Enhancing Li Deposition Behavior through Valence Gradient-Assisted Iron Layer

Uncontrolled lithium (Li) dendrite formation presents major safety risks and challenges in the Li host design. A novel approach is introduced, using a valence gradient in iron nanoparticles (Fe⁰, Fe²⁺, Fe³⁺) to stabilize the anodes. An Fe⁰ component, with fast Li diffusion, ensures a steady supply of Li to Fe²⁺ and Fe³⁺ components, which have slower Li diffusion. This coordinated interplay between fast and slow diffusion uniformizes Li deposition near the substrate, effectively reducing the rate of dendrite growth. The as-prepared framework demonstrates uniform Li plating with a minimal hysteresis voltage after extensive cycling for 1200 h in symmetric cells. Integrated into a full cell with LiFePO₄, it demonstrates outstanding cycling stability for almost 950 cycles with a capacity of 92.2 mA h g^-1 at 1C with an ultralow N/P ratio of 1.19. This valence gradient design strategy broadens the design potential for transition-metal compounds in regulating Li deposition by mitigating interfacial Li⁺ behavior.