Supercapacitors power the Note 9 stylus — but are they ready to replace batteries?

Samsung’s latest Galaxy Note 9 has a nifty new feature: for the first time, the S Pen stylus has Bluetooth and can be charged instantly using a supercapacitor. Sticking the S Pen into the phone for 40 seconds gives it enough juice for 30 minutes of use, so battery life should no longer be a worry. But how exactly does this technology work? And what else could we use supercapacitors for?

Supercapacitors (or ultracapacitors) store energy and, in some ways, are the opposite of batteries. Batteries can hold a decent amount of energy but take a long time to charge, explains Thomas Miller, a materials scientist with the Electrochemical Innovation Lab at University College London. Supercapacitors charge so fast it seems instantaneous, taking...

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