Scientists from Nanyang Technological University (NTU) in Singapore developed a very thin battery that’s about as thin as the human cornea. While smart contact lenses promise an array of applications, from medical monitoring to AR, they require a compact and biocompatible power source. Traditional batteries, which often contain potentially harmful materials and require wired or induction charging, are ill-suited for such applications due to safety and comfort concerns.
The NTU battery uses biocompatible materials, eliminating the need for potentially harmful wires or heavy metals, common in lithium-ion batteries. It features a glucose-based coating, which undergoes a reaction with sodium and chloride ions present in saline solutions. This reaction generates electricity. Intriguingly, the battery’s operation can be extended by human tears, which, although lower in ion concentration compared to saline, still provide charge due to their sodium and potassium content.
The battery, at a mere 0.5mm thickness, reacts with basal tears, maintaining a constant film over our eyes. In terms of electrical metrics, the battery has demonstrated a current of 45 microamperes and a power peak of 201 microwatts, sufficient for smart contact lens operations. For perspective, it can be charged and discharged up to 200 cycles, while standard lithium-ion batteries last for 300 to 500 cycles.
Optimal charging involves immersing the battery in a solution rich in glucose, sodium, and potassium ions for at least eight hours, which can conveniently coincide with the user’s sleeping hours. The team highlighted that the integrated design combining a battery and a biofuel cell obviates the need for additional space-consuming components. They plan further R&D to enhance the battery’s electrical output and are in talks with contact lens manufacturers to integrate their technology.
Yun, J., Li, Z., Miao, X., Li, X., Lee, J. Y., Zhao, W., & Lee, S. W. (2023). A tear-based battery charged by biofuel for smart contact lenses. Nano Energy, 110, 108344. https://doi.org/10.1016/j.nanoen.2023.108344