Authors: Kristoffer Visti Graae, Ph.D., R&D Scientist – Batteries (FOM Technologies)

In the world of battery production, calendering is a critical process, compressing electrode materials through precision rollers to achieve a desired thickness and density. This step is crucial for uniformity, ensuring optimal electrochemical performance by enhancing ion transport kinetics and maximising active material utilisation and energy density.

Why Calendering Matters

To achieve the highest possible volumetric capacity, the porosity of battery electrodes is reduced by compression, in what is known as the calendering step. This has the additional advantage of increasing the electric contact between the active material particles. There is a trade-off between a reduction in porosity, and maintaining a high ionic conductivity, since the latter is related to the penetration of electrolyte into the electrodes. Therefore, tuning the calendering parameters is  the process of balancing ionic conductivity and energy density. Calendering parameters such as pressure, temperature, speed, and roller geometry influence this. By finely tuning these parameters, manufacturers can achieve uniformity in thickness, density, and porosity across electrodes. This uniformity is essential for facilitating electrolyte penetration while maintaining structural integrity, ultimately leading to enhanced mechanical stability and prolonged cycling stability.

Tuneable Parameters

Pressure, the primary driver of calendering, dictates the degree of compaction. Temperature aids in plastic deformation during compression, ensuring malleability without compromising structural integrity. Speed influences processing time and energy consumption, while roller geometry, including surface roughness and curvature, influences contact area and pressure distribution.

The Composition of a High-Quality Electrode

A quality electrode is characterised by a balanced structural composition. Optimal porosity maintains a delicate equilibrium between electrolyte infiltration and structural integrity, while efficient interfacial contact between electrode particles and conductive additives enhances ion transport efficiency. Furthermore, mechanical stability, achieved through proper compaction, mitigates electrode degradation, ensuring reliability over extended cycles.

Microstructural Insights

Calendering leaves a significant imprint on the microstructure of battery electrodes. It induces particle rearrangement and compaction, reducing inter-particle voids and increasing material density. This densification can optimise electrochemical pathways. As a result, this can improve both capacity and rate capabilities. The controlled compression changes pore size distribution, influencing electrolyte infiltration and diffusion kinetics.

In essence, calendering plays a crucial role in battery manufacturing, shaping electrode functionality through precise control of microstructural parameters. By understanding and optimising this process, we advance towards the development of more efficient and sustainable energy storage technologies.

Schreiner, David & Oguntke, Maximilian & Günther, Till & Reinhart, Gunther. (2019). Modelling of the Calendering Process of NMC‐622 Cathodes in Battery Production Analyzing Machine/Material‐Process‐Structure Correlations. Energy Technology. 7. 10.1002/ente.201900840.