We're a long way from practical pure electric airplanes, but a variety of hybrids might make sense. A few groups are advancing technology. Siemens has flown a small general aviation test plane, but more significantly is working on components.
A good lightweight electric motor can produce as much as 1 kilowatt per kilogram of weight and the best automobile electric motors are around 2 kW/kg. The new Siemens motor produces over 5 kW/kg - an amazing power to weight ratio that far exceeds internal combustion engines in cars. Its speed range is such that gearing to the propeller isn't necessary.
This could lead to greater flexibility in airframe design. Some motors may be distributed along the wing with a small gas turbine running a generator located in the airframe. The "transmission" would be power cables. As battery technology progresses one can a hybrid with batteries being used for the power demands of takeoff. Or perhaps an electric motor could be integrated with a turbofan motor connected to a battery to supply more power for takeoff. Ultimately metal air batteries would have power densities such that pure electric airplanes are possible.