A temperature-based hibernating battery has been developed at U.S. Pacific National Northwest Laboratory (PNNL) as a solution for long-term, seasonal energy storage. The self-charge function ceases during the battery’s idling period, making it ideal for long-term electricity storage without loss of electricity for several months.

Consisting of an aluminum anode, nickel cathode, molten salt electrolyte and a porous fiberglass separator, the battery operates only at an elevated temperature, at which the molten salt electrolyte is in a liquid state. When idle, the battery is maintained at ambient temperature to avoid self-discharge — effectively “freezing” the electrolytes. During the charging process, the temperature of the battery is raised to 180° C by an external heat source, such as a heating cartridge installed on an industrial-scale system, to bring the electrolytes to a liquid state to initiate ion mobility in the system.

The battery is designed to operate at high temperatures when the electrolyte is molten (charge/discharge) and idle at low temperatures when the electrolyte is frozen. Source: Guosheng Li et al/PNNL

When fully charged, the battery is cooled to the ambient temperature, allowing the electrolyte to solidify and keep the device at an all-solid state. Because the solidified electrolyte does not have ion transport capability, self-discharge of the battery can be cut off while at ambient temperature.

The battery discharges as the optimum operating temperature is reached, providing energy to the grid. Energy density is 260 Wh/kg, higher than available lead-acid and flow batteries, and the freeze-thaw battery described in Cell Reports Physical Science was demonstrated to retain 92% of its capacity over 12 weeks.