Freeze-dried low-tortuous graphite electrodes with enhanced capacity utilization and rate capability

Lithium ion battery electrodes with high rate capability are important for extreme fast charging (XFC) for electric vehicle applications. Making low-tortuous electrodes is one of the approaches to achieve XFC by enhancing ionic transport in the electrodes. In this study, we conducted directional freeze-drying of slurries cast on a copper foil to make graphite electrodes. Low-tortuous structure was created and verified by cross-sectional scanning electron microscope observations and tortuosity measurements. The out-of-plane alignment of graphite flakes, enhanced electrolyte wettability, and low tortuosity of the freeze-dried electrodes were confirmed by X-ray diffraction measurements, wettability tests, and electrochemical impedance measurements, respectively. Electrochemical measurements showed that the freeze-dried electrodes have higher capacity retention (over 8% higher after 90 cycles at C/5) and better rate capability (60% higher capacity at 1C) than the electrodes prepared by the conventional tape-casting method. These enhancements mainly arise from the improved ionic transport by the freeze-drying induced low-tortuous structure. This study provides a proof-of-concept example that tape-casting/freeze-drying can be an effective, low cost, and scalable method to reduce tortuosity and improve electrochemical performance of battery electrodes.