University of Bristol, U.K., published an inspiring press release a few days ago,
Graphite blocks are used to moderate reactions in nuclear reactors. If you study what's happening with them, you will find out that some of the ordinary carbon-12 in these blocks is turning into the radioactive carbon-14, especially on the surface of these blocks.
OK, so why wouldn't you pick some of this carbon-14 and play with it? You may isolate the carbon-14 nuclei by evaporating the blocks and removing a part of the surface. The remainder of the blocks becomes less radioactive as a byproduct. You collect the carbon-14 gas, place it under appropriate pressure and temperature, and transform it into a radioactive diamond.
This radioactive diamond is capable of producing an electric current if exposed to external radioactivity. This radioactivity may be obtained from this carbon-14 diamond itself – even though the experimenters have used nickel-63 in their prototype battery.
So this is a permanent source of energy. It's radioactive and unhealthy and this problem may be solved, they claim, by encapsulating the carbon-14 diamond inside a regular carbon-12 diamond. When you do so, the radioactivity on the surface of the carbon-12 diamond is lower than the radioactivity on the surface of a banana, unless they're lying to us. But that's not necessarily great news. Maybe you don't want to be permanently exposed to a banana, either. ;-)
They say that it's this safe because carbon-14 emits "short-range radiation". I should know what it means and why it's true but I don't know it so if you can give me an explanation, it will be welcome.
How much energy can you get in this way?
They claim that 1 gram of the carbon-14 diamond may produce 15 joules per day. In the smartphone age, for some stupid reasons, we're used to express the energy capacity of a battery in the units of mAh, a milliamperehour. 1 mAh is equal to 3,600/1,000=3.6 joules. Well, 15 divided by 3.6 is just 4.17 mAh. So you really need hundreds of grams to compete with the normal battery which discharge e.g. by 1,000 mAh per day.
But if you're ready to have this somewhat heavy battery or if you use a smaller device, there's some good news. The normal lithium-ion batteries in your phone get discharged to 50% approximately after one day of usage. What about the radioactive diamond batteries? Well, the current is exponentially dropping – like the radioactivity – and it drops to 50% after the half-life of carbon-14 which is 5730 years.
It means that if you insert your lithium-ion or radioactive-diamond battery into your smartphone in the morning, you will be at 50% in the evening or in the year 7746 after the Christ, respectively, assuming that you will still remember who Jesus Christ actually was in 7746 AD. ;-) I apologize to Stephen Hawking for this heretical comment: while Hawking still believes that God doesn't exist, he was empirically shown that His messenger, the Pope, actually does exist. :-)
Obviously, because of this lifetime beating our life expectancy, the radioactive battery is primarily recommended as a source of energy for the implanted gadgets (although wireless charging of your artificial heart can't be so bad, assuming that you find the wireless charger in time) or for devices sent to the outer space.
But maybe such radioactive batteries could replace the lithium-ion batteries in much more conventional situations, too. Will electric carmakers put this stuff into the cars? I've mentioned that the energy released per day is pretty low. But maybe this technology could be improved by using a radioactive isotope with a shorter lifetime. You may try to make a diamond ;-) out of cesium-137. Its lifetime is 70 days. It could discharge for some two months. Note that the battery gets discharged even when you're not driving.
Or if the cesium is too fast for you, try strontium-90 whose half-life is 29 years. That sounds almost perfect. Batteries of the same size as the lithium-ion batteries could give you the same energy per day but they could last for 29 years instead of 1 day. So far, I am mostly joking. You can't really make diamonds out of cesium and strontium which could make the stuff even more risky. But maybe those problems may be solved in some safe enough way.
Aside from the freedom to avoid the periodic charging, an advantage of such batteries is that if some terrorists catch you and want to hear a password, you may break your battery by a hammer, lick the radioactive stuff, and die (I guess!).