ABSTRACT
The preparation of solid polymer electrolytes (SPEs) using poly(ethylene oxide) (PEO) typically involves incorporating fillers or undergoing chemical modifications to reduce crystallinity and enhance conductivity. PEO with a lower molecular weight, known as polyethylene glycol (PEG), exhibits higher conductivity, despite weaker mechanical strength. It is commonly employed as a plasticizer to improve the conductivity of SPEs or to fabricate PEG-based gel polymer electrolytes (GPEs). In this study, we use a straightforward approach to create innovative SPEs by blending liquid polymer electrolytes (LPEs), particularly low-molecular-weight polyethylene glycol (PEG), with a molecular weight of 400 g/mol, and sustainable poly(l-lactide) (PLLA). Solid PEG/PLLA forms are achieved by introducing 30 wt % of PLLA. Subsequently, the addition of lithium salts results in the development of novel PEG/PLLA SPEs. Another focal point of this study involves incorporating 1,3:2,4-dibenzylidene sorbitol (DBS) into these PEG/PLLA systems. DBS, an organic gelator derived from natural sugars, demonstrates self-assembly, leading to the formation of a nanofibrillar network structure. Leveraging DBS's ability to form organogels in liquid organic environments, we facilitate the transformation of low PLLA content LPEs into innovative solvent-free GPEs. Our prepared PEG/PLLA SPEs exhibited a maximum conductivity value of 4.39 × 10-5 S/cm, approximately five times higher than that of neat PEG (10000 g/mol) SPEs. The ionic conductivity exhibited a declining trend as the content of PLLA and DBS increased. However, there was an improvement in electrochemical stability. Furthermore, the incorporation of PLLA and DBS into electrolytes contributed to enhanced mechanical support and stability within the electrolyte layer. This, in turn, mitigated capacity decay and improved the cycling performance of assembled lithium-ion cells.
ABSTRACT
The effects of hydrophobicity of monomers on the structures and properties of 1,3:2,4-dibenzylidene-D-sorbitol (DBS) organogels and nanostructured polymers prepared by templating the self-assembled organogels were investigated in this study. Hydrophobic styrene (St), hydrophilic methyl (methacrylate) (MMA), and their mixtures were chosen as the monomers. Though the gelation time varied, the average diameters (around 10 nm) of DBS nanofibrils found in the resulting organogels did not change significantly, for monomers of different hydrophobicity, as observed by transmission electron microscopy (TEM). Nonetheless, new structures, DBS microaggregates, appeared when the MMA content in the monomers was high enough. These irregular, micrometer-sized DBS structures (microaggregates) may have formed because the aggregated DBS molecules were influenced by the MMA monomers, due to the hydrogen bonding between DBS and MMA. This was confirmed by Fourier transform infrared (FTIR) spectroscopy and could also explain the differences in the gelation time of the DBS organogels: gels form more slowly in MMA than in St because of the competing interaction, hydrogen bonding, between DBS and MMA. Subsequently, we thermally initiated the free-radical polymerization of these St/MMA co-monomers. PS/PMMA copolymers were obtained, and no macroscopic phase separation occurred after the polymerization. Finally, the porous structures of the polymers produced by the solvent extraction of the DBS templates were observed, using TEM.
