Fire hazard of lithium ion batteries and related research progress

Lithium-ionBattery is a kind of high - performance rechargeable battery. Lithium ion battery is different from "lithium battery"

(LithiumBattery), the latter of the anode materials is manganese dioxide or thionyl chloride, and the cathode is lithium battery assembly without charge after the completion of the reservoir has electricity, in the process of charging and discharging cycle to cause internal short circuit batteries, lithium crystallization and usually is prohibited from charging, therefore, should not be lithium ion battery "lithium battery" for short.

The original idea of using lithium in electric discharge originated from the American inventor Edison in the 19th century, who proposed that Li+MnO2=LiMnO2 is the REDOX reaction of electric discharge. But because the chemical properties of lithium is very lively, the processing, storage, use of the requirements are very high, so for a long time has not been used. In the 1980s, bell LABS successfully developed the first rechargeable lithium ion graphite electrode battery. 1991 SONY corp. released the first commercial lithium-ion battery. Since lithium-ion battery technology rapid development, because of the high energy density (mass and volume than nickel cadmium or nickel metal hydride batteries of the same capacity to reduce more than 50%, the energy density of 540 ~ 720 kj/Kg), high open circuit voltage (monomer voltage from 3.3 V to 4.2 V, the equivalent of three series of nickel cadmium or nickel metal hydride batteries), big output power (300 ~ 1500 / Kg), no pollution (do not contain harmful heavy metals such as cadmium, lead, mercury), high cycle life, no memory effect, charging fast, wide working temperature range (20 ~ 60 ℃), and other advantages, It is widely used in consumer electronics, military products,special products and other fields. With the rapid development of electric vehicle technology, lithium ion battery has become an important source of power for electric vehicles and hybrid electric vehicles. It is estimated that the lithium ion battery market will expand by 20% every year. In 2011, the global lithium ion battery market will reach 8 billion usd, and will reach 18 billion usd in 2020.

2. Lithium ion battery fire overview

With the wide application of lithium ion batteries, the fire risk of lithium ion batteries has gradually emerged. Many influential fire accidents have occurred at home and abroad, and large-scale recalls of related products have been triggered.

2.1 fire in the field of lithium ion battery use and transportation

In 2006, a dc-8 cargo plane of an American express company was forced to make an emergency landing after its laptop battery caught fire.

In 2010, one of its Boeing 747 cargo planes crashed in dubai after its lithium-ion batteries caught fire. To this end, the United States federalspecial administration (FAA) repeatedly on the lithium ion battery air transport process safety warning, the international civilspecial industry has also put forward strict restrictions on the transport of lithium ion battery.

2.2 lithium ion battery recycling field fire

November 7, 2009 in Trail, Canada, the lithium ion battery recycling warehouse fire, is the largest impact of this kind of fire accident. The 6,500m2 warehouse, located on the Banks of the Columbia river in southern British Columbia, is owned by Anaheim, calif.-based TOXCOInc. In August 2009, the company received a $9.5 million special grant from the U.S. department of energy to develop recycling technology for lithium-ion batteries.

In case of fire, the warehouse has a large amount of recycled lithium battery and lithium ion battery, including small mobile phone, notebook computer battery and high-power battery used in electric cars. After the fire broke out, it quickly entered the fierce burning stage, and the local government launched the regional emergency response linkage mechanism. The fire was so fierce, and the fear that lithium hydroxide and hydrogen would react with water to make it burn even more fiercely, that firefighters didn't shoot a lot of water, but kept the fire at the periphery to prevent it from spreading. The fire did not fully burn out until the next afternoon, causing some damage to the local environment. The cause of the fire has not been determined, it is estimated that the storage of lithium batteries in the warehouse short circuit overheating, high temperature caused by combustion.

2.3 the fire danger of lithium ion battery for vehicle is of great concern

As an important part of promoting the development of new energy, countries attach great importance to electric vehicles and hybrid vehicle technology. It is estimated that the number of electric vehicles in the United States will reach 1 million in 2015, and the number of electric vehicles produced and sold in China will reach 500,000. Lithium-ion batteries are the most widely used form of energy for electric vehicles. In recent years, there have been many electric vehicle fires related to lithium ion batteries at home and abroad.

On January 7, 2010, a fire broke out in the garage of urumqi bus company on a pure electric bus with a brand of "dual electric" super capacitor and lithium ion battery mixed in. (the car was put into storage due to cold weather on December 23, 2009 and caught fire 15 days later.)

On April 11, 2011, an electric taxi caught fire while driving in hangzhou. On July 18, 2011, a pure electric bus in Shanghai spontaneously ignited due to overheating of its lithium iron phosphate battery.

Since May 2011, the potential fire hazard of lithium ion battery for electric vehicles produced by an American automobile company has attracted great attention from the international automobile industry and the fire protection industry.

The company production of the world's first application of iron phosphate lithium-ion battery plug-in petrol-electric hybrids, by the national highway traffic safety administration (NHTSA) four front and side crash tests, get 5 star safety rating, but three weeks later on June 6, a crash test prototype within the warehouse fire, the fire in the battery compartment. During the collision, the battery compartment was penetrated by the transverse rigid components under the driver's seat, resulting in damage to the coolant circulation system of the lithium ion battery, liquid leakage, short circuit and fire.

In September 2011, NHTSA has carried on the 5th to the car crash test no abnormalities are found, then specifically for the vehicle's lithium-ion battery pack for 6 times test, two groups of cells within a week after the crash test fire successively, the third battery arc discharge and generate fire occurs, the fourth group battery contact overheating phenomenon, with five cells appear slow discharge (confirmed after has nothing to do with the collision), 6 battery fire.

In November 2011, NHTSA and the U.S. department of energy officially launched a product defect investigation into the vehicle, and in three tests, two more prototype vehicles caught fire. This result prompted NHTSA to launch a special investigation into the lithium ion battery pack of this car in 2011. The automobile company immediately put forward the improvement plan of adjusting the transverse rigid components to protect the battery compartment, and installed the cooling liquid level sensor in the battery pack, and recalled and reformed more than 8,000 vehicles sold.

In December 2011, the improved sample car passed the collision test without any abnormality.

In January 2012, a subcommittee of the house oversight committee held a joint hearing with the U.S. government's economic reform commission.

In March 2012, the company announced that it would suspend production of the car for five weeks from the 19th of the month until April 23rd. There have been no reports of fires in actual use.

3. Current status of international studies on fire risk of lithium ion batteries

Up to now, countries have not developed safety storage standards for lithium ion batteries and fire rescue operations procedures. To fill this gap, many countries and organizations are carrying out relevant basic theory and applied technology research.

The national fire protection association (NFPA) has been concerned about the fire safety of lithium ion batteries for a long time. With the support of the us department of energy, it has carried out a number of special research and training programs with institutions such as the American association of automobile engineers (SAE) and enterprises such as general motors. On October 21-22, 2010, SAE and NFPA jointly hosted the first electric vehicle safety standards summit, which identified three key areas of safety standards for electric and hybrid vehicles: vehicle, production environment and emergency response. Battery safety was listed as a top issue. From September 27 to 28, 2011, one of the focuses of the second electric vehicle safety standards summit was the safety of on-board batteries and commercial transportation and storage batteries, and six key research directions were subdivided:

Fire hazard and safety performance of batteries;

Requirements for fixed and mobile fire extinguishing systems for large scale commercially stored batteries; Reassessment of restrictions on battery transport in the field of international transport;

Risk of reignition after battery damage;

Extinguishing agent suitable for battery fire;

Discharge standard under normal and emergency conditions.

In 2011, the property insurance research unit (PIRG) of the NFPA fire research foundation (FPRF) launched a study on the dangers of lithium-ion battery storage and fire fighting methods. In the first stage of the study, the risk and use assessment of lithium ion battery formed by literature search pointed out that the fire risk of lithium ion battery mainly comes from its structure, especially the high energy density and the electrolyte gasification caused by the high temperature when improper charging; Meanwhile, short circuits, overcharging and water stains caused by faulty battery design and raw material defects can cause fires. The report believes that the rapid release of energy thermal runaway is the main cause of electrolyte combustion. Once thermal runaway occurs, the battery temperature rises rapidly, which either directly leads to the combustion explosion of battery materials, or the explosion caused by the intense oxidation reaction between air and lithium after the bursting of the battery shell.

Due to the limited number and scale of tests carried out, the mechanism of heat runaway is not well understood at present. In particular, the characteristics of large-scale combustion of lithium ion batteries and fire extinguishing methods need to be further studied. In August 2011, PIRG held a symposium to determine the next research direction of full-size fire simulation experiment. As the main content of the second phase of the whole project, the research and experiment in 2012 focused on the study of fire risk of two types of lithium ion batteries under large-scale storage conditions: one is small-size products, and the other is large-size products that can be used for electric vehicles and other products. Property insurance team will work with the American association of fire and share about the lithium ion batteries to store the research achievements of fire danger hierarchies, and in accordance with NFPA13 the automatic sprinkler system installation specification to carry out the relevant test, in order to help NFPA13 professional technical committee to determine the lithium ion battery storage space in the design of automatic fire extinguishing system parameters.

In July 2011, the NFPA launched the electric vehicle safety training program to train emergency responders in the safe handling of electric vehicle accidents. The program was funded by a $4.4 million grant from the U.S. department of energy under the U.S. recovery and reinvestment act. NFPA is working with NHTSA to develop emergency response procedures for pure electric vehicles and hybrid electric vehicles, with the participation of the world's major automobile manufacturers. So far, the program has trained about 800 trainers in 20 states, and more than 15,000 people have signed up for online training on electric vehicle safety. The NFPA is seeking the participation of emergency medical assistance and law enforcement agencies in training.

As a research institute specializing in the safety performance of household goods and industrial products, the institute of industrial environment and risk (INERIS) of France established the electric vehicle electrochemical energy storage research institute (STEEVE) in 2010, with the purpose of further understanding the performance of lithium ion batteries, especially to understand the mechanism of fire. The agency's researchers believe that full-scale destructive testing is necessary to truly understand the fire risk of lithium-ion batteries and determine appropriate safety measures. STEEVE plans to present its latest research report at the high risk warehouse protection symposium in Paris on June 27, 2012, aiming to analyze the fire risk of high risk goods in storage facilities and propose new fire safety protection measures.

In recent years, our country has carried out "lithium ion battery thermal hazard mechanism of mutation and explosion dynamics research", in order to reveal the lithium ion battery materials and their mutual kinetic and thermodynamic properties, the use of chemical kinetics, thermal analysis kinetics, thermal spontaneous combustion theory, mutation theory, explore the typical heat production law of lithium ion battery, the internal mutation pattern analysis of lithium ion battery explosion, for the development of lithium ion battery to provide the necessary scientific basis and technical support, to prevent the lithium ion battery fires have important theoretical and practical significance.

In recent years, Chinese scholars have carried out relevant studies on the thermal hazard of lithium ion battery materials, the mechanism of thermal runaway of lithium ion battery and the flame retardant technology of electrolyte to prevent the thermal runaway of lithium ion battery. The thermal stability of common electrolyte of lithium ion batteries, the thermal stability of anode and cathode materials under different charging states, and the thermal stability between electrolyte and anode and cathode were studied in detail by using C80 microcalorimeter and other equipment. The results show that the strong lewis acid action of PF5 in the electrolyte is the main factor to reduce the thermal stability of the electrolyte. The thermal stability of LixCOo2 and its co-existence system with the electrolyte decreases with the increase of the electric degree, while the degree of lithium implantation has little influence on the thermal stability of the co-existence system of the electrolyte and LixC6. On this basis, the dynamic and thermodynamic properties of lithium ion battery materials and their interactions are revealed.

Researchers from the Angle of fire dynamics research, the integrated use of thermal explosion theory, chemical reaction kinetics and thermodynamics theory, combining the thermoelectric coupling between under the action of lithium ion battery materials and their chemical reaction thermodynamics and kinetics characteristics of experimental study, lithium ion batteries are analyzed, the possibility of fire and explosion, proposes the lithium ion battery fire triangle theory and battery explosion theory of Semenov. On the basis of the mutation theory, the explosion process of lithium ion battery was analyzed, and the dovetail mutation was successfully obtained. In this study, the coupling of fire science theory, electrochemistry theory and mutation theory fully revealed the essential law of uncontrolled thermal explosion of lithium ion battery.

Studies have shown that leads to thermal runaway heat mainly comes from the internal chemical reaction heat, based on this, the laboratory system to study the three isopropyl benzene ester phosphate (IPPP) and toluene diphenyl phosphate ester (CDP), etc.) as lithium ion battery flame retardant additives for battery electrolyte, the positive, negative and whole cell performance and the influence law of thermal stability, and put forward the fire retardant agents inhibit the inner mechanism of the thermal runaway. Studies have shown that the addition of IPPP and CDP can not only effectively improve the safety of lithium ion battery, but also have a small impact on the electrochemical performance of the whole battery, thus providing a way to improve the safety of lithium ion battery. The above research provides necessary scientific basis and technical support for the development of lithium ion battery and has important theoretical and practical significance for preventing fire and explosion of lithium ion battery.

4. Summary

ith the expansion of lithium ion battery application, especially in the field of electric vehicle applications of large capacity lithium ion battery, lithium ion battery fire accident will significantly increased, to be carried out regarding the fire danger of basic research, to develop safety use, transport, recycling lithium-ion batteries, standards and procedures, and fire extinguishing technology research to carry out the efficient and practical.

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