Tellurium with Reversible Six-Electron Transfer Chemistry for High-Performance Zinc Batteries

Photoluminescence of Te-Doped Double Perovskite Cs2ZrCl6 Nanocrystals Versus Bulk: Insights From Temperature-Dependent Spectroscopy

Although bulk crystals of lead-free vacancy-ordered double perovskites demonstrated a highly efficient emission, their nanocrystals (NCs) counterparts exhibit inferior optical performance. To understand the reasons behind this phenomenon, Cs2ZrCl6:Te4+ double perovskite NCs are synthesized, and their optical properties are compared with their bulk powders. Temperature-dependent spectroscopy revealed that the NCs sustain a thermal sensitization of the intermediate trap state, which is located between the self-trapped state of the host (Cs2ZrCl6) and the triplet states of the dopant (Te4+). This opens up a pathway for the non-radiative recombination, and thus decreases the energy transfer efficiency from host to dopant. Importantly, this pathway is suppressed in larger (40 nm) Cs2ZrCl6:Te4+ NCs, resulting in their photoluminescence quantum yield of 24%, as compared to 7% for the 22 nm NCs. Furthermore, the emission spectral range of these double perovskite NCs is shown to extended into near-infrared by incorporating rare-earth ions as additional dopants. The study has established a crucial relation between the optical properties and the size effect in lead-free vacancy-ordered double perovskites and thus lays a foundation for further improvement of their optical performance.

Six-electron-conversion selenium cathodes stabilized by dead-selenium revitalizer for aqueous zinc batteries

Aqueous zinc batteries are attractive for large-scale energy storage due to their inherent safety and sustainability. However, their widespread application has been constrained by limited energy density, underscoring a high demand of advanced cathodes with large capacity and high redox potential. Here, we report a reversible high-capacity six-electron-conversion Se cathode undergoing a ZnSe↔Se↔SeCl4 reaction, with Br-/Brn- redox couple effectively stabilizes the Zn | |Se cell. This Se conversion, initiated in a ZnCl2-based hydrogel electrolyte, presents rapid capacity decay (from 1937.3 to 394.1 mAh gSe-1 after only 50 cycles at 0.5 A gSe-1) primarily due to the dissolution of SeCl4 and its subsequent migration to the Zn anode, resulting in dead Se passivation. To address this, we incorporate the Br-/Brn- redox couple into the Zn | |Se cell by introducing bromide salt as an electrolyte additive. The generated Brn- species acts as a dead-Se revitalizer by reacting with Se passivation on the Zn anode and regenerating active Se for the cathode reaction. Consequently, the cycling stability of the Zn | |Se cell is improved, maintaining 1246.8 mAh gSe-1 after 50 cycles. Moreover, the Zn | |Se cell exhibits a specific capacity of 2077.6 mAh gSe-1 and specific energy of 404.2 Wh kg-1 based on the overall cell reaction.

Tailoring Crystalline States of Alloy Coating for High Current Density and Large Areal Capacity of Zn

Due to issues of hydrogen evolution, corrosion, and uncontrolled deposition behaviors at the Zn anode, the practical implementation of Zn-ion batteries has faced significant obstacles. Very limited attention is directed toward various alloy crystalline states for the Zn anode protection primarily due to the challenge of synthesizing high-quality alloy coatings with diverse crystalline states. In this study, the crystalline state of NiCr alloy coating is precisely manipulated using magnetron sputtering, revealing distinct thermodynamic and kinetic changes induced by variation in the crystalline state. This research emphasizes the fundamental understanding of microstructure dynamics and achieves a highly reversible Zn anode at harsh conditions of high current density (80 mA cm-2) and large areal capacity (40 mAh cm-2), thus enabling high-capacity and longevous pouch battery.

Amorphization Stabilizes Te-Based Aqueous Batteries via Confining Free Water

Tellurium (Te), with its rich valence states (-2 to +6), could endow aqueous batteries with potentially high specific capacity. However, achieving complete and stable hypervalent Te0/Te4+ electrochemistry in an aqueous environment poses significant challenges, owing to the sluggish reduction kinetics, easy dissolution of Te4+ species, and a controversial energy storage mechanism. Herein, we demonstrate a crystallographic regulation strategy for robust aqueous Te redox electrochemistry. With strong hydrogen bonding, NH4Ac confines free water, prompting the amorphization of TeO2 (a-TeO2). In situ synchrotron characterization, spectroscopy analysis, electrochemical evaluation, and theoretical calculations reveal a specific 4 e- solid-solid transition pathway (Te to a-TeO2) with accelerated diffusion and charge transfer kinetics, attributed to a closer unoccupied electron orbital to the Fermi level and a reduced water desorption energy barrier in a-TeO2. Impressively, the a-TeO2/Te redox exhibits a high reversible capacity of 834 mAh g-1 (99% of Te redox utilization), superior rate performance (644 mAh g-1 at 10 A g-1), and an ultralong lifespan (over 3000 cycles). These findings prove a new tactic to advance aqueous Te redox electrochemistry toward high-energy aqueous batteries.

Significant Enhancement in the Thermoelectric Performance of the MnSb2Te4 Topological Insulator through Vacancy Regulation and Lattice-Softening Strategies

The topological insulator MnSb2Te4 shows promising potential in thermoelectric applications due to its intrinsically low lattice thermal conductivity. However, its thermoelectric performance is limited by the high carrier concentration, of which the origin is still unclear. In this work, the carrier concentration is successfully tuned from 2.24 × 1021 cm-3 to as low as 9.1 × 1019 cm-3. Transmission electron microscopy and positron annihilation measurements suggest that large amounts of Mn vacancies exist in the septuple layer of MnSb2Te4, which are responsible for the high carrier concentration. The Mn vacancies are suppressed by the excess Mn element and AgSbTe2 alloying, which not only reduces the carrier concentration but also weakens the carrier scattering and thus improves the mobility. The decrease in carrier concentration also leads to reduced electronic thermal conductivity. The excess Mn atoms introduce a strain field in the Mn layer, which enhances phonon scattering. Furthermore, the substitution of Ag for Mn causes lattice softening by weakening the chemical bonds in MnSb2Te4, which leads to reduced phonon velocity and, therefore, further reduction in lattice thermal conductivity. As a result, an extremely low lattice thermal conductivity of 0.44 W m-1 K-1 was obtained at 300 K and it further decreased to 0.17 W m-1 K-1 at 798 K. Finally, a record zT value of 1.53 at 798 K was achieved in Mn1.06Sb2Te4(AgSbTe2)0.04, and the optimal carrier concentration is about 2 × 1020 cm-3.

Reducing Dead Species by Electrochemically-Densified Cathode-Interface-Reaction Layer towards High-Rate-Endurable Zn||I-Br Batteries

Interhalogen-involved aqueous Zn||halogen batteries (AZHBs) are latent high-energy systems for grid-level energy storage, yet usually suffer from poor high-rate endurability caused by the formation of "dead species". Herein, via an electrochemically-densified cathode-interface-reaction layer (CIRL), Zn||I-Br batteries involving interhalogen reactions between the I2 cathode and Br- from the electrolytes are initially achieved with excellent high-rate endurability. Different from that in diluted electrolytes, the CIRL formed in Br--concentrated electrolyte is denser and water-lean, which enables halogen species conversion with a more rapid charge transfer and lower activation energy. More importantly, the CIRL robustly affords a decent I2 conservation by accelerated conversion kinetics and limited species diffusion, thereby endowing the Zn||I-Br batteries with an ultralong high-rate lifespan. The electrochemical mechanism is sufficiently verified by multiple spectral characterizations. Consequently, Zn||I-Br batteries in Br--concentrated (20 m) electrolytes exhibit an overwhelming rate capability and lifespan to those in Br--diluted (2 m) electrolytes. Typically, when cycled at a large current density of 10 A g-1, an ultralong lifespan of over 25,000 cycles is achieved with a high retention of 98.3 %. This study provides new insight into the CIRL-dictated active species conservation for high-rate endurable AZHBs, which could apply to other high-energy interhalogen batteries.

A tellurium iodide perovskite structure enabling eleven-electron transfer in zinc ion batteries

The growing potential of low-dimensional metal-halide perovskites as conversion-type cathode materials is limited by electrochemically inert B-site cations, diminishing the battery capacity and energy density. Here, we design a benzyltriethylammonium tellurium iodide perovskite, (BzTEA)2TeI6, as the cathode material, enabling X- and B-site elements with highly reversible chalcogen- and halogen-related redox reactions, respectively. The engineered perovskite can confine active elements, alleviate the shuttle effect and promote the transfer of Cl- on its surface. This allows for the utilization of inert high-valent tellurium cations, eventually realizing a special eleven-electron transfer mode (Te6+/Te4+/Te2-, I+/I0/I-, and Cl0/Cl-) in suitable electrolytes. The Zn||(BzTEA)2TeI6 battery exhibited a high capacity of up to 473 mAh g-1Te/I and a large energy density of 577 Wh kg-1 Te/I at 0.5 A g-1, with capacity retention up to 82% after 500 cycles at 3 A g-1. The work sheds light on the design of high-energy batteries utilizing chalcogen-halide perovskite cathodes.

Recent Progress on Rechargeable Zn-X (X=S, Se, Te, I2, Br2) Batteries

Recently, aqueous Zn-X (X=S, Se, Te, I2, Br2) batteries (ZXBs) have attracted extensive attention in large-scale energy storage techniques due to their ultrahigh theoretical capacity and environmental friendliness. To date, despite tremendous research efforts, achieving high energy density in ZXBs remains challenging and requires a synergy of multiple factors including cathode materials, reaction mechanisms, electrodes and electrolytes. In this review, we comprehensively summarize the various reaction conversion mechanism of zinc-sulfur (Zn-S) batteries, zinc-selenium (Zn-Se) batteries, zinc-tellurium (Zn-Te) batteries, zinc-iodine (Zn-I2) batteries, and zinc-bromine (Zn-Br2) batteries, along with recent important progress in the design and electrolyte of advanced cathode (S, Se, Te, I2, Br2) materials. Additionally, we investigate the fundamental questions of ZXBs and highlight the correlation between electrolyte design and battery performance. This review will stimulate an in-deep understanding of ZXBs and guide the design of conversion batteries.

Rational Design of Porous Y2O3-MnOx/Carbon Heterostructures with Abundant Oxygen Vacancies for High-Efficiency and Ultrastable Zinc-Ion Storage

Manganese oxides have been considered as the most competitive cathode materials for aqueous zinc-ion batteries (ZIBs) on account of their inherent safety, high operating voltage, environmental friendliness, and cost-effectiveness. Unfortunately, the manganese dissolution, inherently poor electronic conductivity, and the sluggish reaction kinetics of commercial manganese-based oxides severely hinder their practical applications. To address the above issues, we creatively developed hierarchical porous Y2O3-MnOx/C nanorods (named OV-YMO/C) with unique heterostructures and abundant oxygen vacancies via a facile MOF-assisted synthetic process and employed as the advanced cathode. Owing to the well-constructed porous structure, larger surface areas, abundant oxygen vacancies, and strong synergetic coupling effect at the heterogeneous interface, the as-obtained OV-YMO/C cathode exhibited a fascinating discharge capacity of 389.6 mAh g-1 at 0.1 A g-1. Simultaneously, it demonstrated remarkable rate performance (233 mAh g-1 at 4.0 A g-1) and cycling durability (90.6% capacity retention over 3000 cycles at 4.0 A g-1). The fabricated Zn//OV-YMO/C pouch cell could deliver superior flexibility and electrochemical stability under extreme bending conditions. Furthermore, the electrochemical reaction mechanism was comprehensively explored by kinetic analysis and density functional theory (DFT) calculations. The synergistic strategy by subtly combining the MOF-assisted approach, heterojunction engineering, and oxygen defects engineering provides valuable insights into the construction of cathode materials for high-rate and ultrastable aqueous ZIBs.

Gradient Distribution of Zincophilic Sites for Stable Aqueous Zinc-Based Flow Batteries with High Capacity

Current collectors, as reaction sites, play a crucial role in influencing various electrochemical performances in emerging cost-effective zinc-based flow batteries (Zn-based FBs). 3D carbon felts (CF) are commonly used but lack effectiveness in improving Zn metal plating/stripping. Here, a current collector with gravity-induced gradient copper nanoparticles (CF-G-Cu NPs) is developed, integrating gradient conductivity and zincophilicity to regulate Zn deposition and suppress side reactions. The CF-G-Cu NPs electrode modulates Zn nucleation and growth via the zincophilic Cu/CuZn5 alloy has been confirmed by density functional theory (DFT) calculations. Finite element simulation demonstrates the gradient internal structure effectively optimizes the local electric/current field distribution to regulate the Zn2+ flux, improving bottom-up plating behavior for Zn metal and mitigating top-surface dendrite growth. As a result, Zn-based asymmetrical FBs with CF-G-Cu NPs electrodes achieve an areal capacity of 30 mAh cm-2 over 640 h with Coulombic efficiency of 99.5% at 40 mA cm-2. The integrated Zn-Iodide FBs exhibit a competitive long-term lifespan of 2910 h (5800 cycles) with low energy efficiency decay of 0.062% per cycle and high cumulative capacity of 112800 mAh cm-2 at a high current density of 100 mA cm-2. This gradient distribution strategy offers a simple mode for developing Zn-based FB systems.

Bifunctionally Electrocatalytic Bromine Redox Reaction by Single-Atom Catalysts for High-Performance Zinc Batteries

Aqueous zinc-bromine (Zn||Br2) batteries are regarded as one of the most promising energy storage devices due to their high safety, theoretical energy density, and low cost. However, the sluggish bromine redox kinetics and the formation of a soluble tribromide (Br3 -) hinder their practical applications. Here, it is proposed dispersed single iron atom coordinated with nitrogen atoms (FeN5) in a mesoporous carbon framework (FeSAC-CMK) as a conductive catalytic bromine host, which possesses porous structure and electrocatalytic functionality of FeN5 species for enhanced confinement and electrocatalytic effect. The active FeN5 species can fix the bromine (Br0) species to suppress the formation of Br3 - effectively and bifunctionally catalyze the bromide (Br-)/Br° conversion. These free up 1/3 Br- locked by Br3 - complexing agent for enhanced bromine utilization efficiency and conversion reversibility. Accordingly, the Zn||Br2 battery with FeSAC-CMK delivers an impressive specific capacity of 344 mAh g-1 at 0.2 A g-1 and superior rate capability with 164 mAh g-1 achieved even at 20 A g-1, much higher than that of inactive CMK (262 mAh g-1 at 0.2 A g-1; 6 mAh g-1 at only 8 A g-1). Furthermore, the battery demonstrates excellent cycling performance of 88% capacity retention after 2000 cycles.

Non-Epitaxial Electrodeposition of Overall 99 % (002) Plane Achieves Extreme and Direct Utilization of 95 % Zn Anode and By-Product as Cathode

Zn anode protection in Zn-ion batteries (ZIBs) face great challenges of high Zn utilization rate (i.e., depth of discharge, DOD) and high current density due to the large difficulty in obtaining an extreme overall RTC (relative texture coefficient) of Zn (002) plane. Through the potent interaction of Mn(III)aq and H+ with distinct Zn crystal planes under an electric field, large-size Zn foils with a breakthrough (002) plane RTC of 99 % (i.e., close to Zn single crystal) are electrodeposited on texture-less substrates, which is also applicable from recycled Zn. The ultra-high (002) plane RTC remarkably enhances cyclic performance of the Zn anode (70 % DOD @ 45.5 mA cm-2), and the DOD is even up to 95 % (@ 28.1 mA cm-2) with an electrolyte additive of polyaniline. Furthermore, MnO2, the by-product of electrodeposition, is directly used as cathode of both coin cell and pouch battery, surpassing the cyclic performance exhibited by the majority of Zn||MnO2 batteries in previous instances. These results demonstrate the great potential of our strategy for high-performance, low-cost and large-scale ZIBs.

Boosting the Zn2+ storage capacity of MoO3 nanoribbons by modulating the electrons spin states of Mo via Ni doping

Aqueous zinc-ion batteries (AZIBs) have received considerable potential for their affordability and high reliability. Among potential cathodes, α-MoO3 stands out due to its layered structure aligned with the (010) plane, offering extensive ionic insertion channels for enhanced charge storage. However, its limited electrochemical activity and poor Zn2+ transport kinetics present significant challenges for its deployment in energy storage devices. To overcome these limitations, we introduce a new strategy by doping α-MoO3 with Ni (Ni-MoO3), tuning the electron spin states of Mo. Thus modification can activate the reactivity of Ni-MoO3 towards Zn2+ storage and weaken the interaction between Ni-MoO3 and intercalated Zn2+, thereby accelerating the Zn2+ transport and storage. Consequently, the electrochemical properties of Ni-MoO3 significantly surpass those of pure MoO3, demonstrating a specific capacity of 258 mAh g-1 at 1 A g-1 and outstanding rate performance (120 mAh g-1 at 10 A g-1). After 1000 cycles at 8 A g-1, it retains 76 % of the initial capacity, with an energy density of 154.4 Wh kg-1 and a power density of 11.2 kW kg-1. This work proves that the modulation of electron spin states in cathode materials via metal ion doping can effectively boost their capacity and cycling durability.

Effective concentration ratio driven phase engineering of MBE-grown few-layer MoTe2

The polymorphic nature of ultrathin transition metal dichalcogenide (TMDC) materials makes the phase engineering of these materials an interesting field of investigation. Understanding the phase-controlling behavior of different growth parameters is crucial for obtaining large-area growth of a desirable phase. Here, we report a detailed study on the effect of growth parameters for engineering different phases of few-layer MoTe2 on sapphire using molecular beam epitaxy (MBE). Our study shows that the 2H phase of MoTe2 is stabilized in a certain regime of the flux ratio and growth temperature, while on both the lower, as well as, the higher sides of this regime, the 1T' phase is favored. The combined effect of growth parameters is explained using the effective concentration ratio of Te and Mo at the growth surface, which is found to be the primary factor governing the phase selectivity in few-layer MoTe2. XPS and KPFM investigations show the contribution of excess carrier doping in driving the phase change. The effect of the sapphire substrate on the crystallinity and phase-dependent morphological features has also been studied. This knowledge of versatile and controlled phase engineering of few-layer MoTe2 paves the way for fabricating large-scale hetero-phase-based metal-semiconductor heterostructures for future electronic and optoelectronic device applications.

Advances in Aqueous Zinc Ion Batteries based on Conversion Mechanism: Challenges, Strategies, and Prospects

Recently, aqueous zinc-ion batteries with conversion mechanisms have received wide attention in energy storage systems on account of excellent specific capacity, high power density, and energy density. Unfortunately, some characteristics of cathode material, zinc anode, and electrolyte still limit the development of aqueous zinc-ion batteries possessing conversion mechanism. Consequently, this paper provides a detailed summary of the development for numerous aqueous zinc-based batteries: zinc-sulfur (Zn-S) batteries, zinc-selenium (Zn-Se) batteries, zinc-tellurium (Zn-Te) batteries, zinc-iodine (Zn-I2) batteries, and zinc-bromine (Zn-Br2) batteries. Meanwhile, the reaction conversion mechanism of zinc-based batteries with conversion mechanism and the research progress in the investigation of composite cathode, zinc anode materials, and selection of electrolytes are systematically introduced. Finally, this review comprehensively describes the prospects and outlook of aqueous zinc-ion batteries with conversion mechanism, aiming to promote the rapid development of aqueous zinc-based batteries.

Highly Reversible Positive-Valence Conversion of Sulfur Chemistry for High-Voltage Zinc-Sulfur Batteries

Sulfur is a promising conversion-type cathode for zinc batteries (ZBs) due to its high discharge capacity and cost-effectiveness. However, the redox conversion of multivalent S in ZBs is still limited, only having achieved S0/S2- redox conversion with low discharge voltage and poor reversibility. This study presents significant progress by demonstrating, for the first time, the reversible S2-/S4+ redox behavior in ZBs with up to six-electron transfer (with an achieved discharge capacity of ≈1284 mAh g-1) using a highly concentrated ClO4 --containing electrolyte. The developed succinonitrile-Zn(ClO4)2 eutectic electrolyte stabilizes the positive-valence S compound and contributes to an ultra-low polarization voltage. Notably, the achieved flat discharge plateaus demonstrate the highest operation voltage (1.54 V) achieved to date in Zn‖S batteries. Furthermore, the high-voltage Zn‖S battery exhibits remarkable conversion dynamics, excellent cycling performance (85.7% capacity retention after 500 cycles), high efficiency (98.4%), and energy density (527 Wh kg S -1). This strategy of positive-valence conversion of sulfur represents a significant advancement in understanding sulfur chemistry in batteries and holds promise for future high-voltage sulfur-based batteries.

Superhalide-Anion-Motivator Reforming-Enabled Bipolar Manipulation toward Longevous Energy-Type Zn||Chalcogen Batteries

Neutrophilic superhalide-anion-triggered chalcogen conversion-based Zn batteries, despite latent high-energy merit, usually suffer from a short lifespan caused by dendrite growth and shuttle effect. Here, a superhalide-anion-motivator reforming strategy is initiated to simultaneously manipulate the anode interface and Se conversion intermediates, realizing a bipolar regulation toward longevous energy-type Zn batteries. With ZnF2 chaotropic additives, the original large-radii superhalide zincate anion species in ionic liquid (IL) electrolytes are split into small F-containing species, boosting the formation of robust solid electrolyte interphases (SEI) for Zn dendrite inhibition. Simultaneously, ion radius reduced multiple F-containing Se conversion intermediates form, enhancing the interion interaction of charged products to suppress the shuttle effect. Consequently, Zn||Se batteries deliver a ca. 20-fold prolonged lifespan (2000 cycles) at 1 A g-1 and high energy/power density of 416.7 Wh kgSe-1/1.89 kW kgSe-1, outperforming those in F-free counterparts. Pouch cells with distinct plateaus and durable cyclability further substantiate the practicality of this design.

A Tellurium-Boosted High-Areal-Capacity Zinc-Sulfur Battery

Aqueous rechargeable zinc-sulfur (Zn-S) batteries are a promising, cost-effective, and high-capacity energy storage technology. Still, they are challenged by the poor reversibility of S cathodes, sluggish redox kinetics, low S utilization, and unsatisfactory areal capacity. This work develops a facile strategy to achieve an appealing high-areal-capacity (above 5 mAh cm-2) Zn-S battery by molecular-level regulation between S and high-electrical-conductivity tellurium (Te). The incorporation of Te as a dopant allows for manipulation of the Zn-S electrochemistry, resulting in accelerated redox conversion, and enhanced S utilization. Meanwhile, accompanied by the S-ZnS conversion, Te is converted to zinc telluride during the discharge process, as revealed by ex-situ characterizations. This additional redox reaction contributes to the S cathode's total excellent discharge capacity. With this unique cathode structure design, the carbon-confined TeS cathode (denoted as Te1S7/C) delivers a high reversible capacity of 1335.0 mAh g-1 at 0.1 A g-1 with a mass loading of 4.22 mg cm-2, corresponding to a remarkable areal capacity of 5.64 mAh cm-2. Notably, a hybrid electrolyte design uplifts discharge plateau, reduces overpotential, suppresses Zn dendrites growth, and extends the calendar life of Zn-Te1S7 batteries. This study provides a rational S cathode structure to realize high-capacity Zn-S batteries for practical applications.

Halide Exchange in Perovskites Enables Bromine/Iodine Hybrid Cathodes for Highly Durable Zinc Ion Batteries

With the increasing need for reliable storage systems, the conversion-type chemistry typified by bromine cathodes attracts considerable attention due to sizeable theoretical capacity, cost efficiency, and high redox potential. However, the severe loss of active species during operation remains a problem, leading researchers to resort to concentrated halide-containing electrolytes. Here, profiting from the intrinsic halide exchange in perovskite lattices, a novel low-dimensional halide hybrid perovskite cathode, TmdpPb2[IBr]6, which serves not only as a halogen reservoir for reversible three-electron conversions but also as an effective halogen absorbent by surface Pb dangling bonds, C─H…Br hydrogen bonds, and Pb─I…Br halogen bonds, is proposed. As such, the Zn||TmdpPb2[IBr]6 battery delivers three remarkable discharge voltage plateaus at 1.21 V (I0/I-), 1.47 V (I+/I0), and 1.74 V (Br0/Br-) in a typical halide-free electrolyte; meanwhile, realizing a high capacity of over 336 mAh g-1 at 0.4 A g-1 and high capacity retentions of 88% and 92% after 1000 cycles at 1.2 A g-1 and 4000 cycles at 3.2 A g-1, respectively, accompanied by a high coulombic efficiency of ≈99%. The work highlights the promising conversion-type cathodes based on metal-halide perovskite materials.

Zn-based batteries for sustainable energy storage: strategies and mechanisms

Batteries play a pivotal role in various electrochemical energy storage systems, functioning as essential components to enhance energy utilization efficiency and expedite the realization of energy and environmental sustainability. Zn-based batteries have attracted increasing attention as a promising alternative to lithium-ion batteries owing to their cost effectiveness, enhanced intrinsic safety, and favorable electrochemical performance. In this context, substantial endeavors have been dedicated to crafting and advancing high-performance Zn-based batteries. However, some challenges, including limited discharging capacity, low operating voltage, low energy density, short cycle life, and complicated energy storage mechanism, need to be addressed in order to render large-scale practical applications. In this review, we comprehensively present recent advances in designing high-performance Zn-based batteries and in elucidating energy storage mechanisms. First, various redox mechanisms in Zn-based batteries are systematically summarized, including insertion-type, conversion-type, coordination-type, and catalysis-type mechanisms. Subsequently, the design strategies aiming at enhancing the electrochemical performance of Zn-based batteries are underscored, focusing on several aspects, including output voltage, capacity, energy density, and cycle life. Finally, challenges and future prospects of Zn-based batteries are discussed.

Unlocking Four-electron Conversion in Tellurium Cathodes for Advanced Magnesium-based Dual-ion Batteries

Magnesium (Mg) batteries hold promise as a large-scale energy storage solution, but their progress has been hindered by the lack of high-performance cathodes. Here, we address this challenge by unlocking the reversible four-electron Te0/Te4+ conversion in elemental Te, enabling the demonstration of superior Mg//Te dual-ion batteries. Specifically, the classic magnesium aluminum chloride complex (MACC) electrolyte is tailored by introducing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2), which initiates the Te0/Te4+ conversion with two distinct charge-storage steps. Te cathode undergoes Te/TeCl4 conversion involving Cl- as charge carriers, during which a tellurium subchloride phase is presented as an intermediate. Significantly, the Te cathode achieves a high specific capacity of 543 mAh gTe -1 and an outstanding energy density of 850 Wh kgTe -1, outperforming most of the previously reported cathodes. Our electrolyte analysis indicates that the addition of Mg(TFSI)2 reduces the overall ion-molecule interaction and mitigates the strength of ion-solvent aggregation within the MACC electrolyte, which implies the facilized Cl- dissociation from the electrolyte. Besides, Mg(TFSI)2 is verified as an essential buffer to mitigate the corrosion and passivation of Mg anodes caused by the consumption of the electrolyte MgCl2 in Mg//Te dual-ion cells. These findings provide crucial insights into the development of advanced Mg-based dual-ion batteries.

A High-Energy Tellurium Redox-Amphoteric Conversion Cathode Chemistry for Aqueous Zinc Batteries

Rechargeable aqueous zinc batteries are potential candidates for sustainable energy storage systems at a grid scale, owing to their high safety and low cost. However, the existing cathode chemistries exhibit restricted energy density, which hinders their extensive applications. Here, a tellurium redox-amphoteric conversion cathode chemistry is presented for aqueous zinc batteries, which delivers a specific capacity of 1223.9 mAh gTe -1 and a high energy density of 1028.0 Wh kgTe -1. A highly concentrated electrolyte (30 mol kg-1 ZnCl2) is revealed crucial for initiating the Te redox-amphoteric conversion as it suppresses the H2O reactivity and inhibits undesirable hydrolysis of the Te4+ product. By carrying out multiple operando/ex situ characterizations, the reversible six-electron Te2-/Te0/Te4+ conversion with TeCl4 is identified as the fully charged product and ZnTe as the fully discharged product. This finding not only enriches the conversion-type battery chemistries but also establishes a critical step in exploring redox-amphoteric materials for aqueous zinc batteries and beyond.

Unlocking Double Redox Reaction of Metal-Organic Framework for Aqueous Zinc-Ion Battery

Metal-organic frameworks (MOFs) show wide application as the cathode of aqueous zinc-ion batteries (AZIBs) in the future owning to their high porosity, diverse structures, abundant species, and controllable morphology. However, the low energy density and poor cycling stability hinder the feasibility in practical application. Herein, an innovative strategy of organic/inorganic double electroactive sites is proposed and demonstrated to obtain extra capacity and enhance the energy density in a manganese-based metal-organic framework (Mn-MOF-74). Simultaneously, its energy storage mechanism is systematically investigated. Moreover, profiting from the coordination effect, the Mn-MOF-74 features with stable structure in ZnSO4 electrolyte. Therefore, the Zn/Mn-MOF-74 batteries exhibit a high energy density and superior cycling stability. This work aids in the future development of MOFs in AZIBs.

Selenium-Anchored Chlorine Redox Chemistry in Aqueous Zinc Dual-Ion Batteries

Chlorine-based batteries with Cl0 to Cl- redox reaction (ClRR) are promising for high-performance energystorage due to their high redox potential and large theoretical capacity. However, the inherent gas-liquid conversion feature of ClRR together with poor Cl fixation can cause Cl2 leakage, reducing battery reversibility. Herein, we utilize a Se-based organic molecule, diphenyl diselenide (di-Ph-Se), as the Cl anchoring agent and realize an atomic level-Cl fixation through chalcogen-halogencoordinating chemistry. The promoted Cl fixation, with two oxidized Cl0 anchoring on a single Ph-Se, and the multivalence conversion of Se contributeto a six-electron conversion process with up to 507 mAh g-1 and an average voltage of 1.51 V, as well as a high energy density of 665 Wh Kg-1 . Based on the superior reversibility of thedeveloped di-Ph-Se electrode with ClRR, a remarkable rate performance (205 mAh g-1 at 5 A g-1 ) and cycling performance (capacity retention of 77.3 % after 500cycles) are achieved. Significantly, the pouch cell delivers a record arealcapacity of up to 6.87 mAh cm-2 and extraordinary self-discharge performance. This chalcogen-halogen coordination chemistry between the Se electrode and Cl provides a new insight for developing reversible and efficientbatteries with halogen redox reactions.

A Reversible Six-Electron Transfer Cathode for Advanced Aqueous Zinc Batteries

The electrochemical reactions for the storage of Zn2+ while embracing more electron transfer is a foundation of the future high-energy aqueous zinc batteries. Herein, we report a six-electron transfer electrochemistry of nano-sized TeO2 /C (n-TeO2 /C) cathode by facilitating the reversible conversion of TeO2 ↔Te and Te↔ZnTe. Benefitting from the integrated conductive nanostructure and the proton-rich environment in providing optimized electrochemical kinetics (facilitated Zn2+ uptake and high electronic conductivity) and feasible thermodynamic process (low Gibbs free energy change), the as-prepared n-TeO2 /C with stable cycling performance exhibits a superior reversible capacity of over 800 mAh g-1 at 0.1 A g-1 . A precise understanding of the reaction mechanism via ex situ and in situ characterizations presents that the reversible six-electron transfer reaction is proton-dependent, and a proton generating and consuming mechanism of three-phase conversion n-TeO2 /C in the weakly acidic electrolyte is thoroughly revealed.