Janus-particle-based composite solid electrolytes with a root-soil interlocking architecture

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) solid-state electrolytes are considered ideal candidates for solid-state Li metal batteries (SLMBs) due to their high ionic conductivity and excellent chemical stability toward Li metal. However, their practical application is hindered by high interfacial resistance, poor physical contact with Li metal, and the resultant inhomogeneous Li⁺ flux, which collectively induce Li dendrite growth and premature battery failure. To address these challenges, this work proposes an interfacial engineering strategy based on Fe₃O₄@Si/PVDF (PFS-x) Janus particles to construct a “root-soil interlocking” structure. This architecture features dual asymmetric functionalities: the Fe₃O₄ side, rich in oxygen-containing groups, exhibits strong lithiophilicity, effectively adsorbing Li⁺ and promoting uniform nucleation and deposition; the silane-coupler-modified Si/PVDF side establishes robust interfacial bonding with the LLZO surface and facilitates the self-assembly of a continuous three-dimensional ionic transport network. Benefiting from this interlocking structure, the interfacial resistance is significantly reduced from >1000 Ω·cm² to approximately 240 Ω·cm², accompanied by enhanced Li⁺ transport kinetics with an activation energy lowered to 0.1806 eV. Consequently, symmetric Li cells achieve stable cycling for over 5000 h at a current density of 0.1 mA cm^-2. The prepared SLMBs deliver an initial discharge capacity of 165.4 mA h g^-1 at 0.5 C and retain 151.9 mA h g^-1 after 100 cycles with a coulombic efficiency exceeding 99%, whereas the unmodified system fails after approximately 30 cycles. Collectively, this study presents an effective interface optimization strategy using Janus composite materials, offering new insights for the development of high-performance all-solid-state Li metal batteries.