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【論文連結】
https://doi.org/10.1039/D0EE01897J
【作者單位】
Changchun Institute of Applied Chemistry,Chinese Academy of Sciences; University of Science and Technology ofChina; King Abdullah University of Science and Technology
【論文摘要】
1 具有超高理論能量密度的Li-O2電池被認為是下一代儲能鋰離子電池的一個很有前途的繼承者。然而，它們在實際應用中仍然面臨著許多關鍵問題，特別是缺乏既能耐受強氧化環境又能與鋰金屬陽極相容的合適電解質。
2 為了提高鋰氧電池的循環穩定性，設計了一種新的N，N-二甲基乙醯胺（DMA）電解質。與高濃度電解質相比，它也是一種更好的鋰金屬陽極穩定策略。與成本昂貴、對鋰陽極保護能力有限、動力學緩慢、傳質慢的高濃度電解質相比，這種新型電解液對嚴格氧化物種具有更好的耐受性，可以通過促進LiF和LiNxOy共存固體的形成來同時穩定鋰陽極電解液界面（SEI）薄膜，可實現更快的動力學/傳質。
3 因此，對稱電池（1800小時）和Li-O2電池（180次循環）在基於DMA的電解液中均達到最佳循環性能。本研究為電解液調節策略注入了新的活力，為鹼氧電池的發展鋪平了道路。
【圖文摘要】
Fig.1 Lithium metal anode stability in different kinds of DMA-based electrolytes. Overpotential vs. cycle number curves of Li/Li symmetrical batteries with theelectrolyte of 1 M LiTFSI, 3 M LiTFSI, 4 M LiTFSI and 5 M LiTFSI (a), 1 M LiNO3, 4 M LiNO3, 5 M LiNO3 and 6 M LiNO3 (b), 3 MLiNO3, 1.5 M LiTFSI 1.5 M LiNO3, 2 M LiTFSI 1 M LiNO3 and 2.5 M LiTFSI 0.5 M LiNO3 (c) cycled at a capacity of 1 mAh cm-2 and a current density of 1 mA cm-2. Histograms of the cyclelife of Li/Li symmetrical batteries with different concentrations of LiTFSI electrolytes (d), different concentrations of LiNO3 electrolytes (e), and 3 M electrolytes groups (f). Schematics of the performance of Li/Li symmetrical batteries with 4 M LiTFSI (g), 5 M LiNO3 (h), and 2 MLiTFSI 1 M LiNO3 (i).
Fig.2 Electrochemical performance of Li/Li symmetrical batteries. Long-term cycle performance of Li/Li symmetrical batteries with different kinds of electrolytes at current densities of 0.1 mA cm-2 (a), and 1 mA cm-2(b). Insets are the details of the representative voltage vs. time profiles. (c) Rate performance of Li/Li symmetrical batteries under different currentdensities. (d) Comparison of the cycling performance of Li/Li symmetrical batteries with DMA-based electrolytes. Nyquist plots of Li/Li symmetrical batteries before cycling (e), and after cycling for 80 hours (f) at astripping/plating capacity of 1 mAh cm-2 and a current density of 1mA cm-2. Inset in Fig. 2f is the Zoom-in view of the Nyquist plots. (g) Arrhenius curves of different kinds of electrolytes. (h) Arrhenius plotsand corresponding activation energies from Rct in Li/Li symmetrical batteries. (i) CV curves of Li/Li symmetrical batteries with different kinds ofelectrolytes.
Fig.3 Characterization of the lithium deposition morphology and SEI filmcomponents. SEM images of lithium deposition morphology in 5 M LiNO3(a), 4 M LiTFSI (b), and 2 M LiTFSI 1 M LiNO3 (c). In situ optical microscope images of lithium morphology evolution after deposition in 4 MLiTFSI for 0 minute (d) and 30 minutes (e), in 5 M LiNO3 for 0 minute (f) and 30 minutes (g), and in 2 M LiTFSI 1 M LiNO3 for 0 minute (h) and 30 minutes (i). (j) Schematic illustrations of lithium deposition evolution in different kinds of electrolytes. Li 1s XPS spectra oflithium after 40 cycles in 4 M LiTFSI (k), 5 M LiNO3 (l), and 2 MLiTFSI 1 M LiNO3 (m) before and after etching for 5 minutes.
Fig.4 AIMD simulations of electrolyte solvent structure in different kinds ofelectrolytes. Snapshots of the AIMD simulation box for 3 M LiTFSI (a), 2 M LiTFSI 1 M LiNO3 (b), 4 M LiTFSI (c), and 5 M LiNO3 (d) electrolytes. Schematics of the solvation structures in 3 M LiTFSI (e), and 2 M LiTFSI 1 M LiNO3 (f) electrolytes. Radical distribution functions of Li-O (g) and Li-N (h) in different kinds of electrolytes. (i) MSD of differentkinds of electrolytes as a function of the simulation time.
Fig.5 Electrochemical characterization of Li-O2 batteries. (a) Schematic of Li-O2 battery with 2 M LiTFSI 1 M LiNO3 DMA-basedelectrolyte. Discharge and charge profiles of Li-O2 batteries with different kinds of electrolytes at the 1st cycle (b), 50th cycle (c), and the corresponding histogram of the overpotential comparison (d). (e) Rateperformance of Li-O2 batteries with different kinds of electrolytes.(f) Long-term cycle life of Li-O2 batteries with different kinds ofelectrolytes. (g) Summarization of the cycle performances of DMA-based Li-O2batteries reported here and in previous literatures. SEM image (h) and XRDpatterns (i) of lithium metal anode in Li-O2 batteries with 2 MLiTFSI 1 M LiNO3 DMA-based electrolyte after 50 cycles. (j)Comparisons of the performances and properties of the three kinds ofelectrolytes based Li-O2 batteries.
【主要結論】
1通過調整中濃度下Li+的溶劑化結構，穩定Li金屬陽極，實現了DMA基電解質的復興，提高了Li-O2電池的循環壽命。實驗結果和AIMD模擬結果表明，優化後的電解液在DMA中加入2 MLiTFSI 1 M LiNO3，有利於形成LiF和富LiNxOy的SEI膜，保護鋰陽極不受枝晶生長和腐蝕的影響，並能加快傳質和電極動力學，克服了高濃度電解液的優缺點。
2 優化電解液的獨特優勢使Li/Li對稱電池（1800小時）和Li-O2電池（180次循環）在我們所知的基於DMA的電解質的電池中具有最佳的電化學性能。為解決電解液與鋰金屬陽極的不相容性問題提供了一種新的電解液設計準則，為實用鹼性電池的開發提供了新的思路。