Adv. Energy Mater. doi:10.1002/aenm.201100152 (2011)

Although the reduction and oxidation of lithium allows large amounts of energy to be stored in a given mass, about half of the volume of a lithium battery consists of inactive components such as foils, binders and packaging. This reduces energy density and increases cost. Flow batteries, however, store energy in liquids kept in external reservoirs, and pump them into a 'power stack' where ions are exchanged and power extracted. Although this scheme reduces the need for inactive materials, it has also traditionally offered low energy densities. Now, Yet-Ming Chiang and colleagues at the Massachusetts Institute of Technology have shown that the best features of these technologies can be combined.

The researchers replaced the aqueous components of a traditional flow battery with semisolid storage compounds consisting of suspensions of active materials in an electrolyte. This approach allows for a variety of chemistries to be implemented (the MIT team chose a lithium chemistry). A percolating network of nanoscale conductors was also added to the suspensions to facilitate electron flow to current collectors. The resulting cells operate with low mechanical energy dissipation, and have theoretical capacities ten times higher than traditional flow batteries. If successfully scaled, the technology could allow the rapid refuelling of electric vehicles by filling a tank, rather than direct electrical charging.