Slurry casting — in which a slurry of active materials, conductive agents, solvents, and other components are coated onto a current collector — is a commonly adopted electrode manufacturing method for commercial lithium-ion batteries. However, the typical solvents used in the process are not only expensive but also toxic; they evaporate slowly, thereby requiring an energy-intensive and time-consuming drying process. Intensive efforts are underway to develop solvent-free approaches, such as dry-printing (depositing dry materials onto a substrate), with varying successes. Nonetheless, there is still room for improvement in terms of scalability, cost, and electrochemical performance. Now, Yan Wang, Heng Pan, and colleagues in the USA report a potentially scalable and inexpensive dry-printing method for fast-charging electrodes.
In their fabrication process, the researchers started by mixing powders of a nickel–manganese–cobalt (NMC) oxide, a fluoropolymer binder, and a carbon black. The powder mixture was then sprayed onto a current collector foil that was fed continuously to a roll-to-roll processing system. Subsequent calendaring led to the formation of a dense cathode. Similar processes were applied to produce a graphite anode. The researchers then built a single-layer pouch cell (~ 45 mAh) with the NMC cathode and the graphite anode. They demonstrated that it could be charged to 78% capacity in 20 minutes, which outperforms their reference cell made from slurry casting. Examining the microstructure of their electrodes, the researchers suggested that the presence of more pronounced open pores led the dry-printed electrodes to exhibit lower tortuosity and shorter Li-ion diffusion paths than the slurry-casted ones, thereby achieving higher rate performance.
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