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1. Tracking Passivation and Cation Flux at Incipient Solid‐Electrolyte Interphases on Multi‐Layer Graphene using High Resolution Scanning Electrochemical Microscopy

   https://doi.org/10.1002/celc.202101445  

   Zeng, Yunxiong ; Gossage, Zachary T. ; Sarbapalli, Dipobrato ; Hui, Jingshu ; Rodríguez‐López, Joaquín ( March 2022 , ChemElectroChem)

   The solid electrolyte interphase (SEI) is a dynamic, electronically insulating film that forms on the negative electrode of Li⁺batteries (LIBs) and enables ion movement to/from the interface while preventing electrolyte breakdown. However, there is limited comparative understanding of LIB SEIs with respect to those formed on Na⁺and K⁺electrolytes for emerging battery concepts. We used scanning electrochemical microscopy (SECM) for the in situ interfacial analysis of incipient SEIs in Li⁺, K⁺and Na⁺electrolytes formed on multi‐layer graphene. Feedback images using 300 nm SECM probes and ion‐sensitive measurements indicated a superior passivation and highest cation flux for a Li⁺‐SEI in contrast to Na⁺and K⁺‐SEIs. Ex situ X‐ray photoelectron spectroscopy indicated significant fluoride formation for only Li⁺and Na⁺‐SEIs, enabling correlation to in situ SECM measurements. While SEI chemistry remains complex, these electroanalytical methods reveal links between chemical variables and the interfacial properties of materials for energy storage.

    

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2. Coordinated mapping of Li + flux and electron transfer reactivity during solid-electrolyte interphase formation at a graphene electrode

   https://doi.org/10.1039/c9an02637a  

   Gossage, Zachary T. ; Hui, Jingshu ; Sarbapalli, Dipobrato ; Rodríguez-López, Joaquín ( March 2020 , The Analyst)

   Interphases formed at battery electrodes are key to enabling energy dense charge storage by acting as protection layers and gatekeeping ion flux into and out of the electrodes. However, our current understanding of these structures and how to control their properties is still limited due to their heterogenous structure, dynamic nature, and lack of analytical techniques to probe their electronic and ionic properties in situ . In this study, we used a multi-functional scanning electrochemical microscopy (SECM) technique based on an amperometric ion-selective mercury disc-well (HgDW) probe for spatially-resolving changes in interfacial Li + during solid electrolyte interphase (SEI) formation and for tracking its relationship to the electronic passivation of the interphase. We focused on multi-layer graphene (MLG) as a model graphitic system and developed a method for ion-flux mapping based on pulsing the substrate at multiple potentials with distinct behavior ( e.g. insertion–deinsertion). By using a pulsed protocol, we captured the localized uptake of Li + at the forming SEI and during intercalation, creating activity maps along the edge of the MLG electrode. On the other hand, a redox probe showed passivation by the interphase at the same locations, thus enabling correlations between ion and electron transfer. Our analytical method provided direct insight into the interphase formation process and could be used for evaluating dynamic interfacial phenomena and improving future energy storage technologies. 

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3. Observation of an intermediate state during lithium intercalation of twisted bilayer MoS2

   https://doi.org/10.1038/s41467-022-30516-z  

   Wu, Yecun ; Wang, Jingyang ; Li, Yanbin ; Zhou, Jiawei ; Wang, Bai Yang ; Yang, Ankun ; Wang, Lin-Wang ; Hwang, Harold Y. ; Cui, Yi ( May 2022 , Nature Communications)

   Lithium intercalation of MoS₂is generally believed to introduce a phase transition from H phase (semiconducting) to T phase (metallic). However, during the intercalation process, a spatially sharp boundary is usually formed between the fully intercalated T phase MoS₂and non-intercalated H phase MoS₂. The intermediate state,i.e., lightly intercalated H phase MoS₂without a phase transition, is difficult to investigate by optical-microscope-based spectroscopy due to the narrow size. Here, we report the stabilization of the intermediate state across the whole flake of twisted bilayer MoS₂. The twisted bilayer system allows the lithium to intercalate from the top surface and enables fast Li-ion diffusion by the reduced interlayer interaction. TheE_2gRaman mode of the intermediate state shows a peak splitting behavior. Our simulation results indicate that the intermediate state is stabilized by lithium-induced symmetry breaking of the H phase MoS₂. Our results provide an insight into the non-uniform intercalation during battery charging and discharging, and also open a new opportunity to modulate the properties of twisted 2D systems with guest species doping in the Moiré structures.

    

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4. Co-intercalation-free ether electrolytes for graphitic anodes in lithium-ion batteries

   https://doi.org/10.1039/D2EE01489K  

   Ma, Peiyuan ; Mirmira, Priyadarshini ; Eng, Peter J. ; Son, Seoung-Bum ; Bloom, Ira D. ; Filatov, Alexander S. ; Amanchukwu, Chibueze V. ( November 2022 , Energy & Environmental Science)

   Carbonate-based electrolytes are widely used in Li-ion batteries but are limited by a small operating temperature window and poor cycling with silicon-containing graphitic anodes. The lack of non-carbonate electrolyte alternatives such as ether-based electrolytes is due to undesired solvent co-intercalation that occurs with graphitic anodes. Here, we show that fluoroethers are the first class of ether solvents to intrinsically support reversible lithium-ion intercalation into graphite without solvent co-intercalation at conventional salt concentrations. In full cells using a graphite anode, they enable 10-fold higher energy densities compared to conventional ethers, and better thermal stability over carbonate electrolytes (operation up to 60 °C) by producing a robust solvent-derived solid electrolyte interphase (SEI). As single-solvent–single-salt electrolytes, they remarkably outperform carbonate electrolytes with fluoroethylene carbonate (FEC) and vinylene carbonate (VC) additives when cycled with graphite–silicon composite anodes. Our molecular design strategy opens a new class of electrolytes that can enable next generation Li-ion batteries with higher energy density and a wider working temperature window. 

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5. Revealing the Sodium Storage Mechanisms in Hard Carbon Pores

   https://doi.org/10.1002/aenm.202302171  

   Kitsu Iglesias, Luis ; Antonio, Emma N. ; Martinez, Tristan D. ; Zhang, Liang ; Zhuo, Zengqing ; Weigand, Steven J. ; Guo, Jinghua ; Toney, Michael F. ( October 2023 , Advanced Energy Materials)

   Hard carbon (HC) is the most promising anode for the commercialization of sodium‐ion batteries (NIBs); however, a general mechanism for sodium storage in HC remains unclear, obstructing the development of highly efficient anodes for NIBs. To elucidate the mechanism of sodium storage in the pores, operando synchrotron small‐angle X‐ray scattering, wide‐angle X‐ray scattering, X‐ray absorption near edge structure, Raman spectroscopy, and galvanostatic measurements are combined. The multimodal approach provides mechanistic insights into the sodium pore‐filling process for different HC microstructures including the pore sizes that are preferentially filled, the extent to which different pore sizes are filled, and how the defect concentration influences pore filling. It is observed that sodium in the larger pores has an increased pseudo‐metallic sodium character consistent with larger sodium clusters. Furthermore, it is shown that the HCs prepared at higher pyrolysis temperatures have a larger capacity from sodium stored in the pores and that sodium intercalation between graphene layers occurs simultaneously with the pore filling in the plateau region. Opportunities are outlined to improve the performance of HC anodes by fully utilizing the pores for sodium storage, helping to pave the way for the commercialization of sodium ion batteries.

    

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