We are surrounded by electrochemical devices. Hardy lead-acid batteries in our cars, lithium-ion batteries in our computers, and even the neurons that control our bodies, are all electrochemically driven devices. Like a ball falling down a cliff, batteries use a potential energy difference between two materials to generate a flow of charged particles to do something useful. Importantly, the two materials must be physically separated from each other to generate useful current. One limitation of traditional batteries is that, to achieve this separation, the devices must be completely rigid. By comparison, biological systems circumvent this problem by using a soft and flexible cell membrane to create a potential energy difference. Researchers in the Helms lab at Lawrence Berkeley Laboratory are asking: is it possible to emulate this flexible membrane design and create a liquid-based battery? With such a device, the researchers envision that a non-rigid battery could be integrated with flexible circuits for smart textiles, medical implants, and wearables.

The researchers hypothesize that the various components of a battery could be emulated with water-soluble analogs. The basis for this design would be two immiscible water-based solutions, which could be made by dissolving certain polymers or salts. While both solutes dissolve in water, they also repel each other, creating two separate phases that mimic the separation of rigid components seen in traditional batteries. Within these two phases are reactive molecules, which, when separated, create the potential energy difference needed to run the battery. The separation of the reactive molecules is also maintained by special charged molecules that wrap tightly around them and form a fatty membrane barrier, which functions much like a cell membrane. This membrane structure makes it possible to harness the potential energy to do something useful—just like any other battery—while also allowing the device to conform to any shape.