Development of Solid Polymer Electrolyte with Excellent Electrochemical Properties Using High-Energy Electron Beam Irradiation

Lithium-ion batteries (LIBs), an energy storage system used in various fields such as electronic devices, electric vehicles, and unmanned aerial vehicles, consist of a cathode, anode, separator, and electrolyte. Currently, commercialized LIBs employ a liquid electrolyte that utilizes carbonate-based organic solvents. When an exothermal reaction is triggered by overcharge or external shock, the thermally unstable organic solvent can generate flammable gases and lead to ignition, ultimately causing a thermal runaway in LIBs. Due to the safety concerns associated with organic solvent-based liquid electrolytes, research has been conducted on solid electrolytes (SEs) as an alternative to liquid electrolytes (LEs).<br/>Among various SEs, polymer electrolytes (PEs) have garnered attention for their advantageous interfacial properties, form factor, and processability. In this study, the fabrication method for PEs involves <i>in-situ</i> polymerization. PEs created through <i>in-situ</i> polymerization are prepared by injecting a liquid precursor comprising monomers, lithium salt, initiators, and other components into the cell. Typically, thermal initiation is employed as the primary method for PE fabrication. However, thermal initiation comes with drawbacks, including challenges in controlling precursor reactions and the requirement for extended heat treatments.<br/>To address these issues, solid polymer electrolytes (SPEs) are prepared using high-energy electron beam irradiation. SPEs are produced with just tens of seconds of electron beam exposure. Optimized SPEs exhibit an average ionic conductivity of 0.54 mS cm^-1, a lithium transfer number (t_Li+) of 0.69, a wide electrochemical window exceeding 5 V, and excellent properties in suppressing the growth of lithium dendrites. Furthermore, in the NCM811‖SPEs‖Li cell configuration, a discharge capacity of 183 mAh g^-1 (0.1 C, 25 °C) was achieved, with 80% capacity retention after 200 charge/discharge cycles at 0.5 C and 25 °C.