Abstract
Poly(ethylene oxide) (PEO) is the most widely used polymer in the field of solid polymer electrolytes for batteries. It is well known that the crystallinity of polymer electrolytes strongly affects the ionic conductivity and its electrochemical performance. Nowadays, alternatives to PEO are actively researched in the battery community, showing higher ionic conductivity, electrochemical window, or working temperature range. In this work, we investigated polymer electrolytes based on aliphatic polyethers with a number of methylene units ranging from 2 to 12. Thus, the effect of the lithium bis(trifluoromethanesulfone) imide (LiTFSI) concentration on the crystallization behavior of the new aliphatic polyethers and their ionic conductivity was investigated. In all the cases, the degree of crystallinity and the overall crystallization rate of the polymers decreased drastically with 30 wt % LiTFSI addition. The salt acted as a low molecular diluent to the polyethers according to the expectation of the Flory–Huggins theory for polymer–diluent mixtures. By fitting our results to this theory, the value of the interaction energy density (B) between the polyether and the LiTFSI was calculated, and we show that the value of B must be small to obtain high ionic conductivity electrolytes.
Highlights
Dry solid polymer electrolytes (SPEs) have attracted great attention as safe alternatives to liquid electrolytes in different energy storage technologies, such as lithium batteries for electric vehicles [1,2,3].SPEs are formed by complexing an ionic salt within a polymer matrix
Similar results were obtained for SPE-P5 samples, except for the sample with wt lithium bis(trifluoromethanesulfone) imide (LiTFSI), exhibited a larger value than expected. Apart from this particular sample, all the rest behavedwhich as exhibited a larger value than expected. Apart from this particular sample, all the rest behaved expected and the results indicate that the overall crystallization kinetics of these polyethers was as expected and the results indicate that the overall crystallization kinetics of thesethis polyethers was substantially depressed by the incorporation of LiTFSI
The LiTFSI salt acts as a diluent for all the aliphatic polyethers, reducing the crystallization rate and crystallization temperature
Summary
Dry solid polymer electrolytes (SPEs) have attracted great attention as safe alternatives to liquid electrolytes in different energy storage technologies, such as lithium batteries for electric vehicles [1,2,3]. SPEs are formed by complexing an ionic salt within a polymer matrix. Several polymers and salts have been evaluated as SPEs, such as poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), poly(methyl methacrylate) (PMMA), poly(ε-caprolactone) (PCL), polycarbonates (PC), chitosan (CS), poly(vinylpyrrolidone) (PVP), poly(vinyl chloride) (PVC), poly(vinylidene fluoride) (PVDF), and poly(ionic liquid)s [5,6], among other polymers. Different lithium salts have been employed, such as. LiTFSI has been widely employed as its low lattice energy favors salt dissolution and dissociation, leading to enhanced ionic conductivity [8]
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