A Low-Cost Al(OH)3-Modified Fire-Retardant and Shuttle-Limiting Separator for Safe and Stable Lithium–Sulfur Batteries

Lithium–sulfur battery (LSB) possesses high theoretical energy density, but its poor cycling stability and safety issues significantly restrict progress in practical applications. Herein, a low-cost and simple Al(OH)₃-based modification of commercial separator, which renders the battery outstanding fire-retardant and stable cycling, is reported. The modification is carried out by a simple blade coating of an ultrathin composite layer, mainly consisting of Al(OH)₃ nanoparticles and conductive carbon, on the cathode side of the separator. The Al(OH)₃ shows strong chemical absorption ability toward Lewis-based polysulfides and outstanding fire retardance through a self-decomposition mechanism under high heat, while the conductive carbon material acts as a top current collector to prevent dead polysulfide. LSB using the Al(OH)₃-modified separator shows an extremely low average capacity decade per cycle during 1000 cycles at 2 C (0.029%, 1 C = 1600 mA g⁻¹). The pouch cell exhibiting high energy density (426 Wh kg⁻¹) can also steadily cycle for more than 100 cycles with high capacity retention (70.2% at 0.1 C). The effectiveness and accessibility of this Al(OH)₃ modification strategy will hasten the practical application progress of LSBs.     

A High Energy Density Aqueous Battery Achieved by Dual Dissolution/Deposition Reactions Separated in Acid‐Alkaline Electrolyte

Aqueous batteries are facing big challenges in the context of low working voltages and energy density, which are dictated by the narrow electrochemical window of aqueous electrolytes and low specific capacities of traditional intercalation‐type electrodes, even though they usually represent high safety, low cost, and simple maintenance. For the first time, this work demonstrates a record high‐energy‐density (1503 Wh kg^?1 calculated from the cathode active material) aqueous battery system that derives from a novel electrolyte design to expand the electrochemical window of electrolyte to 3 V and two high‐specific‐capacity electrode reactions. An acid‐alkaline dual electrolyte separated by an ion‐selective membrane enables two dissolution/deposition electrode redox reactions of MnO₂/Mn²⁺ and Zn/Zn(OH)₄^2? with theoretical specific capacities of 616 and 820 mAh g^?1, respectively. The newly proposed Zn–Mn²⁺ aqueous battery shows a high Coulombic efficiency of 98.4% and cycling stability of 97.5% of discharge capacity retention for 1500 cycles. Furthermore, in the flow battery based on Zn–Mn²⁺ pairs, more excellent stability of 99.5% of discharge capacity retention for 6000 cycles is achieved due to greatly improved reversibility of the Zn anode. This work provides a new path for the development of novel aqueous batteries with high voltage and energy density.     

10 mAh cm−2 Cathode by Roll-to-Roll Process for Low Cost and High Energy Density Li-Ion Batteries

Roll-to-roll dry processing enables the manufacture of high energy density and low cost Li-ion batteries (LIBs). However, as the thickness of the electrode fabricated by dry processing becomes greater (≥10 mAh cm⁻²), Li-ion migration resistance (R_ion) and charge-transfer resistance (R_ct) in the electrode dramatically increase due to long diffusion lengths for Li-ion and electron. Therefore, it is important to reduce diffusion lengths in the electrode to achieve high energy density LIBs. The dry electrode with a high areal capacity of 10 mAh cm⁻² and low resistance can be achieved by following three characteristics. First, the fibrillization behavior of polytetrafluoroethylene (PTFE) binder is controlled by adjusting the processing temperature during the fibrillization process, which enables uniform distribution of PTFE binder and carbon black (CB). Second, pore size/distribution and conducting network are engineered by multi-dimensional conducting agents, enhancing Li-ions and electrons transport in the electrode. Finally, the structural integrity of LiNi_0.80Co_0.15Al_0.05O₂ (NCA) particles is improved without fractures, which enables uniform pore distribution in the electrode by controlling the calendering step. The prepared 10 mAh cm⁻² dry electrode with homogeneous microstructure shows reduced R_ion and R_ct due to short diffusion lengths, which improves electrochemical performances in LIBs with a high volumetric energy density of ≈710 Wh L⁻¹.     

Constructing Resilient Cross-Linked Network Toward Stable All-Solid-State Lithium-Sulfur Batteries

Lithium-sulfur batteries utilizing sulfide solid electrolytes hold considerable potential for achieving both high energy density and enhanced safety. However, the substantial volume changes experienced by sulfur during cycling result in mechanical stress accumulation, leading to mechanical degradation and thereby degrading overall electrochemical performance. In this study, a stress-buffer strategy is proposed to address this challenge by engineering a mechanically resilient crosslinked structure for the composite sulfur cathode. This structure is accomplished through the integration of a highly flexible thermoplastic elastomer (ethylene vinyl acetate, EVA), which enables stress release during sulfur volume variations by the repeated stretching and shrinking of EVA, thereby maintaining stable ionic/electronic diffusion channels within the electrode. By virtue of the mechanically stable architecture, the stress evolution experienced by the entire sulfur electrode is substantially reduced, witnessing a remarkable decrease of ≈33.7%. Consequently, the S-EVA composite cathode demonstrates exceptional electrochemical performance, especially cycling stability. Notably, the S-EVA composite cathode, with a high loading of 7.5 mg cm⁻², exhibits stable cycling performance close to 3.0 mAh cm⁻² within 50 cycles. This work not only offers novel insights into mitigating the mechanical stress within the electrode but also paves the way for developing durable high-performance all-solid-state batteries.     

The First Report on Excellent Cycling Stability and Superior Rate Capability of Na3V2(PO4)3 for Sodium Ion Batteries

Sodium ion batteries are attractive for the rapidly emerging large‐scale energy storage market for intermittent renewable resources. Currently a viable cathode material does not exist for practical non‐aqueous sodium ion battery applications. Here we disclose a high performance, durable electrode material based on the 3D NASICON framework. Porous Na₃V₂(PO₄)₃/C was synthesized using a novel solution‐based approach. This material, as a cathode, is capable of delivering an energy storage capacity of ～400 mWh/g vs. sodium metal. Furthermore, at high current rates (10, 20 and 40 C), it displayed remarkable capacity retention. Equally impressive is the long term cycle life. Nearly 50% of the initial capacity was retained after 30,000 charge/discharge cycles at 40 C (4.7 A/g). Notably, coulombic efficiency was 99.68% (average) over the course of cycling. To the best of our knowledge, the combination of high energy density, high power density and ultra long cycle life demonstrated here has never been reported before for sodium ion batteries. We believe our findings will have profound implications for developing large‐scale energy storage systems for renewable energy sources.     

In Situ Vertically Aligned MoS2 Arrays Electrodes for Complexing Agent-Free Bromine-Based Flow Batteries with High Power Density and Long Lifespan

Bromine-based flow batteries (Br-FBs) are highly competitive for stationary energy storage due to their high energy density and cost-effectiveness. However, adding bromine complexing agents (BCAs) to electrolytes slows down Br₂/Br⁻ reaction kinetics, causing higher polarization and lower power density of Br-FBs. Herein, in situ vertically aligned MoS₂ nanosheet arrays on traditional carbon felt substrates as electrodes to construct high power–density BCA-free Br-FBs are proposed. MoS₂ arrays exhibit strong adsorption capacity to bromine, which helps the electrodes capture and retain bromine species. Even without BCAs, the battery self-discharge caused by bromine diffusion is also inhibited. Moreover, the rate-determining step of Br₂/Br⁻ reactions is boosted and the vertically aligned array structure provides sufficient sites, motivating Br₂/Br⁻ reaction kinetics and decreasing the battery polarization. The capacity retention rate of the BCA-free Br-FB based on MoS₂ arrays-based electrodes reaches 46.34% after the 24-h standing test at 80 mA cm⁻², meeting the requirements of practical applications. Most importantly, this BCA-free Br-FB exhibits a high Coulombic efficiency of 97.00% and an ultralong cycle life of 1000 cycles at a high current density of 200 mA cm⁻². This work provides an available approach to developing advanced electrode materials for high power–density and long-lifespan Br-FBs.     

Hybrid and Aqueous Lithium‐Air Batteries

Lithium‐air (Li‐air) batteries have become attractive because of their extremely high theoretical energy density. However, conventional Li‐air cells operating with non‐aqueous electrolytes suffer from poor cycle life and low practical energy density due to the clogging of the porous air cathode by insoluble discharge products, contamination of the organic electrolyte and lithium metal anode by moist air, and decomposition of the electrolyte during cycling. These difficulties may be overcome by adopting a cell configuration that consists of a lithium‐metal anode protected from air by a Li⁺‐ion solid electrolyte and an air electrode in an aqueous catholyte. In this type of configuration, a Li⁺‐ion conducting “buffer” layer between the lithium‐metal anode and the solid electrolyte is often necessary due to the instability of many solid electrolytes in contact with lithium metal. Based on the type of buffer layer, two different battery configurations are possible: “hybrid” Li‐air batteries and “aqueous” Li‐air batteries. The hybrid and aqueous Li‐air batteries utilize the same battery chemistry and face similar challenges that limit the cell performance. Here, an overview of recent developments in hybrid and aqueous Li‐air batteries is provided and the factors that influence their performance and impede their practical applications, followed by future directions are discussed.     

An Iodine-Chemisorption Binder for High-Loading and Shuttle-Free Zn–Iodine Batteries

Aqueous zinc–iodine (Zn–I₂) batteries have attracted considerable research interest as an alternative energy storage system due to their high specific capacity, intrinsic safety, and low cost. However, the notorious shuttle effect of soluble polyiodides causes severe capacity loss and poor electrochemical reversibility, restricting their practical usage. Herein, this study reports a bifunctional binder (polyacrylonitrile copolymer, as known as LA133) with strong iodine-chemisorption capability for aqueous Zn–I₂ batteries to suppress polyiodide shuttling. From both calculation and experimental data, this study reveals that the amide and carboxyl groups in LA133 binder can strongly bond to polyiodides, significantly immobilizing them at cathode side. As a result, fewer byproducts, slower hydrogen evolution, and lesser Zn dendrite in the Zn–I₂ battery are observed. Consequently, the battery shows high specific capacity (202.8 mAh g⁻¹) with high iodine utilization efficiency (96.1%), and long cycling lifespan (2700 cycles). At the high mass loading of 7.82 mg cm⁻², the battery can still retain 83.3% of its initial capacity after 1000 cycles. The specific capacity based on total cathode slurry mass reaches 71.2 mAh g⁻¹, higher than most of the recent works. The strategy opens a new avenue to address the shuttling challenge of Zn–I₂ batteries through bifunctional binder.     

Controlled Atomic Solubility in Mn‐Rich Composite Material to Achieve Superior Electrochemical Performance for Li‐Ion Batteries

The quest for high energy density and high power density electrode materials for lithium‐ion batteries has been intensified to meet strongly growing demand for powering electric vehicles. Conventional layered oxides such as Co‐rich LiCoO₂ and Ni‐rich Li(Ni_xMn_yCo_z)O₂ that rely on only transition metal redox reaction have been faced with growing constraints due to soaring price on cobalt. Therefore, Mn‐rich electrode materials excluding cobalt would be desirable with respect to available resources and low cost. Here, the strategy of achieving both high energy density and high power density in Mn‐rich electrode materials by controlling the solubility of atoms between phases in a composite is reported. The resulting Mn‐rich material that is composed of defective spinel phase and partially cation‐disordered layered phase can achieve the highest energy density, ≈1100 W h kg^?1 with superior power capability up to 10C rate (3 A g^?1) among other reported Mn‐rich materials. This approach provides new opportunities to design Mn‐rich electrode materials that can achieve high energy density and high power density for Li‐ion batteries.     

Boosting Ion Diffusion and Charge Transfer by Zincophilic Accordion Arrays to Achieve Ultrafast Aqueous Zinc Metal Batteries

A key challenge to apply aqueous zinc metal batteries (AZMBs) as next-generation energy storage device is to improve the rechargeability at high current densities, which is needed to circumvent slowly ion diffusion in anode and sluggish charge transfer of Zn²⁺. Herein, a zincophilic accordion array derived from MOF is developed as zinc host for simultaneously boosted ion diffusion and charge transfer. The designed host is prepared by etching and disproportionation reactions, the abundant zincophilic Sn sites with nano-size uniform disperse on accordion arrays nanosheets (Sn-AA). Then a composite Zn anode (Sn-AA@Zn) is obtained by compacting Sn-AA host with zinc power (Zn-P). The Sn-AA@Zn anode has an ultra-low activation energy (37.1 kJ mol⁻¹) and nucleation overpotential (10 mV), achieving fast charge transfer of Zinc deposition. In addition, the cycle life of the symmetric cell with Sn-AA@Zn anode exceeds 13 000 cycles at 50 mA cm⁻², which is 32 times than that of the Zn-P anode. And the full cell with Sn-AA@Zn anode and MnO₂ cathode maintains a capacity of 122 mAh g⁻¹ after 5000 cycles at 5 Ag⁻¹. Hopefully, the 3D anode based on Sn-AA@Zn accordion array and Zn-P has significantly improved the rechargeability of AZMB at high current density.     

NiCo2S4 Nanosheets Grown on Nitrogen‐Doped Carbon Foams as an Advanced Electrode for Supercapacitors

To push the energy density limit of supercapacitors, a new class of electrode materials with favorable architectures is strongly needed. Binary metal sulfides hold great promise as an electrode material for high‐performance energy storage devices because they offer higher electrochemical activity and higher capacity than mono‐metal sulfides. Here, the rational design and fabrication of NiCo₂S₄ nanosheets supported on nitrogen‐doped carbon foams (NCF) is presented as a novel flexible electrode for supercapacitors. A facile two‐step method is developed for growth of NiCo₂S₄ nanosheets on NCF with robust adhesion, involving the growth of Ni‐Co precursor and subsequent conversion into NiCo₂S₄ nanosheets through sulfidation process. Benefiting from the compositional features and 3D electrode architectures, the NiCo₂S₄/NCF electrode exhibits greatly improved electrochemical performance with ultrahigh capacitance (877 F g^?1 at 20 A g^?1) and excellent cycling stability. Moreover, a binder‐free asymmetric supercapacitor device is also fabricated by using NiCo₂S₄/NCF as the positive electrode and ordered mesoporous carbon (OMC)/NCF as the negative electrode; this demonstrates high energy density (≈45.5 Wh kg^?1 at 512 W kg^?1).     

Fast Charge-Transfer Rates in Li-CO2 Batteries with a Coupled Cation-Electron Transfer Process

Li-CO₂ batteries with a high theoretical energy density (1876 Wh kg⁻¹) have unique benefits for reversible carbon fixation for energy storage systems. However, due to lack of stable and highly active catalysts, the long-term operation of Li-CO₂ batteries is limited to low current densities (mainly <0.2 mA cm⁻²) that are far from practical conditions. In this work, it is discovered that, with an ionic liquid-based electrolyte, highly active and stable transition metal trichalcogenide alloy catalysts of Sb_0.67Bi_1.33X₃ (X = S, Te) enable operation of the Li-CO₂ battery at a very high current rate of 1 mA cm⁻² for up to 220 cycles. It is revealed that: i) the type of chalcogenide (Te vs S) significantly affects the electronic and catalytic properties of the catalysts, ii) a coupled cation-electron charge transfer process facilitates the carbon dioxide reduction reaction (CO₂RR) occurring during discharge, and iii) the concentration of ionic liquid in the electrolyte controls the number of participating CO₂ molecules in reactions. A combination of these key factors is found to be crucial for a successful operation of the Li-CO₂ chemistry at high current rates. This work introduces a new class of catalysts with potential to fundamentally solve challenges of this type of batteries.     

H2V3O8 Nanowire/Graphene Electrodes for Aqueous Rechargeable Zinc Ion Batteries with High Rate Capability and Large Capacity

Aqueous rechargeable zinc ion batteries are considered a promising candidate for large‐scale energy storage owing to their low cost and high safety nature. A composite material comprised of H₂V₃O₈ nanowires (NWs) wrapped by graphene sheets and used as the cathode material for aqueous rechargeable zinc ion batteries is developed. Owing to the synergistic merits of desirable structural features of H₂V₃O₈ NWs and high conductivity of the graphene network, the H₂V₃O₈ NW/graphene composite exhibits superior zinc ion storage performance including high capacity of 394 mA h g^?1 at 1/3 C, high rate capability of 270 mA h g^?1 at 20 C and excellent cycling stability of up to 2000 cycles with a capacity retention of 87%. The battery offers a high energy density of 168 W h kg^?1 at 1/3 C and a high power density of 2215 W kg^?1 at 20 C (calculated based on the total weight of H₂V₃O₈ NW/graphene composite and the theoretically required amount of Zn). Systematic structural and elemental characterization confirm the reversible Zn²⁺ and water cointercalation electrochemical reaction mechanism. This work brings a new prospect of designing high‐performance aqueous rechargeable zinc ion batteries for grid‐scale energy storage.     

A Novel High Capacity Positive Electrode Material with Tunnel‐Type Structure for Aqueous Sodium‐Ion Batteries

Aqueous sodium‐ion batteries have shown desired properties of high safety characteristics and low‐cost for large‐scale energy storage applications such as smart grid, because of the abundant sodium resources as well as the inherently safer aqueous electrolytes. Among various Na insertion electrode materials, tunnel‐type Na_0.44MnO₂ has been widely investigated as a positive electrode for aqueous sodium‐ion batteries. However, the low achievable capacity hinders its practical applications. Here, a novel sodium rich tunnel‐type positive material with a nominal composition of Na_0.66[Mn_0.66Ti_0.34]O₂ is reported. The tunnel‐type structure of Na_0.44MnO₂ obtained for this compound is confirmed by X‐ray diffraction and atomic‐scale spherical aberration‐corrected scanning transmission electron microscopy/electron energy‐loss spectrum. When cycled as positive electrode in full cells using NaTi₂(PO₄)₃/C as negative electrode in 1 m Na₂SO₄ aqueous electrolyte, this material shows the highest capacity of 76 mAh g^?1 among the Na insertion oxides with an average operating voltage of 1.2 V at a current rate of 2 C. These results demonstrate that Na_0.66[Mn_0.66Ti_0.34]O₂ is a promising positive electrode material for rechargeable aqueous sodium‐ion batteries.     

High‐Performance Reversible Aqueous Zn‐Ion Battery Based on Porous MnOx Nanorods Coated by MOF‐Derived N‐Doped Carbon

Rechargeable aqueous zinc‐ion batteries (ZIBs) have been emerging as potential large‐scale energy storage devices due to their high energy density, low cost, high safety, and environmental friendliness. However, the commonly used cathode materials in ZIBs exhibit poor electrochemical performance, such as significant capacity fading during long‐term cycling and poor performance at high current rates, which significantly hinder the further development of ZIBs. Herein, a new and highly reversible Mn‐based cathode material with porous framework and N‐doping (MnO_x@N‐C) is prepared through a metal–organic framework template strategy. Benefiting from the unique porous structure, conductive carbon network, and the synergetic effect of Zn²⁺ and Mn²⁺ in electrolyte, the MnO_x@N‐C shows excellent cycling stability, good rate performance, and high reversibility for aqueous ZIBs. Specifically, it exhibits high capacity of 305 mAh g^?1 after 600 cycles at 500 mA g^?1 and maintains achievable capacity of 100 mAh g^?1 at a quite high rate of 2000 mA g^?1 with long‐term cycling of up to 1600 cycles, which are superior to most reported ZIB cathode materials. Furthermore, insight into the Zn‐storage mechanism in MnO_x@N‐C is systematically studied and discussed via multiple analytical methods. This study opens new opportunities for designing low‐cost and high‐performance rechargeable aqueous ZIBs.     

Robust Hybrid Solid Electrolyte Interface Induced by Zn-Poor Electric Double Layer for A Highly Reversible Zinc Anode

Aqueous Zn-ion batteries (AZIBs) show great potential in new energy storage devices due to low cost, inherent safety, and environmental friendliness. However, the severe dendrites and side reactions on the anode greatly constrain their practical application. Herein, a novel colloidal electrolyte composed of ZnSO₄ and sodium carboxymethyl cellulose (CMC-Na) has been developed for inhibiting dendrite growth on Zn anode. Molecular dynamics (MD) simulation confirms that CMC-Na alters the electric double layer (EDL) structure of Zn anode surface to reduce the content of water and SO₄²⁻ and inhibit side reactions. More importantly, an organic/inorganic hybrid solid electrolyte interface (SEI) layer is in situ constructed during the cycling, which enables ultrastable Zn plating/stripping (> 2000 h) under high current density (5 mA cm⁻², 5 mAh cm⁻²) and high coulombic efficiency (99.8%) for more than 1000 cycles. Meanwhile, zinc-ion hybrid capacitors (ZIHCs) with the colloidal electrolyte exhibit a favorable capacitance retention of 97% after 15000 cycles at the current density of 2 A g⁻¹. Even at a high current density of 5 A g⁻¹, it still has a capacitance retention of 96% after 30000 cycles. This study presents a novel electrolyte strategy for the formation of ultrastable electrode-electrolyte interfaces in AZIBs.     

Dial the Mechanism Switch of VN from Conversion to Intercalation toward Long Cycling Sodium‐Ion Battery

Transition metal nitrides are promising energy storage materials in regard to good metallic conductivity and high theoretical specific capacity, but their cycling stability is impeded by the huge volume change caused by the conversion reaction mechanism. Here, a simple strategy to produce an intercalation pseudocapacitive‐type vanadium nitride (VN) by one‐step ammonification of V₂C MXene for sodium‐ion batteries is reported. Profiting from a distinctive layered structure pillared by Al atoms in the layer spacing, it delivers a high capacity of 372 mA h g^?1 at 50 mA g^?1 and a desirable rate performance. More importantly, it shows remarkably long cycling stability over 7500 cycles without capacity attenuation at 500 mA g^?1. As expected, it is found that the intercalation pseudocapacitance plays an important role in the excellent performance, by using in situ X‐ray diffraction and ex situ X‐ray absorption structure characterization. Even more remarkable, are the high energy and power density of the sodium‐ion capacitor after coupling with a carbon‐based cathode. The hybrid device possesses an energy density of 78.43 Wh kg^?1 at power density of 260 W kg^?1. The results clearly show that such a unique‐layered VN with outstanding Na storage capability is an excellent new material for energy storage systems.     

Facile Synthesis of a 3D Nanoarchitectured Li4Ti5O12 Electrode for Ultrafast Energy Storage

Despite enormous efforts devoted to the development of high‐performance batteries, the obtainable energy and power density, durability, and affordability of the existing batteries are still inadequate for many applications. Here, a self‐standing nanostructured electrode with ultrafast cycling capability is reported by in situ tailoring Li₄Ti₅O₁₂ nanocrystals into a 3D carbon current collector (derived from filter paper) through a facile wet chemical process involving adsorption of titanium source, boiling treatment, and subsequent chemical lithiation. This 3D architectural electrode is charged/discharged to ≈60% of the theoretical capacity of Li₄Ti₅O₁₂ in ≈21 s at 100 C rate (17 500 mA g^?1 ), which also shows stable cycling performance for 1000 cycles at a cycling rate of 50 C. Additionally, modified 3D carbon current collector with much smaller pores and finer fiber diameters are further used, which significantly improve the specific capacity based on the weight of the entire electrode. These novel electrodes are promising for high‐power applications such as electric vehicles and smart grids. This unique electrode architecture also simplifies the electrode fabrication process and significantly enhances current collection efficiency (especially at high rate). Further, the conceptual electrode design is applicable to other oxide electrode materials for high‐performance batteries, fuel cells, and supercapacitors.     

Ultrathin Reed Membranes: Nature's Intimate Ion-Regulation Skins Safeguarding Zinc Metal Anodes in Aqueous Batteries

The practical realization of aqueous zinc-ion batteries relies crucially on effective interphases governing Zn electrodeposition chemistry. In this study, an innovative solution by introducing an ultrathin (≈2 µm) biomass membrane as an intimate artificial interface, functioning as nature's ion-regulation skin to protect zinc metal anodes is proposed. Capitalizing on the inherent properties of natural reed membrane, including multiscale ion transport tunnels, abundant ─OH groups, and remarkable mechanical integrity, the reed membrane demonstrates efficacy in regulating uniform and rapid Zn²⁺ transport, promoting desolvation, and governing Zn (002) plane electrodeposition. Importantly, a unique in situ electrochemical Zn─O bond formation mechanism between the reed membrane and Zn electrode upon cycling is elucidated, resulting in a robustly adhered interface covering on the zinc anode surface, ultimately ensuring remarkable dendrite-free and highly reversible Zn anodes. Consequently, the approach achieves a prolonged cycle life for over 1450 h at 3 mA cm⁻²/1.5 mAh cm⁻² in symmetric Zn//Zn cells. Moreover, exceptional cyclic performance (88.95%, 4000 cycles) is obtained in active carbon-based cells with an active mass loading of 5.8 mg cm⁻². The approach offers a cost-effective and environmentally friendly strategy for achieving stable and reversible zinc anodes for aqueous batteries.     

Gradient-Structured and Robust Solid Electrolyte Interphase In Situ Formed by Hydrated Eutectic Electrolytes for High-Performance Zinc Metal Batteries

The mechanically and electrochemically stable and ionically conducting solid electrolyte interphase (SEI) is important for the stabilization of metal anodes. Since SEIs are originally absent in aqueous zinc metal batteries (AZMBs), it is very challenging to suppress water-induced side reactions and dendrite growth of Zn metal anodes (ZMAs). Herein, a gradient-structured and robust solid gradient SEI, consisting of B,O-inner and F,O-exterior layer, in situ formed by hydrated eutectic electrolyte for the homogeneous and reversible Zn deposition, is demonstrated. Moreover, the molar ratio of acetamide to Zn salt is modulated to prohibit the water activity and the hydrolysis of BF₄⁻ as well as to achieve high ionic conductivity owing to the regulation of the solvation sheath of Zn²⁺. Consequently, the eutectic electrolyte allows Zn||Zn symmetric cells to achieve a cycling lifespan of over 4400 h at 0.5 mA cm⁻² as well as Zn||PANI full cells to deliver a high capacity retention of 73.2% over 4000 cycles at 1 A g⁻¹ and to demonstrate the stable operation at low temperatures. This work provides the rational design for the hydrated eutectic electrolyte and the corresponding gradient SEIs for dendrite-free and stable Zn anodes even under harsh conditions.