Lithium difluoro(oxalate)borate-based novel nanocomposite polymer electrolytes for lithium ion batteries

BACKROUND: HF formation and poor thermal stability found in commercial lithium ion batteries comprising LiPF6 (and other salts) have hampered the replacement of LiPF6. Therefore, a new kind of electrolyte salt is necessary to replace the one commercially available. RESULTS: A novel lithium difluoro(oxalate)borate (LiDFOB)-based nanocomposite polymer electrolyte has been prepared in a matrix of poly[ (vinylidene fluoride)-co-(hexafluoropropylene)] (PVdF-HFP). The electrolyte contains ethylene carbonate and diethyl carbonate as plasticizers and nanoparticulate Sb2O3 as a filler. Membranes obtained by a solution casting technique were characterized by AC impedance, thermogravimetry and tensile strength measurements and morphological studies. Membranes with 5 wt% Sb2O3 exhibit a room-temperature conductivity of 0.298mS cm(-1), and are thermally stable up to ca 130 degrees C. Furthermore, the nanocomposite membranes show a 125% increase in mechanical stability as compared to filler-free membranes. The structural change from a to beta phases was confirmed by Raman studies. CONCLUSION: One of the important advantages of using LiDFOB lies in its bulkier DFOB anion, which also acts as solid plasticizer, thus improving the basic requirements of the electrolyte, such as mechanical and thermal stabilities, as well ionic conductivity and with a lower filler content. The overcharge tolerance of LiDFOB salt at higher temperature is also to be noted, because of the oxalate moieties. Preliminary investigations confirmed the possibility of using Sb2O3 nanoparticle-filled membranes in industry in the near future. (c) 2008 Society of Chemical Industry.