# Phase‐Change Solvents for Thermally Switchable Ion Conduction in Organogels

## TL;DR

This paper introduces temperature-responsive organogels that can switch ion conductivity on and off, useful for batteries and sensors.

## Contribution

A new class of phase-change organogels with independently tunable charge carriers and solvent phase behavior is introduced.

## Key findings

- Conductivity in the molten state exceeded that in the frozen state by over 10,000-fold.
- The organogels remained stable after 100 freezing/melting cycles and at 90 °C for 3 hours.
- They can function as digital thermal switches or analog temperature sensors depending on solvent composition.

## Abstract

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 h 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.

Organogels containing salts dissolved in phase‐change solvents exhibit thermally switchable ion conduction. The organogels, which display an over 10 000‐fold on‐off ratio and high cycling stability, can be synthesized with a wide range of salts and customizable conductivity/temperature relations for applications in ionotronics and energy storage. Demonstrations as both digital thermal switches and analog temperature sensors highlight the scheme's versatility.