Abstract
Conventional carbonate-based liquid electrolytes have safety issues related to their high flammability and easy leakage. Therefore, it is essential to develop alternative electrolytes for lithium-ion batteries (LIBs). As a potential candidate, solid-polymer electrolytes (SPEs) offer enhanced safety characteristics, while to be widely applied their performance still has to be improved. Here, we have prepared a series of UV-photocrosslinked flexible SPEs comprising poly(ethylene glycol) diacrylate (PEGDA), trimethylolpropane ethoxylate triacrylate (ETPTA), and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) salt, with the addition of polydimethylsiloxane with acrylated terminal groups (acryl-PDMS) to diminish the crystallinity of the poly(ethylene glycol) chain. Polysiloxanes have gained interest for the fabrication of SPEs due to their unique features, such as decrement of glass transition temperature (Tg), and the ability to improve flexibility and facilitate lithium-ion transport. Freestanding, transparent SPEs with excellent flexibility and mechanical properties were achieved without any supporting backbone, despite the high content of lithium salt, which was enabled by their networked structure, the presence of polar functional groups, and their amorphous structure. The highest ionic conductivity for the developed cross-linked SPEs was 1.75 × 10−6 S cm−1 at room temperature and 1.07 × 10−4 S cm−1 at 80 °C. The SPEs demonstrated stable Li plating/stripping ability and excellent compatibility toward metallic lithium, and exhibited high electrochemical stability in a wide range of potentials, which enables application in high-voltage lithium-ion batteries.
Highlights
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.In recent years, the development of rechargeable lithium-ion batteries (LIBs) with enhanced electrochemical performance and safety has gained exceptional importance due to the growing need for sustainable energy and power supply, the miniaturization of devices, and the rapid expansion of the portable electronics market [1,2,3]
The completeness of acrylation was confirmed by peaks of acrylic (C=C) and ester linkage bonds at 1633 cm−1 and 1708 cm−1, respectively, in the FTIR spectra of the product given in Figure 1b [31]
Crosslinked flexible polymer films were prepared by UV-irradiation of the polymer mixture, composed of a-PDMS, poly(ethylene glycol) diacrylate (PEGDA), and ETPTA with LiTFSI
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. There have been several works on polysiloxane containing SPEs, where they were combined with polyethers, PEO, plasticizers, and inorganic particles [18,25,26] In those systems ion conductivity improvement at ambient temperature led to poor dimensional stability and flexibility [27,28]. In this paper we developed free-standing solid polymer electrolytes, using a one step and simple method, which facilitated the development of flexible and mechanically durable all-solid-state LIBs. The cross-linked SPEs were developed by UVphotopolymerization of ethylene glycol units containing oligomers and poly(dimethylsiloxane) (PDMS) with modified terminal groups. The PDMS containing SPEs have improved ionic conductivity (~10−6 S cm−1), at lower temperature compared to conventional PEO based solid state electrolytes (10−8, ~10−7 S cm−1) [32], and demonstrate stable Li plating/stripping behavior and cycling stability toward metallic Li
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