Tailoring multifunctional properties of epoxy-based structural polymer electrolytes by dual curing process.
Topic(s) : Multifunctional and smart composites
Co-authors :
Luiz ACAUAN (UNITED STATES), Marianna ROGERS (UNITED STATES), Armando Neto (UNITED STATES), Jen-Hung FANG , Brian L. WARDLEAbstract :
Structural polymer electrolytes (SPEs) that combine considerable load-bearing mechanical properties and high ionic conductivities are required for multifunctional energy storage devices, which aim to obtain a net weight and volume savings compared to the use of independent monofunctional materials. This concept is highly attractive for a broad range of applications, such as mobile energy storage in portable electronics, hybrid electric vehicles and unmanned aerial vehicles, where weight savings is vital. Such devices can include batteries, fuel cells, and supercapacitors; all requiring multifunctional matrices that can address the conflicting requirements of enabling an ionic path while bearing mechanical load.
SPEs generally fit into three categories: (1) polymers with intrinsic ionic conductivity (e.g. p(VDF-HFP)[1]), (2) a blend of a structural polymer with an ionic medium (e.g. epoxy with ionic liquid[2]) or (3) a “mixture” of (1) and (2), (e.g. copolymers[3]). Literature has shown that the second case normally achieves the best compromise between mechanical properties and ionic conductivity, as long as the two bicontinuous phases (structural and ionic conductive) are highly interpenetrated[4].
In this work, we used EPON 862 (epoxy resin) with Epikure W (hardener) as the structural phase (50%w) and a 1M solution of bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) as the ionic conductive phase (50%w). By reducing the ratio of hardener/epoxy resin (relatively to recommended amount, stated here as 100% of W), we could tailor the ionic conductivity and young modulus (E) of the SPE system. Even with no hardener (0% of W), the SPE yielded a E = 73MPa (similar to polymer electrolytes blended with the same ratio of ionic liquid[5]) which is achievable via lithium salt-catalyzed epoxide ring opening polymerization[6]. When hardener is added to the system at ratios lower then 100% of W, a dual curing process is induced, both by the lithium salt and the aromatic amine from the hardener. At the ratio of 33% of W, the SPE achieved an ionic conductivity of 7.9x10-3 mS/cm and a E of 1.65GPa, twice the E of MVR444 (one the best epoxy/ionic liquid systems in literature[4]), with also higher ionic conductivity. Moreover, no clear interface was visualized between structural and ionic conductive phases by scanning electron microscopy, indicating presence of a highly interpenetrate bicontinuous phase at the nanoscale or even a single continuous phase.
References:
[1]B. Mapleback et al, Nanomaterials 12 (2022) 2558.
[2]N. Shirshovaet et al, J. Mater. Chem. A 1 (2013) 15300.
[3]J. Choiet et al, Mater. Today Chem. 23 (2022) 100663.
[4]Y. Xuet et al, Compos. Sci. Technol. 204 (2021)
[5]J.C. Jansenet et al, Sep. Purif. Technol. 109 (2013) 87–97.
[6]G. Foranet et al, Appl. Sci. 11 (2021) 1561.
SPEs generally fit into three categories: (1) polymers with intrinsic ionic conductivity (e.g. p(VDF-HFP)[1]), (2) a blend of a structural polymer with an ionic medium (e.g. epoxy with ionic liquid[2]) or (3) a “mixture” of (1) and (2), (e.g. copolymers[3]). Literature has shown that the second case normally achieves the best compromise between mechanical properties and ionic conductivity, as long as the two bicontinuous phases (structural and ionic conductive) are highly interpenetrated[4].
In this work, we used EPON 862 (epoxy resin) with Epikure W (hardener) as the structural phase (50%w) and a 1M solution of bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) as the ionic conductive phase (50%w). By reducing the ratio of hardener/epoxy resin (relatively to recommended amount, stated here as 100% of W), we could tailor the ionic conductivity and young modulus (E) of the SPE system. Even with no hardener (0% of W), the SPE yielded a E = 73MPa (similar to polymer electrolytes blended with the same ratio of ionic liquid[5]) which is achievable via lithium salt-catalyzed epoxide ring opening polymerization[6]. When hardener is added to the system at ratios lower then 100% of W, a dual curing process is induced, both by the lithium salt and the aromatic amine from the hardener. At the ratio of 33% of W, the SPE achieved an ionic conductivity of 7.9x10-3 mS/cm and a E of 1.65GPa, twice the E of MVR444 (one the best epoxy/ionic liquid systems in literature[4]), with also higher ionic conductivity. Moreover, no clear interface was visualized between structural and ionic conductive phases by scanning electron microscopy, indicating presence of a highly interpenetrate bicontinuous phase at the nanoscale or even a single continuous phase.
References:
[1]B. Mapleback et al, Nanomaterials 12 (2022) 2558.
[2]N. Shirshovaet et al, J. Mater. Chem. A 1 (2013) 15300.
[3]J. Choiet et al, Mater. Today Chem. 23 (2022) 100663.
[4]Y. Xuet et al, Compos. Sci. Technol. 204 (2021)
[5]J.C. Jansenet et al, Sep. Purif. Technol. 109 (2013) 87–97.
[6]G. Foranet et al, Appl. Sci. 11 (2021) 1561.