Sustainable and cost-effective electrode manufacturing for advanced lithium batteries: the roll-to-roll dry coating process

Abstract

The transition to electric vehicles motivated by global carbon neutrality targets has intensified the demand for lithium-ion batteries (LIBs) with high energy density. While the innovation of cathode/anode active materials has reached a plateau, development of thick electrodes has emerged as a critical breakthrough to achieving high-energy-density LIBs. However, the conventional wet coating process has intrinsic limitations, such as binder migration during the solvent drying process, which becomes increasingly problematic with thick electrodes. To address these challenges, dry coating processes have been actively explored in three main forms: electrostatic spraying, hot pressing with thermoplastic polymers, and roll-to-roll dry coating utilizing the polytetrafluoroethylene binder. This review highlights the roll-to-roll dry coating process, a scalable and industrially viable approach, by introducing its underlying mechanisms, latest developments, and applications in all-solid-state batteries and lithium-sulfur batteries. By combining technical advancements with manufacturing scalability, the roll-to-roll dry coating process demonstrates significant potential to enable next-generation battery systems.

Fig. 1. Demand for sustainable and cost-effective electrode manufacturing for high-energy-density lithium batteries: (a) the history and development of Li-ion batteries according to the worldwide nations and industry. Reproduced with permission from ref. . Copyright (2019) Elsevier B.V. (b) Schematic illustration of the advantages of thick electrodes in terms of energy density of lithium rechargeable batteries.

Fig. 2. Comparison of dry and wet processed electrodes: (a) schematic illustration of degradation of wet-processed thick electrodes during the solvent drying and lamination process by binder migration. (b) Comparison of the electrode microstructure and (c) electrochemical performance. Reproduced with permission from ref. and . Copyright (2023) Elsevier B.V. and copyright (2023) RSC Publishing.

Fig. 3. Various dry coating processes: (a) schematic illustration of electrostatic spray drying, (b) hot pressing and (c) roll-to-roll dry coating processes. Reproduced with permission from ref. , and . Copyright (2017) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, copyright (2023) The Author(s) and copyright (2024) The Authors. Small Science published by Wiley-VCH GmbH. (d) The total number of papers on dry coating processes (electrostatic spray drying, hot pressing and roll-to-roll dry coating processes) and (e) papers on each dry coating process (2016–2024).

Fig. 4. PTFE binder for the roll-to-roll dry coating process: (a) The helical structure of an individual PTFE polymer chain in phase IV and (b) the hexagonal unit cell structure of phase IV PTFE. Reproduced with permission from ref. , copyright (2022) Elsevier Ltd. (c) Phase diagram of PTFE. Reproduced with permission from ref. , copyright (2020) Elsevier Ltd. (d) The true stress–strain curves of PTFE according to the temperature. Reproduced with permission from ref. , copyright (2021) RSC Publishing (e) SEM images of PTFE before and after the fibrillization process. Reproduced with permission from ref. , copyright (2017) Elsevier Ltd. (f) Schematic illustration and (g) SEM images of PTFE fibrillization in the roll-to-roll dry coating process. Reproduced with permission from ref. , copyright (2024) Matthews, Wheeler, Ramírez-González and Grant.

Fig. 5. Main processes of the roll-to-roll dry coating process.

Fig. 6. Relationship between ionic resistance and electrochemical performance of dry thick electrodes: (a) schematic illustration of ionic resistance (R_ion and R_ct). (b) Ionic resistance and (c) C-rate capability of dry electrodes depending on the areal capacity. (d) The schematic illustration of the issue of ultra-high thick electrodes and (e) requirement of main characteristics for dry electrodes with homogeneous microstructures. Reproduced with permission from ref. , copyright (2024) Wiley-VCH GmbH.

Fig. 7. Engineering of the dry mixing process: (a) control of shear force by the dry mixing time. Reproduced with permission from ref. . Copyright (2023) Springer. (b) The schematic illustration of improvement of CNT dispersion in the dry electrode by wet coating of CNTs on NCA. Reproduced with permission from ref. . Copyright (2022) John Wiley & Sons Ltd. (c) The schematic illustration of surface modification of PTFE and carbon black for improvement of PTFE and CB dispersion. Reproduced with permission from ref. . Copyright (2023) Springer. (d) Controlling the size of PTFE to improve the dispersion of the PTFE binder. Reproduced with permission from ref. . Copyright (2023) Springer.

Fig. 8. Engineering of the PTFE fibrillization process (LIBs). Investigation of PTFE fibrillization behavior according to the (a) fibrillization process time, (b) fibrillization process temperature and (c) the number of kneading configurations. Reproduced with permission from ref. , and . Copyright (2024) The Authors. Published by Elsevier B.V., copyright (2024) Wiley-VCH GmbH and copyright (2023) The Authors. Licensee MDPI, Basel, Switzerland.

Fig. 9. Engineering of the PTFE fibrillization process (ASSBs). Investigation of PTFE fibrillization behavior in the solid electrolyte film according to (a) various process parameters and (b) the molecular weight of PTFE. Reproduced with permission from ref. and . Copyright (2023) Wiley-VCH GmbH and copyright (2024) Wiley-VCH GmbH.

Fig. 10. Improvement of lithium ion/electron resistance and chemical stability of dry electrodes (LIBs): (a) ozonation of the SWCNT and its application to the dry cathode process. Reproduced with permission from ref. . Copyright (2023) American Chemical Society. (b) Pore structure of dry-processed SNG and FSG graphite electrodes. Reproduced with permission from ref. . Copyright (2024) The Author(s). Published by Elsevier B.V. (c) SEM images and linear curve fittings of Z′ versus ω^−1/2 in the low-frequency region of SC and PC NMC. Reproduced with permission from ref. . Copyright (2024) Elsevier B.V. (d) Schematic illustration of CEI layers and TEM images of the LiPF₆-cycled and LiClO₄-cycled DPEs. Reproduced with permission from ref. . Copyright (2023) American Chemical Society.

Fig. 11. Improvement of mechanical properties of dry electrodes (LIBs): (a) fabrication procedures of DP-1% F and DP-0% F electrodes. Reproduced with permission from ref. . Copyright (2024) Wiley-VCH GmbH. (b) Fracturing of active materials, effects of the solvent-assisted-binder (SaB) dry process, and capillary stresses in relation to mixture composition during dry processing. Reproduced with permission from ref. . Copyright (2023) The Authors. Published by Elsevier B.V.

Fig. 12. Next-generation batteries (ASSBs): (a) disparity in electrode coverage and Li⁺ diffusion between the wet process and dry process. Reproduced with permission from ref. . Copyright (2024) The Author(s). (b) The conventional cathode with an ionically insulating PTFE binder and SIL-infiltrated EC. Reproduced with permission from ref. . Copyright (2024) RSC Publishing. (c) The role of LiPO₂F₂ as an additive in dry electrodes for ASSBs. Reproduced with permission from ref. . Copyright (2023) Wiley-VCH GmbH.

Fig. 13. Next-generation batteries (Li–S batteries): (a) dry electrode fabrication procedure for a sulfur cathode with high mass loading. Reproduced with permission from ref. . Copyright (2024) Wiley-VCH GmbH. (b) Schematic illustration of the preparation of the LPSCl electrolyte membrane and FeS₂ cathode by the roll-to-roll dry coating process. Reproduced with permission from ref. . Copyright (2024) Elsevier Inc. (c) Schematic illustration and measurement of ionic/electrical conductivity of wet- and dry-processed sulfur cathodes. Reproduced with permission from ref. . Copyright (2022) Science Press. Published by Elsevier B.V.

Fig. 14. Future work on the roll-to-roll dry coating process: (a) storage modulus from DMA measurement. Reproduced with permission from ref. . Copyright (2024) Wiley-VCH GmbH, (b) stress–strain curve from UTM measurement and (c) (107) and (108) planes from XRD measurement of the electrode film. Reproduced with permission from ref. . Copyright (2022) Elsevier Ltd. (d) The LUMO and HOMO energies of polymers and electrolyte solvent. Reproduced with permission from ref. . Copyright (2024) Elsevier Inc. (e) Development of sustainable binder (sericin) for replacing the PTFE binder as a dry coating process binder. Reproduced with permission from ref. . Copyright (2022) The Authors. ChemSusChem published by Wiley-VCH GmbH. (f) Application of conductive additives with various dimensions and specific surface areas for the roll-to-roll dry coating process. Reproduced with permission from ref. . Copyright (2025) RSC Publishing. (g) Application of etched Al current collectors to improve the adhesion between the dry-processed cathode and current collectors. Reproduced with permission from ref. . Copyright (2023) The Author(s).

Joonhyeok Park

Jiwoon Kim

Jaeik Kim

Minsung Kim

Taeseup Song

Ungyu Paik