Freeform fabrication and characterization of Zn-air batteries

Purpose – The paper’s aim is to show the development of materials and methods which allow freeform fabrication of macroscopic Zn-air electrochemical batteries. Freedom of geometric design may allow for new possibilities in performance optimization. Design/methodology/approach – The authors have formulated battery materials which are compatible with solid freeform fabrication (SFF) while retaining electrochemical functionality. Using SFF processes, they have fabricated six Zn-air cylindrical batteries and quantitatively characterized them and comparable commercial batteries. They analyze their performance in light of models from the literature and they also present SFF of a flexible twocell battery of unusual geometry. Findings – Under continuous discharge to 0.25 V/cell with a 100V load, the cylindrical cells have a specific energy and power density in the range of 40-70 J/g and 0.4-1 mW/cm, respectively, with a mass range of 8-18 g. The commercial Zn-air button cells tested produce 30-750 J/g and 7-9 mW/cm under the same conditions, and have a mass range of 0.2-2 g. The two-cell, flexible Zn-air battery produces a nominal 2.8 V, open-circuit. Research limitations/implications – The freeform-fabricated batteries have ,10 percent of the normalized performance of the commercial batteries. High-internal contact resistance, loss of electrolyte through evaporation, and inferior catalyst reagent quality are possible causes of inferior performance. Complicated material preparation and battery fabrication processes have limited the number of batteries fabricated and characterized, limiting the statistical significance of the results. Practical implications – Performance enhancement will be necessary before the packaging efficiency and design freedom provided by freeformfabricated batteries will be of practical value. Originality/value – The paper demonstrates a multi-material SFF system, material formulations, and fabrication methods which together allow the fabrication of complete functional Zn-air batteries. It provides the first quantitative characterization of completely freeform-fabricated Zn-air batteries and comparison to objective standards, and shows that highly unusual, functional battery designs incorporating flexibility, multiple cells, and unusual geometry may be freeform fabricated.