short circuit, resulting in a fire.

　　In September 2011, NHTSA conducted the fifth crash test on the car and found no abnormalities. After that, it conducted six tests on the car's lithium-ion battery pack. Two sets of batteries caught fire within a week of the crash test. , the third set of batteries experienced arc discharge and produced an open flame, the fourth set of batteries overheated at their contacts, the fifth set of batteries experienced slow discharge (later confirmed to have nothing to do with the collision), and the sixth set of batteries burned out.

　　In November 2011, NHTSA and the U.S. Department of Energy officially launched a product defect investigation into this car. During three tests, two more prototype cars caught fire. This result prompted NHTSA to launch a special investigation of the car's lithium-ion battery pack in 2011. The car company quickly proposed an improvement plan to adjust the lateral rigid components to protect the battery compartment, and installed a cooling liquid level sensor in the battery pack. , recalling and modifying more than 8,000 vehicles that have been sold.

　　In December 2011, the improved prototype passed the crash test without any abnormalities.

　　In January 2012, a subcommittee of the Oversight Committee of the U.S. House of Representatives and the Economic Reform Committee of the U.S. government jointly held a hearing.

　　In March 2012, the car company announced that it would suspend production of the car for 5 weeks starting from the 19th of that month until resuming production on April 23. There have been no reports of fires involving this electric vehicle during actual use.

　　3. Current status of international lithium-ion battery fire hazard research

　　As of now, various countries have not yet formulated standards for the safe storage of lithium-ion batteries and fire-fighting and rescue operations procedures. To fill this gap, many countries and organizations are carrying out relevant basic theoretical and applied technology research.

　　The National Fire Protection Association (NFPA) has been paying attention to the fire safety issues of lithium-ion batteries for a long time, and with the support of the U.S. Department of Energy, it has jointly carried out a number of special research and training with organizations such as the Society of Automotive Engineers (SAE) and companies such as General Motors. project. From October 21 to 22, 2010, SAE and NFPA jointly held the first Electric Vehicle Safety Standards Summit, which identified three important areas of safety standards for electric vehicles and hybrid vehicles: vehicles, production environment and emergency rescue. Among them, batteries Safety is listed as a top priority. From September 27 to 28, 2011, at the Second Electric Vehicle Safety Standards Summit, one of the focuses was the safety of vehicle batteries and commercial transportation and storage batteries, and six key research directions were subdivided:

　　Fire hazards and safety performance of batteries;

　　Requirements for fixed and mobile fire-extinguishing systems for large-scale commercial storage of batteries; re-evaluation of restrictions on battery transportation in the international transportation field;

　　Risk of re-ignition after battery damage;

　　Suitable extinguishing agents for battery fires;

　　Discharge standards under normal and accident conditions.

　　In 2011, the Property Insurance Research Group (PIRG) of the NFPA Fire Protection Research Foundation (FPRF) initiated research on the storage hazards and fire extinguishing methods of lithium-ion batteries. In the first stage of the research, the "Hazard and Usage Assessment of Lithium-Ion Batteries" formed through a literature search pointed out that the fire hazard of lithium-ion batteries mainly comes from their construction, especially the high energy density and the high temperature of the electrolyte caused by improper charging. Vaporization; at the same time, short circuit, overcharging and water damage caused by defects in battery design and raw materials may cause fires. The report believes that thermal runaway that rapidly releases energy is the main cause of electrolyte combustion. Once thermal runaway occurs, the battery temperature rises rapidly. The result is either a direct combustion and explosion of the battery material, or the explosion of air and lithium after the battery shell is burst. Explodes due to violent oxidation reaction.

　　Due to the limited number and scale of tests that have been carried out, not much is known about the mechanism of thermal runaway. In particular, the characteristics of large-scale combustion of lithium-ion batteries and fire extinguishing methods require in-depth research. In August 2011, PIRG held a special seminar and determined that the next research direction is a full-scale fire simulation experiment. As the main content of the second phase of the entire project, the focus of the 2012 research test was on the fire hazard research of two types of lithium-ion batteries under large-scale storage conditions: one type is a small-size product, and the other type can be used in electric vehicles. Large size products for other products. The Property Insurance Research Group will cooperate with the National Fire Protection Association and share research results on the classification of fire hazard levels for lithium-ion battery storage, and conduct relevant tests in accordance with NFPA13 "Automatic Sprinkler System Installation Specifications" to help the NFPA13 Professional Technical Committee determine lithium-ion Design parameters for automatic fire extinguishing systems in battery storage locations.

　　In July 2011, NFPA launched an electric vehicle safety training project to provide training for emergency rescue personnel on the safe handling of electric vehicle accidents. The project received a US$4.4 million grant from the US Department of Energy in accordance with the American Recovery and Reinvestment Act. NFPA is cooperating with NHTSA to compile emergency response procedures for pure electric vehicles and hybrid electric vehicles, and the world's major automobile manufacturers are participating in relevant work. Currently, the project has carried out teacher training in 20 states in the United States, trained approximately 800 trainers, and more than 15,000 people have registered to participate in online training on electric vehicle safety. NFPA is seeking emergency medical rescue and law enforcement agency personnel to participate in the training.

　　As an institution specializing in research on the safety performance of daily necessities and industrial products, the French Industrial Environment and Risk Research Institute (INERIS) established the Electrochemical Energy Storage Research Institute for Electric Vehicles (STEEVE) in 2010 to further understand the safety of lithium-ion batteries. performance, especially to understand its fire mechanism. Researchers at the agency believe that comprehensive destructive testing is necessary to truly understand the fire hazards of lithium-ion batteries and determine corresponding safety measures. STEEVE plans to present its latest research report at the High-Risk Warehousing Protection Seminar in Paris on June 27, 2012, aiming to analyze the fire hazards of high-risk goods in warehousing facilities and propose new fire safety protection measures.

　　In recent years, our country has carried out "Research on the Thermal Risk and Explosion Mutation Dynamics Mechanism of Li-ion Batteries" to reveal the kinetic and thermodynamic properties of lithium-ion battery materials and their interactions, using chemical kinetics, thermal analysis kinetics, Basic theories such as thermal spontaneous combustion theory and catastrophe, explore the heat generation laws of typical lithium-ion batteries, analyze the inherent mutation laws of lithium-ion battery explosions, and provide necessary scientific basis and technical support for the development and research of lithium-ion batteries. It is also important for the prevention of lithium-ion batteries. Ion battery fires have important theoretical and practical significance.

　　In recent years, Chinese scholars have conducted relevant research on the thermal hazards of lithium-ion battery materials, the thermal runaway mechanism of lithium-ion batteries, and electrolyte flame retardant technology to prevent thermal runaway of lithium-ion batteries. The researchers used equipment such as the C80 microcalorimeter to conduct detailed studies on the thermal stability of electrolytes commonly used in lithium-ion batteries, the thermal stability of positive and negative electrode materials under different charging states, and the heat between the electrolyte and the positive and negative electrodes. stability. The results show that the strong Lewis acid effect of PF5 in the electrolyte is the main factor that reduces the thermal stability of the electrolyte. The thermal stability of LixCOo2 and its coexistence system with the electrolyte decreases as the degree of charging increases, and the degree of lithium insertion has an impact on the electrolyte. The thermal stability of the system coexisting with LixC6 has little impact. On this basis, the kinetic and thermodynamic properties of lithium-ion battery materials and their interactions are revealed.

　　Starting from the perspective of fire dynamics, the researchers comprehensively used basic theories such as thermal explosion theory, chemical reaction kinetics and thermodynamics, combined with experimental research on the thermodynamics and kinetic characteristics of lithium-ion battery materials and their mutual chemical reactions under thermoelectric coupling. , analyzed the possibility of fire and explosion in lithium-ion batteries, and proposed the triangle theory of lithium-ion battery fire and the Semenov theory of battery explosion. On this basis, the catastrophe theory was used to conduct mutation analysis on the explosion process of lithium-ion batteries, and it was successfully obtained that the explosion of lithium-ion batteries is a swallowtail mutation. This research couples fire science theory, electrochemistry theory and catastrophe theory to comprehensively reveal the essential rules of thermal runaway explosions in lithium-ion batteries.

　　Research shows that the heat that causes battery thermal runaway mainly comes from internal chemical reaction heat. Based on this, the laboratory systematically studied triisopropylphenyl phosphate (IPPP) and toluene diphenyl phosphate (CDP) as lithium-ion batteries. The influence of flame retardant additives on the electrical performance and thermal stability of battery electrolytes, positive electrodes, negative electrodes and full batteries is discussed, and the intrinsic mechanism of flame retardants in inhibiting thermal runaway of batteries is proposed. Studies have shown that adding IPPP and CDP can not only effectively improve the safety of lithium-ion batteries, but also have little impact on the electrochemical performance of the full battery, thus providing a way to improve the safety of lithium-ion batteries. The above research provides the necessary scientific basis and technical support for the development of lithium-ion batteries, and has important theoretical and practical significance for preventing fire and explosions of lithium-ion batteries.

　　4. Summary

　　With the expansion of the application scope of lithium-ion batteries, especially the application of large-capacity lithium-ion batteries in the field of electric vehicles, lithium-ion battery fire accidents will increase significantly. It is urgent to carry out basic research on their fire hazards and formulate plans for safe use, transportation, Standards and procedures for recycling lithium-ion batteries, and research and development of efficient and practical fire-extinguishing technologies.

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