Electrochemically Induced Phase Evolution of Lithium Vanadium Oxide: Complementary Insights Gained via Ex-Situ, In-Situ
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.281
Electrochemically Induced Phase Evolution of Lithium Vanadium Oxide: Complementary Insights Gained via Ex-Situ, In-Situ, and Operando Experiments and Density Functional Theory Jiefu Yin1,ŧ, Wenzao Li1,ŧ, Mikaela Dunkin2,ŧ, Esther S. Takeuchi1,2,3, Kenneth J. Takeuchi1,2, and Amy C. Marschilok1,2,3,* 1. Department of Chemistry, Stony Brook University, Stony Brook, N.Y., 11794.
2. Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, N.Y, 11794.
3. Energy and Photon Sciences Directorate, Brookhaven National Laboratory, Upton, N.Y., 11973.
ŧ Equivalent contributions. *corresponding author: [email protected]
ABSTRACT
Understanding the structural evolution of electrode material during electrochemical activity is important to elucidate the mechanism of (de)lithiation, and improve the electrochemical function based on the material properties. In this study, lithium vanadium oxide (LVO, LiV3O8) was investigated using ex-situ, in-situ, and operando experiments. Via a combination of in-situ X-ray diffraction (XRD) and density functional theory results, a reversible structural evolution during lithiation was revealed: from Li poor α phase (LiV3O8) to Li rich α phase (Li2.5V3O8) and finally β phase (Li4V3O8). In-situ and operando energy dispersive X-ray diffraction (EDXRD) provided tomographic information to visualize the spatial location of the phase evolution within the LVO electrode while inside a sealed lithium ion battery.
INTRODUCTION Lithium vanadium oxides are of interest for application as cathode materials for lithium-ion batteries due to high specific energy density, high working voltage and long cycle life.[1] Among them, the monoclinic layered Li1.nV3O8 (n=0-0.2) (LVO) has especially attracted significance attention due to its theoretical capacity reaching 362 mAh g-1 and desirable high rate capability.[2, 3] The crystalline structure of LVO can be depicted as a layered V 3O8 framework with Li+ cations located in interlayer positions. The anionic V 3O8 framework is composed of double chains of edge-sharing VO6 octahedra and double chains of edge-sharing VO5
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trigonal bi-pyramids linked by corner-sharing oxygens.[4] Previous work has demonstrated that LVO undergoes complicated phase transitions during the lithiation processes when used as a cathode material. Upon lithium insertion, powder x-ray diffraction (XRD) indicates a two-phase process upon transformation from the layered phase α to the defective rock-salt phase β, attributed to contraction of the lattice parameter a and expansion of parameter b.[4, 5] Structural refinement of Li1.2V3O8 has indicated that, per formula unit, one Li+ ion resides in an octahedral site, while the excess lithi
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