Phase-Change Solvents for Thermally Switchable Ion Conduction in Organogels

Conductive media in which ions carry charge through a solution are foundationally important to batteries, supercapacitors, and ionotronic devices. Shifts in ion mobility imposed by physical changes in the solution can dynamically impact the conductivity of the medium. This paper reports a class of temperature-responsive phase-change organogels in which a polymer network is formed within salt solutions in organic solvents with melting points between room temperature and 100 °C. The conductivity in the molten state (up to ~10^-4 to 10^-3 S/cm) exceeded that in the frozen state by over 10,000-fold and remained stable after holding at 90 °C for 3 hours or over 100 freezing/melting cycles. A diverse range of salts can be used, and the conductivity/temperature relationship can be tuned by selecting or mixing solvents with different melting points. Depending on the solvent composition, these phase-change organogels can either produce approximately digital (binary) thermal responses to function as switches or respond continuously as analog temperature sensors or other transducers. An advantage of this strategy over prior literature is that the identity of the charge carrier and the phase behavior of the solvent can be tuned independently, presenting a wide design space for electrolyte materials whose conductivity responds to temperature.