Hard carbons have shown considerable promise as anodes for emerging sodium-ion battery technologies. Current understanding of sodium-storage behaviour in hard carbons attributes capacity to filling of graphitic interlayers and pores, and adsorption at defects, although there is still considerable debate regarding the voltages at which these mechanisms occur. Here, ex situ²³Na solid-state NMR and total scattering studies on a systematically tuned series of hard carbons revealed the formation of increasingly metallic sodium clusters in direct correlation to the growing pore size, occurring only in samples which exhibited a low voltage plateau. Combining experimental results with DFT calculations, we propose a revised mechanistic model in which sodium ions store first simultaneously and continuously at defects, within interlayers and on pore surfaces. Once these higher energy binding sites are filled, pore filling occurs during the plateau region, where the densely confined sodium takes on a greater degree of metallicity.

Identification of defects proved to be beneficial for metal storage and adsorption on graphene, but are detrimental to metal migration, hence affecting the battery performance.

The development and optimization of high‐performance anode materials for alkali metal ion batteries is crucial for the green energy evolution. Atomic scale computational modeling such as density functional theory and molecular dynamics allows for efficient and adventurous materials design from the nanoscale, and have emerged as invaluable tools. Computational modeling cannot only provide fundamental insight, but also present input for multiscale models and experimental synthesis, often where quantities cannot readily be obtained by other means. In this review, an overview of three main anode classes; alloying, conversion, and intercalation‐type anodes, is provided and how atomic scale modeling is used to understand and optimize these materials for applications in lithium‐, sodium‐, and potassium‐ion batteries. In the last part of this review, a novel type of anode materials that are largely predicted from density functional theory simulations is presented. These 2D materials are currently in their early stages of development and are only expected to gain in importance in the years to come, both within the battery field and beyond, highlighting the ability of atomic scale materials design.

Hard carbons are among the most promising materials for alkali‐ion metal anodes. These materials have a highly complex structure and understanding the metal storage and migration within these structures is of utmost importance for the development of next‐generation battery technologies. The effect of different carbon structural motifs on Li, Na, and K storage and diffusion are probed using density functional theory based on experimental characterizations of hard carbon samples. Two carbon structural models—the planar graphitic layer model and the cylindrical pore model—are constructed guided by small‐angle X‐ray scattering and transmission electron microscopy characterization. The planar graphitic layers with interlayer distance 6.5 Å, when the graphitic layer separation becomes so wide that there is negligible interaction between the two graphitic layers. The cylindrical pore model, reflecting the curved morphology, does not increase metal storage, but significantly lowers the metal migration barriers. Hence, the curved carbon morphologies are shown to have great importance for battery cycling. These findings provide an atomic‐scale picture of the metal storage and diffusion in these materials.

Lithium–sulfur batteries (LSBs) are a class of new‐generation rechargeable high‐energy‐density batteries. However, the persisting issue of lithium polysulfides (LiPs) dissolution and the shuttling effect that impedes the efficiency of LSBs are challenging to resolve. Herein a general synthesis of highly dispersed pyrrhotite Fe_1−xS nanoparticles embedded in hierarchically porous nitrogen‐doped carbon spheres (Fe_1−xS‐NC) is proposed. Fe_1−xS‐NC has a high specific surface area (627 m² g⁻¹), large pore volume (0.41 cm³ g⁻¹), and enhanced adsorption and electrocatalytic transition toward LiPs. Furthermore, in situ generated large mesoporous pores within carbon spheres can accommodate high sulfur loading of up to 75%, and sustain volume variations during charge/discharge cycles as well as improve ionic/mass transfer. The exceptional adsorption properties of Fe_1−xS‐NC for LiPs are predicted theoretically and confirmed experimentally. Subsequently, the electrocatalytic activity of Fe_1−xS‐NC is thoroughly verified. The results confirm Fe_1−xS‐NC is a highly efficient nanoreactor for sulfur loading. Consequently, the Fe_1−xS‐NC nanoreactor performs extremely well as a cathodic material for LSBs, exhibiting a high initial capacity of 1070 mAh g⁻¹ with nearly no capacity loss after 200 cycles at 0.5 C. Furthermore, the resulting LSBs display remarkably enhanced rate capability and cyclability even at a high sulfur loading of 8.14 mg cm⁻².