Building Efficient Ion Pathway in Highly Densified Thick Electrodes with High Gravimetric and Volumetric Energy Densities.

A common practice in thick electrode design is to increase porosity to boost charge transport kinetics. However, a high porosity offsets the advantages of thick electrodes in both gravimetric and volumetric energy densities. Here we design a freestanding thick electrode composed of highly densified active material regions connected by continuous electrolyte-buffering voids. By wet calendering of the phase-inversion electrode, the continuous compact active material region and continuous ion transport network are controllably formed. Rate capabilities and cycling stability at high LiFePO4 loading of 126 mg cm-2 were achieved for the densified cathode with porosity as low as 38%. The decreased porosity and efficient void utilization enable high gravimetric/volumetric energy densities of 330 Wh kg-1 and 614 Wh L-1, as well as improved power densities. The versatility of this method and the industrial compatible "roll-to-roll" fabrication demonstrate an important step toward the practical application of thick electrodes.