The functional separator for lithium-ion batteries based on phosphonate modified nano-scale silica ceramic particles

Abstract In lithium-ion batteries (LIBs), benefiting from various functional components, functional separators can possess different capabilities to cope with the risks in complex application scenarios. In this work, a functional separator based on the phosphonate-modified nano-scale silica ceramic particles is fabricated to reduce the safety risks in LIBs. Through an anhydrous polymerization process, dimethyl vinylphosphonate (DMVP), a kind of widely used flame retardants, is grafted on silica (SiO2). Then the modified SiO2 (mSiO2) is coated on the pristine polyethylene separator by a typical coating process. Combining the function of the ceramic and phosphonate, the modified ceramic separator displays substantially enhanced thermal stability, without visual thermal shrink up to 200 °C. The flame resistances of separator itself and pouch cells are also significantly improved, even though flammable electrolyte is added. Different from the case when the phosphonate is used as an additive in electrolyte, the phosphonate is fixed firmly on the separator and not easy to be embedded in carbon anode after battery cycles. The coin cells assembled with the modified separators are away from the irreversible loss of discharge capacity and low Coulombic efficiency for the first cycle, which can be attributed to the firm immobilization of organic phosphonate.