Unilateral modified composite electrolyte by high modulus ceramics filling

Abstract Replacing liquid electrolytes with solid-state electrolytes allows all-solid-state lithium batteries (SSBs) to exhibit excellent safety and high volumetric energy density. Since the large-scale processing of electrolytes might encounter a brittleness issue on the ceramic solid-state electrolytes, the solid polymer electrolytes (SPEs) such as poly(ethylene oxide) (PEO)-based polymer-ceramic composite may present a solution due to its great strength and bendable characteristics. While being inherently flexible, PEO-based electrolyte has relatively low ionic conductivity at room temperature and poor resistance against the hazard of dendrite formation and growth. Although ceramic filler addition has been developed to increase the yield strength and improve the electrochemical properties, high-density fillers lack reinforcement and cause brittle failure. In this work, we propose a unilateral structure that well combines the flexible nature of PEO polymer and low fraction fillers with good inhibition of lithium dendrite growth. In the unilateral structure, the polymer acquires high flatness and wettability to the electrode, and high-density garnet Li_7La_3Zr_2O_12-based filler at the composite surface provides high shear modulus to enhance overall mechanical strength, taking complementary advantages of two kinds of electrolytes. It is further demonstrated that the lithium-ion conductivity strongly depends on the lithium concentration gradient inside the composite electrolyte, and ball-milled ceramics may further disequilibrium the optimum ionic conductivities. Under current density galvanostatic cycling of 0.2 mA/cm^2, a unilateral modified composite electrolyte with merely 15wt% fillers can withstand lithium stripping and plating smoothly for more than 50 h without potential protrusion. Graphical abstract