Fumed oxide-based nanocomposite polymer electrolytes for rechargeable lithium batteries

Rechargeable lithium batteries are promising power sources for portable electronic devices, implantable medical devices, and electric vehicles due to their high-energy density, low self-discharge rate, and environmentally benign materials. However, the high reactivity of lithium metal limits the choice of electrolytes and impedes the commercialization of rechargeable lithium batteries. One way to tackle this problem is to develop electrolytes that are kinetically stable with lithium. Composite polymer electrolytes (CPEs) based on fumed oxides presented in this work are promising candidates for rechargeable lithium batteries.; These CPEs typically consist of a low molecular weight methyl-ended poly(ethylene oxide) (PEO) oligomer + lithium bis(trifluromethylsulfonyl)imide [LiN(CF ₃SO₂)₂] (LiTFSI) + fumed oxides (fumed silica, alumina, titania, or nixed fumed silica/alumina). Electrochemical impedance spectroscopy (EIS), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy were employed to study Li transport of CPEs. Ionic conductivity is affected by fillers but does not vary significantly with filler type or surface chemistry. Inert fillers increase conductivity at temperatures below the melting point (T_m) of the electrolyte but decreases conductivity at temperatures above. Our rheological results show that electrolyte elasticity is increased upon addition of fillers and the extent of increase varies greatly with filler type: some effect physical gels while others produce suspensions, depending on the strength of interactions between surface groups of fillers. In addition, the interfacial stability between electrolyte and lithium metal is enhanced upon addition of fillers, as evidenced by the lower interfacial resistance at open-circuit, lower Li/Li cell potential, and less cell polarization during Li/Li cell cycling than those of the baseline liquid electrolyte. The lithium full-cell (Li + metal oxide cathode) cycling results also show improved cell capacity and capacity retention of composite electrolytes in comparison to the baseline liquid electrolytes.; In summary, our composite electrolytes are promising candidates for lithium battery applications with high room-temperature conductivity, good mechanical strength, stable interface between lithium metal and electrolytes, and reasonable capacity and capacity retention with optimized cathode compositions.