Making battery electrodes: from slurry to slit coils

Electrode manufacturing on one page: slurry mixing in a planetary mixer, slot-die coating and drying with solvent recovery, the coating bead and its defects, calendering between heated rolls, slitting and the cut edge, and the dry route with fibrillated PTFE. The steps and the shares of cost, time and energy are quoted from the cited papers.

1. Slurry mixing: The active material, conductive additive and binder are mixed with the solvent into a uniform slurry: NMP dissolves the PVDF binder of the cathode, while the anode uses SBR in water with CMC. Industry uses planetary mixers for large-volume slurries; mixing takes 30 min to 5 h and is 7.9% of the manufacturing cost (Liu 2021). Adding the carbon to the PVDF/NMP solution before the active material gives a porous carbon/binder network; that sequence doubled the ionic conductivity and the 5C rate performance of an NMC111 electrode (Liu 2021). Aqueous binders are greener and cheaper than those needing hazardous organic solvents (Cholewinski 2021). 2. Coating and drying: The slurry is pumped into a slot die and coated on both sides of the current collector (Al foil for the cathode, Cu foil for the anode), then dried in a long dryer, joined in a roll-to-roll system that runs at over 35 m/min. NMP (boiling point 202 °C) is toxic and strictly regulated: it is recovered by a condenser and distillation and reused with 20–30% loss, while the water vapour from anode slurry is exhausted directly. Coating and drying are 14.96% of the manufacturing cost, and drying and solvent recovery take 46.84% of its energy (Liu 2021). 3. At the slot die: Edge profiles depend mainly on the pressure in the coating bead and on leveling flows downstream; edges are best when the gap between die and substrate equals the wet coating thickness, and raised edges can cause wrinkles and reduce yield (Yoon 2025). Instabilities of the bead meniscus lead to defects: air entrained at the upstream meniscus shows as threading, bubbling and transitional flows, and heating the substrate widens the coating window (Gong 2025). 4. Calendering: Calendering sets the electrode’s bonding, conductivity, density and porosity and bonds it more strongly to the current collector, 5.19% of the manufacturing cost; a higher roll temperature gave lower porosity and compaction resistance and higher adhesion, as PVDF deforms more easily. Two-step roll pressing of a graphite anode raised LCO/graphite retention after 200 cycles from 82.77% to 85.83% (Liu 2021). Redesigning the heating-oil circuit inside a roller cut its surface temperature non-uniformity by 29.8% (Sun 2025). 5. Slitting: Slitting cuts the electrode to width after calendering, at 80–150 m/min with a blade or chisel, 3.09% of the manufacturing cost. Burrs and dross at the cut edge can pierce the separator and short the cell; laser cutting gives a clean edge, but metal spatter is a concern (Liu 2021). 6. Dry electrodes: Four steps: dry mixing; PTFE fibrillation by milling or high-speed airflow; calendering to the target thickness; and joining the self-supporting film to the current collector under heat and pressure. Under shear, PTFE fine powder fibrillates above 19 °C into a fibre network that connects and encapsulates the particles; it is limited in anodes because it is unstable at low voltage (Zhang 2024). A solvent-free 4 mAh cm⁻² NMC111/graphite cell kept 90% of its capacity after 1,500 cycles (Liu 2021). Wet coating suffers binder migration as the solvent dries, worse in thick electrodes (Park 2025).

Starting materials: Active material, conductive carbon and binder (PVDF in NMP for the cathode, SBR and CMC in water for the anode); Al and Cu foil; PTFE for the dry route. Product: Coated, calendered and slit cathode and anode coils.

Liu, Zhang, Wang & Wang, “Current and future lithium-ion battery manufacturing”, iScience 2021 (doi:10.1016/j.isci.2021.102332); Cholewinski et al., “Polymer binders: characterization and development toward aqueous electrode fabrication for sustainability”, Polymers 2021 (doi:10.3390/polym13040631); Yoon, Min, Song & Nam, “Controlling slot-coating edge profiles of battery electrodes”, ACS Appl. Mater. Interfaces 2025 (doi:10.1021/acsami.5c17960); Gong et al., “Numerical and experimental study of meniscus behavior in slot-die coating of lithium-ion battery electrodes with substrate heating”, Langmuir 2025 (doi:10.1021/acs.langmuir.5c04012); Sun et al., “Multi-objective optimization of the heating oil circuit inside the calendering roller for the lithium battery pole piece”, Sci. Rep. 2025 (doi:10.1038/s41598-025-88043-y); Zhang et al., “Dry electrode processing technology and binders”, Materials 2024 (doi:10.3390/ma17102349); Park et al., “Sustainable and cost-effective electrode manufacturing for advanced lithium batteries: the roll-to-roll dry coating process”, Chem. Sci. 2025 (doi:10.1039/d5sc00059a); Lim et al., “Validating the virtual calendering process with 3D-reconstructed composite electrode: an optimization framework for electrode design”, Small 2025 (doi:10.1002/smll.202410485); Sim, Lee, Li & Manthiram, “Influence of calendering on the electrochemical performance of LiNi₀.₉Mn₀.₀₅Al₀.₀₅O₂ cathodes in lithium-ion cells”, ACS Appl. Mater. Interfaces 2021 (doi:10.1021/acsami.1c12543).

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