High critical current density in Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 electrolyte via interfacial engineering with complex hydride

Abstract Garnet‐type solid‐state batteries (SSBs) are considered to be one of the most promising candidates to realize next‐generation lithium metal batteries with high energy density and safety. However, the dendrite‐induced short‐circuit and the poor interfacial contact impeded the practical application. Herein, interface engineering to achieve low interfacial resistance without high temperature calcination was developed, which Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) was simply coated with complex hydride (Li 4 (BH 4 ) 3 I (3L1L)) in various mass ratios n (Li 4 (BH 4 ) 3 I)‐(100− n )LLZTO (10 ≤ n ≤ 40). The interfacial conductivity increases by more than three orders of magnitude from 8.29 × 10 −6 S·cm −1 to 1.10 × 10 −2 S·cm −1 . Symmetric Li cells exhibit a high critical current density (CCD) of 4.0 mA·cm −2 and an excellent cycling stability for 200 h at 4.0 mA·cm −2 . SSBs with polymeric sulfur‐polyacrylonitrile (SPAN) cathode achieve a high discharge capacity of 1149 mAh·g −1 with a capacity retention of 91% after 100 cycles (0.2 C). This attempt guides a simple yet efficient strategy for obtaining a stable Li/LLZTO interface, which would promote the development of solid‐state batteries.