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The layered transition metal chalcogenides MCrX2 (M = Ag, Cu; X = S, Se, Te) are of interest for energy storage because chemically Li-substituted analogs were reported as superionic Li+ conductors. The coexistence of fast ion transport and reducible transition metal and chalcogen elements suggests that this family may offer multifunctional capability for electrochemical storage. Here, we investigate the electrochemical reduction of AgCrSe2 and CuCrSe2 in non-aqueous Li- and Na-ion electrolytes using electrochemical measurements coupled with ex situ characterization (scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy). Both compounds delivered high initial specific capacities (~ 560 mAh/g), corresponding to 6.64 and 5.73 Li+/e- per formula unit for AgCrSe2 and CuCrSe2, respectively. We attribute this difference to distinct reduction pathways: 1) Li+ intercalation to form LiCrSe2 and extruded Ag or Cu, 2) conversion of LiCrSe2 to Li2Se, and 3) formation of an Ag-Li alloy at the lowest potential, operative only in AgCrSe2. Consistent with this proposed mechanism, step 3 was absent during reduction of AgCrSe2 in a Na-ion electrolyte since Ag does not alloy with Na. These results demonstrate the complex reduction chemistry of MCrX2 in the presence of alkali ions, providing insights into the use of MCrX2 materials as alkali ion superionic conductors or high capacity electrodes for lithium or sodium-ion type batteries.
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Carbon Quantum Dot Modified Reduced Graphene Oxide Framework for Improved Alkali Metal Ion Storage Performance
Abstract Organic materials with redox‐active oxygen functional groups are of great interest as electrode materials for alkali‐ion storage due to their earth‐abundant constituents, structural tunability, and enhanced energy storage properties. Herein, a hybrid carbon framework consisting of reduced graphene oxide and oxygen functionalized carbon quantum dots (CQDs) is developed via the one‐pot solvothermal reduction method, and a systematic study is undertaken to investigate its redox mechanism and electrochemical properties with Li‐, Na‐, and K‐ions. Due to the incorporation of CQDs, the hybrid cathode delivers consistent improvements in charge storage performance for the alkali‐ions and impressive reversible capacity (257 mAh g−1at 50 mA g−1), rate capability (111 mAh g−1at 1 A g−1), and cycling stability (79% retention after 10 000 cycles) with Li‐ion. Furthermore, density functional theory calculations uncover the CQD structure‐electrochemical reactivity trends for different alkali‐ion. The results provide important insights into adopting CQD species for optimal alkali‐ion storage.
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- Award ID(s):
- 1805052
- PAR ID:
- 10370440
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 18
- Issue:
- 35
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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