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In Situ Converting Conformal Sacrificial Layer Into Robust Interphase Stabilizes Fluorinated Polyanionic Cathodes for
Peng Gong1,2, Shibo Chai2, Xingjie Li2
1School of Integrated Circuits, Huazhong University of Science and Technology, Wuhan, 430074, P. R. China.
Summary
Researchers developed a new method to improve sodium-ion storage by converting harmful by-products into a protective layer. This enhances the stability and performance of sodium vanadium oxy-fluorophosphates (NVOPF) in aqueous electrolytes.
Area of Science:
- Materials Science
- Electrochemistry
- Energy Storage
Background:
- Sodium vanadium oxy-fluorophosphates (NVOPF) are promising for high-voltage, high-capacity aqueous sodium-ion storage.
- Interfacial degradation and hydrofluoric acid (HF) by-products limit the cycle life of NVOPF in aqueous electrolytes.
Purpose of the Study:
- To overcome the limitations of NVOPF in aqueous electrolytes by in situ converting harmful HF derivatives into a protective cathode electrolyte interphase (CEI).
- To demonstrate the effectiveness of an aluminum oxide (Al2O3) sacrificial layer for generating a robust, fluorine-containing CEI.
Main Methods:
- Precoating NVOPF with a conformal Al2O3 sacrificial layer to generate an AlF3-rich CEI in situ.
- Characterizing the evolved CEI chemistry and its impact on interfacial reactions, vanadium dissolution, and Na+ transport.
- Integrating the modified NVOPF with a pseudocapacitive anode and hydrogel electrolyte to construct a quasi-solid-state sodium-ion hybrid capacitor.
Main Results:
- The AlF3-rich CEI effectively mitigates interfacial side reactions, inhibits vanadium dissolution, and enhances Na+ transport kinetics.
- Significant improvements in cycling stability (3.15x capacity retention), rate capability, and low-temperature performance (1.5x capacity at -20°C) were achieved.
- The developed quasi-solid-state sodium-ion hybrid capacitor demonstrated excellent cycle life (77.0% after 1000 cycles), high energy/power densities, and safety.
Conclusions:
- In situ formation of a protective CEI via an Al2O3 sacrificial layer is a viable strategy to enable unstable electrode materials like NVOPF in aqueous electrolytes.
- The approach significantly enhances electrochemical performance and stability, paving the way for practical aqueous sodium-ion energy storage.
- The study highlights the potential for advanced interfacial engineering in developing next-generation energy storage devices and systems.
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