Spontaneous and field-induced crystallographic reorientation of metal electrodeposits at battery anodes

Oriented Metal Stripping for Highly Reversible Zinc Anode

Aqueous zinc metal batteries are a viable candidate for next-generation energy storage systems, but suffer from poor cycling efficiency of the Zn anode. Emerging approaches aim to regulate zinc plating behavior to suppress uncontrolled dendrites, while the stripping process is seldom considered. Herein, an oriented metal stripping strategy is demonstrated to stabilize the Zn anode by removing high-index facets for exposing the (002) plane through the addition of anionic additive sodium citrate (SC). Consequently, high-index facets that coordinate strongly with SC are preferentially stripped out due to a reduced stripping barrier, rendering stable (002) facet preponderant in epitaxial plating. After repeat stripping/plating, the ultra-high proportion of 93% for (002) and large-size grains of ≈100 µm (six times larger than before) can be obtained. Zn anode shows continuous 25 000 cycles with low overpotential at 100 mA cm-2 in symmetric cells and more than 70 h of stable operation even at an ultra-high depth of discharge of 92.3%. Moreover, an extremely long lifespan of 12 000 cycles at 10 A g-1 with a high capacity retention of 89% is achieved by the assembled Zn//I2 battery. This work provides a distinctive approach to improving the stripping process to design highly efficient zinc anodes for promising aqueous zinc metal batteries.

Achieving Dendrite-Free and By-Product-Free Aqueous Zn-Ion Battery Anode via Nicotinic Acid Electrolyte Additive with Molecule-Ion Conversion Mechanism

The widespread adoption of aqueous Zn ion batteries is hindered by the instability of the Zn anode. Herein, an elegant strategy is proposed to enhance the stability of Zn anode by incorporating nicotinic acid (NA), an additive with a unique molecule-ion conversion mechanism, to optimize the anode/electrolyte interface and the typical ZnSO4 electrolyte system. Experimental characterization and theoretical calculations demonstrate that the NA additive preferentially replaces H2O in the original solvation shell and adsorbs onto the Zn anode surface upon conversion from molecule to ion in the electrolyte environment, thereby suppressing side reactions arising from activated H2O decomposition and stochastic growth of Zn dendrites. Simultaneously, such a molecule-to-ion conversion mechanism may induce preferential deposition of Zn along the (002) plane. Benefiting from it, the Zn||Zn symmetric battery cycles stably for 2500 h at 1 mA cm-2, 1 mAh cm-2. More encouragingly, the Zn||AC full batteries and the Zn||AC full batteries using NA electrolyte and Zn||VO2 full batteries also exhibit excellent performance improvements. This work emphasizes the role of variation in the form of additives (especially weak acid-based additives) in fine-tuning the solvation structure and the anode/electrolyte interface, hopefully enhancing the performance of various aqueous metal batteries.

Ion Depletion Microenvironments Mapped at Active Electrochemical Interfaces with Operando Freezing Cryo-Electron Microscopy

Interfacial structural and chemical evolution underpins safety, energy density, and lifetime in batteries and other electrochemical systems. During lithium electrodeposition, local nonequilibrium conditions can arise that promote heterogeneous lithium morphologies but are challenging to directly study, particularly at the nanoscale. Here we map chemical microenvironments at the active copper/electrolyte interface during lithium electrodeposition, presenting operando freezing cryogenic electron microscopy (cryo-EM), a new method, to lock in structures arising in coin cells. We find local ion depletion is correlated with lithium whiskers but not planar lithium, and we hypothesize that depletion stems from root-growing whiskers consuming ions at the growth interface while also restricting ion transport through local electrolyte. This can allow dangerous lithium morphologies to propagate, even in concentrated electrolytes, as ion depletion favors dendritic growth. Operando freezing cryo-EM thus reveals local microenvironments at active electrochemical interfaces to enable direct investigation of site-specific, nonequilibrium conditions that arise during operation of energy devices.

Controllable Solid Electrolyte Interphase by Ionic Environment Regulation for Stable Zn-Ion Battery

Artificial solid electrolyte interphase in organic solutions is effective and facile for long-cycling aqueous zinc ion batteries. However, the specific effects on different ionic environments have not been thoroughly investigated. Herein, pyromellitic acid (PA) are employed as organic ligand to coordinate with Zn2+ under various ionic environments. The connection between the ionic environment and reaction spontaneity is analyzed to provide insights into the reasons behind the effectiveness of the SEI layer and to characterize its protective impact on the zinc anode. Notably, the PA solution (pH4) lacking OH- contributes to the formation of a dense and ultrathin SEI with Zn-PA coordination, preventing direct contact between the anode and electrolyte. Moreover, the presence of organic functional groups facilitates a uniform flux of Zn2+. These advantages enable stable cycling of the PA4-Zn symmetric cell at a current density of 3 mA cm-2 for over 3500 h. The PA4-Zn//MVO full cell demonstrates excellent electrochemical reversibility. Investigating the influence of the ionic environment on SEI generation informs the development of novel SEI strategies.

Rational Electrochemical Design of Cuprous Oxide Hierarchical Microarchitectures and Their Derivatives for SERS Sensing Applications

Rational morphology control of inorganic microarchitectures is important in diverse fields, requiring precise regulation of nucleation and growth processes. While wet chemical methods have achieved success regarding the shape-controlled synthesis of micro/nanostructures, accurately controlling the growth behavior in real time remains challenging. Comparatively, the electrodeposition technique can immediately control the growth behavior by tuning the overpotential, whereas it is rarely used to design complex microarchitectures. Here, the electrochemical design of complex Cu2O microarchitectures step-by-step by precisely controlling the growth behavior is demonstrated. The growth modes can be switched between the thermodynamic and kinetic modes by varying the overpotential. Cl- ions preferably adhered to {100} facets to modulate growth rates of these facets is proved. The discovered growth modes to prepare Cu2O microarchitectures composed of multiple building units inaccessible with existing methods are employed. Polyvinyl alcohol (PVA) additives can guarantee all pre-electrodeposits simultaneously evolve into uniform microarchitectures, instead of forming undesired microstructures on bare electrode surfaces in following electrodeposition processes is discovered. The designed Cu2O microarchitectures can be converted into noble metal microstructures with shapes unchanged, which can be used as surface-enhanced Raman scattering substrates. An electrochemical avenue toward rational design of complex inorganic microarchitectures is opened up.

Extended Battery Compatibility Consideration from an Electrolyte Perspective

The performance of electrochemical batteries is intricately tied to the physicochemical environments established by their employed electrolytes. Traditional battery designs utilizing a single electrolyte often impose identical anodic and cathodic redox conditions, limiting the ability to optimize redox environments for both anode and cathode materials. Consequently, advancements in electrolyte technologies are pivotal for addressing these challenges and fostering the development of next-generation high-performance electrochemical batteries. This review categorizes perspectives on electrolyte technology into three key areas: additives engineering, comprehensive component analysis encompassing solvents and solutes, and the effects of concentration. By summarizing significant studies, the efficacy of electrolyte engineering is highlighted, and the review advocates for further exploration of optimized component combinations. This review primarily focuses on liquid electrolyte technologies, briefly touching upon solid-state electrolytes due to the former greater vulnerability to electrode and electrolyte interfacial effects. The ultimate goal is to generate increased awareness within the battery community regarding the holistic improvement of battery components through optimized combinations.

Controlling Electrodeposition in Nonplanar High Areal Capacity Battery Anodes via Charge Transport and Chemical Modulation

Controlling the morphological evolution of electrochemical crystal growth in battery anodes is of fundamental and practical importance, particularly towards realizing practical, high-energy batteries based on metal electrodes. Such batteries require highly reversible plating/stripping reactions at the anode to achieve a long cycle life. While conformal electrodeposition and electrode reversibility have been demonstrated in numerous proof-of-concept experiments featuring moderate to low areal capacity (≤3 mA h/cm2) electrodes, achieving high levels of reversibility is progressively challenging at the higher capacities (e.g., 10 mA h/cm2), required in applications. Nonplanar, "3D" electrodes composed of electrically conductive, porous substrates are conventionally thought to overcome trade-offs between reversibility and capacity because they hypothetically "host" the electrodeposits in an electronically conducting framework, providing redundant pathways for electron flow. Here, we challenge this hypothesis and instead show that a nonplanar substrate with moderate electrical conductivity (ideally, with an electrical conductance similar to the ionic conductance of the electrolyte) and composed of a passivated cathode-facing surface efficiently regulates electro-crystallization. In contrast, an architecture with a high intrinsic electrical conductivity or with a high electrical conductivity coating on the front surface results in dominantly out-of-plane growth, making the 3D architecture in effect function as a 2D substrate. Using Zn as an example, we demonstrate that interconnected carbon fiber substrates coated by SiO2 on the front and Cu on the back successfully ushers electroplated Zn metal into the 3D framework at a macroscopic length scale, maximizing use of the interior space of the framework. The effective integration of electrodeposits into the 3D framework also enables unprecedented plating/stripping reversibility >99.5% at high current density (e.g., 10 mA/cm2) and high areal capacities (e.g., 10 mA h/cm2). Used in full-cell Zn||NaV3O8 batteries with stringent N/P ratios of 3:1, the substrates are also shown to enhance cycle life.

Inert Group-Containing Electrolyte Additive Enabling Stable Aqueous Zinc-Ion Batteries

Aqueous zinc ion batteries (AZIBs) are considered promising energy storage devices because of their high theoretical energy density and cost-effectiveness. However, the ongoing side reactions and zinc dendrite growth during cycling limit their practical application. Herein, trisodium methylglycine diacetate (Na3MGDA) additive containing the additional inert group methyl is introduced for Zn anode protection, and the contribution of methyl as an inert group to the Zn anode stability is discussed. Experimental results reveal that the methyl group with various effects enhances the interaction between the polar groups in Na3MGDA and the Zn2+/Zn anode. Thus, the polar carboxylate negative ions in MGDA anions can more easily modify the solvation structure and adsorb on the anode surface in situ to establish a hydrophobic electrical double layer (EDL) layer with steric hindrance effects. Such the EDL layer exhibits a robust selectivity for Zn deposition and a significant inhibition of parasitic reactions. Consequently, the Zn||Zn symmetric battery presents 2375 h at 1 mA cm-2, 1 mAh cm-2, and the Zn||V6O13 full battery provides 91% capacity retention after 1300 cycles at 3 A g-1. This study emphasizes the significant role of inert groups of the additive on the interfacial stability during the plating/stripping of high-performance AZIBs.

Reversing Zincophobic/Hydrophilic Nature of Metal-N-C via Metal-Coordination Interaction for Dendrite-Free Zn Anode with High Depth-of-Discharge

Dendrite-free Zn metal anodes with high depth-of-discharge (DoD) and robust cycle performances are highly desired for the practical application of aqueous Zn-ion batteries. Herein, the zincophobic/hydrophilic nature of Metal-N-C through manipulating the electronic interactions between metal and coordination atoms is successfully reversed, thereby fabricating a zincophilic/hydrophobic asymmetric Zn-N3Py+1Pr-C (consisting of a Zn center coordinated with 3 pyridinic N atoms and 1 pyrrolic N atom) host, which realizes uniformed Zn deposition and a long lifespan with high DoD. The experimental and theoretical investigations demonstrate weakened interaction between pyrrolic N and metal center in the asymmetric Zn-N3Py+1Pr-C triggers downshift of the Zn 3d-band-center and a new localization nonbonding state in the N and C 2p-band, resulting in preferred Zn adsorption to water adsorption. Consequently, the asymmetric Zn-N3Py+1Pr-C host delivers small Zn nucleation overpotential and high Coulombic efficiency of 98.3% over 500 cycles. The symmetric cells with Zn-N3Py+1Pr-C@Zn anode demonstrate 500 h dendrite-free cycles at DoD up to 50%. The Zn-N3Py+1Pr-C@Zn/S-PANI full cell also shows a robust long-term cycle performance of 1000 cycles at 10 A g-1. This strategy of constructing zincophilic/hydrophobic Metal-N-C may open up their application for the dendrite-free metal anode.

Single [0001]-oriented zinc metal anode enables sustainable zinc batteries

The optimization of crystalline orientation of a Zn metal substrate to expose more Zn(0002) planes has been recognized as an effective strategy in pursuit of highly reversible Zn metal anodes. However, the lattice mismatch between substrate and overgrowth crystals has hampered the epitaxial sustainability of Zn metal. Herein, we discover that the presence of crystal grains deviating from [0001] orientation within a Zn(0002) metal anode leads to the failure of epitaxial mechanism. The electrodeposited [0001]-uniaxial oriented Zn metal anodes with a single (0002) texture fundamentally eliminate the lattice mismatch and achieve ultra-sustainable homoepitaxial growth. Using high-angle angular dark-filed scanning transmission electron microscopy, we elucidate the homoepitaxial growth of the deposited Zn following the "~ABABAB~" arrangement on the Zn(0002) metal from an atomic-level perspective. Such consistently epitaxial behavior of Zn metal retards dendrite formation and enables improved cycling, even in Zn||NH4V4O10 pouch cells, with a high capacity of 220 mAh g-1 for over 450 cycles. The insights gained from this work on the [0001]-oriented Zn metal anode and its persistently homoepitaxial mechanism pave the way for other metal electrodes with high reversibility.

Self-Zincophilic Dual Protection Host of 3D ZnO/Zn⊂CF to Enhance Zn Anode Cyclability

Zn dendrite growth and side reactions restrict the practical use of Zn anode. Herein, the design of a novel 3D hierarchical structure is demonstrated with self-zincophilic dual-protection constructed by ZnO and Zn nanoparticles immobilized on carbon fibers (ZnO/Zn⊂CF) as a versatile host on the Zn surface. The unique 3D frameworks with abundant zinc nucleation storage sites can alleviate the structural stress during the plating/stripping process and overpower Zn dendrite growth by moderating Zn2+ flux. Moreover, given the dual protection design, it can reduce the contact area between active zinc and electrolyte, inhibiting hydrogen evolution reactions. Importantly, density functional theory calculations and experimental results confirm that the introduced O atoms in ZnO/Zn⊂CF enhance the interaction between Zn2+ and the host and reduce Zn nucleation overpotential. As expected, the ZnO/Zn⊂CF-Zn electrode exhibits stable Zn plating/stripping with low polarization for 4200 h at 0.2 mA cm-2 and 0.2 mAh cm-2 . Furthermore, the symmetrical cell displays a significantly long cycling life of over 1800 h, even at 30 mA cm-2 . The fabricated full cells also show impressive cycling performance when coupled with V2 O3 cathodes.

Ordered planar plating/stripping enables deep cycling zinc metal batteries

Metal anodes are emerging as culminating solutions for the development of energy-dense batteries in either aprotic, aqueous, or solid battery configurations. However, unlike traditional intercalation electrodes, the low utilization of "hostless" metal anodes due to the intrinsically disordered plating/stripping impedes their practical applications. Herein, we report ordered planar plating/stripping in a bulk zinc (Zn) anode to achieve an extremely high depth of discharge exceeding 90% with negligible thickness fluctuation and long-term stable cycling. The Zn can be plated/stripped with (0001)Zn preferential orientation throughout the consecutive charge/discharge process, assisted by a self-assembled supramolecular bilayer at the Zn anode-electrolyte interface. Through real-time tracking of the Zn atoms migration, we reveal that the ordered planar plating/stripping is driven by the construction of in-plane Zn─N bindings and the gradient energy landscape at the reaction fronts. The breakthrough results provide alternative insights into the ordered plating/stripping of metal anodes toward rechargeable energy-dense batteries.

Eco-friendly treatment of copper smelting flue dust for recovering multiple heavy metals with economic and environmental benefits

Handling flue dust in an environmentally friendly manner has become an urgent task for pollution prevention in the copper industry. Here, driven by the low-carbon notion, we report a process that enables the selective retrieval of multiple metals (As, Cu, Pb, Zn, and Bi) from copper smelting flue dust (CSFD). This process employed low-temperature roasting to separate arsenic from heavy metals, thereby eliminating the tedious separation steps required by existing processes. Subsequently, Zn and Cu were dissolved in water, while Pb and Bi were left as a solid residue. We achieved 98.23% extraction of Cu via Zn cementation at a micro-voltage of 0.50 V. Utilizing the difference in solubility, Bi was selectively dissolved from the residue using a NaCl-HCl medium, which enabled the subsequent production of metallic Bi through electrowinning. Finally, more than 99% of Pb in the solid was reduced to elemental Pb by mechanochemical reduction. Through optimized process conditions, high-purity As2O3 (99.04%), lead ingot (99.95%), metallic copper (94.16%), and bismuth (99.20%) were obtained. Our economic assessment revealed significant advantages, demonstrating the industrial feasibility of this process. Consequently, this study presents an effective and cost-efficient system for CSFD disposal while minimizing the environmental impact and fostering a circular economy.

Thermally Healable Electrolyte-Electrode Interface for Sustainable Quasi-Solid Zinc-ion Batteries

Quasi-solid zinc-ion batteries using hydrogel electrolytes show great potential in energy storage devices owing to their intrinsic safety, fewer side reactions and wide electrochemical windows. However, the dendrite issues on the zinc anodes cannot be fundamentally eliminated and the intrinsic anode-electrolyte interfacial interspace is rarely investigated. Here, we design a dynamically healable gelatin-based hydrogel electrolyte with a highly reversible sol-gel transition, which can construct a conformal electrode-electrolyte interface and further evolve into a stable solid-solid interface by in situ solidification. The unique helical gelatin chain structure provides a uniform channel for zinc ion transport by the bridging effect of sulfate groups. As a consequence, the dynamically healable interface enables dendrite-free zinc anodes and repeatedly repairs the anode-electrolyte interfacial interspaces by the reversible sol-gel transition of gelatin electrolyte to retain long-lasting protection for sustainable zinc-ion batteries.

Surface Patterning of Metal Zinc Electrode with an In-Region Zincophilic Interface for High-Rate and Long-Cycle-Life Zinc Metal Anode

The undesirable dendrite growth induced by non-planar zinc (Zn) deposition and low Coulombic efficiency resulting from severe side reactions have been long-standing challenges for metallic Zn anodes and substantially impede the practical application of rechargeable aqueous Zn metal batteries (ZMBs). Herein, we present a strategy for achieving a high-rate and long-cycle-life Zn metal anode by patterning Zn foil surfaces and endowing a Zn-Indium (Zn-In) interface in the microchannels. The accumulation of electrons in the microchannel and the zincophilicity of the Zn-In interface promote preferential heteroepitaxial Zn deposition in the microchannel region and enhance the tolerance of the electrode at high current densities. Meanwhile, electron aggregation accelerates the dissolution of non-(002) plane Zn atoms on the array surface, thereby directing the subsequent homoepitaxial Zn deposition on the array surface. Consequently, the planar dendrite-free Zn deposition and long-term cycling stability are achieved (5,050 h at 10.0 mA cm-2 and 27,000 cycles at 20.0 mA cm-2). Furthermore, a Zn/I2 full cell assembled by pairing with such an anode can maintain good stability for 3,500 cycles at 5.0 C, demonstrating the application potential of the as-prepared ZnIn anode for high-performance aqueous ZMBs.

Interphase Modulated Early-Stage Zn Electrodeposition Mechanism

Zn electrodeposition mechanism is a cornerstone of dendritic issue exploration in Zn-ion battery. Investigation of the inherent early-stage Zn plating kinetics and its dependence on the reactivity of anode-electrolyte interphase is crucial. Herein, the kinetic evolution of Zn plating on three characteristic substrates is quantified: fresh Zn, commercial Zn foil, and Zn foil with spontaneously generated solid-electrolyte interphase (SEI). Using scanning electrochemical microscopy analysis, the original interphase regulation of Zn deposit orientation and the competitive reaction between Zn deposition and SEI passivation are studied in situ. Furthermore, the SEI layer can suppress the dendrite growth at initial state by guiding the horizontal alignment of Zn flakes and promote Zn plating process. This approach provided a feasible consideration into interphase engineering of various metal anodes.

Oriented Zinc Metal Anode Based on Directional Recognition and Assembly

The practical application of aqueous zinc batteries are highly limited by unsatisfied Zn anodes for the unavoidable dendrite growth and side reactions. Crystal orientation engineering is an effective way to overcome these inherent drawbacks. However, how to achieve Zn plating with manipulated crystallographic orientation is still a great challenge. Herein, a uniform (002)-oriented Zn metal anode is reported based on a directional cation recognition and crystal assembly strategy. The activated layered double hydroxide (Act-LDH) exhibits favorable adsorption energy with Zn2+ and high lattice matching with Zn (002) plane, which can be served as directional recognition layer to anchor Zn2+ and regulate crystallographic orientation of Zn as well. As demonstration, Zn crystals with ultrahigh ratio of (002)/(100) plane of 15.7 are assembled parallelly on horizontal Act-LDH, in which high CE of 99.85% maintains over 18 000 cycles. The symmetric battery with (002)-oriented Zn shows stable plating/stripping process over 1650 and 420 h at 1 mA cm-2 /0.5 mA h cm-2 and 10 mA cm-2 /5 mA h cm-2 , respectively, which is 9 and 12 times higher than unoriented polycrystalline Zn. Moreover, as-assembled full battery displays high specific capacity of 120 mA h g-1 at 2 A g-1 over 1800 cycles.

Electrolyte and Additive Engineering for Zn Anode Interfacial Regulation in Aqueous Zinc Batteries

Aqueous Zn-metal batteries (AZMBs) have gained great interest due to their low cost, eco-friendliness, and inherent safety, which serve as a promising complement to the existing metal-based batteries, e.g., lithium-metal batteries and sodium-metal batteries. Although the utilization of aqueous electrolytes and Zn metal anode in AZMBs ensures their improved safety over other metal batteries meanwhile guaranteeing their decent energy density at the cell level, plenty of challenges involved with metallic Zn anode still await to be addressed, including dendrite growth, hydrogen evolution reaction, and zinc corrosion and passivation. In the past years, several attempts have been adopted to address these problems, among which engineering the aqueous electrolytes and additives is regarded as a facile and promising approach. In this review, a comprehensive summary of aqueous electrolytes and electrolyte additives will be given based on the recent literature, aiming at providing a fundamental understanding of the challenges associated with the metallic Zn anode in aqueous electrolytes, meanwhile offering a guideline for the electrolytes and additives engineering strategies toward stable AZMBs in the future.

F-Doped Carbon Nanoparticles-Based Nucleation Assistance for Fast and Uniform Three-Dimensional Zn Deposition

Aqueous Zn metal-based batteries have considerable potential as energy storage system; however, their application is extremely limited by dendrite development and poor reversibility. In this study, to overcome both challenges, F-doped carbon nanoparticles (FCNPs) are uniformly constructed on substrates (Ti, Zn, Cu, and steel) by a plasma-assisted surface modification, which endows reversible and uniform deposition of Zn metal. FCNPs with high surface charge density act as nucleation assistors and form numerous homogenous Zn nucleation sites toward Zn 3D growth, which improves Zn plating kinetic and results in uniform Zn deposition. Furthermore, the ZnF₂  solid electrolyte interface generated during cycling contributes to rapid mass transfer and enhances Zn reversibility, but also suppresses the side reaction. Accordingly, the half-cell of P-Ti coupled with Zn exhibits an average Coulombic efficiency of 99.47% with 500 cycles. The symmetric cell of the P-Zn anode presents a lifespan of over 1500 h at the current density of 5 mA cm^-2 . Notably, the cell works for 100 h at 50 mA cm^-2 . It is believed that this ingenious surface modification broadens revolutionary methods for uniform metallic deposition, as well as the dendrite-free rechargeable batteries system.

Zinc-Contained Alloy as a Robustly Adhered Interfacial Lattice Locking Layer for Planar and Stable Zinc Electrodeposition

Stable zinc (Zn)/electrolyte interface is critical for developing rechargeable aqueous Zn-metal batteries with long-term stability, which requires the dense and stable Zn electrodeposition. Herein, an interfacial lattice locking (ILL) layer is constructed via the electro-codeposition of Zn and Cu onto the Zn electrodes. The ILL layer shows a low lattice misfit (δ = 0.036) with Zn(002) plane and selectively locks the lattice orientation of Zn deposits, enabling the epitaxial growth of Zn deposits layer by layer. Benefiting from the unique orientation-guiding and robustly adhered properties, the ILL layer enables the symmetric Zn||Zn cells to achieve an ultralong life span of >6000 h at 1 mA cm^-2 and 1 mAh cm^-2 , a low overpotential (65 mV) at 10 mAh cm^-2 , and a stable Zn plating/stripping for >90 h at an ultrahigh Zn depth of discharge (≈85%). Even with a limited Zn supply and a high current density (8.58 mA cm^-2 ), the ILL@Zn||Ni-doped MnO₂ cells can still survive for >2300 cycles.

Rationalized Electroepitaxy toward Scalable Single-Crystal Zn Anodes

Electroepitaxy is recognized as an effective approach to prepare metal electrodes with nearly complete reversibility. Nevertheless, large-scale manipulation is still not attainable owing to complicated interfacial chemistry. Here, the feasibility of extending Zn electroepitaxy toward the bulk phase over a mass-produced mono-oriented Cu(111) foil is demonstrated. Interfacial Cu-Zn alloy and turbulent electroosmosis are circumvented by adopting a potentiostatic electrodeposition protocol. The as-prepared Zn single-crystalline anode enables stable cycling of symmetric cells at a stringent current density of 50.0 mA cm^-2 . The assembled full cell further sustaines a capacity retention of 95.7% at 5.0 A g^-1 for 1500 cycles, accompanied by a controllably low N/P ratio of 7.5. In addition to Zn, Ni electroepitaxy can be realized by using the same approach. This study may inspire rational exploration of the design of high-end metal electrodes.

Gradient Electrolyte Strategy Achieving Long-Life Zinc Anodes

Aqueous Zn-ion batteries are plagued by a short lifespan caused by localized dendrites. High-concentration electrolytes are favorable for dense Zn deposition but have poor performance in batteries with glass-fiber separators. In contrast, low-concentration electrolytes can wet the separators well, ensuring the migration of zinc ions, but the dendrites grow rapidly. In this work, we propose an electrolyte gradient strategy wherein a zinc-ion concentration gradient is established from the anode to the separator, ensuring that the separator keeps a good wettability in low-concentration areas and the zinc anode achieves dendrite-free deposition in a high-concentration area. By using this strategy in a common electrolyte, zinc sulfate, a Zn||Zn symmetric cell achieves 14 000 ultralong cycles (exceeding 8 months) at 5 mA cm^-2 and 1 mAh cm^-2 . When the current is further increased to 20 mA cm^-2 , the symmetric cell could still run for over 10 000 cycles. Assembled Zn||NVO full cells also demonstrate prominent performance. At a high current of 16 mA cm^-2 , the NVO cathode with high loading (8 mg cm^-2 ) still has a capacity of 58% after 1200 cycles. Overall, the gradient electrolyte strategy provides a promising approach for practical long-life Zn anodes with the advantages of simple operation and low cost.

Metal Anodes with Ultrahigh Reversibility Enabled by the Closest Packing Crystallography for Sustainable Batteries

The ever-growing annual electricity generated from sustainable and intermittent energy such as wind and solar power requires cost effective and reliable electrochemical energy storage. Rechargeable batteries based on multivalent metal anodes such as Zn, Al, and Fe, taking advantage of large-scale production and affordable cost, have emerged as promising candidates. However, the uncontrollable dendrite-like metal deposition on regular substrate caused by disordered metal crystallization usually leads to premature failure of batteries and even safety concerns when the dendrite bridges the electrodes. Here it is reported that a series of metal anodes (Zn, Co, Al, Ni, and Fe) with multiple crystal structures (hexagonal close-packed, face-centered cubic, and body-centered cubic) can achieve dendrite-free and epitaxial deposition on single-crystal Cu(111) substrates enabled by the closest packing crystallography. Moreover, the closest packed facets are aligned horizontally with the substrates, resulting in compact planar construction and excellent chemical stability even at an unprecedented current density of 1 A cm^-2 . The full cells under a practical anode-to-cathode capacity ratio of 2.3 show a cycling life span of over 800 cycles with Coulombic efficiency of > 99.9%. The universal approach of regulating metal electrodeposition in this work is expected to boost the development of emerging sustainable energy storage/conversion devices.

Addition of Dioxane in Electrolyte Promotes (002)-Textured Zinc Growth and Suppressed Side Reactions in Zinc-Ion Batteries

The reversibility and cyclability of aqueous zinc-ion batteries (ZIBs) are largely determined by the stabilization of the Zn anode. Therefore, a stable anode/electrolyte interface capable of inhibiting dendrites and side reactions is crucial for high-performing ZIBs. In this study, we investigated the adsorption of 1,4-dioxane (DX) to promote the exposure of Zn (002) facets and prevent dendrite growth. DX appears to reside at the interface and suppress the detrimental side reactions. ZIBs with the addition of DX demonstrated a long-term cycling stability of 1000 h in harsh conditions of 10 mA cm^-2 with an ultrahigh cumulative plated capacity of 5 Ah cm^-2 and shows a good reversibility with an average Coulombic efficiency of 99.7%. The Zn//NH₄V₄O₁₀ full battery with DX achieves a high specific capacity (202 mAh g^-1 at 5 A g^-1) and capacity retention (90.6% after 5000 cycles), much better than that of ZIBs with the pristine ZnSO₄ electrolyte. By selectively adjusting the Zn²⁺ deposition rate on the crystal facets with adsorbed molecules, this work provides a promising modulation strategy at the molecular level for high-performing Zn anodes and can potentially be applied to other metal anodes suffering from instability and irreversibility.

Surface Engineering for Ultrathin Metal Anodes Enabling High-Performance Zn-Ion Batteries

Zn-ion batteries with low cost and high safety have been regarded as a promising energy storage technology for grid storage. It is well-known that the metal anode surface orientation is vital to its reversibility. Herein, we demonstrate a facile route to control the Zn metal anode surface orientation through electrodeposition with electrolyte additives. An ultrathin (101)-inclined Zn metal anode (down to 2 μm) is obtained by adding a small amount of dimethyl sulfoxide (DMSO) in the ZnSO₄ aqueous electrolyte. Scanning electron microscopy indicates the formation of flat terrace-like surfaces, while in situ optical observations demonstrate the reversible plating and stripping. DFT calculations reveal that the large reconstruction of the Zn-(101) surface with DMSO and H₂O adsorption to lower the interface energy is the main driving force for surface preference. Raman, XPS, and ToF-SIMS characterizations are performed to unveil the surface SEI components. Exceptional electrochemical performance is demonstrated for the (101)-inclined Zn metal anode in a half cell, which could cycle for 200 h with a low overpotential (<50 mV). The Zn||V₂O full cells are assembled, showing much better cycle performance for the 5 μm (101)-inclined Zn metal anode as compared to the commercialized 10 μm Zn metal foil, with a maximum specific capacity of 359 mAh/g and >170 mAh/g after over 300 cycles. We hope this study will spur further interest in the control of surface crystallographic orientation for a stable ultrathin Zn metal anode.

MoS2 -Mediated Epitaxial Plating of Zn Metal Anodes

Metal-based anodes (Li, Zn, etc.) are regarded as promising solutions for next-generation advanced batteries due to their high theoretical specific capacities. However, most of these metal anodes suffer from dendrite growth, which severely restricts their practical applications. Recently, epitaxial anode metal deposition by choosing a suitable substrate has received tremendous attention as an effective strategy to suppress dendrites. However, the epitaxial relationship between plated metal and the substrate has been a subject of debate. Herein, large-area, mono-orientated 2D material (MoS₂ ) is used, for the first time, to electrodeposit truly epitaxial Zn anodes. The continuous (without edges) mono-orientated MoS₂ films are shown to be an effective strategy for suppressing metal dendrites. In addition, the epitaxial nature of the electrodeposited Zn anode is proven by pole figure analysis, which provides the first demonstration of truly epitaxial Zn anode growth over large area as metal anode protection strategy through epitaxy.

Interface Engineering of Zinc Electrode for Rechargeable Alkaline Zinc-Based Batteries

Rechargeable aqueous zinc-based batteries have gained considerable interest because of their advantages of high theoretical capacity, being eco-friendly, and cost effectiveness. In particular, zinc-based batteries with alkaline electrolyte show great promise due to their high working voltage. However, there remain great challenges for the commercialization of the rechargeable alkaline zinc-based batteries, which are mainly impeded by the limited reversibility of the zinc electrode. The critical problems refer to the dendrites growth, electrode passivation, shape change, and side reactions, affecting discharge capacity, columbic efficiency, and cycling stability of the battery. All the issues are highly associated with the interfacial properties, including both electrons and ions transport behavior at the electrode interface. Herein, this work concentrates on the fundamental electrochemistry of the challenges in the zinc electrode and the design strategies for developing high-performance zinc electrodes with regard to optimizing the interfaces between host and active materials as well as electrode and electrolyte. In addition, potential directions for the investigation of electrodes and electrolytes for high-performance zinc-based batteries are presented, aiming at promoting the development of rechargeable alkaline zinc-based batteries.

Nanoscale Ultrafine Zinc Metal Anodes for High Stability Aqueous Zinc Ion Batteries

Aqueous Zn batteries (AZBs) are a promising energy storage technology, due to their high theoretical capacity, low redox potential, and safety. However, dendrite growth and parasitic reactions occurring at the surface of metallic Zn result in severe instability. Here we report a new method to achieve ultrafine Zn nanograin anodes by using ethylene glycol monomethyl ether (EGME) molecules to manipulate zinc nucleation and growth processes. It is demonstrated that EGME complexes with Zn²⁺ to moderately increase the driving force for nucleation, as well as adsorbs on the Zn surface to prevent H-corrosion and dendritic protuberances by refining the grains. As a result, the nanoscale anode delivers high Coulombic efficiency (ca. 99.5%), long-term cycle life (over 366 days and 8800 cycles), and outstanding compatibility with state-of-the-art cathodes (ZnVO and AC) in full cells. This work offers a new route for interfacial engineering in aqueous metal-ion batteries, with significant implications for the commercial future of AZBs.

In Situ Alloying Sites Anchored on an Amorphous Aluminum Nitride Matrix for Crystallographic Reorientation of Zinc Deposits

Secondary aqueous zinc-ion batteries (ZIBs) are considered as one of the promising energy storage devices, but their widespread application is limited by the Zn dendrite issues. In this work, we propose a rational design of surface protective coatings to solve this problem. Specifically, a silver (Ag) nanoparticle embedded amorphous AlN matrix (AlN/Ag) protective layer is developed. The former would alloy in situ with Zn to form AgZn₃ alloy sites, which subsequently induce the Zn deposition with preferred (002) facets. The latter can effectively alleviate the structural expansion during repeated Zn plating/stripping. Consequently, the delicately designed AlN/Ag@Zn anode delivers an enhanced stability with a long lifespan of more than 2600 h at 1 mA cm^-2 and 1 mAh cm^-2. Moreover, the AlN/Ag@Zn||Mn_1.4V₁₀O₂₄·nH₂O full batteries can be operated for over 8000 cycles under 5 A g^-1. Our work not only suggests a promising Zn anode protective coating but also provides a general strategy for the rational design of surface protective layers for metal anodes.

Design principles for heterointerfacial alloying kinetics at metallic anodes in rechargeable batteries

How surface chemistry influences reactions occurring thereupon has been a long-standing question of broad scientific and technological interest. Here, we consider the relation between the surface chemistry at interfaces and the reversibility of electrochemical transformations at rechargeable battery electrodes. Using Zn as a model system, we report that a moderate strength of chemical interaction between the deposit and the substrate-neither too weak nor too strong-enables highest reversibility and stability of the plating/stripping redox processes. Focused ion beam and electron microscopy were used to directly probe the morphology, chemistry, and crystallography of heterointerfaces of distinct natures. Analogous to the empirical Sabatier principle for chemical heterogeneous catalysis, our findings arise from competing interfacial processes. Using full batteries with stringent negative electrode-to-positive electrode capacity (N:P) ratios, we show that such knowledge provides a powerful tool for designing key materials in highly reversible battery systems based on Earth-abundant, low-cost metals such as Zn and Na.

Chemical Welding of the Electrode-Electrolyte Interface by Zn-Metal-Initiated In Situ Gelation for Ultralong-Life Zn-Ion Batteries

A compatible and robust electrode-electrolyte interface is favorable in resolving the severe dendritic growth and side reactions of aqueous Zn-ion batteries toward commercial-standard lifespan and charging-discharging rate. Herein, a chemical welding strategy through in situ construction of a gel electrolyte that enables Zn-ion batteries to achieve ultralong life and reversibility is reported. The gel electrolyte is spontaneously formed on the Zn anode surface by redox polymerization with the initiation of Zn metal. The direct participation of the Zn anode in the chemical synthesis of the gel electrolyte brings a well-bonded and water-poor electrode-electrolyte interface, which not only alleviates side reactions but also enables preferential (002) Zn deposition. The in situ symmetric cell thus prepared delivers an ultralong lifespan of 5100 h (>212 days), and a hybrid capacitor with the in situ electrolyte runs smoothly over 40 000 cycles at 20 A g^-1 . Even at an ultrahigh current density of 40 mA cm^-2  and capacity of 40 mAh cm^-2 , the cell still operates stably for 240 h, alongside a high Zn utilization with 87% depth of discharge. The in situ gel electrolyte integrating robust interface and preparation of all-in-one cells demonstrate a commercializable path for aqueous Zn-storage devices.

A solid-to-solid metallic conversion electrochemistry toward 91% zinc utilization for sustainable aqueous batteries

The diffusion-limited aggregation (DLA) of metal ion (Mⁿ⁺) during the repeated solid-to-liquid (StoL) plating and liquid-to-solid (LtoS) stripping processes intensifies fatal dendrite growth of the metallic anodes. Here, we report a new solid-to-solid (StoS) conversion electrochemistry to inhibit dendrites and improve the utilization ratio of metals. In this StoS strategy, reversible conversion reactions between sparingly soluble carbonates (Zn or Cu) and their corresponding metals have been identified at the electrode/electrolyte interface. Molecular dynamics simulations confirm the superiority of the StoS process with accelerated anion transport, which eliminates the DLA and dendrites in the conventional LtoS/StoL processes. As proof of concept, 2ZnCO₃·3Zn(OH)₂ exhibits a high zinc utilization of ca. 95.7% in the asymmetry cell and 91.3% in a 2ZnCO₃·3Zn(OH)₂ || Ni-based full cell with 80% capacity retention over 2000 cycles. Furthermore, the designed 1-Ah pouch cell device can operate stably with 500 cycles, delivering a satisfactory total energy density of 135 Wh kg^-1.

Artificial Interphase Layer for Stabilized Zn Anodes: Progress and Prospects

The burgeoning Li-ion battery is regarded as a powerful energy storage system by virtue of its high energy density. However, inescapable issues concerning safety and cost aspects retard its prospect in certain application scenarios. Accordingly, strenuous efforts have been devoted to the development of the emerging aqueous Zn-ion battery (AZIB) as an alternative to inflammable organic batteries. In particular, the instability from the anode side severely impedes the commercialization of AZIB. Constructing an artificial interphase layer (AIL) has been widely employed as an effective strategy to stabilize the Zn anode. This review specializes in the state-of-the-art of AIL design for Zn anode protection, encompassing the preparation methods, mechanism investigations, and device performances based on the classification of functional materials. To begin with, the origins of Zn instability are interpreted from the perspective of electrical field, mass transfer, and nucleation process, followed by a comprehensive summary with respect to functions of AIL and its designing criteria. In the end, current challenges and future outlooks based upon theoretical and experimental considerations are included.

Designing interphases for practical aqueous zinc flow batteries with high power density and high areal capacity

Aqueous zinc flow batteries (AZFBs) with high power density and high areal capacity are attractive, both in terms of cost and safety. A number of fundamental challenges associated with out-of-plane growth and undesirable side reactions on the anode side, as well as sluggish reaction kinetics and active material loss on the cathode side, limit practical deployment of these batteries. We investigated artificial interphases created using a simple electrospray methodology as a strategy for addressing each of these challenges. The effectiveness of the electrospray interphases in full cell zinc-iodine flow batteries was evaluated and reported; it is possible to simultaneously achieve high power density [115 milliwatts per square centimeter (mW/cm²)] and high areal capacity [25 milliampere hour per square centimeter (mA·hour/cm²)]. Last, we extended it to aqueous zinc-bromine and zinc-vanadium flow batteries of contemporary interest. It is again found that high power density (255 and 260 mW/cm², respectively) and high areal capacity (20 mA·hour/cm²) can be simultaneously achieved in AZFBs.

Self-repairing interphase reconstructed in each cycle for highly reversible aqueous zinc batteries

Aqueous zinc (Zn) chemistry features intrinsic safety, but suffers from severe irreversibility, as exemplified by low Coulombic efficiency, sustained water consumption and dendrite growth, which hampers practical applications of rechargeable Zn batteries. Herein, we report a highly reversible aqueous Zn battery in which the graphitic carbon nitride quantum dots additive serves as fast colloid ion carriers and assists the construction of a dynamic & self-repairing protective interphase. This real-time assembled interphase enables an ion-sieving effect and is found actively regenerate in each battery cycle, in effect endowing the system with single Zn²⁺ conduction and constant conformal integrality, executing timely adaption of Zn deposition, thus retaining sustainable long-term protective effect. In consequence, dendrite-free Zn plating/stripping at ~99.6% Coulombic efficiency for 200 cycles, steady charge-discharge for 1200 h, and impressive cyclability (61.2% retention for 500 cycles in a Zn | |MnO₂ full battery, 73.2% retention for 500 cycles in a Zn | |V₂O₅ full battery and 93.5% retention for 3000 cycles in a Zn | |VOPO₄ full battery) are achieved, which defines a general pathway to challenge Lithium in all low-cost, large-scale applications.

Metallic zinc is an ideal anode material for aqueous rechargeable batteries but reversibility is a challenge. Here, the authors realise a dynamic real-time reconstructed interphase on zinc anode formed by graphitic carbon nitride quantum dot as an electrolyte additive to improve the performance of Zn metal anodes.

Crystallographically Textured Electrodes for Rechargeable Batteries: Symmetry, Fabrication, and Characterization

The vast of majority of battery electrode materials of contemporary interest are of a crystalline nature. Crystals are, by definition, anisotropic from an atomic-structure perspective. The inherent structural anisotropy may give rise to favored mesoscale orientations and anisotropic properties whether the material is in a rest state or subjected to an external stimulus. The overall perspective of this review is that intentional manipulation of crystallographic anisotropy of electrochemically active materials constitute an untapped parameter space in energy storage systems and thus provide new opportunities for materials innovations and design. To that end, we contend that crystallographically textured electrodes, as opposed to their textureless poly crystalline or single-crystalline analogs, are promising candidates for next-generation storage of electrical energy in rechargeable batteries relevant to commercial practice. This perspective is underpinned first by the fundamental─to a first approximation─uniaxial, rotation-invariant symmetry of electrochemical cells. On this basis, we show that a crystallographically textured electrode with the preferred orientation aligned out-of-plane toward the counter electrode represents an optimal strategy for utilization of the crystals' anisotropic properties. Detailed analyses of anisotropy of different types lead to a simple, but potentially useful general principle that "P_ec//P_c" textures are optimal for metal anodes, and "P_ec//S_c" textures are optimal for insertion-type electrodes.

Lanthanum nitrate as aqueous electrolyte additive for favourable zinc metal electrodeposition

Aqueous zinc batteries are appealing devices for cost-effective and environmentally sustainable energy storage. However, the zinc metal deposition at the anode strongly influences the battery cycle life and performance. To circumvent this issue, here we propose the use of lanthanum nitrate (La(NO3)3) as supporting salt for aqueous zinc sulfate (ZnSO4) electrolyte solutions. Via physicochemical and electrochemical characterizations, we demonstrate that this peculiar electrolyte formulation weakens the electric double layer repulsive force, thus, favouring dense metallic zinc deposits and regulating the charge distribution at the zinc metal|electrolyte interface. When tested in Zn||VS2 full coin cell configuration (with cathode mass loading of 16 mg cm-2), the electrolyte solution containing the lanthanum ions enables almost 1000 cycles at 1 A g-1 (after 5 activation cycles at 0.05 A g-1) with a stable discharge capacity of about 90 mAh g-1 and an average cell discharge voltage of ∼0.54 V.

Interface Coordination Stabilizing Reversible Redox of Zinc for High-Performance Zinc-Iodine Batteries

Aqueous Zn batteries (AZBs) have attracted extensive attention due to good safety, cost-effectiveness, and environmental benignity. However, the sluggish kinetics of divalent zinc ion and the growth of Zn dendrites severely deteriorate the cycling stability and specific capacity. The authors demonstrate modulation of the interfacial redox process of zinc via the dynamic coordination chemistry of phytic acid with zinc ions. The experimental results and theoretical calculation reveal that the in-situ formation of such inorganic-organic films as a dynamic solid-electrolyte interlayer is efficient to buffer the zinc ion transfer via the energy favorable coordinated hopping mechanism for the reversible zinc redox reactions. Especially, along the interfacial coating layer with porous channel structure is able to regulate the solvation structure of zinc ions along the dynamic coordination of the phytic acid skeleton, efficiently inhibiting the surface corrosion of zinc and dendrite growth. Therefore, the resultant Zn anode achieves low voltage hysteresis and long cycle life at rigorous charge and discharge circulation for fabricating highly robust rechargeable batteries. Such an advanced strategy for modulating ion transport demonstrates a highly promising approach to addressing the basic challenges for zinc-based rechargeable batteries, which can potentially be extended to other aqueous batteries.

Unveiling the Synergistic Effect of Ferroelectric Polarization and Domain Configuration for Reversible Zinc Metal Anodes

The tendency of zinc (Zn) anodes to form uncontrolled Zn electrodeposits and the occurrence of side-reactions at Zn-electrolyte interfaces are a fundamental barrier hampering broad applications of aqueous rechargeable Zn-based batteries. Herein, a ferroelectric domain-mediated strategy is proposed to manipulate the Zn plating behavior and achieve controllable Zn growth orientation by coating Zn foil with a ferroelectric tetragonal KTN (t-KTN) layer. The ferroelectric domain of t-KTN single crystals exhibits periodic distribution of upward and downward polarizations, corresponding to alternating positively and negatively charged surfaces. The charged ferroelectric surfaces can manipulate the transfer kinetics of Zn ions and the concentration distribution of anions via the interplay between ferroelectric dipoles and adsorbed ions. With the synergistic effect of the ferroelectric polarization and domain configurations, the well-aligned interlamellar arrays composed of electrodeposited Zn are formed in the initial deposition process, which enable selective deposition within interlamellar arrays and eliminate the dendrite growth during the following plating process. As a result, the t-KTN layer-modified Zn anode enables reversible Zn plating/stripping with low voltage hysteresis for over 1200 h at 1 mA cm^-2 in symmetric cells, and the assembled full cell exhibits a significantly enhanced cycling stability of over 5500 cycles at 5 A g^-1 .

Nitrogen-Doped Carbon Fibers Embedded with Zincophilic Cu Nanoboxes for Stable Zn-Metal Anodes

The practical application of Zn-metal anodes (ZMAs) is mainly impeded by the limited lifespan and low Coulombic efficiency (CE) resulting from the Zn dendrite growth and side reactions. Herein, a 3D multifunctional host consisting of N-doped carbon fibers embedded with Cu nanoboxes (denoted as Cu NBs@NCFs) is rationally designed and developed for stable ZMAs. The 3D macroporous configuration and hollow structure can lower the local current density and alleviate the large volume change during the repeated cycling processes. Furthermore, zincophilic Cu and in-situ-formed Cu-Zn alloy can act as homogeneous nucleation sites to minimize the Zn nucleation overpotential, further guiding uniform and dense Zn deposition. As a result, this Cu NBs@NCFs host exhibits high CE of Zn plating/stripping for 1000 cycles. The Cu NBs@NCFs-Zn electrode shows low voltage hysteresis and prolonged cycling life (450 h) with dendrite-free behaviors. As a proof-of-concept demonstration, a Zn-ion full cell is fabricated based on this Cu NBs@NCFs-Zn anode, which demonstrates decent rate capability and improved cycling performance.

Non-Electrode Components for Rechargeable Aqueous Zinc Batteries: Electrolytes, Solid-Electrolyte-Interphase, Current Collectors, Binders, and Separators

Rechargeable aqueous zinc batteries (AZBs) are one of the promising options for large-scale electrical energy storage owing to their safety, affordability and environmental friendliness. During the past decade, there have been remarkable advancements in the AZBs technology, which are achieved through intensive efforts not only in the area of electrode materials but also in the fundamental understandings of non-electrode components such as electrolytes, solid electrolyte interphase (SEI), current collectors, binders, and separators. In particular, the breakthroughs in the non-electrode components should not be underestimated in having enabled the AZBs to attain a higher energy and power density beyond that of the conventional AZBs, proving their critical role. In this article, the recent research progress is comprehensively reviewed with respect to non-electrode components in AZBs, covering the new-type of electrolytes that have been introduced, attempts for the tailoring of SEI, and the design efforts for multi-functional current collectors, binders and separators, along with the remaining challenges associated with these non-electrode components. Finally, perspectives are discussed toward future research directions in this field. This extensive overview on the non-electrode components is expected to guide and spur further development of high-performance AZBs.

Production of fast-charge Zn-based aqueous batteries via interfacial adsorption of ion-oligomer complexes

Aqueous zinc batteries are attracting interest because of their potential for cost-effective and safe electricity storage. However, metallic zinc exhibits only moderate reversibility in aqueous electrolytes. To circumvent this issue, we study aqueous Zn batteries able to form nanometric interphases at the Zn metal/liquid electrolyte interface, composed of an ion-oligomer complex. In Zn||Zn symmetric cell studies, we report highly reversible cycling at high current densities and capacities (e.g., 160 mA cm⁻²; 2.6 mAh cm⁻²). By means of quartz-crystal microbalance, nuclear magnetic resonance, and voltammetry measurements we show that the interphase film exists in a dynamic equilibrium with oligomers dissolved in the electrolyte. The interphase strategy is applied to aqueous Zn||I₂ and Zn||MnO₂ cells that are charged/discharged for 12,000 cycles and 1000 cycles, respectively, at a current density of 160 mA cm⁻² and capacity of approximately 0.85 mAh cm⁻². Finally, we demonstrate that Zn||I₂-carbon pouch cells (9 cm² area) cycle stably and deliver a specific energy of 151 Wh/kg (based on the total mass of active materials in the electrode) at a charge current density of 56 mA cm⁻².

Aqueous zinc batteries attract interest because of their potential for cost-effective and safe electricity storage. Here, the authors develop an in situ formed ion-oligomer nanometric interphase strategy to enable fast-charge aqueous Zn cells.

Vertical Crystal Plane Matching between AgZn3 (002) and Zn (002) Achieving a Dendrite-Free Zinc Anode

Metallic zinc anodes in zinc-ion batteries suffer from problematic Zn dendrite chemistry. Previous works have shown that preferred-orientation crystal planes can help dendrite-free metal anodes. This work reports a nanothickness (≈570 nm) AgZn₃  coating to regulate the Zn growth. First, AgZn₃ @Zn anode avoids the problem, in Ag@Zn anode, that the rate of electrochemical Ag-Zn alloying is slower than that of Zn dendrites growth. Batteries life increased from 112 h (pure Zn) and 932 h (Ag@Zn) to 1360 h (AgZn₃ @Zn) at 2 mA cm^-2  and 1 mAh cm^-2 . Then, plasma sputtering can remove nonconductive ZnO and improve Zn-ion affinity, which brings a longer life for AuZn₃ @Zn (423 h), CuZn₃ @Zn (385 h), and AgZn₃ @Zn (1150 h) than pure Zn (93 h) at 1 mAh cm^-2 . More importantly, AgZn₃ (002) has a high matching with the Zn (002), which can guide ordered Zn epitaxial deposition, thereby achieving dense and dendrite-free Zn growth. This work clearly captures the fascinating structure of the densely stacked Zn layers on the AgZn₃  layer. This strategy not only improves the performance of zinc-ion batteries greatly but will also help one understand the matching mechanism of the (002) vertical crystal plane.

Temperature-Dependent Nucleation and Electrochemical Performance of Zn Metal Anodes

A fundamental understanding of the nucleation and growth behaviors of Zn metal anodes over a wide range of temperatures is of great value for suppressing Zn dendrite growth. However, work focused on the early nucleation and growth behavior of Zn metal at various temperatures is still absent. Here, we study the effect of cycling temperature on Zn nuclei size and areal density and find that low temperature induces a smaller and dense nucleus, which prevents the formation of dendrites. Based on this finding, a cooling-treatment-based self-healing strategy is developed to in situ eliminate dendrites, which effectively prolongs the lifespan of the Zn anode by 520%. This novel self-healing strategy could be employed as a reliable strategy for restoring batteries in situ to reach a longer lifespan.

Quantitative Lithiation Depth Profiling in Silicon Containing Anodes Investigated by Ion Beam Analysis

The localisation and quantitative analysis of lithium (Li) in battery materials, components, and full cells are scientifically highly relevant, yet challenging tasks. The methodical developments of MeV ion beam analysis (IBA) presented here open up new possibilities for simultaneous elemental quantification and localisation of light and heavy elements in Li and other batteries. It describes the technical prerequisites and limitations of using IBA to analyse and solve current challenges with the example of Li-ion and solid-state battery-related research and development. Here, nuclear reaction analysis and Rutherford backscattering spectrometry can provide spatial resolutions down to 70 nm and 1% accuracy. To demonstrate the new insights to be gained by IBA, SiOx-containing graphite anodes are lithiated to six states-of-charge (SoC) between 0–50%. The quantitative Li depth profiling of the anodes shows a linear increase of the Li concentration with SoC and a match of injected and detected Li-ions. This unambiguously proofs the electrochemical activity of Si. Already at 50% SoC, we derive C/Li = 5.4 (< LiC6) when neglecting Si, proving a relevant uptake of Li by the 8 atom % Si (C/Si ≈ 9) in the anode with Li/Si ≤ 1.8 in this case. Extrapolations to full lithiation show a maximum of Li/Si = 1.04 ± 0.05. The analysis reveals all element concentrations are constant over the anode thickness of 44 µm, except for a ~6-µm-thick separator-side surface layer. Here, the Li and Si concentrations are a factor 1.23 higher compared to the bulk for all SoC, indicating preferential Li binding to SiOx. These insights are so far not accessible with conventional analysis methods and are a first important step towards in-depth knowledge of quantitative Li distributions on the component level and a further application of IBA in the battery community.