Over the last twenty years, a slew of ever-lighter, ever-more-powerful rechargeable batteries

has enabled the rise of smartphones, miniature high definition cameras, drones, commercially

competitive electric cars, wireless headphones, and so on.

It seems like we're moving towards a future where the entire planet is battery-powered,

but there are two big factors that will come into play: 1) how light and energy dense we

can make batteries, and 2) whether we'll even be able to physically manufacture enough

batteries.

This video covers part 1 of this question, and Brian of Real Engineering is covering

part 2 – we'll link to his video at the end.

Ok, so batteries have been getting better and better, and nowadays, they can store over

twice as much energy per kilogram as in the 1990s , which means they're half the weight

for the same energy stored.

Hence all the drones and smart phones.

So what's the limit to this trend?

Batteries are, in principle, fairly simple: take two partially dissolved metals, one whose

atoms want to dissolve more and give up electrons, and one whose atoms want to deposit back on

the solid bit but need spare electrons to do so.

When you put these two together connected with a wire or some other conductor , they'll

satisfy each others' wants, either dissolving more or depositing more, and sending the electrons

to each other along the wire.

Voilá: electricity!

And if you force electricity backwards through the wire they'll reverse their dissolving

and depositing, otherwise known as “re-charging”.

The intrinsic limits to how lightweight batteries can be are imposed by two factors: the weight

of the two materials you use, and how much energy they give off per electron traded.

So you want the lightest materials that produce the most energy per electron.

Metals from the left side of the periodic table, like lithium, sodium and beryllium,

really want to lose electrons, while atoms from the right side like fluorine, oxygen,

and sulfur really want electrons.

And atoms close to the top are lighter weight, so we can just slap together lithium and fluorine

and make a perfect battery, right?

Unfortunately, no – lithium and fluorine are way too reactive – one of the only well-documented

practical uses of a lithium fluorine reaction I could find was incredibly powerful and dangerous

rocket fuel.

In practice, the electrochemistry of batteries is incredibly complicated, and requires combining

metals that work well together chemically, electrically, and controllably at normal temperatures

and pressures . For example, oxygen is a gas, sulfur is a horrible conductor, and sodium

needs to be molten – challenges to using any of them to make batteries.

The current standard for lightweight, rechargeable and commercially safe batteries uses lithium

and graphite on one side, with a variety of options for the other side, often cobalt oxide

. Lithium atoms are what either dissolve or deposit in order to transfer electrons, hence

the name “lithium ion”, while the other materials are dead weight along for the ride

– I mean, they play important chemical roles, but they greatly increase the weight-per-electron

transferred.

So how much lighter will batteries get?

Theoretical calculations put the minimum possible weight for lithium ion batteries at around

half what they currently are . A lighter candidate currently being developed

is the lithium-sulfur battery , which has a similar amount energy-per-electron as lithium-ion

batteries, but lithium and sulfur are lighter than lithium and cobalt, oxygen and carbon

, so a battery with equivalent capacity can in principle weigh around a third as much

. Even better, lithium-oxygen batteries , while

still an incredibly far-off technology, are theoretically four times lighter than lithium

sulfur batteries.

But that's pretty close to the limit for chemical-reaction-based batteries – there

aren't really any materials that give off more energy per electron for a given weight

than lithium on the dissolving side and fluorine on the depositing side , and a lithium-fluorine

battery – as dangerous and impossible as it is – is limited to only be about 10%

lighter than a lithium-oxygen battery . So the theoretical lower limit for batteries,

period, is about 5% of current weights.

But that's an incredible long-shot, everything-works-out, perfect world scenario.

More likely is that we end up combining pretty-good batteries with supercapacitors, fuel cells,

hydropower and other mechanical energy storage types, and airplanes will probably always

have to use some sort of hydrocarbon fuel.

Or maybe we'll finally figure out fusion.

Ok, so here's an example of the amazing battery technology we have available today

: this battery pack is crazy small and light – it's basically eight of these with

some clever circuitry – and it has enough energy to charge a smartphone 10 times, which

is equivalent to running this LED lightbulb for 10 hours.

The makers of this ridiculous battery pack, Anker, are sponsoring this video and also

running a ridiculous contest where they're giving away ten prizes of two thousand dollars

plus one of their battery packs – they're asking for video submissions about a time

that running out of power was awkward or unpleasant – you know, like how Apollo 13 almost ran

out of batteries, or how I only made it halfway through mowing the lawn last week.

You can find out more about Anker's batteries and the contest by going to the links in the

video description.

And one aspect of batteries I haven't mentioned at all yet is power delivery - aka, how quickly

they can charge your devices – this battery pack is smart enough to detect what you've

got plugged in in order to optimize charging time.

And of course don't forget to check out Brian's video about whether or not it's

even possible to make enough batteries to power the planet.