3D printing of layered vanadium disulfide for water-in-salt electrolyte zinc-ion batteries†

Miniaturized aqueous zinc ion batteries are attractive energy storage devices for wearable electronics, owing to their safety and low cost. Layered vanadium disulfide (VS₂) has demonstrated competitive charge storage capability for aqueous zinc ion batteries, as a result of its multivalent states and large interlayer spacing. However, VS₂ electrodes are affected by quick oxide conversion, and they present predefined geometries and aspect ratios, which hinders their integration in wearables devices. Here, we demonstrate the formulation of a suitable ink for extrusion-based 3D printing (direct ink writing) based on micro flowers of layered VS₂ obtained using a scalable hydrothermal process. 3D printed architectures of arbitrary design present electrochemically active, porous and micron-sized struts with tuneable mass loading. These were used as cathodes for aqueous zinc-ion battery electrodes. The 3D printed VS₂ cathodes were assembled with carbon/zinc foil anodes to form full cells of zinc-ion, demonstrating a capacity of ∼1.98 mA h cm⁻² with an operating voltage of 1.5 V. Upon cycling a capacity retention of around 65% was achieved after ∼100 cycles. The choice of the electrolyte (a water-in-salt electrolyte) and the design of the pre-processing of the 3D printed cathode ensured improved stability against dissolution and swift oxidation, notorious challenges for VS₂ in an aqueous environment. This works paves the way towards programmable manufacturing of miniaturized aqueous batteries and the materials processing approach can be applied to different materials and battery systems to improve stability.