Sandwiched polyimide-composite separator for lithium-ion batteries via electrospinning and electrospraying

A novel type of sandwiched separator for lithium-ion batteries has been developed by combining electrospinning and electrospraying techniques. This separator consists of three layers in which the top and bottom layers are prepared by electrospinning a poly(amic acid) ammonium salt (PAAS) solution and the middle layer is obtained by electrospraying a mixture of the PAAS solution and inorganic nanoparticles (SiO(2)or Al2O3). Subsequently, the sandwiched separators are imidized at 250 degrees C in a nitrogen atmosphere. The morphology, porosity, thermal stability, mechanical strength, wettability and electrochemical performance of sandwiched separators were examined and the results were compared with those of a commercial separator (SV718). The thermal properties of the sandwiched separators and SV718 were determined using a thermal gravimetric analyzer and a differential scanning calorimeter. The sandwiched separators had no melting peak, whereas SV718 had a melting peak at 139 degrees C, demonstrating the higher thermal stability of sandwiched separators. The electrolyte contact angles of sandwiched separators were around 11.5 degrees, which were significantly lower than that of SV718. Moreover, the porosity and electrolyte uptake of sandwiched separators were over 81% and 910%, respectively, while those values of SV718 were 43% and 121%, respectively. The higher porosity, electrolyte uptake, and wettability of the sandwiched separators resulted in the better their cycling performance and higher specific-discharge capabilities than SV718.