Page | 003 Mechanical Abuse
As the name implies, this is where something physically impacts the battery. Dropping, crushing, and striking the battery are examples of mechanical abuse. In this scenario, the physical damage, if severe enough, may deform or tear
the separator. When the separator is compromised, there’s the potential for an internal short (the cathode and anode contacting), causing rapid heating and subsequent thermal runaway.
Thermal Abuse
Another form of abuse is from extreme temperatures. Most if not all batteries should come with a recommended operating and storage temperature range, and it’s critical to stay within these limits. In the case of thermal abuse, the separator can collapse, again paving the way for a potential internal short leading to a thermal runaway condition. This generally isn’t a problem when using the battery, but in more extreme climates it’s very easy to exceed manufacturer specifications. Think of a cordless drill or vape pen sitting in the hot interior of a vehicle in Arizona or Florida in the middle of July and you get the idea.
Electrical Abuse
The third form of abuse can happen when the battery is repeatedly overcharged or used with an incompatible charger. Even with “smart chargers” that shut off when a battery’s State of Charge (SOC) reaches 100%, there is the possibility for damage. In this instance, microscopic structures known as dendrites can form over time. Just like the part of the nerve cells in our brain that share the same name, dendrites are like tendrils that grow, and if the growth is significant enough, can pierce the separator. Again, a compromised separator can result in a short, causing thermal runaway.
Battery Quality Issues
Aftermarket batteries that are now widely available may not have the same quality and construction standards as their Original Equipment Manufacturer (OEM) counterparts and are therefore susceptible to thermal runaway. Couple this with the fact that aftermarket batteries may be used on OEM-type chargers they weren’t intended for, and the risk is compounded. Given that aftermarket batteries are typically much less costly than OEM versions, they are very attractive as replacements from a commercial standpoint and quite prolific. In fact, the number of battery fires are on the rise for this reason alone, according to an article in the Wall Street Journal. Of these causes, battery quality flaws tend to be the most common in triggering thermal runaway. Even something as simple as a tiny metal particle that gets stuck in the battery case or a design flaw in the protection circuit that is meant to prevent overcharging can cause the battery to fail. Regardless of what causes a battery to fail, it sets off a chain rection that ultimately leads to flames.
The Stages of Battery Failure
There are four stages a lithium-ion battery will go through as it fails. Though the exact process may vary depending on what triggers the failure, it will generally follow these four steps.
1. Abuse: Battery failure starts with electrical, thermal, or mechanical abuse as laid out above — assuming the battery was manufactured properly. Failure could also be triggered by a faulty design.
2. Off-gas generation: After the battery has been abused, the electrolyte solution will start to vaporize and produce flammable gasses. As those gasses accumulate, the battery’s internal temperature and pressure will increase.
3. Smoke generation: As the battery fails, it leads to a short circuit of the cathode and anode. Energy flows through
the battery rapidly, raising its temperature to more than 500°F, causing smoke to leak out of the battery. Comprised of vaporized electrolyte, the smoke is flammable, and signals the onset of thermal runaway. Because thermal runaway is a chain-reaction event, one overheated cell causes an adjacent cell to overheat until all cells within the battery are failing. It can even extend to the other batteries stored nearby.
4. Fire generation: The last phase of the cycle is fire. A fire may break out before or after thermal runaway, producing flames or an explosion should thermal runaway occur first. Either way, once a battery produces flammable smoke, it will almost certainly reach the fire phase and extend to nearby combustibles.
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How to Prevent Lithium-Ion Battery Fires
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