Traditional lithium-ion batteries have carbon electrodes, which are relatively bulky for the energy they provide. To slim electrodes down, researchers have turned to that paragon of self-assembly, the virus. A team at the Massachusetts Institute of Technology engineered a long tubular virus called M13 to sheathe itself in proteins that glom onto cobalt and gold atoms. The scientists dipped a polymer electrolyte film into a solution containing the virus, then into a solution of metal atoms, yielding a thin, transparent sheet coated in cobalt oxide and gold. The result, an electrode, stores almost three times as much energy as the carbon-based kind, the researchers reported online April 6 in Science. Next, the goal is to build a counter electrode and, ultimately, a self-assembling battery.