Improved Voltage and Cycling for Li<sup>+</sup> Intercalation in High‐Capacity Disordered Oxyfluoride Cathodes

Ren, Siying; Chen, Ruiyong; Maawad, Emad; Dolotko, Oleksandr; Guda, Alexander A.; Шаповалов, В. В.; Wang, Di; Hahn, Horst; Fichtner, Maximilian

doi:10.1002/advs.201500128

Cited by 63 publications

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“…Other diffraction peaks (200, 220 and 222) can be well resolved from both ND and SXRD. 20,27 Complementary diffraction data from XRD and ND confirm that the cycled VO2F (LixVO2F) crystallizes in a disorder rock-salt structure (Fig. 6b).…”

Section: Structural Transition Into Disordered Rock-salt Phasementioning

confidence: 79%

“…A direct modification of the anion sublattice through fluorine incorporation/substitution in electrode materials has been proven to be an effective strategy to modify and optimize electrochemical performance. 20,[27][28][29][30][31] Fluorinated materials are generally synthesized through solution routes using highly toxic and corrosive fluorine-containing acids, [32][33][34] or by a direct fluorination under reactive conditions of F2 gas at high temperature. 35 So far, various coordination polymers containing vanadium oxyfluoride matrix have been synthesized and structurally determined.…”

Section: Introductionmentioning

confidence: 99%

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Lithiation-driven structural transition of VO₂F into disordered rock-salt Li_xVO₂F

et al. 2016

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We synthesize a new vanadium oxyfluoride VO2F (rhombohedral, R3,¯ c) through a simple one-step ball-milling route and demonstrate its promising lithium storage properties with a high theoretical capacity of 526 mAh g -1 . Similar to V2O5, VO2F transfers into active disordered rock-salt (Fm3,¯ m) phase after initial cycling against lithium anode, as confirmed by diffraction and spectroscopic experiments. The newly formed nanosized LixVO2F remains its crystal structure over further cycling between 4.1 and 1.3 V. A high capacity of 350 mAh g -1 at 2.5 V was observed at 25°C and 50 mA g -1 . Furthermore, superior performance was observed for VO2F in comparison with a commercial crystalline V2O5, in terms of discharge voltage, voltage hysteresis and reversible capacity.

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Section: Structural Transition Into Disordered Rock-salt Phasementioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Lithiation-driven structural transition of VO₂F into disordered rock-salt Li_xVO₂F

et al. 2016

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“…The energy positions and shapes of the Va nd Cr L 3,2 edges indicate that both transition metals exist in trivalent states in the cycled samples (discharged states). [14,17,18] Moreover,t he Oa nd FK edges for cycled Li 2 Cr 0.2 V 0.8 O 2 Fh avet he same shapes as that in the as-synthesized Li 2 VO 2 Fm aterial. [13] Va nd Cr K-edge X-ray absorption near-edge structure (XANES) spectra were recordedfor the pristine and cycled sam- [19] For Li 2 Cr 0.2 V 0.8 O 2 F, Cr was not completely oxidized with ac harge cutoffv oltage of 4.1 V, which may contribute to the enhanced cycling performance by stabilizing the crystal lattice.…”

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confidence: 96%

“…The selected area electron diffraction (SAED) pattern and the electron diffractioni ntensity profile in Figure 3c revealt hat as ingle-phase cubic host exists.A ll peaks in the intensity profile can be assignedt ot he FmÀ3m phase. [14] It is believed that the stable crystal structure for Li 2 Cr 0.2 V 0.8 O 2 Fi sr esponsible for its durable cycling performance.…”

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High‐Performance Low‐Temperature Li⁺ Intercalation in Disordered Rock‐Salt Li–Cr–V Oxyfluorides

Chen

Ren

et al. 2016

ChemElectroChem

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Li-ion batteries have driven the technological evolution of portable electronics, automotive, and stationarya pplications over the past decades.[1] However, the poor low-temperature performance of Li-ion batteries impedes their specific applications, such as fora erospace, defense, and transportation systems.[2] When operating at reduced temperatures, especially below 0 8C, the kinetic performance of the employed materials, governed by the intrinsic transport property for electrons and Li ions, becomes ac ritical factor determining the deliverable capacity.[3] Classic Li-ion battery cathode materials suffer from substantial capacity loss, [4] severe voltage hysteresis, [5] and change in voltage profiles.[6] As reported, from 25 to 0 8C, ac ommercialL iFePO 4 -based cell has ac apacity retention of only 42 %. [7] The sluggish kinetics of Li + transport and the reduced electronic conductivity in the solid LiFePO 4 phase at low temperatures leads to the voltage profiles evolving from ap lateau-like to sloping regime.[8] For layered Ni-Mn-Co oxides, [9] ad ischarge voltage downshift of 0.5 Vh as been observed when reducing the temperature from 25 to À20 8C. [6] In addition, the performance deteriorationo fa node materials and the appliede lectrolytes at low temperatures contributet ot he poor overall battery performance. [2,10] At sub-ambient temperatures, Li platingt ends to occur at the graphite anode,o wing to the reduced Li + intercalation into graphite.[11] At temperatures below À10 8C, the ionic mobility in the electrolyte solution and conductivity of the conventional binary carbonate electrolyte fall rapidly.[12] The optimization of the electrolyte formulations for different electrode materials at low temperatures still remains to be solved. Nevertheless, exploring new cathodem aterials with well-retaineds pecific energiesa tr educed temperatures is am ore decisive step towards broad applications of Li-ion batteries.We have recentlyr eportedt hat an ew cathode material, Li 2 VO 2 F, with ad isordered rock-salt structure can deliver ah igh initial intercalation capacity when cycling at al ow current rate.[13] However,L i 2 VO 2 Fs uffers from capacity fading whilst cycling. It has been found that the poor cycling performance of Li 2 VO 2 Fc an be improved by substituting Cr forVi nt his system.[14] Moreover,t he cyclability of the mixed V/Cr oxyfluorides depends on the applied chargecutoff voltages and operation temperature. Af acile Li + chemical diffusion in such ac lass of materials favors the kinetic properties.[15] Herein,w ee xplore the composition-dependent, low-temperature properties of the oxyfluorides and examine the structural features responsible for the cycling performance.The low-temperature rate capabilities of Li 2 VO 2 F, Li 2 CrO 2 F, and Li 2 Cr 0.2 V 0.8 O 2 Fw ere first evaluated at À10 8Ca tv arious current densities from 26 to 1050 mA g À1 ,a nd then back again at 26 mA g À1 (Figures 1a-c

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Symmetric Electrodes for Electrochemical Energy‐Storage Devices

et al. 2016

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Increasing environmental problems and energy challenges have so far attracted urgent demand for developing green and efficient energy‐storage systems. Among various energy‐storage technologies, sodium‐ion batteries (SIBs), electrochemical capacitors (ECs) and especially the already commercialized lithium‐ion batteries (LIBs) are playing very important roles in the portable electronic devices or the next‐generation electric vehicles. Therefore, the research for finding new electrode materials with reduced cost, improved safety, and high‐energy density in these energy storage systems has been an important way to satisfy the ever‐growing demands. Symmetric electrodes have recently become a research focus because they employ the same active materials as both the cathode and anode in the same energy‐storage system, leading to the reduced manufacturing cost and simplified fabrication process. Most importantly, this feature also endows the symmetric energy‐storage system with improved safety, longer lifetime, and ability of charging in both directions. In this Progress Report, we provide the comprehensive summary and comment on different symmetric electrodes and focus on the research about the applications of symmetric electrodes in different energy‐storage systems, such as the above mentioned SIBs, ECs and LIBs. Further considerations on the possibility of mass production have also been presented.

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Improved Voltage and Cycling for Li⁺ Intercalation in High‐Capacity Disordered Oxyfluoride Cathodes

Abstract: New high‐capacity intercalation cathodes of Li2VxCr1−xO2F with a stable disordered rock salt host framework allow a high operating voltage up to 3.5 V, good rate performance (960 Wh kg−1 at ≈1 C), and cycling stability.

Cited by 63 publications

References 50 publications

Lithiation-driven structural transition of VO₂F into disordered rock-salt Li_xVO₂F

Lithiation-driven structural transition of VO₂F into disordered rock-salt Li_xVO₂F

High‐Performance Low‐Temperature Li⁺ Intercalation in Disordered Rock‐Salt Li–Cr–V Oxyfluorides

Symmetric Electrodes for Electrochemical Energy‐Storage Devices

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Improved Voltage and Cycling for Li+ Intercalation in High‐Capacity Disordered Oxyfluoride Cathodes

Abstract: New high‐capacity intercalation cathodes of Li2VxCr1−xO2F with a stable disordered rock salt host framework allow a high operating voltage up to 3.5 V, good rate performance (960 Wh kg−1 at ≈1 C), and cycling stability.

Cited by 63 publications

References 50 publications

Lithiation-driven structural transition of VO2F into disordered rock-salt LixVO2F

Lithiation-driven structural transition of VO2F into disordered rock-salt LixVO2F

High‐Performance Low‐Temperature Li+ Intercalation in Disordered Rock‐Salt Li–Cr–V Oxyfluorides

Symmetric Electrodes for Electrochemical Energy‐Storage Devices

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Improved Voltage and Cycling for Li⁺ Intercalation in High‐Capacity Disordered Oxyfluoride Cathodes

Lithiation-driven structural transition of VO₂F into disordered rock-salt Li_xVO₂F

Lithiation-driven structural transition of VO₂F into disordered rock-salt Li_xVO₂F

High‐Performance Low‐Temperature Li⁺ Intercalation in Disordered Rock‐Salt Li–Cr–V Oxyfluorides