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

Abstract

The development of new battery concepts, chemistries and fabrication processesis driven by the bloom of emerging applications in a variety of fields ranging fromthe Internet of Things to Smart Healthcare. Shape factor-free and shapeconformablepower sources are highly desired for integration with complex-shapeelectronic devices. Herein, a new fabrication process for shape-conformablebatteries is explored. Battery cells having targeted shapes are fabricated andassisted by 3D printing. Then, flowable semi-solid electrodes are used to fill inthe prefabricated parts of the battery cell. The use of injectable hydrogelelectrolytes enables semi-solid electrodes to possess special rheologicalproperties as they are flowable during fabrication process, while gelation of theelectrolytes ensures their immobility during battery operation. Herein, poly(vinylalcohol) : gallic acid gels are investigated for aqueous Zn – LiFePO4 batteries.After evaluation of the effect of electrode formulation in the rheological propertiesas well as the ionic and electronic properties, simple-shape and UBU-shapebatteries were fabricated using the best formulation. The prototype achievedareal capacities above 3 mAh cm-2, utilization rate between 150 and 180 mAh g-1 (LFP), and capacity fading of 0.2 % h-1. While the prototype demonstrated thefeasibility of the proposed fabrication process, improvements are still required.Shrinking of gel electrolytes and parasitic electrochemical reactions associatedwith the battery chemistry and the operation conditions are identified as the mainchallenges to be addressed for improving the performances.