What makes phone Batteries catch Fire or Explode: Is your Phone Safe?

If you follow tech and have spent any time of YouTube, you already know Zack from JerryRigEverything. The guy who scratches, burns, and bends expensive phones to see what breaks first. The whole process is called Durability test.

One such test became dramatic. Zack bent a Pixel 10 Pro Fold until it snapped. Then it caught fire.

This time, it was the battery. Flames, smoke, the whole dramatic scene.

The video went viral in tech circles, and for good reason: watching a $1,800 phone turn into a chemical fire is objectively alarming.

But it also raises the question everyone thinks about but rarely asks: what actually makes a lithium-ion battery explode?

The answer involves chemistry, mechanical stress, and a process with an appropriately dramatic name: thermal runaway. Let’s break it down.

How Your Battery Works (When It’s Not On Fire)

Every rechargeable battery in your phone, laptop, and wireless earbuds uses lithium-ion chemistry.

At the basic level. A battery converts chemical energy into electrical energy. The electricity flows out of the battery in the form of electrons as a result of chemical reaction that happens inside the battery. A battery stores energy chemically.

The “ion” part is important lithium ions (charged atoms) shuttle back and forth between two electrodes, and that movement stores and releases energy.

Every battery has two terminals, positive terminal and a negative terminal as shown below.

Generally in an electric battery used in our electronic devices, the Positive terminal is called cathode and the negative terminal is called anode. As, you can see below in image. To get the general idea about terminals in a battery.

Here’s the basic setup inside every lithium-ion cell:

Anode (negative terminal): Usually made of graphite, this is where lithium ions hang out when the battery is charged.

Cathode (positive terminal): Typically a lithium metal oxide compound. When you use your phone, ions flow here.

Separator: A thin polyethylene membrane think, plastic wrap, but engineered that keeps the anode and cathode from touching.

Electrolyte: A liquid or gel that lithium ions travel through. It’s chemically designed to conduct ions, but not electrons.

When you charge your phone, lithium ions move from cathode to anode. When you use your phone, they flow back. The separator’s job is critical: keep the electrodes apart while letting ions pass through. As long as that separator stays intact, everything works beautifully.

The problem starts when it doesn’t.

What Goes Wrong: The Short Circuit

Battery fires don’t happen because lithium-ion chemistry is inherently unstable. They happen because something damages the carefully engineered structure that keeps things stable.

The most common failure mode is separator breakdown. When that thin polyethylene membrane gets compromised whether through puncture, crushing, bending, or manufacturing defects the anode and cathode can make direct contact. That’s a short circuit.

In a short circuit, electrons suddenly have a direct path between terminals instead of flowing through your phone’s circuitry. Current spikes dramatically. And here’s the key physics: electrical resistance generates heat. More current means more heat. A lot more heat, very quickly.

Now we get to the cascade. Thermal Runaway

Thermal Runaway: The Self-Sustaining Fire

Lithium-ion batteries are stable at normal temperatures. But once internal temperature crosses a certain threshold (usually around 80-100°C), the chemistry starts breaking down.

The electrolyte that liquid carrying ions around is flammable. It has to be; the chemicals that make good electrolytes also happen to be reactive. At high temperatures, it begins to vaporize and decompose.

The separator starts melting. Remember, it’s polyethylene basically plastic. It softens and start melting with increased temperature. As it melts, more direct contact between electrodes occurs, generating more heat.

The cathode material begins breaking down, releasing oxygen. Now you have fuel (electrolyte vapors), heat (from the short circuit), and oxygen (from decomposing cathode). That’s the fire triangle, all contained inside a sealed aluminum pouch.

This is thermal runaway: heat causes chemical breakdown, which generates more heat, which accelerates breakdown, which generates even more heat. It’s self-sustaining. Once it starts, it doesn’t stop until all the reactive material is consumed.

The result is smoke, flames, and sometimes if pressure builds up faster than the battery’s safety vents can release it : an explosion. Not a bomb-like explosion, but a violent rupture that sprays burning electrolyte in all directions.

What Happened to the Pixel 10 Pro Fold IN JerryRig Everything Video

Zack’s durability test is straightforward: he bends the phone until something breaks. With foldables, “something” is usually the hinge or inner display. With the Pixel 10 Pro Fold, it was the battery.

When he applied bending force, the internal structure of the battery deformed. Since the Foldable phones use thin Batteries. Bending them becomes relatively easy. The thin Lithium-ion cells and layered pouches they’re not designed to handle significant mechanical stress. Bending compresses the layers unevenly, and in this case, it damaged the separator badly enough to create a short circuit.

The short circuit generated heat. Heat triggered thermal runaway. Thermal runaway turned a $1,800 phone into a fire hazard in seconds.

This is the inherent risk of lithium-ion batteries under extreme physical stress.

The Galaxy Note 7: When Manufacturing Defects Cause the Same Problem

You remember the Galaxy Note 7 recall. In 2016, Samsung shipped phones with batteries that had a design flaw: the internal structure was too cramped. The positive and negative electrodes were too close together, with insufficient separator material between them.

Normal use charging, discharging, slight expansion from heat caused the electrodes to come into contact. Short circuit. Thermal runaway. Fire.

Samsung recalled 2.5 million phones. It cost them over $5 billion and became the definitive example of lithium battery safety failures.

The mechanics were identical to what happened with the Pixel 10 Pro Fold. The difference: the Note 7 didn’t require extreme bending. It failed under normal conditions because the design was flawed from the start.

Why Your Phone Is (Probably) Safe

Here’s the reassuring part: modern lithium-ion batteries in consumer devices are exceptionally safe under normal use. The failure rate is measured in parts per million. You’re statistically more likely to have issues with almost any other component in your phone.

We also cover in detail about Myths of Smartphones batteries in our post.

Manufacturers have learned from disasters like the Note 7. Current safety measures include:

Redundant separators: Multiple layers of membrane material, so a single defect won’t cause failure.

Pressure vents: Built-in weak points that release pressure before it builds to explosive levels.

Thermal cutoffs: Circuitry that disconnects the battery if temperature exceeds safe thresholds.

Charging management: Software that limits charging speed and maximum voltage as batteries age, reducing stress on degraded cells.

Rigorous testing: Drop tests, puncture tests, overcharge tests, extreme temperature tests all before a battery design gets approved for production.

Battery fires make headlines precisely because they’re rare. When one happens, it’s news. The millions of phones that charge safely every night don’t make news.

What You Should Actually Worry About

While catastrophic failure is unlikely, battery degradation is inevitable. Over time, repeated charge cycles cause microscopic damage to electrodes and electrolyte. The separator can develop tiny defects. Internal resistance increases.

Degraded batteries are more vulnerable to thermal runaway, especially under stress like fast charging or high temperatures.

Watch for these warning signs:

• Physical swelling: If your phone’s back is bulging or the screen is separating, the battery is failing. Stop using it immediately.
• Unexpected shutdowns: If your phone dies at 40% battery, internal resistance may be causing voltage drops that trigger safety shutdowns.
• Excessive heat during charging: Warm is normal. Hot to the touch is not.
• Rapid capacity loss: If your phone suddenly goes from lasting all day to needing a midday charge, something’s wrong internally.

And the practical advice nobody wants to hear: replace your battery every 2-3 years, whether it seems necessary or not. Batteries are consumables. Using a degraded battery increases risk.

Basic safety practices for Smartphone batteries:

• Don’t leave your phone in direct sunlight (heat accelerates degradation)
• Use quality charging cables and adapters (cheap chargers can deliver unstable voltage)
• Avoid extreme temperatures (both hot and cold stress the chemistry)
• Don’t charge your phone under a pillow or in enclosed spaces (limits heat dissipation)

The Pixel 10 Pro Fold fire was dramatic, but it wasn’t mysterious. Extreme mechanical stress damaged the battery’s internal structure, created a short circuit, and triggered thermal runaway. It’s the same mechanism behind every lithium-ion battery fire, from the Galaxy Note 7 to hoverboards to laptop recalls.

The good news: this requires either significant physical damage or serious manufacturing defects. Your phone isn’t going to spontaneously combust. But lithium-ion batteries do carry inherent risk, and that risk increases as they age.

Treat them with a little respect watch for warning signs, replace aging batteries, don’t subject them to extreme conditions and the odds of having a problem remain vanishingly small.

Just maybe don’t bend your foldable phone or any smartphone until it breaks. Leave that to Zack – Scratches at a level 6 with deeper grooves at a level 7