Biomimetic spatially graded electrolytes: facilitating rapid ion conduction and dendrite-mitigated operation in...

Electrode-electrolyte interfaces are of paramount significance in solid-state batteries. However, the enhancement of lithium (Li) conduction and the mitigation of Li dendrite formation constitute a dual challenge to interfacial structural design, as conventional rigid interfaces fail to balance ionic mobility and mechanical blocking. Herein, we report a biomimetic soft-hard-soft hierarchical architecture as an interfacial transition layer between the anode and solid electrolyte. Breaking from conventional rigid designs, this architecture leverages synergistic layer interactions to redistribute interfacial stress: the soft layer's electrospun network establishes 3D ion-transport pathways that accelerate Li⁺ conduction, while the poly(vinylidene fluoride) (PVDF) hard layer-mechanically reinforced by the underlying soft substrate-simultaneously suppresses dendrite penetration and enhances structural integrity. Consequently, the hierarchical structure achieves a tensile strength of 49.2 ± 2.1 MPa (n = 3) MPa, an electrochemical window of 5.20 ± 0.08 V (n = 3), and an ionic conductivity of (2.82 ± 0.09) × 10^-4 S cm^-1 (n = 3) cm^-1 at 25 °C. This performance directly enables high-performance cycling in LiFePO₄ || Li cells 136.3 ± 2.8 mAh g^-1 (n = 3) at 1.0C, 93.8 ± 0.8% (n = 3) capacity retention after 200 cycles, 99.5 ± 0.3% (n = 3) coulombic efficiency). The ionic conductivity and interfacial stability of the novel interface are significantly superior to those of commercial solid-state electrolyte films. This study highlights the potential of the bio-inspired spatial gradient electrolyte to simultaneously enhance Li⁺ conductivity and mitigate dendrite formation.