All‐Solid‐State Batteries with Ultralow Interfacial Resistance Enabled by Functional Garnet‐Type Mixed Ion‐Electron Conductive Interlayer

Abstract All‐solid‐state batteries (ASSBs) are regarded as the next‐generation advanced energy storage technology owing to their superior safety and high energy density. However, the poor solid‐solid interfacial contact and uncontrollable Li dendrite growth are the formidable challenges facing ASSBs. Herein, a composition‐optimized porous mixed conductive garnet interfacial layer Li 7 Pr 3 Zr 1.8 Ce 0.2 O 12 (LPZO‐0.20Ce) is fabricated on Ta‐doped garnet‐type electrolyte Li 6.4 La 3 Zr 1.6 Ta 0.4 O 12 (LLZTO) (denoted as LPZO‐0.20Ce‐LLZTO) by spark plasma sintering (SPS) method. The replacement of Zr 4+ by the multivalent Ce 4+ cation reduces the bandgap and thus increases the electronic conductivity of the garnet. The mixed ionic/electronic conductivity of porous LPZO‐0.20Ce allows the growth of lithium into the interlayer, reducing the interfacial resistance and suppressing the formation of Li dendrites. The LPZO‐0.20Ce‐LLZTO based symmetric cell exhibits high critical current density (CCD) of 3.2 mA cm −2 and is capable of cycling for 1200 h at 0.5 mA cm −2 . In addition, LPZO‐0.20Ce‐LLZTO based full cell matched with high‐loading LiNi 0.8 Co 0.1 M 0.1 O 2 (NCM811) cathode (20.3 mg cm −2 ) can run stably over 120 cycles. This work proposes a practical strategy for constructing stable interphase between Li metal electrode and solid‐state electrolyte.