“Duet‐Insurance” Eutectic Electrolytes for Zinc‐Ion Capacitor Pouch Cells

Abstract

Eutectic electrolytes are emerging to be explored to meet the high demand for aqueous zinc-ion capacitors (AZICs) due to their high electrochemical stability and environmental-friendly feature. Notably, a large-scale requirement for a practical AZIC has been addressed to balance decent performance and increase package size. Thus, a "duet-insurance" eutectic electrolyte (DIEE) is proposed by introducing successively heavy water (D 2 O) and dimethyl sulfoxide in an aqueous chaotropic Zn salt solution, which hindered the severe irreversibility of Zn anodes compared to that lacking this dual-solvent protection. For example, the optimal DIEE delivered a high capacitance of 352.9 F g −1 at 0.5 A g −1 and excellent capacitance retention of ≈100% over 30,000 cycles at 2 A g −1 implementing in pouch cells and showing the ability to operate at a low temperature. Besides, experimental (e.g., nuclear magnetic resonance spectroscopy, Raman spectroscopy, electric double-layer capacitance, etc.) and theoretical techniques (e.g., molecular dynamics simulation, density functional theory) illustrate the vital presence of contact ion pairs and aggregates ion species. Ultimately, this efficient DIEE system employing "duetinsurance" protections provides a promising direction for designing novel eutectic electrolytes for AZICs chemistries.

Highly Solubilized Urea as Effective Proton Donor‐Acceptors for Durable Zinc‐Ion Storage Beyond Single‐Anion Selection Criteria

“…For instance, the proton signals of H 2 O in 1 H NMR spectra experienced an upfield shift with increased urea additions, which indicates originate HB breakage within H 2 O followed by numerous HB formations of (H 2 O) O─H … O═C (urea) and/or (H 2 O) H─O … H─N (urea) derived from the eutectic effect of urea‐H 2 O mixtures ( Figure a). [ 27 ] While the proton signals of urea went downfield shift, addressing the HB complex formation due to the increased urea participation. [ 28 ] Further, a similar phenomenon about the upfield shift has been observed in 67 Zn resonance signals, suggesting weakened interactions between the lone‐pair electrons on water oxygen and Zn 2+ (Figure 1b).…”

A Trifunctional Electrolyte Enables Aqueous Zinc Ion Batteries with Long Cycling Performance

“…These results strongly confirm that the SADS additive efficiently stabilizes the Zn anode and demonstrates significant competitiveness compared to previous electrolyte optimization strategies, as summarized in Table S1 (Supporting Information). [21,25,[55][56][57][58][59][60][61][62] The coulombic efficiency (CE) of Zn||Cu coin cells assembled with different electrolytes, as shown in Figure 5e, was used to understand the reversibility of the Zn plating/stripping process. The Zn||Cu cell with the 0.2 m SADS-containing electrolyte achieves an average CE of 99.24%, significantly higher than that of the pristine ZnSO 4 electrolyte.…”

Eutectic Electrolytes Convoying Low-Temperature Metal-Ion Batteries

“…The decrease in T f can be calculated using the following formula, normalΔ T normalf = T water − T solute = K normalf m where T water is the thermodynamic freezing point of water (0 °C); T solute is the freezing point of the solute; K f is the depression constant of the freezing point (1.86 °C kg mol –1 for water); and m is the total mole number of anions and cations . In addition, as the temperature decreases, the water–eutectic interaction improves due to the formation of multiple and strong H-bonds, , which is significantly different from that in the case of high-concentration electrolyte compositions (i.e., they rely on large salt quantities to eliminate the water proportion in an electrolyte system) with a fast “drop” in T f . Increasing the concentration of salts in electrolytes will probably result in larger solvated-ion clusters compared to low-concentration electrolytes with corresponding low ionic conductivity (medium inset in Figure a) and high viscosity (upper inset in Figure a) at sub-zero temperatures, inescapably hindering ion transport in the bulk electrolyte. , As a result, it is reasonable to add H 2 O as the second Lewis base source coupling with the above ternary Lewis-acid/chaotropic anion/Lewis-base (“triangular-eutectic” model) as the state-of-the-art patterning of the “quadrilateral-eutectic” model (Figure b).…”

“…The strength of Lewis acid–base interactions varies from relatively weak H-bonding (4 kJ mol –1 ) to very strong covalent bonds (>100 kJ mol –1 ), while the realistic eutectic electrolytes are far beyond a Lewis-related chemical reaction. Notably, some monovalent (e.g., Li + , Na + , and K + ) − and multivalent (e.g., Zn 2+ , Mg 2+ , Al 3+ , and Ca 2+ ) − cations are typical members of Lewis acids that are prone to interact with various molecules incorporating Lewis-base moieties (e.g., amide, , diol, urea, nitrile, , sulfoxide, and sulfones , ) for the mature formation of eutectic electrolytes (Figure a,b). Van der Waals forces, the third type of interaction, are stronger than the primary molecular interactions of each component, and currently, specific studies on van der Waals forces in eutectic electrolytes are lacking …”