Cryoporometry for short T ₂ samples: A T ₁ filter method applied to battery electrode characterization

Area of Science:

• Materials Science
• Analytical Chemistry
• Physical Chemistry

Background:

• Pore size distribution is crucial for transport in porous media.
• Traditional cryoporometry using T2 relaxation is unsuitable for paramagnetic materials like LFP and NMC due to short relaxation times.
• Gas adsorption and mercury injection have limitations for macropore characterization in certain materials.

Purpose of the Study:

• To develop and validate a cryoporometry method for determining pore size distribution in paramagnetic porous materials.
• To overcome the limitations of T2 relaxation-based cryoporometry for materials like lithium-iron phosphate (LFP) and nickel-manganese-cobalt oxides (NMC).
• To utilize T1 contrast for phase separation in NMR cryoporometry experiments.

Main Methods:

• Implementation of a Peltier-based system for precise temperature control (±0.05 °C) within an NMR probe.
• Application of slow temperature ramps (down to 0.002 °C/min) for accurate pore size analysis.
• Utilizing T1 relaxation contrast to differentiate between liquid and frozen octamethylcyclotetrasiloxane (OMCTS) phases in paramagnetic samples.

Main Results:

• Demonstrated successful application of T1 contrast for phase separation in cryoporometry of paramagnetic materials.
• Characterized pore size distribution in LFP and NMC cathode materials, relevant to battery technology.
• Investigated temperature-dependent T1 variations of bulk frozen OMCTS.

Conclusions:

• The proposed T1-based NMR cryoporometry is a viable alternative for pore size analysis in paramagnetic porous materials.
• This method provides essential pore size data for materials where conventional techniques fail.
• The findings are directly applicable to the characterization of industrial battery cathode materials.