Lithium batteries are literally the powerhouse behind the mobile gadget revolution: They're reliable, they don't have a serious multiple-cycle "memory effect" like Ni-Cad batteries do, they can be fashioned into all sorts of shapes, and they're good a providing significant amounts of charge. But they're far from perfect--a fuss about their fire-hazard habits is in the headlines right now , for example. This is because they're actually very sophisticated inside, and the electrolyte the lithium is dissolved in is often toxic and flammable.
But now scientists have found a way  to remove some of the barriers that prevent an alternative tech--aqueous lithium ion batteries--working as efficiently, and in the future these power cells may take up some of the load of "normal" lithium ion batteries. The advantage of an aqueous Li-ion cell are obvious right there in the name: They're water based, and thus potentially less poisonous and explodey. The tech's been in existence for a while, but never seen mainstream adoption due to the very, very poor lifespan of the design. It's typical to see the capacity of an aqueous unit fall to less than 50% of charge after just a thousand cycles.
Which is where the clever bit of new thinking comes in. By tweaking the oxygen content in a lithium sulphate/water electrolyte, the team discovered that the cells retained up to 90% of their capacity after a thousand cycles--much closer to the performance of more "normal" Li-cells. A few drawbacks do remain, though: The power retention of the devices is reduced. The developers see that the system could have uses in situations where its safety is desirable though, such as hybrid-engine city buses, or where wind turbines or other alt-power generators are producing spare electrical capacity that needs to be stored.
iPad Li-ion battery image via iFixit