Lithium ion batteries are now pretty much the standard high performance battery, they have a relatively high capacity and are becoming more affordable. They are used in most laptop and phone batteries and have recently been used in the Tesla Roadster sports car. However there are still major issues, the cathodes change shape and degrade over time, causing an electric car battery to only last 2-3 years. This is related to the batteries using a liquid electrolyte between the active electrodes, which also requires lots of infrastructure to hold everything apart, avoid short circuits, and keep the electrolyte in. One solution to this problem is to use solid electrolytes, which can allow ions to move whilst remaining solid, unfortunately these normally have to be made using vacuum deposition systems like computer chips, which are very expensive.
A company called Planar Energy has developed a process for making these solid state batteries using printing techniques which are far cheaper than the deposition. They have also apparently increased the conductivity of the solid electrolyte to be comparable with the conventional electrolytes and made high quality electrolytes by using chemical self assembly processes.
Apparently the batteries have a capacity similar to the best high performance conventional batteries, but should survive longer, have three times the capacity, lose energy more slowly and be safer than conventional Li-ion batteries. Even if they don't manage the half the current price per kW hour, they do sound promising.