A review on the application of iron(III) fluorides as positive electrodes for secondary cells

Abstract

Among the many industrial and research level applications of fluorides like microelectronics, polymers, agronomy, imaging, dental composites, uranium enrichment processes or catalysis, there is a recent and growing interest for these ionic compounds in the field of energy storage and conversion. Li-ion technology in particular, has been attracted to fluorides due to the possibility of morethan-one electrode reaction. In fact, these reactions can potentially enhance the energy stored in commercial cells (conversion reactions). By reaction with lithium, transition metal fluorides such as MnF 3 , FeF 3 , CoF 3 or CuF 2 , can be reduced to the respective zero valent metal/LiF mixture with resulting high theoretical capacities ranging from 3 to 4.2 times the amount currently delivered by commercial LiFePO 4 (170 mAh g-1). Since, in practice, the most of the research efforts are being put into iron trifluoride due to chemical (relatively mild synthesis conditions), electrochemical (lower polarization than MnF 3 for example) and environmental (Fe is more environmentally friendly than Co) reasons, in this review we will focus on the electrochemistry, synthesis strategies and amelioration techniques for the high oxidation state ferric fluoride and its derivatives.

Rhombohedral iron trifluoride with a hierarchized macroporous/mesoporous texture from gaseous fluorination of iron disilicide

“…1 Besides, each of the two contributions involved roughly 0.5 electron. This behavior is in agreement with a transformation reported in literature operating initially through a two-phase region related with the 3.35 V voltage plateau up to Li 0.5 FeF 3 and then through a solid-solution reaction centered at 3 V that involves insertion of lithium in Li 0.5+x FeF 3 up to LiFeF 3 [9], [23] . The reverse scan depicts a dissymmetric charge curve with two main electrochemical steps and leads to a coulombic efficiency of 88 %.…”

“…Many attempts have been then dedicated to decreasing the particle size of such materials and to increase their conductivity by high energy ball-milling them with conductive carbon [6] or focusing on hydrated phases, because of the presence of water favoring the ionic conductivity [7]. Iron trifluoride has attracted substantial interest due to its electromotive force value of 3.2 V and a large theoretical capacity of 711 mAh.g -1 for a redox process of three exchanged electrons [8], [9]. This capacity value is larger from the practical capacity obtained for the operational cathode materials of secondary batteries made of LiFePO 4 or LiCoO 2 .…”

Hydrothermal synthesis of K3FeF6 and its electrochemical characterization as cathode material for lithium-ion batteries

“…The Li-rich fluorides Li 2 MnF 5 and Li 3 MF 6 (M = V, Cr, Fe) concerning theoretical investigations have been published recently [13,[23][24][25][26]. And Li 3 VF 6 [27], LiMnF 4 [28] and LiFe 2 F 6 [29] relating to electrochemical properties for Li cells have been reported as well.…”

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

“…7 Iron fluoride is particularly interesting because it has the highest theoretical energy density of 1950 Wh kg -1 (2.74 V, 712 mAh g -1 ) and is non-toxic, environmentally friendly, cheap and abundant. 8 Traditionally, FeF 3 /C composites have been prepared by ball-milling commercial rhombohedral r-FeF 3 with carbon black to reduce the primary particle size and to coat the r-FeF 3 nanoparticles with an electrically conducting layer of carbon. 9 This approach leads to materials with large initial capacity up to the theoretical maximum of 712 mAh g -1 , but poor cycle stability as the carbon coating is incomplete and not attached strongly enough to the FeF 3 particle surface.…”