The use of gel polymer electrolytes (GPEs) is of great interest to build high-performing rechargeable lithium metal batteries (LMBs) owing to the combination of good electrochemical properties and improved safety. Herein, we report a facile and scalable one-pot preparation method of a GPE based on highly safe polyethylene glycol dimethyl ether (PEGDME) plasticizer in a poly­(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) polymer matrix. The prepared GPE exhibits excellent safety (nonflammability and thermal stability up to 250 °C) and outstanding electrochemical properties at room temperature (high ionic conductivity of 3.4 × 10–4 S cm–1 and high lithium transference number). Moreover, high loading LiFePO4 (6–7 mg cm–2) LMB using such GPE delivers a good C-rate response and high capacity (ca. 1 mAh cm–2 at C/10) with an excellent retention of 98% after 60 cycles in coin cell configuration. Notably, the prototype pouch cell (ca. 19 mAh at C/10) provides remarkable safety, mechanical flexibility, and strong tolerance toward bending and cutting. These results suggest that the prepared GPE is a promising candidate for the development of high performance, flexible, and safe LMBs that operate at room temperature, as well as for other energy storage systems beyond lithium-ion technologies.

Li-S batteries, as the most promising post Li-ion technology, have been intensively investigated for more than a decade. Although most previous studies have focused on liquid systems, solid electrolytes, particularly all-solidstate polymer electrolytes (ASSPEs) and quasi-solid-state polymer electrolyte (QSSPEs), are appealing for Li-S cells due to their excellent flexibility and mechanical stability. Such Li-S batteries not only provide significantly improved safety but are also expected to augment the all-inclusive energy density compared to liquid systems. Therefore, this perspective briefly summarizes the recent progress on polymer-based solid-state Li-S batteries, with a special focus on electrolytes, including ASSPEs and QSSPEs. Furthermore, future work is proposed based on the existing development and current challenges.

Lithium−sulfur batteries are attracting extensive attention for energy storage owing to their high theoretical energy density. However, their practical implementation is hindered because of inherent issues of the technology such as the shuttling effect of the polysulfide intermediates and the formation of dendritic lithium metal (Li 0 ) deposits during battery operation leading to the short cycle life of the cell. It is generally accepted that the formation of robust solid electrolyte interphase (SEI) layers on the surface of the Li 0 anode is an effective way to mitigate these issues. Herein, the use of salt additives, lithium (difluoromethanesulfonyl)-LiDFTFSI} and lithium tricyanomethanide [LiC(CN) 3 , LiTCM], added to the classical solid polymer electrolyte (SPE) comprising lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and poly(ethylene oxide) (PEO) is proposed, with the aim to improve the quality of the SEI layer on the Li 0 anode. Through this approach, SEI layers with good mechanical integrity and Li-ion conductivity are formed thanks to the beneficial anion chemistry of these salt additives, allowing the PEO-based all-solid-state lithium−sulfur cells to be cycled for more than 100 cycles with good rate capability and Coulombic efficiency. These results attest to the great importance of electrolyte additives, even at small doses, to improve the battery performance through the selective modification of SEI components.

Introducing a small dose of an electrolyte additive into solid polymer electrolytes (SPEs) is an appealing strategy for improving the quality of the solid–electrolyte–interphase (SEI) layer formed on the lithium metal (Li°) anode, thereby extending the cycling life of solid-state lithium metal batteries (SSLMBs). In this work, we report a new type of SPEs comprising a low-cost, fluorine-free salt, lithium tricyanomethanide, as the main conducting salt and a fluorinated salt, lithium bis­(fluorosulfonyl)­imide (LiFSI), as the electrolyte additive for enhancing the performance of SPE-based SSLMBs. Our results demonstrate that a homogeneous and stable SEI layer is readily formed on the surface of the Li° electrode through the preferential reductive decomposition of LiFSI, and consequently, the cycle stabilities of Li°||Li° and Li°||LiFePO4 cells are significantly improved after the incorporation of LiFSI as an additive. The intriguing chemistry of the salt anion revealed in this work may expedite the large-scale implementation of SSLMBs in the near future.