Auswahl der wissenschaftlichen Literatur zum Thema „SEI stability“

The lithium-mediated method of electrochemical nitrogen reduction, pioneered by Tsuneto et al1 then verified by Andersen et al2, is currently the sole paradigm capable of unequivocal electrochemical ammonia synthesis. Such a system could allow the production of green, distributed ammonia for use as fertiliser or a carbon-free fuel. However, despite great improvements in Faradaic efficiency and stability since just 20193, fundamental understanding of the mechanisms governing nitrogen reduction and other parasitic reactions is lacking. Lithium Ion Battery (LIB) research can provide insight; since both lithium-mediated electrochemical ammonia synthesis and LIBs utilise an organic solvent and lithium salt, both form a Solid Electrolyte Interphase (SEI), which is electronically insulating but ionically conducting, at the electrode surface. In LIBs, this is necessary to stabilize and cycle low potential materials4. In lithium-mediated ammonia synthesis, the SEI could also have a critical role in controlling the access of protons and other key reactants to the catalytically active sites and promoting greater selectivity toward nitrogen reduction to ammonia5. While some characterisation of the SEI has been carried out for the lithium-mediated nitrogen reduction system6, the literature still lacks holistic studies which aim to carefully characterise the bulk electrolyte and SEI components and link them to system performance. In this work we use insight from battery science to tackle a significant stability problem in lithium-mediated nitrogen reduction. The traditional electrolyte employed by Tsuneto et al. was 0.2 M LiClO4 in a 99:1 tetrahydrofuran to ethanol mix. While this system can produce ammonia, the working electrode potential becomes more negative over time. Our initial investigations show that this problem stems from an unstable SEI which becomes increasingly organic. Simply by raising the concentration of LiClO4 in the electrolyte, we vastly improve stability, as shown in figure 1(a), and boost Faradaic efficiency. Bulk electrolyte salt solvation properties are investigated through Raman spectroscopy, as shown in figure 1(b). Here we observe the emergence of a shoulder at around 930 cm-1 with increasing LiClO4 concentration, which we assign to the emergence of Contact-Ion-Pairs (CIPs) through comparison to Density Functional Theory calculations. These CIPs mean that perchlorate anion degradation products are more abundant in the formed SEI, as shown in our X-Ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass spectrometry results. This more inorganic SEI protects the electrolyte against further degradation, preventing the working electrode drift to more negative potentials. We then link this behaviour to a peak observed in the Faradaic efficiency of ammonia synthesis at 0.6 M LiClO4 by also considering decreasing N2 solubility and diffusivity, as well as a more ionically conductive SEI, in an increasingly concentrated electrolyte. We also present never-before seen cross-sectional images of the SEI using cryogenic Focussed Ion Beam milling and Scanning Electron Microscopy, further aiding understanding of how salt solvation affects the morphology of the formed SEI and system performance. Our results emphasise the need to consider SEI properties in electrolyte design for lithium-mediated nitrogen reduction, as well as the need to balance desirable SEI properties with desirable bulk electrolyte properties. Tsuneto, A., Kudo, A. & Sakata, T. Efficient Electrochemical Reduction of N 2 to NH 3 Catalyzed by Lithium . Chemistry Letters vol. 22 851–854 (1993). Andersen, S. Z. et al. A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements. Nature 570, 504–508 (2019). Westhead, O., Jervis, R. & Stephens, I. E. L. Is lithium the key for nitrogen electroreduction? Science. 372, 1149–1150 (2021). Peled, E. & Menkin, S. Review—SEI: Past, Present and Future. J. Electrochem. Soc. 164, A1703–A1719 (2017). Singh, A. R. et al. Electrochemical Ammonia Synthesis—The Selectivity Challenge. ACS Catal. 7, 706–709 (2017). Li, K. et al. Enhancement of lithium-mediated ammonia synthesis by addition of oxygen. Science. 1597, 1593–1597 (2021). Figure 1

Abstract In order to improve the stability and safety of lithium (Li) metal anodes, an innovative artificial solid electrolyte interface (SEI) film of Li Poly (tert-butyl acrylate-co-ethyl acrylate-co-methacrylic acid) (LiPTBEM) has been designed. This thin and uniformly artificial SEI is stable, which can suppress the continuous side reactions between the electrolyte and Li metal, improve the stability of modified Li metal anodes, and achieve better electrochemical performance. Symmetric batteries with LiPTBEM exhibit significantly improved cycling stability, indicating that LiPTBEM is a promising artificial SEI film.

A solid electrolyte interphase (SEI) is generated on the anode of lithium ion batteries during the first few charging cycles. While the SEI generated for LiPF6/carbonate based electrolytes is stable on graphite anodes, the stability of the SEI is poor for LiPF6/carbonate based electrolytes with lithium metal anodes. However, modification of the carbonate based electrolytes via incorporation of alternative salts and/or electrolyte additives significantly improves the stability of the SEI and the cycle life of lithium metal anodes. Investigations of the SEI structure have been conducted via a combination of XPS, IR-ATR, SEM, and TEM. Mechanisms for the generation of the complicated mixture of products are presented along with the differences in the SEI structure and function.

Mechanical stability of the solid electrolyte interphase (SEI) is crucial to mitigate the capacity fade of lithium–ion batteries because the rupture of the SEI layer results in further consumption of lithium ions in newly generated SEI layers. The SEI is known as a heterogeneous bilayer and consists of an inner inorganic layer connecting the particle and an outer organic layer facing the electrolyte. The growth of the bilayer SEI over cycles alters the stress generation and failure possibility of both the organic and inorganic layers. To investigate the probability of mechanical failure of the bilayer SEI, we developed the electrochemical-mechanical coupled model with the core–double-shell particle/SEI layer model. The growth of the bilayer SEI is considered over cycles. Our results show that during charging, the stress of the particle changes from tensile to compressive as the thickness of bilayer SEI increases. On the other hand, in the SEI layers, large compressive radial and tensile tangential stress are generated. During discharging, the compressive radial stress of the bilayer SEI transforms into tensile radial stress. The tensile tangential and radial stresses are responsible for the fracture and debonding of the bilayer SEI, respectively. As the thickness ratio of the inorganic to organic layers increases, the fracture probability of the inorganic layer increases, while that of the organic layer decreases. However, the debonding probability of both layers is decreased. In addition, the SEI covering large particles is more vulnerable to fracture, while that covering small particles is more susceptible to debonding. Therefore, tailoring the thickness ratio of the inorganic to organic layers and particle size is important to reduce the fracture and debonding of the heterogeneous bilayer SEI.

The silicon solid electrolyte interphase (SEI) faces cyclical cracking and reconstruction due to the ~350% volume expansion of Si which leads to shortened cell life during electrochemical cycling. Understanding the SEI morphology/chemistry and more importantly its dynamic evolution from delithiated and lithiated states is paramount to engineering a stable Si anode. Fluoroethylene carbonate (FEC) is a preferred additive with widely demonstrated enhancement of the Si cycling. Thus, insights into the effects of FEC on the dynamics of the resulting SEI may provide hints toward engineering the Si interface. Herein, ATR-FTIR, AFM, tip IR, and XPS probing all show pronounced relative invariance of the FEC-generated SEI compared to the FEC-free SEI between adjacent lithiated and delithiated states beyond the formation cycles. The SEI of Si thin film model surfaces in the baseline 1 M LiPF6 in EC:EMC (1:1) undergoes major morphological and chemical speciation swings between half-cycles while comparatively the SEI upon addition of FEC displays far less dynamic evolution. This morphology and chemistry stability of the FEC-SEI supports the enhanced cycling stability of silicon anodes in FEC-containing electrolytes. The experimental evidence gathered suggests that the FEC-SEI invariance is enabled by an elastomeric polycarbonate matrix that preserves the SEI integrity against the expansion of silicon upon lithiation. In turn, less electrolyte-consuming reconstruction occurs which manifests as and high LiF content from one half-cycle to the next. This work provides critical insights to enhance the silicon anode stability via targeted SEI engineering, namely that LiF protected by an elastomeric protective matrix may be key to buffering the unavoidable mechanical disruption. Figure 1

The chemical-mechanical stability of solid–electrolyte interphase (SEI) is probably the most critical factor determining the performance of alkali metal anode (Li, Na, etc.) in secondary batteries. Although extensive advanced characterization methods have been carried out to study SEI layers of Na metal anode, including solid state nuclear magnetic resonance1, 2, cryogenic transmission electron microscopy3, etc., the structural/componential evolution of SEI is still an uncharted territory due to its transient formation process and complicated components. In this work, we systematically analyze the SEI formation and dissolution processes via jointly combining multiple in-situ characterization technologies. By revealing spatial-temporal resolved information of SEI evolution, the buried origin of chemical-mechanical instability of SEI in Na anode is further clarified, which provides valuable guidelines for SEI engineering. A dynamic SEI formation/dissolution model of Na metal anode is demonstrated as follow: Quantitative evaluation methods for the chemical instability (i.e., solubility) and mechanical instability (i.e., modulus) are designed. According to the mass variation in EQCM and the modulus measurement in in-situ AFM, we firstly quantitatively observe the chemical and mechanical stability evolution during SEI formation process. The dynamic evolution picture of SEI formation has been explicitly established. We discover the instantaneous electrochemical formation process of SEI is obviously divided into two stages based on the potential. It is revealed that the formation of efficient passivation layer anchored on Na surface during the 1st (passivating) stage (2.3 – 1 V vs Na/Na+) (Scheme 1 a-b) is the critical factor to construct stable SEI. In absence of passivation layer, the Na mental surface will trigger unrestricted electrolyte decomposition and homogenous components distribution during the subsequent (growing) stage. The dissolution model of SEI was revealed related to its spatial distribution of organics and inorganics. SEI with layered structure evolved from a compact passivation layer is found to have higher stability than that with homogenously distributed components. The inorganic species in the latter structure tend to detach from the SEI with the dissolution of organics, resulting in poor SEI chemical stability (Scheme 1 c and e). By contrast, SEIs with hierarchical structure growing based on the top of a passivation layer exhibits lower dissolution tendency (Scheme 1 d and f). The dynamic analysis of SEI evolution of Na anode presented in this work not only sheds light on how to construct a stable SEI, but also provides guiding significance in unveiling the seemingly complicated interfacial chemistry in batteries via a concerted characterization approach. References Gao, L.N., Chen, J.E., Chen, Q.L. et al. The chemical evolution of solid electrolyte interface in sodium metal batteries. Science Advances 8, 4606 (2022). Xiang, Y., Zheng, G., Liang, Z. et al. Visualizing the growth process of sodium microstructures in sodium batteries by in-situ 23Na MRI and NMR spectroscopy. Nat. Nanotechnol. 15, 883–890 (2020). Han, B., Zou, Y., Zhang, Z. et al. Probing the Na metal solid electrolyte interphase via cryo-transmission electron microscopy. Nat Commun 12, 3066 (2021). Figure 1