The Re3dOx – Recycling project (project number 03ET6156) was a consortium effort funded by the German Federal Ministry of Education and Research. The consortium comprised Eisenhuth, Technische Universität Chemnitz (TUC), Zwickau‑Bergbau‑Technik (ZBT) and Fumatech. Eisenhuth coordinated the project, organised regular project meetings and managed the overall progress. TUC focused on in‑situ characterisation of new and recycled materials, the development of a system model for the full life cycle of a vanadium redox flow battery (VRFB) and the assessment of closed‑ and open‑loop recycling potentials. ZBT carried out extrusion trials to produce bipolar plates (BPP) from recycled compound material, characterised the resulting plates, demonstrated a proof‑of‑concept for resource‑efficient extrusion using comb‑structured plates and evaluated the suitability of recycled material for fuel‑cell applications. Fumatech contributed additional expertise in material testing and analysis. The project ran from 2019 to 2021, culminating in a series of publications and conference presentations, notably an eight‑page paper and a talk at the ECCM 20 conference.
Technically, the project achieved a comprehensive analysis of recycling pathways for VRFB components. A high‑filled compound (85 wt % graphite in polypropylene) was produced in a ring extruder by ZBT and processed into bipolar plates via injection moulding. The plates were then milled back into powder and re‑extruded, allowing a 100 % recycling loop that was repeated six times. Electrical characterisation revealed a clear decrease in plate resistance with each recycling step, while mechanical testing in a three‑point bending test showed a significant increase in bending strength and a concurrent reduction in elongation. Thermogravimetric analysis (TGA) of the recycled compounds indicated no loss of graphite filler up to 500 °C, but above 650 °C the recycled samples exhibited higher mass‑loss rates, reflecting a progressive reduction in particle size with each recycling cycle. Differential scanning calorimetry (DSC) did not reveal obvious polymer degradation, whereas gel‑permeation chromatography (GPC) showed a shift of the molecular‑weight distribution toward lower values after the first extrusion step, with further degradation observed after subsequent recycling cycles. The GPC data suggested a lower limit of polymer breakdown beyond which additional recycling produced only marginal quality changes.
In addition to material characterisation, the consortium developed a system model that integrates manufacturing, use, and end‑of‑life stages of a VRFB. This model enabled a quantitative comparison of the environmental and economic impacts of closed‑loop recycling (re‑use of recovered components) versus open‑loop recycling (conversion into new products). The analysis demonstrated that closed‑loop recycling offers substantial reductions in material consumption and greenhouse‑gas emissions, while open‑loop recycling can still provide value when closed‑loop options are limited. The project also produced a set of guidelines for the design of recyclable VRFB components, including recommendations for material selection, manufacturing processes, and end‑of‑life handling.
Overall, the Re3dOx project delivered a detailed, data‑driven assessment of recycling strategies for VRFB components, combining experimental work on recycled compounds and plates with advanced characterisation techniques and life‑cycle modelling. The findings provide a solid scientific basis for the development of more sustainable energy‑storage systems and inform policy and industry stakeholders about the feasibility and benefits of recycling in the emerging field of redox‑flow batteries.