Everyone step back for a bit, and remember one thing: Mathematical models are made, and then we find components that match those models. Or... we find a bunch of cheap stuff, then we make math that describes them. That's it.
A diode for example has I = x^V (yes, exponential
amounts of current are let through the higher the voltage is), effectively turning any voltage-source into a current source (in practice, batteries are current-limited and voltage-limited. If you hit the current-limit first, then voltage will drop to meet the maximum current. So we usually pretend that diodes are one-way with a "voltage drop", because that's a lot easier than exponents). Or things catch on fire (aka: fuses, which catch on fire at 3A safely, preventing other
things from catching on fire). We also tend to not use things that catch on fire (exception: Lithium Ion, because consumers want even more energy storage in smaller and lighter form factors. So we put up with the whole Lithium-fire issue)
There are plenty of electrical components that don't follow Ohm's law: Capacitors, Inductors, Transistors... in fact, that's why
they are used. Because we can manipulate electricity when these different things affect electricity differently.
The three "ideal" electrical components: capacitors (dv = IC), inductors (di = LV), and resistors (V=IR) don't even match up to all passives! Ferrite Beads are utterly ridiculous components: acting like an inductor at less than 10MHz, and acting like a resistor at 100MHz, and then they act like a capacitor at 1GHz (I'm grossly simplifying here, but that's kinda how people think of Ferrite Beads). We use Ferrite Beads because their unique frequency-dependent nature allows for filtering applications. Also, they're cheap as all fuck and very effective.
So why do we use V=IR? Because its easy to remember, easy to calculate, and there's a bunch of super-cheap components called resistors that follow the math. It turns out that you can sorta-kinda-maybe pretend that everything has some combination of resistance / capacitance / inductance. (except when you can't: like transistors or diodes) We can pretend
that batteries are a Voltage source with internal resistance. But lets be honest here: a lead-acid battery is about Pb + HSO4- -> PbSO4 + H+ + 2e-, and any discussion about batteries without discussing the chemical reaction is utter shit.
But it turns out that Voltage Source + Resistor is actually kinda close to how batteries "feel like" when you're working with them. Its easy math, but it tells us jack shit about how batteries really work. You really need to discuss chemistry.
In fact, we can pretend that batteries are a current source with an internal parallel resistance
. And that of course, can be converted into a voltage source + resistor. Its mathematically equivalent. Pretend it to be whatever you want it to be, it doesn't matter as long as the math comes out right at the end.
It also means that these models are utterly worthless for describing things chemically. Because these are ideal mathematical constructs that were designed to work on anything
. Just like how all of physics turns out to be a Taylor series polynomial
, all of electronics turn out to be a Thevenin-equivalent circuit because Thevenin-equivalent circuits can represent a lot of shit!
So why do Lithium-based batteries explode? Well...
The further you go to the top-left, the more reactive the elements are. We started with Lead-acid batteries (using the metal Pb, #82 on the periodic table). As a metal, Lead is heavy... but we can use more "powerful" elements if we want to get lighter batteries. Latter batteries (NiCD or NiMH) use Nickle #28 on the periodic table. Notice that it's "up" and "left" from Pb, which means it is more reactive.
You know what? Lets just cut to the chase. What's the most reactive metal on the Periodic Table? Well... that's easy. The one on the top-left, a little substance known as Lithium. #3 on the periodic table, a single
valance electron in the 2s shell. Its literally explosive. Yeah, lets pack a whole punch of that into a metal can and see what happens.
So yeah, Lithium-batteries explode because Lithium is a crazy metal
Now yes, technically... Lithium-ion batteries just use Lithium-ions. They don't (typically) have solid bunches of Lithium lying around, ready to explode. But when Lithium-ion batteries are used incorrectly, Lithium builds up and the batteries can explode.
A typical Lithium-ion battery actually uses Lithium-Metal-Oxides (like LiCoO2) and LiC (Lithiated Carbon), and they transfer the lithium-atoms back and forth to store energy, or to release its stored energy. But if those Li atoms get out of whack, the Lithium can break free from its bonds and start reacting with the outside world (which is explosive). Or thermal runaway just... makes the whole battery get overheated to the point of fire. Lots of different reasons why Lithium-ion batteries can explode.
Sooo... no one really knows why Samsung's batteries explode. There are too many legitimate reasons and possibilities. Undervoltage cause lithium plating. Overcharging can cause lithium plating. Thermal runaway causes fires. Whatever the issue is... its Samsung's problem to figure out.
First Strike +1/+1 and Indestructible.