Electrochemical Properties of Solid Electrolytes with High Content of Non-Sintered Ceramics
Authors: Sawada Komei , Okuda Daisuke , Ishikawa Masashi 
Published: December 2024

1.Introduction
All-solid-state lithium-ion batteries are rechargeable batteries that use either polymeric or inorganic solid ionic conductor as the electrolyte1). All-solid-state lithium-ion batteries with solid polymer electrolytes have long been investigated because of their ease of handling. There are two types of solid polymer electrolytes currently under consideration: gel-based and dry types2). Gel type has high ionic conductivity because this is swollen by organic solvents, but safety is compromised due to leakage of organic solvents. On the other hand, dry type does not use organic solvents, so there is no risk of leakage, but that has lower ion conductivity than gel type. In response to this problem, research was conducted to improve ion conductivity by adding inorganic filler to the dry system for making it amorphous2); however, the improvement in ion conductivity was not sufficient because an inorganic filler has no ionic conductivity. In this study, therefore, a new composite solid electrolyte with higher ionic conductivity than that of conventional solid electrolytes was prepared by using an inorganic oxide solid-state electrolyte (ISE) as an inorganic filler in a dry polymer. its electrochemical properties were also investigated.
2.Experimental
To prepare the composite solid electrolyte, an inorganic filler dispersion was prepared by dispersing LICGC (PW-01, Ohara) as ISE and 3-aminopropyltriethoxysilane as dispersing agent in tetrahydrofuran. The inorganic filler dispersion was combined with polycaprolactone (PCL) and lithium bis(fluorosulfonyl)imide (LiFSI) to prepare a LICGC slurry. The LICGC slurry was dried at 40°C for 12 hours and then pressurized to prepare PCL-LICGC (150 μm film thickness). Instead of PCL, polylactic acid (PLA) and polyethylene oxide (PEO) was applied for preparing PLA-LICGC and PEO-LICGC for comparison. A Li symmetric cell was fabricated to measure the ionic conductivity of each LICGC, and their ionic conductivity and activation energy during the ion transfer process at 25-55°C were evaluated. The electrochemical properties of each LICGC were also investigated using the Li symmetric cell, and charge-discharge measurements were performed at different current densities. The fabricated composite solid electrolytes are indicated with the name of the polymeric material used in this section and the content of LICGC at the end of the name sequence.
3.Results and discussion
PCL-LICGC50, PLA-LICGC50, and PEO-LICGC50 showed 2.12 × 10-4, 1.22 × 10-5, and 4.32 × 10-7 S cm-1 at 25°C, respectively, indicating that PCL-LICGCs have higher ionic conductivity than the other LICGCs; the ionic conductivity of PCL-LICGC50 was found to be higher than that of other composite electrolytes. In addition, PCL-LICGC50 showed 4.5 times higher ionic conductivity than PLA-LICGC50, an ester-based polymer of the same genus. This is due to the lower activation energy of PCL-LICGC50 in the ion transfer process and the higher diffusion rate of Li⁺ in the LICGC than that of PLA-LICGC50.
PCL-LICGC50 can be charged and discharged stably at current densities of 0.177 mA cm-2 for more than 600 hours and 0.354 mA cm-2 for more than 60 hours, respectively. Conventional inorganic solid electrolytes were stable at 0.177 mA cm-2 for more than 600 hours. These results indicate that the PCL-LICGC50 fabricated in this study has better charge-discharge characteristics than the conventional solid electrolytes. On this presentation, we will report the variations in ionic conductivity and activation energy when the composition ratio of LICGC is changed, as well as charge-discharge characteristics under a high current density.
4.Acknowledgments
PCL and PLA used in this study were provided by Toagosei Co., Ltd.
5.References
1) J. Wen et al., Mater. Express, 2, 197 (2012).
2) J. Feng et al., Nano Converg., 8, 2 (2021).