It’s one of the major areas of research right now. Lots of links on the subject.
http://www.asianscientist.com/2014/08/in-the-lab/beating-lithium-ion-batteries-flat-2014/
Not to mention magnesium battery research
http://spectrum.ieee.org/energywise/semiconductors/materials/taiwanese-researchers-report-progress-towards-a-magnesiumion-battery