Lithium-ion batteries use lithium in ionic form instead of solid metallic form, are usually rechargeable, and are commonly used to power mobile phones, laptops, tablets, cameras, power tools, and micromobility devices such as electric bikes and scooters. While lithium-ion batteries are generally considered safe，in the U.S. alone, flights are grounded on average every 10 days due to lithium-ion battery fires, according to the Federal Aviation Administration. To address this fire hazard, the causes of lithium electronic fires have been explored.
Causes of lithium-ion battery fires
The essence of lithium-ion battery fire is that the heat inside the battery is not released in accordance with the design intent, causing internal and external combustion of the ignition point of the combustible material after the fire, caused by the main reasons are external short circuit, external high temperature and internal short circuit.
Internal short circuit: due to battery abuse, such as overcharging and over-discharging caused by the branch crystal, battery production process impurities such as dust, etc., will deteriorate the generation of piercing the diaphragm, micro-short-circuit, the release of electrical energy leads to temperature rise, temperature rise brought about by the chemical reaction of the material to expand the short-circuit path, the formation of a larger short-circuit current, the accumulation of such mutually reinforcing damage, resulting in thermal runaway.
External short circuit:Take electric vehicle as an example. The probability of danger in actual vehicle operation is very low, firstly, the whole vehicle system is equipped with fuses and battery management system BMS, and secondly, the battery can withstand short-time high current impact. In extreme cases, when the short circuit point crosses the vehicle fuse and the BMS fails, a longer external short circuit will generally cause the weak point of the connection in the circuit to burn out, and seldom lead to thermal runaway of the battery. Now, more PACK companies have adopted the practice of adding fuses in the circuit, which is more effective in preventing the hazards caused by external short circuit.
External high temperature: Due to the characteristics of lithium-ion battery structure, SEI film, electrolyte, EC, etc. will decompose at high temperature, and the decomposition of electrolyte will react with positive and negative electrodes, and the diaphragm of the battery cell will melt and decompose, and the multiple reactions will lead to a large amount of heat. The melting of the diaphragm leads to an internal short circuit, and the release of electrical energy increases the production of heat. This cumulative mutual enhancement of the destructive use, the consequence is to lead to the rupture of the core explosion-proof membrane, electrolyte spraying, combustion and fire.
Specifically speaking, to understand why those batteries keep catching fire, first you need to understand how a lithium-ion battery works. On each end there’s an electrode – one is positive (the anode) and the other is negative (the cathode). In between is a liquid called an electrolyte. When charging, the lithium ions move to the anode, and when discharging they move to the cathode. Pretty simple.Problems occur when they move too fast.If it moves too fast, lithium plates begin to form around the anode, creating a short circuit and generating heat. That heat, if it builds up, can ignite the flammable electrolyte, and you’ve got a battery fire.
That’s not the only thing that can cause a short circuit. If, during the manufacturing process, small holes are created or fragments of metal are left behind in the casing, then the same thing can happen. The greater number of cells used in newer devices increases the chance of a failure.
In a lithium-ion battery, you’ll find pressurized containers that house a coil of metal and a flammable, lithium-containing liquid. The manufacturing process creates tiny pieces of metal that float in the liquid. If the battery gets hot through use or recharging, the pieces of metal can move around, much like grains of rice in a pot of water. If a piece of metal gets too close to the separator, it can puncture the separator and cause a short circuit. There are a few possible scenarios for what can go wrong in the case of a short circuit:
- If it creates a spark, the flammable liquid can ignite, causing a fire.
- If it causes the temperature inside the battery to rise rapidly, the battery can explode due to the increased pressure.
- If it causes the temperature to rise slowly, the battery can melt, and the liquid inside can leak out.
In addition, The problems of today’s lithium-ion batteries can be traced largely to dendrites, tiny threadlike structures that form on the surface of an electrode over repeated cycles of charging and discharging.
Dendrites are sharp bits of lithium metal that grow from the anode. These fibers can spread like kudzu vines into the electrolyte, pierce the separator and make their way to the cathode. It’s amazing how such tiny little things can cause so much destruction: They were responsible, for example, for the fires that grounded the worldwide fleet of Boeing 787s in 2013.
Dendrites tend to grow when the battery is overcharged, because that’s when the lithium ions migrating into the anode can no longer find a berth. Normally, the ions slip between the atomic layers of the anode, a process called intercalation, but when the space between the layers is all filled up—as can happen during overcharging—there’s nowhere else for the lithium to go but onto the surface. There they form the seeds of a metallic crystal, which grows with each new charge-discharge cycle.
That is to say, when the battery cell is overcharged, the excessive release of lithium from the positive electrode will change the structure of the positive electrode, and too much released lithium will easily fail to be inserted into the negative electrode, which will also easily cause lithium precipitation on the surface of the negative electrode. Overcharging is the main cause of overheating in lithium-ion batteries, and the needle-like lithium metal crystals on the pole pieces will trigger a micro-short circuit, and the gradually rising battery temperature will vaporize the electrolyte and increase the internal pressure of the battery pack, which will lead to intense oxidation reactions inside the battery and cause battery combustion. Further explained is that overcharging triggered combustion does not necessarily occur in the battery charging, may occur in the material is not burned, the battery shell is not propped up, with the accumulation of heat inside the battery to the natural temperature of the battery, spontaneous combustion or even explosion occurs. In lithium batteries over-discharge, will lead to the negative electrode carbon sheet layer structure collapse, when charging again to use, it is very easy to internal short circuit, triggering a fire.
Insufficient capacity of the anode of lithium-ion batteries: When the capacity of the anode part of the positive part of the lithium-ion battery is insufficient, the lithium atoms appearing during charging can not be inserted into the interlayer structure of the anode graphite, and they will precipitate on the surface of the anode, forming crystals. Long-term formation of crystals in lithium-ion batteries will lead to a short circuit, when the core is discharged sharply, there will be a lot of heat, burning the diaphragm. High temperatures will cause the electrolyte to decompose into gas, when the pressure is too high, the battery cell will explode.
Excessive water content: when charging, water can react with lithium to generate lithium oxide, so that the capacity loss of the battery cell, easy to overcharge the battery cell and generate gas, the decomposition voltage of water is low, charging is easy to decompose and generate gas, when this series of generated gas will make the internal pressure of the battery cell increase, when the shell of the battery cell can not withstand, the battery cell will explode.
Lithium-ion battery overcharging: When the battery cell is overcharged, the excessive discharge of lithium from the positive electrode will cause the structure of the positive electrode to change, and too much lithium is easily inserted into the negative electrode, which will also easily cause lithium precipitation on the surface of the negative electrode.
Lithium-ion batteries are frequently used in micromobility devices like e-bikes and scooters because they are lightweight, making them lighter to lift and easier to travel with. Although they need to be handled with care to avoid damage, they are typically safe when packaged in a hard case.
Lithium-ion batteries pack a lot of power in a small package. They have a high energy-density rate, meaning they are highly reactive and will store more energy per weight then other batteries. They contain two types of electrodes: a cathode and an anode, with a substance called polypropylene separating the two. However, since the battery is small, the protective layer is also small, and if the cathode and anode accidentally touch, the flammable liquid inside may ignite and cause the temperature to rise to more than 1,000 degrees Fahrenheit. The extreme heat will cause the pressure to build up and the battery to explode, leading to severe burn injuries.
Lithium-ion activity and low initial burst temperature, when subjected to overhead falling object impact, or by the speed of about 3.5m / s object free fall impact, in its internal instantaneous generation of 25J energy, so that the temperature of the battery rises 120 ℃, the heat quickly accumulated to the initial burst temperature of the battery, triggering thermal runaway and chain reaction type of explosion, is very likely to cause serious injuries and deaths. For example, in the early morning of May 26, 2012, Shenzhen, a BYD E6 car was hit by a luxury sports car from the left rear of the fire, resulting in the death of three people in the car.
What to do if your lithium-ion battery catches fire
To prevent injuries associated with accidents involving lithium-ion batteries, the National Fire Protection Association recommends that users always follow the manufacturer’s instructions regarding storage, use, charging, and maintenance. Certain manufacturer-authorized chargers will cycle on and off before the battery is completely charged to avoid overcharging. However, since ultra-fast chargers don’t typically cycle power, they should not be used to charge lithium-ion batteries unless the manufacturer’s instructions recommend them. Lithium-ion batteries should always be removed from the charger once they are fully charged, and should be stored in a cool, dry location away from exit doors or anything that might catch fire.
When installing lithium-ion batteries, they should be inspected for signs of damage like bulging, cracking, hissing, leaking, escalating temperature, and smoking. If any of these signs are present, the battery and device should be placed in an area away from flammable materials. Lithium-ion batteries should never be thrown away in the trash – recycling them at a battery recycling location is recommended.
Lithium batteries are dangerous when they catch fire. If a pouch or prismatic lithium-ion battery gets punctured, you must get away immediately, as these types are liable to catch fire quickly. You should alert the fire department if possible, and if no fire has erupted after 24 hours or you’ve contained a small one, you can safely remove the battery from your electrical system. If you puncture a cylindrical cell, remove the punctured cylindrical cell from your electrical system with caution as soon as you can, placing it where a fire won’t spread in case it ignites.
In the event of a lithium-ion battery fire, it should immediately be put out with water, halon (a clean agent that evaporates quickly leaving no residue), or halon replacement. When the fire is out, the remaining lithium cells must be cooled by pouring water over the battery to stop a further increase in temperature. Ice should not be used, and the battery should not be covered with water because this will trap heat. Once the fire is out, do not try to pick up the device or serious injury could result.
The degree of harm of lithium battery fire is self-evident, so we should remain cautious when using lithium batteries. Remember to never overcharge, try to use the original lithium-ion battery charger charging, stored in the appropriate temperature environment.