Flame-retardant Cellulose Based Composite Aerogel Membranes for Lithium Ion Batteries

Cellulose gel is first prepared by ionic liquid dissolution and regeneration, and then, boehmite, an aluminum oxide hydroxide (AOOH), is incorporated into cellulose gel via in situ " sol-gel" method. After supercritical CO2 drying, the cellulose/AlOOH composite aerogel membranes (CAAMs) are prepared. Related properties are investigated by Fourier transform infrared spectrometry (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectra (EDS), transmission electron microscopy (1EM), dynamic mechanical analysis (DMA), and microscale combustion calorimeter (MCC), and ignition tests. And the CAAMs are further characterized in terms of electrochemical stability and electrochemical performance in lithium-ion batteries (LIBs) and are compared to a commercial polypropylene separator membrane (Celgard 2400). The in-situ formed nanofibrous AlOOHs are overlapped with each other, creating a network structure and homogeneously distribution in the membrane, which endows the CAAMs with compact morphology and uniform pore structure with porosity around 83.9% and an average pore size about 23 nm. The results demonstrate that the CAAMs have excellent flame retardancy and show self-extinguishing behaviors, and the peak of heat release rate (PHHR), the heat release capacity (HRC), and the total heat release (THR) are significantly reduced. Compared to Celgard 2400 that are easily softened at high temperatures, the CAAMs have almost no dimensional change at 150 degrees C for 30 min and display excellent thermal stability. The CAAMs have superior affinity for the polar liquid electrolyte and therefore the CAAMs have higher uptake of liquid electrolytes of 350% and higher ionic conductivity of 3.1 mS/cm in contrast with 90% and 0.53 mS/cm for the polypropylene separators. LIBs assembled with the CAAMs show better electrochemical stability at a voltage below 4.7 V versus Li/Li+. The capacity retention was 90.2% after 100 times cycling tests and the specific discharge capacity was 80.7 mA h g(-1) at a fast charge/discharge rate of 4 C/4 C, which were better than those of commercial polypropylene separators. To sum up, this novel cellulose based composite aerogel membrane has great potential for the development of highly safe LIBs.