Dry-processed electrodes represent a significant advancement in battery manufacturing, eliminating the need for solvents and the associated energy-intensive drying steps. The control of porosity in these electrodes is a critical factor determining their electrochemical performance, particularly in terms of electrolyte infiltration and ion transport. Unlike wet-processed electrodes, where porosity is largely dictated by solvent evaporation and binder migration, dry-processed electrodes rely on alternative mechanisms to create and manage pore structures.

Porosity in dry-processed electrodes is primarily generated through mechanical and thermal processes. The absence of solvents means that pore formation must be engineered through particle packing dynamics, binder distribution, and compaction forces. Dry mixing of active materials, conductive additives, and binders creates a heterogeneous powder blend where voids naturally exist between particles. The size and distribution of these voids depend on the particle morphology, size distribution, and mixing homogeneity. Fibrous binders, such as polytetrafluoroethylene (PTFE), are often used to create a fibrillated network that binds particles while maintaining interstitial spaces. The fibrillation process, achieved through shear forces during mixing, directly influences the resulting porosity.

Compaction is another key step in porosity control. Calendering or pressing the dry electrode adjusts the pore structure by reducing large voids while preserving smaller, interconnected pores. The applied pressure must be carefully optimized—excessive compaction reduces porosity to levels that hinder electrolyte infiltration, while insufficient compaction leads to poor mechanical integrity and high electrical resistance. Studies have shown that dry-processed electrodes typically achieve porosities ranging from 30% to 50%, depending on the materials and processing conditions. The pore size distribution tends to be broader compared to wet-processed electrodes, with a higher fraction of larger pores due to the absence of solvent-induced shrinkage.

The relationship between processing parameters and pore structure is complex. Mixing time and intensity affect binder fibrillation, with longer mixing generally creating a more extensive fibril network that supports higher porosity. However, overmixing can degrade binder effectiveness or fracture active material particles, leading to undesirable pore collapse. Compaction pressure and speed also play a role; slower compression allows for better particle rearrangement, resulting in a more uniform pore distribution. Temperature during processing can influence binder behavior, with some dry processes employing moderate heat to soften binders and improve adhesion without fully melting them.

Electrolyte infiltration in dry-processed electrodes is strongly influenced by pore connectivity and wettability. The absence of solvent residues, which can block pores in wet-processed electrodes, often improves wetting characteristics. However, the broader pore size distribution can lead to uneven electrolyte distribution if larger pores dominate. Capillary action drives electrolyte into smaller pores, but if these are insufficiently connected, ion transport pathways may be disrupted. Surface treatments or additives are sometimes incorporated to enhance wettability without compromising mechanical stability.

Ion transport in dry-processed electrodes is affected by the tortuosity of the pore network. Tortuosity, a measure of path length relative to electrode thickness, tends to be lower in dry-processed electrodes due to the presence of larger, more direct pathways. This can reduce ionic resistance compared to wet-processed electrodes, where smaller, more tortuous pores are common. However, if porosity is too high or poorly distributed, electronic conductivity may suffer due to reduced particle-to-particle contact. Balancing ionic and electronic transport is essential for optimal performance.

Comparisons between dry- and wet-processed electrode porosity reveal distinct advantages and trade-offs. Wet-processed electrodes typically exhibit more uniform pore sizes due to the controlled evaporation of solvents, resulting in a denser, more homogeneous structure. This uniformity can enhance rate capability by providing consistent ion transport pathways. However, wet processing often introduces binder migration, where binders concentrate near the surface during drying, creating regions of low porosity that impede electrolyte access. Dry processing avoids this issue, as binders are uniformly distributed from the outset. Additionally, dry-processed electrodes eliminate the cracking and delamination risks associated with solvent evaporation, improving mechanical robustness.

The impact of porosity on electrochemical performance has been quantified in various studies. Dry-processed electrodes with optimized porosity demonstrate comparable or superior capacity retention under high-rate cycling compared to wet-processed counterparts. The improved electrolyte accessibility and lower tortuosity contribute to this performance, particularly in thick electrodes where ion transport limitations are more pronounced. However, achieving consistent porosity control at scale remains a challenge for dry processing, as variations in raw materials or processing conditions can lead to batch-to-batch variability.

Future developments in dry electrode processing are likely to focus on advanced binder systems and precision compaction techniques. Binders with tunable fibrillation behavior could enable finer control over pore structure, while in-line monitoring systems may improve consistency during manufacturing. The environmental and energy benefits of dry processing, coupled with its potential for high-performance electrodes, make it a promising avenue for next-generation battery production. Understanding and controlling porosity will remain central to unlocking its full potential.