In this article for IoT Insider, Ellie Gabel posits the question of whether supercapacitors are the answer to improving battery performance for IoT wearables
Wearables are an exciting field in the IoT market. They could make health care more accessible or bring smartphone functions to everyday accessories or articles of clothing. As promising as these gadgets are, battery performance remains a problem.
A wearable device needs to last for extended periods between charging cycles to be practical. Like many other IoT gadgets, it also doesn’t have room for larger batteries, and more advanced functionality typically pushes energy needs even further. While lithium-ion battery technology has come a long way, some researchers think supercapacitors are a better long-term solution.
What are supercapacitors?
Unlike batteries, supercapacitors — also called ultracapacitors and electric double-layer capacitors (EDLCs) — transfer electricity without a chemical reaction. They store energy through a voltage differential between two oppositely charged plates. As a result, they hold power electrostatically, leading to far greater life spans.
These components have existed in some form since 1957, but they have yet to replace batteries in most contexts. They’re most common in rapid charging and discharging applications instead of long-term storage. However, some recent breakthroughs may change that, especially as wearable IoT devices become a bigger segment within the electronics industry.
Supercapacitors versus batteries for wearables
Supercapacitors have several advantages over batteries for wearables. Most notably, they can withstand one million load cycles, whereas the most efficient lithium-ion batteries can only go through roughly 20,000. As a result, a supercapacitor-powered wearable would last far longer before needing replacement.
A normal IoT device may not need to worry about load cycles because it can stay plugged in or not require frequent charging. Wearables, however, may see regular use every day and don’t have the luxury of plugging into the wall. Consequently, these resilience improvements make a big impact.
Temperature resistance is another key benefit. EDLCs can operate as normal between negative 40 and 85 degrees Celsius — double that of a li-ion alternative. Considering wearables must function in outdoor environments, this edge would make them more practical, even in extreme weather conditions. Other IoT gadgets like smart cameras would also benefit from this functionality.
Physical considerations deserve attention, too. These components are generally smaller and lighter-weight than electrochemical alternatives. Some are even flexible — one study made them out of bamboo fabric and metal oxide inks. Being thin and flexible overcomes the convenience issue of traditional batteries. Wearables could feature more power cells without becoming bulky or stiff.
Are supercapacitors ready for implementation?
Given these advantages, supercapacitors seem like an ideal choice for wearable IoT devices. However, some challenges remain. The biggest is EDLCs have a massive power density but a much lower energy density than batteries. Thus, they struggle to hold enough charge to power a device over a long period.
Discharge curves present a similar issue. A typical ultracapacitor discharges 75% of its energy after its voltage drops to half its maximum, at which point a battery would release far more. In practical terms, that means the supercapacitor fails to deliver all the power it stores, even if it holds less of it and releases it faster.
A few recent EDLC projects have produced better results. The flexible bamboo solution achieved an energy density of 37.8 megawatts per cubic centimetre, which is significantly higher than earlier supercapacitors. It may not be enough to power a complex wearable quite yet, but it shows promise.
Another study found a different solution — pairing ultracapacitors with flexible solar cells for electricity generation. While solar power is typically slow, EDLCs charge quickly, making them an optimal pairing. The experiment found a supercapacitor could run a display for 25 minutes after just 10 seconds of charging.
Piezoelectric generation or similar energy harvesting systems could produce similar results, making up for EDLCs’ low density. Such solutions may not be viable for stationary IoT devices, but wearables are unique in that they stay on the user. As a result, they move more, making piezoelectricity or movement harvesting worth consideration.
Such breakthroughs suggest the world could be on the cusp of a supercapacitor shift. This technology may not be ready to replace batteries in wearables yet, but it could get there in the coming years.
The future of wearable electronics could be changing
As the wearable IoT sector booms, attention should turn to supercapacitors. EDLCs still have some challenges to overcome before they’re practical enough for commercial use in this area, but they’re getting close.
An ultracapacitor-powered wearable could be smaller, charge faster and withstand a wider range of conditions. Those benefits are hard to ignore for any IoT device, so it’s a mistake to count out supercapacitors just yet.
Author: Ellie Gavel, Associate Editor at Revolutionized
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