Meaning
This analytical technique measures the pore size distribution and total porosity of solid materials by forcing mercury into them. By applying controlled high pressure to submerge the sample in mercury, the instrument calculates the volume of intruded liquid. Mercury intrusion porosimetry determines the pore sizes from the applied pressure using the Washburn equation for non-wetting liquids.
The method is used to characterize the porous electrodes and separators of battery cells to optimize their rate performance. It is limited to open pores that are accessible from the exterior of the sample, ignoring closed internal voids.
Analytical Operation
The test involves placing the electrode or separator sample into a glass penetrometer, which is then evacuated to remove air. Mercury is introduced into the chamber, and pressure is gradually increased from vacuum up to several thousand atmospheres. Because mercury is a non-wetting liquid with a high contact angle, it resists entering the pores until forced by pressure.
The instrument measures the volume of mercury that enters the pores at each pressure increment to build a distribution curve. This high-pressure process is highly effective for characterizing pores ranging from several nanometers to hundreds of micrometers in diameter.
Procurement Application
Sourcing groups rely on this porosimetry data to qualify electrode materials and ensure manufacturing consistency between production batches. The pore structure of the anode and cathode directly affects the electrolyte absorption rate and the power capability of the cell. Purchasing agreements specify the required porosity range to ensure that the cells can handle high-rate charging without lithium plating.
Sourcing engineers use this test to verify that the supplier’s electrode calendering process has achieved the correct active material density. This quality gate prevents the purchase of cells with poor ion transport properties and inadequate electrolyte wetting.
Methodological Limits
The high pressures required to force mercury into the smallest pores can mechanically deform or compress fragile polymer separators. This deformation can lead to inaccurate pore size measurements by artificially altering the pore structure during the test. The method is also destructive, generating hazardous waste containing mercury that requires specialized disposal procedures and safety protocols.
It cannot measure closed pores, which can lead to an underestimation of the total porosity of some sintered electrode materials. These limitations require that the results be validated using complementary techniques like gas adsorption or capillary flow porometry.
