Conversion-type cathode materials such as perovskite-type
MF
3 (
M = Fe and Ti) show promise for use in large-scale lithium-ion batteries by virtue of their low cost and large specific capacities. However, the FeF
3 cathode shows a large overpotential during discharge-charge cycles, such that the rechargeable capacity is almost gone after a few cycles. To overcome this drawback, we elucidated the detailed mechanism of the deterioration of the rechargeable capacity for the FeF
3 cathode. In the initial cycle, the cathode returned to the initial FeF
3 structure from LiF and Fe. However, the diffraction peak of LiF and Fe after the 20th cycle was sharper than that after the initial discharge state; that is, the growth of the LiF and Fe crystal contributed to the lower cyclability of FeF
3. On the other hand, the TiF
3 cathode showed an initial discharge/charge capacity of 730/620 mAh g
−1 between 0.5 and 4.0 V, and the discharge-charge overpotential of TiF
3 was still smaller than that of FeF
3. In addition, the cyclability of the TiF
3 cathode were better than that of the FeF
3 cathode, not only in insertion reaction region, but also in conversion reaction region.
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