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 Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particles (CIP-200 nm) exhibits the highest ionic conductivity of 1.6 x 10(-4) S cm(-1) at 30 degrees C and excellent flexibility, the PIC electrolyte with 80 vol% 5 mu m LLZTO (PIC-5 mu m) shows the highest tensile strength of 12.7 MPa. A sandwich-type composite electrolyte (SCE) with hierarchical garnet particles (a PIC-5 mu m 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 degrees C. The LiFePO4/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.