Zeolitic imidazolate framework-cellulose nanofiber hybrid membrane as Li-Ion battery separator: Basic membrane property and battery performance

Zeolitic imidazolate framework-8 (ZIF8) concept was introduced in the fabrication of li-ion battery (LIB) separator for the first time. The ZIF8 crystals were synthesized on the surface of cellulose nanofibers (CNFs) by mixing 2-methylimidazole (Hmim) with zinc nitrate hexahydrate (Zn) in methanol. ZIF8- or Zn (mim)2-CNF composite membrane was fabricated and the effect of ZIF8 on the pore structure of CNF network was investigated. The pores of the ZIF8-CNF membrane distributed more homogeneously than that of the pure CNF membrane. The porosity increased from 42% (pure CNF membrane) to 55% (composite membrane). The successful synthesis of ZIF8 crystals on CNF surface was confirmed through elemental composition and crystalline structure analysis of the composite. Compared with polymer based separator, the ZIF8-2-CNF membrane exhibited better thermal stability, mechanical property (isotropic vs. anisotropic), thermal expansion behavior (15.53 vs. 178.90 ppm/k), and surface wettability (13.31° vs. 96.18°). The LIB fabricated with ZIF8-CNF membrane had a comparable cycling stability and a better discharge retention stability (88.3% vs 80.2%) in comparison with these of a tri-layer commercial polymer membrane. The environmentally friendly ZIF8-CNF nanocomposite membrane can be considered as a good alternative for manufacturing LIBs.