Electrochemical Changes in Lithium-Battery Electrodes Studied Using ⁷Li NMR and Enhanced ¹³C NMR of Graphene and Graphitic Carbons

Abstract

An anode composed of tin-core, graphitic-carbon-shell nanoparticles distributed on graphene nanosheets, Sn@C-GNs, is studied during the lithiation process. 7 Li NMR provides an accurate measure of the stepwise reduction of metallic Sn to lithium-tin alloys and reduction of the graphitic carbon. The metallic nanoparticle cores are observed to form ordered, crystalline phases at each step of the lithiation process. The 7 Li 2D experiments presented provide insight into the proximity of the various phases, reflecting the mechanism of the electrochemical reaction. In particular, a sequential model of nanoparticle lithiation, rather than a simultaneous process, is suggested. Movement of lithium ions between two elements of the nanostructured Sn@C-GNsmaterial-the metallic core and carbon shell-is also observed. Conventional 13 C SSNMR experiments on <5 mg of active material from electrochemical cells were found to be impossible, but signal enhancements (up to 18 fold) via the use of extended echo trains in conjunction with magic-angle spinning enabled NMR characterization of the carbon. We demonstrate that the 13 C data is extremely sensitive to the added electron density when the graphitic carbon is reduced. We also investigate ex situ carbon electrodes from cycled Li-O 2 cells, where we find no evidence of charge sharing between the electrochemically active species and the graphitic carbon in the 13 C NMR.

Lithium‐Pretreated Hard Carbon as High‐Performance Sodium‐Ion Battery Anodes

“…The 7 Li NMR spectra in Figure 5 a showed a sharp lithium metal peak at 260 ppm for pretreated HC from both electrolytes . Both samples showed another broad feature in the vicinity of 0 ppm, which can be deconvoluted into a major peak of the lithium‐ion within the SEI (peak 1 at ≈0 ppm) and a small peak of the lithium‐ion inserted into carbon layers (peak 2 at ≈4 ppm) . The profound relative intensity of lithium metal peak over the sum of peaks 1 and 2 in these two samples indicates that lithium metal reacted with the electrolyte rigorously in the carbonate electrolyte, whereas in the TEGDME electrolyte, the lithium metal largely sustained.…”

“…To understand the underlying mechanism of the HC pretreatment with SLMP in sodium-ion electrolyte and correlate the different electrochemical performance with the SEI, solid-state nuclear magnetic resonance (NMR), XPS, and scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) mapping analysis were performed on HC electrodes pretreated in TEGDME and carbonate electrolytes, respectively. [38,39] The profound relative intensity of lithium metal peak over the sum of peaks 1 and 2 in these two samples indicates that lithium metal reacted with the electrolyte rigorously in the carbonate electrolyte, whereas in the TEGDME electrolyte, the lithium metal largely sustained. The 7 Li NMR spectra in Figure 5a showed a sharp lithium metal peak at 260 ppm for pretreated HC from both electrolytes.…”

Mixed Molybdenum Oxides with Superior Performances as an Advanced Anode Material for Lithium-Ion Batteries

“…According to the XRD and NMR results of lithiation samples of MoO 2 (Figure S4), the intermediate phase Li 0.98 MoO 2 still exist after 5 cycles, which helps stabilize the structure44. The much more stable Li 0.98 MoO 2 in the lithiated MMO nanoparticles may be attributed to the high concentraion of MoO 3 around MoO 2 in MMO.…”

Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts

“…In order to increase the sensitivity of the 15 N MAS experiments, we used the Carr–Purcell–Meiboom–Gill pulse sequence (CPMG). 33 It works well for NMR resonances that have long spin-state lifetimes but significant inhomogeneous broadening. Fig.…”