Composite gel-polymer electrolyte for high-loading polysulfide cathodes

Abstract

Lithium–sulfur batteries with a high-capacity cathode and high cell energy density have been regarded as next-generation energy-storage systems because of their suitability for high-energy-density devices with a low cost. However, the intermediate lithium polysulfides easily dissolve in liquid electrolytes and irreversibly diffuse from the cathode. In this study, we develop a high-loading polysulfide cathode featuring a polymethyl methacrylate (PMMA)-based gel-polymer electrolyte (GPE). The PMMA-based GPE inhibits the diffusion of liquid polysulfides by the strong chemical bonding between the carbonyl groups of the GPE and lithium sulfides, while offering high lithium-ion transfer for the high-loading cathode to attain outstanding electrochemical performance. Moreover, to investigate and increase the lithium-ion conductivity of the GPE, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is mixed with PMMA at five concentrations. Material and electrochemical analyses reveal that under a high sulfur loading of 4 mg cm⁻², the cell with the PMMA-based GPE containing 90 wt% PMMA and 10 wt% LiTFSI exhibits the lowest impedance and highest electrochemical utilization and stability. In addition, the PMMA-based GPE allows the cell to attain higher sulfur loadings (8 and 10 mg cm⁻²), while exhibiting a high areal capacity of 7.1 mA h cm⁻² and a high energy density of 15 mW h cm⁻². Therefore, the PMMA-based GPE enhances the electrochemical stability and improves the efficiency and safety of the high-loading polysulfide cathode, which are the key factors for high-energy-density lithium–sulfur cells.