Empirical correlation of quantified hard carbon structural parameters with electrochemical properties for sodium-ion batteries using a combined WAXS and SANS analysis

Abstract

This study highlights the advantages of using wide-angle X-ray scattering (WAXS) and small-angle neutron scattering (SANS) methods to analyse turbostratic d-glucose-derived hard carbons (GDCs) over a wide range of length scales. It demonstrates the reasons for the superior performance of hard carbons (HCs) pyrolysed at 1100 °C compared to those pyrolysed at 700 °C, 1000 °C, or 1400 °C in sodium-ion batteries (SIBs). Twelve WAXS and thirteen SANS structural parameters were simultaneously determined for HCs. The investigation incorporates WAXS-derived interlayer spacing, a3, into the SANS analysis of HCs. The Ruland and Smarsly algorithm is emphasised over the commonly used Scherrer and Bragg equations. Thus, the collective analysis of nanostructure highlights the necessity for a revision in applying widely used characterisation techniques when dealing with disordered HCs. The study suggests that an a3 value of 0.373 nm best suits GDC-1100 as a SIB anode material. Comparing HCs prepared at different pyrolysis temperatures, GDC-1100 exhibits the most compatible parameters, resulting in the highest specific capacity value. The model-free SAS analysis indicates hierarchical structural changes at nanoscopic (SANS) and atomic (WAXS) scales simultaneously. The interplay between dynamic a3 and static parameters, such as the graphene layer extent La and the Ruland length, lR, favours plateau capacity, contributing to sodium ion storage. The study demonstrates the suitability of the WAXS/SANS toolbox for empirically correlating hard carbons' structural characteristics with the electrochemical performance of SIBs.