Perovskite‐type solid‐state electrolytes exhibit great potential for the development of all‐solid‐state lithium batteries due to their high Li‐ion conductivity (approaching 10−3 S cm−1), wide potential window, and excellent thermal/chemical stability. However, the large solid–solid interfacial resistance between perovskite electrolytes and electrode materials is still a great challenge that hinders the development of high‐performance all‐solid‐state lithium batteries. In this work, a perovskite‐type Li0.34La0.51TiO3 (LLTO) membrane with vertically aligned microchannels is constructed by a phase‐inversion method. The 3D vertically aligned microchannel framework membrane enables more effective Li‐ion transport between the cathode and solid‐state electrolyte than a planar LLTO membrane. A significant decrease in the perovskite/cathode interfacial resistance, from 853 to 133 Ω cm2, is observed. It is also demonstrated that full cells utilizing LLTO with vertically aligned microchannels as the electrolyte exhibit a high specific capacity and improved rate performance.

Ceramic oxide electrolytes are outstanding due to their excellent thermostability, wide electrochemical stable windows, superior Li‐ion conductivity, and high elastic modulus compared to other electrolytes. To achieve high energy density, all‐solid‐state batteries require thin solid‐state electrolytes that are dozens of micrometers thick due to the high density of ceramic electrolytes. Perovskite‐type Li0.34La0.56TiO3 (LLTO) freestanding ceramic electrolyte film with a thickness of 25 µm is prepared by tape‐casting. Compared to a thick electrolyte (>200 µm) obtained by cold‐pressing, the total Li ionic conductivity of this LLTO film improves from 9.6 × 10−6 to 2.0 × 10−5 S cm−1. In addition, the LLTO film with a thickness of 25 µm exhibits a flexural strength of 264 MPa. An all‐solid‐state Li‐metal battery assembled with a 41 µm thick LLTO exhibits an initial discharge capacity of 145 mAh g−1 and a high capacity retention ratio of 86.2% after 50 cycles. Reducing the thickness of oxide ceramic electrolytes is crucial to reduce the resistance of electrolytes and improve the energy density of Li‐metal batteries.

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