WHY SHAPE MATTERS

Four things geometry controls

Ion path How far ions travel between the electrodes

Electron path How far charge travels through the current collectors (resistance)

Packing How much active material fits in the volume or footprint

Compliance Whether the device can bend, stretch, or fold

Short paths mean high power; lots of material means high energy; flexibility opens new uses. You rarely get all three.

MACRO FORM • CYLINDRICAL

The jelly roll

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Two long strips of coated metal foil, with a porous separator between them, are wound into a tight spiral and sealed in a metal can with electrolyte. Unrolled, it's a very large stacked pair of electrodes folded into a small volume.

A huge electrode area rolled into a compact, sturdy cylinder.

MACRO FORM • CYLINDRICAL

Strengths and catches

Strengths

Mature winding machinery borrowed from batteries and capacitors, efficient use of volume inside the cell, and a rugged sealed can

Catches

Round cans leave gaps when packed into modules, and a single tab makes charge run along the whole foil, adding resistance

The fix for that resistance: multiple tabs or offset foils that shorten the current path.

MACRO FORM • COIN / BUTTON

Stacked discs

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A coin cell stacks two electrode discs with a separator between them, pressed together by a spring or spacer inside a crimped two-part metal case. It's the simplest sandwich you can seal.

Good at

Tiny, cheap, easy to assemble; the everyday test vehicle for new electrode materials; memory backup

Limited by

Small capacity and relatively high resistance, so modest power

MACRO FORM • POUCH / PRISMATIC

Flat stacks and folded strips

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Flat electrode plates are stacked with separators between them, or one long strip is folded in a zigzag. The stack is sealed in a heat-sealed foil pouch or a rigid rectangular case. Each plate connects to a tab, so many plates work in parallel.

Strengths Best fit for rectangular products, thin and light, short current paths

Catches Pouches can swell if gas forms, and need good seals and gentle compression

MACRO FORMS COMPARED

Three cells, three personalities

Cylindrical Wound roll · large, rugged, power-oriented cells

Coin / button Stacked discs · tiny, low-power backup and lab testing

Pouch / prismatic Stacked or folded plates · thin, flat, packs neatly

Same electrodes, same electrolyte: only the arrangement changes the trade between size, resistance, and packability.

BUILDING BLOCKS

Series and parallel

In parallel

Capacitance adds up (more area); voltage stays the same

In series

Voltage rating adds up; overall capacitance drops

A single cell is rated for only a modest voltage, roughly 1 V for water-based electrolytes up to about 2.5–3 V for organic ones. Higher voltages come from stringing cells in series, which needs balancing so no cell drifts past its rating.

Stacked plates inside a cell are parallel; cells in a module are often in series.

UNIT 13 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered cylindrical, coin/button, and pouch cells, and how cells combine into modules.