Rational Design of Hierarchical “Ceramic-in-Polymer” and “Polymer-in-Ceramic” Electrolytes for Dendrite-Free Solid-State Batteries

Solid polymer electrolytes as one of the promising solid-state electrolytes have received extensive attention due to their excellent flexibility. However, the issues of lithium (Li) dendrite growth still hinder their practical applications in solid-state batteries (SSBs). Herein, composite electrolytes from “ceramic-in-polymer” (CIP) to “polymer-in-ceramic” (PIC) with different sizes of garnet particles are investigated for their effectiveness in dendrite suppression. While the CIP electrolyte with 20 vol% 200 nm Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) particles (CIP-200 nm) exhibits the highest ionic conductivity of 1.6 × 10 −4 S cm −1 at 30 °C and excellent flexibility, the PIC electrolyte with 80 vol% 5 µm LLZTO (PIC-5 µm) shows the highest tensile strength of 12.7 MPa. A sandwich-type composite electrolyte (SCE) with hierarchical garnet particles (a PIC-5 µm interlayer sandwiched between two CIP-200 nm thin layers) is constructed to simultaneously achieve dendrite suppression and excellent interfacial contact with Li metal. The SCE enables highly stable Li plating/stripping cycling for over 400 h at 0.2 mA cm −2 at 30 °C. The LiFePO 4 /SCE/Li cells also demonstrate excellent cycle performance at room temperature. Fabricating sandwich-type composite electrolytes with hierarchical filler designs can be an effective strategy to achieve dendrite-free SSBs with high performance and high safety at room temperature.