Supercapacitors are an indispensable electronic component in many IoT applications today. This is especially true as many IoT devices increasingly integrate energy-harvesting devices onboard as a means of extending battery life. These kinds of systems often employ supercapacitors and batteries working as two discrete components in unison to power the device.
Judging by the cost of battery replacement alone, it’s no wonder that companies are looking for a more sustainable power option for IoT devices. Image used courtesy of Xidas
IoT company Xidas is now challenging this common design practice with its newest product, which brings a lithium-ion battery and a supercapacitor together in one device.
The Need for Supercapacitors in Energy-Harvesting IoT
For some IoT designs, supercapacitors have become a staple for a few reasons. While energy-harvesting techniques in IoT may seem to be a sustainable solution, these sources are not reliable for continuous power. Without a storage element, the device only works when energy is being harvested; for solar harvesting, a device would only work during daylight!
In many devices, a rechargeable battery is a solution to the problem. But IoT, a low-power technology by nature, is unique. These designs often concern RF communication, employing protocols such as IEEE 802.15.4 (Zigbee), 802.11 (WLAN), or GSM/GPRS. These protocols require significantly higher peak power for transmitting data across wireless networks, and the peaks can occur with a high frequency.
IoT devices experience power pulses when transmitting. Image used courtesy of Medium
This is where a supercapacitor trumps a battery: it can charge and discharge at a significantly faster rate than standard lithium-ion batteries. In addition, the large spikes can plummet a battery’s voltages to unusable levels and damage a battery. This makes supercapacitors better suited for providing high-frequency pulses than lithium-ion batteries.
The supercapacitor will act as a buffer, storing the energy needed for the RF activity.
Supercapacitors and Batteries—A Natural Team?
While supercapacitors beat out batteries in some ways, a supercapacitor by itself often isn’t sufficient. Typically, supercapacitors are not as suited for long-term storage as lithium-ion batteries due to their high discharge rates. This becomes a problem when an energy harvesting device (like a solar panel) isn’t producing electricity, and energy must be stored long term—not only for peak power but also to support the device’s operation in general.
Side-by-side comparison of the performance of a supercapacitor with a Li-ion battery. Image used courtesy of Maxwell Technologies and Battery University
In most energy-harvesting IoT devices, a supercapacitor will be augmented by a rechargeable battery for this reason. Often the battery will work by charging the supercapacitor at low power, then when power bursts are required, the supercapacitor can supply what’s needed. If the needed peak power exceeds the amount the battery can supply, then the battery can charge the supercapacitor at low power and the supercapacitor can deliver the high-power bursts.
In this way, the benefits of rechargeable (i.e. Li-ion or Li-Po) batteries are combined with the benefits of supercapacitors in an IoT device.
Xidas Claims the Best of Both Worlds
Xidas, a company focused on IoT solutions, has pitched a novel design structure that could enhance the symbiotic benefits of rechargeable batteries and supercaps. Instead of separating a battery and a supercapacitor from one other, why not integrate both into one energy-storing device?
The new RHB-1530. Image used courtesy of Xidas
The company explains that the new RHB-1530 integrates a pulse capacitor with a rechargeable lithium battery to yield large pulse discharge capability—even in extreme temperatures ranging from -40°C to 85°C. The device aims to offer the functionality of both a rechargeable battery and a supercapacitor to simplify design and decrease BOM.
RHB-1530 specs. Image used courtesy of Xidas
According to the datasheet, the device has a capacitor of 240 mAh at 4.1 V, pulse current capacities of 3000 mA, and a maximum discharge end voltage of 2.5 V. These specs may bode well for IoT needs to accommodate high peak power requirements while also maintaining workable voltage levels.
The Ongoing Discourse of IoT Power
Powering IoT devices has been a rolling design conversation in recent months. While Arm recently announced its intentions to repurpose RFID technology for “battery-less IoT,” smaller companies like e-peas and Sequans have combined a photovoltaic cell-based ICs and dual-cell supercapacitors along with LTE-M/NB-IoT modules for “non-stop, zero-maintenance” power.
Alternately, companies like Innophase are investigating multi-protocol modules to tackle the high power consumption challenges of Wi-Fi on battery-powered IoT devices. Researchers have also shown keen interest in advancing supercapacitor technology—with some investigating fast-charging supercapacitors and others exploring lightweight supercap materials to extend battery life for mobile electronic devices.
Xidas advancement of combining a supercapacitor with a rechargeable battery represents yet another method to create smaller, simpler, and more efficient IoT designs.
What’s your take on the move toward battery-less IoT? What advances seem promising to you and what challenges may still need to be overcome? Share your thoughts in the comments below.