Novel Coated Separator with Poly(ethylene glycol)Borate Ester for Lithium Secondary Batteries

Separator is a porous membrane placed between electrodes of opposite polarity, permeable to ionic flow but preventing electric contact of the electrodes. Generally, the polyethylene(PE)-based separators have been used in conventional lithium batteries, because they have advantages of excellent porous structure, high mechanical strength, and also they can effectively prevent the thermal runaway resulting from rapid overcharging of the battery. However, they show poor compatibility with liquid electrolyte due to their hydrophobic property. Many studies have been progressed for substitution with other materials or complement their properties to enhance the affinity with liquid electrolytes[1,2]. Recently, several researchers have studied anion receptors as a new additive for advanced electrolytes with higher electrochemical and thermal stability[3-5]. Anion receptors can form complexes with anions and thereby restrict the decomposition reaction of anions and also increase lithium ion transference number and dissociation fraction of lithium salt. However, anion receptor such as tris(pentafluorophenyl) borane (TPFPB) should be added plentifully in the liquid electrolyte even if it is very expensive and can generate side-reactions with electrode materials. In this study, we prepared novel coated separator with Poly(vinyl acetate) (PVAc) and PEG borate. For abovementioned problems, PVAc has a good affinity with liquid electrolytes, and PEG borate has an ability of anion recepting and stabilizing. We compare the electrochemical property and cyclic performance of novel coated PE separator with those of the pure PE separator.