Electrochemical Properties of Solid Electrolytes with High Content of Non-Sintered Ceramics

1.Introduction All-solid-state lithium-ion batteries are rechargeable batteries that use either polymeric or inorganic solid ionic conductor as the electrolyte 1) . 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 types 2) . 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 amorphous 2) ; 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 sho