A ZIF-8 composite SiO2-enhanced high-performance PEO-based solid-state electrolyte for Li-metal batteries

Abstract

Solid-state lithium batteries (SSLBs) are promising energy-storage devices. However, the low ionic conductivity of solid electrolytes and poor interface stability are two challenges to their commercial application. To alleviate these problems, we investigated three different composite modes of ZIF-8 and SiO₂: (1) mechanical mixing of ZIF-8 and mesoporous SiO₂ (ZIF-8+SiO₂); (2) mesoporous SiO₂ spheres adsorbed on the surface of ZIF-8 (ZIF-8/SiO₂); (3) mesoporous SiO₂ shell deposited on the surface of ZIF-8 (ZIF-8@SiO₂). In particular, ZIF-8@SiO₂/IL was obtained when ZIF-8@SiO₂ with a hierarchical pore structure was used as the host of the Li⁺-containing ionic liquid (IL). By combining ZIF-8@SiO₂/IL as a filler with polyethylene oxide and lithium bis(trifluoromethanesulfonyl)imide, the composite electrolyte (PZS-3) showed excellent performance. PZS-3 showed a high ionic conductivity (2.35 × 10⁻⁴ S cm⁻¹ at 30 °C), wide electrochemical stability window (5.5 V), and high Li⁺ transference number (0.6), and excellent compatibility with the Li metal and electrodes. An SSLB composed of LiFePO4/PZS-3/Li exhibited outstanding cycling stability with an initial discharge capacity of 155.6 mA h g⁻¹ at 0.2 C and capacity retention of 96.5% after 100 cycles. This novel design strategy offers a promising approach for MOFs composited with other inorganic materials to construct prospective hierarchical Li⁺ channels.