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Potassium-Ion batteries: sustainable strategies

Subject Area Synthesis and Properties of Functional Materials
Term from 2021 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 448719339
 
Final Report Year 2025

Final Report Abstract

In course of the energy transition towards more sustainable power generation, e-mobility and portable electronics, cost-effective and sustainable energy storage solutions are key. K-ion batteries (KIBs) ranks high amongst the potential battery chemistries, in terms of energy density and prospective costs and abundance of raw materials. In this respect KIBs are expected to compete with graphite/LiFePO4 chemistries and outperform Na-ion batteries. KIBs show a broad technological overlap with other monovalent cell chemistries and could even leverage existing value chains of Li-based battery technologies (e.g. for graphite electrodes). Research results over the past 10 years clearly demonstrated that KIBs won’t be a drop-in solution and rather pose element-specific challenges related to the high reactivity of potassium and its intercalation compounds towards electrolyte components, poor passivation properties of the solid electrolyte interphase (SEI) and (solid-state) diffusion limitations in the active materials. Along the three major cell components, negative and positive electrodes and electrolyte, “Potassium-Ion Batteries: Sustainable Strategies” (KIBSS) set out to address these challenges through novel material developments, and gaining deeper understanding of the degradation pathways and failure mechanisms in KIBs (including dual-ion cell concepts). For this reason, investigating hard carbon from renewable feedstocks and Fe-based Prussian white electrodes played a central role from a sustainability perspective. The teams at IFW Dresden and KIT combined surface-analytical, electrochemical and bulk-analytical techniques, also at synchrotron facilities, as a complementary approach for a better holistic understanding of the cell chemistry. A major part of the work focused on the SEI formation on carbonaceous electrodes (graphite & hard carbons) in different electrolyte environments with the aim to increase cycle life and capacity loss through thinner, yet more protective passivation layers. It was observed repeatedly that experimental results from half-cell setups, i.e. electrochemical tests against K- metal, lead to strong interferences in the analysis of electrode interfaces and electrolyte compositions, owing to the evolution of parasitic compounds that a root cause for self-discharge (in presence of potassium). In contrast, full cell configurations based on graphite negative electrodes and Prussian white (K2Fe[Fe(CN)6]) or polyanionic KVPO4F displayed fundamentally different aging behaviour, highlighting the need of revisiting established testing procedures in the KIB field (or post-Li field in general) that were carried over from Li-ion technologies. Overall, the results suggest that a more dedicated electrolyte and surface/interface design strategies are still needed for the targeted cycle life and energy, with concentrated electrolyte salt mixtures and sulfur-based electrolyte additives pointing into a promising direction.

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