In‐Situ Construction of Electronically Insulating and Air‐Stable Ionic Conductor Layer on Electrolyte Surface and Grain Boundary to Enable High‐Performance Garnet‐Type Solid‐State Batteries

Abstract Lithophobic Li 2 CO 3 /LiOH contaminants and high‐resistance lithium‐deficient phases produced from the exposure of garnet electrolyte to air leads to a decrease in electrolyte ion transfer ability. Additionally, garnet electrolyte grain boundaries (GBs) with narrow bandgap and high electron conductivity are potential channels for current leakage, which accelerate Li dendrites generation, ultimately leading to short‐circuiting of all‐solid‐state batteries (ASSBs). Herein, a stably lithiophilic Li 2 ZO 3 is in situ constructed at garnet electrolyte surface and GBs by interfacial modification with ZrO 2 and Li 2 CO 3 (Z+C) co‐sintering to eliminate the detrimental contaminants and lithium‐deficient phases. The Li 2 ZO 3 formed on the modified electrolyte (LLZTO‐(Z+C)) surface effectively improves the interfacial compatibility and air stability of the electrolyte. Li 2 ZO 3 formed at GBs broadens the energy bandgaps of LLZTO‐(Z+C) and significantly inhibits lithium dendrite generation. More Li + transport paths found in LLZTO‐Z+C by first‐principles calculations increase Li + conductivity from 1.04×10 −4 to 7.45×10 −4 S cm −1 . Eventually, the Li|LLZTO‐(Z+C)|Li symmetric cell maintains stable cycling for over 2000 h at 0.8 mA cm −2 . The capacity retention of LiFePO 4 |LLZTO‐(Z+C)|Li battery retains 70.5% after 5800 ultralong cycles at 4 C. This work provides a potential solution to simultaneously enhance the air stability and modulate chemical characteristics of the garnet electrolyte surface and GBs for ASSBs.