It's the common problem with almost anything in physics or chemistry.
The Good Stuff has some horrible flaw that makes it incredibly dangerous.
When we invented refrigerators first, they used ammonia as a refrigerant which was awesome at moving heat around. It's still used industrially but people die from ammonia leaks. Then they swapped it for freon, which was just about as good at moving heat around, but rotted holes in the ozone layer. So they got replaced with R-134 which wasn't as bad for the ozone layer (but still not great), slightly more toxic, and still quite nasty stuff to handle.
At present the best bet for refrigerants turns out to be good old propane, which if anything is a little too good at moving heat around (and your evaporator will freeze if you're not careful), reasonably non-toxic (don't breathe it in, but unlike ammonia a tiny amount in a room won't dissolve your lungs), and its only real downside is that it burns. People are worried about using C3 or C5 (pentane) refrigerant in cars, but the worst that would happen is you'd release about a deodorant can's worth of the stuff into something that's already on fire and contains maybe 70 litres of petrol. Your petrol tank is a bomb, made of a leaky plastic bucket full of explosive. The aircon having a cupful of LPG in it is not your problem in an accident.
Thus it is with batteries.
It turns out that one of the best kinds of batteries you can make in terms of longevity, power density, and stability is a couple of bits of lead in a bucket of sulphuric acid. They work great. They're in production today, and will probably be forever. Your car has at least one (mine has three, a massive one up front for starting the engine and a couple of smaller ones in the back for running things like the radios and inverter when I'm stopped).
However, lead compounds are pretty nasty, sulphuric acid is pretty nasty, they're heavy, they will stop working if you leave them discharged, and in general people would like something smaller, less corrosive, and less dependent on digging up vast areas of China to pull poisonous dust out of the ground.
So we have NiCads (oh dear, cadmium, one of the nastiest poisonous metals because it's poisonous all by itself - it doesn't need to be complexed to something organic to get in you), then NiMH (cheaper, non-toxic, and more-or-less a drop-in replacement for NiCads in any given application). Then we've got the various rechargeable lithium batteries which can do exciting things when damaged.
But for high power density, low cost, and and high current applications where you don't have to worry about carrying them or tipping them over, you're going to be stuck with lead in a bucket of acid for a while I suspect.