Fe Site Order and Magnetic Properties of Fe 1/4 NbS 2

Lawrence, Erick A.; Huai, Xudong; Kim, Dongwook; Avdeev, Maxim; Chen, Yu; Skorupskii, Grigorii; Miura, Akira; Ferrenti, Austin; Waibel, Moritz; Kawaguchi, Shogo; Ng, Nicholas; Kaman, Bobby; Cai, Zijian; Schoop, Leslie; Kushwaha, Satya; Liu, Feng; Tran, Thao T.; Ji, Huiwen

doi:10.1021/acs.inorgchem.3c02652

Abstract Iron ion batteries using Fe²⁺as a charge carrier have yet to be widely explored, and they lack high‐performing Fe²⁺hosting cathode materials to couple with the iron metal anode. Here, it is demonstrated that VOPO₄∙2H₂O can reversibly host Fe²⁺with a high specific capacity of 100 mAh g⁻¹and stable cycling performance, where 68% of the initial capacity is retained over 800 cycles. In sharp contrast, VOPO₄∙2H₂O's capacity of hosting Zn²⁺fades precipitously over tens of cycles. VOPO₄∙2H₂O stores Fe²⁺with a unique mechanism, where upon contacting the electrolyte by the VOPO₄∙2H₂O electrode, Fe²⁺ions from the electrolyte get oxidized to Fe³⁺ions that are inserted and trapped in the VOPO₄∙2H₂O structure in an electroless redox reaction. The trapped Fe³⁺ions, thus, bolt the layered structure of VOPO₄∙2H₂O, which prevents it from dissolution into the electrolyte during (de)insertion of Fe²⁺. The findings offer a new strategy to use a redox‐active ion charge carrier to stabilize the layered electrode materials.

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