Some scientists at MIT have found a way to allow lithium ion batteries to charge as rapidly as supercapacitors.
Nature published a very interesting paper by MIT researchers Byoungwoo Kang & Gerbrand Ceder this week: Battery materials for ultrafast charging and discharging. In it they claim that they have discovered a way to make a lithium iron phosphate (LiFePO4) battery charge and discharge about as fast as a supercapacitor. In practice, this could make plug-in hybrids and electric cars much more practical (charging time would mostly be limited by the availability of fast-charging stations with fat "electrical pipes", and regenerative braking would be more effective), as well as some smart grid tricks to better use intermittent renewables.
According to the researchers, this technology shouldn't be very expensive because it uses current materials. They speculate that it may begin to come to the market in 2-3 years, and could allow lithium ion batteries to recharge in mere seconds (assuming a high voltage power source were available). Cool stuff!