Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

The role of electrolyte anions in the Na-O2 battery: implications for NaO2 solvation and the stability of the sodium SEI formation in glyme-ethers.

Herein we investigate the influence of the sodium salt anion on the performance of Na-O2 batteries. To illustrate the solvent-solute interactions in various solvents, we use 23Na-NMR to probe the environment of Na+ in presence of different anions (ClO4-, PF6-, OTf- or TFSi-). Strong solvation of either the Na+ or the anion leads to solvent-separated ions where the anion has no measurable impact on the Na+ chemical shift. Contrarily, in weakly solvating solvents the increasing interaction of the anion (ClO4- &lt; PF6- &lt; TFSi- &lt; OTf-) can indeed stabilize the Na+ due to formation of contact-ion-pairs. However, by employing these electrolytes in Na-O2 cells we demonstrate that changing from low DN anions (ClO4-) to high DN anions (OTF-) does not result in elevated battery performance. Nevertheless, a strong dependence of the solid electrolyte interphase (SEI) stability on the choice of sodium salt was found. By correlating physical properties with the chemical SEI composition, the crucial role of the anion in the SEI formation process is revealed. The remarkable differences and consequences for long-term stability are further established by cycling Na coin-cells, where electrolytes using NaTFSi are absolutely detrimental for metallic sodium, employing NaOTF and NaClO4 leads to short-term stability and only the combination of DME with NaPF6 allows for high efficiency and performance. </p

The Role of the Electrode Surface in Na–Air Batteries: Insights in Electrochemical Product Formation and Chemical Growth of NaO 2

The Na–air battery, because of its high energy density and low charging overpotential, is a promising candidate for low‐cost energy storage, hence leading to intensive research. However, to achieve such a battery, the role of the positive electrode material in the discharge process must be understood. This issue is herein addressed by exploring the electrochemical reduction of oxygen, as well as the chemical formation and precipitation of NaO2 using different electrodes. Whereas a minor influence of the electrode surface is demonstrated on the electrochemical formation of NaO2, a strong dependence of the subsequent chemical precipitation of NaO2 is identified. In the origin, this effect stems from the surface energy and O2/O2− affinity of the electrode. The strong interaction of Au with O2/O2− increases the nucleation rate and leads to an altered growth process when compared to C surfaces. Consequently, thin (3 µm) flakes of NaO2 are found on Au, whereas on C large cubes (10 µm) of NaO2 are formed. This has significant impact on the cell performance and leads to four times higher capacity when C electrodes with low surface energy and O2/O2− affinity are used. It is hoped that these findings will enable the design of new positive electrode materials with optimized surfaces

The role of the electrode surface in Na–Air batteries: Insights in electrochemical product formation and chemical growth of NaO2

The Na–air battery, because of its high energy density and low charging overpotential, is a promising candidate for low‐cost energy storage, hence leading to intensive research. However, to achieve such a battery, the role of the positive electrode material in the discharge process must be understood. This issue is herein addressed by exploring the electrochemical reduction of oxygen, as well as the chemical formation and precipitation of NaO2 using different electrodes. Whereas a minor influence of the electrode surface is demonstrated on the electrochemical formation of NaO2, a strong dependence of the subsequent chemical precipitation of NaO2 is identified. In the origin, this effect stems from the surface energy and O2/O2− affinity of the electrode. The strong interaction of Au with O2/O2− increases the nucleation rate and leads to an altered growth process when compared to C surfaces. Consequently, thin (3 µm) flakes of NaO2 are found on Au, whereas on C large cubes (10 µm) of NaO2 are formed. This has significant impact on the cell performance and leads to four times higher capacity when C electrodes with low surface energy and O2/O2− affinity are used. It is hoped that these findings will enable the design of new positive electrode materials with optimized surfaces

High Capacity Na–O 2 Batteries: Key Parameters for Solution-Mediated Discharge

International audienc

High capacity Na-O2 batteries – Key parameters for solution-mediated discharge

The Na-O2 battery offers an interesting alternative to the Li-O2 battery, which is still the source of a number of unsolved scientific questions. In spite of both being alkali metal-O2 batteries, they display significant dif-ferences. For instance, Li-O2 batteries form Li2O2 as the discharge product at the cathode, whereas Na-O2 batteries usually form NaO2. A very important question that affects the performance of the Na-O2 cell con-cerns the key parameters governing the growth mechanism of the large NaO2 cubes formed upon reduction, which are a requirement of viable capacities and high performance. By comparing glyme-ethers of various chain lengths we show that, the choice of solvent has a tremendous effect on the battery performances. In contrast to the Li-O2 system, high solubilities of the NaO2 discharge product do not necessarily lead to in-creased capacities. Herein we report the profound effect of the Na+ ion solvent shell structure on the NaO2 growth mechanism. Strong solvent-solute interactions in long-chain ethers shift the formation of NaO2 to-wards a surface process resulting in submicrometric crystallites and very low capacities (ca. 0,2 mAh/ cm2(geom)). In contrast, short-chains, which facilitate desolvation and solution-precipitation, promote the for-mation of large cubic crystals (ca. 10 um), enabling high capacities (ca. 7.5 mAh/cm2(geom)). This work provides a new way to look at the key role that solvents play in the metal-air system

High Capacity NaO2 Batteries: Key Parameters for Solution-Mediated Discharge

The Na-O2 battery offers an interesting alternative to the Li-O2 battery, which is still the source of a number of unsolved scientific questions. In spite of both being alkali metal-O2 batteries, they display significant dif-ferences. For instance, Li-O2 batteries form Li2O2 as the discharge product at the cathode, whereas Na-O2 batteries usually form NaO2. A very important question that affects the performance of the Na-O2 cell con-cerns the key parameters governing the growth mechanism of the large NaO2 cubes formed upon reduction, which are a requirement of viable capacities and high performance. By comparing glyme-ethers of various chain lengths we show that, the choice of solvent has a tremendous effect on the battery performances. In contrast to the Li-O2 system, high solubilities of the NaO2 discharge product do not necessarily lead to in-creased capacities. Herein we report the profound effect of the Na+ ion solvent shell structure on the NaO2 growth mechanism. Strong solvent-solute interactions in long-chain ethers shift the formation of NaO2 to-wards a surface process resulting in submicrometric crystallites and very low capacities (ca. 0,2 mAh/ cm2(geom)). In contrast, short-chains, which facilitate desolvation and solution-precipitation, promote the for-mation of large cubic crystals (ca. 10 um), enabling high capacities (ca. 7.5 mAh/cm2(geom)). This work provides a new way to look at the key role that solvents play in the metal-air system

High Capacity Na–O₂ Batteries: Key Parameters for Solution-Mediated Discharge

The Na–O₂ battery offers an interesting alternative to the Li–O₂ battery, which is still the source of a number of unsolved scientific questions. In spite of both being alkali metal–O₂ batteries, they display significant differences. For instance, Li–O₂ batteries form Li₂O₂ as the discharge product at the cathode, whereas Na–O₂ batteries usually form NaO₂. A very important question that affects the performance of the Na–O₂ cell concerns the key parameters governing the growth mechanism of the large NaO₂ cubes formed upon reduction, which are a requirement of viable capacities and high performance. By comparing glyme-ethers of various chain lengths, we show that the choice of solvent has a tremendous effect on the battery performance. In contrast to the Li–O₂ system, high solubilities of the NaO₂ discharge product do not necessarily lead to increased capacities. Herein we report the profound effect of the Na⁺ ion solvent shell structure on the NaO₂ growth mechanism. Strong solvent–solute interactions in long-chain ethers shift the formation of NaO₂ toward a surface process resulting in submicrometric crystallites and very low capacities (ca. 0.2 mAh/cm²_(geom)). In contrast, short chains, which facilitate desolvation and solution-precipitation, promote the formation of large cubic crystals (ca. 10 um), enabling high capacities (ca. 7.5 mAh/cm²_(geom)). This work provides a new way to look at the key role that solvents play in the metal–air system