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Summary With an extremely high theoretical energy density, solid-state lithium-sulfur (Li-S) batteries (SSLSBs) are emerging as one of the most feasible chemistries; however, their energy efficiency and long-term cyclability are severely hampered by the lithium metal (Li°) dendrite formation during repeated discharge/charge cycles and the shuttling of aggressive polysulfide intermediates between two electrodes. Herein, we report (difluoromethanesulfonyl) (trifluoromethanesulfonyl)imide anion [N(SO2CF2H)(SO2CF3)]−, hereafter DFTFSI−, as a designer anion for high-performance polymer-based SSLSBs. In contrast to the widely used bis(trifluoromethanesulfonyl)imide anion [N(SO2CF3)2]− (TFSI−), DFTFSI-based SSLSBs provide superior interfacial stability against Li°, extremely high discharge and areal capacities, very high Coulombic efficiency, and long-term cyclability, surpassing the reported literature values, in terms of gravimetric energy density. This work opens a new door for accelerating the practical deployment of SSLSBs in the future.

The anion chemistry of lithium salts plays a pivotal role in dictating the physicochemical and electrochemical performance of solid polymer electrolytes (SPEs), thus affecting the cyclability of all-solid-state lithium metal batteries (ASSLMBs). The bis(trifluoromethanesulfonyl)imide anion (TFSI- ) has long been studied as the most promising candidate for SPEs; however, the Li-ion conductivities of the TFSI-based SPEs still remain low (Li-ion transference number: ca. 0.2). In this work, we report new hydrogen-containing anions, conceived based on theoretical considerations, as an electrolyte salt for SPEs. SPEs comprising hydrogen-containing anions achieve higher Li-ion conductivities than TFSI-based ones, and those anions are electrochemically stable for various kinds of ASSLMBs (Li-LiFePO4 , Li-S, and Li-O2 batteries). This opens up a new avenue for designing safe and high-performance ASSLMBs in the future.

Inverse vulcanization copolymers (p(S-DVB)) from the radical polymerization of elemental sulfur and divinylbenzene (DVB) have been studied as cathode active materials in poly(ethylene oxide) (PEO)-based all-solid-state Li-S cells. The Li-S cell comprising the optimized p(S-DVB) cathode (80:20 w/w S/DVB ratio) and lithium bis(fluorosulfonyl)imide/PEO (LiFSI/PEO) electrolyte shows high specific capacity (ca. 800 mAh g −1 ) and high Coulombic efficiency for 50 cycles. Most importantly, polysulfide (PS) shuttle is highly mitigated due to the strong interactions of PS species with polymer backbone in p(S-DVB). This is demonstrated by the stable cycling of the p(S-DVB)-based cell using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/PEO electrolyte, where successful charging cannot be achieved even at the first cycle with plain elemental S-based cathode material due to the severe PS shuttle phenomenon. These results suggest that inverse vulcanization copolymers are promising alternatives to elemental sulfur for enhancing the electrochemical performance of PEO-based all-solid-state Li-S cells.

Nanocomposite solid polymer electrolytes (NSPEs) comprising lithium salt based on two representative sulfonylimide anions (i.e., bis(fluorosulfonyl)imide ([N(SO2F)2]−, FSI−) and bis(trifluoromethanesulfonyl)imide ([N(SO2CF3)2]−, TFSI−)) have been prepared by simply dissolving the corresponding lithium salt in poly(ethylene oxide) matrix in the presence of inert nano-sized Al2O3 fillers. The physicochemical and electrochemical properties of the FSI- and TFSI-based NSPEs are investigated, in terms of phase transition, ion transport behavior, chemical and electrochemical compatibility with Li metal. With the addition of nano-sized Al2O3 fillers, a significant improvement in chemical and electrochemical compatibility with Li metal has been observed in both the FSI- and TFSI-based NSPEs. Particularly, the symmetric cell using the FSI-based NSPE can be continuously cycled for > 1000 h at 70 °C. The Li | LiFePO4 cell with the FSI-based NSPEs shows good cycling stability and capacity retention. These promising results make them attractive electrolytes for safe and stable rechargeable Li metal batteries.

New synthesis route of polysalt with single ion conductivity based on functionalization of polyacrylic acid is reported for all solid state lithium metal batteries. Poly[(trifluoromethyl)sulfonyl acrylamide] PA–LiTFSI was synthesized in two steps reaction. The degree of functionalization of the polymer backbone by anion of lithium salt bis(trifluoromethane)sulfonimide (LiTFSI) was confirmed by ICP analysis. An ionic conductivity equal 1,77 10 −5 S cm −1 at 80 °C of polysalt blended with PEO is reported. Easy process-able polysalt blended with PEO exhibits good mechanical properties and high transference number.

Driven by the growing demand in energy and the challenge of finding new green energy sources to replace the excessively used fossil fuels, electrochemical energy storage arises as the key alternative to meet the needs of current society. Among all the available electrochemical storage devices, lithium-ion batteries (LIBs) have been extensively investigated as the most suitable choice. Besides, there has been an increasing interest in the research of rechargeable lithium metal batteries (LMBs), where a higher energy density can be achieved compared to the state of art LIBs technologies, due to the high specific capacity provided by lithium metal electrode. As one of the most critical components, the choice of the electrolyte is very important for preparing safe and high performance LMBs. Most of the commercial batteries are built up with liquid electrolytes based on lithium salts and organic solvents. However, safety concerns such as volatilization, flammability and explosion has tipped the scale in favor of the search of solvent-free solid electrolytes, for which solid polymer electrolytes (SPEs) emerge as one of the most promising choices. In addition to the excellent flexibility, ease of processing and low cost, SPEs can mitigate the Li dendrite growth that takes place in conventional liquid electrolytes, attenuate the interfacial resistance, and improve the electrode-electrolyte compatibility compared to their inorganic solid electrolytes counterparts. Nevertheless, the low Li-ion conductivity, several orders of magnitude lower than those of the conventional liquid electrolytes, remains as the major hindrance towards the practical deployment of all solid-state lithium polymer batteries (ASSLPBs).1,2 Moreover, SPEs are usually characterized by a low lithium-ion transference number (T Li + < 0.5) and consequently are more susceptible to polarization phenomena that eventually limit the power density and cycle life of ASSLPBs.3 Thus, studies on new polymer electrolytes is urgent to improve the performance of ASSLPBs and meet the market requirements. Inspired by these challenges, in this presentation the performance of new flexible and highly conductive SPEs is provided. Furthermore, the role of different additives on the performance of novel single lithium-ion conducting solid polymer electrolytes (SLIC-SPEs) is elucidated. References: Mauger, A., Armand, M., Julien, C. M. & Zaghib, K. Challenges and issues facing lithium metal for solid-state rechargeable batteries. J. Power Sources 353, 333–342 (2017). Fan, L., Wei, S., Li, S., Li, Q. & Lu, Y. Recent Progress of the Solid-State Electrolytes for High-Energy Metal-Based Batteries. Adv. Energy Mater. 1702657, 1702657 (2018). Zhang, H. et al. Single lithium-ion conducting solid polymer electrolytes: advances and perspectives. Chem. Soc. Rev. 46, 797–815 (2017).