Fluidelectrolytes

Fluidelectrolytes are electrolytes that are in liquid form and enable the transport of charged species by diffusion and migration of ions in a fluid medium. They are used in electrochemical devices to support ionic conduction while maintaining electrical connectivity between electrodes. Fluidelectrolytes can be aqueous, organic solvent-based, or composed of ionic liquids, and they may include additives to modify conductivity, viscosity, and chemical stability.

Water-based fluids (aqueous electrolytes) typically offer high ionic conductivity and wide availability but have limited electrochemical stability windows due to water at ~1.23 V. Non-aqueous organic solvent electrolytes often pair with lithium or sodium salts to provide broader windows (3-5 V) but can raise flammability and volatility concerns. Ionic liquids are salts that are liquid at room temperature and can provide wide stability windows and thermal stability but often have higher viscosity and lower conductivity. The electrolyte’s conductivity depends on salt concentration and temperature; viscosity and dielectric constant influence ion mobility. The transference number and the formation of solid-electrolyte interphases affect long-term device performance.

Fluidelectrolytes are central to many energy storage and electrochemical technologies, including lithium-, sodium-, and redox-flow batteries, supercapacitors, electrochromic devices, and electrolysis. They also play roles in sensors and electroplating. Selection involves trade-offs among ionic conductivity, electrochemical stability, chemical compatibility with electrode materials, safety, and operating temperature.

Preparation involves dissolving the appropriate salt in a selected solvent or combining a salt with an ionic liquid, with stringent control of moisture and purity. Challenges include flammability of organic solvents, corrosion, leakage, volatility, and the need to balance high conductivity with wide electrochemical stability. Ongoing research seeks safer, more conductive, and more stable fluidelectrolytes through solvent engineering, additive strategies, and new ionic liquids or gel formulations.