In Situ Raman and Nuclear Magnetic Resonance Study of Trapped Lithium in the Solid Electrolyte Interface of Reduced Graphene Oxide

Abstract

Motivated by its high surface area and electrical conductivity, reduced graphene oxide (rGO) flakes have been intensively studied as potential anode materials for lithium ion battery (LIB). The high capacity in rGO (600–1000 mA h g–1) compared to graphite (372 mA h g–1) suggest that a different lithiation mechanism may be operational in the former. The high capacity of rGO should be attributed to its high surface area and associated defective sites, however, these may act as trapping sites and undergo side reactions with the solvent and lithium ions to form the solid electrolyte interphase (SEI) upon lithiation, resulting in irreversible capacity loss (ICL) during the initial cycles. Elucidating the temporal evolution of SEI layer on rGO and quantifying the amount of trapped lithium will be useful in developing strategies to mitigate the ICL process. Herein, the Li intercalation mechanism in rGO and graphite was investigated using in situ Raman spectroscopy and in situ time-resolved nuclear magnetic resonance (NMR) to provide insights into the origins of the high capacity and ICL loss in rGO. Finally, the dynamic and static SEI passive layer formed on rGO flakes was monitored, and a method was developed to quantify the amount of Li+ trapped in the SEI layer.

N‐Doping and Defective Nanographitic Domain Coupled Hard Carbon Nanoshells for High Performance Lithium/Sodium Storage

“…Meanwhile, the G‐band of N‐GCNs shows unconspicuous red‐shifts from OCV to ≈0.2 V in LIBs (Figure a) and from OCV to 0.01 V in SIBs (Figure c) during discharge process. This can be accounted for the charge transfer effects from the adsorption of Li + /Na + ions and the according formation of SEI layer (below ≈0.8 V in LIBs (Figure b) and ≈0.6 V in SIBs (Figure d)) . These Li + /Na + ions randomly accommodate the nanoporous defective sites and fully cover the N‐GCNs surface at relatively higher voltage, thus causing the early disappearance of G‐band.…”

“…Figure S4a shows the CV curves for the first five cycles of the electrode at a scanning rate of 0.1 mV s −1 in the voltage range of 0.01–3.0 V versus Li + /Li. In the first discharge cycle, the irreversible peaks at 0.75 V of LIBs should be attributed to the solid electrolyte interphase (SEI) film formation and the decomposition of the electrolyte, and the peak at 1.7 V is caused by the loss of some irreversible lithium storage sites during the initial lithiation process . While the sharp peak at ≈0.01 V can also be imputed to the irreversible reaction of electrolyte with surface functional groups and the formation of SEI film .…”

Understanding Surface and Interfacial Chemistry in Functional Nanomaterials via Solid‐State NMR

“…In these materials, the residual oxygen functional groups such as hydroxyl, epoxy, and carboxylic moieties may interact with Li in addition to the usual intercalation chemistry, resulting in irreversible capacity loss. Recently, Tang et al elucidated the temporal evolution of the SEI layer on rGO and quantified the amount of trapped lithium by in situ NMR and Raman . Figure shows the in situ 7 Li NMR spectra corresponding to specific potential stages (i.e., open‐circuit voltage, the end of the discharge, the end of charge, etc.).…”

“…Stacked in situ 7 Li NMR spectra of the rGO composite obtained during the galvanostatic charge/discharge cycles in the ranges of: a) −150 to +150 ppm, the broad dark‐green peak is attributed to a combination of lithium intercalation in the rGO lattice and lithium adsorbed on the rGO; the sharp light‐green peaks at about 0 ppm are attributed to the electrolytes; and b) 200–300 ppm; 244 ppm (violet) and 250 ppm (blue) are from the skin layer (10 µm) of the flat Li‐metal battery surface while 265 ppm (orange) is attributed to the nano‐/microstructured Li‐metal fibers. Reproduced with permission . Copyright 2016, American Chemical Society.…”

Applications of Conventional Vibrational Spectroscopic Methods for Batteries Beyond Li‐Ion

“…Carbonaceous materials are a family of many allotropes, such as graphite, graphene, carbon nanotubes, fullerenes, and amorphous carbon, which have been instrumental in LIBs, NIBs, KIBs, and AIBs. Raman spectroscopy is a powerful tool for characterizing the structures of carbonaceous materials in terms of defects, and the topochemistry of ion insertion into carbonaceous materials . Highly crystalline carbon structures are built by the stacking of single‐layer carbon sheet—graphene.…”