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.

Bromide‐ion batteries can provide higher energy densities compared to conventional lithium‐ion batteries, but the high water solubility of bromide salts may require all‐solid‐state cells. Fortunately, the low Young's modulus of bromide salts is an advantage in terms of fabricating high‐performance all‐solid‐state cells. The present study provides the first‐ever demonstration of an all‐solid‐state bromide‐ion battery. In this work, a novel, single‐phase, K‐doped PbBr2 electrolyte was prepared by mechanical milling, and highly dense pellets were readily obtained from this material by uniaxial cold pressing, because of its low modulus. An initial discharge capacity equal to 87 % of the theoretical capacity was exhibited by an experimental battery when using a BiBr3 positive electrode. This concept of a bromide shuttle battery is expected to promote the research of next‐generation batteries incorporating new active materials and based on conversion‐type reactions.

A single-phase all-solid-state battery was made from amorphous Na3V2(PO4)3 (NVP) powder, which was prepared from mechanical milling of the crystalline NVP. It was found that the structure of the amorphous...