High performance of polyethylene composite separators modified by carbon nanotube, lithium salt and SiO2 nanoparticles for lithium ion batteries

Abstract

In this work, the polyethylene (PE) separator is firstly modified with bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) solution, and then coated with a solution of hydroxyl functionalized carbon nanotube (CNT), nano-SiO2 and polyvinyl alcohol (PVA) on its one side. The obtained composite separator (PE@LiSiO2CNT) is with a thermal shrinkage of 14% at 150 °C for 0.5 h, and the ionic conductivity can be as high as 1.69 × 10-3 S cm-1. Furthermore, the specific discharge capacity of the assembled lithium ion batteries (LIBs) reaches 164 mAh g-1 at 0.2 C, and the coulomb efficiency remains above 99% after 250 cycles. This can be attributed to the network structure of SiO2 and CNT which increases the porosity of the separator and improves the electrolyte uptake. Besides, the CNT effectively alleviates the self-aggregation of SiO2, and promotes the rapid electrochemical reactions between the separator and the cathode. And it can also allow the free diffusion of lithium ions through its walls and channels with high efficiency, thus reducing the charge transfer resistance and improving the battery performance. Therefore, the modified separator with excellent dimensional thermal stability and electrochemical performance are successfully obtained, which are helpful to the development of LIBs.