Mechanism of Sodium Ion Storage in Na7[H2PV14O42] Anode for Sodium-Ion Batteries

Chia Ching Lin, Wei Hsiang Lin, Shao Chu Huang, Chih Wei Hu, Tsan Yao Chen, Chi Ting Hsu, Hao Yang, Ali Haider, Zhengguo Lin, Ulrich Kortz, Ulrich Stimming, Han Yi Chen

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27 Scopus citations

Abstract

In this work, the authors explore the sodium salt of the 14-vanado(V)phosphate, Na7[H2PV14O42], as a potential anode material for sodium-ion batteries (NIBs). The multi-electron redox activity of the polyoxovanadate [H2PV14O42]7-leads to high capacity. This polyanion is synthesized by a simple aqueous solution procedure and isolate as a sodium salt with different numbers of crystal waters, Na7[H2PV14O42]·nH2O (n = 15–24). Na7[H2PV14O42] as anode in NIBs exhibits a high and reversible capacity of 322 mA h g−1 at 25 mA g−1 with a high cycling stability (with capacity retention of 87% after 120 cycles). Some of the V5+ ions in [H2PV14O42]7- can be reduced to V3+ after being discharged to 0.01 V versus Na/Na+, resulting in an average oxidation state of V3.7+, as based on ex situ X-ray photoelectron spectroscopy and in situ synchrotron X-ray absorption near edge structure studies. The crystalline material becomes amorphous during the charge/discharge processes, which can be observed by in situ synchrotron X-ray diffraction, indicating that functionality does not require crystallinity. The authors propose that the charge storage mechanism of Na7[H2PV14O42] anodes mainly involves redox reactions of V accompanied by insertion/extraction of Na ions in-between polyoxo-14-vanadate ions and adsorption/desorption of Na ions on the surface of the vanadate material.

Original languageEnglish
Article number1800491
JournalAdvanced Materials Interfaces
Volume5
Issue number15
DOIs
StatePublished - 9 Aug 2018
Externally publishedYes

Keywords

  • anode
  • in situ X-ray absorption near edge structure
  • in situ X-ray diffraction
  • polyoxometalates
  • sodium-ion batteries

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