These previous reports on the dry LIB electrode process have mainly focused on improving performance by changing the coating process or the binder, but alternative ways such as employing new conductive agents or current collectors have been rarely explored in addressing the core challenges of solvent-free electrode fabrication, which include weak cohesive strength, low deformability, high cell polarization, and low rate capability.Ĭarbon nanotubes (CNTs) are among the most avidly studied and utilized materials for multipurpose LIB electrode fabrication owing to their remarkable electronic conductivity, mechanical strength, resistance to chemical degradation, etc 22, 23. However, the scalability of dry spray-coating remains in question, and the additional coating step also complicates the manufacturing process 20, 21. Another method involves electrostatically spray-coating the electrode material onto the Al current collector, followed by hot roll press compaction of a dry LiCoO 2 (LCO) electrode. However, the prepared electrode has proven unsuitable for electrode roll-to-roll fabrication, as it requires exceedingly high pressure (20–500 MPa) for its fabrication and is easily fractured when bent. The use of holey graphene results in a binderless electrode configuration with a rate capability comparable to that of conventional LFP electrodes 19. The recent progress in dry LIB electrode technology involves dry-pressing a mixture of LiFePO 4 (LFP) active material powder and holey graphene to form a freestanding composite electrode. Moreover, it can pave a path to battery miniaturization as the absence of solvent elevates the maximum threshold of active mass loading, allowing the fabrication of higher mass-loading electrodes 14, 15, 16, 17, 18. The dry process is considered a new electrode fabrication method for post-LIB electrodes since it offers unparalleled advantages in terms of operating cost and energy efficiency when compared to the conventional solvent process.
Owing to these alarming issues, many battery researchers and manufacturers are currently working toward eradicating NMP from the electrode fabrication process.
Thus, prolonged exposure can be hazardous to the health of the workers as well as can potentially lead to fire hazards 13. Moreover, NMP is not only toxic (known to cause male infertility) but also flammable. However, this expensive organic solvent evaporates very slowly, and its drying and recovery constitute a notable portion (approximately 78%) of the total electrode production cost 12. The fabrication of conventional LIB electrodes involves the coating of metallic current collectors with a viscous slurry made by mixing the active material, the conductive agent, and a polymeric binder such as polyvinylidene fluoride (PVDF), in N-methyl-2-pyrrolidone (NMP) solvent 9, 10, 11. Although LIBs are well known as clean energy storage devices, they are yet to become a silver bullet for sustainable development due to the toxic volatile solvent pollution that occurs during the early stage of their electrode fabrication 6, 7, 8. Rechargeable lithium-ion batteries (LIBs) have become a new energy storage device in various fields owing to the global interest in green technologies and increased awareness of environmental issues 1, 2, 3, 4, 5. Notably, the mechanical strength and performance of the fabricated LiNi 0.7Co 0.1Mn 0.2O 2 (NCM712) dry press-coated electrodes (DPCEs) far exceed those of conventional slurry-coated electrodes (SCEs) and give rise to high loading (100 mg cm −2, 17.6 mAh cm −2) with impressive specific energy and volumetric energy density of 360 Wh kg −1 and 701 Wh L −1, respectively. Herein, we report an industrially viable and sustainable dry press-coating process that uses the combination of multiwalled carbon nanotubes (MWNTs) and polyvinylidene fluoride (PVDF) as a dry powder composite and etched Al foil as a current collector. In addition to being unsustainable, the use of this expensive organic solvent substantially increases the cost of battery production, as it needs to be dried and recycled throughout the manufacturing process. The current lithium-ion battery (LIB) electrode fabrication process relies heavily on the wet coating process, which uses the environmentally harmful and toxic N-methyl-2-pyrrolidone (NMP) solvent.
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