Abstract
Lithium batteries are in high demand in different technological fields. However, the operating temperature is required to be below 70 °C, and this limits their use in applications demanding high-energy rechargeable batteries that are able to operate at temperatures above 100 °C. Poly(ethylene oxide) (PEO) is, currently, the reference solid polymer electrolyte (SPE) employed in solid-state lithium batteries. However, the application of PEO at higher temperatures is restricted due to the loss of mechanical properties. In this article, we show that the polymer blending strategy of blending PEO with poly(l,l-lactide) (PLA) allows extending its use in batteries at high temperatures (100 °C). This improvement is due to the mechanical reinforcement of PEO solid electrolytes associated with the presence of PLA crystals. Thus, two solid electrolyte systems based on PEO/PLA blends with either a LiTFSI salt or a lithium single-ion polymer (poly(lithium-1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl)imide), PLiMTFSI) were investigated and compared. Differential scanning calorimetry (DSC) results indicate that regardless of the concentration of LiTFSI or PLiMTFSI in the blend, crystals of PLA are present with melting peaks at 160–170 °C and the lithium salt distributes preferentially in the PEO-rich amorphous phases. The ionic conductivity is negatively affected by the incorporation of PLA in the blends. However, at high temperatures (>70 °C), ionic conductivities of ∼10–4 S cm–1 were obtained for both systems. DMTA results showed that PLA addition increases the mechanical properties of the electrolytes, yielding storage modulus values of ∼106 Pa for the PEO/PLA/LiTFSI blend and ∼107 Pa or higher for the PEO/PLA/PLiMTFSI blend at high temperatures (100 °C). Finally, both ternary blends were compared in a symmetrical lithium battery at 100 °C, and the single-ion conducting PEO/PLA/PLiMTFSI system presented lower overpotentials, which is reflected in a lower polarization inside the lithium battery.
Highlights
Developing safe, high-specific-capacity energy storage devices is a challenge
DMTA results showed that PLA addition increases the mechanical properties of the electrolytes, yielding storage modulus values of ∼106 Pa for the Poly(ethylene oxide) (PEO)/PLA/ lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) blend and ∼107 Pa or higher for the PEO/PLA/PLiMTFSI blend at high temperatures (100 °C). Both ternary blends were compared in a symmetrical lithium battery at 100 °C, and the single-ion conducting PEO/PLA/PLiMTFSI system presented lower overpotentials, which is reflected in a lower polarization inside the lithium battery
New solid polymer electrolytes were designed by polymer blending of a high Tm PLA into conducting PEO for high-temperature lithium batteries
Summary
Developing safe, high-specific-capacity energy storage devices is a challenge. Lithium batteries are the best choice in energy storage devices from the point of view of energy density and durability. PLA is a widely used biobased semicrystalline polymer characterized by its good mechanical properties, biodegradability, and biocompatibility.[18] the advantages of PEO/PLA blends are that in addition to improving the mechanical properties of the electrolyte, certain electrochemical properties, such as lithium-ion transference number and electrochemical stability, can be improved This makes it a suitable material for applications in different areas, such as chemical engineering, medical equipment, electronic devices, and industrial packaging. The second system is a ternary blend in which poly(lithium-1-[3-(methacryloyloxy)propylsulfonyl]-1(trifluoromethanesulfonyl)imide) (PLiMTFSI) is used as a lithium single-ion conducting polymer since the development of single-ion polymer electrolytes has advantages in that there is no polarization within the cell, as well as the lithium-ion transport number is close to unity.[22,23] The ionic conductivity and mechanical properties of these ternary blends were evaluated Their performance as solid polymer electrolytes in a symmetrical lithium battery at a high temperature was evaluated (i.e., 100 °C). 60 PEO 40 PLA 0 wt % LiTFSI 60 PEO 40 PLA 5 wt % LiTFSI 60 PEO 40 PLA 10 wt % LiTFSI 60 PEO 40 PLA 15 wt % LiTFSI 60 PEO 40 PLA 30 wt % LiTFSI 50 PEO 50 PLiMTFSI 0 wt % PLA 50 PEO 50 PLiMTFSI 5 wt % PLA 50 PEO 50 PLiMTFSI 10 wt % PLA 50 PEO 50 PLiMTFSI 15 wt % PLA 50 PEO 50 PLiMTFSI 20 wt % PLA 50 PEO 50 PLiMTFSI 30 wt % PLA
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