THE TRADEOFF

Batteries vs. capacitors

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Batteries

High energy density, but slower charge/discharge and a limited cycle life — the chemical reactions inside wear out.

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Capacitors

Extremely high power density and near -instant charge/discharge, but store only a small amount of energy.

Neither one alone is a great fit for a device that needs to store real energy AND deliver quick bursts of power.

THE RAGONE PLOT

Plotting energy against power

ENERGY DENSITY ↑ vs ↑ POWER DENSITY

A Ragone plot compares energy density (how much energy fits per unit mass or volume) against power density (how fast that energy can be delivered). Capacitors sit in the high-power, low-energy corner. Batteries sit in the high-energy, lower-power corner.

Supercapacitors were developed specifically to occupy the gap in between.

THE MIDDLE GROUND

Where supercapacitors fit

🔋 ← ⚡ → 🔌

Supercapacitors — also called electrochemical capacitors or ultracapacitors — offer significantly higher energy density than conventional capacitors while keeping high power density, rapid charge-discharge, and exceptional cycle life (often past a million cycles).

Key idea Supercapacitors don't beat batteries on energy or beat capacitors on power — they get "good enough" at both at once.

WHY IT MATTERS

Biomedical power budgets

Neural interfaces ~0.47 µW (low-power recording) up to ~200 mW (high-channel-count stimulators)

Continuous glucose monitors ~10 µW for sensing, processing, and wireless communication

Cardiac pacemakers 10–100 µW, sustained for years off one implanted power source

These devices need long-term energy capacity AND the ability to deliver power quickly — exactly the gap supercapacitors are built to fill.

THE DEVICE IN THIS COURSE

A real research device

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This course is grounded in original thesis research: a glassy-carbon interdigitated micro supercapacitor, built with 3D electrodes and tested in a PBS electrolyte to simulate physiological conditions.

Every formula and fabrication step in this course ties back to a device that was actually designed, built, and electrochemically tested.

UNIT 1 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered the Ragone plot, and why batteries, capacitors, and supercapacitors trade off energy against power.