期刊
CHEMISTRY OF MATERIALS
卷 25, 期 18, 页码 3614-3622出版社
AMER CHEMICAL SOC
DOI: 10.1021/cm4013816
关键词
Na rechargeable batteries; mixed-polyanion cathode; electrochemical mechanism; One-phase reaction; structural evolution
资金
- Human Resources Development program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) [20124010203320]
- World Premier Materials grant
- Korea government Ministry of Trade, Industry and Energy
- National Research Foundation of Korea (NRF)
- Korean Government (MSIP) [2012M2B2A4029335, NRF-2012]
- Supercomputing Center in Korea Institute of Science and Technology Information [KSC-2011-C2-51]
- Korea Evaluation Institute of Industrial Technology (KEIT) [20124010203320] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
Compounds with a mixed polyanion framework have recently gained attention as a new class of compounds for material exploration. The potential tunability of the structure by using various combinations of polyanions can potentially lead to a novel cathode. However, the redox reaction in complex structures often involves complex structural evolutions during the electrochemical reaction, which require careful analysis. We investigated the electrochemical mechanism of NaxFe3(PO4)(2)(P2O7) (1 <= x <= 4), which was recently proposed as a promising mixed-polyanion cathode for Na rechargeable batteries, using first principles calculations and experiments. We discovered that the de/sodiation of the NaxFe3(PO4)(2)(P2O7) electrode occurs via a one-phase reaction with a reversible Fe2+/Fe3+ redox reaction and accompanies an exceptionally small volumetric change of less than 4%. Na ion intercalation usually induces a large volumetric change in conventional systems; therefore, this small volume change is unusual and was attributed to the open framework of polyanion compounds with P2O7 dimers that are capable of rotating and distorting to accommodate the structural change. Structural robustness was further observed at even highly charged states at temperatures as high as 530 degrees C from in situ X-ray diffraction (XRD) and differential scanning calorimetry (DSC). We believe that the improved understanding of the electrochemical mechanism provided here will expedite the optimization of the new Na4Fe3(PO4)(2)(P2O7) electrode for Na rechargeable batteries.
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