Characterizing microporous carbon anodes on a standard physisorption instrument

Microporous carbon characterization is fast becoming essential to a future-proof battery industry, but standard N₂ gas adsorption analysis often falls short. For accurate insights, you need a dual-probe approach.

Read on to learn how instruments with dual gas adsorption, like TriStar II Plus from Micromeritics, provide a complete view of mesopores and micropores in these microporous materials.

Why do battery manufacturers need microporous carbons?

Silicon-carbon (Si-C) anodes and sodium-ion batteries are evolving fast. They provide an answer to graphite electrodes reaching their technical limits, scarce supplies of lithium and cobalt, unstable supply chains, and pressure to deliver higher energy density at lower costs. And both technologies rely on microporous carbon materials.

Why? Microporosity provides a strong buffer for silicon deposition in Si-C anodes and efficient ion intercalation in sodium-ion batteries. Biomass-derived microporous carbon also help lower costs and reduction in environmental footprint.

All this means microporous carbons are fast becoming essential to a future-proof battery industry – and so are reliable micropore characterization technologies.

Characterizing a broad pore range using dual gas isotherms

When characterizing the finest micropores, standard N₂ gas adsorption instruments often fall short. The absence of low-pressure transducers makes ultra-low-pressure regions inaccessible, leaving the narrowest micropores undetected. This could result in underperforming cells, batch-to-batch inconsistencies, and waste of critical resources. To prevent this, Micromeritics TriStar II Plus 3030 offers easy switching between multiple gas adsorption options:

• Nitrogen (N₂) adsorption, for a broad view of mesopores and larger micropores
• Carbon dioxide (CO₂) adsorption at 273 K, for more efficient probing of smaller pore sizes. Because CO₂ is smaller and more linear than N₂, it can diffuse into narrow pores. At 273 K, this happens more rapidly

Complementing this, the non-local density functional theory (NLDFT) model lets you precisely determine micropore size distributions across this broad pore range. You can also calculate cumulative specific surface area more accurately than with a simple BET estimation.

How we analyzed biomass-derived microporous hard carbon anodes on the TriStar II Plus 3030

We put these features to the test by analyzing a biomass-derived hard carbon anode material on the TriStar II Plus 3030.

The N₂ adsorption isotherm indicated the presence of micropores and 20-30 Å mesopores. But, as expected, the NLDFT pore size distribution analysis of this isotherm did not reveal pores below 9 Å.

The dual-gas NLDFT Advanced pore size distribution (PSD) method, using both N₂ and CO₂ isotherms, provided a complete picture. It revealed pores as low as 3.578 Å , giving the full pore size distribution for both the micro- and mesopore ranges.

With surface area reaching as high as 1525 m²/g, the case study revealed that this biomass-derived carbon is an ideal precursor for high-silicon-content anodes, opening opportunities to recycle waste while enhancing specific capacity.

Our advice: Use an instrument like TriStar II Plus 3030 with multiple gas options and easy switching between gases to stay ahead of Si-C anode and sodium-ion battery developments. The method presented here provides a reliable way to measure pore volume, surface area, and pore size distribution in your microporous anode materials.

Download our application note for full details of how we analyzed biomass-derived microporous hard carbon anodes on the TriStar II Plus 3030.