Earlier quoted context omitted.
It's important to note, though, that this kind of breakthrough is hardly the kind of invention that Musk is interested in. The world of batteries doesn't revolve around Elon and Tesla. This is sort of a big deal for those of us who design small electronic devices, not electric cars. Not having to factor in the potential fire hazard of a rechargeable battery for a keychain that the user has in his pocket or thrown in…
The global energy storage market is and will continue to be driven by electric vehicles (no pun intended!) and consumer electronics. For these applications a faster charge/discharge is nice to have, a non-flammable material is nice to have but a high energy density is a MUST HAVE which Aluminum-ions don't. My interpretation of a big deal is relative to the number of people it will positively influence. I wouldn't con…
As for consumer electronics, it's worth remembering that there are probably thousands of coin-cell operated keychains for every smartphone whose energy density capacity is not being satisfied by our current technology. There are a lot of consumer electronic devices for which current battery technology is OK -- better density would be an improvement, as it is everywhere, but it's no longer the hog it is for smartphones. For those, ease of recycling, lack of fire hazard and the slightly simpler circuitry really are important.