Why does a mobile battery explodes?

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2016-09-19 02:06

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Edited by RIPKILLER at 2016-09-18 23:44

Everyone of us must have heard about the recent case where many of Samsung's Galaxy Note7 battery is exploding isn't?

One question must have come to our mind why does the battery explodes? What are the reasons?

Well read on ...

Lets start from basic .. How does the battery works?


How your phone battery works?

The first thing we need to understand is how exactly the lithium-ion battery in your phone works. The name gives us a hint — electricity is carried from one electrode to another using charged lithium ions.

Lithium-ion batteries store, transfer and release energy because of natural chemical reactions. The battery has two electrodes — an anode and a cathode. The cathode is connected to the positive (+) connection on the battery and holds positively charged ions, and the anode is connected to the negative (-) connection and holds (you guessed it) negatively charged ions.
Between the two electrodes is what's called an electrolyte. The electrolyte in a lithium battery is (usually) an organic solvent paste that has a very large number of metallic salts (in most cases, that metal is lithium) as part of its makeup. This makes it electrically conductive — electricity can pass through it. The anode and the cathode are in the electrolyte and separated by a physical barrier so they can't touch.
When you discharge the battery (when you're using your phone and not charging it) the cathode pushes its positively charged ions away and the negatively charged anode attracts them. Electricity flows out from the anode, through your device, then back to the cathode. Yes, electricity travels through a loop and isn't "used up" by the thing being powered. When you charge your phone, the reverse happens and ions travel from the cathode through the electrolyte to the anode.

When these ions come in contact with the charged atoms in an electrode, an electrochemical reaction called oxidation-reduction (redox) frees the charged electrons to travel out through the battery contacts, which are connected to the electrodes. This continues to charge the lithium ions in the electrolyte until there aren't enough left that can hold a positive charge that's strong enough to move through the electrolyte paste, and your battery will no longer charge.
Lithium is the lightest metal — number three on the periodic table. It's also very excitable, making it easy to create a powerful chemical reaction. This makes it a near-perfect metal to use in a portable rechargeable battery. It's lightweight, easy to recharge and continues to hold a charge for a long time.

  


You must have now understood how exactly does a battery works right?

Now main topic why does it explodes? What are the reasons?


What can make a battery explode?

For starters, let's define what explode means in this case. The electrolyte paste inside a lithium-ion battery is extremely volatile. It can (and will) react violently to other metals, and has a very low (180-degrees Celsius) melting point. Inside a sealed battery casing, the pressure generated can build up until the casing is ruptured, then rapidly escape. The pressure carries out extremely hot electrolyte fluids which can cause other things to catch fire. Some lithium batteries are vented with an escape hole so they won't rupture under pressure. When the battery casing ruptures and superheated liquid filled with melted metals is expelled under pressure, it causes an explosion.

There are two easy ways to make a lithium battery explode — heat, and physical damage.
Let's look at both.


Overheating and overcharging


This is the most common reason a battery fails. Something goes wrong in the charging circuit and the input power continues to drive the chemical reaction. One place in the battery will eventually get too hot and, since it is still being charged, it can't cool down, causing what's known as thermal runaway.
In this case, the hot portion starts to generate its own heat, which makes other areas in the electrolyte overheat, and they cause more spots in the battery to overheat. The heat expands the electrolyte and creates steam, building pressure until the battery casing splits and forces out all the pressure and some very hot, very sticky (and very flammable once exposed to the air) gooey liquid.
When such a rupture happens, it can cause physical damage to the things that are close to it — when holding a phone, circuit boards and glass or plastic. These materials can also catch fire from the heat, which in turn makes the escaped electrolyte ignite and act like napalm — fire that sticks to things until it burns through them or burns itself out.
The thermal runaway process can happen very quickly, and things can go from "normal" to catastrophic failure inside the battery before the heat is even transferred through your phone to your hands. Thankfully, the hundreds of millions of lithium batteries produced every year have an extremely low (almost statistically insignificant) failure rate due to thermal runaway, partially because of safety measures like non-flammable additives to the electrolyte and coatings.
When your phone tells you that it's too hot and won't charge or run at full speed, it needs to cool down so thermal runaway doesn't happen. Listen to the little pop-up and let it cool.

  


Mechanical damage


Lithium batteries are designed to be lightweight, deliver high output, and be easy to charge. This means that the outside shell and the barrier(s) separating the electrodes are very thin and light, with most of the weight coming from the parts that can actually power your phone.
Because the partitions and case are thin, they're fairly easy to puncture or tear. If the structure of the battery itself is damaged in a way that makes the electrodes touch, a short circuit will happen. The instant electrical discharge is explosive, which can (and will) heat the electrolyte and create pressure to push it out through any ruptures in the battery case. It's hot, it's flammable and it's in contact with a spark. That's a recipe for disaster.
It's hot, it's flammable and it's in contact with a spark. That's a recipe for disaster.
A thin casing is also a safety precaution, though it sounds crazy. Thinner metal is easier to rupture, so less pressure can generate inside a sealed case — essentially creating a vent hole. Pushing out flammable hot liquid under pressure isn't a good thing. Letting more pressure build until it ruptures a thicker case is worse.
Other metals coming in contact with the electrolyte paste can also create a spark that leads to failure. I'll let you search YouTube yourself to see incredibly silly people puncturing phone batteries to make them explode. The reaction to foreign metal does the same thing as a short, but on a smaller scale.




Hope this thread explains everything clearly and clears the point on how does a battery work and it explodes. Sometimes because of our own mistakes battery's can explode too . So keep the important things in mind !