Synthesis, Crystal Structure, and Electrochemical Properties of Alluaudite Na_1.702Fe₃(PO₄)₃ as a Sodium-Ion Battery Cathode

Abstract

Sodium-ion batteries hold promise as an enabling technology for large-scale energy storage that is safer, less expensive, and lower environmentally impactful than their equivalent lithium-ion batteries. Reported herein is the one-pot hydrothermal synthesis, crystal structure, and electrochemical properties of a promising sodium-ion battery cathode material, an alluaudite phase of Na1.702Fe3(PO4)3. After ball milling and carbon coating, this material exhibits a reversible capacity of ∼140 mAh/g with good cycling performance (93% of the initial capacity is retained after 50 cycles) and excellent rate capability. This alluaudite compound and its method of preparation is a promising cathode for large-scale battery applications that are earth-abundant and sustainable.

High‐Abundance and Low‐Cost Metal‐Based Cathode Materials for Sodium‐Ion Batteries: Problems, Progress, and Key Technologies

“…[160] A one-pot hydrothermal synthetic method was employed to fabricate alluaudite Na 1.702 Fe 3 (PO 4 ) 3 (Figure 12c). [149] Goodenough's group reported that Fe-substituted NASICON-type Na 3 FeV(PO 4 ) 3 can exhibit both excellent rate capability and very stable cycling performance. [161] The presence of V can elevate the working potential, while Fe can stabilize the structure for longer cycling.…”

“…Reproduced with permission. [149] Copyright 2017, American Chemical Society; and d) orthorhombic Na 2 FePO 4 F. Reproduced with permission. [150] Copyright 2017, American Chemical Society.…”

Polyanionic Insertion Materials for Sodium‐Ion Batteries

“…Alluaudite NaMnFe 2 (PO 4 ) 3 [144] Monoclinic (C2/c) 50 mAh g −1 , 2.7 V (Q Th = ≈100 mAh g −1 ) Na 2 Fe 3 (PO 4 ) 3 [146] Monoclinic (C2/c) 140 mAh g −1 , 2.7 V (Q Th = ≈150 mAh g −1 ) Na 1.702 Fe 3 (PO 4 ) 3 [147] Monoclinic (C2/c) 140 mAh g −1 , 2.95 V (Q Th = ≈160 mAh g −1 ) Na 1.86 Fe 3 (PO 4 ) 3 [148] Monoclinic (C2/c) 100 mAh g −1 , 3.0 V (Q Th = ≈160 mAh g −1 ) Na 2 Co 2 Fe(PO 4 ) 3 [149] Monoclinic (C2/c)…”

“…[146] Several other Na x Fe 3 (PO 4 ) 3 (x = 1.702, 1.86) alluaudites have been recently reported, where due cathode optimization with ball milling has enabled high reversible capacity close to 140 mAh g −1 involving a distinct 3 V activity. [147,148] Co-and Ni-based alluaudites have been reported with dual cathode/anode operation giving rise to capacity over 100 mAh g −1 with an average potential of 3 V. [149] Overall, while alluaudites form an interesting system, they suffer from low redox potential and poor electrochemical activity, limiting their practical application. One approach may be to switch to SO 4 -based alluaudites as described in the following section.…”

“…In another attempt, various Na 2 Fe 3− x Mn x (PO 4 ) 3 alluaudites were tested showing a reversible capacity close to 140 mAh g −1 . Several other Na x Fe 3 (PO 4 ) 3 ( x = 1.702, 1.86) alluaudites have been recently reported, where due cathode optimization with ball milling has enabled high reversible capacity close to 140 mAh g −1 involving a distinct 3 V activity . Co‐ and Ni‐based alluaudites have been reported with dual cathode/anode operation giving rise to capacity over 100 mAh g −1 with an average potential of 3 V …”