Cluster level entropy enhancement in neutral acetate electrolytes enables economical and durable zinc air batteries

Abstract

Neutral zinc–air batteries provide a viable alternative to alkaline systems by avoiding salt creep and carbonate passivation. Among candidate electrolytes, acetate-based formulations are particularly attractive for their low cost, sustainability, and compatibility with ambient-air operation. However, their widespread adoption is limited by a trade-off between two concentration regimes. Dilute electrolytes trigger side reactions and lack ionic strength, while concentrated ones suffer from kinetic limitations due to contact ion pair clustering. Here, we propose a cluster-level entropy enhancement strategy that optimizes the mesoscopic configuration of the electrolyte by disrupting large clusters in concentrated acetate electrolytes. This entropy enhancement improves zinc ion diffusivity and kinetics, mitigates interfacial concentration gradients, and maintains local ionic strength for fast electrochemical reactions, as evidenced by various synchrotron X-ray techniques and theoretical simulations. Consequently, the zinc–air batteries in neutral electrolyte deliver over 1800 hours at 0.1 mA cm^-2 (1 mAh cm^-2, 61.4% round-trip efficiency) and 500 hours at 1 mA cm^-2 (12 mAh cm^-2, 51.2% round-trip efficiency) in ambient air. This study extends the application of sustainable acetate electrolytes in neutral zinc–air batteries and illustrates a mesoscopic tuning approach applicable to aqueous energy systems with metal electrodes and concentrated solvents.

Introduction

Rechargeable zinc–air batteries offer high theoretical energy density, low cost, and intrinsic safety, making them attractive for next-generation energy storage^1,2. Over the past decade, much effort has focused on improving air electrode reversibility via four-electron oxygen evolution and reduction (OER/ORR) reactions^3,4. Indeed, substantial progress has been made in the development of high-activity, low-cost catalysts applied to the positive electrode^5,6. Our previous studies have contributed to this field, proposing dynamic catalysis⁷, surface reconstruction strategies⁸, and electrode/electrolyte structure engineering⁹. However, commercialization of zinc–air batteries remains hindered by persistent challenges^10,11. A primary barrier lies in the use of concentrated alkaline electrolytes to support ORR/OER reactions¹², which induce dendrite growth and passivation, severely limiting reversibility¹³. Moreover, exposure to CO₂ in ambient air forms insoluble carbonates on the positive electrode, blocking pores and degrading performance^14,15. Thus, designing electrolytes with adaptive local environments is essential for enabling long-term zinc–air battery operation.

To address these issues, various strategies involving additives or alternative aqueous electrolytes have been explored to suppress undesired reactions. For example, zinc acetate has been used as a sustainable additive to enhance zinc electrode stability by partially replacing hydroxide coordination, thus suppressing ZnO formation while preserving ionic strength^16,17. Desipite this, reversibility remains limited in alkaline environments due to unresolved side reactions and corrosion^18,19. Neutral electrolytes offer greater chemical stability and reduced corrosion burden^20,21. Recently, cost-effective zinc acetate has been investigated as a standalone electrolyte system for neutral zinc–air batteries²². Particularly, dilute solutions offer high ionic mobility and suppress dead-zinc formation (Fig. 1a, gray spot in the dilute region). Nonetheless, like most reported diluted electrolytes, the high content of active water led to poor interfacial stability and side reactions. A recent study²³ demonstrated that supporting salts or hydrotropic agents can overcome solubility limits and create a Zn²⁺-rich local environment, enabling prolonged Zn stripping/plating. Yet, as will be extensively discussed in this study, we find that intrinsic contact ion pairs (CIPs) in acetate electrolytes tend to aggregate into large ion clusters in high-concentration regions. While these clusters offer some stabilization, they severely impair overall electrolyte kinetics (Fig. 1a, marked by the gray spot in the concentrated region), posing a critical limitation for multi-electron systems like Zinc-air batteries. Although the sustainable and cost-effective zinc acetate electrolyte holds great potential for enabling neutral zinc–air batteries and avoiding harsh alkaline conditions, its practical application remains challenging due to current technological limitations²⁴.

Fig. 1: Concept and validation of an entropy enhancement strategy for zinc acetate electrolytes.

a Schematic of the entropy-driven design to break the trade-off between corrosion in dilute and poor kinetics in concentrated systems. b Supporting salt enables Zn²⁺ solubilization but leads to large ion clusters and mesoscopic heterogeneity. c Entropy-enhanced dissolution by DMC addition leading to disrupted ion cluster. d viscosity comparison of concentrated (ZN₃A₅·10H₂O), entropy-enhanced (ZN₃A₅·10H₂O-EE), and dilute (1Zn1Na) electrolytes under varying shear rates; inset shows clustering under stress in the concentrated system. e Schematic of entropy-enhanced transport showing improved ion mobility in both bulk and at the electrode interface. In both illustrations, red spheres represent [Zn²⁺---Ac^-] contact ion pair, white spheres represent fully dissociated Na⁺ or Ac− ions, blue spheres denote water molecules, and green spheres indicate dimethyl carbonate (DMC) disruptors.

Recent advances in solvation engineering of aqueous electrolytes have deepened the understanding of Zn²⁺ coordination and opened alternative avenues to design electrolytes with tailored structures and interfacial dynamics^25,26,27. Since the first report in 2023²⁸, entropy-tuned electrolytes have gained growing attention as their compositional complexity offers promising routes to enhance ionic conductivity, solubility, and interfacial stability, particularly in concentrated systems where sluggish ion transport and unstable electrode reactions remain critical challenges²⁹. In aqueous systems, entropy-regulation strategies typically involve the introduction of multiple functional components to manipulate solvation structures and interfacial behaviors³⁰. Representative approaches include incorporating mixed cations or anions to tune solvation shells and modulate electric double layer^31,32, co-solvents to weaken hydrogen-bond networks³³, and solvated additives to suppress side reactions and regulate solid electrolyte interphase chemistry³⁴. Despite the significant progress, the inclusion of compositionally diverse species raises additional concerns over side reactions, increased cost, and dubious electrolyte stability, underscoring the need for alternative entropy-regulation with improved structural simplicity and reliability³⁵.

Herein, we propose a cluster-level entropy-enhancement strategy that leverages the intrinsic solvophobicity of large ion clusters. Unlike multi-salt/additive “high-entropy” systems that rely on compositional complexity, our approach tunes configurational entropy at the mesoscopic level by regulating ion-cluster configuration in a bi-salt electrolyte. Specifically, by introducing non-aqueous structural disruptors into the system, these molecules (such as DMC, which serves as a model disruptor in this study) weakly interact with and perturb large ion clusters into smaller, more dispersed units with greater configurational freedom. This structural transition increases the system’s entropy, reducing ion association, enhancing Zn²⁺ transport, and improving overall electrolyte dynamics. Consequently, it effectively overcomes the trade-off between electrolyte kinetics and electrochemical stability even at high acetate salt concentrations (Fig. 1a yellow spot on the red line). This entropy-enhanced zinc acetate electrolyte, featuring a smaller ion cluster, effectively mitigates concentration gradients near the electrode and enables rapid electrochemical interfacial reactions. Combined with the ZnO₂ positive electrode chemistry, the resulting Zn-air battery delivers over 1800 h of stable cycling at 0.1 mA cm⁻² and 400 h at 1 mA cm⁻² in ambient air, showing competitive performance compared with recent acetate-based and other neutral zinc–air batteries. Beyond extended lifespan, our neutral zinc acetate electrolyte demonstrates favorable attributes in affordability, sustainability, safety, and kinetics compared with systems such as 6 M KOH and 3 M Zn(OTF)₂. This work presents a cost-effective and sustainable electrolyte for zinc-air battery systems. Its applicability across multiple carbonate solvents suggests that the cluster-level entropy tuning strategy can be applied to electrolyte design in various metal–based aqueous batteries.

Results

Entropy-enhanced strategy for concentrated zinc acetate electrolyte

To systematically elucidate the entropy enhancement strategy for breaking the performance trade-offs, three types of electrolytes, dilute, concentrated, and an entropy-enhanced acetate system, were prepared and investigated. Dilute electrolyte was prepared via a regular dissociation process as illustrated in Fig. S1, consisting of 1 M Zn(AC)₂ and 1 M NaAC bi-salt electrolyte (denoted as 1Zn1Na). However, even in dilute conditions, Zn²⁺ and AC⁻ (acetate anion) readily form intrinsic CIPs due to strong bidentate coordination. These CIPs hinder further concentration increases since they spontaneously aggregate through hydrophobic interactions between the –CH₃ groups on acetate (Fig. S2)^36,37. To reach higher concentrations and overcome solubility limits, excess NaAC was introduced as a supporting salt to enhance Zn(AC)₂ dissociation (Fig. 1b). This method macroscopically results in a homogeneous solution resembling the dilute system. However, CIPs persist at the mesoscopic scale and tend to aggregate into large ion clusters, exhibiting liquid–liquid phase separation (LLPS) like protein aggregation in aqueous media^38,39. This mesoscale phase instability significantly hinders ion mobility and the practical usability of the concentrated system. Our entropy-enhancement strategy addresses this issue by exploiting the inherent solvophobicity of clustered ionic domains in concentrated electrolytes. By introducing dimethyl carbonate (DMC) as a structural disruptive agent which weakly interacts with Zn²⁺ and embeds into ion clusters via outer-sphere contacts, large CIP clusters are broken into smaller, more mobile aggregates with greater configurational entropy (Fig. 1c), thereby improving electrolyte homogeneity and ion transport.

We first optimized the concentrated electrolyte composition by adjusting the Zn(AC)₂/NaAC molar ratio and the water content (R). As evaluated and discussed in Fig. S3a, b, a Zn²⁺:Na⁺:H₂O ratio of 1:3:10 (denoted as ZN₃A₅·10H₂O, where Z represents Zn²⁺, N represents Na⁺, A represents AC⁻) was identified as an optimal balance, considering Zn²⁺ concentration, viscosity, ionic conductivity, and pH, thereby providing a sustainable neutral electrolyte. Despite favorable properties, the ZN₃A₅·10H₂O contains large ion clusters and lacks long-term kinetic stability. Rheological measurements reveal a high viscosity of ~37.5 mPa s, nearly 10 times that of the dilute 1Zn1Na system (~3.7 mPa s), along with pronounced shear-thickening behavior at high shear rates (10–100 s⁻¹) (Fig. 1d). These observations suggest that external environmental stress accelerates the coalescence of CIPs into larger aggregates and even salt precipitation by overcoming ionic shielding (inset image in Fig. 1d), thereby sharply increasing viscosity. Similar behavior was observed at higher Zn²⁺ concentrations (Fig. S4), where the onset of phase separation shifts to lower shear rates, indicating widespread cluster formation.

In our entropy-enhanced electrolyte, ZN₃A₅·10H₂O-EE, the introduced DMC interacts with the hydrophobic tails of Ac⁻, disrupting CIP–CIP interactions and preventing the clustering phenomenon. As a result, viscosity drops from 37.5 to 12.3 mPa s, and the system exhibits enhanced dynamic stability even under high shear (>100 s⁻¹). Additionally, the incorporation of organic molecules into the electrolyte structure expands the operational window and introduces interphase chemistry at the metal electrode interface. Moreover, DMC modulates the extended solvation structure of Zn²⁺, improving electrolyte kinetics by optimizing solvation strength and the local electrochemical environment. This enhancement improves ion cluster transport in the bulk electrolyte and facilitates interfacial charge transfer (Fig. 1e), thereby mitigating concentration gradients and promoting uniform diffusion, as detailed in the following section.

The Zn²⁺ local environment variation in the ion cluster

The entropy-driven disruption of ion clusters was initially examined using isothermal titration calorimetry (ITC), a sensitive method for probing molecular interactions⁴⁰. As shown in Fig. 2a, the setup includes a sample cell containing the target electrolyte and a reference cell with a buffer for heat detection. By incrementally injecting DMC into different electrolytes, we derived the system’s ΔS and ΔG based on variations in enthalpy (ΔH). Initially, DMC was injected into water and 1Zn1Na for comparison (Fig. S5a, b). They showed similar thermal responses (dQ/dt < 0 after stabilized) due to the immiscibility between water and DMC, primarily reflecting interfacial effects rather than molecular interactions. In contrast, sequential DMC injection into concentrated ZN₃A₅·10H₂O produced distinct, consistent endothermic peaks (dQ/dt > 0, Fig. 2b), reflecting significant heat absorption and enabling quantitative thermodynamic analysis of microenvironmental changes. As shown in Fig. 2c and Table S1, these peaks arise from partial disruption of CIP clusters by DMC, weakening ionic associations and increasing configurational entropy (ΔS = 43.4 cal mol⁻¹ K⁻¹), reducing ion cluster size and promoting structural disorder within the electrolyte. Despite requiring energy to overcome intra-cluster interactions (ΔH = +3.85 kcal mol⁻¹), the process is entropy-driven and thermodynamically favorable (ΔG = −9.17 kcal mol⁻¹). These findings indicate that DMC mediates distinct interactions with the disrupted clusters, leading to a more disordered yet stable microenvironment that benefits battery performance. Moreover, the consistent thermodynamic behavior observed in other carbonate-based systems (Figs. S6–S8) supports the broader applicability of this entropy modulation strategy in Zn-based electrolytes.

Fig. 2: The Zn²⁺ local environment rearrangement and investigation in different electrolyte systems.

a Schematic of isothermal titration calorimetry (ITC) setup used to monitor entropy-enhanced cluster disruption. b The thermogram for dimethyl carbonate (DMC) interaction in ZN₃A₅ 10H₂O electrolyte with a series of 29 injections and c the calculated thermal dynamics parameters. The inset image illustration of Gibbs free energy change during the entropy-enhanced process (from ZN₃A₅·10H₂O to ZN₃A₅ 10H₂O-EE), and the schematics of ion cluster configurational change undergo an endothermic process (ΔH > 0 kcal mol⁻¹). Red spheres represent [Zn²⁺---Ac⁻] contact ion pair, white spheres represent fully dissociated Na⁺ or Ac⁻ ions, blue spheres denote water molecules, and green spheres indicate dimethyl carbonate (DMC) disruptors. d The Raman spectra and e ATR-IR secretum of different electrolyte systems.

To further reveal entropy-enhanced effects on local Zn²⁺ coordination and mesoscopic structure, Raman spectroscopy was employed to probe Zn²⁺–AC⁻ contact ion pair (CIP) coordination. As shown in Fig. 2d, no peaks appear in the low-frequency region (<500 cm⁻¹), indicating suppression of the Zn²⁺-(H₂O)₆ vibration (~390 cm⁻¹) across all electrolyte systems⁴¹. This effect helps reduce water-involved side reactions, including the hydrogen evolution reaction during the desolvation at the negative electrode/electrolyte interface⁴². The C–C stretching vibration serves as probe for understanding the complexation between Zn²⁺ and acetate CIPs^43,44. In 1 M Zn(AC)₂, the ν(C–C) peak appears near 948 cm⁻¹, characteristic of bidentate ion pairing (BIP) between Zn²⁺ and AC⁻ due to strong coulombic interaction. With NaAC as a supporting salt, the peaks in 1Zn1Na and ZN₃A₅·10H₂O exhibit significant blue shifts to near 942 cm⁻¹, indicating an increased presence of monodentate contact ion pairs (MIP) in the electrolyte systems⁴⁵. This shift arises because fully dissociated Na⁺ and AC⁻ ions elevate the overall ionic strength of the electrolyte, enhancing the ionic shielding effect. Consequently, the coordination strength between Zn²⁺ and Ac⁻ decreases, and one coordination site of AC⁻ is released from the Zn²⁺—AC⁻ CIPs. The peak in ZN₃A₅·10H₂O-EE shifts slightly to a lower wavenumber than that in ZN₃A₅·10H₂O, while maintaining the MIP state of the electrolyte system. It’s worth mentioning that at excessive NaAC concentrations, the system shifts toward a solvent-shared ion pair (SSIP) state, with a shoulder at ~910 cm⁻¹ indicating free acetate anion in ZN₁₀A₁₂·20H₂O system. While it increases the overall ionic conductivity of the electrolytes, the hydrolysis of NaAC raises pH and viscosity, hindering the reversibility of Zinc stripping/plating.

The regulation of electrolyte configuration via entropy tuning also modulates water activity, as shown by changes in O–H vibrations (3000–3750 cm⁻¹)^46,47. The peak of strong hydrogen bond water (at 3253 cm⁻¹) can be clearly observed in 1 M Zn(AC)₂ since the BIP state of acetate anion exposes the hydrophobic −CH₃ groups. Water molecules will form 4-coordinate hydrogen-bonded water (4-HBW) and polyhedral cages of tetrahedrally hydrogen-bonded water molecules surround –CH₃ groups, showing high activity and inducing the side reaction at the negative electrode interface⁴⁸. The intensity of 4-HBW decreases with increasing Zn²⁺ concentration. Correspondingly, the higher content of bonded water (3410 cm⁻¹) can be attributed to the in-phase vibrations of water molecules captured by the –C=O groups of the acetate anion. In particular, the addition of DMC further disrupts water-water interactions, thereby increasing the thermodynamic stability of ZN₃A₅·10H₂O-EE and expanding the water splitting window up to 2.53 V (Fig. S9)⁴⁹.

The configuration change in CIP was further examined via attenuated total reflectance-infrared spectroscopy (ATR-IR), which sensitively detects polar vibrations, especially carboxyl group modes (ν_s(COO⁻), ν_a(COO⁻))⁵⁰. The defined Δν (the difference in the wavenumber, Δν = ν_a(COO⁻)-ν_s(COO⁻)), serves as an indicator of the acetate coordination mode. As illustrated in Fig. 2e, the two bands observed at 1450 cm⁻¹ and 1536 cm⁻¹ are assigned to the symmetry ν_s(COO⁻) and asymmetry ν_a(COO⁻), respectively, in solid Zn(AC)₂·2H₂O as in ref. ⁵¹. The Δν increases upon NaAC addition (Δν 1Zn1Na > Δν 1 M Zn(AC)₂), consistent with Raman trends. This confirms that the bonding strength between acetate anions and Zn²⁺ decreases across the sequence (ZN₃A₅·10H₂O-EE > ZN₃A₅·10H₂O > 1Zn1Na > 1 M Zn(AC)₂), facilitating cluster disintegration and mesoscale homogeneity.

Various synchrotron-based X-ray techniques and MD simulations were utilized to reveal the structural configuration around Zn²⁺ in electrolyte systems. Zn K-edge X-ray absorption spectroscopy (XAS) was conducted on dilute 1Zn1Na, concentrated ZN₃A₅·10H₂O, and Entropy-enhanced ZN₃A₅·10H₂O-EE electrolytes (Fig. 3a). The X-ray absorption near-edge structure (XANES) spectra highlight energy level differences among the four electrolyte systems, reflecting distinct local chemical environments around Zn²⁺. The absorption edge shifts to lower energy levels in the order of ZN₃A₅·10H₂O < 1Zn1Na < 1 M Zn(AC)₂, suggesting reduced Zn–O electron transfer and a weakened Zn²⁺–AC⁻ interaction. Notably, the entropy-enhanced process does not introduce additional inner solvation structures around Zn²⁺, as evidenced by the minimal change in edge energy in XANES between ZN₃A₅·10H₂O-EE and ZN₃A₅·10H₂O (inset image of Fig. 3a)⁵². This indicates that DMC does not directly participate in the inner solvation shell around Zn²⁺ or alter its oxidation state. Instead, it resides outside the primary coordination sphere and perturbs the outer solvation structure through weak solvophobic and dielectric interactions, which destabilize CIP networks and facilitate cluster fragmentation⁵³.

Fig. 3: Synchrotron X-ray characterization and theoretical calculation variation of ion cluster structure.

a XANES and b EXAFS spectra showing local Zn²⁺ coordination in different electrolytes. c High-energy X-ray scattering structures S(q) of different electrolyte systems. d MD snapshot of ion cluster configuration in ZN₃A₅·10H₂O-EE electrolyte. In the surface mesh analysis snapshot (e), the white, red, purple, cyan, black, and green balls represent the H, O, Zn, Na, C (in AC⁻), and C (in DMC) atoms, respectively. f Experimental ion cluster structure G(r) obtained from the PDF X-ray spectrum (upper image) and simulated g(r) profiles depicting Zn²⁺–DMC interactions within ion clusters (bottom image).

Fourier-transformed extended X-ray absorption fine structure illustrated the solvation shell variation around Zn²⁺ (Fig. 3b). In all electrolytes, the dominant Zn–O peak indicates solvation is primarily confined to the first coordination shell. Zn–O bond lengths increase from 1.84 Å in 1 M Zn(AC)₂ to 1.89 Å and 1.93 Å in 1Zn1Na and ZN₃A₅·10H₂O, respectively, indicating weakened Zn²⁺–AC⁻ coordination. This result aligns with Raman and ATR-IR data, confirming a coordination shift from BIP to MIP. Notably, the addition of DMC shortens the Zn–O bond to 1.90 Å in ZN₃A₅·10H₂O-EE and decreases peak intensity. The observed spectral change reflects a partial reorganization of the Zn²⁺ coordination environment, not through direct Zn–DMC coordination, but rather due to the suppression of long-range ion-cluster interactions and the partial collapse of the extended solvation shell. DMC molecules embedded within the ion clusters facilitate this compaction, leading to reinforced Zn–O interactions and the formation of smaller, more dynamic clusters while preserving the MIP coordination state.

The extended solvation and ion cluster structures, especially smaller ion clusters in ZN₃A₅·10H₂O-EE, were further characterized and proved in the synchrotron-based high-energy (55 keV) X-ray scattering data S(q). Similar to X-ray diffraction (XRD) for crystalline materials, S(q) reveals short-range structural correlations in liquid electrolytes, particularly those related to mesoscopic ion clustering^54,55. As shown in Fig. 3c, only a broad peak appears for the 1Zn1Na electrolyte for high scattering vector (Q) value around 10 Å⁻¹. This indicates the absence of a network structure in the local electrolyte environment, and that the detected configuration mainly reflects atomic packing distances, likely arising from CIPs between Zn²⁺ and AC, as previously discussed in Raman and EXAFS. In contrast, ZN₃A₅·10H₂O and ZN₃A₅·10H₂O-EE exhibit pronounced S(q) signals in the low-Q region (0.4–1.9 Å⁻¹) and medium-Q region (2–5 Å⁻¹), indicating the formation of mesoscopic ion clusters in electrolyte systems. Moreover, ZN₃A₅·10H₂O-EE shows a slight increase in Q value and a reduced S(q) intensity compared to ZN₃A₅·10H₂O, suggesting that the entropy-enhancement process with DMC not only reduces the size of ion clusters but also increases the proportion of denser clusters, thereby lowering viscosity and improving ionic conductivity in electrolyte. These findings are further supported by molecular dynamics (MD) simulations (Fig. 3d, e). Simulation snapshots confirm that Zn²⁺ is primarily coordinated by acetate via monodentate ion pairs (MIP) rather than BIP structures. Besides, a distinct ion cluster structure composed of interconnected CIP units is observed in Fig. 3e. Notably, DMC molecules (highlighted by the gray arrow) insert into the centers of large clusters and fragment larger aggregates into smaller units, as confirmed by surface mesh analysis.

To further validate ion cluster rearrangement, we compared the experimental pair distribution function (PDF, G(r)) with simulated radial distribution functions (RDF, g(r)) from MD (Supplementary Data 1). As shown in the PDF data (top panel of Fig. 3f), the ZN₃A₅·10H₂O-EE electrolyte exhibits several additional peaks beyond the typical Zn–O distances (1.8–2 Å), located at approximately 2.3–2.9 Å, 2.5–3.0 Å, 2.7–3.5 Å, and 4.3–5.8 Å, compared to ZN₃A₅·10H₂O. These longer distances are significantly larger than those typical inner-shell solvation and can be attributed to Zn²⁺ weak interactions with DMC molecules as verified by the RDF data from MD simulation (bottom panel of Fig. 3f), specifically Zn²⁺–O₁ (carbonyl oxygen in DMC, whose structure is shown in Fig. S10), Zn²⁺–C (esterified carbonyl carbon in DMC), Zn²⁺–O₂ (ether oxygen in DMC), and Zn²⁺–H (methyl hydrogen in DMC). Additionally, Fig. S11 offers macroscopic evidence of DMC integration into the concentrated electrolyte. Unlike the dilute 1Zn1Na electrolyte, which remains immiscible with DMC, ZN₃A₅·10H₂O-EE shows complete miscibility, forming a clear and homogeneous solution after entropy enhancement.

The ion clusters, carried by water, form hydrodynamic entities that govern electrolyte diffusivity as described by the Stokes–Einstein equation:

$$D=\frac{{k}_{B}T}{6{{{\rm{\pi }}}}\eta {{{\rm{R}}}}}$$

(1)

Where ${k}_{B}$ is the Boltzmann constant, T is the temperature, $\eta$ is the viscosity, and R represents the hydrodynamic radius. The inverse relationship between diffusivity (D) and hydrodynamic radius (R) was verified by dynamic light scattering⁵⁶. As shown in Fig. S12, near the 1.6 M solubility limit, Zn(AC)₂ forms either small clusters (~0.83 nm) fully hydrated by water, or large stacked clusters (~295.8 nm) dominated by BIP-state CIPs and hydrated sheaths. In contrast, no hydrodynamic clusters are detected in 1Zn1Na, as the dilute environment and complete dissociation of NaAC prevent cluster formation. The main peak for ZN₃A₅·10H₂O appears at 10.1 nm and shifts to 2.01 nm in ZN₃A₅·10H₂O-EE and is consistent with X-ray scattering results, confirming that entropy-driven cluster disruption reduces hydrodynamic radius and enhances ion diffusivity. This, in turn, effectively mitigates the concentration gradient near the electrode, enabling smoother and faster interfacial chemistry⁵⁷.

Stripping/plating reversibility and electrolyte

The reversibility of asymmetric Zn||Cu cells was evaluated at 0.5 mA cm⁻² with 2 h cycling (Fig. 4a). Overall, the average coulombic efficiency (CE) increased with Zn²⁺ concentration. 1 M Zn(AC)₂ and 1Zn1Na exhibited CE values of ~96.5% and ~98.2%, respectively, but both failed within 100–200 cycles due to dendrite growth and side reactions. In contrast, the concentrated ZN₃A₅·10H₂O electrolyte extends cycling life beyond 300 cycles with CE ~99.1%, benefiting from higher Zn²⁺ content and reduced water activity. Remarkably, entropy-enhanced ZN₃A₅·10H₂O-EE delivered 600 stable cycles with CE up to 99.7% and minimal voltage hysteresis (Fig. 4b), reflecting suppressed dead-zinc formation and H₂ evolution as further confirmed by gas chromatography (Fig. S10). Corrosion resistance was further assessed via Tafel polarization (Fig. S14). Compared with 1Zn1Na and ZN₃A₅·10H₂O, ZN₃A₅·10H₂O-EE exhibited a lower corrosion current density and more positive electrode potential, indicating reduced side reactions and alleviated corrosion rate of the zinc negative electrode.

Fig. 4: The electrochemical behavior of three electrolyte systems, 1Zn1Na, ZN₃A₅·10H₂O and ZN₃A₅·10H₂O-EE.

a Columbic Efficiency (CE) of Zn plating/striping reaction measured by Zn/Cu with different electrolyte systems. The dashed line represents the stable CE over 600 cycles in ZN₃A₅·10H₂O_H electrolyte. b Voltage-Capacity curve of Zn||Cu cell with ZN₃A₅·10H₂O-EE electrolyte. c The Zn²⁺ transference number was measured by electrochemical polarization (the insets are associated with EIS measurements) of Zn||Zn cell in ZN₃A₅·10H₂O-EE. d Cycle performance of Zn||Zn cell at 1 mA cm⁻², 1 mAh cm⁻² in three electrolyte systems. e Chronoamperogram test of Zn||Zn cell in different electrolyte systems after 10th cycles at a voltage of −150 mV and corresponding SEM morphology characterization of Zn²⁺ plating in Zn||Zn cell with f 1Zn1Na, g ZN₃A₅·10H₂O and h ZN₃A₅·10H₂O-EE electrolyte. The scale bar: 20 μm in (f), (g) and 10 μm in (h), respectively.

The Zn²⁺ transference number, an important parameter indicating electrolyte diffusivity, is defined as the fraction of the total current carried by Zn²⁺ and reflects its electro-mobility. This can be calculated via the sand’s time as follows⁵⁸:

$${t}_{{Zn}}^{2+}={I}_{s}\frac{\Delta V-{I}_{0}{R}_{0}}{\Delta V-{I}_{s}{R}_{s}}$$

(2)

Where ${I}_{o}$ and ${I}_{s}$ are the initial and stable state current, respectively ΔV is the polarization applied potential, R₀ and Rs are the resistance before and after polarization, respectively. As shown in Figs. 4c and S15, the entropy-enhanced ZN₃A₅·10H₂O-EE, with smaller ion clusters and higher ionic conductivity, leads to a significant increase in Zn²⁺ transference number from 0.235 in ZN₃A₅·10H₂O to 0.537.

The enhanced electrolyte stability is further demonstrated by the Zn||Zn symmetric cell (Fig. 4d). Compared to the concentrated ZN₃A₅·10H₂O electrolyte system where polarization gradually increases with operation, the platform overpotential of ZN₃A₅·10H₂O-EE remains constant at 1 mA cm⁻² for over 2000 h without any soft short-circuit phenomena (inset Fig. 4d), accumulating over 2 Ah cm⁻² capacity. Even under high current density and high areal capacity conditions, the ZN₃A₅·10H₂O-EE electrolyte maintains promising electrochemical stability (Fig. S16). In comparison, the 1Zn1Na and ZN₃A₅·10H₂O cells fail after ~200 h and ~800 h, respectively, due to inferior Zn²⁺ transport and unstable interfacial environments. In ZN₃A₅·10H₂O, continuous Zn plating/stripping promotes CIP aggregation and clustering, which impairs mass transfer and desolvation kinetics. This is reflected in the increasing electrolyte resistance R_s) over time (Fig. S17a). Specifically, ZN₃A₅·10H₂O-EE maintains a low and stable R_s (13.7∼26.3 Ω) from the 10th to 500th cycle, whereas R_s in ZN₃A₅·10H₂O increases from 30.2 to 181.1 Ω, indicating cluster-induced viscosity buildup. Charge-transfer resistance (R_ct) further reflects interfacial stability. R_ct in ZN₃A₅·10H₂O rises from 409 to 1055 Ω over 500 cycles, while ZN₃A₅·10H₂O-EE exhibits only a slight increase in R_ct (Fig. S17b), suggesting stable electrochemical reactions at the interface. DRT analysis (Fig. S18) further reveals that interfacial ion clusters are not merely inherited from the bulk electrolyte but are dynamically formed during cycling as an extension of the solvation process where multiple solvated Zn²⁺ species further aggregate through shared anions or overlapping coordination shells beyond the primary solvation⁵⁹. The incorporation of DMC into the ion-cluster environment in ZN₃A₅·10H₂O-EE facilitates rapid desolvation and reduces cluster size, thereby mitigating interfacial concentration gradients. This results in a consistently low nucleation overpotential of ~34 mV even after 2000 h. For comparison, ZN₃A₅·10H₂O starts at ~45 mV, rising above 100 mV after 700 h.

The nucleation and growth behavior of Zn negative electrode was further investigated using chronoamperometry (CA, Fig. 4e). The dilute 1Zn1Na electrolyte exhibits an increasing current trend over a 600 s deposition process, similar to the previously reported 2D diffusion model of Zn²⁺ ions, leading to an uncontrolled growth of porous Zn dendrites. ZN₃A₅·10H₂O partially suppresses 2D diffusion at the cost of reducing the absolute current but still exhibits persistent interfacial instability. In sharp contrast, the ZN₃A₅·10H₂O-EE electrolyte suppresses planar diffusion and quickly achieves stable 3D diffusion, indicating more nucleation sites and a dense zinc plating layer due to the disparate clustering behavior and diffusivities. These trends are also confirmed by scanning electron microscopy (SEM). In dilute 1Zn1Na (Fig. 4f), Zn deposits show flake-like, loosely stacked morphologies typical of 2D growth. ZN₃A₅·10H₂O (Fig. 4g) exhibits denser Zn deposition but with large protrusions and rough surfaces due to limited bulk and interfacial diffusion. In sharp contrast, ZN₃A₅·10H₂O-EE (Fig. 4h) delivers a uniform and compact Zn layer, free from dendritic or protrusive features, highlighting the advantage of entropy-tuned electrolyte environments.

To resolve the spatial-temporal evolution of zinc plating beyond conventional surface-level observations, we developed an operando projection X-ray microscopy (PXM) platform enabling real-time 2D/3D morphological imaging. As shown in Fig. 5a, the setup uses high-flux synchrotron X-rays focused on a zinc electrode housed in a custom Kapton cell. Two vertically aligned Zn plates are fixed using titanium electrodes connected to a potentiostat for electrochemical control. A Fresnel zone plate serves as the objective lens, and images are recorded on a CCD detector (The detailed experimental setup is provided in Fig. S19). After 50 plating/stripping cycles, significant differences in Zn growth behavior were observed between electrolytes. Phase-contrast imaging based on grayscale gradients enables clear differentiation of dense versus porous Zn morphologies. In the concentrated ZN₃A₅·10H₂O electrolyte, the deposited Zn layer grows rapidly, exhibiting rough surfaces with obvious dendritic protrusions (Fig. 5b). This behavior is attributed to large ion clusters, which restrict Zn²⁺ diffusivity and create local concentration gradients near the interface. In contrast, the entropy-enhanced ZN₃A₅·10H₂O-EE electrolyte exhibits stable and uniform Zn deposition as shown in Fig. 5c, with a much smoother surface and no visible protrusions or dendritic features.

Fig. 5: The operando synchrotron projection X-ray microscopy (PXM) characterization on Zn deposition.

a Illustration of the measurement setup for the PXM characterization. b Operando images of Zinc plating in ZN₃A₅·10H₂O (left) and c ZN₃A₅·10H₂O-EE (right) electrolyte. d Morphological evolution of single Zn active nuclei particle in ZN₃A₅·10H₂O and e ZN₃A₅·10H₂O-EE.

3D profiling of early-stage nucleation further reveals these microstructural differences. In ZN₃A₅·10H₂O, the initial Zn nuclei are relatively large (20–25 μm, Fig. 5d1), and subsequent growth results in a porous, uneven morphology. The restricted ion transport caused by large clusters leads to rapid Zn²⁺ accumulation near the deposition interface, forming high local concentration gradients and rough particle surfaces. As plating proceeds (Fig. 5d2, d3), polarization intensifies, further obstructing diffusion pathways and triggering tip-enhanced dendrite growth. This results in the formation of secondary dendrites along the edges of primary spines, producing gaps between original and newly formed nuclei. These voids contribute to a highly porous structure, as illustrated in the 3D phase-contrast profile (Fig. 5d4). By contrast, in ZN₃A₅·10H₂O-EE, the initial nuclei are significantly smaller (5–10 μm, Fig. 5e1). The presence of disrupted ion clusters enhances ionic conductivity and suppresses concentration gradients, leading to more uniform Zn²⁺ distribution and dense, compact particle growth (Fig. 5e2–e4). Together, these observations demonstrate that the entropy-enhanced electrolyte enables more controlled Zn nucleation and plating by modulating both interfacial deposition behavior and bulk-phase ion transport. Compared to ZN₃A₅·10H₂O, ZN₃A₅·10H₂O-EE exhibits reduced concentration polarization and more uniform interfacial current distribution, effectively mitigating dendrite formation and promoting stable zinc deposition.

To validate these effects, multiphysics modeling based on a modified Li model was used to simulate the electrolyte–interface behavior⁶⁰. The relationship between concentration gradient and local current density is illustrated in the extended Butler–Volmer equation as followed:

$$j={j}_{0}{\left(\frac{{C}_{{Zn}}}{{C}_{{Zn}}^{*}}\right)}^{{\alpha }_{c}}\left\{exp \left[\frac{{\alpha }_{{{{\rm{a}}}}}{zF}\eta }{{RT}}\right]-exp \left[-\frac{{\alpha }_{{{{\rm{c}}}}}{zF}\eta }{{RT}}\right]\right\}$$

(3)

where j signifies the current density, j₀ is the exchange current density, C_Zn is the local Zn concentration at the electrode–electrolyte interface, ${C}_{{{\mathrm{Zn}}}}^{*}$ is the reference Zn concentration in electrolytes, α_c and α_a are the cathodic and anodic charge-transfer coefficients, z is the number of electrons and η is the overpotential. As shown in Fig. S20, Zn²⁺ depletion at 1 mA cm⁻² induces a sharp concentration gradient near deposited zinc in the concentrated ZN₃A₅·10H₂O electrolyte. In contrast, ZN₃A₅·10H₂O-EE exhibits a much milder gradient due to differences in key electrochemical parameters such as ion transference numbers, zinc ion concentrations, and ionic conductivities (Detailed data in Table S5). These differences in cluster kinetics induce a substantial difference in current density acting on zinc nuclei. As reflected in Fig. S21, the heterogeneous current density in concentrated ZN₃A₅·10H₂O induces Zn²⁺ preferential deposition, leading to dendritic morphological evolution. Conversely, the ZN₃A₅·10H₂O-EE electrolyte enables dense and uniform growth, contributing to extended device lifespan.

Zinc-air battery operated in ambient air

Conventional alkaline electrolytes (e.g., 6 M KOH) offer high ionic conductivity and kinetic stability, supporting efficient ORR/OER in Zn–air batteries. However, in ambient air, they suffer from salt creep, passivation, and poor reversibility, limiting cycle life and charge/discharge efficiency. In comparison, neutral electrolytes are CO₂-tolerant and better suited for long-term use. The reaction mechanism depends on the specific neutral electrolyte system employed¹. Here, a ZnO₂-based two-electron reaction, compatible with acetate electrolytes, was adopted to support full-cell operation, as expressed in Eq. 4 and Eq. 5⁶¹.

$${{{\rm{Positive\; electrode}}}}:{{\mbox{Zn}}}^{2+}+{{{{\rm{O}}}}}_{2}-2{{\mbox{e}}}^{-}={{\mbox{ZnO}}}_{2}$$

(4)

$${{{\rm{Negative\; electrode}}}}:{{{{\rm{Zn}}}}}^{2+}+{2{{{\rm{e}}}}}^{-}={{{\rm{Zn}}}}$$

(5)

Rate capability was evaluated using the ZN₃A₅·10H₂O-EE electrolyte (Fig. 6a). From 0.1 to 2 mA cm⁻², the cell exhibits minor polarization. At 5 mA cm⁻², increased overpotential is observed, likely limited by the catalytic activity of the carbon-based air positive electrode. Nonetheless, the performance remains competitive compared to recently reported neutral systems, with high round-trip efficiency and significantly reduced costs (Table S7 and Fig. S22).

Fig. 6: Electrochemical performance and comparison of neutral Zinc-air battery in acetate-based electrolyte.

a The rate performance of the neutral Zinc-air battery in ZA₃N₅·10H₂O-EE electrolyte with a fixed capacity of 12 mAh cm⁻². b The ex-XRD of Zinc negative electrode after 5th cycles in dilute 1Zn1Na, concentrated ZA₃N₅·10H₂O and entropy-enhanced ZA₃N₅·10H₂O-EE electrolyte, respectively. ZHA: Zinc hydroxyacetate hydrate. ZHC: Zinc hydroxycarbonate hydrate. c The Zinc utilization measurement is characterized by the Galvanostatic discharge profiles in ZA₃N₅·10H₂O and ZA₃N₅·10H₂O-EE electrolyte, respectively. Insets are photographs of the Zinc negative electrode after discharge in ZA₃N₅·10H₂O (left), and ZA₃N₅·10H₂O-EE (right) electrolytes. d The long-term cycling performance of neutral Zinc-air battery at a current density of 0.1 mA cm⁻² for 10 h and e performance comparison of lifetime and accumulated capacity in Zn-air battery between our ion cluster-engineered electrolytes with other non-alkaline electrolyte systems. The source of the literature data shown in this figure can be found in Supplementary Information, Table S7. The comparisons were made under lab-scale testing conditions f. The Radar plot of assessing three popular electrolyte systems (Including our ZN₃A₅·10H₂O-EE neutral electrolyte, non-alkaline 3 M Zn(OTF)₂ electrolyte, and traditional 6 M KOH electrolyte) for Zinc-air batteries. The grade of 0 represents poor performance and 1 stands for the opposite. The calculation procedure and the grade values are provided in Supplementary Note 1 in Supporting Information.

To confirm the Zn||ZnO₂ reaction reversibility, we monitored pH using a Swagelok cell (Fig. S23). In ZN₃A₅·10H₂O-EE, pH remains stable at 6.8–7.4 over multiple cycles (Fig. S24a), indicating OH− is not involved in the reaction. In contrast, the ZN₃A₅·10H₂O electrolyte exhibits irreversible pH drift (Fig. S24b), pointing to side reactions. Ex situ XRD was performed to identify reaction products after 5th discharging/charging process. As shown in Fig. S24c, the characteristic peak confirms the formation of ZnO₂ discharge products at the positive electrode, which disappear upon charging in the ZA₃N₅·10H₂O-EE electrolyte. At the negative electrode, ZN₃A₅·10H₂O-EE promotes compact Zn deposition, reflected in a high I₀₀₂/I₁₀₁ peak ratio (Fig. 6b). This effect is attributed to steric repulsion in Zn²⁺–Ac⁻ ion pairs near the interface, which guides tight metal packing supported by previous studies⁶². Additionally, no side products at negative electrode were detected in ZN₃A₅·10H₂O-EE electrolyte. In contrast, concentrated ZA₃N₅·10H₂O forms zinc hydroxyacetate, while 1Zn1Na leads to zinc hydroxycarbonate byproducts, both tied to sluggish desolvation, cathodic OH⁻ accumulation, as well as subsequent reactions with acetate anions in the electrolyte⁶³.

These electrochemical and interfacial advantages translate directly to discharge behavior under ambient air. The ZN₃A₅·10H₂O-EE cell delivers a stable discharge plateau at ~1.0 V for over 100 h (Fig. 6c), with an areal capacity of 58.3 mAh cm⁻² and a specific capacity of 710.6 mAh g⁻¹, corresponding to 87.4% zinc utilization (inset, right). Replacing the Zn foil with electrochemically deposited Zn on a Ti substrate (Fig. S25, fixed areal capacity of 12 mAh cm⁻²) enables a higher Zn utilization of 94.1% with higher current density. In comparison, the ZN₃A₅·10H₂O system achieves only 52% utilization. When replacing the carbon catalytic materials with a developed FeCo-based dynamic catalyst from our group featuring hollow nanostructures (Fig. S26), the discharge voltage further increases and the Zn utilization reaches 94.3% (Fig. S27), demonstrating the compatibility of the electrolyte with advanced catalysts.

The prepared ZA₃N₅·10H₂O-EE can support stable operation of the neutral zinc-air cell for over 1800 h in ambient air, rather than pure O₂, at a low current density of 0.1 mA cm⁻² with a 10-h charging/discharging period (Fig. 6d). Maintaining the same charging/discharging capacity at ten times higher current density (Fig. S28) enables zinc-air battery operation for over 400 h, demonstrating robust stability and reversibility. Even at higher practical areal capacities (e.g., 12 mAh cm⁻², Fig. S29), the entropy-enhanced electrolyte maintains stable electrochemical performance comparable to that observed at lower capacities, confirming its robustness under more demanding scenarios. Compared to other reported non-alkaline zinc-air battery systems (Fig. 6e and Tables S6, S7), our system demonstrates comparable in accumulated capacity, round-trip efficiency, and lifespan, even rivaling alkaline systems with significantly better battery life at both low and high current densities. To facilitate a direct comparison, Table 1 summarizes key metrics of representative non-alkaline and neutral electrolytes for Zn–air battery systems, further demonstrating the favorable performance of our entropy-enhanced system under ambient conditions. Beyond the enhanced bulk ion transport from smaller clusters in ZA₃N₅·10H₂O-EE, interfacial chemistry also plays a critical role in performance, as detailed in Figs. S30 and S31. Employing ZA₃N₅·10H₂O-EE as a neutral electrolyte forms a hydrophobic organic interphase that promotes reaction kinetics and suppresses side reactions. By contrast, dense ion clustering in its LLPS state in ZA₃N₅·10H₂O electrolyte promotes severe side reactions, including ZnCO₃ formation induced by CO₂ ingress. This disparity impacts not only the long-term stability and cycle life but also the continuous discharge rate and overall power output (Fig. S32).

Table 1 Performance benchmarks of representative neutral aqueous electrolytes for rechargeable Zn–air batteries

In addition to its competitive performance among neutral electrolyte systems, our work emphasizes a holistic approach to sustainability and practicality in Zn-air battery design. To illustrate this, we compare three representative electrolyte systems, as shown in Fig. 6f: the conventional 6 M KOH, the organic salt 3 M Zn(OTf)₂, and our proposed entropy-enhanced ZA₃N₅·10H₂O-EE electrolyte system. The evaluation is based on five key criteria: affordability, sustainability, lifetime, safety, and kinetics, for which detailed calculations are provided in Supplementary Note 1. While 6 M KOH offers low cost and high conductivity, its corrosivity and short cycle limit practical use. Alternative 3 M Zn(OTf)₂ electrolytes reported recently improved stability but at the expense of high cost and poor environmental compatibility. In contrast, our ZA₃N₅·10H₂O-EE electrolyte integrates low volatility, cost-effectiveness, and environmental sustainability with high zinc utilization, long cycle life, and reliable reversibility. Thanks to reduced water activity, ZA₃N₅·10H₂O-EE exhibits ultralow volatility in ambient air, significantly mitigating electrolyte loss. Additionally, as DMC is incorporated into the CIPs ion cluster network rather than existing as a free solvent, its volatility and environmental exposure are effectively suppressed (Fig. S33). This structural confinement helps maintain the electrolyte configuration and ion transport characteristics over extended use. Finally, a prototype square cell (Fig. S34) delivered 60 mAh at 10 mA, operating below 2 V during charge and ~1 V during discharge—matching lab-scale performance and demonstrating promise for practical scale-up.

Discussion

In this study, we proposed a cluster-level entropy enhancement strategy to optimize a sustainable and cost-effective acetate-based electrolyte for neutral zinc-air batteries, achieving extended operational lifetimes in ambient air without the need for complex cell engineering or suffering from corrosive drawbacks. Rather than relying on multicomponent formulations, our approach enhances configurational entropy by disrupting the large ion clusters inherently formed in concentrated acetate electrolytes. This mesoscale structural reorganization mitigates Zn²⁺ transport limitations and diffusion constraints in the bulk phase—similar to the behavior observed in dilute solutions—while maintaining low side reactions, dendrite-free deposition, and a sufficient local ionic strength for rapid electrochemical reactions at the interface, comparable to salt-concentrated electrolytes. These electrolyte modifications were validated through spectroscopic analyses, advanced in-situ synchrotron X-ray characterizations, and theoretical modeling. Furthermore, we developed operando PXM to visualize the spatiotemporal evolution during Zn plating/stripping, revealing how ion cluster dynamics (arising from differences in cluster structure) influence local deposition behavior near the zinc negative electrode. Ultimately, entropy-enhanced acetate-based electrolyte enabled long-term battery operation over 1800 h at 0.1 mA cm⁻² and 400 h at 1 mA cm⁻² under ambient air with high round-trip efficiency. Notably, despite the introduction of organic DMC as a cluster disruptor, the overall system retains environmental compatibility, as DMC is readily biodegradable, exhibits low toxicity, and remains stably confined within the ion cluster network, effectively minimizing evaporation and environmental exposure. Beyond neutral Zn–air systems, this cluster-level entropy enhancement strategy provides a generalizable pathway for designing electrolytes across other metal–air batteries employing acetate salts and advanced electrocatalysts. Moreover, its compatibility with various carbonate solvents indicates feasibility for extension to other Zn-based energy storage systems, thereby reinforcing the versatility and universality of this approach.

Method

Electrolyte preparation

All chemicals were purchased from Sigma-Aldrich and used directly for electrolyte preparation without further purification. The chemicals included anhydrous zinc acetate (Zn(CH₃COO)₂, Zn(AC)₂, > 99%), anhydrous sodium acetate (NaCH₃COO, NaAC, >99%), DMC (anhydrous, >99%), hydrogen peroxide solution (30% w/w in water), cobalt nitrate hexahydrate (reagent grade, 98%), and iron nitrate (ACS reagent, >98%). Zinc foil (99.9%, 100 μm and 50 μm), stainless steel mesh (500 mesh), Nickel mesh (99.9%, 500 mesh, pore size 50 μm), titanium foil (20 μm), copper foil (20 μm), coin cell case (CR2032) and glass fiber filter paper (GF/B, Whatman) were purchased from Cyber Electrochemical Materials Network.

Three types of electrolytes were prepared: dilute, concentrated, and entropy enhanced. Zn(AC)₂ and NaAC were dissolved in Milli-Q water at 40 °C and stirred for 1 h before storage at 23 ± 1 °C and an ambient relative humidity of ~40%. The dilute electrolyte (1Zn1Na) contained 1 mol L⁻¹ Zn(AC)₂ and 1 mol L⁻¹ NaAC. For the concentrated electrolyte ZN₃A₅·10H₂O consisted of Zn(AC)₂, NaAC, and H₂O at a molar ratio of 1:3:10, corresponding to Zn²⁺:Na⁺: CH₃COO⁻:H₂O = 1:3:5:10. In this notation, Z = Zn²⁺, N = Na⁺, A = acetate, and H₂O = water. For entropy-enhanced electrolyte, the ZN₃A₅·10H₂O was first deoxygenated by N₂ purging to prevent DMC degradation, followed by stepwise addition of 200 µL DMC in four aliquots (50 µL each) at 40 °C. After each addition, the solution was stirred until clear. Elevated temperature facilitated disruption of large ion clusters and reorganization of CIPs. The final ZN₃A₅·10H₂O-EE electrolyte was obtained after cooling to room temperature (23 ± 1 °C). Detailed molar ratios of all formulations are listed in Table S1.

Electrode preparation

Commercial zinc foil with a thickness of 50 μm was ultrasonically cleaned in a mixed solution of ethanol and acetone for 20 min. After wiping with a dust-free cloth, it was allowed to air dry. The treated zinc foil was then cut into 15 mm diameter disks and used as zinc anodes in various types of cells. The air positive electrode for the acetate-based neutral Zn–air battery was fabricated by mixing 0.7 g Vulcan XC-72R (CABOT), 0.2 g synthesized ZnO₂, and 0.1 g PTFE binder with 3 mL isopropanol (Sigma-Aldrich) in a mortar to form a homogeneous paste. The mass ratio of ZnO₂: carbon black: PTFE is 20:70:10. The mixture was pressed onto hydrophobic carbon paper (FuelCell Store), followed by drying at 40 °C to evaporate the isopropanol.

ZnO₂ powder was synthesized based on a reported method with slight modifications. Briefly, 3 g zinc acetate was dissolved in 50 mL water at 40 °C under stirring (300 rpm), followed by dropwise addition of 10 mL 30 wt% H₂O₂. The mixture was stirred overnight at 40 °C, filtered, rinsed with water, and vacuum-dried at 70 °C. FeCo-based hollow catalysts were synthesized following a modified reported procedure. Briefly, 0.1 mmol cobalt nitrate was dissolved in 8 mL glycerol and 40 mL isopropanol, stirred at 600 rpm for 40 min, transferred to a 100 mL Teflon-lined autoclave, and heated at 180 °C for 6 h. After cooling, the precipitate was collected by centrifugation, washed with ethanol, and dried at 60 °C. In the cation-carving step, 0.2 g of the Co precursor was ultrasonically dispersed in 20 mL anhydrous ethanol, then mixed with 0.2 mmol FeSO₄·7H₂O dissolved in 100 mL ethanol–water (1:1) under N₂. The combined solution was stirred at 5000 rpm for 10 min under N₂ bubbling, and the resulting pink powder was collected by centrifugation (7000 rpm) and washed with ethanol. Subsequently, during ammonization, the precursor was polymer-coated with dopamine hydrochloride in 0.01 M Tris buffer (pH ~8.5, material-to-dopamine ratio 2:1), stirred at 500 rpm for 5 h, and then calcined at high temperature.

Electrochemical measurements

Unless otherwise specified, all cell assembly was conducted under ambient laboratory conditions (23 ± 2 °C, 40–60% RH), with no additional humidity control applied. Zn||Zn symmetric and Zn||Cu asymmetric cells were assembled in CR2032 coin-type cells using different acetate-based electrolytes and glass fiber (Whatman GF/B) separators with 120 μL electrolyte. The dimensions of all electrodes we used in coin-type cells are circular with a diameter of 12 mm. The glass fiber separators we used were 16 mm in diameter and 675 μm in thickness. A cut-off potential of 0.9 V (vs. Zn/Zn²⁺) was applied for the Zn||Cu based CE measurement, and the CE for Zn||Cu is calculated as the ratio of discharge capacity divided by the charge capacity in the preceding charge cycle. Linear sweep voltammetry (LSV) and Tafel plots were recorded using a Biologic VSP-300 workstation in a three-electrode configuration (vs. Ag/AgCl). For Tafel measurements, LSV was performed at a scan rate of 0.2 mV s⁻¹ from +0.2 V to −0.2 V. The corrosion current density (j_corr) was extracted by linear fitting of the Tafel region and determining the intercept at the open-circuit potential (OCV = 0 V). Electrochemical impedance spectroscopy (EIS) measurements were conducted using a Bio-Logic VMP3 workstation. EIS spectra were recorded from Zn||Zn symmetric cells in potentiostatic mode, with a sinusoidal perturbation amplitude of 10 mV over the frequency range of 100 kHz–10 mHz. Prior to each measurement, the cells were stabilized at open-circuit potential for 20 min. Neutral Zn–air battery performance was evaluated using two types of cells: 1. Lab-scale configuration: A Swagelok-type three-neck cell (Fig. S23) was used for pH monitoring, galvanostatic discharge tests, and long-term cycling. Glass fiber B was used as the separator. The cell was assembled by stacking Zn foil and a pre-fabricated air positive electrode, operated under ambient air conditions. A cut-off capacity of 1, 5 and 12 mAh cm⁻² were applied for the Swagelok-type zinc–air battery in the manuscript. The areal capacity for the lab-scale cell was calculated based on the geometric area of the positive electrode (1.13 cm²). The mass loading of the ZnO₂ for neutral Zn-air battery is from 3.5 mg cm⁻² to 21.4 mg cm⁻² based on the capacity requirement (1 mAh cm⁻² or 12 mAh cm⁻²) for measurement. 2. Prototype configuration: For large-area testing (Fig. S34), a pouch-like configuration was adopted. Zn foil (5 × 5 cm²) and the coated side of the air positive electrode (mass loading ≈ 21.4 mg cm⁻²) were placed face-to-face, separated by a glass fiber B membrane. The back side of the air positive electrode was exposed to ambient air through a channel in the casing. Nickel mesh (500 mesh, pore size 50 μm) was used as the current collector for the air positive electrode. A cut-off capacity of 60 mAh was applied for the square type of zinc–air battery. The areal capacity for the square cell (Fig. S34) was calculated based on the cell geometry (5 × 5 cm²). Both the coin cells and the prismatic (square) Zinc-air cells were tested in the wet lab without specific air convection. The testing environment was maintained at 23 ± 1 °C and an ambient relative humidity of ~40%.

Zinc utilization calculation

The Zinc utilization calculation was calculated based on the ratio between the experimentally discharged capacity (mAh) and the theoretical capacity of the consumed Zn metal, using the following equation:

$${{{\mathrm{Zn}}}}\; {{{\rm{utilization}}}}\,\left(\%\right)=\frac{{Q}_{{{\mathrm{discharge}}}}}{{n}_{{Zn}}\times \frac{{zF}}{3.6}}\times 100\%$$

(S1)

Where Q is the total discharge capacity in mAh which collected from the experiment, n is the number of moles of Zn involved in the reaction, based on the Zn mass, F is the Faraday constat (96485 C mol⁻¹), z is the electron transfer in the reaction, the factor 3.6 utilized in the equation is converted from the total charge from the coulombs (C) to milliampere-hours (mAh), as 1 mAh = 0.001 Ah*3600 = 3.6 C. In our example, a 100 μm Zn foil was used as the negative electrode in a Swagelok-type cell. The initial Zn mass was calculated based on the tested area (1.13 cm⁻²) and foil thickness (100 μm). Assuming complete utilization of the active Zn and a theoretical specific capacity of 820 mAh g⁻¹, we obtained a zinc utilization of 87.4 and 52% for ZN₃A₅·10H₂O-EE and ZN₃A₅·10H₂O in our system. All the specific capacity was calculated by considering only the mass of the Zn plate used. Additionally, the power density was calculated based on the geometric area of the positive electrode (1.13 cm²).

Characterization

Rheology and thermodynamics

Electrolyte viscosity was measured using a Malvern Kinexus Ultra+ rheometer in rotational mode. A solvent trap was employed to minimize evaporation during measurement. ITC was performed to evaluate thermodynamic parameters using a one-site binding model. From the titration curves, key values including the association constant (Kₐ), enthalpy change (ΔH), entropy change (ΔS), free energy change (ΔG), and binding stoichiometry (N) were extracted. The molar ratio was calculated based on the concentrations of DMC (ligand) and concentrated electrolyte (aptamer equivalent).

Microscopy and spectroscopy

Morphology and energy-dispersive X-ray spectroscopy (EDS) were analyzed via field-emission SEM (UltraPlus FESEM, 20 kV). XRD patterns were collected using a Rigaku Ultima IV (Cu Kα radiation), and Raman spectra were obtained with a WITec alpha300R confocal Raman microscope (532 nm laser). X-ray photoelectron spectroscopy (XPS) was performed using a PHI 5000 VersaProbe III. Surface etching was conducted via Ar⁺ sputtering to reveal bulk chemical composition, and all spectra were calibrated to the C 1s peak at 284.8 eV. Cells were opened under ambient air, after which the residual separator and electrolyte were carefully removed. The electrodes were rinsed with deionized water to clean the surface prior to the ex situ SEM, XPS, and XRD measurement.

Synchrotron-based techniques

Scattering profiles and PDF analyses were conducted at the Brockhouse XRD and Scattering Beamline (BXDS-WHE) of the Canadian Light Source, using a transmission geometry and high-energy wiggler source. XAS, including XANES and EXAFS, was carried out at the HXMA beamline (061D) using a superconducting wiggler source with Si(111) monochromator and Rh-coated mirrors. Operando PXM (as shown in Fig. 5) was performed at the BMIT-BM beamline using a filtered white beam. Zn plating dynamics were resolved via absorption contrast and analyzed using Fiji software, with the electrolyte manually set as the reference background (lowest absorption).

MD simulation

Force fields details

Force fields (FFs) for acetate and DMC were generated through wavefunction calculations using ORCA-v5.0 at the B3LYP/def2-TZVP level. Partial charges were subsequently determined using Multiwfn, and the FF parameters were extracted using AMBER Tools GAFF. The SPC/E water-FF was applied for water molecules, while Zn²⁺ and Na⁺ ions were parameterized based on calculated optimized hydration free energies. Non-bonded interactions were modeled with cut-off distances set to 9 Å and 10 Å, with the Lorentz–Berthelot combining rules used for non-bonded interactions. Long-range Coulombic interactions were addressed using the particle-particle, particle-mesh method with a precision of 0.0001.

Simulation and MD analysis protocol

The electrolyte system was constructed using the Moltemplate package with a composition ratio of (Zn: Na: acetate: H₂O: DMC = 1:3:5: 10:0.5), incorporating 1110 water molecules. MD simulations were performed using the large-scale atomic/molecular parallel simulator package. The SHAKE algorithm was employed to constrain the behavior of water molecules. In the simulations, a Verlet integrator with a timestep of 1.0 femtosecond (fs) was utilized. The Nose–Hoover thermostat and barostat were employed, with damping factors for temperature and pressure set to 10²fs and 10⁵fs, respectively.

The electrolyte structure was analysis by the RDF by following equation.

$${{{\rm{g}}}}({{{\rm{r}}}})=\frac{{{{\rm{d}}}}{{{\rm{N}}}}({{{\rm{r}}}})}{\uprho \uppi 4{{{\rm{r}}}}^{2}{{{\rm{d}}}}{{{\rm{r}}}}}$$

where N(r) is the atom number in the spherical shell, ρ is the number density of the whole system, and r is the distance from molecules.