FeF₃ as Reversible Cathode for All‐Solid‐State Fluoride Batteries

Abstract

Fluoride batteries are attracting intensive attention because they can provide a higher energy density than conventional lithium‐ion batteries. Among various metal fluorides, FeF3 is a promising candidate for the cathode material of fluoride batteries because of its high theoretical capacity. In this report, the reversibility of an FeF3 cathode is investigated in conjunction with fluorite‐type Ba0.6La0.4F2.4 as the electrolyte and Pb as the counter‐electrode material. For the first time, the discharge–charge performance of a fluoride battery using FeF3 cathode is investigated. The initial discharge capacity is 579 mAh g−1, and a capacity of 461 mAh g−1 is retained at the 10th cycle. The reversible conversion reaction mechanism for FeF3 is clarified by X‐ray diffraction and X‐ray adsorption spectroscopy. The results revealed that FeF3 is reduced to FeF2 at the first‐stage plateau and then to Fe metal at the second‐stage plateau; they also reveal that the reverse process proceeded during charging. Ex situ scanning electron microscopy observations show that the morphology of the cathode changed reversibly and that, when the battery is in the discharged state, voids are present because of shrinkage of the electrode.

In situ Electrolyte Design: Understanding the Prospects and Limitations of a High Capacity Ca(BH4)2 Anode for All Solid State Batteries

“…The Such a capacity retention with increased electrode thickness is not universally observed in “in situ ” LIB solid electrolyte systems. For example, MgCl 2 exhibits a significant decrease in the initial lithitated capacity when the thickness of the electrode layer is increased [27] . Comparing these results demonstrates that the ionic conductivity of the in situ solid electrolyte plays an essential role in the charge‐discharge performance of the composite electrode (viz.…”

“…Comparing these results demonstrates that the ionic conductivity of the in situ solid electrolyte plays an essential role in the charge‐discharge performance of the composite electrode (viz. LiCl: σ=5.9×10 −5 S cm −1 at 120 °C [27] vs. LiBH 4 : σ≈10 −3 S cm −1 at 120 °C). Nevertheless, when comparing the extended cycling performance of the thicker electrode to the original cell of sample 2 (Fig.…”

“…For example, MgCl 2 exhibits a significant decrease in the initial lithitated capacity when the thickness of the electrode layer is increased. [27] Comparing these results demonstrates that the ionic conductivity of the in situ solid electrolyte plays an essential role in the charge-discharge performance of the composite electrode (viz. LiCl: σ = 5.9×10 À 5 S cm À 1 at 120 °C [27] vs. LiBH 4 : σ � 10 À 3 S cm À 1 at 120 °C).…”

La-Al Intermetallic Alloy Anode for Realizing High-Energy Fluoride-Ion Battery

“…[9][10][11][12][13][14] While, in the early days, the practical capacities of anodes and cathodes in the fluoride-ion batteries had been considerably lower than 100 mAh g -1 , the cathodes have recently shown improvements in discharge capacities (up to 200-500 mAh g -1 ). [15][16][17][18] However, the capacities of anodes are still one order of magnitude smaller than the cathodes, and moreover, their cycle stabilities are also very low. 19,20 To realize a fluoride-ion battery for practical use, it is vital to synthesize a new conceptual anode material with excellent electrochemical performance.…”