Development of a water based process for stable conversion cathodes on the basis of FeF3

A facile water based synthesis method for HTB-FeF3/rGO and r-FeF3/rGO composites was developed using FeF3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF3/rGO were cast in ambient air and the calendered electrode shows a stable specific energy of 470 Wh kg(-1) (210 mA h g(-1), 12 mA g(-1)) after 100 cycles in the range 1.3-4.3 V with very little capacity fading. The good cycle stability is attributed to the intimate contact of FeF3 nanoparticles with reduced graphene oxide carbon surrounding. Using a combination of in situ XRD, XAS and ex situ Mossbauer spectroscopy, we show that during discharge of HTB-FeF3/rGO composite Li is intercalated fast into the tunnels of the HTB-FeF3 structure up to x = 0.92 Li. The Li intercalation is followed by slow conversion of HTB-LixFeF3 to LiF and Fe nanoparticles below 2.0 V. During charge, the LiF and Fe phases are slowly transformed to amorphous FeF2 and FeF3 phases without reformation of the HTB-FeF3 framework structure. At an elevated temperature of 55 degrees C a much higher specific energy of 780 Wh kg(-1) was obtained. (c) 2016 Elsevier B.V. All rights reserved.