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Potassium‐ion storage is being explored by researchers for its advantages in forming graphite‐based intercalation compounds, with cost‐effective production compared to lithium‐ion systems. However, its poor performance in graphite‐based platforms, owing to the volume expansion required for intercalation, has demanded alternative materials for reversible potassiation. Herein, we demonstrate a simple one‐step pyrolysis approach to develop an amorphous hard carbon material from commercial cellulose for high‐performance potassium‐ion batteries (KIB). The larger interlayer spacing (~0.4 nm) alongside the electronegative oxygen functional groups promotes potassium‐ion storage. High capacity, good rate and long cycling performance with lower‐volume expansion could be credited to the amorphous carbon that possesses turbostratic nanodomains. Further, oxygen functional groups on the carbon material are identified in our experimental studies, and density functional theory simulations indicate that these are likely to enhance the potassium ion capacity of the materials.

We report density functional theory calculations for two siligraphene membranes, SiC and SiC, to assess their suitability as lithium ion anode materials. We find high capacities of 627.09 and 955.84 mA h g for the SiC and SiC monolayers, respectively. Both membranes also facilitate excellent lithium mobility with barriers of less than 0.5 eV. We find van der Waals stacked bilayer configurations for both siligraphenes. The volume expansion in the bilayer for SiC on lithiation is 28%, whereas the expansion for SiC is much higher at 62%. Both bilayers remain stable under high lithium loading. For the first time for siligraphene materials, we report bulk configurations for SiC and SiC. Here we find that the siligraphenes form three-dimensional structures with cavities and channels. The layers are not held together by van der Waals forces, but rather by single silicon-silicon and single silicon-carbon bonds. Surprisingly, these three-dimensional siligraphene bulk structures have a larger average interlayer distance than the van der Waals structures which yields an expansion due to lithiation of 20% for SiC and a very small expansion of 4% for SiC.

Computational methods are used to show that graphene nanoribbons bind sodium (Na) and calcium (Ca) more strongly than graphene sheets. The binding strength is further enhanced by functionalizing the edge of the nanoribbon with oxygen-containing groups. Strengthening of the binding of these metal atoms to graphitic materials is important for applications including metal-ion batteries. Our results are obtained using density functional theory calculations of the binding of sodium and calcium to hydrogen, hydroxyl, carbonyl, and carboxyl groups at the edge of zigzag and armchair nanoribbons. Both hydrogen passivation and hydroxyl functionalization result in moderate binding of Na and Ca with binding energies varying from -1.0 to -1.9 eV for the nanoribbons considered. An increase in binding compared to graphene does not just occur at the edge, but extends across the nanoribbon. Furthermore, carbonyl and carboxyl groups bound both metal atoms more strongly, with binding energies between -1.6 and -3.1 eV. Increasing the number of these groups at the edge increases the binding strength of the metal adatoms. When there is a high number of oxygen-containing groups at the edge, the effect of the oxygen-containing groups is also evident away from the edge of the nanoribbon for sodium and calcium. It is demonstrated that this is at least partly due to the change in the electronic structure spanning the entire width of the nanoribbons considered.

We demonstrate an approach to prepare nitrogen-rich hard carbon (N-HCS) from biomass as a robust anode material for sodium-ion batteries. A reversible capacity of ∼520 mA h g−1 at a current density of 20 mA g−1 along with an excellent rate performance was obtained. When cycled at a high current density of 1 A g−1, the N-HCS was stable for over 1000 cycles delivering a capacity of ∼204 mA h g−1. Density functional theory (DFT) computations verified that nitrogen doping enhances the interaction of sodium ions with the carbon, leading to a significantly improved storage capacity. This work provides new physical insights into the relationship between sodium-ion storage and nitrogen-containing hard carbon materials.