Solvent Structure Research Articles

Suitable Stereoscopic Configuration of Electrolyte Additive Enabling Highly Reversible and High-Rate Zn Anodes.

Electrolyte additive engineering is a crucial method for enhancing the performance of aqueous zinc-ion batteries (AZIBs). Recently, most research predominantly focuses on the role of functional groups in regulating electrolytes, often overlooking the impact of molecule stereoscopic configuration. Herein, two isomeric sugar alcohols, mannitol and sorbitol, are employed as electrolyte additives to investigate the impact of the stereoscopic configuration of additives on the ZnSO4 electrolyte. Experimental analysis and theoretical calculations reveal that the primary factor for improving Zn anode performance is the regulation of the solvation sheath by these additives. Among the isomers, mannitol exhibits stronger binding energies with Zn2+ ions and water molecules due to its more suitable stereoscopic configuration. These enhanced bindings allow mannitol to coordinate with Zn2+, contributing to solvation structure formation and reducing the active H2O molecules in the bulk electrolyte, resulting in suppressed parasitic reactions and inhibited dendritic growth. As a result, the zinc electrodes in mannitol-modified electrolyte exhibit excellent cycling stability of 1600 h at 1 mA cm-2 and 900 h at 10 mA cm-2, respectively. Hence, this study provides novel insights into the importance of suitable stereoscopic molecule configurations in the design of electrolyte additives for highly reversible and high-rate Zn anodes.

Tailoring the Whole Deposition Process from Hydrated Zn2+ to Zn0 for Stable and Reversible Zn Anode

The practical application of aqueous zinc‐ion batteries (ZIBs) indeed faces challenges primarily attributed to the inherent side reactions and dendrite growth associated with the Zn anode. In the present work, N‐Methylmethanesulfonamide (NMS) is introduced to optimize the transfer, desolvation, and reduction of Zn2+, achieving highly stable and reversible Zn plating/stripping. The NMS molecule can substitute one H2O molecule in the solvation structure of hydrated Zn2+ and be preferentially chemisorbed on the Zn surface to protect Zn anode against corrosion and hydrogen evolution reaction (HER), thereby suppressing byproducts formation. Additionally, a robust N‐rich organic and inorganic (ZnS and ZnCO3) hybrid solid electrolyte interphase is in situ generated on Zn anode due to the decomposition of NMS, resulting in enhanced Zn2+ transport kinetics and uniform Zn2+ deposition. Consequently, aqueous cells with the NMS achieve a long lifespan of 2300 h at 1 mA cm−2 and 1 mAh cm−2, high cumulative plated capacity of 3.25 Ah cm−2, and excellent reversibility with an average coulombic efficiency (CE) of 99.7% over 800 cycles.

Tailoring the Whole Deposition Process from Hydrated Zn2+ to Zn0 for Stable and Reversible Zn Anode.

The practical application of aqueous zinc-ion batteries (ZIBs) indeed faces challenges primarily attributed to the inherent side reactions and dendrite growth associated with the Zn anode. In the present work, N-Methylmethanesulfonamide (NMS) is introduced to optimize the transfer, desolvation, and reduction of Zn2+, achieving highly stable and reversible Zn plating/stripping. The NMS molecule can substitute one H2O molecule in the solvation structure of hydrated Zn2+ and be preferentially chemisorbed on the Zn surface to protect Zn anode against corrosion and hydrogen evolution reaction (HER), thereby suppressing byproducts formation. Additionally, a robust N-rich organic and inorganic (ZnS and ZnCO3) hybrid solid electrolyte interphase is in situ generated on Zn anode due to the decomposition of NMS, resulting in enhanced Zn2+ transport kinetics and uniform Zn2+ deposition. Consequently, aqueous cells with the NMS achieve a long lifespan of 2300 h at 1 mA cm-2 and 1 mAh cm-2, high cumulative plated capacity of 3.25 Ah cm-2, and excellent reversibility with an average coulombic efficiency (CE) of 99.7 % over 800 cycles.

Analysis of NADES and its water tailoring effects constructed from inulin and L-proline based on structure, physicochemical and antifreeze properties

The structure, physicochemical and anti-freeze properties of natural deep eutectic solvent (NADES) composed of inulin and L-proline (molar ratio of 1:11) were investigated. Proton nuclear magnetic resonance (1H NMR), Fourier infrared spectroscopy (FTIR), and Raman spectroscopy revealed extensive hydrogen bonding in the pure NADES system, and the addition of water weakens the hydrogen bonding interactions between the components. The smaller transverse relaxation time (T2) represents the stronger hydrogen bond strength, and NADES+40 % H2O exhibited a large T2 (71.68 ms). When 10 % water was added, the viscosity decreased from 3620 mPa·s to 1777 mPa·s, but the conductivity increased to approximately twice the original value. Furthermore, adding 10 % water lowered the glass transition temperature (Tg) of NADES by 5.6 °C. NADES+10 % H2O exhibited favorable thermal stability and freezing resistance, as evidenced by the fact that approximately 82.61 % of the ice crystals area <200 μm2 after 30 min of crystallization. The changes in the structure, physicochemical, and anti-freezing properties of water-tailored NADES are expected to enable the design of novel antifreeze agents.

Dual ion regulation enables High-Coulombic-efficiency lithium metal batteries

Lithium (Li) metal batteries are ideal alternatives for pursuing high-energy-density batteries. Nevertheless, their subpar cycling capabilities and safety problems remain a significant concern because of the insufficient reversibility of Li plating/stripping processes. Herein, potassium trifluoromethanesulfonate (KOTf) is proposed as an electrolyte additive to achieve high Coulombic efficiency during cycling, which could be assigned to the synergistic regulation effect of anions and cations in KOTf. On the one hand, the OTf- helps form an anion-rich solvation structure, which could be preferentially reduced to obtain a robust and conductive inorganic-rich SEI film to stabilize the lithium metal anode. On the other hand, the existence of K+ induces the generation of K+-rich positive charge shielding layer, further hindering the growth of Li dendrite. The KOTf-assisted Li||Cu cell shows a high Coulombic efficiency (CE) of 99.7 % and an extremely long-cycle life of 700 cycles with an average CE of 99.01 % under 0.5 mA cm−2 and 0.5 mAh cm−2. The excellent lithium metal stripping/plating efficiency is mainly due to the OTf--derived inorganic-rich SEI and the electrostatic shielding effect of K+. This work emphasizes the important role of salts’ anions and cations in determining the CE of LMBs and provides an effective strategy to improve the cycling performance of LMBs.

Regulating the Solvation Structure in Polymer Electrolytes for High‐Voltage Lithium Metal Batteries

AbstractSolid polymer electrolytes are promising electrolytes for safe and high‐energy‐density lithium metal batteries. However, traditional ether‐based polymer electrolytes are limited by their low lithium‐ion conductivity and narrow electrochemical window because of the well‐defined and intimated Li+‐oxygen binding topologies in the solvation structure. Herein, we proposed a new strategy to reduce the Li+‐polymer interaction and strengthen the anion‐polymer interaction by combining strong Li+‐O (ether) interactions, weak Li+‐O (ester) interactions with steric hindrance in polymer electrolytes. In this way, a polymer electrolyte with a high lithium ion transference number (0.80) and anion‐rich solvation structure is obtained. This polymer electrolyte possesses a wide electrochemical window (5.5 V versus Li/Li+) and compatibility with both Li metal anode and high‐voltage NCM cathode. Li||LiNi0.5Co0.2Mn0.3O2 full cells with middle‐high active material areal loading (~7.5 mg cm−2) can stably cycle at 4.5 V. This work provides new insight into the design of polymer electrolytes for high‐energy‐density lithium metal batteries through the regulation of ion‐dipole interactions.

Regulating the Solvation Structure in Polymer Electrolytes for High-Voltage Lithium Metal Batteries.

Solid polymer electrolytes are promising electrolytes for safe and high-energy-density lithium metal batteries. However, traditional ether-based polymer electrolytes are limited by their low lithium-ion conductivity and narrow electrochemical window because of the well-defined and intimated Li+-oxygen binding topologies in the solvation structure. Herein, we proposed a new strategy to reduce the Li+-polymer interaction and strengthen the anion-polymer interaction by combining strong Li+-O (ether) interactions, weak Li+-O (ester) interactions with steric hindrance in polymer electrolytes. In this way, a polymer electrolyte with a high lithium ion transference number (0.80) and anion-rich solvation structure is obtained. This polymer electrolyte possesses a wide electrochemical window (5.5 V versus Li/Li+) and compatibility with both Li metal anode and high-voltage NCM cathode. Li||LiNi0.5Co0.2Mn0.3O2 full cells with middle-high active material areal loading (~7.5 mg cm-2) can stably cycle at 4.5 V. This work provides new insight into the design of polymer electrolytes for high-energy-density lithium metal batteries through the regulation of ion-dipole interactions.

Liberating Lithium Ions from Polymer Matrix via Harnessing Ion‐Dipole Interaction Toward Stable Solid‐State Lithium Metal Batteries

AbstractAlthough polymer electrolytes have shown great potential in solid‐state lithium metal batteries (LMBs), the polymer chain segments anchor the movement of lithium ions (Li+), which induces the low ionic conductivity of the electrolytes and limits their application. Herein, a strategy of harnessing ion‐dipole interactions is proposed to liberate lithium ions from polymer chains. The adiponitrile (ADN) molecular dipole with strong bond dipole moment (C≡N, 11.8 × 10−30 C m) is introduced into the polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐HFP) polymer matrix, achieving an electrolyte with high ionic conductivity of 5.1 × 10−4 S cm−1 at 30 °C. It is demonstrated that the strong ion‐dipole interaction between C≡N and Li+ weakens the ion‐dipole interaction of F···…Li+, facilitating Li+ dissociation and liberating Li+ from polymer chains. Moreover, a hybrid and unsaturated solvation structure is formed with the ADN molecular dipole, PVDF‐HFP polymer chain, and TFSI− anion, corresponding to the solvent‐separated ion pair (SSIP) solvation structure. Thus, the obtained electrolyte realizes high ionic conductivity and lithium‐ion transference number (0.74). Consequently, the assembled lithium symmetric cell delivers stable Li stripping/plating reversibility over 900 h. Additionally, the Li|LiFePO4 full cells exhibit long‐term cycling stability at 0.5 C over 300 cycles with a capacity retention of 96.4% and ultralong cycling of 1000 cycles at a high rate (5 C).

Effect of water on eutectic solvents: Structural properties and physical interactions with CO2

Deep eutectic solvents (DESs) are versatile solvents for various applications including CO2 separations due to their good solvent strength, low volatilities, high thermal stabilities, and tunable properties. Properties of DESs alter with the presence of water and especially in applications where the solvent is in direct contact with air such as CO2 removal from the atmosphere. This study employs classical molecular dynamics (MD) simulations to examine the impact of water (0 to 70 wt%) on the liquid structure and physical interactions in a eutectic solvent composed of an ionic liquid (IL) 1-ethyl-3-methylimidazolium 2-cyanopyrrolide, [EMIM][2CNPyr], that functions as a hydrogen bond acceptor (HBA) and with three different hydrogen bond donors (HBDs): ethylene glycol (EG), propylene glycol (PG), and monoethanolamine (MEA). It is found that water preferentially solvates HBDs and weakens the hydrogen-bonding interactions between [2CNpyr] and the HBDs, thus resulting in significant structural changes that lead to enhanced interactions between CO2 and [EMIM], [2CNpyr], and MEA. Although these systems represent CO2-chemisorbing solvents in practice, the physical interactions in the presence of water as examined herein provides guidance on their phase behavior and tuning of physical properties by composition for targeted applications including CO2 separations.

Super Hydrous Solvated Structure of Chaotropic Ca2+ Contributes Superior Anti‐Freezing Aqueous Electrolytes and Stabilizes the Zn anode

AbstractThe further development of aqueous zinc (Zn)‐ion batteries (AZIBs) is constrained by the high freezing points and the instability on Zn anodes. Current improvement strategies mainly focus on regulating hydrogen bond (HB) donors (H) of solvent water to disrupt HBs, while neglecting the environment of HB‐acceptors (O). Herein, we propose a mechanism of chaotropic cation‐regulated HB‐acceptor via a “super hydrous solvated” structure. Chaotropic Ca2+ can form a solvated structure via competitively binding O atoms in H2O, effectively breaking the HBs among H2O molecules, thereby reducing the glass transition temperature of hybrid 1 mol L−1 (M) ZnCl2+4 M CaCl2 electrolyte (−113.2 °C). Meanwhile, the high hydratability of Ca2+ contributes to the water‐poor solvated structure of Zn2+, suppressing side reactions and uneven Zn deposition. Benefiting from the anti‐freezing electrolyte and high reversible Zn anode, the Zn||Pyrene‐4,5,9,10‐tetraone (PTO) batteries deliver an ultrahigh capacity of 183.9 mAh g−1 at 1.0 A g−1 over 1600‐time stable cycling at −60 °C. This work presents a cheap and efficient aqueous electrolyte to simultaneously improve low‐temperature performances and Zn stability, broadening the design concepts for antifreeze electrolytes.

Toward Ultralow Temperature Lithium Metal Batteries: Advancing the Feasibility of 1,3‐Dioxolane Based Localized High‐Concentration Electrolytes via Lithium Nitrate

AbstractLithium metal batteries (LMBs) suffer severe capacity deterioration due to sluggish ionic transport kinetics at extremely low temperatures, which limits their practical operation. Selecting solvents with low desolvation energy, and promoting interfacial Li+ transport in solid electrolyte interphase (SEI) are regarded as effective methods to improve electrochemical performances. Herein, 1,3‐dioxolane (DOL) with weak solvating power is adopted for designing a DOL‐based localized high concentration electrolyte (DLHCE) with LiNO3 as a multifunctional additive. The strong coordination between NO3− and DOL molecules not only inhibits the polymerization of DOL at high lithium bis(fluorosulfonyl)imide (LiFSI) concentration, but also reduces the solvent‐diluent miscibility and extends the salt‐solvent solubility. As a result, an anion‐dominated solvation structure is obtained that derives an inorganic‐rich SEI composed of LiF and Li3N, guiding the uniform deposition of Li at low temperature. Remarkably, the Li||LiFePO4 cells retain 53.6% of room temperature capacity at −40 °C, and also present potential application of Li||NCM811 cells under cryogenic environments.

Super Hydrous Solvated Structure of Chaotropic Ca2+ Contributes Superior Anti-Freezing Aqueous Electrolytes and Stabilizes the Zn anode.

The further development of aqueous zinc (Zn)-ion batteries (AZIBs) is constrained by the high freezing points and the instability on Zn anodes. Current improvement strategies mainly focus on regulating hydrogen bond (HB) donors (H) of solvent water to disrupt HBs, while neglecting the environment of HB-acceptors (O). Herein, we propose a mechanism of chaotropic cation-regulated HB-acceptor via a "super hydrous solvated" structure. Chaotropic Ca2+ can form a solvated structure via competitively binding O atoms in H2O, effectively breaking the HBs among H2O molecules, thereby reducing the glass transition temperature of hybrid 1 mol L-1 (M) ZnCl2+4 M CaCl2 electrolyte (-113.2 °C). Meanwhile, the high hydratability of Ca2+ contributes to the water-poor solvated structure of Zn2+, suppressing side reactions and uneven Zn deposition. Benefiting from the anti-freezing electrolyte and high reversible Zn anode, the Zn||Pyrene-4,5,9,10-tetraone (PTO) batteries deliver an ultrahigh capacity of 183.9 mAh g-1 at 1.0 A g-1 over 1600-time stable cycling at -60 °C. This work presents a cheap and efficient aqueous electrolyte to simultaneously improve low-temperature performances and Zn stability, broadening the design concepts for antifreeze electrolytes.

Trace Small Molecular/Nano-Colloidal Multiscale Electrolyte Additives Enable Ultra-Long Lifespan of Zinc Metal Anodes.

Electrolyte additives are efficient to improve the performance of aqueous zinc-ion batteries (AZIBs), yet the current electrolyte additives are limited to fully water-soluble additives (FWAs) and water-insoluble additives (WIAs). Herein, trace slightly water-soluble additives (SWAs) of zinc acetylacetonate (ZAA) were introduced to aqueous ZnSO4 electrolytes. The SWA system of ZAA is composed of a FWA part and a WIA part in a dynamic manner of dissolution equilibrium. The FWA part exists as soluble small molecules, which efficiently regulate Zn2+ ion solvation structure, while the WIA part exists as insoluble nano-colloids, which in-situ form a thick and robust solid electrolyte interface film on zinc metal anodes (ZMAs). Such small molecular/nano-colloidal multiscale electrolyte additives of ZAA are capable to not only improve ionic conductivity and transference number but also inhibit corrosion, hydrogen evolution, and Zn dendrite on ZMAs. The SWA-based Zn∥Zn half battery delivers a superb cumulative plating capacity of 15 Ah cm-2 under 1 mAh cm-2 and 20 mA cm-2, and the SWA-based NH4V4O10∥Zn pouch cell obtains a capacity retention of 67.8% within 4000 cycles under 4 A g-1. The study provides innovative insights for rational design of electrolyte additives, which may pave the way for the practicality of AZIBs.

Variant‐Localized High‐Concentration Electrolyte without Phase Separation for Low‐Temperature Batteries

AbstractDual‐ion batteries (DIBs) present great application potential in low‐temperature energy storage scenarios due to their unique dual‐ion working mechanism. However, at low temperatures, the insufficient electrochemical oxidation stability of electrolytes and depressed interfacial compatibility impair the DIB performance. Here, we design a variant‐localized high‐concentration solvation structure for universal low‐temperature electrolytes (ν‐LHCE) without the phase separation via introducing an extremely weak‐solvating solvent with low energy levels. The unique solvation structure gives the ν‐LHCE enhanced electrochemical oxidation stability. Meanwhile, the extremely weak‐solvating solvent can competitively participate in the Li+‐solvated coordination, which improves the Li+ transfer kinetics and boosts the formation of robust interphases. Thus, the ν‐LHCE electrolyte not only has a good high‐voltage stability of &gt;5.5 V and proper Li+ transference number of 0.51 but also shows high ionic conductivities of 1 mS/cm at low temperatures. Consequently, the ν‐LHCE electrolyte enables different types of batteries to achieve excellent long‐term cycling stability and good rate capability at both room and low temperatures. Especially, the capacity retentions of the DIB are 77.7 % and 51.6 %, at −40 °C and −60 °C, respectively, indicating great potential for low‐temperature energy storage applications, such as polar exploration, emergency communication equipment, and energy storage station in cold regions.

Variant-Localized High-Concentration Electrolyte without Phase Separation for Low-Temperature Batteries.

Dual-ion batteries (DIBs) present great application potential in low-temperature energy storage scenarios due to their unique dual-ion working mechanism. However, at low temperatures, the insufficient electrochemical oxidation stability of electrolytes and depressed interfacial compatibility impair the DIB performance. Here, we design a variant-localized high-concentration solvation structure for universal low-temperature electrolytes (ν-LHCE) without the phase separation via introducing an extremely weak-solvating solvent with low energy levels. The unique solvation structure gives the ν-LHCE enhanced electrochemical oxidation stability. Meanwhile, the extremely weak-solvating solvent can competitively participate in the Li+-solvated coordination, which improves the Li+ transfer kinetics and boosts the formation of robust interphases. Thus, the ν-LHCE electrolyte not only has a good high-voltage stability of >5.5 V and proper Li+ transference number of 0.51 but also shows high ionic conductivities of 1 mS/cm at low temperatures. Consequently, the ν-LHCE electrolyte enables different types of batteries to achieve excellent long-term cycling stability and good rate capability at both room and low temperatures. Especially, the capacity retentions of the DIB are 77.7 % and 51.6 %, at -40 °C and -60 °C, respectively, indicating great potential for low-temperature energy storage applications, such as polar exploration, emergency communication equipment, and energy storage station in cold regions.

12‐Ah‐Level Li‐Ion Pouch Cells Enabling Fast Charging at Temperatures between −20 and 50 °C

AbstractAchieving fast‐charging capabilities in Li‐ion batteries (LIBs)—charging 80% of the battery capacity within 15 minutes—while maintaining an acceptable cycle life remains challenging due to various polarizations occurring at elevated charge rates. Such a goal is more tough at subzero, as temperature reduction slows the kinetics process including electrolyte mass transport and electrode charge transfer, substantially increasing the risk of lithium plating. Herein, it is found that adding LiFSI to a LiPF6 carbonate‐based electrolyte alters the Li+ solvation structure, endowing the dual‐salt electrolyte with a higher Li+ diffusion coefficient and lower desolvation energy. Benefit from the smaller structural change and the formation of a robust, conductive solid electrolyte interphase, the 12Ah‐pouch cells based on LiNi0.52Co0.2Mn0.28O2 cathodes and graphite anodes demonstrate fast‐charging capabilities and stable cycling performance across a wide temperature range of −20 to 50 ℃: charging 89% and 93% of pouch cell capacity within 4 minutes at 25 and 50 ℃ and 82% within 15 minutes at −20 ℃, maintaining capacity retention of 94% after 2000 cycles at 8C at 0 ℃ and 89% after 350 cycles at −20 ℃ at 4C. This work might offer new insights into enhancing the fast‐charging capabilities of LIBs under extreme conditions.

PyDFT-QMMM: A modular, extensible software framework for DFT-based QM/MM molecular dynamics.

PyDFT-QMMM is a Python-based package for performing hybrid quantum mechanics/molecular mechanics (QM/MM) simulations at the density functional level of theory. The program is designed to treat short-range and long-range interactions through user-specified combinations of electrostatic and mechanical embedding procedures within periodic simulation domains, providing necessary interfaces to external quantum chemistry and molecular dynamics software. To enable direct embedding of long-range electrostatics in periodic systems, we have derived and implemented force terms for our previously described QM/MM/PME approach [Pederson and McDaniel, J. Chem. Phys. 156, 174105 (2022)]. Communication with external software packages Psi4 and OpenMM is facilitated through Python application programming interfaces (APIs). The core library contains basic utilities for running QM/MM molecular dynamics simulations, and plug-in entry-points are provided for users to implement custom energy/force calculation and integration routines, within an extensible architecture. The user interacts with PyDFT-QMMM primarily through its Python API, allowing for complex workflow development with Python scripting, for example, interfacing with PLUMED for free energy simulations. We provide benchmarks of forces and energy conservation for the QM/MM/PME and alternative QM/MM electrostatic embedding approaches. We further demonstrate a simple example use case for water solute in a water solvent system, for which radial distribution functions are computed from 100ps QM/MM simulations; in this example, we highlight how the solvation structure is sensitive to different basis-set choices due to under- or over-polarization of the QM water molecule's electron density.

Ab initio molecular dynamics study of hydroxyl positioning in butanediol and its impact on deep eutectic solvent structure

Electrolytes play a crucial role in enhancing the performance of energy storage devices, including batteries and supercapacitors. However, traditional electrolytes, such as aqueous solutions, organic solvents, and ionic liquids, exhibit inherent limitations and challenges. Deep eutectic solvents have recently emerged as promising alternatives due to their environmentally friendly nature and favorable properties. Despite their widespread applications in various domains, their potential as electrolytes remains relatively underexplored. This study investigates three distinct types of deep eutectic solvents derived from different isomers of butanediols combined with choline chloride. Ab initio molecular dynamics simulations are employed to analyze the microstructure of these deep eutectic solvents, focusing on non-covalent electrostatic interactions, hydrogen bonding patterns, and vibrational spectra. The results reveal significant differences in the structural configuration of hydrogen bond acceptors and hydrogen bond donors and their interactions within the deep eutectic solvents. Specifically, the positioning of functional groups in hydrogen bond donors significantly impacts the hydrogen bonding network and the interaction with monoatomic ions. Moreover, the vibrational spectra analysis highlights the existence of hydrogen bonds involving stretching modes of the OH group, as evidenced by redshift deviations. Overall, this study provides valuable insights into the unique features of deep eutectic solvents as potential electrolytes for energy storage applications. The comprehensive analysis of their microstructure and vibrational properties enhances our understanding of deep eutectic solvent utilization and opens avenues for further research in sustainable energy storage.

Stabilizing electrode-electrolyte interface via crown ether-containing selective coating for dendrite-free Na-K anode-based solid-state sodium batteries

Sodium-potassium (Na-K) alloy is considered a promising anode material due to its liquid characteristics at room temperature. However, unstable interfaces and disastrous ion exchange between Na-K alloy anodes and solid-state Na electrolytes (SSNEs) have hindered further applications of solid-state Na batteries (SSNBs) based on Na-K anodes. In this work, a specially designed Na+/K+ selective gel coating with 15-crown 5-ether (15C5) is constructed on the beta-alumina solid electrolyte (BASE) to achieve a good match with Na-K anodes. The coordination of 15C5 with Na+ forms Na+-permeable complexes and affects the electrolyte solvation structure in the gel coating, resulting in the formation of solid electrolyte interfaces (SEIs) that lack K+ channels and are organically rich, which effectively inhibit the ion exchange and stabilize the interface. Benefitting from the selective coating, the cycling lifetime of the Na-K|Gel-BASE-Gel|Na-K symmetric cell reaches over 1000 h, and the Na-K|Gel-BASE-Gel|Na3V2(PO4)3 full cell exhibits great long-cycle stability and excellent rate performance at room temperature. This work extends the application of Na-K anodes and provides a suggestion for achieving high-performance SSNBs at room temperature.

Unveiling the Failure Mechanism of Zn Anodes in Zinc Trifluorosulfonate Electrolyte: The Role of Micelle-like Structures.

Zinc trifluorosulfonate [Zn(OTf)2] is considered as the most suitable zinc salt for aqueous Zn-ion batteries (AZIBs) but cannot support the long-term cycling of the Zn anode. Here, we reveal the micelle-like structure of the Zn(OTf)2 electrolyte and reunderstand the failing mechanism of the Zn anode. Since the solvated Zn2+ possesses a positive charge, it can spontaneously attract OTf- with the hydrophilic group of -SO3 and the hydrophobic group of -CF3 via electrostatic interaction and form a "micelle-like" structure, which is responsible for the poor desolvation kinetics and dendrite growth. To address these issues, an antimicelle-like structure is designed by using ethylene glycol monomethyl ether (EGME) as a cosolvent for highly reversible AZIBs. The modified electrolyte shows lower dissociation ability to Zn(OTf)2 and higher coordination tendency with Zn2+ compared to the Zn(OTf)2 electrolyte, resulting in the unique solvation structure of Zn2+(H2O)1.2(OTf-)2(EGME)2.8, which significantly reduces the charge of micelle, damages the micelle-like structure, and boosts the desolvation kinetics. Moreover, the reduction of EGME and OTf- can form a robust dual-layered SEI with high Zn2+ ion conductivity. Consequently, the Zn/Cu asymmetric coin cell using ZT-EGME can work at a high rate and a capacity of 50 mA cm-2 and 5 mA h cm-2 for more than 120 cycles, while its counterparts using ZT can barely work. Moreover, a 505.1 mA h pouch cell with practical parameters including a lean electrolyte supply of 15 mL A h-1 and an N/P ratio of ∼3.5 can work for 50 cycles.