Tailoring Electron‐Blocking and Ionic‐Transport Interface via Functional Carbon Dots for Durable Garnet‐Based Solid‐State Batteries

Abstract Garnet oxides Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZTO) have been identified as highly potential solid electrolytes for solid‐state Li batteries (SSLBs). Nevertheless, existing methods for interfacial engineering fail to entirely prevent the intrusion of lithium dendrites. Herein, one optimized garnet‐based SSB is presented via the construction of an ion‐conductive and electronically insulating LLZTO|Li interface, triggered by the reaction of N‐doped carbon dots (NCDs) with lithium. Finite‐element simulations and density functional theory (DFT) calculations reveal that a functional interface with electron‐blocking characteristics is established by the formation of Li 2 O and Li 3 N during the reaction, effectively hindering electron transfer and preventing the subsequent dendritic penetration into the LLZTO pellet. Furthermore, Li 3 N with high ionic conductivity is utilized to facilitate ion migration at the interface, thereby promoting uniform lithium deposition. Therefore, an interfacial resistance of 6.3 Ω cm 2 is successfully realized, and the Li‐NCD|LLZTO|Li‐NCD symmetric cells maintained stable Li plating/stripping cycles for more than 5000 h at 0.1 mA cm −2 and 850 h at 0.4 mA cm −2 . Moreover, the LFP|LLZTO|Li‐NCD full cell displays enhanced cycling performance (92.7% capacity retention after 100 cycles). This research offers new perspectives on the rational design of the garnet‐based electrolyte and the Li metal interface.