Semi-solid electrodes based on injectable hydrogel electrolytes for shape-conformable batteries

Abstract

The development of new battery concepts, chemistries and fabrication processes is driven by the bloom of emerging applications in a variety of fields ranging from the Internet of Things to Smart Healthcare. Shape factor-free and shape-conformable power sources are highly desired for integration with complex-shape electronic devices. Herein, a new fabrication process for shape-conformable batteries is explored. Battery cells having targeted shapes are fabricated and assisted by 3D printing. Then, flowable semi-solid electrodes are used to fill in the prefabricated parts of the battery cell. The use of injectable hydrogel electrolytes enables semi-solid electrodes to possess special rheological properties as they are flowable during the fabrication process, while gelation of the electrolytes ensures their immobility during battery operation. Herein, poly(vinyl alcohol):gallic acid gels are investigated for aqueous Zn–LiFePO4 batteries. After evaluation of the effect of electrode formulation on the rheological properties as well as the ionic and electronic properties, simple-shape and UBU-shape batteries were fabricated using the best formulation. The prototype achieved areal capacities above 3 mA h cm−2, utilization rate between 150 and 180 mA h g−1 (LFP), and capacity fading of 0.2% h−1. While the prototype demonstrated the feasibility of the proposed fabrication process, improvements are still required. Shrinking of gel electrolytes and parasitic electrochemical reactions associated with the battery chemistry and the operation conditions are identified as the main challenges to be addressed for improving the performance.