Application Of Modified Separators In High-Energy Density Lithium-sulfur Batteries

In recent year,rechargeable batteries as energy storage device have been widely used in various fields,such as portable electronic devices,electric vehicles and scalable power station.Nowadays,it deserves to develop high energy batteries due to the limitation in energy density of commercial lithium ion battery.Compared with the traditional LIBs,lithium-sulfur?Li-S?batteries have an advantage in theoretical energy density(2600 Wh kg^-1).Additionally,with the natural abundance and environment-friendly of element sulfur,Li-S batteries tend to be next-generation commercial batteries.However,there still exist several challenging issues impeding the pratical application of Li-S batteries,including insulative nature of sulfur and discharge products,volume expansion during discharge and the shuttle effect.Focused on the issues above,we carry on two researches on the modification of commercial separator to improve performance of Li-S batteries as follows:1.The carboxylated Super P was prepared by acidification treatment of conductive carbon black.Then we fabricated double layered SP/f-SP modified separator to relieve existed issues in Li-S batteries.The negatively charged carboxy group on the face of f-SP can reject the diffusion of anionic polysulfide species due to the electrostatic interactions,while decline of conductivity results in the low utilization of active material.The conductive Super P coating with porous structure can accommodate soluble polysulfide by physical adsorbtion,thus improving the utilization of sulfur.For the sulfur cathodes with mass loading of 2 mg cm^-2,cells with modified separators display excellent charge and discharge performance.With the current rate of 0.2 C,the initial discharge capacity is promoted from945 mAh g^-11 to 1345 mAh g^-1 and delievers the capacity of 1045 mAh g^-11 after 100 cycles.Additionally,the average capacity decay rate is 0.056%during 600 cycles.2.We fabricated a rGO and molybdenum phosphide nanocrystal composite coating layer on Celgard separator to improve the electrochemical performance for Li-S batteries.Through the research on mechanism,the nanoscale MoP can trap polysulfides by strong chemical adsorbtion to restrain the diffusion of polysulfides;The rGO as conductive network facilitates the redoc reaction at the cathode surface.Hence,the interface contact resistance between cathode and separator can be reduced greatly.For the sulfur cathodes with high sulfur content?77%wt?and high mass loading(⁴ mg cm^-2),superior rate performance is obtained in cells with MoP/rGO coated separator.With the current rate of 0.5 C,the first discharge capacity is 880 mAh g^-1 and maintains 86.3%of the capacity after300 cycles.Moreover,the reversible capacity still reaches 570 mAh g^-11 at the current density of 2 C.In order to pursue for practical application,the pouch cell was further assembled with MoP/rGO coated separator.Apparently,the discharge capacity pouch cell decay from1083 mAh g^-1 to 759 mAh g^-1 after 120 cycles,...