All-Space Li ⁺ Transport Kinetics: A Design Principle Enabled by Synergistic Coupling of Co-Originated Dual-Gradient for Ultrastable Li Metal Anodes

The simple superposition of multiple gradient structures in three-dimensional (3D) Li anodes can, in principle, integrate the advantages of individual gradients to further regulate Li deposition. However, this “mere superposition” approach often fails to deliver satisfactory cycling stability, and no definitive guideline for achieving true gradient synergistic effects is available. Here, we propose that enhancing the all-space Li+ transport kinetics should serve as the core principle for 3D Li anode gradients designing. Through a facile thermal-compounding process, a 50 μm-thick Li–Mg–Sn alloy film and carbon cloth (CC) sheet are tightly integrated on the stainless-steel substrate at elevated temperature, forming a lithiophilically modified carbon fiber skeleton. Simultaneously, a co-originated dual-gradient structure─comprising pore-size gradient and ion-transport-pathway gradient─is formed in situ within the skeleton. The two ion-transport pathways at the bottom offset the limited Li+ diffusion in small pores, boosting all-space Li+ transport kinetics throughout the 3D host and guiding preferential Li deposition at the electrode bottom. The symmetric cell sustains cycling stability over 5000 h with an ultralow polarization voltage of ∼14 mV at 1 mA cm–2/1 mAh cm–2 and >1200 h at 3 mA cm–2/3 mAh cm–2. When paired with a LiFePO4 cathode (1.69 mAh cm–2), the full cell retains 80% capacity after 1300 cycles at 1 C. This dual-gradient synergistic coupling ensures rapid Li+ transport across the entire electrode, fundamentally enabling a bottom-up Li-plating, significantly extending the cycle life of the 3D Li composite anode, and providing insights for future gradient design.