Overlooked Factors Required for Electrolyte Solvents in Li–O₂ Batteries: Capabilities of Quenching ¹O₂ and Forming Highly‐Decomposable Li₂O₂

Abstract

Although sufficient tolerance against attack by superoxide radicals (O 2 À ) has been mainly recognized as an important property for Li-O 2 battery (LOB) electrolytes, recent evidence has revealed that other critical factors also govern the cyclability, prompting a reconsideration of the basic design guidelines of LOB electrolytes. Here, we found that LOBs equipped with a N,N-dimethylacetamide (DMA)based electrolyte exhibited better cyclability compared with other standard LOB electrolytes. This superior cyclability is attributable to the capabilities of quenching 1 O 2 and forming highly decomposable Li 2 O 2 . The 1 O 2 quenching capability is equivalent to that of a tetraglyme-based electrolyte containing a several millimolar concentration of a typical chemical quencher. Based on these overlooked factors, the DMA-based electrolyte led to superior cyclability despite its lower O 2 À tolerance. Thus, the present work provides a novel design guideline for the development of LOB electrolytes.

True Location of Insulating Byproducts in Discharge Deposits in Li–O2 Batteries

“…The retreating front during charging process has been shown to also locate at the Li 2 O 2 /electrolyte interface. 32 Therefore, because of the reaction between Li 2 O 2 and the electrolyte, new byproducts should be localized at the Li 2 O 2 /electrolyte interface, which is continuously exposed during charging (Figure 6b). To verify this speculation, we conducted ToF-SIMS measurements on the sample surface after one discharge−charge cycle.…”

“…This result is reasonable given that the discharge reaction occurs at the Li 2 O 2 /electrolyte interface in this system. 32 Concretely, because Li 2 CO 3 , a side-reaction product, is constantly generated at the growing interface, it is uniformly distributed inside the discharge products, as schematically shown in Figure 6a. This conclusion is consistent with that deduced from the previously discussed ToF-SIMS analysis results.…”

“…As previously mentioned, we have clarified that both growing front at discharge and retreating front at charge reactions locate at the Li 2 O 2 /electrolyte interface in the LiNO 3 /DMA systems used in the present work. 32 Thus, the insulating byproducts formed by the reaction between the electrolyte and Li 2 O 2 during discharge should, in principle, be incorporated into the discharge deposits as the Li 2 O 2 growth progresses, as schematically shown in Figure 6a. We confirmed this behavior experimentally by analyzing the depth profiles using XPS and ToF-SIMS, which confirmed that no significant difference existed in the chemical composition.…”

“…In light of the above issues, the aim of this study is set to determine the true locations of insulating byproducts in individual discharge products in the LOB system, where both the growing and retreating front during discharging and charging have already been clarified as the Li 2 O 2 /electrolyte interface through various analytical techniques. 32 ■ EXPERIMENTAL SECTION Cell Configuration. The electrochemical cell used in this study has been described elsewhere.…”

Electrochemical Characteristics of Lithium-Air Secondary Battery Using Amide-Based Ionic Liquids

“…For example, it has recently been reported that the amide-based electrolytes exhibit a good cycling performance. 8 On the other hand, one of the attractions of nonvolatile ionic liquids (ILs) is that they exhibit various physical…”