Temperature Responsive Composite Gel-Polymer Electrolytes for Lithium-Sulfur Batteries

Abstract

Due to its high theoretical capacity of 1672 mAh g-1 and high energy density of 2600 Wh kg-1 sulfur is an attractive candidate as a cathode material for rechargeable lithium battery [1-2]. However, both LIBs and Li/S batteries rely on conventional liquid organic carbonate based electrolytes, which intrinsically has several critical drawbacks including volatility, flammability and potential leakage, which are triggering the safety issues [3]. Therefore, investigation for safer and more reliable electrolytes is urged, and polymer electrolytes are promising candidate in this regard. Poly(ethylene oxide)-based solid polymer electrolytes are common examples of a safe electrolyte. However, since they are limited by low ion conductivity at ambient temperature, the development of novel gel electrolytes, which entraps large amount of liquid electrolyte batteries attracts big interest. One of the major problems of sulfur cathode comes from solubility and shuttling phenomenon of the long chain lithium polysulfides in a conventional organic solvent based electrolyte, which causes a rapid irreversible loss of sulfur of the cathode over repeated cycles, and deposition of products of their transformation on the anode, leading to both electrodes degradation. In this work, we develop novel composite gel polymer electrolytes (GPEs) with high conductivity, high organic solvent uptake and high mechanical and thermal stability, which advantageously use the complementary properties of temperature-responsive polymer and ceramic filler. The composite GPEs are fabricated allowing for facile transport of Li+ ions but preventing leakage of electrolyte solution contained within the polymer membrane structure. Such GPEs have three unique features: electrolyte solution immobilization during battery cycling with rapid lithium ion transport, blocking of polysulfides shuttling phenomenon and battery shut down function in case of temperature increase. Furthermore, addition of functionalized natural and synthetic clay nanoparticles as ceramic filler allows overcoming the main problem of GPE – the loss of their mechanical strength when they are plasticized. We have combined polymers and temperature responsive polymers with Li-ion containing salt solutions. Among the inorganic layered hosts, montmorillonite and halloysite offer high aspect ratio, high cation exchange capacity, large specific surface area, appropriate interlayer charge. Undesired diffusion of polysulfide through electrolyte in Li/S batteries might be hindered in case of using composite GPE. A Li/S polymer cell containing a composite GPE has exhibited a good cycling performance with improved coulombic efficiency. The systems are under investigation with evaluation of polymer matrices and their ratio in the composite electrolyte.