One of the most exciting developments in modern battery technology is the 3D microbattery.
The principle is that the distance that ions have to pass between the electrodes can be reduced to micron dimensions, as in a thin film battery; however in the 3D battery the thin film is topologically folded into a macro-sized structure of the required dimensions. The result will be high power from cheaper and safer materials and an increase in the energy conversion efficiency of a full charge-discharge cycle.
The big question we are addressing in our next phase of research is how to fabricate such a structure cheaply.