Reasons for Electric Vehicle Lithium Battery Fires
With the proliferation of electric vehicles, there have been various incidents of electric vehicle battery explosions in recent years.
According to official data, most of these incidents occur during the charging process, while a smaller portion result from spontaneous combustion leading to explosions, with lithium battery fires being the most common cause among all incidents.
However, considering the maturity of lithium battery technology, why is it more prone to catching fire when used in electric vehicles?
Let’s explore the reasons behind lithium battery fires.
Reasons for Electric Vehicle Lithium Battery Fires
The fundamental cause of lithium battery ignition is the inability to dissipate heat within the battery as intended, leading to ignition after reaching the ignition point of internal and external combustion materials.
The main reasons for this are external short circuits, high external temperatures, and internal short circuits.
1. Internal Short Circuit
Currently, there are two main causes of internal short circuits in batteries: mechanical and electrochemical factors.
(1) In cases of mechanical mishandling, the most common scenario is when the battery experiences compression or puncture, leading to physical damage.
This can result in the battery separator being punctured, creating a direct connection between the positive and negative electrode plates, causing an internal short circuit and the release of significant heat.
(2) Battery abuse, such as overcharging, overdischarging leading to dendrite formation, and impurities or dust in the battery production process, can trigger electrochemical instability.
These factors worsen the formation of punctures in the separator, leading to micro-short circuits.
The release of electrical energy increases the temperature, and the temperature rise triggers chemical reactions in the materials, which further expands the short-circuit path, resulting in a larger short-circuit current. This cumulative and reinforcing destruction leads to thermal runaway.
2. External Short Circuit
Taking electric cars as an example, the probability of hazardous events occurring during actual vehicle operation is very low for two reasons:
- The entire vehicle system is equipped with fuses and aBattery Management System (BMS).
- The battery can withstand short-duration high-current impacts.
In extreme cases, the short circuit point bypasses the vehicle’s fuse, and simultaneously, the BMS fails.
A relatively long-duration external short circuit generally results in the burning of weak points in the circuit, rarely causing the battery to undergo a thermal runaway event.
Nowadays, many PACK (battery pack) companies adopt the practice of adding fuses in the circuit, which is more effective in preventing the harm caused by external short circuits.
3. External High Temperature
Due to the characteristics of lithium battery structure, the SEI film, electrolyte, EC, etc., will undergo decomposition reactions at high temperatures.
Moreover, the decomposition products of the electrolyte will react with the positive and negative electrodes, causing the battery separator to melt and decompose, generating a significant amount of heat.
The melting of the separator leads to an internal short circuit, and the release of electrical energy increases the production of heat.
This cumulative and mutually reinforcing destructive effect results in the rupture of the battery’s explosion-proof membrane, the ejection of the electrolyte, and combustion leading to a fire.
Why do lithium batteries tend to catch fire in electric vehicles?
So why do lithium batteries tend to catch fire in electric vehicles?
The usage environment of electric vehicles is different from that of 3C digital devices, and various complex situations make it more likely for the above three reasons to cause fires.
Additionally, there are the following erroneous human factors:
(1) Many unscrupulous businesses, in pursuit of quick profits, recycle and reuse used battery cells and assemble them into battery packs.
These inferior lithium batteries enter the market without safety guarantees and can easily lead to accidents when users purchase such low-quality products.
(2) Some individuals make unauthorized modifications to the vehicle’s electrical wiring, replace batteries with higher capacity ones, or tamper with the wiring, leading to electrical faults.
Or it can happen when users purchase substandard chargers, charge for extended periods, or charge in confined spaces, among other factors, which can also lead to fires.