2025 AIChE Annual Meeting
(413b) Molecular Design of Eutectic Electrolytes for Aqueous Lithium- and Zinc-Ion Batteries
Aqueous batteries offer intrinsic safety and cost-effectiveness, making them attractive for next-generation energy storage systems. However, their widespread adoption is hindered by the narrow electrochemical stability window (ESW) of water (~1.23 V), which leads to parasitic reactions such as hydrogen evolution, oxygen evolution, and poor interfacial stability. To overcome this challenge, we have developed a series of eutectic electrolyte systems with tailored solvation structures to suppress water reactivity and enhance the stability of both aqueous lithium-ion and zinc-ion batteries. Our previous work introduced a ternary eutectic system composed of LiTFSI, water, and acetamide, which successfully expanded the ESW to ~5.1 V. Molecular dynamics (MD) simulations revealed strong interaction between Li-TFSI and weakened H2O-H2O network in ternary eutectic solvent. Also, the electrolyte confines water within the Li⁺ solvation shell, disrupting the hydrogen bond network and limiting free water activity. By intentionally extending the operating voltage to promote SEI formation, a dense LiF-rich interphase was formed, suppressing water decomposition and enabling 76% capacity retention over 1000 cycles. DFT simulation showed that water can be de-solvate with a low energy barrier and decomposed into OH- on the LTO surface. The OH- then attacks TFSI, leading
to the formation of a LiF rich SEI layer. A thick LiF SEI layer has a larger electron tunneling barrier, which prevents water reactions. Building on this, we designed a quaternary eutectic system by introducing caprolactam, a cyclic amide with low dielectric constant and large steric hindrance. MD and DFT calculations showed that caprolactam preferentially locates outside the primary solvation shell, where it forms hydrogen bonds with free water molecules while minimizing its interaction with Li⁺. This spatial arrangement effectively restricts water diffusion to the electrode interface, reducing hydrogen evolution reaction (HER) activity. Also, for aqueous Zn-ion batteries, we developed a novel ZnSO₄-based eutectic electrolyte incorporating L-asparagine monohydrate (L-ASPA). The introduction of L-ASPA leads to a reduced desolvation energy barrier for Zn²⁺ during cycling, which facilitates more reversible plating/stripping behavior. RDF and desolvation energy calculations show decreased water content in the primary solvation shell, correlating with enhanced stability and suppressed side reactions. These findings demonstrate a generalizable solvation engineering strategy through eutectic design, offering promising routes to overcome long-standing challenges in aqueous battery systems.
to the formation of a LiF rich SEI layer. A thick LiF SEI layer has a larger electron tunneling barrier, which prevents water reactions. Building on this, we designed a quaternary eutectic system by introducing caprolactam, a cyclic amide with low dielectric constant and large steric hindrance. MD and DFT calculations showed that caprolactam preferentially locates outside the primary solvation shell, where it forms hydrogen bonds with free water molecules while minimizing its interaction with Li⁺. This spatial arrangement effectively restricts water diffusion to the electrode interface, reducing hydrogen evolution reaction (HER) activity. Also, for aqueous Zn-ion batteries, we developed a novel ZnSO₄-based eutectic electrolyte incorporating L-asparagine monohydrate (L-ASPA). The introduction of L-ASPA leads to a reduced desolvation energy barrier for Zn²⁺ during cycling, which facilitates more reversible plating/stripping behavior. RDF and desolvation energy calculations show decreased water content in the primary solvation shell, correlating with enhanced stability and suppressed side reactions. These findings demonstrate a generalizable solvation engineering strategy through eutectic design, offering promising routes to overcome long-standing challenges in aqueous battery systems.