Effect of Charge Transfer upon Li- and Na-Ion Insertion in Fine-Grained Graphitic Material as Probed by NMR

Abstract

We investigated the insertion−extraction behaviors of Li and Na ions in graphitic materials using solidstate NMR. A unique advantage of high-degree 13 C-isotope enrichment of graphitic material allowed sensitive and metastable graphite intercalation compounds to be measured in a short time. Ex situ 13 C magic-angle spinning NMR spectra of 13 C fine-grained graphite are presented as a function of state-of-charge. The observations are discussed with respect to graphite intercalation phenomena, which include the effects of charge transfer and the demagnetizing field. Dramatic narrowing of the 13 C NMR signal in metal-intercalated graphite evidences quasi-complete charge transfer occurring between lithium and graphite host material and resulting in reducing the macroscopic field effects. Upon Na insertion, incomplete charge transfer is observed and explained by inaccessibility of graphitic interlayer space for Na ions in our study. In addition, critical issues of reversibility of Li-and Na-ion electrochemical cells and solid electrolyte interphase formation are considered on the atomic scale. The knowledge gained in the present work can be applied to advanced high-power-density electrode materials for safe and fast-charging metal-ion batteries or for novel spintronic concepts with controlled spin-polarized charge carrier injection and transport combined with the possibility to manipulate magnetic anisotropy.

Sustainable SiC Composite Anodes, Graphite Accelerated Lithium Storage

“…69,70 Nonetheless, Li insertion minimizes the demagnetizing effects and enhances field homogeneity, resulting in improved NMR spectral resolution. 68 Therefore, in the cycled 29 Si spectra, the narrower peak shifts to lower ppm and deconvoluted to reveal a peak at −8.3 ppm for irreversible Li x SiC and a peak at −21 ppm for hexagonal SiC, agreeing well with the pristine SiC/HC systems. 71 Figure 5 SEM images reveal the morphologies of SiC/HC/30G and SiC/O/30G before and after cycling.…”

“…Vyalikh et al 67 subjected possible unobservable 13 C spins in MAS NMR to the reduced resolution in low sample volume and demagnetizing fields within graphitic regions. 68 In contrast to the single −16.5 ppm 29 Si NMR peak for cubic SiC observed in pristine SiC/HC, a second broad peak centered around −34 ppm is present in the SiC/HC/30G composites (Fig. 4c).…”

Design Strategies to Enable the Efficient Use of Sodium Metal Anodes in High‐Energy Batteries

“…It is essential to control the reactions between the highly reactive Na anode and the liquid electrolyte to achieve stable Na anodes. Solvents, salts, and additives in electrolytes have been intensively investigated to improve the performance of Na anodes because these components in the electrolytes can decompose and be incorporated into the SEI . Thus, they can be used to tailor the physicochemical properties of the SEI.…”