The Multifunctional Use of an Aqueous Battery for a High-Capacity Jellyfish Robot

The batteries that power Untethered Underwater Vehicles (UUVs) serve a single purpose—to provide energy to electronics and motors; the more energy required, the bigger the robot must be to accommodate space for more batteries. This size dependency is further exacerbated by the high gravimetric density of batteries, requiring bigger hulls to displace water the equivalent weight of the batteries. With the increased size, comes increased moments of inertia, reducing maneuverability. By choosing batteries that are primarily liquid (i.e. Redox Flow Batteries, RFBs), the increased weight can be distributed for improved capacity with reduced inertial moment; and, when also being used as hydraulic fluid, reduce the overall weight of the AUV. In this paper, we formed an RFB into the shape of a jellyfish, using two redox chemistries and architectures: (i) a secondary ZnBr₂ battery with high power density, and (ii) a hybrid primary/secondary ZnI₂ battery with high capacity. Our choice of a Jellyfish shape demonstrates a low inertial moment architecture, a hemisphere, facilitated by the easy shaping of fluid batteries. In our robot, the RFB electrolyte also provides hydraulic force transmission to control the shape of the jellyfish’s bell, causing it to sink or swim. Finally, our choice of catholyte to fill the bell allows us to quickly recharge the battery by emptying the fluid and replacing it with pre-charged electrolyte (analogous to a gas station).