From Almonds to Power: The Incredible Science Behind Edible Rechargeable Batteries

While it may not be the best pizza topping, researchers from Italy recently developed the world’s first fully edible rechargeable battery, which has the potential to power low-energy ingestible electronics and biodegradable sensors while also being biocompatible and causing no immune system response or bowel obstruction. 

Unlike other batteries that may contain toxic chemicals such as Li-Ion, the edible battery is made from non-toxic ingredients such as nori, beeswax encapsulation, and a water-based electrolyte that contains vitamin B2, quercetin, and activated charcoal to promote biochemical reactions and provide the recharging capability, making it an energy harvester for IoT devices. 

What challenges do ingestible electronics present, what did the researchers develop, and how could such electronics change the future?

What challenges do ingestible electronics present?

Ingestible electronics, or smart pills, are an exciting new technology with potential applications in healthcare. However, the development and deployment of ingestible electronics pose several safety challenges that must be addressed.

One of the primary concerns with ingestible electronics is their need to be biocompatible, meaning they do not trigger an autoimmune response from living tissue. In order to achieve this, an ingestible device must be made from biologically inert materials, such as special grades of glass, and unreactive metals, such as gold and titanium. Any foreign object inside the human body that isn’t biologically inert will result in a reaction from the immune system. However, as such objects are virtually impossible for the body to break down, it is possible for the body to have a fatal reaction via fever and/or sepsis.  

Another safety concern with ingestible electronics is the use of chemicals in their construction. Some of the chemicals used in the fabrication of these devices may be toxic or have adverse health effects should they leak from a faulty device. For example, the use of lead or other heavy metals in the fabrication of ingestible electronics can be harmful to the body, but the effects of such poisoning don’t show immediately.

There is also concern about the potential for ingestible electronics to cause bowel obstruction or other complications. Such devices need to be designed to pass through the digestive system intact, but there is a risk that they could become lodged or cause damage to the gastrointestinal tract. Blockages can quickly lead to impaction, which, if not treated immediately, can result in serious health complications. 

Researchers develop the first edible rechargeable battery

Recently, researchers from the Italian Institute of Technology (IIT), led by Ivan K. Ilic and including Valerio Galli, Leonardo Lamanna, Pietro Cataldi, Lea Pasquale, Valerio F. Annese, Athanassia Athanassiou, and Mario Caironi, have demonstrated what is believed to be the world’s first edible rechargeable battery in their groundbreaking study titled "An Edible Rechargeable Battery" published on 15 March 2023. Unlike traditional ingestible devices, this new battery is safe to consume, meaning that ingestible devices using this innovative power source that accidentally breaks down inside the body will not have harmful consequences. 

To make the battery, the researchers turned to edible foods, including almonds, sushi, and capers, to find biochemical reactions that can generate electricity. In the case of this new battery, the researchers turned to vitamin B2 in almonds as the anode and quercetin (found in capers) as the cathode. The researchers utilised activated charcoal to increase electrical conductivity, and a water-based electrolyte provided the medium needed for ion transportation. Finally, nori (seaweed sheets used in sushi) was used as a separator (to keep the electrodes away from each other), and the electrodes were then encapsulated in beeswax. 

The edible battery is able to produce a voltage of 0.65V which is sufficiently low to prevent damage to the digestive tract, and its ability to provide 48uA for 10 minutes (or 1uA for one hour) enables for powering low-energy circuits. In addition, the battery has the ability to be recharged, something that no other edible battery has yet managed to achieve. "The full battery demonstrated a discharging plateau at ≈0.65 V and capacity of up to 7.2 mAh g−1," and "In addition, the battery has the ability to be recharged, something that no other edible battery has yet managed to achieve.".

Fully edible battery cell. a) A fully edible battery was assembled using beeswax as packing, gold-laminated ethyl cellulose (EC/Au) as a current collector, RF/AC or Q/AC composite as electrode material, the aqueous solution of NaHSO4 as an electrolyte, and nori algae as a separator. b) Galvanostatic charging–discharging capacities for 100 cycles at a current of 240 µA. c) Corresponding charging-discharging curves. d) Galvanostatic charging–discharging capacities for 18 cycles at a current of 48 µA. e) Corresponding charging–discharging curves. f) List of ingredients found in a fully edible battery cell. g) An LED powered by two edible cells connected in series.

How could such a device help future electronics?

By far, one of the biggest applications for an edible battery is for use in ingestible devices. While other battery technologies do exist, the ability for a battery to be edible essentially eliminates any risk should the device leak when inside the body. At the same time, ingestible devices could be made to dissolve after taking readings from specific parts of the digestive tract, such as the oesophagus and stomach. 

However, ingestible devices using this battery would not be able to take full advantage of its recharging capability. As such, this battery could also help other areas of electronics, including short-lived biodegradable sensors deployed at scale in wild areas. If used in conjunction with a switch-mode power supply and energy harvester, it’s possible for this battery to help low-energy IoT devices, and the ability for the battery to safely breakdown makes it non-toxic to animals that may eat it. 

While this battery will certainly make a poor pizza topping, what the researchers have demonstrated here is a real feat of research and development. "However, in the short term it could also replace the toxic battery technologies currently used in ingestible electronic devices." If the battery can be refined further, increasing its output voltage and energy storage, it may eventually become a viable alternative to Li-Ion batteries in medical and environmental applications. "An easily implementable edible battery, such as the one demonstrated here, is poised to unlock a vast number of applications in healthcare, pharmacology, and food science, boosting the transition from ingestible to fully edible technologies and devices.". Citation: All quotes are taken from Ilic, I. K., Galli, V., Lamanna, L., Cataldi, P., Pasquale, L., Annese, V. F., Athanassiou, A., & Caironi, M. (2023). An Edible Rechargeable Battery. [Source] Advanced Materials published by Wiley-VCH GmbH. [https://doi.org/10.1002/adma.202211400].