Differential Analysis of Surface-Dominated vs. Bulk-Dominated Electrochemical Processes in Lithium Iron Phosphate Cathodes

초록

We employed electrophoretic deposition (EPD) using AC voltage to prepare lithium iron phosphate(LFP) Li-ion battery electrodes with varying the LFP thickness, to compare bulk-limited electro chemicalreaction with the surface-limited electrochemical reactions. We analyzed the electrochemical performances ofthe thin and thick LFP electrodes at various scan rates. They revealed that with increasing scan rates, bothelectrode types showed a greater reliance on surface capacitive effects for charge storage. Significantly, thethin LFP electrode predominantly exhibited capacitive charge storage, surpassing diffusion-based storagemechanisms. This was in contrast to the performance of the thicker electrode, which had a lower capacitivecontribution. Quantitative assessment using the Randles-Sevcik equation further confirmed the superiorperformance of the thin LFP electrode. The Li-ion diffusion coefficient of the thin LFP electrode wassubstantially higher (9.6×10-9 cm2·V-1·s-1) compared to the thick electrode (2.0×10-9 cm2·V-1·s-1), indicatingenhanced ionic mobility in the surface-limited electrochemical reaction. These findings emphasize thesignificant advantages of thinner LFP electrodes, and induced surface limited electrochemical reaction, inhigh-rate applications, including higher capacitive charge storage and more favorable ion diffusioncharacteristics. The advantages conferred by the enhanced capacitive charge storage and superior iondiffusion in thin LFP electrodes have profound implications for the design and optimization of next-generationhigh-rate batteries. By focusing on tailoring electrode thickness, we can harness the full potential of surfacelimitedreactions, pushing the boundaries of what is currently achievable in terms of power density, chargingspeed, and cycle life in LFP-based energy storage technologies. These enhancements align with the growingneed for high-performing, reliable energy storage solutions in an increasingly electrified and energy-consciousworld.

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