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.

Polytetrafluoroethylene (PTFE) has been widely used as a lubrication additive for reducing friction and wear; however, the hydrophobic nature of PTFE restricts its application in eco-friendly water-based lubrication systems. In this study, for the first time, we designed novel PTFE@silica Janus nanoparticles (JNs) to meet the requirement for additives in water-based lubricants, which have excellent dispersion stability in water attributed to the unique amphiphilic structure. By introducing the lubrication of the aqueous dispersion of the JNs with a concentration of 0.5 wt%, the coefficient of friction (COF) and wear volume were reduced by 63.8% and 94.2%, respectively, comparing to those with the lubrication of pure water. Meanwhile, the JNs suspension also exhibits better lubrication and wear-resistance performances comparing to commercial silica and PTFE suspensions. The excellent tribological behaviors of PTFE@silica JNs as nano-additives could be attributed to the synergetic effect of the two components, where the PTFE provided lubrication through the formed tribofilms on the friction pairs, and the rigid silica further enhanced the wear-resistance performance. Most importantly, the unique structure of JNs makes it possible to use PTFE as an additive in water-lubrication systems. Our study shed light on the design and application of novel JNs nanomaterials as additives to meet the requirements of future industrial applications.