Calender Roll Temperature versus Chemistry

So what is the optimum calender roll temperature versus chemistry? We looked at a number of papers to offer an initial roll temperature and reasoning behind it. This is not extensive and as we have seen there are a number of other aspects that need to be considered such as energy use, LCA and capital investment.

NMC

The role of temperature in NMC calendering is primarily to allow the thermoplastic binder (like PVDF) to more easily plastically deform, fill voids, and better disperse within the electrode, potentially combining with other binder particles to form a superior structural conductive network. Increasing calendering temperatures generally leads to decreasing porosities and lower line load efforts.

• NMC111: the conductivity mainly depends on the calendering temperature, likely because the deformability of PVDF increases with temperature [1].
• NMC622: a study covering roll temperatures of 85 °C, 120 °C, and 145 °C [2]
  • temperature was found to be not as significant as mass loading and porosity.
  • maximizing gravimetric capacity at low C-rates, 85°C was recommended. For higher C-rates, higher temperatures were found to give better results.

LFP

In the paper [3] LFP cathodes rolled at temperatures ranging from 25 °C to 120 °C. They found the optimum roll temperature for LFP was 100°C based on these studies.

• at 100 °C, the process achieved the optimal reduction in film resistance (approximately 2.1%).
• optimal reductions in both ohmic and charge-transfer impedance were observed at around 100 °C.
• high C-rate performance and good cycling stability were achieved with a roll temperature of 100 °C in LFP cathodes utilizing Carbon Nanotubes (CNTs).
• maximum peeling force was observed near 60 °C

Sodium Ion

For hard carbon anodes, the most relevant parameters in calendering are the gap between the rollers, the calendering temperature, and the interaction between these two [4].

• increasing the temperature from 60 °C to 100 °C systematically decreases the irreversible capacity of the first cycle.
• while lower electrode thicknesses and porosities are typically obtained at high temperatures (100 °C), the combination of a low gap (40 µm) and high temperatures (100 °C) is considered too aggressive for hard carbon anodes.
  • this aggressive condition led to damage, such as cracks and imperfections in the electrode microstructure, resulting in poor electrochemical performance.
• intermediate calendering conditions (temperatures typically in the range of 60–80 °C and larger roller gaps) are suggested as optimal for hard carbon anodes to avoid microstructure damage.

Sulfur Cathodes (Li-S)

For thermally sensitive materials like sulfur cathodes, low-temperature calendering systems are necessary to prevent thermal degradation.

• use chilled rollers to compress electrode materials at controlled temperatures, often maintained below 50 °C.
• operating at low temperatures minimizes risks such as:
  • binder migration
  • particle agglomeration
  • unwanted chemical reactions
  • acceleration of lithium polysulfide dissolution

Overall

• Lower temperatures (such as 85 °C, compared to 120 °C or 145 °C) are advantageous for lowering overall manufacturing costs.

This post has been built based on the support of and sponsorship from: Resonate Testing Ltd, Quarto Technical Services, Eatron Technologies and About:Energy

References

1. M. Abdollahifar, H. Cavers, S. Scheffler, A. Diener, M. Lippke, A. Kwade, Insights into Influencing Electrode Calendering on the Battery Performance. Adv. Energy Mater. 2023, 13, 2300973
2. M.F.V. Hidalgo, G. Apachitei, D. Dogaru, M. Faraji-Niri, M. Lain, M. Copley, J. Marco, Design of experiments for optimizing the calendering process in Li-ion battery manufacturing, Journal of Power Sources, Volume 573, 2023, 233091
3. Zhaocai LYU, Yuxi WANG, Zhitao WANG, Xiaohui SUN, Jingkang LI. Influence of heated calendering process on cathode film performance of lithium-ion batteries. Energy Storage Science and Technology, 2024, 13(5): 1443-1450
4. Jaione Martínez de Ilarduya Martínez de San Vicente, Na-ion battery development: from electrode processing studies to heat generation model of a monolayer pouch cell, Thesis, UNIVERSIDAD DEL PAÍS VASCO EUSKAL HERRIKO UNIBERTSITATEA, October 2019

See also: Calendering