THE SCORECARD

Supercapacitor versus lithium-ion battery

Power Very high: often ten times a battery's, or more

Energy Much lower: roughly 5 Wh/kg versus 100–250 Wh/kg

Cycle life Hundreds of thousands to millions of cycles, versus about a thousand to a few thousand

Charge time Seconds to minutes, versus around an hour

Temperature Often −40 to 65 °C, wider than most batteries

Self-discharge Faster: a charged cell drifts down over days to weeks

Batteries win on energy; supercapacitors win on power and endurance.

DUTY CYCLE

Read the load, not the label

kW or kWh?

Ask two questions: how much energy in total, and how fast must it move? A phone needs plenty of energy delivered slowly, which suits a battery. A crane lowering a load needs a burst of power for a few seconds, again and again, which suits a supercapacitor.

Total energy points to batteries. Fast, repeated bursts point to supercapacitors.

CYCLES ARE MONEY

Cost per cycle, not per kWh

Per kWh Supercapacitors cost much more for each unit of energy stored

Per kW For each unit of power delivered, they can be cheaper

Per cycle Over a million cycles, the price of each cycle becomes tiny

Maintenance A device that outlives the equipment saves replacements and downtime

For frequent cycling, lifetime cost beats sticker price.

WHEN THEY LOSE

Limits, not flaws

⏳

Long, slow energy

Hours of runtime need an energy density supercapacitors can't offer

💤

Idle for months

Self-discharge leaks a stored charge away when nothing is using it

📉

Sagging voltage

Voltage falls in step with the charge, so electronics may need a converter

These limits are why hybrids exist, which we'll meet in the last unit.

UNIT 37 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered power, cycle life, and cost per cycle, compared with batteries.