Directional LiFePO4 cathode structure by freeze tape casting to improve lithium ion diffusion kinetics

Abstract

Batteries with fast recharge rates while maintaining sufficient capacity are highly attractive for applications such as electric transportation and electrical storage of renewable sources. Designing an electrode structure that enables facile transport of lithium ions and electrons is an effective way to enhance capacity retention at fast charge and discharge rates. Here, we report a LiFePO4 (LFP) cathode as the model electrode with directional microstructure using an in-house developed freeze tape casting (FTC) technique. The microstructure and electrochemical performance of the electrodes with different freeze velocity and solid content were investigated, and an optimized directional electrode microstructure was obtained. The optimized LFP electrode exhibited competitive discharge capacities of 123.8 and 40.7 mA h g−1 at 0.1 and 15 C respectively, where 15 C represents ~4 min charge or discharge. For comparison, the capacity of conventional LFP cathodes containing typical tortuous porous microstructures often drops to negligible levels at the fast charge and discharge rate of 15 C. A relatively large cathode (~10 cm × 5 cm) containing the directional microstructure was fabricated, demonstrating the scalability of the FTC technique.