Revealing Closed Porosity in Hard Carbon by SAXS
Hard carbon is a key anode material for next-generation sodium-ion batteries. Its performance is strongly governed by nanoscale porosity, including both open and closed pores. While gas adsorption quantifies accessible surface area, small-angle X-ray scattering (SAXS) enables determination of total specific surface area (SSA) independent of pore accessibility. The SAXSpoint 700 provides a powerful platform for this complementary analysis.
Introduction
Hard carbon is a non-graphitizable carbon material produced by pyrolysis of organic precursors. Its structure consists of curved graphene fragments, turbostratic stacking, and a complex network of nano-voids and micropores.
For electrochemical energy storage, particularly sodium-ion systems, closed micropores play an important role in charge storage and influence capacity, efficiency, and cycling stability. A comprehensive understanding of both accessible and inaccessible porosity is therefore essential.
Complementary Surface Area Determination
Nitrogen adsorption (BET) remains the established method for determining gas-accessible specific surface area. It provides valuable information on open porosity and surface accessibility.
However, in disordered carbons such as hard carbon, a significant fraction of pores may be closed and therefore not accessible to gas molecules. SAXS complements BET by probing electron density contrast and detecting both open and closed pore structures.
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