Porous garnet as filler of solid polymer electrolytes to enhance the performance of solid-state lithium batteries

In order to enhance the ionic conductivity of solid polymer electrolytes (SPEs) and their structural rigidity against lithium dendrite during lithium-ion battery (LIB) cycling, we propose porous garnet Li_6.4La₃Zr₂Al_0.2O₁₂ (LLZO), as the filler to SPEs. The porous LLZO with interlinked grains was synthesized via a resol-assisted cationic coordinative co-assembly approach. The porous structure of LLZO with high specific surface area facilitates the interaction between polymer and filler and provides sufficient entrance for Li⁺ migration into the LLZO phase. Furthermore, the interconnection of LLZO grains forms continuous inorganic pathways for fast Li⁺ migration, which avoid the multiple diffusion for Li⁺ in interface. As a result, the SPEs with porous LLZO (SPE-PL) show a high ionic conductive of 0.73 mS·cm⁻¹ at 30 °C and lithium-ion transference number of 0.40. The porous LLZO with uniformly dispersed pores also acts as an ion distributor to regulate ionic flux. The lithium-symmetrical batteries assembled with SPE-PL show a highly stable Li plating/stripping cycling for nearly 3000 h at 0.1 mA·cm⁻². The corresponding Li/LiFePO₄ batteries also exhibit excellent cyclic performance with capacity retention of 75% after nearly 500 cycles. This work brings new insights into the design of conductive fillers and the optimization of SPEs.