Sodium batteries[1] could be the answer to grid storage batteries. Sodium can be extracted from seawater (e.g. desalination plants, there's a huge supply of salt readily available), and while it's heavier than lithium, it's chemically similar. It's heavier weight probably makes it less suitable for transport, at least initially but ideal for grid storage if/when they figure out how to produce the batteries commercially.
[Side note: some interesting quotes from the above link...
In 2012, the French researcher decided to take the bull by the horns and make the most of France's know-how in sodium batteries. "For lithium, all fundamental research had been conducted in Europe, especially in France," Tarascon points out. "Yet it was in Japan that the technology was transferred and brought to market, allowing Sony to launch its first lithium-ion battery in 1991. As a result, 95% of Li-ion production today takes place in Asia." It is out of the question to repeat history. The CNRS (responsible for fundamental research) and the LITEN-CEA (in charge of technology transfer) have thus joined forces with around 15 industrial players such as Renault, Saft, and Alstom to create the RS2E network dedicated to new-generation batteries. Their stated objective is to ensure research AND development, in order to bring sodium-ion batteries to market on European soil as soon as they are ready.]
The biggest drawback of batteries today is high costs, not physical parameters. A BEV with Model S range could be as popular as the Toyota Camry if it could be profitably sold for the same pre-rebate MSRP as a Camry. Tesla doesn't need to find a metal lighter than lithium; they just need to bring lithium ion costs down.
For stationary energy storage energy density is even less important and costs are even more important. IMO the best way to make stationary energy storage affordable would be to increase battery cycle life, via chemistry tweaks and/or charge controller tweaks. You don't have to compete so fiercely on lowering up-front costs if you're selling to institutional customers and can demonstrate lowered lifetime costs.
I'm not going to proclaim that lithium ion batteries will certainly win the storage wars. But I think there's an interesting historical example from photovoltaics. In 1976 terrestrial PV cells were mostly made out of crystalline silicon and a lot of researchers were searching for materials that could lower PV costs either by increasing conversion efficiency or by being cheaper than high purity silicon. The search never stopped, and maybe some day silicon will be overthrown. But in 2016 crystalline silicon is still the most common, most efficient, and least expensive option for making terrestrial PV cells. Iterative improvements on the incumbent technology kept it ahead of all the many disruptive alternatives proposed over the decades. Maybe the same will happen with battery chemistry (either lithium ion or another one that's already been commercialized, like sodium ion) -- iterative improvements that keep disruptors forever playing catch-up.
Isn't there a huge potential in Lithium air or aluminum air? I get that it's hard to achieve reliable rechargeable tech there.. but if we're looking at theoretical capacity there should be plenty of opportunity, no?
As for the shorter term, have you looked at SolidEnergy? If their tech lives up to their promises I think it could really tip the scales for EVs. If it's relevant for grid storage I don't know.
Energy transitions from wood to coal to natural gas to renewables etc... usually take decades to switch over.
As well, there's no exponential growth in solar. We may be hitting the S-curve flat line on battery storage.
We can't keep moving left on the periodic table. Lead Acid ---> Lithium Ion. Where to move to next?
Lithium Fluoride batteries are scary because of the reactivity...got that noble gas, ya know?
Zinc ion rumors abound, but those ions are big, really tough. Zinc is a huge ion and thus you can only stick a few in the electrode.
Any chemists on hackernews or am I forever alone?