Design Of The Aqueous Slurry Composed Of Conductive Additive And Polymer Binder For High-sulfur-loading Lithium-sulfur Batteries

Lithium-sulfur(Li-S)battery is a promising candidate for next-generation high-energy-density batteries due to its high specific energy density of 2600 Wh kg-1.As the cathode material of Li-S battery,sulfur is environmental friendly,low cost and abundant.However,the cathodes of Li-S batteries also face some challenges.Firstly,the poor conductivities of elemental sulfur and Li2S/Li2S2 reduce the utilization of active materials,leading to low charge/discharge capacities.Secondly,the volume change of sulfur during the charge/discharge processes can reach 80%,which is harmful to the structural integrity of sulfur cathodes.Finally,lithium poly sulfide intermediates produced during the charge/discharge processes are soluble in the electrolyte and can shuttle between cathode and anode,resulting in the rapid capacity decay of cathodes.Until now,the capacity and cycling stability and the sulfur loading of sulfur cathodes are usually improved by synthesizing sulfur host materials,constructing self-supporting electrode structures,and designing polymer binders.Unfortunately,due to the complex processing technology and high cost,these strategies are difficult to meet the requirements of practical application.How to develop high-performance,high-sulfur-loading cathodes based on commercially available materials and traditional slurry-coating procedure is highly desired but remains a big challenge.To solve this problem,aqueous slurry consists of commercial conductive agent and polymer binder is developed in this thesis to construct high-sulfur-loading slurry-coated cathodes.The main research contents of this thesis are as follows:(1)Based on the exploration of the cathode slurry-making process,an aqueous slurry composed of conductive additive and polymer binder was prepared using the polymer binder LA133 and a variety of commercial carbon materials.Then the influences of different carbon materials and slurry-making processes on the structural parameters and electrochemical properties of sulfur cathodes were explored.This aqueous slurry can both improve the areal sulfur loading and electrochemical properties of sulfur cathodes.By using the developed aqueous slurry,the Super-P/S cathode with 4 mg cm-2 of sulfur exhibited a specific discharge capacity of 775 mAh g’1 after 50 cycles at 0.2 C.(2)Based on the carboxy-rich polyacrylic acid and the hydroxy-rich xanthan gum,a modified aqueous slurry was further prepared using conductive additive and a functional two-component binder.This binder not only can increase the areal sulfur loading by its intermolecular interaction,but also has a high polysulfide-adsorption capability.The modified aqueous slurry has good applicability to diverse sulfur host materials to fabricate large-size high-sulfur-loading cathodes(>5 mg cm-2).Both the coin cells and pouch cells showed that the modified aqueous slurry can significantly improve the specific capacities and cycling stabilities of high-sulfur-loading cathodes.The super-P/S cathode with 10.5 mg cm-2 of sulfur delivered a high areal capacity of 10.17 mAh cm-2 after 50 cycles at 1 mA cm-2.