Studies On Polysulfonamide-based Separators For Highly Safe Lithium Ion Batteries

Along with the increasing energy shortage and environmental pollution, thedevelopment of the electric car industry is imminent, which brings higher requirementfor the high-power and highly safe of lithium ion batteries.Considering the safety performance of lithium-ion batteries, two kinds of newpolysulfonamide-based separators have been successfully explored, and the physicaland electrochemical properties of these composite separators were investigated.Compared to the commercial polypropylene separators (Celgard2500), those newseparators exhibited higher porosity, higher electrolyte wettability, better thermalstability and electrochemical stability. It was demonstrated that the cells using thecomposite nonwoven separators exhibited much better rate capability and cycleperformance. The main works are listed as follows:Firstly, the porous SPN composite separator obtained by an electrospinning andcoating SiO2process exhibited outstanding properties, such as porosity, Gurley value,wettability and mechanical strength. The SPN separator could maintain dimensionalstability at200oC and the electrochemical stability windows is5.0V (vs. Li+/Li). Theionic conductivity of electrolyte-soaked SPN separator is2.1×103S cm-1at roomtemperature. The cells using the SPN separator showed better rate capability and cycle performance than the cells using the commerical Celgard2500separator at roomtemperature. The cycle performance of the LiFePO4/Li cell using the SPN separatorwas investigated at elevated temperature. The discharge capacity retention of the cellafter40cycles was93%at120oC, which further demonstrated that SPN separatorcould be applied in the highly safe lithium ion batteries.Secondly, a core-shell structured PSA@PVDF-HFP composite separator wasexploited via coaxial electrospinning technique, and PSA and PVDF-HFP were used asthe core layer and shell layer, respectively. The PSA@PVDF-HFP composite separatordisplayed higher porosity, excellent Gurley value, electrolyte wettability, mechanicalstrength and superior thermal stability. The ionic conductivity of electrolyte-soakedPSA@PVDF-HFP separator is1.97×103S cm-1at room temperature and theelectrochemical stability windows is5.1V (vs. Li+/Li）. Moreover, it was demonstratedthat the cell assembled with PSA@PVDF-HFP separator displayed superior ratecapability and better cycle performance. Notably, these attractive characteristics wouldendow PSA@PVDF-HFP composite separator a promising separator for lithium ionbatteries.