High-Voltage Phosphate Cathodes for Rechargeable Ca-Ion Batteries

1st and 2nd cycle galvanostatic discharge-charge curves of (a) NaV2(PO4)3 at 3.5 mA g-1 and (b) FePO4 at 7.5 mA g-1 at room temperature. The insets show the corresponding differential capacity plots. Cycling performance of (c) NaV2(PO4)3 and (d) FePO4.

Scientific Achievement

Two functional polyanionic phosphate materials, NASICON-type NaV2(PO4)3 and olivine-type FePO4, are demonstrated as high voltage Ca-ion battery cathodes for the first time.

Significance and Impact

This work highlights one of the first examples of a stable and high- capacity energy storage system based on calcium-ion chemistry.  Associated theoretical work helps identify pathway and diffusion problems that are unique to these MV systems.

Research Details

  • NaV2(PO4)3 electrodes are found to reversibly intercalate 0.6 mol of Ca2+ (81 mA h g-1) near 3.2 V (vs. Ca2+/Ca) with stable cycling performance. The olivine framework material FePO4 reversibly intercalates 0.2 mol of Ca2+ (72 mA h g-1) near 2.9 V (vs. Ca2+/Ca) in the first cycle.
  • The electrochemical Ca2+ insertion into NaV2(PO4)3 and FePO4 are studied in detail using synchrotron X-ray diffraction, density functional theory calculation, X-ray absorption spectroscopy, electron energy loss spectroscopy and energy dispersive X-ray spectroscopy.
  • Reversible changes in crystal structure, oxidation state, and composition are confirmed.

Download this highlight

DOI: 10.1021/acsenergylett.0c01663

Latest Updates

See All