Printed Coplanar Batteries: Materials, Processing and Parametrisation
Authors:   , Rassek Patrick L. 
Published: December 2021

Fully screen-printed zinc-manganese dioxide (Zn|MnO2) batteries can power printed electronics devices. However, large-scale market implementation of such batteries has been impeded due to complexity in manufacturing and insufficient long-term stability. This work looks at key production parameters of current collector passivation, calendering of electrodes, electrode spacing and interfacial area and evaluates their effect on battery performance. Many commercially available conductive inks used to screen-print current collectors were developed for other applications and suffer power consuming parasitic side reactions inside electrochemical cells. A practical strategy to avoid corrosion of metallic current collectors adversely affecting battery performance is to print carbon black passivation layers, which is employed in this work. The stability of printed current collectors and passivation layers in common electrolyte solutions has been addressed using cyclic voltammetry (CV) experiments to identify pinhole-related anodic peak currents. Current integration over time enabled quantification and comparison of the passivation capability of individually fabricated protective carbon black layers. Printed layer thicknesses of at least 7 µm were required for the avoidance of pinholes in the protective passivation layers. The protective functionality was further enhanced by printing of passivation layer thicknesses of up to 25 µm and modification of the printing process to double prints wet-on-dry. Coplanar Zn|MnO2 batteries have a lower manufacturing complexity than stack-type batteries but lower interest in coplanar batteries can be attributed to reduced electrical and electrochemical performance due to layout-specific issues. Batteries comprising series connections or smaller gap widths between electrodes are typically printed to overcome these limitations. The focus of this study is the optimisation of battery performance characteristics by process and layout modification while enhancing processability on a wide range of screen printing machines. Thus, coplanar batteries prepared were calendered as part of the systematic electrode post-treatment. Battery layouts were modified by incremental gap width enlargement and a gap length extension. Individual effects of the electrical performance were monitored by electrochemical impedance spectroscopy (EIS) measurements and discharge experiments. Calendering of zinc anodes reduced charge transfer resistances of the batteries. Gap width extensions in a range between 1 mm and 5 mm showed only marginal impact on discharge performance metrics. Increase of the electrode interfacial area resulted in an improved current capability, raised short circuit currents by 45 %, and enhanced the durability against mechanical stress and thermal intake during battery activation and encapsulation. This work contributes to the optimisation of fully screen-printed coplanar Zn|MnO2 batteries by a predictable stability of passivation layers and an improved battery performance by Zn electrode calendering. Reduced requirements on registration due to increased electrode spacing and an enhanced process stability during encapsulation enable production of printed batteries at industrial-scale.