Electron and Ion Transport In Li<sub>2</sub>O<sub>2</sub>

Gerbig, Oliver; Merkle, Rotraut; Maier, Joachim

doi:10.1002/adma.201300264

Cited by 189 publications

(216 citation statements)

References 31 publications

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“…However, both KO2 and alkali peroxides are considered insulating, although debate exists in the literature regarding the conductivity of KO2, and both have little or no solubility in this solvent. [20,32,33] We note that the effect can also be observed in other solvents such as dimethyl sulfoxide (DMSO) and diethylene glycol dimethyl ether (diglyme), Figure S3. By holding at a low potential to drive reduction of O2 to K2O2, very similar amounts of capacity were consumed to form the surface film, suggesting the products in three solvents had very similar conductivities.…”

Section: Figure 1amentioning

confidence: 87%

“…Siegel et al have suggested conductivity within the bulk by formation of hole and electron polarons and defects in the form of site vacancies. [18,19] In practice, the Li2O2 film formed on discharge is restricted to a thickness of 7 nm due to its low electric conductivity, 10 -12 -10 -11 S cm -1 at 100 o C. [20,21] As a result, surface route discharge in the Li-O2 battery typically results in a low capacity and premature cell death and therefore the solution route is overwhelmingly desired. [1] In addition, similar studies of the Na-O2 system also suggest that conductivity of NaO2 is limited and that discharge by a surface route is not a dominant discharge pathway, [14,22] although calculation shows that NaO2 has a higher conductivity than LiO2.…”

Section: Cathodementioning

confidence: 99%

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High capacity surface route discharge at the potassium-O2 electrode

Chen

Jovanov

Gao

et al. 2018

Journal of Electroanalytical Chemistry

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Discharge by a surface route at the cathode of an aprotic metal-O2 battery typically results in surface passivation by the non-conducting oxide product. This leads to low capacity and early cell death. Here we investigate the cathode discharge reaction in the potassium-O2 battery and demonstrate that discharge by a surface route is not limited to growth of thin (<10 nm) metal oxide layers. Electrochemical analysis and in situ Raman confirmed that the product of the cathode reaction is a combination of KO2 and K2O2, depending on the applied potential. Use of the low donor number solvent, acetonitrile, allows us to directly probe the surface route. Rotating ring-disk electrode, electrochemical quartz crystal microbalance and scanning electron microscope characterisations clearly demonstrate the formation of a thick > 1 µm product layer, far in excess of that possible in the related lithium-O2 battery. These results demonstrate a high-capacity surface route in a metal-O2 battery for the first time and the insights revealed here have significant implications for the design of the K-O2 battery.

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Section: Figure 1amentioning

confidence: 87%

Section: Cathodementioning

confidence: 99%

High capacity surface route discharge at the potassium-O2 electrode

Chen

Jovanov

Gao

et al. 2018

Journal of Electroanalytical Chemistry

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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%

“…8d, at sudden-death, which for the 1 M LiTFSI-DME cell is 3.4 μF/cm 2 ( Figure 7). This corresponds to a theoretical Li 2 O 2 thickness of ∼5.3 nm, which was estimated using a dielectric constant of Li 2 O 2 of 35 48 and Eq. 10.…”

mentioning

confidence: 99%

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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“…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: 89%