Scalable and Flexible Li-Ion Conducting Film Using a Sacrificial Template for High-Voltage All-Solid-State Batteries

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The safety issues concerning conventional Li+ ion batteries (LIBs) are attributed to the use of flammable organic liquid electrolyte (LE), which could result in fire and explosion. To address the safety issues and increase the durability, All-solid-state Li+ ion batteries (ASLBs) using inorganic solid electrolyte (SE) are considered as an ideal alternative for developing safe LIBs. Their wide range of operating temperature, from room temperature to over 90°C, is also an important advantage with regards to energy storage systems.SE can be classified into two types: sulfide-based SEs and oxide-based SEs. First, in the case of sulfide-based SEs, thio-LISICON, and Li-argyrodite are present and these have high ionic conductivity that are comparable to LE . Furthermore, a sulfide-based SE with a polymer electrolyte has been extensively investigated as well. However, one of the major disadvantages of a sulfide-based SE is that it is chemically unstable in air as it reacts with moisture in the air to produce H2S gas, which is a hazardous.On the contrary, oxide- based SEs including garnet, NASICON type may be attractive because they not only have high ionic conductivity but also, are chemically stable in air. Given these aspects, many researchers are devoted to the combination of oxide-based SEs and polymer electrolytes by adding oxide-based SE powders in a polymer matrix, as polymer electrolytes exhibit more suitable mechanical properties than those of ceramics, but show low ionic conductivity at room temperature.The combination of oxide-based SEs and polymers have paved new ways to create better electrolytes which incorporate both the high ionic conductivity of the oxide-based SE and the stable mechanical properties of polymers. In the case of composite electrolytes, many researchers anticipated that the higher the oxide-based SE (herein, ceramic) content in a composite electrolyte, the higher the Li+ ion conduction contribution from the ceramic. To investigate the effect of Li+ ion conduction from ceramic powders, analytical research studies according to the ceramic content have been conducted. Unexpectedly, even if the ratio of ceramic powder is increased, the ceramic’s contribution to Li+ ion conductivity could not be confirmed as there is no path for the Li+ ions to percolate through the ceramic due to high interfacial resistance in the ceramic powders. Furthermore, this ceramic powder acts as a resistor due to high interfacial resistances between the ceramic powder and polymer electrolyte. In this work, scalable and flexible composite electrolyte film (SFCEF) was fabricated based on a fiber-shaped ceramic and polymer support. Ceramic fibers of Li1.3Ti1.7Al0.3(PO4)3 (LATP) were prepared by sintering the precursor-coated sacrificial template and then infiltrated with a polyethylene oxide (PEO) polymer to obtain the FSCEF. The LATP fibers induced continuous Li+ ion channels, allowing the FSCEF to show an ionic conductivity exceeding 10−4 S cm−1 at 60 °C. The synergistic action of the ceramic frameworks and supportive PEO resulted in enhanced mechanical flexibility. Furthermore, the possibility of using a FSCEF in all-solid-state batteries was confirmed by conducting electrochemical performance tests on a Li/FSCEF/LCO (LiCoO2) cell. We expect that the herein reported findings will contribute to the synthesis of thin and flexible solid-state electrolyte films with manufacturing scalability for promising high-voltage all-solid-state batteries.