Nanoscale Nucleation and Growth of Electrodeposited Lithium Metal

Interfacial studies on the effects of patterned anodes for guided lithium deposition in lithium metal batteries

The lifetime and health of lithium metal batteries are greatly hindered by nonuniform deposition and growth of lithium at the anode-electrolyte interface, which leads to dendrite formation, efficiency loss, and short circuiting. Lithium deposition is influenced by several factors including local current densities, overpotentials, surface heterogeneity, and lithium-ion concentrations. However, due to the embedded, dynamic nature of this interface, it is difficult to observe the complex physics operando. Here, we present a detailed model of the interface that implements Butler-Volmer kinetics to investigate the effects of overpotential and surface heterogeneities on dendrite growth. A high overpotential has been proposed as a contributing factor in increased nucleation and growth of dendrites. Using computational methods, we can isolate the aspects of the complex physics at the interface to gain better insight into how each component affects the overall system. In addition, studies have shown that mechanical modifications to the anode surface, such as micropatterning, are a potential way of controlling deposition and increasing Coulombic efficiency. Micropatterns on the anode surface are explored along with deformations in the solid-electrolyte interface layer to understand their effects on the dendritic growth rates and morphology. The study results show that at higher overpotentials, more dendritic growth and a more branched morphology are present in comparison to low overpotentials, where more uniform and denser growth is observed. In addition, the results suggest that there is a relationship between surface chemistries and anode geometries.

High-Capacity and Long-Life Zinc Electrodeposition Enabled by a Self-Healable and Desolvation Shield for Aqueous Zinc-Ion Batteries

Artificial interfaces can alleviate the side reactions and the formation of the metallic (e.g. , Li, Na, and Zn) dendrites. However, the traditional ones always break down during the repeated plating/stripping and fail to regulate the electrodeposition behaviors of the electrodes. Herein, a self-healable ion regulator (SIR) is designed as a desolvation shield to protect the Zn electrodes and guide the Zn electrodeposition. Benefiting from the intermolecular hydrogen bonds, SIR shows a superb capability to in-situ repair the plating/stripping-induced creaks. Besides, the results of theoretical calculations and electrochemical characterizations show that the coating reduces water molecules in the solvated sheath of hydrated Zn2+ and restrains the random Zn2+ diffusion on the Zn surface. Even with a coating layer of only 360 nm, the SIR-modified Zn electrode exhibits excellent long-term stability for > 3500 h at 2 mAh cm-2 and > 950 h at an ultrahigh areal capacity of 20 mAh cm-2 .

Inhibiting Dendrite Growth via Regulating the Electrified Interface for Fast-Charging Lithium Metal Anode

Extreme fast charging (XFC), with a recharging time of 15 min, is the key to the mainstream adoption of battery electric vehicles. Lithium metal, in the meantime, has re-emerged as the ultimate anode because of its ultrahigh specific capacity and low electrochemical potential. However, the low lithium-ion concentration near the lithium electrode surface can result in uncontrolled dendrite growth aggravated by high plating current densities. Here, we reveal the beneficial effects of an adaptively enhanced internal electric field in a constant voltage charging mode in XFC via a molecular understanding of the electrolyte-electrode interfaces. With the same charging time and capacity, the increased electric field stress in dozens of millivolts, compared with that in a constant current mode, can facilitate Li⁺ migrating toward the negatively charged lithium electrode, mitigating Li⁺ depletion at the interface and thereby suppressing dendrites. In addition, more NO₃ ^- ions are involved in the solvation sheath that is constructed on the lithium electrode surface, leading to the nitride-enriched solid electrolyte interphase and thus favoring lower barriers for Li⁺ transport. On the basis of these merits, the Li||Li₄Ti₅O₁₂ battery runs steadily for 550 cycles with charging current peaks up to 27 mA cm^-2, and the Li||S full cells exhibit extended life-spans charged within 12 min.

Separator Effect on Zinc Electrodeposition Behavior and Its Implication for Zinc Battery Lifetime

Uncontrolled zinc electrodeposition is an obstacle to long-cycling zinc batteries. Much has been researched on regulating zinc electrodeposition, but rarely are the studies performed in the presence of a separator, as in practical cells. Here, we show that the microstructure of separators determines the electrodeposition behavior of zinc. Porous separators direct zinc to deposit into their pores and leave "dead zinc" upon stripping. In contrast, a nonporous separator prevents zinc penetration. Such a difference between the two types of separators is distinguished only if caution is taken to preserve the attachment of the separator to the zinc-deposited substrate during the entire electrodeposition-morphological observation process. Failure to adopt such a practice could lead to misinformed conclusions. Our work reveals the mere use of porous separators as a universal yet overlooked challenge for metal anode-based rechargeable batteries. Countermeasures to prevent direct exposure of the metal growth front to a porous structure are suggested.

A Powerful Protocol Based on Anode-Free Cells Combined with Various Analytical Techniques

Lithium (Li) metal is the ultimate negative electrode due to its high theoretical specific capacity and low negative electrochemical potential. However, the handling of lithium metal imposes safety concerns in transportation and production due to its reactive nature. Recently, anode-free lithium metal batteries (AFLMBs) have drawn much attention because of several of their advantages, including higher energy density, lower cost, and fewer safety concerns during cell production compared to LMBs. Pushing the reversible Coulombic efficiency (CE) of AFLMBs up to 99.98% is key to achieving their 80% capacity retention over more than 1000 cycles. However, interfacial irreversible phenomena such as electrolyte decomposition reactions on both electrodes, dead Li formation, and Li dendrite formation result in poor capacity retention and short circuits in LMBs and AFLMBs. Therefore, it is of great importance and scientific interest to explore those interfacial irreversible phenomena to improve the cell's cycle life. Although significant contributions toward mitigating electrolyte decomposition, dead lithium, and dendritic lithium formation have been reported at the lithium anode, real irreversible phenomena are usually hidden or difficult to discover due to excess lithium employed in LMBs and simultaneous events taking place in both electrodes or at the interfaces.An integrated protocol is suggested to include Li||Cu, cathode||Li, and cathode||Cu configurations to provide overall quantification and determination of various sources of irreversible Coulombic efficiency (irr-CE) in AFLMBs and LMBs. Combining Li||Cu, cathode||Li, and cathode||Cu configurations is essential for separating the root sources of the capacity loss and irr-CE in LMBs and AFLMBs. Remarkably, integrating an anode-free cell with various analytical techniques can serve as a powerful protocol to decouple and quantify those interfacial irreversible phenomena according to our recent reports.In this Account, we focus on the protocol based on an anode-free cell combined with various analytical methods to investigate interfacial irreversible phenomena. Complementary advanced tools such as transmission X-ray microscopy (visualizing Li plating/stripping mechanism), nuclear magnetic resonance spectroscopy (quantifying dead lithium), and gas chromatography-mass spectroscopy (decoupling interfacial reactions) were employed to extract the intrinsic reasons and sources of individual irreversible reactions in LMBs and AFLMBs. Quantitative evaluation of nucleation and growth of Li metal deposition are addressed, along with solid electrolyte interphase (SEI) fracture, visualization of lithium dendrite growth, decoupling of oxidative and reductive electrolyte decomposition mechanisms, and irreversible efficiency (i.e., dead Li and SEI formation) to reveal the intrinsic causes of individual irr-CE in AFLMBs. Meanwhile, an anode-free protocol can also be utilized as a powerful and multifunctional tool to develop electrolyte formulations or artificial layers for LMBs and AFLMBs. Therefore, we also suggest that the anode-free configurations with significant irreversible phenomena can effectively screen and develop new electrolytes. Finally, the concepts of the protocol with an anode-free cell combined with various advanced analytical tools can be extended to provide an in-depth understanding of other metal batteries and solid-state anode-free metal batteries.

Cryogenic electron microscopy reveals that applied pressure promotes short circuits in Li batteries

Li metal anodes are enticing for batteries due to high theoretical charge storage capacity, but commercialization is plagued by dendritic Li growth and short circuits when cycled at high currents. Applied pressure has been suggested to improve morphology, and therefore performance. We hypothesized that increasing pressure would suppress dendritic growth at high currents. To test this hypothesis, here, we extensively use cryogenic scanning electron microscopy to show that varying the applied pressure from 0.01 to 1 MPa has little impact on Li morphology after one deposition. We show that pressure improves Li density and preserves Li inventory after 50 cycles. However, contrary to our hypothesis, pressure exacerbates dendritic growth through the separator, promoting short circuits. Therefore, we suspect Li inventory is better preserved in cells cycled at high pressure only because the shorts carry a larger portion of the current, with less being carried by electrochemical reactions that slowly consume Li inventory.

Formation sequence of solid electrolyte interphases and impacts on lithium deposition and dissolution on copper: an in situ atomic force microscopic study

Copper is the most widely used substrate for Li deposition and dissolution in lithium metal anodes, which is complicated by the formation of solid electrolyte interphases (SEIs), whose physical and chemical properties can affect Li deposition and dissolution significantly. However, initial Li nucleation and growth on bare Cu creates Li nuclei that only partially cover the Cu surface so that SEI formation could proceed not only on Li nuclei but also on the bare region of the Cu surface with different kinetics, which may affect the follow-up processes distinctively. In this paper, we employ in situ atomic force microscopy (AFM), together with X-ray photoelectron spectroscopy (XPS), to investigate how SEIs formed on a Cu surface, without Li participation, and on the surface of growing Li nuclei, with Li participation, affect the components and structures of the SEIs, and how the formation sequence of the two kinds of SEIs, along with Li deposition, affect subsequent dissolution and re-deposition processes in a pyrrolidinium-based ionic liquid electrolyte containing a small amount of water. Nanoscale in situ AFM observations show that sphere-like Li deposits may have differently conditioned SEI-shells, depending on whether Li nucleation is preceded by the formation of the SEI on Cu. Models of integrated-SEI shells and segmented-SEI shells are proposed to describe SEI shells formed on Li nuclei and SEI shells sequentially formed on Cu and then on Li nuclei, respectively. "Top-dissolution" is observed for both types of shelled Li deposits, but the integrated-SEI shells only show wrinkles, which can be recovered upon Li re-deposition, while the segmented-SEI shells are apparently top-opened due to mechanical stresses introduced at the junctions of the top regions and become "dead" SEIs, which forces subsequent Li nucleation and growth in the interstice of the dead SEIs. Our work provides insights into the impact mechanism of SEIs on the initial stage Li deposition and dissolution on foreign substrates, revealing that SEIs could be more influential on Li dissolution and that the spatial integration of SEI shells on Li deposits is important to improving the reversibility of deposition and dissolution cycling.

Interfacial Engineering Strategy for High-Performance Zn Metal Anodes

Due to their high safety and low cost, rechargeable aqueous Zn-ion batteries (RAZIBs) have been receiving increased attention and are expected to be the next generation of energy storage systems. However, metal Zn anodes exhibit a limited-service life and inferior reversibility owing to the issues of Zn dendrites and side reactions, which severely hinder the further development of RAZIBs. Researchers have attempted to design high-performance Zn anodes by interfacial engineering, including surface modification and the addition of electrolyte additives, to stabilize Zn anodes. The purpose is to achieve uniform Zn nucleation and flat Zn deposition by regulating the deposition behavior of Zn ions, which effectively improves the cycling stability of the Zn anode. This review comprehensively summarizes the reaction mechanisms of interfacial modification for inhibiting the growth of Zn dendrites and the occurrence of side reactions. In addition, the research progress of interfacial engineering strategies for RAZIBs is summarized and classified. Finally, prospects and suggestions are provided for the design of highly reversible Zn anodes.

Nanoscale electrodeposition: Dimension control and 3D conformality

Electrodeposition with a long history has been considered one of the important synthesis techniques for applying various applications. It is a feasible route for fabricating nanostructures using diverse materials due to its simplicity, cost-effectiveness, flexibility, and ease of reaction control. Herein, we mainly focus on the nanoscale electrodeposition with respect to dimension control and three-dimensional (3D) conformality. The principles of electrodeposition, dimensional design of materials, and uniform coatings on various substrates are presented. We introduce that manipulating synthesis parameters such as precursors, applied current/voltage, and additives affect the synthesis reaction, resulting in not only dimensional control of materials from three-dimensional structures to zero-dimensional atomic-level but also conformal coatings on complicated substrates. Various cases regarding morphology control of metal (hydro)oxides, metals, and metal-organic frameworks according to electrodeposition conditions are summarized. Lastly, recent studies of applications such as batteries, photoelectrodes, and electrocatalysts using electrodeposited materials are summarized. This review represents significant advances in the nanoscale design of materials through methodological approaches, which are highly attractive from both academic and commercial aspects.

Designing and Demystifying the Lithium Metal Interface toward Highly Reversible Batteries

Reversible lithium (Li) plating/stripping is essential for building practical high-energy-density batteries based on Li metal chemistry, which unfortunately remains a severe challenge. In this contribution, it is demonstrated that through the rational regulation of strong Li⁺ -anion coordination structures in a highly compatible low-polarity solvent, 2-methyl tetrahydrofuran, the Li plating/stripping assisted by a nucleation modulation procedure delivers a remarkably high average Coulombic efficiency under rather demanding conditions (99.7% and 99.5% under 1.0 mA cm^-2 , 3.0 mAh cm^-2 and 3.0 mA cm^-2 , 3.0 mAh cm^-2 , respectively). The exceedingly reversible cycling obtained herein is fundamentally correlated with the flattened Li deposition and minimized solid electrolyte interphase (SEI) generation/reconstruction in the customized condition, which notably restrains the growth rates of both dead Li⁰ (0.0120 mAh per cycle) and SEI-Li⁺ (0.0191 mAh per cycle) during consecutive cycles. Benefiting from the efficient Li plating/stripping manner, the assembled anode-free Cu|LiFePO₄ (2.7 mAh cm^-2 ) coin and pouch cells exhibit impressive capacity retention of 43.8% and 41.6% after 150 cycles, respectively, albeit with no optimization on the test conditions. This work provides guidelines into the targeted interfacial design of high-efficiency working Li anodes, aiming to pave the way for the practical deployment of high-energy-density Li metal batteries.

Influence of sub-zero temperature on nucleation and growth of copper nanoparticles in electrochemical reactions

Cu metal nanostructures have attracted wide interest of study as catalysts for CO₂ reduction reaction and other applications. Controlling the structure and morphology of Cu nanostructures during synthesis is crucial for achieving desired properties. Here, we studied temperature effects on electrochemical deposition of Cu nanoparticles. We found the size, nucleation density, and crystallinity of Cu nanoparticles are strongly influenced by low temperature processing. The electrodeposition at low temperature (-20°C) results in clusters of assembled small Cu nanoparticles, which is distinctly different from the large individual highly crystalline Cu nanoparticles obtained from the room temperature process. The differences in Cu nanoparticle morphology and crystallinity are attributed to the variations in reduction reaction rate and surface diffusion. The limitation of the reaction rate promotes multiple nuclei, and low surface diffusion induces poor crystallinity. This study deepens our understanding of low-temperature effects on electrochemical processes assisting the design of diverse hierarchical catalytic materials.

Regulating Lithium Plating and Stripping by Using Vertically Aligned Graphene/CNT Channels Decorated with ZnO Particles

Lithium (Li) metal is regarded as the ultimate anode material for use in Li batteries due to its high theoretical capacity (3860 mA h g^-1 ). However, the Li dendrites that are generated during iterative Li plating/stripping cycles cause poor cycling stability and even present safety risks, and thus severely handicap the commercial utility of Li metal anodes. Herein, we describe a graphene and carbon nanotube (CNT)-based Li host material that features vertically aligned channels with attached ZnO particles (designated ZnO@G-CNT-C) and show that the material effectively regulates Li plating and stripping. ZnO@G-CNT-C is prepared from an aqueous suspension of Zn(OAc)₂ , CNTs, and graphene oxide by using ice to template channel growth. ZnO@G-CNT-C was found to be mechanically robust and capable of guiding Li deposition on the inner walls of the channels without the formation of Li dendrites. When used as an electrode, the material exhibits relatively low polarization for Li plating, fast Li-ion diffusion, and high Coulombic efficiency, even over hundreds of Li plating/stripping cycles. Moreover, full cells prepared with ZnO@G-CNT-C as Li host and LiFePO₄ as cathode exhibit outstanding performance in terms of specific capacity (155.9 mA h g^-1 at 0.5 C), rate performance (91.8 mA h g^-1 at 4 C), cycling stability (109.4 mA h g^-1 at 0.5 C after 800 cycles). The methodology described can be readily adapted to enable the use of carbon-based electrodes with well-defined channels in a wide range of contemporary applications that pertain to energy storage and delivery.

Unlocking the Allometric Growth and Dissolution of Zn Anodes at Initial Nucleation and an Early Stage with Atomic Force Microscopy

Zn anodes have gained intensive attention for their environmental-friendliness and high volumetric capacity but are limited by their severe dendrite formation. Understanding the initial nucleation behavior is critical for manipulating the uniform deposition of Zn. Herein, the allometric growth and dissolution of Zn in the initial nucleation and early stages are visualized with in situ atomic force microscopy in aqueous ZnCl2 electrolytes. Zn nuclei grow via a horizontal radial direction and dissolve reversibly in a top-down process. The critical nucleation radius and density are dependent on the electrolyte concentration of ZnCl2, namely, the initial nucleus size is proportional to the ratio of surface free energy between deposited Zn and the electrolyte and overpotentials for Zn electrodeposition, and the density is inversely proportional to the cube of this ratio. This investigation provides guidelines for regulating uniform metal electrodeposition and yields benefits for the development of anode-free batteries.

Manipulating Uniform Nucleation to Achieve Dendrite-Free Zn Anodes for Aqueous Zn-Ion Batteries

The essence of Zn dendrite formation is ultimately derived from Zn nucleation and growth during the repeated Zn plating/stripping process. Here, the nucleation process of Zn has been analyzed using ex situ scanning electron microscopy to explore the formation of the initial Zn dendrite, demonstrating that the formation of tiny protrusions (the initial state of Zn dendrites) is caused by the inhomogeneity of Zn nucleation. Based on this, the uniform Zn nucleation is promoted by the Ni₅Zn₂₁ alloy coating (ZnNi) on the surface of Zn foil by electrodeposition, and the mechanism of ZnNi-promoted even nucleation is further analyzed with the assistance of density functional theory (DFT). The DFT results indicate that the ZnNi displays a stronger binding ability to Zn compared to the bare Zn, suggesting that Zn nuclei will preferentially form around ZnNi instead of continuing to grow on the surface of the initial Zn nuclei. Therefore, the designed Zn metal anode (Zn@ZnNi) can be ultra-stable for over 2200 h at a current density of 2 mA cm^-2 in the symmetric cell. Even at a much higher current density of 20 mA cm^-2, the extra-long life of over 2200 cycles (over 530 h) can be achieved. Moreover, the full cell with the Zn@ZnNi anode exhibits extra-long cycling performance for 500 cycles with a capacity of 207.7 mA h g^-1 and 1100 cycles (148.5 mA h g^-1) at a current density of 0.5 and 1 A g^-1, respectively.

Realizing Spherical Lithium Deposition by In Situ Formation of a Li2S/Li-Sn Alloy Mixed Layer on Carbon Paper for Stable and Safe Li Metal Anodes

Uncontrollable formation of Li dendrites and volume expansion have always been serious obstacles to the practical application of Li metal anodes. Three-dimensional (3D) frameworks are proven to accommodate Li to suppress volume expansion, but the lithiophobic surface tends to cause uncontrollable formation of Li dendrites. Here, uniform SnS₂ nanosheets are coated on the carbon paper (SnS₂@CP) skeleton and then transformed into a mixed layer of Li₂S/Li-Sn after lithiation. Under the joint action of the lithiophilic Li-Sn alloy and low-diffusion energy barrier Li₂S, the dual effects of strong adsorption and rapid diffusion of Li are realized. As a result, Li deposits homogeneously within the whole framework; as the plating amount increases, dendrite-free spherical Li is demonstrated, and the thickness of the electrode stays almost unchanged even at a high areal capacity of 10 mA h cm^-2. The SnS₂@CP electrodes present an ultralow nucleation overpotential (ca. 4 mV), high Coulombic efficiency (above 96.6% for more than 450 cycles), and stable cycle life (>1500 h), indicating that the 3D framework with the Li₂S/Li-Sn alloy mixed coating has excellent lithiophilicity and fast Li transport kinetics, thus effectively inhibiting the formation of Li dendrites. All the findings give new insights into the design strategy for stable and safe Li metal anodes.

Zn Metal Anodes for Zn-Ion Batteries in Mild Aqueous Electrolytes: Challenges and Strategies

Over the past few years, rechargeable aqueous Zn-ion batteries have garnered significant interest as potential alternatives for lithium-ion batteries because of their low cost, high theoretical capacity, low redox potential, and environmentally friendliness. However, several constraints associated with Zn metal anodes, such as the growth of Zn dendrites, occurrence of side reactions, and hydrogen evolution during repeated stripping/plating processes result in poor cycling life and low Coulombic efficiency, which severely impede further advancements in this technology. Despite recent efforts and impressive breakthroughs, the origin of these fundamental obstacles remains unclear and no successful strategy that can address these issues has been developed yet to realize the practical applications of rechargeable aqueous Zn-ion batteries. In this review, we have discussed various issues associated with the use of Zn metal anodes in mildly acidic aqueous electrolytes. Various strategies, including the shielding of the Zn surface, regulating the Zn deposition behavior, creating a uniform electric field, and controlling the surface energy of Zn metal anodes to repress the growth of Zn dendrites and the occurrence of side reactions, proposed to overcome the limitations of Zn metal anodes have also been discussed. Finally, the future perspectives of Zn anodes and possible design strategies for developing highly stable Zn anodes in mildly acidic aqueous environments have been discussed.

Dendrites-Free Zn Metal Anodes Enabled by an Artificial Protective Layer Filled with 2D Anionic Nanosheets

Metallic zinc (Zn) has been considered to be an ideal anode material for aqueous batteries, but is impeded by the growth of Zn dendrites and its side reactions with an aqueous electrolyte. Here, it is reported that an artificial protective layer filled with novel 2D Zn²⁺ adsorbed Sb₃ P₂ O₁₄ ^3- (denoted as Zn-Sb₃ P₂ O₁₄ ) nanosheets provide an effective route to mitigate the above challenging problems. The Zn-Sb₃ P₂ O₁₄ protection layer not only avoids the direct contact with the aqueous electrolyte to suppress the side reactions but also allows for Zn-ions to pass through the protection layer rapidly. Moreover, the 2D Sb₃ P₂ O₁₄ ^3- skeleton with negative charge also confines the 2D diffusion of Zn-ion along the lateral surface of Zn anode, resulting in a uniform electron-deposition. This unique protection layer not only enables dendrite-free Zn plating/stripping with an average Coulombic efficiency of 99.2% for 200 cycles, but also sustains the symmetric Zn||Zn cell over 1300 h at 1 mA cm^-2 and 1 mAh cm^-2 as well as for 450 h at 10 mA cm^-2 and 10 mAh cm^-2 . Such advantages bring high reversibility to full Zn batteries with MnO₂ cathodes, which deliver a discharge capacity of 111.7 mAh g^-1 after 1000 cycles.

Effectively Regulating More Robust Amorphous Li Clusters for Ultrastable Dendrite-Free Cycling

A disordered phase in Li-deposit nanostructure is greatly attractive, but plagued by the uncontrollable and unstable growth, and the nanoscale characterization in the structure. Here, fully characterized in cryogenic transmission electron microscopy (cryo-TEM), more robust amorphous-Li (ALi) clusters are revealed and effectively regulated on heteroatom-activating electronegative sites and an advanced solid electrolyte interphase (SEI) layer. Heteroatom-activating electronegative sites capably enhance the electrostatic interaction of Li+ and heteroatom-doping graphene-like film (HDGs), meaning lower Li diffusion barrier and larger binding energy that is confirmed by small nucleation overpotentials of 13.9 and 10 mV at 0.1 mA cm-2 in the fluoroethylene carbonate-adding ester-based (FEC-ester) and LiNO3 -adding ether-based (LiNO3 -ether) electrolytes. Orderly multilayer SEI structure comprised of inorganic-rich components enables fast ion transports and durable capabilities to construct highly reversible and long-term plating/stripping cycling. ALi cluster anodes exhibit non-crystalline morphologies and perform ultrastable dendrite-free cycling over 2800 times. Stable ALi clusters are also grown in LiFePO4 (LFP) (LFP-ALi-HDGs-N||LiFePO4 [LFP]) full cells with advantageous capacities up to 165.5 and 164.3 mAh g-1 in these optimized electrolytes at 0.1 C; the remarkable capacity retentions maintain to 93% and 91% after 150 cycles at 0.2 C. Structure viability, electrochemical reversibility, and excellent performance in ALi clusters are effectively regulated.

A Dual-Functional Fibrous Skeleton Implanted with Single-Atomic Co-Nx Dispersions for Longevous Li-S Full Batteries

Although lithium-sulfur (Li-S) batteries have long been touted as next-generation energy storage devices, the rampant dendrite growth at the anode side and sluggish redox kinetics at the cathode side drastically impede their practical application. Herein, a dual-functional fibrous skeleton implanted with single-atom Co-N_x dispersion is devised as an advanced modificator to realize concurrent regulation of both electrodes. The rational integration of single-atomic Co-N_x sites could convert the fibrous carbon skeleton from lithiophobic to lithiophilic, helping assuage the dendritic formation for the Li anode. Meanwhile, the favorable electrocatalytic activity from the Co-N_x species affording a lightweight feature effectively enables expedited bidirectional conversion kinetics of sulfur electrochemistry, thereby inhibiting the polysulfide shuttle. Moreover, the interconnected porous framework endows the entire skeleton with good mechanical robustness and fast electron/ion transportation. Benefiting from the synergistic effects between atomically dispersed Co-N_x sites and three-dimensional conductive networks, the integrated Li-S full batteries can achieve a reversible areal capacity (>7.0 mAh cm^-2) at a sulfur loading of 6.9 mg cm^-2. This work might be beneficial to the development of practically viable Li-S batteries harnessing single-atom mediators.

Growth Mechanism of Micro/Nano Metal Dendrites and Cumulative Strategies for Countering Its Impacts in Metal Ion Batteries: A Review

Metal-ion batteries are capable of delivering high energy density with a longer lifespan. However, they are subject to several issues limiting their utilization. One critical impediment is the budding and extension of solid protuberances on the anodic surface, which hinders the cell functionalities. These protuberances expand continuously during the cyclic processes, extending through the separator sheath and leading to electrical shorting. The progression of a protrusion relies on a number of in situ and ex situ factors that can be evaluated theoretically through modeling or via laboratory experimentation. However, it is essential to identify the dynamics and mechanism of protrusion outgrowth. This review article explores recent advances in alleviating metal dendrites in battery systems, specifically alkali metals. In detail, we address the challenges associated with battery breakdown, including the underlying mechanism of dendrite generation and swelling. We discuss the feasible solutions to mitigate the dendrites, as well as their pros and cons, highlighting future research directions. It is of great importance to analyze dendrite suppression within a pragmatic framework with synergy in order to discover a unique solution to ensure the viability of present (Li) and future-generation batteries (Na and K) for commercial use.

The carrier transition from Li atoms to Li vacancies in solid-state lithium alloy anodes

The stable cycling of energy-dense solid-state batteries is highly relied on the kinetically stable solid-state Li alloying reactions. The Li metal precipitation at solid-solid interfaces is the primary cause of interface fluctuations and battery failures, whose formation requires a clear mechanism interpretation, especially on the key kinetic short board. Here, we introduce the lithium alloy anode as a model system to quantify the Li kinetic evolution and transition from the alloying reaction to the metal deposition in solid-state batteries, identifying that there is a carrier transition from Li atoms to Li vacancies during lithiation processes. The rate-determining step is charge transfer or Li atom diffusion at different lithiation stages.

Design and Fabrication of a Sandwichlike Zn/Cu/Al-Zr Coating for Superior Anticorrosive Protection Performance of ZM5 Mg Alloy

A new three-layered film was fabricated on magnesium (Mg) alloy via electroplating to guard against corrosion in a chloride aqueous environment, which consisted of an underlying double-layered zinc/copper (Zn/Cu) and a top aluminum-zirconium (Al-Zr) layer. The Zn/Cu underlayers not only impeded the galvanic corrosion between the Al-Zr coating and Mg alloy but also improved the adhesive ability between the substrate and the upper Al-Zr layer. Herein, we discussed the nucleus sizes of Al-Zr coatings at the stage of nucleation carried out with different contents of ZrCl₄ in AlCl₃-1-butyl-3-methylimidazolium chloride ionic liquid. The sandwichlike three-layered Zn/Cu/Al-Zr coatings were systematically investigated by surface morphology, phase structure, hardness, anticorrosion performances, and first-principles calculations. The corrosion current density declined from 1.461 × 10^-3 A·cm^-2 of bare Mg to 4.140 × 10^-7 A·cm^-2 of the Zn/Cu/Al-Zr3 sample. Neutral salt spray testing demonstrated that the Zn/Cu/Al-Zr3 sample showed no evident signs of corrosion after 6 days of exposure. The enhancement of the corrosion protection property was related to the fact that the application of the Cu layer changed the corrosion direction from initial longitudinal corrosion to extended lateral corrosion and the top Al-Zr coating hindered the transmission of aggressive ions. In addition, upon increasing the Zr content in the alloy films, the Fermi energy reduced initially and then increased. The Al-Zr3 alloy with 8.3 atom % Zr showed the lowest Fermi energy (-3.0823 eV), which exhibited the most efficient corrosion protection. These results showed that the prepared three-layered coating provided reliable corrosion protection to Mg alloy and may thus promote its practical applications.

High Interfacial-Energy and Lithiophilic Janus Interphase Enables Stable Lithium Metal Anodes

The stability of solid electrolyte interphase (SEI) layers is critical for developing lithium (Li) metal batteries. However, the fabrication of stable SEI layers is plagued by un-controlled structures, properties, and functions. Here a controllable design of an ordered LiF-rich and lithiophilic hybrid Janus interphase (LiF-HJI) is reported using organic fluorination reagent as a functional SEI precursor. The LiF-HJI with a lower crystalline LiF layer and an upper Li organosulfide layer provides high interfacial energy with the Li metal and strong Li-ion affinity, allows homogenous Li-ion distribution, fast and uniform Li-ion transport, and excellent mechanical and passivation properties, enabling stable Li metal anodes under harsh conditions, such as high deposition capacities (6 mA h cm^-2 ), current densities (10 mA cm^-2 ), and rates (5 C). Stable LiF-HJI@Li greatly improves cycling stability and capacity retention (80.1% after 300 cycles) of Li||LiNi_0.8 Co_0.1 Mn_0.1 O₂ cells at a commercial-level areal capacity (≈4.2 mA h cm^-2 ). Even under a lean-electrolyte condition of 3 g Ah^-1 , 80% capacity retention can be maintained after 100 cycles, demonstrating excellent cycling performance under such harsh conditions.

Reducing Water Activity by Zeolite Molecular Sieve Membrane for Long-Life Rechargeable Zinc Battery

Aqueous electrolytes offer major advantages in safe battery operation, green economy, and low production cost for advanced battery technology. However, strong water activity in aqueous electrolytes provokes a hydrogen evolution reaction and parasitic passivation on electrodes, leaving poor ion-transport in the electrolyte/electrode interface. Herein, a zeolite molecular sieve-modified (zeolite-modified) aqueous electrolyte is proposed to reduce water activity and its side-reaction. First, Raman spectroscopy reveals a highly aggressive solvation configuration and significantly suppressed water activity toward single water molecule. Then less hydrogen evolution and anti-corrosion ability of zeolite-modified electrolyte by simulation and electrochemical characterizations are identified. Consequently, a zinc (Zn) anode involves less side-reaction, and develops into a compact deposition morphology, as proved by space-resolution characterizations. Moreover, zeolite-modified electrolyte favors cyclic life of symmetric Zn||Zn cells to 4765 h at 0.8 mA cm^-2 , zinc-VO₂ coin cell to 3000 cycles, and pouch cell to 100 cycles. Finally, the mature production technique and low-cost of zeolite molecular sieve would tremendously favor the future scale-up application in engineering aspect.

Covalent Organic Frameworks and Their Derivatives for Better Metal Anodes in Rechargeable Batteries

Metal anodes based on a plating/stripping electrochemistry such as metallic Li, Na, K, Zn, Ca, Mg, Fe, and Al are recognized as promising anode materials for constructing next-generation high-energy-density rechargeable metal batteries owing to their low electrochemical potential, high theoretical specific capacity, superior electronic conductivity, etc. However, inherent issues such as high chemical reactivity, severe growth of dendrites, huge volume changes, and unstable interface largely impede their practical application. Covalent organic frameworks (COFs) and their derivatives as emerging multifunctional materials have already well addressed the inherent issues of metal anodes in the past several years due to their abundant metallophilic functional groups, special inner channels, and controllable structures. COFs and their derivatives can solve the issues of metal anodes by interfacial modification, homogenizing ion flux, acting as nucleation seeds, reducing the corrosion of metal anodes, and so on. Nevertheless, related reviews are still absent. Here we present a detailed review of multifunctional COFs and their derivatives in metal anodes for rechargeable metal batteries. Meanwhile, some outlooks and opinions are put forward. We believe the review can catch the eyes of relevant researchers and supply some inspiration for future research.

Flame-Retardant and Polysulfide-Suppressed Ether-Based Electrolytes for High-Temperature Li-S Batteries

Lithium-sulfur (Li-S) batteries are drawing huge attention as attractive chemical power sources. However, traditional ether-based solvents (DME/DOL) suffer from safety issues at high temperatures and serious parasitic reactions occur between the Li metal anodes and soluble lithium polysulfides (LiPSs). Herein, we propose a polysulfide-suppressed and flame-retardant electrolyte operated at high temperatures by introducing an inert diluent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl (TTE) into the high-concentration electrolyte (HCE). Li dendrites are also efficiently suppressed by the formed LiF-rich protective layer. Furthermore, the shuttle effect is mitigated by the decreased solubility of LiPSs. At 60 °C, Li-S batteries using this nonflammable ether-based electrolyte exhibit a high capacity of 666 mAh g^-1 over 100 cycles at a current rate of 0.2C, showing the greatly improved high-temperature performance compared to batteries with traditional ether-based electrolytes. The improved electrochemical performance across a range of temperatures and the enhanced safety suggest that the electrolyte has a great practical prospect for safe Li-S batteries.

Self-Assembling Films of Covalent Organic Frameworks Enable Long-Term, Efficient Cycling of Zinc-Ion Batteries

Despite their safety, nontoxicity, and cost-effectiveness, zinc aqueous batteries still suffer from limited rechargeability and poor cycle life, largely due to spontaneous surface corrosion and formation of large Zn dendrites by irregular and uneven plating and stripping. In this work, these untoward effects are minimized by covering Zn electrodes with ultrathin layers of covalent organic frameworks, COFs. These nanoporous and mechanically flexible films form by self-assembly-via the straightforward and scalable dip-coating technique-and permit efficient mass and charge transport while suppressing surface corrosion and growth of large Zn dendrites. The batteries demonstrated have excellent capacity retention and stable polarization voltage for over 420 h of cycling at 1 mA cm^-2 . The COF films essential for these improvements can be readily deposited over large areas and curvilinear supports, enabling, for example, foldable wire-type batteries.

Effective Solid Electrolyte Interphase Formation on Lithium Metal Anodes by Mechanochemical Modification

Lithium metal batteries are gaining increasing attention due to their potential for significantly higher theoretical energy density than conventional lithium ion batteries. Here, we present a novel mechanochemical modification method for lithium metal anodes, involving roll-pressing the lithium metal foil in contact with ionic liquid-based solutions, enabling the formation of an artificial solid electrolyte interphase with favorable properties such as an improved lithium ion transport and, most importantly, the suppression of dendrite growth, allowing homogeneous electrodeposition/-dissolution using conventional and highly conductive room temperature alkyl carbonate-based electrolytes. As a result, stable cycling in symmetrical Li∥Li cells is achieved even at a high current density of 10 mA cm^-2. Furthermore, the rate capability and the capacity retention in NMC∥Li cells are significantly improved.

Organic-Inorganic Hybrid SEI Induced by a New Lithium Salt for High-Performance Metallic Lithium Anodes

The practical application of the metallic lithium anode is suppressed by the highly unstable interface between electrolytes and lithium metal during the process of lithium plating/stripping. A perfect solid electrolyte interphase (SEI) can inhibit detrimental parasitic reactions, thereby improving the cycling performance of the metallic lithium anode. In this work, a high-purity solid lithium difluorobis(oxalato) phosphate (LiDFOP) is synthesized and an outstanding organic-inorganic hybrid SEI is obtained in an ether-based electrolyte for the first time induced by LiDFOP. The preferential reduction of LiDFOP can form an SEI rich in LiF and Li_xPO_yF_z species, thereby improving the conductivity and stability of the SEI. In addition, cationic-induced ring-opening polymerization between LiDFOP and 1,3-dioxolane endows the SEI with excellent adaptability to the reiterative volume change of the metallic lithium anode. Therefore, the Li/Cu battery maintains a high coulombic efficiency of 98.37% at a current density of 2 mA/cm² for 200 cycles, and the Li/Li symmetrical battery shows stable voltage hysteresis over 1000 h even under the condition of 5 mA/cm². The Li/S battery fabricated employing the electrolyte with LiDFOP shows significant improvement of cycling performance as well. These results manifest that the formation of an organic-inorganic hybrid SEI from LiDFOP can be employed as a new strategy to overcome the problem from the unstable SEI in metallic lithium batteries.

Understanding and Controlling the Nucleation and Growth of Zn Electrodeposits for Aqueous Zinc-Ion Batteries

Aqueous Zn-ion batteries (AZBs) have been proposed as one of the most promising electrical energy-storage systems due to their low cost, high safety, environmental friendliness, and high energy density. However, their application is impeded by the Zn dendrite growth, which may puncture the separator, causing an internal short circuit. Although numerous efforts have been devoted to alleviating dendrite issues by structural design, surface modification, or electrolyte optimization, there are few works focusing on the fundamental research to understand the formation of Zn dendrites, which is critical to address the dendrites issue. In this work, we have systematically investigated the nucleation and growth behaviors of Zn on a stainless steel substrate. We reveal the dependence of Zn growth morphology on cycling conditions (current density and areal capacity) and further elucidate the intricate correlation with cycle life. It is observed that higher current density corresponds to higher nuclei density with a smaller size of zinc deposits and lower areal capacity render smaller zinc flakes, which contributes to the long cycle life of Zn-ion batteries. Based on these findings, a seeding protocol is then proposed to improve the uniformity and compaction of the Zn electrode. The methodology and findings here can potentially be applied to study the nucleation and growth of other metals.

Confinement of Zinc Salt in Ultrathin Heterogeneous Film to Stabilize Zinc Metal Anode

Aqueous zinc metal batteries (AZMBs) have drawn great attention due to the high theoretical capacity, low redox potential, and abundance reserves. However, the practical application of rechargeable AZMBs are hindered by the poor reversibility of Zn metal anode, owing to easy dendrite growth and serious side reactions. Herein, the preparation of heterogeneous interfacial film with highly dispersed and confined zinc salt in a 2D channel by coassembling polyamide 6, zinc trifluoromethanesulfonate, and layered double hydroxides, which significantly suppresses the dendrite formation, H₂ evolution reaction as well as O₂ corrosion is reported. The as-developed Zn anodes exhibit a long cycling life up to 1450 h with low reversible deposition potential. Moreover, the assembled Zn||Mn battery delivers a high initial capacity of 321 mAh g^-1 and a low capacity decay of ≈0.05% per cycle after 590 cycles, which is promising for high-performance AZMBs. A fluorescent film to realize the in situ observation of the Zn anode during cycling, which provides a new chance for visual observation of the working state of the Zn interface, is also assembled.

Fast Li Plating Behavior Probed by X-ray Computed Tomography

Uneven lithium plating/stripping is an essential issue that inhibits stable cycling of a lithium metal anode and thus hinders its practical applications. The investigation of this process is challenging because it is difficult to observe lithium in an operating device. Here, we demonstrate that the microscopic lithium plating behavior can be observed in situ in a close-to-practical cell setup using X-ray computed tomography. The results reveal the formation of porous structure and its progressive evolution in space over the charging process with a large current. The elaborated analysis indicates that the microstructure of deposited lithium makes a significant impact on the subsequent lithium plating, and the impact of structural inhomogeneity, further exaggerated by the large-current charging, can lead to severely uneven lithium plating and eventually cell failure. Therefore, a codesign strategy involving delicate controls of microstructure and electrochemical conditions could be a necessity for the next-generation battery with lithium metal anode.

Lithium-Rich Anti-perovskite Li2OHBr-Based Polymer Electrolytes Enabling an Improved Interfacial Stability with a Three-Dimensional-Structured Lithium Metal Anode in All-Solid-State Batteries

All-solid-state lithium-metal batteries, with their high energy density and high-level safety, are promising next-generation energy storage devices. Their current performance is however compromised by lithium dendrite formation. Although using 3D-structured metal-based electrode materials as hosts to store lithium metal has the potential to suppress the lithium dendrite growth by providing a high surface area with lithiophilic sites, their rigid and ragged interface with solid-state electrolytes is detrimental to the battery performance. Herein, we show that Li₂OHBr-containing poly(ethylene oxide) (PEO) polymer electrolytes can be used as a flexible solid-state electrolyte to mitigate the interfacial issues of 3D-structured metal-based electrodes and suppress the lithium dendrite formation. The presence of Li₂OHBr in a PEO matrix can simultaneously improve the mechanical strength and lithium ion conductivity of the polymer electrolyte. It is confirmed that Li₂OHBr does not only induce the PEO transformation of a crystalline phase to an amorphous phase but also serves as an anti-perovskite superionic conductor providing additional lithium ion transport pathways and hence improves the lithium ion conductivity. The good interfacial contact and high lithium ion conductivity provide sufficient lithium deposition sites and uniform lithium ion flux to regulate the lithium deposition without the formation of lithium dendrites. Consequently, the Li₂OHBr-containing PEO polymer electrolyte in a lithium-metal battery with a 3D-structured lithium/copper mesh composite anode is able to improve the cycle stability and rate performance. The results of this study provide the experimental proof of the beneficial effects of the Li₂OHBr-containing PEO polymer electrolyte on the 3D-structured lithium metal anode.

Sustainable and Robust Graphene Cellulose Paper Decorated with Lithiophilic Au Nanoparticles to Enable Dendrite-free and High-Power Lithium Metal Anode

Lithium metal anodes (LMAs) with high energy density have recently captured increasing attention for development of next-generation batteries. However, practical viability of LMAs is hindered by the uncontrolled Li dendrite growth and infinite dimension change. Even though constructing 3D conductive skeleton has been regarded as a reliable strategy to prepare stable and low volume stress LMAs, engineering the renewable and lithiophilic conductive scaffold is still a challenge. Herein, a robust conductive scaffold derived from renewable cellulose paper, which is coated with reduced graphene oxide and decorated with lithiophilic Au nanoparticles, is engineered for LMAs. The graphene cellulose fibres with high surface area can reduce the local current density, while the well-dispersed Au nanoparticles can serve as lithiophilic nanoseeds to lower the nucleation overpotential of Li plating. The coupled relationship can guarantee uniform Li nucleation and unique spherical Li growth into 3D carbon matrix. Moreover, the natural cellulose paper possesses outstanding mechanical strength to tolerate the volume stress. In virtue of the modulated deposition behaviour and near-zero volume change, the hybrid LMAs can achieve reversible Li plating/stripping even at an ultrahigh current density of 10 mA cm^-2 as evidenced by high Coulombic efficiency (97.2 % after 60 cycles) and ultralong lifespan (1000 cycles) together with ultralow overpotential (25 mV). Therefore, this strategy sheds light on a scalable approach to multiscale design versatile Li host, promising highly stable Li metal batteries to be feasible and practical.

Hydrometallurgical enhanced liberation and recovery of anode material from spent lithium-ion batteries

The efficient recycling of spent anode material (SAM) from spent lithium-ion batteries (LIBs) is generally critical in terms of electronic waste recyclingas well as increasing resource shortage and environmental problems. This research reported a novel and green method to recycle lithium, copper foil, and graphite from SAM by water leaching treatment. The results indicated that 100% of graphite was exfoliated from the anode material and 92.82% leaching efficiency of lithium was obtained under the optimal conditions of 80 °C, 60 g/L, 300 rpm, and 60 min, respectively. This finding revealed that the SAM got a full liberation characteristic due to the removal of binder, which produced an ideal leaching lithium efficiency rivaling the acids' performance. The mechanism of the liberation of SAM and lithium leaching is presented based on the analysis of results. The graphite was purified and recovered after water leaching treatment. Besides, lithium was recovered in the form of lithium carbonate (Li₂CO₃)_, and the copper foil was recovered in a sheet. This study endeavors to develop an economical and environmentally feasible plan to recycle graphite, copper, and lithium from SAM.

Effect of Electrolyte Additives on the Cycling Performance of Li Metal and the Kinetic Mechanism Analysis

Lithium metal secondary batteries (LMBs) have extremely high energy densities and are considered the most promising energy storage and conversion systems in the future. We start with the formation and growth process of the Li metal deposited layer to reveal and clarify the reasons for the apparent comprehensive performance of the Li metal anode. Specifically, under the conditions of ether electrolyte and typical additives, the apparent Coulombic efficiency, micromorphology of the deposition layer, SEI information, and the kinetic mechanism of the Li plating/stripping process under a series of current density conditions are studied. The results show that in the electrolyte containing LiNO₃, Li metal exhibits excellent cycling performance, the Li plating layer is denser, and the particles in the plating layer are smooth and uniform. In the electrolyte containing FEC, the performance of Li metal is also improved to some extent. Then, we use microelectrode technology to obtain the kinetic parameters of elementary steps in the deposition process of Li metal and find that the stability of the kinetic parameters of mass transfer, interface, and surface steps and their good matching degree are conducive to the good cycling stability of the Li metal anode. This study reveals the kinetic relationship among the apparent comprehensive performances of Li metal, the electrolyte composition, and operating conditions, which provides a reliable dynamic reference for screening and optimizing electrolytes.

Polymorph Evolution Mechanisms and Regulation Strategies of Lithium Metal Anode under Multiphysical Fields

Lithium (Li) metal, a typical alkaline metal, has been hailed as the "holy grail" anode material for next generation batteries owing to its high theoretical capacity and low redox reaction potential. However, the uncontrolled Li plating/stripping issue of Li metal anodes, associated with polymorphous Li formation, "dead Li" accumulation, poor Coulombic efficiency, inferior cyclic stability, and hazardous safety risks (such as explosion), remains as one major roadblock for their practical applications. In principle, polymorphous Li deposits on Li metal anodes includes smooth Li (film-like Li) and a group of irregularly patterned Li (e.g., whisker-like Li (Li whiskers), moss-like Li (Li mosses), tree-like Li (Li dendrites), and their combinations). The nucleation and growth of these Li polymorphs are dominantly dependent on multiphysical fields, involving the ionic concentration field, electric field, stress field, and temperature field, etc. This review provides a clear picture and in-depth discussion on the classification and initiation/growth mechanisms of polymorphous Li from the new perspective of multiphysical fields, particularly for irregular Li patterns. Specifically, we discuss the impact of multiphysical fields' distribution and intensity on Li plating behavior as well as their connection with the electrochemical and metallurgical properties of Li metal and some other factors (e.g., electrolyte composition, solid electrolyte interphase (SEI) layer, and initial nuclei states). Accordingly, the studies on the progress for delaying/suppressing/redirecting irregular Li evolution to enhance the stability and safety performance of Li metal batteries are reviewed, which are also categorized based on the multiphysical fields. Finally, an overview of the existing challenges and the future development directions of metal anodes are summarized and prospected.

Observation of lithium stripping in super-concentrated electrolyte at potentials lower than regular Li stripping

Lithium plating/stripping was investigated under constant current mode using a copper powder electrode in a super-concentrated electrolyte of lithium bis(fluorosulfonyl)amide (LiFSA) with methylphenylamino-di(trifluoroethyl) phosphate (PNMePh) and vinylene carbonate (VC) as additives. Typical Li plating/stripping for Cu electrodes in organic electrolytes of conventional lithium batteries proceeds at potentials of several millivolts versus a Li counter electrode. In contrast, a large overpotential of hundreds of millivolts was observed for Li plating/stripping with the super-concentrated electrolyte. When Li stripping started immediately after Li plating and with no rest time between plating and stripping, two potential plateaus, i.e., two-step Li stripping, was observed. The potential plateau for the 1st stripping step appeared at -0.2 V versus a Li metal counter electrode. The electrical capacity for the 1st stripping step was 0.04 mA h cm-2, which indicates irregular Li stripping. Two-step Li stripping was also recorded using cyclic voltammetry. The electrochemical impedance spectroscopy (EIS) studies indicated that the two-step Li stripping behaviour reflected two different solid electrolyte interphases (SEIs) on electrodeposited Li in a Cu electrode. The SEI for the 1st-step stripping was in a transition period of the SEI formation. The open circuit voltage (OCV) relaxation with an order of tens of hours was detected after Li plating and before Li stripping. The in operando EIS study suggested a decrease of the charge transfer resistance in the Cu powder electrode during the OCV relaxation. Since the capacitance for the voltage relaxation was a dozen microfarads, it had a slight contribution to the 1st-step Li stripping behaviour. The voltage relaxation indicated the possibility that it is difficult for Li ions to be electrodeposited or that the Li plating is in a quasi-stable state.

A Dendrite-Free Tin Anode for High-Energy Aqueous Redox Flow Batteries

Metal-based aqueous redox flow batteries (ARFBs) such as zinc-based ARFBs have attracted remarkable attention owing to their intrinsic high energy density. However, severe dendrite issues limit their efficiency and lifespan. Here an aqueous metal anode operating between Sn(OH)₆ ^2- (stannate) and metal Sn is presented, providing a reversible four-electron transfer at -0.921 V vs standard hydrogen electrode. In strong contrast to severe Zn dendrites, the Sn(OH)₆ ^2- /Sn electrode shows smooth and dendrite-free morphology, which can be attributed to its intrinsic low-surface-energy anisotropy which facilitates isotropic crystal growth of Sn metal. By coupling with iodide/tri-iodide (I^- /I₃ ^- ), the static Sn-I cell demonstrates a stable cycling for 500 cycles (more than 2 months). In contrast, the state-of-the-art Zn anode suffers from serious dendrites and lasts less than 45 cycles (190 h) in Zn-I cells. A stable continuous flow cycling of Sn-I cell achieves a Sn areal capacity of 73.07 mAh cm^-2 at an average discharge voltage of 1.3 V for 350 h. The alkaline Sn electrode demonstrates dendrite-free morphology and superior performance in cycle life and areal capacity compared to state-of-the-art Zn metal anodes, offering a promising metal anode for high-energy ARFBs and other metal-based rechargeable aqueous batteries.