GEL & SOLID-STATE

Take away the puddle

polymer + liquid → gel

Liquids leak, need a separator, and want a rigid case. A gel polymer electrolyte holds a liquid electrolyte inside a polymer network, so it acts like a soft solid while ions still move through it. A true solid electrolyte goes further and has no free liquid at all.

Gels trade some conductivity for leak-free, bendable devices.

RECIPES

Three families of gels and solids

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Hydrogels

A polymer such as PVA plus water and an acid, base, or salt (H₂SO₄, H₃PO₄, KOH). The go-to for lab micro devices and wearables

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Organogels & ionogels

A polymer such as PVDF-HFP holding an organic solvent or an ionic liquid, for a wider window

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Solid polymers & inorganics

Ions hop along polymer chains (PEO plus a salt) or through ceramics and glasses. Safest, but slowest

The liquid inside a gel sets the window; the polymer sets the shape.

THE GEL AS SEPARATOR

The gel doubles as the separator

Fills the gap In in-plane and fiber devices, the gel sits between electrodes and keeps them apart

Leak-free and bendable No puddle to escape when a device flexes, folds, or stretches

Thin Lets the whole device stay slim and lightweight

Catch: conductivity Ions move slower than in a free liquid

Catch: pore contact A thick gel struggles to fill deep pores, so it is cast thin and runny, then allowed to set

For 3D micro-electrodes, getting the gel into the structure is a fabrication problem.

PAIRING WITH GEOMETRY

Match the electrolyte to the device shape

Coin cell or wound can Free liquid plus a porous separator, sealed tight

Pouch Liquid or gel, with foil sealing that keeps moisture out

In-plane micro device A gel, or a thin liquid layer held under a cover

Fiber and textile Gel between the fibers, so it flexes and doesn't drip

Stretchable film A stretchable hydrogel or ionogel

Implant or skin patch Neutral, biocompatible electrolytes such as body-like saline

Part 4's shapes are only practical when the electrolyte can live inside them.

UNIT 23 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered leak-free, bendable electrolytes that double as the separator.