pH-Triggered Molecular Switch Toward Texture-Regulated Zn Anode.

Zn electrodes in aqueous media exhibit an unstable Zn/electrolyte interface due to severe parasitic reactions and dendrite formation. Here, a dynamic Zn interface modulation based on the molecular switch strategy is reported by hiring γ-butyrolactone (GBL) in ZnCl2 /H2 O electrolyte. During Zn plating, the increased interfacial alkalinity triggers molecular switch from GBL to γ-hydroxybutyrate (GHB). GHB strongly anchors on Zn surface via triple Zn-O bonding, leading to suppressive hydrogen evolution and texture-regulated Zn morphology. Upon Zn stripping, the fluctuant pH turns the molecular switch reaction off through the cyclization of GHB to GBL. This dynamic molecular switch strategy enables high Zn reversibility with Coulombic efficiency of 99.8 % and Zn||iodine batteries with high-cyclability under high Zn depth of discharge (50 %). This study demonstrates the importance of dynamic modulation for Zn electrode and realizes the reversible molecular switch strategy to enhance its reversibility.

A Natural Biopolymer Film as a Robust Protective Layer to Effectively Stabilize Lithium-Metal Anodes.

Li metal is considered as an ideal anode for Li-based batteries. Unfortunately, the growth of Li dendrites during cycling leads to an unstable interface, a low coulombic efficiency, and a limited cycling life. Here, a novel approach is proposed to protect the Li-metal anode by using a uniform agarose film. This natural biopolymer film exhibits a high ionic conductivity, high elasticity, and chemical stability. These properties enable a fast Li-ion transfer and feasiblity to accomodate the volume change of Li metal, resulting in a dendrite-free anode and a stable interface. Morphology characterization shows that Li ions migrate through the agarose film and then deposit underneath it. A full cell with the cathode of LiFPO4 and an anode contaning the agarose film exhibits a capacity retention of 87.1% after 500 cycles, much better than that with Li foil anode (70.9%) and Li-deposited Cu anode (5%). This study provides a promising strategy to eliminate dendrites and enhance the cycling ability of lithium-metal batteries through coating a robust artificial film of natural biopolymer on lithium-metal anode.

Protein Interfacial Gelation toward Shuttle-Free and Dendrite-Free Zn-Iodine Batteries.

Aqueous zinc-iodine (Zn-I2) batteries hold potential for large-scale energy storage but struggle with shuttle effects of I2 cathodes and poor reversibility of Zn anodes. Here, an interfacial gelation strategy is proposed to suppress the shuttle effects and improve the Zn reversibility simultaneously by introducing silk protein (SP) additive. The SP can migrate bidirectionally toward cathode and anode interfaces driven by the periodically switched electric field direction during charging/discharging. For I2 cathodes, the interaction between SP and polyiodides forms gelatinous precipitate to avoid the polyiodide dissolution, evidenced by excellent electrochemical performance, including high specific capacity and Coulombic efficiency (CE) (215 mAh g-1 and 99.5% at 1 C), excellent rate performance (≈170 mAh g-1 at 50 C), and extended durability (6000 cycles at 10 C). For Zn anodes, gelatinous SP serves as protective layer to boost the Zn reversibility (99.7% average CE at 2 mA cm-2) and suppress dendrites. Consequently, a 500 mAh Zn-I2 pouch cell with high-loading cathode (37.5 mgiodine cm-2) and high-utilization Zn anode (20%) achieves remarkable energy density (80 Wh kg-1) and long-term durability (>1000 cycles). These findings underscore the simultaneous modulation of both cathode and anode and demonstrate the potential for practical applications of Zn-I2 batteries.

Cyclohexanedodecol-Assisted Interfacial Engineering for Robust and High-Performance Zinc Metal Anode.

Aqueous zinc-ion batteries (AZIBs) can be one of the most promising electrochemical energy storage devices for being non-flammable, low-cost, and sustainable. However, the challenges of AZIBs, including dendrite growth, hydrogen evolution, corrosion, and passivation of zinc anode during charging and discharging processes, must be overcome to achieve high cycling performance and stability in practical applications. In this work, we utilize a dual-functional organic additive cyclohexanedodecol (CHD) to firstly establish [Zn(H2O)5(CHD)]2+ complex ion in an aqueous Zn electrolyte and secondly build a robust protection layer on the Zn surface to overcome these dilemmas. Systematic experiments and theoretical calculations are carried out to interpret the working mechanism of CHD. At a very low concentration of 0.1 mg mL-1 CHD, long-term reversible Zn plating/stripping could be achieved up to 2200 h at 2 mA cm-2, 1000 h at 5 mA cm-2, and 650 h at 10 mA cm-2 at the fixed capacity of 1 mAh cm-2. When matched with V2O5 cathode, the resultant AZIBs full cell with the CHD-modified electrolyte presents a high capacity of 175 mAh g-1 with the capacity retention of 92% after 2000 cycles under 2 A g-1. Such a performance could enable the commercialization of AZIBs for applications in grid energy storage and industrial energy storage.

Polyiodide Confinement by Starch Enables Shuttle-Free Zn-Iodine Batteries.

Aqueous Zn-iodine (Zn-I2 ) batteries have been regarded as a promising energy-storage system owing to their high energy/power density, safety, and cost-effectiveness. However, the polyiodide shuttling results in serious active mass loss and Zn corrosion, which limits the cycling life of Zn-I2 batteries. Inspired by the chromogenic reaction between starch and iodine, a structure confinement strategy is proposed to suppress polyiodide shuttling in Zn-I2 batteries by hiring starch, due to its unique double-helix structure. In situ Raman spectroscopy demonstrates an I5 - -dominated I- /I2 conversion mechanism when using starch. The I5 - presents a much stronger bonding with starch than I3 - , inhibiting the polyiodide shuttling in Zn-I2 batteries, which is confirmed by in situ ultraviolet-visible spectra. Consequently, a highly reversible Zn-I2 battery with high Coulombic efficiency (≈100% at 0.2 A g-1 ) and ultralong cycling stability (>50 000 cycles) is realized. Simultaneously, the Zn corrosion triggered by polyiodide is effectively inhibited owing to the desirable shuttling-suppression by the starch, as evidenced by X-ray photoelectron spectroscopy analysis. This work provides a new understanding of the failure mechanism of Zn-I2 batteries and proposes a cheap but effective strategy to realize high-cyclability Zn-I2 batteries.

Cubic MnS-FeS2 Composites Derived from a Prussian Blue Analogue as Anode Materials for Sodium-Ion Batteries with Long-Term Cycle Stability.

Cubic N,S codoped carbon coating MnS-FeS2 composites (MnS-FeS2@NSC) with a hollow structure were prepared and used as anode materials for sodium-ion batteries. MnS-FeS2@NSC exhibits excellent cycle performance and high rate capability and delivered a reversible capacity of 501.0 mAh g-1 after 800 cycles at a current density of 0.1 A g-1 with a capacity retention of 81%. More importantly, the MnS-FeS2@NSC anode holds long-term cycle stability; the capacity can remain 134.0 mAh g-1 after 14 500 cycles at 4 A g-1. Kinetic analysis demonstrated that Na+ storage follows a pseudocapacitive dominating process, which is ascribed to the origin of the outstanding rate performance of the MnS-FeS2@NSC material. The enhancement of electrochemical performance is attributed to the hollow structure and the N,S codoped carbon coating structure, which can reduce the diffusion distance for sodium ions and electrons, alleviate volume expansion during sodium-ion insertion/extraction, and retain the structural integrity effectively. Furthermore, a two-step sodiation processes with FeS2 sodiation prior to MnS was demonstrated by X-ray diffraction (XRD), and the electrochemical impedance spectroscopy (EIS) spectra might indicate that the accumulation of the metallic elements in the preconversion reaction can accelerate the transfer of electrons and ions in the further conversion process.

Dynamic electrocatalyst with current-driven oxyhydroxide shell for rechargeable zinc-air battery.

Recent fruitful studies on rechargeable zinc-air battery have led to emergence of various bifunctional oxygen electrocatalysts, especially metal-based materials. However, their electrocatalytic configuration and evolution pathway during battery operation are rarely spotlighted. Herein, to depict the underlying behaviors, a concept named dynamic electrocatalyst is proposed. By selecting a bimetal nitride as representation, a current-driven "shell-bulk" configuration is visualized via time-resolved X-ray and electron spectroscopy analyses. A dynamic picture sketching the generation and maturation of nanoscale oxyhydroxide shell is presented, and periodic valence swings of performance-dominant element are observed. Upon maturation, zinc-air battery experiences a near two-fold enlargement in power density to 234 mW cm-2, a gradual narrowing of voltage gap to 0.85 V at 30 mA cm-2, followed by stable cycling for hundreds of hours. The revealed configuration can serve as the basis to construct future blueprints for metal-based electrocatalysts, and push zinc-air battery toward practical application.

Aluminum-Based Metal-Organic Frameworks Derived Al2O3-Loading Mesoporous Carbon as a Host Matrix for Lithium-Metal Anodes.

Li-metal anode attracts great focus owing to its ultra-high specific capacity and the lowest redox potential. However, the uncontrolled growth of Li dendrite leads to severe security issues and limited cycle life. Herein, Al2O3 loading mesoporous carbon (Al2O3@MOF-C) derived from Al-based metal-organic frameworks (Al-MOFs) was investigated as the stable host matrix for Li metal, in which, Al2O3 was served as nano seeds for the Li deposition and decrease the Li nucleation overpotential. Except that, the high specific surface area and wide pore distribution can also buffer the volume changes of Li and fasten electron transfer, hence a dendrite-free morphology was observed even after 50 cycles at 2 mA cm-2. High Li coulombic efficiency of 97.9% after 100 cycles at 1 mA cm-2, 1 mAh cm-2, and 97.6% after 50 cycles at 1 mA cm-2 and 6 mAh cm-2 were performed by Al2O3@MOF-C electrodes. Good performances were also obtained for Li-sulfur and LiFePO4 batteries. The performances of Al2O3@MOF-C@Li were compared with Li foil and Cu@Li in full cell configurations. The electrochemical tests of full cells based on Al2O3@MOF-C@Li indicated that this Al-based functional host matrix can enhance the Li-utilization and lead to significant enhancement of the cycling performance of Li anodes.

Novel Sulfur Host Composed of Cobalt and Porous Graphitic Carbon Derived from MOFs for the High-Performance Li-S Battery.

A composite consisting of cobalt and graphitic porous carbon (Co@GC-PC) is synthesized from bimetallic metal-organic frameworks and employed as the sulfur host for high-performance Li-S batteries. Because of the presence of a large surface area (724 m2 g-1) and an abundance of macro-/mesopores, the Co@GC-PC electrode is able to alleviate the debilitating effect originating from the volume expansion/contraction of sulfur species during the cycling process. Our in situ UV/vis analysis indicates that the existence of Co@GC-PC promotes the adsorption of polysulfides during the discharge process. Density functional theory calculations show a strong interaction between Co and Li2S and a low decomposition barrier of Li2S on Co(111), which is beneficial to the following Li2S oxidation in the charge process. As a result, at 0.2C, the discharge capacity of the S/Co@GC-PC cathode is stabilized at 790 mAh g-1 after 220 cycles, much higher than that of a carbon-based cathode, which delivers a discharge capacity of 188 mAh g-1.

Layered/Spinel Heterostructured and Hierarchical Micro/Nanostructured Li-Rich Cathode Materials with Enhanced Electrochemical Properties for Li-Ion Batteries.

Although holding a high capacity, Li-rich materials are far from the demand of practical market because of their inherent drawbacks, such as poor initial efficiency and rate capability. Herein, Li-rich materials of Li1.16Mn0.6Ni0.12Co0.12O2 have been prepared via a one-step solvothermal strategy. The detail characterizations demonstrate that the as-prepared materials present morphology of nanoparticle-aggregated hierarchical microspheres and a heterostructure of layered and Li4Mn5O12-type spinel components. Compared to materials of pure-layered structure, layered/spinel heterostructured materials exhibit simultaneously great reversible capacity (302 mAh g-1 at 0.2 C), high initial Coulombic efficiency (94% at 0.2 C) and remarkable rate capability (193 mAh g-1 at 10 C).