A General Method to Fabricate Free-Standing Electrodes: Sulfonate Directed Synthesis and their Li⁺ Storage Properties

For materials based on a spatially varied conversion reaction, Li⁺ storage properties largely hinge on the rational design of the concurrent electronic and ionic pathways in the electrode. We herein present a scalable approach for integrating size-tunable Fe₃O₄ nanocrystals with hierarchical porous carbon foam by employing sulfonated high internal phase emulsion polymers (polyHIPE) as the carbon source and substrate. To verify the feasibility of our configuration design, the electrodes of such a type were directly evaluated in pouch cells without using an auxiliary binder or a metallic current collector: The best performing composite electrode, with optimized oxide size range, exhibits a good capacity retention of 89.7% of the first charge capacity after 100 cycles and high rate durability up to 4 A g^-1. Furthermore, this synthetic approach was also applied to develop carbon/FeS free-standing anodes using the sulfonate groups as the sulfur source, demonstrating its generic applicability to the fabrication of other free-standing electrodes with enhanced Li⁺ storage properties.