Polypyrrole-enveloped Prussian blue nanocubes with multi-metal synergistic adsorption toward lithium polysulfides: high-performance lithium-sulfur batteries

The development of lithium-sulfur (Li-S) batteries is largely hindered by the shuttling and poor electronic conductivity of polysulfide. To solve these two problems simultaneously, we report a new strategy that combines the advantages of Prussian blue analogues (PBAs) with the conductive characteristic of polypyrrole (ppy) to construct FeCoNi PBA-S-ppy composite. The open metal centers in PBAs act as Lewis acid sites with good affinity to the negatively charged polysulfide anions, while the open framework structure allows effective storage of sulfur and confinement of lithium polysulfides (LiPS). Herein, the polysulfide redox reaction mechanism and kinetics are revealed by using in situ X-ray diffraction. The adsorption ability test and electrochemical performance assessment together with density functional theory calculations reveal that the FeCoNi PBA can achieve enhanced LiPS absorption ability and better cycling performance than the FeNi and FeCo PBAs. This can be attributed to the multi-metal synergistic adsorption toward LiPS within FeCoNi PBA, which can act as an effective chemical-anchor to capture LiPS. After combining the FeCoNi PBA with ppy, a physical barrier formed, and the improvement of the conductivity resulted in remarkable electrochemical performance. We believe that PBAs can play a beneficial role in guaranteeing more stable and efficient Li-S batteries.