Enhancement of the ionic conductivity of a composite polymer electrolyte via surface functionalization of SSZ-13 zeolite for all-solid-state Li-metal batteries

Abstract

To mitigate the safety issues of liquid electrolyte-based Li-ion batteries, there is a growing interest in the development of solid-state electrolyte (SSE) based Li-metal batteries. Regrettably, most SSEs have low ionic conductivity (σ), which significantly lowers the performance of the Li-metal batteries. However, a composite polymer electrolyte (CPE) offers a higher σ value, which still needs to be improved for a reliable Li-metal battery. Here, a superior CPE (MZ-CPE) was synthesized using modified SSZ-13 (M-SSZ-13) as a ceramic filler. Polyethylene oxide (PEO) and lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI) were used as the substrate and Li-salt, respectively. Due to the upgraded and hydrophobic surface of M-SSZ-13, the dispersion of the Li-salt in PEO is significantly improved. Thus, the value of σ was greatly enhanced, which helps to make better interfacial contact with the electrodes. The MZ-CPE electrolyte with 5 wt% M-SSZ-13 (5% MZ-CPE) provided an outstanding σ value of 5.34 × 10⁻² S cm⁻¹ (@ 70 °C) along with a Li-ion transference number of 0.85. Besides, the obtained discharge specific capacities were 154 and 194 mA h g⁻¹ using LiFePO₄ and LiNiCoAlO₂ cathodes, respectively at the discharge current density of 0.1C. For LiFePO₄ cathode, the capacity retention was 94.1% after 80 cycles @ 60 °C. These results indicate that hydrophobic zeolite containing composite polymer electrolytes could be a potential alternative for solid-state Li-metal batteries.