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1. Review of Emerging Concepts in SEI Analysis and Artificial SEI Membranes for Lithium, Sodium, and Potassium Metal Battery Anodes

   https://doi.org/10.1002/aenm.202002297  

   Liu, Wei ; Liu, Pengcheng ; Mitlin, David ( October 2020 , Advanced Energy Materials)

   Anodes for lithium metal batteries, sodium metal batteries, and potassium metal batteries are susceptible to failure due to dendrite growth. This review details the structure–chemistry–performance relations in membranes that stabilize the anodes’ solid electrolyte interphase (SEI), allowing for stable electrochemical plating/stripping. Case studies involving Li, Na, and K are presented to illustrate key concepts. “Classical” versus “modern” understandings of the SEI are described, with an emphasis on the new structural insights obtained through novel analytical techniques, including in situ liquid‐secondary ion mass spectroscopy, titration gas chromatography, and tip‐enhanced Raman spectroscopy. This Review highlights diverse approaches for increasing SEI stability, either by inserting a secondary layer between the native SEI and the separator, or by combining the membrane with a native SEI to form a hybrid composite. Exciting and nonintuitive findings are discussed, such as that the metal anode roughness profoundly affects the SEI structure and stability, or that organic artificial SEI‐layers may be more effective than the native inorganic–organic SEIs. Emerging multifunctional architectures are presented, which serve a dual role as metal hosts and metal surface protection layers. Throughout the Review, fruitful future research directions and the critical areas where there is incomplete understanding are discussed.

    

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2. Using NMR spectroscopy to link structure to function at the Li solid electrolyte interphase

   https://doi.org/10.1016/j.joule.2024.04.016  

   Svirinovsky-Arbeli, Asya ; Juelsholt, Mikkel ; May, Richard ; Kwon, Yongbeom ; Marbella, Lauren E ( May 2024 , Joule)

   The performance of Li metal batteries is tightly coupled to the composition and properties of the solid electrolyte interphase (SEI). Even though the role of the SEI in battery function is well understood (e.g., it must be electronically insulating and ionically conductive, it must enable uniform Li+ flux to the electrode to prevent filament growth, it must accommodate the large volume changes of Li electrodeposition), the challenges associated with probing this delicate composite layer have hindered the development of Li metal batteries for practical applications. In this review, we detail how nuclear magnetic resonance (NMR) spectroscopy can help bridge this gap in characterization due to its unique ability to describe local structure (e.g., changes in crystallite size and amorphous species in the SEI) in conjunction with ion dynamics while connecting these properties to electrochemical behavior. By leveraging NMR, we can gain molecular-level insight to aid in the design of Li surfaces and enable reactive anodes for next-generation, high-energy-density batteries. 

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3. In situ formation of a multicomponent inorganic-rich SEI layer provides a fast charging and high specific energy Li-metal battery

   https://doi.org/10.1039/C9TA05063A  

   Sun, Ho-Hyun ; Dolocan, Andrei ; Weeks, Jason A. ; Rodriguez, Rodrigo ; Heller, Adam ; Mullins, C. Buddie ( July 2019 , Journal of Materials Chemistry A)

   The performance of the rechargeable Li metal battery anode is limited by the poor ionic conductivity and poor mechanical properties of its solid-electrolyte interphase (SEI) layer. To overcome this, a 3 : 1 v/v ethyl methyl carbonate (EMC) : fluoroethylene carbonate (FEC) containing 0.8 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.2 M lithium difluoro(oxalate)borate (LiDFOB) dual-salts with 0.05 M lithium hexafluorophosphate (LiPF 6 ) was tested to promote the formation of a multitude of SEI-beneficial species. The resulting SEI layer was rich in LiF, Li 2 CO 3 , oligomeric and glass borates, Li 3 N, and Li 2 S, which enhanced its role as a protective yet Li + conductive film, stabilizing the lithium metal anode and minimizing dead lithium build-up. With a stable SEI, a Li/Li[Ni 0.59 Co 0.2 Mn 0.2 Al 0.01 ]O 2 Li-metal battery (LMB) retains 75% of its 177 mA h g −1 specific discharge capacity for 500 hours at a coulombic efficiency of greater than 99.3% at the fast charge–discharge rate of 1.8 mA cm −2 . 

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4. Single‐Solvent‐Based Electrolyte Enabling a High‐Voltage Lithium‐Metal Battery with Long Cycle Life

   https://doi.org/10.1002/aenm.202300918  

   Li, Yuanqin ; Liu, Mingzhu ; Wang, Kang ; Li, Chengfeng ; Lu, Ying ; Choudhary, Aditya ; Ottley, Taylor ; Bedrov, Dmitry ; Xing, Lidan ; Li, Weishan ( June 2023 , Advanced Energy Materials)

   The application of Li‐metal‐anodes (LMA) can significantly improve the energy density of state‐of‐the‐art lithium ion batteries. Lots of new electrolyte systems have been developed to form a stable solid electrolyte interphase (SEI) films, thereby achieving long‐term cycle stability of LMA. Unfortunately, the common problem faced by these electrolytes is poor oxidation stability, which rarely supports the cycling of high‐voltage Li‐metal batteries (LMBs). In this work, a new single‐component solvent dimethoxy(methyl)(3,3,3‐trifluoropropyl) silane is proposed. The electrolyte composed of this solvent and 3 mLiFSI salt successfully supports the long‐term cycle stability of limited‐Li (50 µm)||high loading LiCoO₂(≈20 mg cm⁻²) cell at 4.6 V. Experiments and theoretical research results show that the outstanding performance of the electrolyte in high‐voltage LMBs is mainly attributed to its unique solvation structures and its great ability to build a highly stable and robust interphase on the surface of LMA and high‐voltage cathodes. Interestingly, this proposed electrolyte system builds a stable SEI film rich in LiF and Li₃N on the surface of LMA by improving the two‐electron reduction activity of FSI⁻without adding LiNO₃, the well‐known additive used for LMBs. The design idea of the proposed electrolyte can guide the development of high‐voltage LMBs.

    

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5. Revealing the Role of Lithium Carbonate at Lithium Metal Anodes Through Study of Gas-Reacted Interphases

   https://doi.org/10.1149/1945-7111/ad6d92  

   Steinberg, Katherine ; Gallant, Betar_M ( August 2024 , Journal of The Electrochemical Society)

   A stable, ionically-conductive solid electrolyte interphase (SEI) is vital to lithium (Li) metal anodes, yet key properties of common SEI phases remain unknown. Among these, Li₂CO₃, central to foundational SEI models, has been difficult to probe given its metastability on Li. To address this, we adopted two approaches: (i) synthesis and study of model Li₂CO₃-based SEI and (ii) cycling and titration-based analysis of SEI from Li–Cu cells with or without additive CO₂, with the aim of modulating Li₂CO₃content natively. In (i), reductive instability of Li₂CO₃led to co-formation of Li₂O and Li₂C₂in a multiphasic film with a Li⁺conductivity (∼8 × 10⁻⁹S cm⁻¹) more than 4x higher than previously-measured Li₂O or LiF films. Li₂CO₃content in native interphases from (ii) was found to correlate with decreased inactive Li⁰accumulation and improved Coulombic efficiency (CE) across diverse electrolytes having moderate CE. In high CE electrolytes, however, capacity losses become dominated by SEI formation rather than inactive Li⁰, and Li₂CO₃enrichment had negligible impact. This work updates understanding of SEI Li₂CO₃formed in modern electrolytes, reveals a leading mechanism by which Li₂CO₃can boost CE despite its metastability, and indicates the potential and limitations of enriching this phase through electrolyte design.

    

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