Development of nano-sized LiFePO₄ dry cathodes with enhanced flexibility and mechanical robustness for roll-to-roll dry coating process

Abstract

The polytetrafluoroethylene (PTFE) binder-based roll-to-roll dry coating process has emerged as a promising alternative to conventional slurry-based methods for fabricating thick electrodes in high-energy-density lithium-ion batteries (LIBs). However, applying nano-sized lithium iron phosphate (LiFePO₄, LFP) to this process remains challenging, as the high specific surface area of nano-sized LFP leads to the formation of short and thin PTFE fiber network that cannot ensure the mechanical integrity of dry cathode at low PTFE binder content. Consequently, the nano-sized LFP dry cathode suffers from poor flexibility and mechanical brittleness, limiting its applicability in roll-to-roll processing. In this study, we investigated the fibrillization behavior of PTFE binders depending on the particle size of LFP, to elucidate the origin of mechanical degradation in nano-sized LFP dry cathodes. Our results revealed that nano-sized LFP facilitates excessive PTFE fibrillization, generating fragile and weak networks with short and long PTFE fibers, leading to the mechanical degradation of nano-sized LFP dry cathodes. To address this issue, we introduced a two-step extrusion process that promotes the formation of thick and long PTFE fiber networks within nano-sized LFP dry cathodes. This strategy enabled the fabrication of flexible and mechanically robust nano-sized LFP cathode film with only 2 wt% PTFE binder. The developed LFP dry cathodes exhibited excellent compatibility with thick electrode designs and achieved high areal capacities (7 mAh cm^-2, 2.7 g/cc), offering a scalable solution for next-generation LFP-based LIBs.

Keywords

Li-ion batteries / thick electrode / roll-to-roll dry coating process / lithium iron phosphate / PTFE fibrillization

References

[1] Yang Z,Lin F.Sustainable electric vehicle batteries for a sustainable world: perspectives on battery cathodes, environment, supply chain, manufacturing, life cycle, and policy.Adv Energy Mater2022;12:2200383

[2] Frith JT,Ulissi U.A non-academic perspective on the future of lithium-based batteries.Nat Commun2023;14:420 PMCID:PMC9879955

[3] Jamil S,Fasehullah M.Challenges and prospects of nickel-rich layered oxide cathode material.J Alloys Compd2022;909:164727

[4] Li W,Manthiram A.High-nickel layered oxide cathodes for lithium-based automotive batteries.Nat Energy2020;5:26-34

[5] Nekahi A,Li X,Zaghib K.Sustainable LiFePO₄ and LiMn_xFe_1-xPO₄ (x=0.1-1) cathode materials for lithium-ion batteries: a systematic review from mine to chassis.Mater Sci Eng R Rep2024;159:100797

[6] Ramasubramanian B,Chellappan V,Ramakrishna S.Recent development in carbon-LiFePO₄ cathodes for lithium-ion batteries: a mini review.Batteries2022;8:133

[7] Zhong Z,Zhu C,Kong L.Nano LiFePO₄ coated Ni rich composite as cathode for lithium ion batteries with high thermal ability and excellent cycling performance.J Power Sources2020;464:228235

[8] Yang X,Wang C.Thermally modulated lithium iron phosphate batteries for mass-market electric vehicles.Nat Energy2021;6:176-85

[9] Gao F,Xue J.Preparation and characterization of nano-particle LiFePO₄ and LiFePO₄/C by spray-drying and post-annealing method.Electrochim Acta2007;53:1939-44

[10] Ji G,Liang Z.Direct regeneration of degraded lithium-ion battery cathodes with a multifunctional organic lithium salt.Nat Commun2023;14:584 PMCID:PMC9898549

[11] Kuang Y,Kirsch D.Thick electrode batteries: principles, opportunities, and challenges.Adv Energy Mater2019;9:1901457

[12] Wu J,Ju Z.From fundamental understanding to engineering design of high-performance thick electrodes for scalable energy-storage systems.Adv Mater2021;33:2101275

[13] Boyce AM,Huang C.Design of scalable, next-generation thick electrodes: opportunities and challenges.ACS Nano2021;15:18624-32

[14] Chang JH,Kim I.Binder migration: frequently observed yet overlooked phenomena in electrode processing for lithium-ion batteries.J Energy Storage2024;83:110729

[15] Lu Y,Yuan H,Huang J.Dry electrode technology, the rising star in solid-state battery industrialization.Matter2022;5:876-98

[16] Sung K,Choi J,Yoon J.Enhanced adhesion in PTFE-based dry electrodes with hydrogen bonding co-binder integration for advanced lithium-ion batteries.Chem Eng J2025;511:161789

[17] Zhang K,Wang X.Dry electrode processing technology and binders.Materials2024;17:2349 PMCID:PMC11123077

[18] Kim J,Kim M.10 mAh cm^-2 cathode by roll-to-roll process for low cost and high energy density Li-ion batteries.Adv Energy Mater2024;14:2303455

[19] Horst M,Bahlmann L.Effect of active material morphology on PTFE-fibrillation, powder characteristics and electrode properties in dry electrode coating processes.Powder Technol2025;451:120451

[20] Wang X,Zhang K.A polytetrafluoroethylene-based solvent-free procedure for the manufacturing of lithium-ion batteries.Materials2023;16:7232 PMCID:PMC10673244

[21] Lee K,Nam JS,Kim Y.Dry-film technology employing cryo-pulverized polytetrafluoroethylene binder for all-solid-state batteries.Chem Eng J2024;487:150221

[22] Kang J,Jang S.Bollard-anchored binder system for high-loading cathodes fabricated via dry electrode process for Li-ion batteries.Adv Mater2025;37:2416872

[23] Zhang Y,Wang Z,Lou F.Recent technology development in solvent-free electrode fabrication for lithium-ion batteries.Renew Sustain Energy Rev2023;183:113515

[24] Kwon K,Han S.Low-resistance LiFePO₄ thick film electrode processed with dry electrode technology for high-energy-density lithium-ion batteries.Small Sci2024;4:2300302

[25] Al-Samet MA.Improving the lithium-ion diffusion and electrical conductivity of LiFePO₄ cathode material by doping magnesium and multi-walled carbon nanotubes.J Alloys Compd2023;947:169680

[26] Naoi K,Iwama E.Ultrafast charge-discharge characteristics of a nanosized core-shell structured LiFePO₄ material for hybrid supercapacitor applications.Energy Environ Sci2016;9:2143-51

[27] Luo Y,Koratkar N.Densification of alloying anodes for high energy lithium-ion batteries: critical perspective on inter- versus intra-particle porosity.Adv Sci2024;11:2403530 PMCID:PMC11425885

[28] Wiegmann E,Leeb M.Sustainable lithium ferro-phosphate cathode manufacturing: a semi-dry approach with water-based processing and polytetrafluorethylene binders.Batteries2023;9:567

[29] Kim B,Yu J.Conductive agent-controlled tortuosity in solvent-free thick-film electrodes for high-energy lithium-ion batteries.Energy Environ Mater2025;e70019

[30] Wang XQ,Han JC.Crystallization behavior of polytetrafluoroethylene (PTFE).J Appl Polym Sci2002;83:990-6

[31] Starkweather HW,Jones GA.The heat of fusion of polytetrafluoroethylene.J Polym Sci Polym Phys Ed1982;20:751-61

[32] Ferry L,Vassoille R.Study of polytetrafluoroethylene crystallization.Acta Polym1995;46:300-6

[33] Jiang R,Xu Z,Zhao L.Improving the continuous microcellular extrusion foaming ability with supercritical CO₂ of thermoplastic polyether ester elastomer through in-situ fibrillation of polytetrafluoroethylene.Polymers2019;11:1983 PMCID:PMC6960977

[34] Jiang G,Xiong J,Yuan S.Enhanced performance of LiFePO₄ originating from the synergistic effect of graphene modification and carbon coating.J Alloys Compd2018;767:528-37

[35] Kim I,Jang H.Troubleshooting carbon nanotube bundling using electrostatic energy-driven dispersion for LiFePO₄ bimodal thick electrode in lithium-ion batteries.ACS Nano2025;19:15941-52

[36] Launey ME.On the fracture toughness of advanced materials.Adv Mater2009;21:2103-10

[37] Soderholm KJ.Review of the fracture toughness approach.Dent Mater2010;26:e63-77

[38] Seidl C,Frey M,Michaelis A.Comparison of electronic resistance measurement methods and influencing parameters for LMFP and high-nickel NCM cathodes.Batteries2024;10:105

[39] Li H,Wu D,Zhu Y.Ultrahigh-capacity and fire-resistant LiFePO₄-based composite cathodes for advanced lithium-ion batteries.Adv Energy Mater2019;9:1802930

[40] Zhang B,Zhang Y,Qiao Y.Reliable impedance analysis of Li-ion battery half-cell by standardization on electrochemical impedance spectroscopy (EIS).J Chem Phys2023;158:054202