X‐Ray Spectromicroscopy Investigation of Heterogeneous Sodiation in Hard Carbon Nanosheets with Vertically Oriented (002) Planes

Abstract

Hard carbon (HC) is a promising anode material for sodium‐ion batteries, but the performance remains unsatisfactory and the sodiation mechanism in HC is one of the most debated topics. Here, from self‐assembled cellulose nanocrystal sheets with crystallographic texture, unique HC nanosheets with vertically oriented (002) planes are fabricated and used as a model HC to investigate the sodiation mechanisms using synchrotron scanning transmission X‐ray microscopy (STXM) coupled with analytical transmission electron microscopy (TEM). The model HC simplifies the 3D sodiation in a typical HC particle into a 2D sodiation, which facilitates the visualization of phase transformation at different states of charge. The results for the first time unveil that the sodiation in HC initiates heterogeneously, with multiple propagation fronts proceeding simultaneously, eventually merging into larger aggregates. The spatial correlation between the preferential adsorption and nucleation sites suggests that the heterogeneous nucleation is driven by the local Na‐ion concentration, which is determined by defects or heteroatoms that have strong binding to Na ions. By identifying intercalation as the dominant sodium storage mechanism in the model HC, the findings highlight the importance of engineering the graphene layer orientation and the structural heterogeneity of edge sites to enhance the performances.

N and S co-doped nanosheet-like porous carbon derived from sorghum biomass: mechanical nanoarchitecturing for upgraded potassium ion batteries

“…38 In addition, the twisty lattice fringe in NSSC-600 demonstrates a highly disordered structure, which can provide the void for the accommodation of the K cluster during the K-ion (de)intercalation processes. 39 Next, the XRD spectra of the carbon samples were obtained to investigate their crystalline phase (Fig. 2e).…”

“…38 In addition, the twisty lattice fringe in NSSC-600 demonstrates a highly disordered structure, which can provide the void for the accommodation of the K cluster during the K-ion (de)intercalation processes. 39…”

Laboratory X-ray Microscopy Study of Microcrack Evolution in a Novel Sodium Iron Titanate-Based Cathode Material for Li-Ion Batteries

“…In addition, gradients of the chemical potential or the concentration of elements in a (large) particle might significantly accelerate the intragranular fracture processes [13,48]. However, to address the SOC heterogeneity in the particles, the 3d-metal charge state has to be quantified in a spatially resolved manner by applying high-resolution spectroscopic techniques such as X-ray absorption spectromicroscopy or spectrotomography [49][50][51]. Although it is not possible with state-of-the-art laboratory nano-XCT tools because of the use of characteristic X-rays (Cu-Kα), the developed electrochemical operando cell is well suited to X-ray absorption spectroscopy studies.…”

Understanding of Sodium Storage Mechanism in Hard Carbons: Ongoing Development under Debate

“…[53,55,56] As the microstructure of hard carbon is inhomogeneous, the size of turbostratic nanodomains or the pseudo-graphitic region area is crucial parameters that could influence the Na-storage capacity of interlayer insertion, apart from the d 002 value. Li et al [57] highlighted the importance of graphene layer orientation and edge sites' structural heterogeneity to increase the nucleation density of the Na x C intercalation compounds. More recently, Katsuyama et al [58] proposed that the Na + intercalation capacity in wood-derived hard carbons was proportional to the crystallite interlayer area with a correlation coefficient of 0.94.…”