Thin Solid Electrolyte Membrane Using Porous Template for High Energy Density All-Solid-State Batteries

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All-solid-state batteries (ASBs) offer a promising alternative to current Li-ion batteries (LIBs) due to the intrinsic safety conferred by solid electrolytes (SEs), which eliminate the flammability risk associated with liquid electrolytes. ASBs also hold potential for enhanced energy density through the utilization of high energy density Li metal (3860 mAh g-1) or anode-less systems[1]. Driven by these two motivations, for the past two decades, a tremendous amount of research has been focused on developing novel SE materials that demonstrate high ionic conductivity [2-4]. The state-of-the-art SE materials now exhibit room temperature ionic conductivity of >10-2 S/cm, even surpassing that of liquid electrolytes.Despite significant progress in SE research, however, the commercialization of ASBs faces challenges, primarily due to processing constraints associated with lab-scale fabrication methods. Most research on sulfide SEs still relies on thick pellet-type configurations due to the simplicity of fabrication via cold pressing SE powders. However, such thick SE pellets drastically reduce cell-level energy density in terms of both gravimetric and volumetric measures, which ironically results in poor energy density of ASB cells. Fabricating SEs into thin membranes is therefore crucial for achieving ASB energy densities surpassing those of conventional LIBs. Meanwhile, scalability and cost-effectiveness of fabrication methods are also paramount for feasible ASB production.We address these challenges by employing a mechanically robust porous template in combination with a slurry fabrication technique to create an extremely thin SE membrane with a thickness of 31 μm. The macro-porosity of the template facilitates the selection of compatible SE-solvent-binder combinations while ensuring mechanical integrity in the final SE membrane. The fabricated membrane exhibits exceptional ionic conductivity exceeding 0.5 mS/cm, resulting in enhanced areal conductance compared to pellet-type counterparts due to its reduced thickness. Importantly, our fabrication method employs scalable and cost-effective protocols suitable for roll-to-roll manufacturing processes, ensuring realistic production scalability. Incorporation of this thin SE membrane into ASBs significantly boosts cell-level energy densities by 8- and 6-fold in gravimetric and volumetric terms, respectively, compared to pellet-type configurations. These findings highlight the potential of SE membranes in overcoming key obstacles to ASB commercialization, paving the way for safer and more efficient energy storage solutions. Acknowledgment This work was supported by the Development Program of Core Industrial Technology (No. 20012326) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea).