Study of structural changes that occurred during charge/discharge of carbon-coated SiO anode by nuclear magnetic resonance

Unraveling the Reaction Mechanisms of SiO Anodes for Li-Ion Batteries by Combining in Situ 7Li and ex Situ 7Li/29Si Solid-State NMR Spectroscopy

“…CR2032 coin type cells were assembled with copper foil coated electrodes or pellet electrodes, using a glass fiber separator (Whatman, GLASS MICROFIBER FILTERS) and Li-metal as counter electrode and LP30 electrolyte (EC:DMC = 1:1 + 1 M LiPF 6 ). For 29 Si NMR samples, a polyethylene separator (Celgard ® 3501) was added between the glass fiber separator and electrode to avoid glass fiber contamination of the electrode. In the case of high capacity pellet electrodes, 10 wt.-% fluoroethylene carbonate (FEC) was also added (i.e., 90:10, LP30:FEC by mass) to help avoid short circuits from Li dendrite growth at the Li metal counter electrode.…”

“…Single-pulse excitation was used in combination with a recycle delay of 3 s. The sample rotation rate was 12.5 kHz. MAS 29 Si NMR spectra were recorded on Bruker Avance III 500 and Avance I 400 spectrometers operating at 29 Si NMR frequencies of 99.36 and 79.49 MHz, respectively. Rotor-synchronized Hahn-echo spectra were typically obtained at spinning speeds of 8 kHz with recycle delays of 1 or 30 s to detect the signals of Li x Si or Li 4 SiO 4 respectively.…”

“…NMR raw data handling and processing was done using Bruker Topspin. The 7 Li and 29 Si chemical shifts were referenced to solid Li 2 CO 3 and Trimethylsilylpropanoic acid both at 0 ppm, respectively.…”

“…A small peak is observed at 0 ppm in all spectra often as a shoulder of the stronger Li x Si signals, which arises from the solid electrolyte interface (SEI) and/or the super-P/CMC-Na matrix. Figure 6b presents the full set of the ex situ 29 Si MAS NMR spectra acquired for the pure-Si electrodes of Figure 6a as well as for the micron-sized Si powder. The pristine Si powder gives rise to a narrow 29 Si NMR signal at -82 ppm, which corresponds to a crystalline Si environment.…”

“…Despite its promise, the chemical evolution and compounds formed during SiO lithiation remain the subject of debate, preventing a rational choice of an optimized SiO anode. [18][19][20][21][22][23][24][25][26][27][28][29][30] In particular, the role of the SiO 2 and/or lithium silicates and size of (any) silicon domains and the role in these structural and morphological motifs in performance remains unclear. Most reports have identified at least two phases in lithiated SiO, a lithium silicide (Li x Si) phase and a lithium silicate (as summarized in Table S1, supporting information).…”