Researchers develop ultrafast rechargeable, non-pyrophoric, flexible aluminium-ion battery

Energy densities and voltages are still in the NiMH range and will need further improvement to compete with current Li-ion, but the high recharge speed and lifetime cycle numbers at least 7 times those of Li-ion are very promising. Also, the long life and safety make it a good candidate for grid storage applications (as for home solar panel systems):

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Boffins build bendy ALUMINIUM battery that recharges in MINUTES
Short on volts, long on potential, doesn't explode
7 Apr 2015 - Iain Thomson

Researchers at Stanford University have published details of a new type of aluminum battery that's flexible and cheap - so they say - and which has the potential to replace lithium-ion and alkaline batteries.

"We have developed a rechargeable aluminum battery that may replace existing storage devices, such as alkaline batteries, which are bad for the environment, and lithium-ion batteries, which occasionally burst into flames," said Hongjie Dai, a professor of chemistry at Stanford. "Our new battery won't catch fire, even if you drill through it."

The research, published in the latest issue of boffinry rag Nature, details how the battery uses an aluminum anode and graphite cathode suspended in an ionic liquid electrolyte. The entire unit is cased in a flexible polymer pouch, and can be recharged in minutes with very little degradation to the battery's performance....

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http://www.theregister.co.uk/2015/04/07/aluminum_battery_breakthrough/