Deep Eutectic Solvents as Electrolytes for Zn Batteries: Between Blocked Crystallization, Electrochemical Performance and Corrosion Issues

Deep eutectic solvents (DESs) are an emerging class of ionic liquids with high tunability and promise for battery applications. In this study, we investigated acetamide-based DESs for Zn batteries, focusing on a synergistic mixture of two known acetamide (Ace)-based DESs: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>Ace</mml:mi> <mml:mn>4</mml:mn></mml:msub> <mml:msub><mml:mi>ZnCl</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> <mml:annotation>${{\rm{Ace}}_{\rm{4}} {\rm{ZnCl}}_{\rm{2}} }$</mml:annotation> </mml:semantics> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>Ace</mml:mi> <mml:mn>4</mml:mn></mml:msub> <mml:msub><mml:mi>ZnTFSI</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> <mml:annotation>${{\rm{Ace}}_{\rm{4}} {\rm{ZnTFSI}}_{\rm{2}} }$</mml:annotation> </mml:semantics> </mml:math> . By combining these two DESs in various ratios, we aimed to enhance ionic conductivity and optimize electrochemical performance while addressing corrosion concerns. The resulting ternary mixtures exhibit superior ionic mobility, with the highest conductivity observed for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>Ace</mml:mi> <mml:mn>4</mml:mn></mml:msub> <mml:msub><mml:mrow><mml:mo>(</mml:mo> <mml:mi>ZnTFSI</mml:mi></mml:mrow> <mml:mn>2</mml:mn></mml:msub> <mml:msub><mml:mo>)​</mml:mo> <mml:mrow><mml:mn>0</mml:mn> <mml:mrow><mml:mo>.</mml:mo> <mml:mn>85</mml:mn></mml:mrow> </mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mo>(</mml:mo> <mml:mi>ZnCl</mml:mi></mml:mrow> <mml:mn>2</mml:mn></mml:msub> <mml:msub><mml:mo>)​</mml:mo> <mml:mrow><mml:mn>0</mml:mn> <mml:mrow><mml:mo>.</mml:mo> <mml:mn>15</mml:mn></mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> <mml:annotation>${{\rm{Ace}}_{\rm{4}} {\rm{(ZnTFSI}}_{\rm{2}} {\rm{)}}_{{\rm{0}}{\rm{.85}}} {\rm{(ZnCl}}_{\rm{2}} {\rm{)}}_{{\rm{0}}{\rm{.15}}} }$</mml:annotation> </mml:semantics> </mml:math> , which balances performance and stability. However, increased ionic mobility introduces crystallization challenges, limiting liquid-phase stability. Despite these challenges, the optimized DES mixture demonstrates excellent cycling performance with reduced overpotentials and acceptable corrosion levels, offering a viable pathway for scalable Zn battery applications.