How Calendering Shapes Composite Cathode Performance in Polymer-Based Solid-State Batteries: Insights From a Manufacturing Study

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Polymer-based solid-state batteries (SSBs) have emerged as one of the most promising technologies for next-generation energy storage because they offer the potential for higher energy density and improved safety compared with conventional lithium-ion batteries. Among their key components, the composite cathode plays a critical role in determining electrochemical performance and manufacturing quality. One of the most influential production stages is the calendering process, which compresses the electrode to reduce porosity and improve ionic transport. However, the effectiveness of calendering depends strongly on the material composition of the composite cathode. The reviewed study systematically investigates how different ratios of active material and solid electrolyte influence porosity, surface roughness, and compaction behavior during calendering. By providing a detailed experimental evaluation of these relationships, the research contributes valuable knowledge for optimizing polymer-based solid-state battery manufacturing while improving electrode quality and production consistency.

Bibliographic Information

Item Information
Article Title Influence of Calendering on the Variation in Material Compositions of the Composite Cathode of Polymer-Based Solid-State Batteries
Authors Jonas Dhom; Eric Cordes; Christoph Berger; Florian Steinlehner; Rüdiger Daub
Journal Engineering Reports
Volume 8
Issue 2
Publication Year 2026
Article Number e70591
DOI https://doi.org/10.1002/eng2.70591
Publisher John Wiley & Sons Ltd.
License Creative Commons Attribution (CC BY)
ISSN 2577-8196 (Online)
Keywords calendering process; composite cathode; porosity; solid-state battery; surface-related roughness

1. Research Background

The rapid expansion of electric vehicles and large-scale energy storage systems has intensified the demand for batteries that combine high energy density with improved operational safety. Solid-state batteries have become one of the leading candidates for meeting these requirements because they replace flammable liquid electrolytes with solid materials while offering the potential for higher energy densities than conventional lithium-ion batteries.

Among various solid-state battery technologies, polymer-based solid-state batteries attract considerable industrial interest because of their relatively good processability and compatibility with existing manufacturing technologies. Nevertheless, producing high-quality composite cathodes remains a significant challenge. The composite cathode accounts for a substantial proportion of manufacturing costs and directly influences electrochemical performance through its internal microstructure.

The manufacturing route for polymer-based composite cathodes typically includes material mixing, slurry coating, drying, and calendering. Of these steps, calendering is particularly important because it compresses the electrode, decreases porosity, improves particle contact, and enhances ionic conductivity. However, excessive or insufficient compression may adversely affect electrode integrity and battery performance, making process optimization essential.

Although extensive knowledge has been established for calendering conventional lithium-ion battery cathodes, these findings cannot be directly transferred to polymer-based solid-state batteries. Unlike lithium-ion electrodes, which require sufficient porosity for liquid electrolyte infiltration, polymer-based solid-state composite cathodes benefit from substantially lower porosity to facilitate efficient ion transport through the solid electrolyte network. Consequently, the relationships between material composition, porosity development, and calendering behavior require dedicated investigation.

The reviewed study addresses this knowledge gap by systematically examining how different proportions of lithium iron phosphate (LFP) active material and solid electrolyte influence the physical characteristics of composite cathodes before and after calendering. The investigation evaluates porosity, compaction behavior, thickness reduction, viscosity, and surface-related roughness, providing a comprehensive understanding of how material formulation affects manufacturing outcomes. Rather than focusing solely on electrochemical performance, the research emphasizes manufacturing-process optimization to improve the quality and consistency of polymer-based solid-state battery electrodes.

2. Research Objective

  • To investigate how different proportions of active material and solid electrolyte influence the calendering behavior of polymer-based composite cathodes.
  • To evaluate the effects of material composition on cathode porosity before and after the calendering process.
  • To examine the relationship between material formulation, coating characteristics, and surface-related roughness.
  • To determine how calendering parameters influence electrode compaction and thickness reduction for different composite cathode formulations.
  • To improve understanding of the causal relationships between material composition and manufacturing performance in polymer-based solid-state battery production.
  • To provide practical guidance for optimizing composite cathode manufacturing processes capable of achieving low porosity and improved electrode quality.

3. Why This Research Matters

  • Supports next-generation battery manufacturing. The study advances manufacturing knowledge for polymer-based solid-state batteries, a technology expected to play an important role in future electric mobility and energy storage systems.
  • Improves understanding of calendering. The research explains how material composition influences the effectiveness of the calendering process, one of the most critical stages in composite cathode production.
  • Optimizes electrode porosity. By identifying how active material and solid electrolyte ratios affect porosity, the study provides valuable guidance for producing cathodes with improved ionic conductivity.
  • Enhances manufacturing consistency. Understanding the interaction between formulation, viscosity, compaction, and surface roughness helps manufacturers produce more uniform composite cathodes with fewer process variations.
  • Provides practical process knowledge. The findings assist battery manufacturers in selecting appropriate material formulations and calendering conditions to improve production quality without relying solely on trial-and-error experimentation.
  • Strengthens battery engineering research. The work contributes new experimental evidence linking slurry composition, drying behavior, porosity evolution, and mechanical compaction within polymer-based solid-state battery manufacturing.
  • Supports industrial scalability. By clarifying manufacturing-process relationships, the study contributes to the broader goal of scaling polymer-based solid-state battery production for commercial applications.

4. Research Methodology

The study employed an experimental manufacturing approach to investigate how variations in composite cathode material composition influence the calendering behavior of polymer-based solid-state batteries. The researchers systematically varied the proportions of active material and solid electrolyte while maintaining a constant conductive carbon content. The investigation combined slurry characterization, electrode fabrication, calendering experiments, and post-process material characterization to establish causal relationships between material formulation and manufacturing performance.

Experimental Design

  • A laboratory-based experimental investigation of polymer-based composite cathodes.
  • Comparative evaluation of three composite cathode formulations containing different lithium iron phosphate (LFP) and solid electrolyte contents.
  • Assessment of electrode characteristics before and after the calendering process.

Composite Cathode Formulations

Three composite cathode formulations were prepared by varying the proportions of lithium iron phosphate (LFP) and solid electrolyte while maintaining conductive carbon at a constant concentration. The investigated formulations consisted of:

  • 65 wt% LFP : 25 wt% Solid Electrolyte : 10 wt% Conductive Carbon
  • 70 wt% LFP : 20 wt% Solid Electrolyte : 10 wt% Conductive Carbon
  • 75 wt% LFP : 15 wt% Solid Electrolyte : 10 wt% Conductive Carbon

These formulations enabled systematic evaluation of how increasing active material content affected slurry properties, electrode structure, and calendering performance.

Material Preparation

The composite cathodes were manufactured through a sequence of mixing, coating, drying, and calendering processes. Lithium iron phosphate served as the active material, while polyethylene oxide (PEO) and lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) formed the solid electrolyte system. Conductive carbon was incorporated to improve electrical conductivity. Material preparation was conducted under controlled argon atmosphere to minimize contamination from oxygen and moisture.

Viscosity Evaluation

The rheological behavior of each slurry formulation was measured using a rheometer across a wide range of shear rates. A conventional lithium-ion battery cathode slurry was also characterized as a reference. This comparison allowed the researchers to evaluate how changes in material composition influenced slurry processability during coating.

Coating and Drying

The prepared slurries were coated onto aluminum current collectors using controlled doctor blade gaps to obtain different electrode thicknesses. Following coating, the electrodes were dried under controlled atmospheric conditions before vacuum drying to remove residual solvent. Measurements of coating thickness, mass loading, area capacity, and porosity were subsequently performed.

Calendering Process

Calendering experiments were carried out using laboratory-scale rolling equipment. To prevent adhesion of the polymer-based composite cathodes to the rollers, copper foil was incorporated into the calendering setup. The researchers evaluated different roller gaps while maintaining constant roller temperature and web speed, enabling systematic investigation of compaction behavior across different material compositions.

Material Characterization

Multiple characterization techniques were employed throughout the investigation. Electrode porosity was calculated from thickness, density, and mass measurements. Surface-related roughness was measured using laser scanning microscopy before and after calendering, while scanning electron microscopy (SEM) was used to observe microstructural changes and particle adhesion at the electrode-current collector interface.

Performance Assessment

The manufacturing performance of each formulation was evaluated using several indicators, including slurry viscosity, mass loading, area capacity, porosity after drying, porosity after calendering, compaction rate, electrode thickness reduction, and surface-related roughness. These complementary measurements provided a comprehensive assessment of how material composition affected manufacturing quality.

5. Key Findings

Material Composition Strongly Influenced Electrode Porosity

The proportion of active material significantly affected electrode porosity. Composite cathodes containing higher lithium iron phosphate content consistently exhibited greater porosity after drying, whereas formulations with higher solid electrolyte content produced denser electrode structures with lower initial porosity.

Calendering Successfully Reduced Electrode Porosity

Regardless of the initial formulation, the calendering process effectively reduced composite cathode porosity. Although electrodes containing higher active material required more aggressive compaction, the process successfully compressed all investigated formulations toward substantially lower porosity levels.

Higher Active Material Content Increased Compaction Requirements

Electrodes with greater lithium iron phosphate content required smaller roller gaps during calendering to achieve porosity levels comparable with formulations containing larger proportions of solid electrolyte. This demonstrates that material composition directly influences process parameter selection during manufacturing.

Surface Roughness Improved After Calendering

Calendering consistently reduced the surface-related roughness of the composite cathodes. Formulations containing higher solid electrolyte content exhibited smoother surfaces both before and after compression, indicating that material composition contributes to improved electrode surface quality.

Higher Solid Electrolyte Content Produced Better Surface Quality

The investigation showed that increasing the proportion of solid electrolyte resulted in lower surface roughness. More homogeneous particle packing likely contributed to smoother electrode surfaces, which may improve contact between the composite cathode and adjacent battery components.

Microstructural Contact Was Enhanced

Scanning electron microscopy demonstrated that calendering improved the adhesion between the composite cathode coating and the aluminum current collector. The compressed electrodes displayed better interfacial contact, indicating improved structural integrity after processing.

Slurry Composition Affected Manufacturing Behavior

Variations in active material and solid electrolyte ratios altered slurry viscosity and influenced subsequent coating and drying behavior. These differences ultimately affected electrode thickness, mass loading, porosity, and calendering response, highlighting the importance of formulation design during manufacturing.

Manufacturing Parameters Were Closely Interconnected

The study demonstrated that viscosity, coating thickness, mass loading, porosity, compaction, and surface roughness are strongly interrelated. Changes introduced during material formulation propagated through subsequent manufacturing stages, emphasizing the need to optimize the complete production workflow rather than individual processes in isolation.

6. Scientific Contribution

  • Provides a comprehensive understanding of calendering behavior. The study systematically explains how composite cathode material composition influences porosity, compaction, and surface characteristics during the manufacturing of polymer-based solid-state batteries.
  • Clarifies composition–process relationships. By varying active material and solid electrolyte proportions, the research establishes clear relationships between material formulation and manufacturing performance throughout coating, drying, and calendering.
  • Advances knowledge of polymer-based solid-state battery manufacturing. The findings address a relatively underexplored aspect of electrode production by focusing specifically on manufacturing optimization rather than electrochemical performance alone.
  • Integrates multiple material characterization techniques. The combination of rheological measurements, porosity analysis, surface roughness evaluation, thickness measurements, and scanning electron microscopy provides a comprehensive assessment of manufacturing quality.
  • Identifies practical mechanisms governing electrode quality. The study demonstrates how variations in slurry composition propagate through multiple manufacturing stages to influence the final physical characteristics of composite cathodes.
  • Supports future manufacturing optimization. The experimental evidence offers a scientific foundation for selecting appropriate material formulations and calendering conditions when developing polymer-based solid-state battery production processes.

7. Industrial Implications

  • Improves solid-state battery manufacturing. The findings provide practical guidance for optimizing composite cathode production in industrial-scale polymer-based solid-state battery manufacturing.
  • Enhances manufacturing consistency. Understanding how formulation influences porosity and compaction enables manufacturers to produce electrodes with more uniform structural properties.
  • Supports quality control. The relationships identified between material composition, porosity, and surface roughness can assist manufacturers in establishing more reliable production standards.
  • Optimizes calendering parameters. The study demonstrates that roller gap selection should be adjusted according to electrode composition rather than applying identical processing conditions to all formulations.
  • Reduces manufacturing defects. Better understanding of compaction behavior can minimize undesirable electrode defects while improving adhesion between the cathode coating and current collector.
  • Supports commercial scale-up. The research contributes valuable process knowledge that may facilitate the transition of polymer-based solid-state batteries from laboratory development toward industrial production.
  • Contributes to next-generation battery technology. Improved manufacturing quality of composite cathodes supports broader efforts to commercialize safer, higher-energy-density batteries for electric vehicles and advanced energy storage systems.

8. Research Limitations

  • The investigation evaluated only three composite cathode formulations by varying the proportions of lithium iron phosphate (LFP) and solid electrolyte while maintaining a constant conductive carbon content. Other material combinations commonly used in polymer-based solid-state batteries were beyond the scope of the study.
  • The research focused exclusively on manufacturing-related properties, including viscosity, porosity, thickness, compaction behavior, and surface-related roughness. Electrochemical performance indicators such as cycle life, rate capability, and long-term battery stability were not experimentally evaluated.
  • Calendering experiments were performed under controlled laboratory conditions using fixed roller temperature and web speed. The influence of wider industrial processing conditions, including different temperatures, rolling speeds, and continuous production environments, was not investigated.
  • Only one active material chemistry based on lithium iron phosphate (LFP) and one polymer electrolyte system consisting of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) were examined. The findings may therefore require further validation before being generalized to other solid-state battery chemistries.
  • Although scanning electron microscopy demonstrated improvements in microstructural contact after calendering, the study did not directly quantify the resulting electrochemical improvements through complete battery cell testing.
  • The research primarily examined immediate manufacturing outcomes after calendering. Long-term mechanical stability, aging behavior, and durability of the compressed composite cathodes were not addressed.

9. Future Research Opportunities

  • Investigate additional active material and solid electrolyte chemistries to determine whether the observed calendering behavior is applicable across different polymer-based solid-state battery systems.
  • Evaluate the electrochemical performance of calendered composite cathodes through complete battery cell assembly, including capacity retention, cycling stability, and rate capability.
  • Study the influence of broader calendering parameters, including roller temperature, web speed, rolling pressure, and multiple calendering passes on electrode quality.
  • Develop predictive manufacturing models that integrate slurry rheology, coating behavior, drying characteristics, and calendering outcomes to optimize production efficiency.
  • Investigate the relationship between microstructural evolution during calendering and lithium-ion transport within polymer-based composite cathodes.
  • Assess the long-term mechanical integrity and durability of calendered electrodes under repeated charge-discharge cycles and realistic operating conditions.
  • Explore advanced in-line monitoring techniques for measuring porosity, thickness, and surface quality during industrial electrode manufacturing.
  • Apply similar experimental approaches to other promising solid-state battery architectures and alternative electrode manufacturing technologies.
  • Combine experimental manufacturing studies with numerical simulations and machine learning techniques to develop intelligent process optimization strategies for next-generation battery production.

10. Potential for Public Policy Citation

Although this study focuses primarily on manufacturing science, its findings have meaningful implications for policies supporting advanced battery technologies, sustainable transportation, and industrial innovation. Improving the manufacturing quality of polymer-based solid-state batteries contributes to broader efforts aimed at increasing energy efficiency, enhancing battery safety, and accelerating the transition toward low-carbon mobility.

The research also supports policy initiatives that encourage the development of domestic battery manufacturing capabilities by providing experimentally validated knowledge for optimizing electrode production processes. Such manufacturing improvements are particularly relevant for industrial modernization strategies, advanced materials research programs, and investments in clean energy technologies.

Furthermore, the study offers valuable technical evidence for organizations developing manufacturing standards, quality assurance guidelines, and industrial best practices for emerging solid-state battery technologies. As commercialization of solid-state batteries continues to expand, process optimization studies such as this one may help inform future manufacturing frameworks and technology roadmaps.

11. Who Should Read This Paper?

  • Researchers working on solid-state battery materials and manufacturing technologies.
  • Battery engineers involved in composite cathode fabrication and process optimization.
  • Materials scientists investigating polymer electrolytes, electrode microstructures, and battery interfaces.
  • Manufacturing engineers responsible for scaling laboratory battery production to industrial processes.
  • Graduate students studying battery technology, energy storage systems, materials engineering, or advanced manufacturing.
  • Industrial researchers developing next-generation lithium-based energy storage technologies.
  • Process engineers seeking to improve electrode quality through optimized coating, drying, and calendering operations.
  • Government agencies, research organizations, and innovation centers supporting battery manufacturing and sustainable energy technologies.

12. Final Thoughts

This study provides a thorough experimental investigation into one of the most critical manufacturing stages of polymer-based solid-state batteries: the calendering of composite cathodes. Rather than focusing exclusively on electrochemical performance, the research demonstrates how material formulation directly influences manufacturing behavior, electrode microstructure, and final product quality.

A major strength of the work is its systematic evaluation of multiple manufacturing characteristics, including slurry viscosity, coating behavior, porosity evolution, surface-related roughness, compaction, and microstructural changes. By integrating these complementary measurements, the authors establish a clear understanding of how variations in active material and solid electrolyte composition affect the overall production process.

The findings emphasize that successful manufacturing of polymer-based solid-state batteries requires careful coordination between material formulation and processing parameters rather than optimization of individual production steps in isolation. The demonstrated relationships between composition, porosity, and calendering provide practical guidance for improving manufacturing consistency while supporting future industrial scale-up.

Overall, this research represents a valuable contribution to advanced battery manufacturing by expanding current understanding of composite cathode processing and providing experimentally supported knowledge that can assist both researchers and industry in developing more reliable and efficient polymer-based solid-state battery production technologies.

13. Suggested Citations

UNP–Teknomekanik Style

Dhom, J., Cordes, E., Berger, C., Steinlehner, F., & Daub, R. (2026). Influence of Calendering on the Variation in Material Compositions of the Composite Cathode of Polymer-Based Solid-State Batteries. Engineering Reports, 8(2), e70591. https://doi.org/10.1002/eng2.70591

APA (7th Edition)

Dhom, J., Cordes, E., Berger, C., Steinlehner, F., & Daub, R. (2026). Influence of calendering on the variation in material compositions of the composite cathode of polymer-based solid-state batteries. Engineering Reports, 8(2), e70591. https://doi.org/10.1002/eng2.70591

IEEE Style

J. Dhom, E. Cordes, C. Berger, F. Steinlehner, and R. Daub, "Influence of Calendering on the Variation in Material Compositions of the Composite Cathode of Polymer-Based Solid-State Batteries," Engineering Reports, vol. 8, no. 2, Art. no. e70591, 2026, doi:10.1002/eng2.70591.

Harvard Style

Dhom, J., Cordes, E., Berger, C., Steinlehner, F. and Daub, R., 2026. Influence of Calendering on the Variation in Material Compositions of the Composite Cathode of Polymer-Based Solid-State Batteries. Engineering Reports, 8(2), e70591. Available at: https://doi.org/10.1002/eng2.70591.

Vancouver Style

Dhom J, Cordes E, Berger C, Steinlehner F, Daub R. Influence of Calendering on the Variation in Material Compositions of the Composite Cathode of Polymer-Based Solid-State Batteries. Engineering Reports. 2026;8(2):e70591. doi:10.1002/eng2.70591.

Chicago (Author–Date)

Dhom, Jonas, Eric Cordes, Christoph Berger, Florian Steinlehner, and Rüdiger Daub. 2026. "Influence of Calendering on the Variation in Material Compositions of the Composite Cathode of Polymer-Based Solid-State Batteries." Engineering Reports 8 (2): e70591. https://doi.org/10.1002/eng2.70591.

MLA (9th Edition)

Dhom, Jonas, et al. "Influence of Calendering on the Variation in Material Compositions of the Composite Cathode of Polymer-Based Solid-State Batteries." Engineering Reports, vol. 8, no. 2, 2026, article e70591. Wiley, https://doi.org/10.1002/eng2.70591.

14. Editorial Note

This article is an independent scholarly review prepared for the Engineering Research Insights blog. The review summarizes the research objectives, experimental methodology, principal findings, and broader engineering significance of the original publication while maintaining scientific accuracy based solely on the published research article.

Readers interested in reproducing the experiments, examining the complete dataset, reviewing the detailed figures and tables, or citing the research in academic work are strongly encouraged to consult and cite the original peer-reviewed article published by Engineering Reports (John Wiley & Sons Ltd.) using its official DOI: https://doi.org/10.1002/eng2.70591.

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