As demand grows for lithium-ion batteries that combine high energy density, fast power delivery, and long service life, conventional cathodes face a persistent trade-off between capacity and stability. LiFePO₄ (LFP) offers excellent safety and cycling durability but limited practical capacity, while organic redox-active materials can provide higher charge storage yet often suffer from dissolution and poor structural integration. Researchers from Korea University, Hanyang University, DGIST, and collaborating institutions, led by Professors Jinhan Cho, Byung-Hyun Kim, and Yongmin Ko, developed a redox-active ligand-stabilized LFP cathode that integrates porphyrin molecules with nanoscale LFP, combining LFP’s robust two-phase lithium-storage mechanism with multi-electron redox activity.
Why This Cathode Matters
LFP typically delivers around 140–165 mAh g-1 at 1 C, limiting its energy density despite excellent structural stability. The researchers addressed this limitation using amine-functionalized apo-porphyrin (NH2-PP), directly anchored onto 19 ± 5 nm LFP nanoparticles. This molecular integration enables complementary charge-storage mechanisms while suppressing the dissolution and rearrangement that commonly limit organic redox materials.
Innovative Design and Mechanism
The cathode employs an interfacial interaction-mediated layer-by-layer architecture combining NH2-PP-functionalized LFP nanoparticles with a conductive multiwalled carbon nanotube (MWCNT) network. Ligand exchange anchors NH2-PP onto the LFP surface, while hydrogen bonding assembles the nanoparticles with functionalized MWCNT layers. Thermal annealing at 250 °C converts these interactions into covalent amide bonds, creating a robust, interconnected conductive framework. Beyond the conventional Fe2+/Fe3+ redox of LFP, the porphyrin ligands provide additional dual-ion redox activity involving Li⁺ and PF6⁻, with an eight-electron transfer associated with the porphyrin framework.
Outstanding Performance
The resulting PP-LFP/MWCNT textile cathode delivers approximately 260 mAh g-1 at 20 mA g-1 (~0.1 C), exceeding pristine LFP’s theoretical capacity and outperforming a slurry-cast electrode (~191 mAh g-1). The porphyrin contribution accounts for approximately 27.7% of charge storage. At 2000 mA g-1 (10 C), the cathode retains 140 mAh g-1 and recovers 94% of its capacity when the current returns to 20 mA g-1. It also maintains >93% capacity after 2000 cycles at 1 C and ~80% after 1300 cycles at 10 C, with nearly 100% Coulombic efficiency.
Applications and Future Outlook
The porous textile architecture enables conformal coating of three-dimensional fibers while maintaining efficient ion and electron transport. Areal capacity increases with layer number, reaching approximately 1.1 mAh cm-2 for 10 layers, while three stacked electrodes achieve ~6.0 mWh cm-2. In pouch cells, the cathode retains 72% capacity after 500 cycles at 1000 mA g-1. By molecularly integrating redox-active porphyrins with stable LFP and conductive textile networks, this strategy offers a promising pathway toward high-capacity, high-rate, and durable lithium-ion battery cathodes