Elucidation of the Sodium-Ion Storage Behaviors in Hard Carbon Anodes through Pore Architecture Engineering
Wenbin Jian, Xueqing Qiu, Huaican Chen, Jian Yin, Wen Yin, Husam N. Alshareef, Wenli Zhang
Abstract
Hard carbon stands out as an auspicious anode material for commercial sodium-ion batteries, yet the correlation between plateau-potential capacity and its pore architecture remains poorly understood. In this study, we systematically investigated the sodium-ion storage behavior in hard carbons with tailored pore architecture. The plateau-potential capacity of hard carbon is attributed to the filling of sodium clusters within closed nanopores and open nanopores that are impervious to the solvent molecules of the electrolyte. Small-angle X-ray scattering (SAXS) has been shown to be an effective method for estimating the volume of nanopores that can store sodium clusters. A rapid and user-friendly butanol pycnometry technique is designed to assess the volume of nanopores available for sodium-ion storage. This method has established a linear correlation between the nanopore volume detected and the plateau-potential capacity measured experimentally. We identified two scenarios where the plateau-potential capacity deviates from the congruence linear relationship established by SAXS and butanol pycnometry techniques. First, sodium clusters are unable to fill nanopores larger than 4 nm and could only partially fill those larger than 2 nm. Second, the diffusion of Na + ions is impeded in graphene nanodomains with tight interlayer spacing and extended crystalline planes.