Structure Evolution and Thermal Stability of High-Energy- Density Li-Ion Battery Cathode Li<sub>2</sub>VO<sub>2</sub>F

Wang, Xiaoya; Huang, Yiqing; Ji, Dongsheng; Omenya, Fredrick; Karki, Khim; Sallis, Shawn; Piper, Louis F. J.; Wiaderek, Kamila M.; Chapman, Karena W.; Chernova, Natasha A.; Whittingham, M. Stanley

doi:10.1149/2.1071707jes

Cited by 29 publications

(58 citation statements)

References 32 publications

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“…a and V decrease during charge with Li + extraction, and increase during discharge, with Li + insertion. The overall lattice volume varies only by 2.1 % in this voltage window, again similarly to recently reported DRS materials ,. When fully discharged, the lattice constant and lattice volume are slightly bigger than the initial values for the pristine material (1.0 %).…”

Section: Resultssupporting

confidence: 88%

“…As can be seen after the first charge and discharge, LiVO 2 exhibits slight structural changes when cycled between 3.0–1.9 V (compared with the pristine material). The lattice parameter a , as well as the lattice volume V (see Figure b), almost linearly changes upon cycling, suggesting a reversible single‐phase insertion process, as already observed in related disordered rock salt materials,, and which is also in line with the observed voltage profiles (Figure b). a and V decrease during charge with Li + extraction, and increase during discharge, with Li + insertion.…”

Section: Resultssupporting

confidence: 82%

“…When fully discharged, the lattice constant and lattice volume are slightly bigger than the initial values for the pristine material (1.0 %). This might be explained by an additional Li + uptake upon discharge in the defective lattice structure induced by the high‐energy ball milling synthesis ,. However, no additional reflections for potential rock salt to spinel (with Li + insertion in tetrahedral 8a sites) or rock salt to layered phase transitions are observed in the pattern.…”

Section: Resultsmentioning

confidence: 93%

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Reversible Delithiation of Disordered Rock Salt LiVO₂

et al. 2018

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A rigid crystal lattice, in which cations occupy specific positions, is generally regarded as a critical requirement to enable Li+ diffusion in the bulk of conventional cathode materials, whereas disorder is generally considered as detrimental. Herein, we demonstrate that facile and reversible insertion and extraction of Li+ is possible with LiVO2, a new cation‐disordered rock salt compound (space group: Fmtrue3‾ m), which is, to the best of our knowledge, described for the first time. This new polymorph of LiVO2 is synthesized by mechanical alloying. Rietveld refinements of the X‐ray diffractions patterns and SAED (selected‐area electron diffraction) patterns attested the formation of the disordered LiVO2 rock salt phase. Galvanostatic cycling experiments were employed to characterize the electrochemical performance of the material, demonstrating that reversible cycling over 100 cycles with a discharge capacity around 100 mAh g−1 is possible.

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Section: Resultssupporting

confidence: 88%

Section: Resultssupporting

confidence: 82%

Section: Resultsmentioning

confidence: 93%

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Reversible Delithiation of Disordered Rock Salt LiVO₂

et al. 2018

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“…To account for this disorder-enabled fluorine incorporation, we construct finite temperature phase diagrams for the LiF-LMO systems from cluster expansion Monte Carlo simulations. The melting point of lithium fluoride at 845 °C and high temperature decomposition of the oxides [36,37] and oxyfluorides [38] limits the temperature range for which these phase diagrams are directly applicable. This approach has been used previously to study Li-vacancy phase diagrams in Li x CoO 2 , [32,33] Li x NiO 2 , [34] and to study the effect of disorder on voltage.…”

Section: Resultsmentioning

confidence: 99%

Fluorination of Lithium‐Excess Transition Metal Oxide Cathode Materials

Richards

Dacek

Kitchaev

et al. 2017

Advanced Energy Materials

128

204

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do not require lithium ions to pass directly adjacent to a transition metal (0-TM channels). [3] These pathways are present only at high lithium concentrations, with the percolation threshold a function of the crystal structure and degree of cation disorder. The Li-excess requires high-valent metals for charge compensation and typically reduces the active TM content of the compound. Thus, a key aspect of the design and optimization of this class of cathode materials is the maximization of transition metal redox capacity, while maintaining the Li-excess level greater than the percolation threshold to ensure acceptable rate capability.Early work in disordered lithium-excess rock salt materials focused on the vanadium systems Li 3 V 2 O 5[4] and Li 2−x VO 3 , [5] where the large lithium concentration is charge compensated by the high-valence states of vanadium. More recently, a number of studies have reported lithiumexcess compositions of a range of lithium transition metal oxide (LMO) cathodes through the substitution of a high-valent cation on the metal site, forming a solid solution between LiMO 2 and Li 2 MoO 3 , [1] Li 4 MoO 5 , [6][7][8] Li 3 NbO 4 , [9][10][11] Li 3 SbO 4 , [12] or Li 2 TiO 3 . [13,14] The disadvantages of this strategy for introducing lithium excess are the high atomic mass of the high-valent metal substitutions and their redox inactivity at useful voltages, both of which reduce the theoretical TM capacity of this class of materials. For example, the composition Li 1.1 Co 0.833 Mo 0.066 O 2 , which is at the threshold for 0-TM percolation in the disordered rock salt structure, decreases the theoretical gravimetric TMcapacity from 275 mA h g −1 for pristine LiCoO 2 to 235 mA h g −1 for the Co 3+/4+ redox couple. While in some cases, reversible oxygen redox can add extra capacity, [15] too much oxygen redox is likely to lead to oxygen loss at the surface, accompanied by capacity loss and/or impedance growth. [16] An alternative strategy to ensure charge balance at a lithiumexcess composition is the substitution of a lower valence halide for the oxygen anion. Fluorine substitution to the same lithium-excess level as in the previously considered Mo-substituted compound results in the composition Li 1.1 Co 0.9 O 1.8 F 0.2 , which has a theoretical TM-capacity of 260 mA h g −1 , significantly higher than when Li excess is compensated by a high-valent metal as in Li 1.1 Co 0.833 Mo 0.066 O 2 . In early demonstrations of this strategy, Chen et al. have reported high initial capacity in the Li 2 VO 2 F [17] and Li 2 CrO 2 F [18] disordered rock salt compounds, Fluorination of Li-ion cathode materials is of significant interest as it is claimed to lead to significant improvements in long-term reversible capacity. However, the mechanism by which LiF incorporates and improves performance remains uncertain. Indeed, recent evidence suggests that fluorine is often present as a coating layer rather than incorporated into the bulk of the material. In this work, first-principles calculations are used to inves...

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“…24 It is due to the fact that the electrochemical reaction is primarily a surface reaction, and the surface state of the cathode material largely determines its properties. [25][26][27][28][29] Therefore, in this study, a thin CoS 2 layer was successfully coated on FeS 2 via the hydrothermal method and a subsequent heat-treatment. The CoS 2 coating improved the thermal stability and electrochemical performance of FeS 2 .…”

mentioning

confidence: 99%

CoS₂Coatings for Improving Thermal Stability and Electrochemical Performance of FeS₂Cathodes for Thermal Batteries

Ning

Liu

Xie

et al. 2018

J. Electrochem. Soc.

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The cathode material pyrite (FeS 2 ) (core) was coated with 2.5, 5.0, 7.5, and 10.0 wt% CoS 2 (shell) (denoted as FeS 2 @CoS 2 ) by the hydrothermal method and a subsequent heat-treatment to form composites with enhanced thermal stability and electrochemical performance. Importantly, results indicate indicated that CoS 2 particles with a complete crystal structure had been successfully coated on the FeS 2 surface. The sample coated with the optimal amount of CoS 2 , which was determined to be 7.5 wt%, showed the highest thermal decomposition temperature (610.6 • C) and excellent specific capacity (as high as 320 mA h g −1 at 520 • C and 200 mA cm −2 at a cutoff voltage of 1.6 V), in compared to that of pure FeS 2 (551.3 • C, 240 mA h g −1 ). Because CoS 2 is an excellent electrical conductor, the surface of FeS 2 is modified by CoS 2 , which leads to the change of the microstructure of FeS 2 surface, which enhances the intercalation of ionic electrolyte and enhances the electrical conductivity of FeS 2 . In the meantime, CoS 2 has high thermal stability and exhibits low solubility in the molten electrolyte, which reduces the elemental sulfur loss of FeS 2 during discharge and thereby increases the electrochemical capacity.

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Structure Evolution and Thermal Stability of High-Energy- Density Li-Ion Battery Cathode Li₂VO₂F

Cited by 29 publications

References 32 publications

Reversible Delithiation of Disordered Rock Salt LiVO₂

Reversible Delithiation of Disordered Rock Salt LiVO₂

Fluorination of Lithium‐Excess Transition Metal Oxide Cathode Materials

CoS₂Coatings for Improving Thermal Stability and Electrochemical Performance of FeS₂Cathodes for Thermal Batteries

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Structure Evolution and Thermal Stability of High-Energy- Density Li-Ion Battery Cathode Li2VO2F

Cited by 29 publications

References 32 publications

Reversible Delithiation of Disordered Rock Salt LiVO2

Reversible Delithiation of Disordered Rock Salt LiVO2

Fluorination of Lithium‐Excess Transition Metal Oxide Cathode Materials

CoS2Coatings for Improving Thermal Stability and Electrochemical Performance of FeS2Cathodes for Thermal Batteries

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Product

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Structure Evolution and Thermal Stability of High-Energy- Density Li-Ion Battery Cathode Li₂VO₂F

Reversible Delithiation of Disordered Rock Salt LiVO₂

Reversible Delithiation of Disordered Rock Salt LiVO₂

CoS₂Coatings for Improving Thermal Stability and Electrochemical Performance of FeS₂Cathodes for Thermal Batteries