A Poly(ethylene oxide)/Lithium bis(trifluoromethanesulfonyl)imide-Coated Polypropylene Membrane for a High-Loading Lithium–Sulfur Battery

• Main Authors: Li-Ling Chiu, Sheng-Heng Chung
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Polymers
• Subjects: lithium–sulfur battery; polysulfide; separator; gel polymer electrolyte; high active-material loading
• Online Access: https://www.mdpi.com/2073-4360/13/4/535

In lithium–sulfur cells, the dissolution and relocation of the liquid-state active material (polysulfides) lead to fast capacity fading and low Coulombic efficiency, resulting in poor long-term electrochemical stability. To solve this problem, we synthesize a composite using a gel polymer electrolyte and a separator as a functional membrane, coated with a layer of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The PEO/LiTFSI-coated polypropylene membrane slows the diffusion of polysulfides and stabilizes the liquid-state active material within the cathode region of the cell, while allowing smooth lithium-ion transfer. The lithium-sulfur cells with the developed membrane demonstrate a high charge-storage capacity of 1212 mA∙h g⁻¹, 981 mA∙h g⁻¹, and 637 mA∙h g⁻¹ at high sulfur loadings of 2 mg cm⁻², 4 mg cm⁻², and 6 mg cm⁻², respectively, and maintains a high reversible capacity of 534 mA∙h g⁻¹ after 200 cycles, proving its ability to block the irreversible diffusion of polysulfides and to maintain the stabilized polysulfides as the catholyte for improved electrochemical utilization and stability. As a comparison, reference and control cells fabricated using a PEO-coated polypropylene membrane and a regular separator, respectively, show a poor capacity of 662 mA∙h g⁻¹ and a short cycle life of 50 cycles.