Composite polymer electrolytes with uniform distribution of ionic liquid-grafted ZIF-90 nanofillers for high-performance solid-state Li batteries

The stable structure, high porosity and surface functionality endow metal organic frameworks (MOFs) nanoparticles as excellent nanofillers for high-performance poly (ethyleneoxide)-based solid polymer electrolytes (PEO SPEs). However, the agglomeration of MOFs severely limits their potential applications. Herein, a novel zeolitic imidazolate framework-90 nanofiller grafted with imidazole ionic liquid containing siloxane groups (ZIF-90-g-IL) is prepared by dehydration condensation reaction, which enables the uniform distribution of the nanofiller in PEO SPEs. The resulting composite PEO SPE with ZIF-90-g-IL nanofillers delivers higher ionic conductivity of 1.17 × 10-4 S/cm at 30 °C and lithium ion transference number of 0.44, wider electrochemical stability window of 4.8 V, and stronger ability to inhibit lithium dendrite growth than the PEO SPE with unmodified ZIF-90. The strong interaction of ZIF-90-g-IL with PEO is caused by the chelation of quaternary ammonium cations of ionic liquid groups on the ZIF-90-g-IL surface with oxygen containing a lone pair of electrons of PEO, resulting in a uniform distribution of the nanofillers in PEO. The LFP||Li half cells with the PEO/ZIF-90-g-IL SPE exhibit good cycling performance with 71% capacity retention (101 mAh g−1) after 500 cycles at 2C under 60 °C, and show excellent cycling performance with 97.4% capacity retention (148 mAh g−1) after 30 cycles at 0.1C under 30 °C. The composite SPE is also used for high-voltage NCM811||Li half cells. The capacity retention is 63% (99 mAh g−1) after 100 cycles at 0.1C under 60 °C. The results imply ZIF-90-g-IL as effective nanofillers for SPEs showing a great potential application in all solid-state lithium metal batteries.