In Situ Construction of Functional Customized Elastic Li ⁺ Conducting Interlayer for High‐Performance Garnet‐Type Solid‐State Lithium Metal Batteries

Regulating the intrinsic volumetric fluctuations of lithium metal, ensuring efficient Li⁺ transport, and suppressing detrimental dendrite growth remain critical challenges for the commercialization of solid-state lithium metal batteries (SSLMBs). Therefore, the development of a multi-dimensional interfacial engineering strategy is of paramount importance. Herein, a multifunctional elastic interlayer is designed to facilitate the diffusion of Li⁺ by introducing phytic acid macromolecules (PA). The introduction of PA not only reinforces the mechanical robustness of the elastic skeleton, enabling it to effectively buffer the volume change during lithium deposition/stripping, but also modulates the solvation environment within the interlayer. This regulation promotes the formation of an anion-rich solvation structure and constructs a stable SEI layer rich in LiF and Li_xPO₄ on the surface of Li. Owing to the elastic interlayer and stable SEI, the assembled lithium symmetric cell achieves a high critical current density (CCD) of 4.6 mA cm^-2 and maintains stable cycling for over 500 h at 1.0 mA cm^-2. Furthermore, the pouch cell incorporating with high-loading NCM83 cathode retains a discharge capacity of 3.18 mAh cm^-2 after 35 cycles, highlighting the practical potential of this interfacial design strategy.