Short-range Li diffusion vs. long-range ionic conduction in nanocrystalline lithium peroxide Li2O2—the discharge product in lithium-air batteries

Dunst, Andreas; Epp, Viktor; Hanzu, Ilie; Freunberger, Stefan; Wilkening, Martin

doi:10.1039/c4ee00496e

Cited by 109 publications

(118 citation statements)

References 101 publications

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“…Of note, the ratio between the experimentally found thickness (based on the change in capacitance) and the expected thickness (calculated from the passed charge) in Figure S10a was approximately 4 throughout discharge and the reason for this behavior is unclear. It is perhaps interesting to note the discrepancy between the experimentally found dielectric constant of Li 2 O 2 (ε = 30-35) 48,49 and that calculated for bulk Li 2 O 2 using DFT (ε = 7.5-12.5), 50 which also happens to differ by a factor of roughly 4. It is possible that the O 2 gradients inside the pores during discharge are large enough to yield an appreciable diffusion resistance, which in this case would lead to an overestimation of the polarization resistance of the porous electrode.…”

mentioning

confidence: 88%

An Electrochemical Impedance Spectroscopy Study on the Effects of the Surface- and Solution-Based Mechanisms in Li-O₂Cells

Knudsen

Vegge

McCloskey

et al. 2016

J. Electrochem. Soc.

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The maximum discharge capacity in non-aqueous Li-O 2 batteries has been limited to a fraction of its theoretical value, largely due to a conformal deposition of Li 2 O 2 on the cathode surface. However, it has recently been established that additives that increase the shielding of either O 2 − or Li + will activate the formation of toroidal shaped Li 2 O 2 , thereby dramatically increasing cell capacity. Here we apply porous electrode theory to electrochemical impedance measured at the Li-O 2 cathode to investigate changes in the surface-and ionic resistance within the pores under conditions where either the surface-mechanism or the solution-mechanism is favored. Our experimental observations show that (i) an additional charge transfer process is observed in the impedance spectrum where the solution-based mechanism is favored; (ii) that the changes in the ionic resistance in the cathode during discharge (related to Li 2 O 2 build up) is much greater in cells where the solution-based mechanism is activated and can qualitatively determine the extent of discharge product deposited within the pores of the cathode versus the deposition extent at the electrode/electrolyte interface; and (iii) that the observed "sudden-death" during discharge is a consequence of the increasing charge transfer resistance regardless of whether Li 2 O 2 forms predominantly through either the surface-or solution-based mechanism. The Li-O 2 battery has, since Jiang and Abraham's seminal 1996 report, 1 received significant attention due to its high theoretical specific energy and energy density of 3500 Wh/kg and 3400 Wh/L, respectively.2 These values are based on the overall cell reaction in non-aqueous electrolytes that can be described as 2Li + O 2 Li 2 O 2 , with the forward reaction corresponding to discharge and the reverse direction to charge. To understand how to more appropriately engineer a practical Li-O 2 cathode and electrolyte, the mechanism of Li 2 O 2 formation has been the focus of significant research in the past 10 years. Laorie et al. 3,4 initially showed that varying Lewis basicity of the electrolyte substantially influenced the electrochemical kinetics and reversibility of the Li/O 2 reaction. Deposition morphology of Li 2 O 2 was also found to be influenced by electrolyte properties 5 and current density 6,7 with large (∼500-1000 nm) toroids or thin (∼5 nm) conformal films of Li 2 O 2 forming under various conditions. These observations have been explained by two independent reaction mechanisms that appear to be influenced primarily by electrolyte Lewis acidity or basicity, 5,8,9 which can be tuned through solvent, 5 anion, 9 and additive 8 selection. These two main reaction pathways for Li 2 O 2 deposition are referred to here as either the surface-or solution-based mechanism. The surface mechanism (Figure 1a) occurs in electrolytes with low Lewis basicity and acidity, where LiO 2 is insoluble, disallowing diffusion away from its initial site of formation and resulting in conformal Li 2 O 2 film formation during discha...

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confidence: 88%

An Electrochemical Impedance Spectroscopy Study on the Effects of the Surface- and Solution-Based Mechanisms in Li-O₂Cells

Knudsen

Vegge

McCloskey

et al. 2016

J. Electrochem. Soc.

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“…In this study, we combined time-domain nuclear magnetic resonance (NMR) spectroscopy with broadband conductivity spectroscopy to quantify short-range as well as long-range Na + ion diffusivities. Using only NMR spin-lattice relaxometry working at atomic scale 36,37 we managed to get a sneak peek at the very rapid exchange processes the Na ions are performing at temperatures very well below ambient. The data collected provide a first experimental rationale for the very high ionic conductivity observed in NZSP-type compounds.…”

Section: Introductionmentioning

confidence: 99%

Fast Na ion transport triggered by rapid ion exchange on local length scales

Lunghammer

Prutsch

Breuer

et al. 2018

Sci Rep

Self Cite

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The realization of green and economically friendly energy storage systems needs materials with outstanding properties. Future batteries based on Na as an abundant element take advantage of non-flammable ceramic electrolytes with very high conductivities. Na3Zr2(SiO4)2PO4-type superionic conductors are expected to pave the way for inherently safe and sustainable all-solid-state batteries. So far, only little information has been extracted from spectroscopic measurements to clarify the origins of fast ionic hopping on the atomic length scale. Here we combined broadband conductivity spectroscopy and nuclear magnetic resonance (NMR) relaxation to study Na ion dynamics from the µm to the angstrom length scale. Spin-lattice relaxation NMR revealed a very fast Na ion exchange process in Na3.4Sc0.4Zr1.6(SiO4)2PO4 that is characterized by an unprecedentedly high self-diffusion coefficient of 9 × 10−12 m2s−1 at −10 °C. Thus, well below ambient temperature the Na ions have access to elementary diffusion processes with a mean residence time τNMR of only 2 ns. The underlying asymmetric diffusion-induced NMR rate peak and the corresponding conductivity isotherms measured in the MHz range reveal correlated ionic motion. Obviously, local but extremely rapid Na+ jumps, involving especially the transition sites in Sc-NZSP, trigger long-range ion transport and push ionic conductivity up to 2 mS/cm at room temperature.

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“…The efficiency and long-term behavior of the batteries is expected to significantly depend on the electric and dynamic properties of the discharge products formed [7]; the same holds for the Li-oxygen system. Such information is, however, rarely available so far [8][9][10]. To our knowledge, the electric conductivity of defect-rich nanocrystalline Na 2 O 2 at room temperature has not been reported as yet.…”

Section: Introductionmentioning

confidence: 93%

“…To compare these conductivity values with practical ones the gold sputtered sodium peroxide pellets were assembled into air-tight Swagelok-cells and measured at room temperature on the Parstat MC potentiostat, see above. For this purpose, a constant voltage U of 0.5 V was applied across the symmetrical Au|Na 2 O 2 |Au pellet and the change of the current I over time (t) was recorded, see also [9]. In figure 3 When a material with mixed electronic and ionic conductivity is electrically polarized, at the beginning, both ions and electrons will contribute to the total conductivity of the sample.…”

Section: Polarization Measurementsmentioning

confidence: 99%

Partial electronic conductivity of nanocrystalline Na₂O₂

Philipp

Lunghammer

Hanzu

et al. 2017

Mater. Res. Express

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Short-range Li diffusion vs. long-range ionic conduction in nanocrystalline lithium peroxide Li₂O₂—the discharge product in lithium-air batteries

Abstract: Conductivity spectroscopy and 7Li spin-locking NMR relaxometry reveal enhanced ion dynamics in nanocrystalline Li2O2 prepared by high-energy ball milling.

Cited by 109 publications

References 101 publications

An Electrochemical Impedance Spectroscopy Study on the Effects of the Surface- and Solution-Based Mechanisms in Li-O₂Cells

An Electrochemical Impedance Spectroscopy Study on the Effects of the Surface- and Solution-Based Mechanisms in Li-O₂Cells

Fast Na ion transport triggered by rapid ion exchange on local length scales

Partial electronic conductivity of nanocrystalline Na₂O₂

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Short-range Li diffusion vs. long-range ionic conduction in nanocrystalline lithium peroxide Li2O2—the discharge product in lithium-air batteries

Abstract: Conductivity spectroscopy and 7Li spin-locking NMR relaxometry reveal enhanced ion dynamics in nanocrystalline Li2O2 prepared by high-energy ball milling.

Cited by 109 publications

References 101 publications

An Electrochemical Impedance Spectroscopy Study on the Effects of the Surface- and Solution-Based Mechanisms in Li-O2Cells

An Electrochemical Impedance Spectroscopy Study on the Effects of the Surface- and Solution-Based Mechanisms in Li-O2Cells

Fast Na ion transport triggered by rapid ion exchange on local length scales

Partial electronic conductivity of nanocrystalline Na2O2

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Resources

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Short-range Li diffusion vs. long-range ionic conduction in nanocrystalline lithium peroxide Li₂O₂—the discharge product in lithium-air batteries

An Electrochemical Impedance Spectroscopy Study on the Effects of the Surface- and Solution-Based Mechanisms in Li-O₂Cells

An Electrochemical Impedance Spectroscopy Study on the Effects of the Surface- and Solution-Based Mechanisms in Li-O₂Cells

Partial electronic conductivity of nanocrystalline Na₂O₂