TY - JOUR
T1 - Computational Investigation and Experimental Realization of Disordered High-Capacity Li-Ion Cathodes Based on Ni Redox
AU - Ji, Huiwen
AU - Kitchaev, Daniil A.
AU - Lun, Zhengyan
AU - Kim, Hyunchul
AU - Foley, Emily
AU - Kwon, Deok Hwang
AU - Tian, Yaosen
AU - Balasubramanian, Mahalingam
AU - Bianchini, Matteo
AU - Cai, Zijian
AU - Clément, Raphaële J.
AU - Kim, Jae Chul
AU - Ceder, Gerbrand
N1 - Publisher Copyright:
© 2019 American Chemical Society.
PY - 2019/4/9
Y1 - 2019/4/9
N2 - In cation-disordered rocksalt Li-ion cathode materials, an excess of Li with respect to the transition metal content is necessary for the creation of percolating pathways for Li transport. Because of the lower amount of redox-active transition metal, a substantial part of the charge transfer must occur via less reversible oxygen redox. Fluorination can be used to minimize this dependence on oxygen redox by increasing the amount of low-valent transition metal in the compound, but it adds complexity to materials design. Here, we investigate the feasibility of using computationally constructed phase diagrams to facilitate the search for optimal oxyfluorides. We use the phase diagram of LiF-Li3NbO4-NiO to identify Li1.13Ni0.57Nb0.3O1.75F0.25 and Li1.19Ni0.59Nb0.22O1.46F0.54 as two promising compositions and demonstrate that they can be successfully synthesized. These compounds exhibit significantly reduced hysteresis and higher energy density than the previously reported Li1.3Ni0.27Nb0.43O2 compound in this space. Although we generally attribute the improved performance to the increased Ni content enabled by fluorination, a more nuanced relation between fluorination and the cycling behavior is revealed through electrochemical tests, X-ray absorption spectroscopy, solid-state nuclear magnetic resonance spectroscopy, and density functional theory. We find that fluorination increases the voltage, improves cycle life, but reduces the accessibility of Ni redox. Consideration of these effects will facilitate the future design of optimized disordered-rocksalt oxyfluoride cathodes.
AB - In cation-disordered rocksalt Li-ion cathode materials, an excess of Li with respect to the transition metal content is necessary for the creation of percolating pathways for Li transport. Because of the lower amount of redox-active transition metal, a substantial part of the charge transfer must occur via less reversible oxygen redox. Fluorination can be used to minimize this dependence on oxygen redox by increasing the amount of low-valent transition metal in the compound, but it adds complexity to materials design. Here, we investigate the feasibility of using computationally constructed phase diagrams to facilitate the search for optimal oxyfluorides. We use the phase diagram of LiF-Li3NbO4-NiO to identify Li1.13Ni0.57Nb0.3O1.75F0.25 and Li1.19Ni0.59Nb0.22O1.46F0.54 as two promising compositions and demonstrate that they can be successfully synthesized. These compounds exhibit significantly reduced hysteresis and higher energy density than the previously reported Li1.3Ni0.27Nb0.43O2 compound in this space. Although we generally attribute the improved performance to the increased Ni content enabled by fluorination, a more nuanced relation between fluorination and the cycling behavior is revealed through electrochemical tests, X-ray absorption spectroscopy, solid-state nuclear magnetic resonance spectroscopy, and density functional theory. We find that fluorination increases the voltage, improves cycle life, but reduces the accessibility of Ni redox. Consideration of these effects will facilitate the future design of optimized disordered-rocksalt oxyfluoride cathodes.
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U2 - 10.1021/acs.chemmater.8b05096
DO - 10.1021/acs.chemmater.8b05096
M3 - Article
AN - SCOPUS:85064226085
SN - 0897-4756
VL - 31
SP - 2431
EP - 2442
JO - Chemistry of Materials
JF - Chemistry of Materials
IS - 7
ER -