An “Ion Harvester” Battery in Soil Empowered by a Microfluidic Pump and Interlayer Confinement within Micro‐Swiss‐Rolls

Abstract

A significant challenge arises in powering distributed tiny sensors that gather high‐resolution soil data are crucial for advancing digital and geospatial technologies in the field. Traditional batteries and solar cells are unsuitable due to size mismatches. Microbial fuel cells lack stability in delivering constant power. Soil naturally contains redox‐active ions, such as Zn2+ and Mn2+, which can be harvested and utilized for electrochemical energy storage. To facilitate access to soluble ions, a microfluidic pump based on micro‐Swiss‐roll structures via micro‐origami is developed. Spontaneous capillary flow allows for efficient liquid extraction. The micro‐Swiss‐roll architecture shows significant improvements in redox reversibility and charge transfer within micrometer‐thick interlayer space. Notably, the interference of Zn0/2+ and Mn(II)/Mn(IV) reactions is suppressed. Consequently, the battery using a micro‐Swiss‐roll electrode shows high voltage and energy efficiency at high currents up to 10 µA, with cycling stability of 300 times. A twin‐micro‐Swiss‐roll architecture of 0.385 ± 0.006 mm2 is used for energy storage in wet soil, yielding over 40 times more energy as compared to soil‐microbial fuel cells. A conceptual demonstration of an integrated irrigation water sensor and micro‐Swiss‐roll battery highlights the potential of microbattery development in addressing the critical challenge of powering tiny sensors in the soil.