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.
