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.
Rechargeable aqueous batteries with Zn2+as a working‐ion are promising candidates for grid‐scale energy storage because of their intrinsic safety, low‐cost, and high energy‐intensity. However, suitable cathode materials with excellent Zn2+‐storage cyclability must be found in order for Zinc‐ion batteries (ZIBs) to find practical applications. Herein, NaCa0.6V6O16·3H2O (NaCaVO) barnesite nanobelts are reported as an ultra‐stable ZIB cathode material. The original capacity reaches 347 mAh g−1at 0.1 A g−1, and the capacity retention rate is 94% after 2000 cycles at 2 A g−1and 83% after 10 000 cycles at 5 A g−1, respectively. Through a combined theoretical and experimental approach, it is discovered that the unique V3O8layered structure in NaCaVO is energetically favorable for Zn2+diffusion and the structural water situated between V3O8layers promotes a fast charge‐transfer and bulk migration of Zn2+by enlarging gallery spacing and providing more Zn‐ion storage sites. It is also found that Na+and Ca2+alternately suited in V3O8layers are the essential stabilizers for the layered structure, which play a crucial role in retaining long‐term cycling stability.
more » « less- NSF-PAR ID:
- 10459773
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 9
- Issue:
- 38
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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