Local mobility in electrochemically inactive sodium in hard carbon anodes after the first cycle

Abstract

Sodium ion batteries are a promising alternative to current lithium ion battery technology, providing relatively high capacity and good cycling stability at low cost.

A revised mechanistic model for sodium insertion in hard carbons

“…The effect of increasing sodium concentration in the graphitic bilayer model has previously been characterised. 40 For these atomic scale simulations, spin-polarised density functional theory (DFT) calculations as implemented in the Vienna Ab initio Simulation Package (VASP, version 5.3.5) [41][42][43][44][45] were employed. To model the ion-electron interaction the projector-augmented wave method (PAW) was utilized, 46 and the plane wave cut-off (800 eV) and k-space integrals (9 Â 9 Â 1 and 5 Â 5 Â 2 G-centred Monkhorst-Pack grid, for the surface and bulk models, respectively) were chosen so that the total energy was converged to 1 meV per atom.…”

“…Energy & Environmental Science Paper and migration as a function of interlayer distance. 40,56 The sodium binding energy, E b , was calculated according to eqn (1): 57…”

Defects in Hard Carbon: Where Are They Located and How Does the Location Affect Alkaline Metal Storage?

“…[ 7,38,39,74 ] The effect of surface, interlayer distance, pore size, carbon morphology, defects, and heteroatoms will be dependent on pyrolysis/carbonization temperature (with less surface area, fewer defects, and more graphitic character observed with increasing pyrolysis temperature) and the initial reagents (where oxygen and nitrogen dopants can be introduced to tune material properties). [ 21,27,36,39,75 ] Additionally, the main contribution to Li storage in HC comes from intercalation, with initial contribution from surface adsorption as confirmed by in situ Raman analysis of Li in HCs. [ 33,65,76–79 ] For KIBs, the graphitic stacks’ interlayer distances accessible to Na + and Li + storage can be inaccessible, with greater interlayer distances required.…”

“…[ 33 ] The latter were further confirmed by muon spin rotation spectroscopy. [ 21 ] Employing the simulation model described herein, the effect of curvature, graphitic stack interlayer, and defect location on metal adsorption will be explored. This gives important insight adding to the previous knowledge of metal adsorption on defective planar basal plane surfaces, metal intercalation in nondefective graphitic stacks, and metal adsorption on curved motifs.…”

Elucidating the Effect of Planar Graphitic Layers and Cylindrical Pores on the Storage and Diffusion of Li, Na, and K in Carbon Materials

“…[ 29,30 ] A recent muon spin rotation spectroscopy study measured the average Na diffusion activation energy as 0.08 eV for a fully sodiated hard carbon. [ 59 ] To evaluate the metal diffusion in different carbon motifs found in hard carbon, and to investigate if similar behavior would be expected for the Li and K diffusion in hard carbon, NEB calculations are used to calculate the metal migration barriers between two adjacent sites (resulting in two adjacent sites with the same binding energies presented in Figures 3 and 5) in the two models. Figure shows the migration barriers as a function of interlayer distance for the planar graphitic layer model, while Figure shows the migration barriers as a function of pore diameter for the CNT model.…”