ic9b03058_si_001.pdf (6.17 MB)
Structure, Magnetism, and Electrochemistry of LiMg1–xZnxVO4 Spinels with 0 ≤ x ≤ 1
journal contribution
posted on 2019-12-14, 03:03 authored by Takeshi Uyama, Kazuhiko Mukai, Ikuya YamadaNegative electrode materials with lower operating voltages
are urgently required to increase the energy density of lithium-ion
batteries. In this study, LiMgVO4 with a Na2CrO4-type structure, LiZnVO4 with a phenacite
structure, and their mixture were treated under a high pressure of
12 GPa and a high temperature of 1273 K, and their electrochemical
reactivities were examined in a nonaqueous lithium cell. Synchrotron
X-ray diffraction (XRD) measurements and Raman spectroscopy revealed
that the LiMg1–xZnxVO4 samples with 0 ≤ x ≤ 1 are in a single phase of the inverse spinel structure
that forms a solid solution compound over the whole x range. All of the samples were brown or light black due to the presence
of a small amount of V4+ ions with S =
1/2 and oxygen deficiencies. Since the majority of the vanadium ions
are located at the route of the Li+ ion conduction pathway,
no rechargeable capacity (Qrecha) would
be expected. Nevertheless, all LiMg1–xZnxVO4 samples exhibited
a Qrecha value of more than 200 mAh g–1 with an operating voltage of ∼0.8 V. This
operating voltage is ∼1.6 V lower than that of LiV2O4 with a normal spinel structure. Furthermore, the x = 0.5 sample demonstrated an extremely stable cycle performance
over 1 month. Ex situ XRD measurements clarified that the reversible
electrochemical reaction can be attributed to the movement of vanadium
ions from the tetrahedral 8a to octahedral 16c sites during the initial
discharge reaction. Details regarding the crystal structure, magnetism,
and electrochemistry of LiMg1–xZnxVO4 are presented.