用于锂离子电池的阻燃型纤维素基复合气凝胶膜

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

以离子液体为溶剂,制备了纤维素水凝胶,进而通过"溶胶-凝胶"过程在纤维素凝胶中原位生成勃姆石(AlOOH),并经超临界二氧化碳干燥制得了纤维素/AlOOH复合气凝胶膜.所形成的纳米纤维状AlOOH相互搭接形成了网络结构,使复合气凝胶膜的微观形貌更加致密、孔结构更加均匀.AlOOH的引入赋予了纤维素材料优异的阻燃性能.相对于高温易软化的商用聚丙烯隔膜,纤维素/AlOOH复合气凝胶膜在150°C下30 min无尺寸变化,具有更好的高温尺寸稳定性.纤维素/AlOOH复合气凝胶膜具有优异的电解液亲和性,吸液率为350%,离子电导率为3.1 mS/cm,以纤维素/AlOOH复合气凝胶膜组装的锂电池表现出了更好的电化学稳定性,并且经过100次循环测试后,容量保持率为90.2%,在4 C/4 C的高倍率充放电测试中放电比容量为80.7 mA h g-1,均优于商用聚丙烯隔膜.由于同时具备了优异的耐高温与阻燃性能和良好的电化学性能,这类新型的纤维素基复合气凝胶膜在高性能锂离子电池领域具有潜在的应用.

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(TEM), 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 °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.