Why Do 18650 Batteries Explode?

Lithium-ion 18650 batteries power many of our devices today, from laptops and electric cars to medical equipment. However, they can be dangerous if handled improperly. In this comprehensive guide, as a professional 18650 battery pack manufacturer, I explain what causes 18650 battery explosions and how to prevent them.

Overview Of 18650 Lithium-Ion Batteries

18650 refers to the size of these cylindrical batteries – they are 18mm in diameter and 65mm tall. The numerals 18-650 give them their name. These batteries have higher energy density than older battery technologies, plus the ability to be recharged hundreds of times. This combination of portability and long runtimes led to the rapid adoption of 18650 lithium-ion cells across many industries.

Common uses of 18650s:

• Laptop battery packs
• LED flashlights and headlamps
• Electric bicycles
• Power tools like drills
• Electric cars like Teslas
• Vaping devices
• Solar powered battery banks
• Uninterrupted Power Supplies (UPS)

With so many lithium cells in use today, safety is paramount. LSI Keywords Under the right conditions, these batteries can catch fire or even explode.

Why Do Lithium 18650 Batteries Explode

The reactants inside a lithium ion battery are flammable. The electrolyte is a volatile liquid solvent that allows lithium ions to flow between electrodes. The cathode and anode are separated by a porous plastic film called a separator.

If that separator breaks down or the battery shorts internally, catastrophic failure can occur via thermal runaway:

1. Internal short circuit leads to rapid, uncontrolled discharge.
2. Massive current flow causes internal heating.
3. Electrolyte solvents vaporize, building pressure.
4. Porous plastic separator melts.
5. Direct contact between cathode and anode causes more discharge.
6. Thermal runaway results, battery vents hot gases/fire.

This thermal runaway chain reaction is what leads to explosion risk in 18650 lithium-ion batteries.

Key Factors In Thermal Runaway

Several scenarios can independently or jointly cause thermal runaway in 18650 cells:

Overcharging – Applying excess voltage exacerbates chemical reactions and heat generation inside a li-ion battery. This accelerates wear on internal components. Prolonged overcharging eventually leads to thermal runaway.

External Short Circuit – If something conductive bridges the positive and negative terminals externally, massive current flows through the cell and intense Joule heating results. Thermal runaway quickly follows.

Internal Short Circuit – Defects in manufacturing can leave microscopic metal shards inside a 18650 cell. Vibration and shock can cause these conductive particles to bridge cathode to anode, creating an internal short circuit. Thermal runaway follows rapidly as the cell discharges its entire capacity very quickly.

Crushing/Puncturing – Mechanical damage to the cylindrical casing exposes reactive chemicals inside to air/moisture. This can ignite the electrolyte or trigger an internal short circuit between electrodes.

High Temperature – Storing batteries above 130°F accelerates chemical degradation mechanisms that reduce performance and lifespan. Prolonged exposure to high temperatures causes separators to break down over time. This eventually leads to internal shorts and thermal runaway.

Deep Discharge – Discharging 18650 cells below 2.5 volts per cell for extended periods causes copper in the anode to dissolve, eventually shorting it. This copper dissolution also forms sharp lithium dendrites that can pierce separators. These effects set the stage for thermal runaway during recharge.

Poor Venting – Cylindrical lithium-ion cells require thermal and current interrupt devices to mitigate thermal runaway. If the internal pressure exceeds casing limits, gases also need to safely vent. 18650 batteries without sufficient safety mechanisms and venting pose explosion risks.

Age/Wear – All lithium-ion cells degrade via calendar aging and repeated charging/discharging over time. This wear manifests itself via lost capacity and higher internal resistance. Both effects generate more heat during use, while aged separators become more fragile. This combination raises the probability of thermal runaway in old 18650 batteries.

In summary, 18650 lithium-ion batteries contain highly reactive chemicals prone to chain reaction thermal runaway when damaged or mishandled. Multiple independent factors can trigger this dangerous process.

Preventing Lithium-Ion 18650 Batteries Explosions

While the risk of explosion exists, properly manufactured 18650 lithium-ion cells have integrated protection to mitigate hazards under normal operating conditions. Several best practices also reduce safety risks:

Use Quality Batteries From Reputable Manufacturers – Well engineered cells with redundant protections are less likely to fail even after prolonged aging effects take their toll. Stick to name brand 18650s from trustworthy suppliers.

Handle Cells Gently – Do not crush, puncture, or disassemble a lithium 18650 battery under any circumstances. Avoid dropping or shocking the cell. Any mechanical damage raises explosion risk.

Do Not Overheat – Do not store lithium cells where ambient temperatures exceed 130°F. Never throw batteries into a fire. Overheating accelerates aging and can directly trigger thermal runaway.

Do Not Overcharge – Use a smart battery charger that automatically stops delivering current when the 18650 cell reaches 4.2 volts. Overcharging strains internal components and heats the cell. Prolonged overcharging causes explosions.

Do Not Overdischarge – Using a li-ion battery when its voltage drops far below 3 volts per cell for extended time damages its internal structure. Recharging a deeply discharged cell spikes the risk of thermal runaway.

Avoid Short Circuits – Prevent any external short circuits across the positive and negative terminals. Use fuses or other protection upstream in any high current application. Shorts lead to extreme heat buildup within seconds.

Monitor State of Charge – Charge lithium-ion 18650 batteries before they drop below 20% state of charge to avoid deep discharge damage. Also do not leave batteries at fully charged 4.2 volts for extended periods when not in use to limit aging effects.

Handle Old Batteries With Care – Lost capacity and elevated internal resistance cause aged li-ion cells to run hotter during use. They may no longer handle charge/discharge rates considered safe when new. Higher likelihood of failure means you should charge/use old 18650 cells cautiously. Or recycle them.

By sticking to these guidelines, most lithium battery safety issues can be avoided altogether. Accidents still happen on occasion with defective cells or uninformed handling. But the vast majority of 18650 explosions are completely preventable.

The Bottom Line

Remember: lithium-ion batteries are high energy devices containing volatile chemicals prone to uncontrolled chain reactions under certain adverse conditions. While this enables the compact, lightweight, rechargeable capabilities we enjoy in modern gadgets, it also introduces non-trivial safety considerations to bear in mind during transport, storage, usage, and disposal of 18650 cells.

What precautions do you take when dealing with lithium batteries? Let me know in the comments!