Abstract
Solid single-ion conducting electrolytes based on well-defined block copolymers show great potential for use in lithium batteries. Here, we report on triblock copolymers with an ion conductive poly(ethylene oxide) (PEO) center block and two flanking blocks of poly(lithium 2,3,5,6–tetrafluorostyrene-4-trifluoromethanesulfonamide). The copolymers were prepared through atom transfer radical polymerization (ATRP) of pentafluorostyrene using a bidirectional PEO macroinitiator, followed by quantitative nucleophilic aromatic substitution of the p-fluorine atoms with sodium trifluoromethanesulfonamide. The ionic content of the copolymers was readily regulated by controlling the monomer feed ratio in the ATRP to obtain [EO]/[Li] between 4 and 88, and thermal decomposition occurred only above ~300 °C to indicate a high thermal stability. Above the melting point of the PEO center block, a copolymer containing 16 wt% of the flanking blocks ([EO]/[Li] = 40) reached a conductivity of 5.7·10-6 S cm-1 at 70 °C. The overall results indicate that well-designed polymers functionalized with lithium (N-perfluorophenyl)trifluoromethanesulfonamide groups show promise as solid single-ion conducting electrolytes. (Less)
Highlights
Solvent-free solid polymer electrolytes (SPEs) have during the past few decades been extensively studied as safe electrolyte materials for rechargeable lithium batteries
In the last two decades, many different types of single Li+-conducting SPEs have been reported.[15−23] The most extensively studied are di- and triblock copolymers containing poly(ethylene oxide) (PEO) blocks combined with the lithium salt of poly(styrene trifluoromethanesulfonimide) PSTFSILi, first demonstrated by Bouchet et al.[24−28] Variations include the replacement of the PEO center block with polymethacrylates bearing short EO side chains (PPEOMA),[26,29] replacement of the PSTFSILi block with polymethacrylates bearing aliphatic trifluoromethanesulfonimide side chains (PTFSIMALi),[30] and use of a polymethacrylate backbone instead of a polystyrene one, for example, PPEOMA-b-PTFSIMALi.[31]
Four PEOTfnPPFSLiy single-ion conducting BAB triblock copolymers with different values of y, that is, with different block lengths and [EO]/[Li] ratios were prepared in accordance with Scheme 1
Summary
Solvent-free solid polymer electrolytes (SPEs) have during the past few decades been extensively studied as safe electrolyte materials for rechargeable lithium batteries. ACS Applied Energy Materials was attributed to the lower glass transition temperature of PTFSIMALi compared to PSTFSILi. In a previous work, we prepared triblock copolymers consisting of a PEO center block and two end blocks of the lithium salt of poly(2,3,5,6-tetrafluorostyrene-4-sulfonate) sPPFSLi.[33] Here, we report on the synthesis of single-ion conducting block copolymer SPEs with high Li+ conductivity functionalized with a lithium (N-perfluorophenyl)trifluoromethanesulfonamide [LiN(Pfp)(Tf)] salt. We prepared triblock copolymers consisting of a PEO center block and two end blocks of the lithium salt of poly(2,3,5,6-tetrafluorostyrene-4-sulfonate) sPPFSLi.[33] Here, we report on the synthesis of single-ion conducting block copolymer SPEs with high Li+ conductivity functionalized with a lithium (N-perfluorophenyl)trifluoromethanesulfonamide [LiN(Pfp)(Tf)] salt This salt has previously been prepared and electrochemically characterized by Huber and co-workers.[34] Both the electrochemical stability and ionic conductivity of LiN(Pfp)(Tf) solutions (0.1 M) in an ethylene carbonate:dimethyl carbonate (1:3 w/w) mixture were slightly lower than those of a corresponding LiTFSI solution but still sufficiently high for applications involving lithium-ion batteries. Preparation of PEO-TfnPPFSLiy Copolymers by Synthesis of the Br-PEO-Br Macroinitiator, ATRP of PFS, and Substitution Using Sodium trifluoromethanesulfonamidea
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