Research and development professionals in the battery industry are always in search of the most efficient and safest battery technologies to fuel the energy needs of our world today and into the future. In order to optimize their design efforts, battery developers rely on accurate physical property characterization for battery components such as the anode, cathode, or separator. Important properties that guide design include surface area, pore size and pore volume, porosity (% open space), and density.
The surface area is a critical property for the anode, cathode, and even separator materials. Surface area differences affect performance variables such as capacity, impedance, discharge rate capability, and charging rates. Deviations from the expected surface area can also indicate impurities or undesirable particle size for component manufacturers. BET surface area measurements are routinely used to evaluate the accessible surface area of battery components all the way down to very low surface area materials, even less than 0.01 m2/g, and is measured using manometric or flow physisorption techniques.
Pore Size and Volume
The determination of pore volume and pore size is also of interest for battery materials. For example, changes in the pore size distribution of an electrode material could indicate phase transformations or structural changes in the material over the course of its practical use. These measurements can also be used to determine the correlation between a material’s compression and annealing temperature and its resulting pore size distribution. Pore volume is also an important property. For example, in a battery separator, this volume must be able to host a sufficient amount of liquid electrolyte for efficient ionic conductivity. Mercury intrusion porosimetry and gas sorption are routinely used to assess these properties.
The choice of technique is dictated by the pore size range within the material, with gas sorption being used for micropores (< 2 nm) and mesopores (2-50 nm) and mercury intrusion being used for large mesopores (> 5 nm) and macropores (> 50 nm).
Through-Pore Size and Permeability
For battery separators, the through-pore (pore that starts at one end and empties out the other) size distribution may be more important for a given application than a total pore size distribution. Characterization of the through pores can be done using capillary flow porometry. Permeability analyses can also be performed in order to get a sense of the structural nature of the pores. As an example, a tortuous pathway helps to isolate the positive electrode particles from the negative electrode material, but increases the effective resistance caused by the separator, thereby reducing battery efficiency and lifetime.
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This information has been sourced, reviewed and adapted from materials provided by Anton Paar GmbH.
For more information on this source, please visit Anton Paar GmbH.