A facile water based synthesis method for HTB-FeF 3 /rGO and r-FeF 3 /rGO composites was developed using FeF 3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF 3 /rGO were cast in ambient air and the calendared electrode showed a stable specific energy of 470 Wh kg-1 (210 mAh g-1 , 12 mA g-1) after 100 cycles in the range 4.3-1.3 V with very little capacity fading. The good cycle stability is attributed to the intimate contact of FeF 3 nanoparticles with reduced graphene oxide carbon surrounding. We show using a combination of in situ XRD, XAS and ex situ Mössbauer spectroscopy that during discharge of HTB-FeF 3 /rGO composite Li is intercalated fast into the tunnels of the HTB-FeF 3 structure up to x = 0.95 Li followed by slow conversion to LiF and Fe nanoparticles below 2.0 V. During charge, the LiF and Fe phases are slowly transformed to amorphous FeF 2 and FeF 3 phases without reformation of the HTB-FeF 3 framework structure. At an elevated temperature of 55 °C a much higher specific energy of 780 Wh kg-1 was obtained.
A facile water based synthesis method for HTB-FeF 3 /rGO and r-FeF 3 /rGO composites was developed using FeF 3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF 3 /rGO were cast in ambient air and the calendared electrode showed a stable specific energy of 470 Wh kg -1 (210 mAh g -1 , 12 mA g -1 ) after 100 cycles in the range 4.3-1.3 V with very little capacity fading. The good cycle stability is attributed to the intimate contact of FeF 3 nanoparticles with reduced graphene oxide carbon surrounding. We show using a combination of in situ XRD, XAS and ex situ Mössbauer spectroscopy that during discharge of HTB-FeF 3 /rGO composite Li is intercalated fast into the tunnels of the HTB-FeF 3 structure up to x = 0.95 Li followed by slow conversion to LiF and Fe nanoparticles below 2.0 V. During charge, the LiF and Fe phases are slowly transformed to amorphous FeF 2 and FeF 3 phases without reformation of the HTB-FeF 3 framework structure. At an elevated temperature of 55 °C a much higher specific energy of 780 Wh kg -1 was obtained.
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