Search for: All records

Na-ion batteries (NIBs) are proposed as a promising candidate for beyond Li-ion chemistries, however, a key challenge associated with NIBs is the inability to achieve intercalation in graphite anodes. This phenomenon has been investigated and is believed to arise due to the thermodynamic instability of Na-intercalated graphite. We have recently demonstrated theoretical calculations showing it is possible to achieve thermodynamically stable Na-intercalated graphene structures with a fluorine surface modifier. Here, we present experimental evidence that Na + intercalation is indeed possible in fluorinated few-layer graphene (F-FLG) structures using cyclic voltammetry (CV), ion-sensitive scanning electrochemical microscopy (SECM) and in situ Raman spectroscopy. SECM and Raman spectroscopy confirmed Na + intercalation in F-FLG, while CV measurements allowed us to quantify Na-intercalated F-FLG stoichiometries around NaC 14–18 . These stoichiometries are higher than the previously reported values of NaC 186 in graphite. Our experiments revealed that reversible Na + ion intercalation also requires a pre-formed Li-based SEI in addition to the surface fluorination, thereby highlighting the critical role of SEI in controlling ion-transfer kinetics in alkali-ion batteries. In summary, our findings highlight the use of surface modification and careful study of electrode-electrolyte interfaces and interphases as an enabling strategy for NIBs. 

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. 

Ions at battery interfaces participate in both the solid-electrolyte interphase (SEI) formation and the subsequent energy storage mechanism. However, few in situ methods can directly track interfacial Li + dynamics. Herein, we report on scanning electrochemical microscopy with Li + sensitive probes for its in situ , localized tracking during SEI formation and intercalation. We followed the potential-dependent reactivity of edge plane graphite influenced by the interfacial consumption of Li + by competing processes. Cycling in the SEI formation region revealed reversible ionic processes ascribed to surface redox, as well as irreversible SEI formation. Cycling at more negative potentials activated reversible (de)intercalation. Modeling the ion-sensitive probe response yielded Li + intercalation rate constants between 10 −4 to 10 −5 cm s −1 . Our studies allow decoupling of charge-transfer steps at complex battery interfaces and create opportunities for interrogating reactivity at individual sites. 

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.