Measurement of porosity of solid-state battery materials

Porosity generally refers to the proportion of the total pore volume of a porous material to its surrounding/apparent volume (total pore volume+closed pore volume+skeleton volume). If the sample is a collection of particles such as powder or large particle aggregates, porosity also includes the pore volume between particles. In the lithium battery industry, electrode porosity is an important measurement indicator.

1. Determination of true volume of materials:

For large volume particles (diameter>500um) or bulk materials, the BUD-TD20 true density analyzer is used to determine the skeleton density of the material. The ideal gas equation (PV=nRT) and the principle of Boma's law (P1V1=P2V2) are used, and helium gas is used as the test medium to calibrate the true volume of the material (skeleton volume+closed cell volume) in a fixed volume chamber and at a constant temperature.

2. Determination of apparent volume of materials:

(1) If it is a regular block, such as a cylinder, cube, etc., it can be calculated using mathematical formulas.

(2) If it is an irregular block: obtain the material density through drainage method and calculate the apparent volume.

(3) If it is a powder: the density is known, calculate the apparent volume; The density is unknown, and the total pore volume (0.35-200nm pore range) can be obtained through SSA4000 specific surface area and pore size analyzer. The true volume can be obtained through TD2200, and the sum of the two is the apparent volume.

(4) Irregular block with matrix: Obtain porosity directly through BUD-TD20 porosity specific testing mode.

3. Determination of porosity of polarizer

As described in section 2, the polarizer can be made into equal circular pieces, and the apparent volume of each piece can be calculated using mathematical formulas, and the total apparent volume can be obtained by adding them up. Then, the same amount of polarizer can be placed into the BUD-TD20 porosity analyzer for testing to obtain the porosity.