Suppress Dendrite Growth Research Articles

Working Principles of Lithium Metal Anode in Pouch Cells

AbstractLithium metal battery has been considered as one of the potential candidates for next‐generation energy storage systems. However, the dendrite growth issue in Li anodes results in low practical energy density, short lifespan, and poor safety performance. The strategies in suppressing Li dendrite growth are mostly conducted in materials‐level coin cells, while their validity in device‐level pouch cells is still under debate. It is imperative to address dendrite issues in pouch cells to realize the practical application of Li metal batteries. This review presents a comprehensive overview of the failure mechanism and regulation strategies of Li metal anodes in practical pouch cells. First, the gaps between the scientific findings in materials‐level coin cells and device‐level pouch cells are underscored. Specific attention is paid to the mechanistic understanding and quantitative discussion on the failure mechanisms of pouch‐type Li metal batteries. Subsequently, recently proposed strategies are reviewed to suppress dendrite growth in pouch cells. The state‐of‐the‐art electrochemical performance of pouch cells, especially the cell‐level energy density and lifespan, is critically concerned. The review concludes with an attempt to summarize the scientific and engineering understandings of pouch‐type Li metal anodes and propose some novel insights for the practical applications of Li metal batteries.

Electrochemical Characterization of a Drawn Thin-Film Glassy Mixed Oxy-Sulfide-Nitride Phosphate Electrolyte for Applications in Solid-State Batteries

Thin-film glassy solid-state electrolytes (GSEs) are being considered for applications in energy storage devices; fully-dense thin-film glassy electrolyte materials are able to minimize power loss while suppressing dendrite growth. The glass with the composition Na4P2S5.8O0.92N0.18 (NaPSON) was chosen because it balances the high conductivity of a sulfide chemistry with the high processability and electrochemical stability of an oxy-nitride chemistry. NaPSON thin-film GSE ribbons with thicknesses that range from 50 to 150 μm were drawn using a process of softening and drawing of a cast and annealed preform. Electrochemical impedance spectroscopy (EIS) was used on varying thicknesses of thin-film to investigate and compare the ionic conductivity of Na+ in the thin film compared to the bulk sample. Area specific resistance models as a function of time were created to compare the trend of bulk and interfacial resistances of different thicknesses. Thin-film samples were made into symmetric cells and cycled. The cycling of the symmetric cells gave insight into the behavior and durability of the electrolyte under applied voltage and sustained current. These results show that drawn thin-film electrolytes are a viable research direction for all solid-state batteries.

Electrochemical Characterization of a Drawn Thin-Film Glassy Mixed Oxy-Sulfide-Nitride Phosphate Electrolyte Material for Applications in Solid-State Batteries

Thin-film glassy solid-state electrolytes are often considered for applications in energy storage devices; fully-dense thin-film glassy electrolyte materials are able to minimize power loss while suppressing dendrite growth. The glass with the composition Na4P2S5.8O0.92N0.18 (NaPSON) was chosen because it balances the high conductivity of a sulfide chemistry with the high processability and electrochemical stability of an oxy-nitride chemistry. NaPSON thin-film glassy solid-state electrolyte ribbons with thicknesses that range from 75 to 600 μm were drawn using a process of softening and drawing of a cast and annealed preform. Raman spectroscopy was run on the thin-film samples to ensure the material was structurally similar after processing across different thicknesses and remelts. Electrochemical impedance spectroscopy (EIS) was used on varying thicknesses of thin-film to investigate and compare the ionic conductivity of Na+ in the thin film compared to the bulk sample. Area specific resistance models as a function of time were created to compare the trend of bulk and interfacial resistances of different thicknesses. Thin-film samples were made into symmetric cells and cycled. The cycling of the symmetric cells gave insight into the behavior and durability of the electrolyte under applied voltage and sustained current. These results show that drawn thin-film electrolytes are a solid research direction.

Electrochemical-Piezoelectric Mechanism for Dendrite Growth

On immersing two lithium metal electrodes in a solution containing lithium salt and applying a voltage, lithium metal will deposit on the electrode connected to the lower voltage. This process is known as electrodeposition. It has been widely observed that under moderate currents, lithium ions do not deposit to a flat surface but rather spontaneously form sharp needle shapes known as dendrites. Dendrite formation is a major barrier for realizing the lithium metal battery, which not only causes capacity loss but also leads to internal short circuit and safety hazard [1].We report a discovery that the use of a soft piezoelectric film as separator can effectively suppress the formation of lithium dendrite and stabilize the lithium surface during electrodeposition system [2, 3]. When the film is deformed by any local protrusion because of surface instability of the deposited lithium, a local piezoelectric overpotential is generated to suppress lithium deposition on the protrusion. We have established a theory that integrates electrochemistry, piezoelectricity and mechanics. We developed multiphysics computations to simulate dendrite growth in contact with a piezoelectric film. We find that the dendrite-suppression capability is over 6 orders stronger than the limit of mechanical blocking by any separators or solid-state electrolytes. Simulations show that the mechanism ensures deposition to form a flat surface even if the initial substrate surface has significant protrusions, suggesting its robustness and effectiveness against manufacturing defects. We show that the mechanism is so strong that even a weak piezoelectric material is highly effective, opening up a wide range of materials. REFERENCES Liu, G. and Lu, W. A model of concurrent lithium dendrite growth, SEI growth, SEI penetration and regrowth. Electrochem. Soc.(2017) 164: A1826.Liu, G., Wang, D., Zhang, J., Kim, A. and Lu, W. Preventing dendrite growth by a soft piezoelectric material. ACS Mater. Lett.(2019) 1: 498-505.Gao, T., Rainey, C. and Lu, W. Piezoelectric mechanism and a compliant film to effectively suppress dendrite growth. ACS Appl. Mater. Interfaces. (2020) 12: 51448–51458.

A Multiphysics Understanding of Lithium Dendrite Growth Mechanism and Mitigation Strategy in All-Solid-State Batteries

With the merits of high energy density from lithium metal electrode and safety performance improved by inorganic electrolyte, all-solid-state batteries (ASSBs) are considered promising candidates for future lithium-ion batteries. However, dendrite growth induced battery short-circuit (SC) failure are the obstacles on the commercialization road of ASSBs. To unravel the dendrite growth mechanism, the electrochemical-mechanical coupled multiphysics model is developed from the cell level, based on which the dendrite mitigation strategy is further proposed by adding heterogeneous blocks (HBs) into solid electrolytes (SEs). It’s discovered that the electrochemical overpotential induced mechanical stress is capable of driving the crack propagation, which provides space for the dendrite growth to penetrate through the solid electrolyte, eventually causing the SC. Larger charging rate and smaller electrolyte conductivity results in earlier SC. Higher fracture toughness increases the cracking energy to suppress dendrite growth, while Young’s modulus affects both the driving force and resisting force for crack propagation. By adopting HBs in SEs, the dendrite growth behavior can be modulated. We discover that the length ratio between HB and SE dominates the dendrite mitigation effect. Single HB in large ratio, and multiple HBs in medium ratio with specific arrangement, are capable of completely suppressing dendrite growth-induced SC risk. Furthermore, multilayer SE in more layers and smaller Young’s modulus shows promising dendrite mitigation effect by delaying SC time. Results give out a comprehensive understanding of dendrite growth mechanism as well as an effective strategy to mitigate dendrite, providing guidance on the design of more robust and practical ASSBs with dendrite-suppression electrolyte.

Deformation-tolerant metal anodes for flexible sodium–air fiber batteries

Although flexible sodium–air (Na–air) batteries with high theoretical energy density offer promising opportunities for next-generation smart electronics, enhancing the safety and efficiency of flexible sodium metal anodes under dynamic and continuous deformation remains a challenge. Here, a flexible sodiated carbon nanotube layer to suppress dendrite growth under various deformations is demonstrated through a Fermi level-driven spontaneous synthetic process. The resulting sodiated carbon nanotube layer, which has a spontaneously formed solid–electrolyte interface and a robust interlocked structure, creates a uniformly distributed electric field and stable interface even under deformation, affording dendrite-free flexible Na metal anodes. With this deformation-tolerant Na metal anode, we have constructed a new family of highly flexible Na–air fiber batteries with excellent cycling performance for 400 cycles at a current density of 1000 ​mA·g−1 and a capacity limit of 500 mAh·g−1 under dynamic deformation. These Na–air fiber batteries can be further woven into self-powering systems to support flexible electronic devices.

Modulation of hydrogel electrolyte enabling stable zinc metal anode

The uneven flux and strong solvation of Zn2+ ions in aqueous electrolytes bring undesirable dendritic deposition and side reactions to zinc metal anodes (ZMAs). Hydrogel electrolytes have considerable mechanical strength and limited water content, which can suppress dendrite growth and alleviate side reactions. Nevertheless, the design of hydrogel electrolytes with desired electrochemical and mechanical properties is still challenged due to the lack of understanding of how structural features affect performances. Herein, we systematically investigate the hydrogel electrolytes for ZMAs by regulating their crosslinking and grafting structures. Experiments and theoretical simulations emphasize the importance of the network structure and the polymetric anions bonded on the hydrogel. The PSX gel crosslinked by carboxyl-grafted polyvinyl alcohol and xanthan gum shows superior performance, contributed by its abundant -COO− groups and stable three-dimensional structure. The PSX electrolyte shows high ionic conductivity (18.86 mS cm−1) and a considerable Zn2+ transference number (0.8). Zn//Zn cells with PSX electrolytes deliver long cycle lives accompanied by uniform zinc deposition, few by-products, and suppressed hydrogen evolution. When paired with V2O5 or active carbon cathodes, the PSX electrolyte also shows good compatibility and excellent performance. Flexible pouch cells are further demonstrated to work normally under different deformation and stress conditions.

Moisture-assistant chlorinated separator with dual-protective interface for ultralong-life and high-rate lithium metal batteries

Metallic lithium (Li) is among the most promising anodes due to their high theoretical capacity (3860 mAh g–1) and the lowest redox potentials (−3.04 V vs standard hydrogen electrode). However, the application of lithium metal batteries (LMBs) has encountered by the uncontrollable growth of Li dendrite and unstable solid electrolyte interface (SEI). Therefore, regulating a compositionally favorable and Li+-permeable SEI is crucial for the development of long-life LMBs. Previous studies have revealed the moisture as a detrimental inducement to cell degradation. Beyond current understanding, inorganic LiCl with adsorption of moisture is first applied to protect Li anode, where the hydrated and chlorinated separator has introduced LiF/artificial SEI dual-layer simultaneously with much improved cycle stability and interface compatibility over the non-hydrated counterparts. Meanwhile, the modified separator (with hydrated LiCl/poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) layer) has synergistically achieved the suppression of dendrite growth and interface distortion, restraining the decay of Li deposition/stripping for better cycle stability. Accordingly, the lifespan of modified Li|Li cell is extended to over 2700 h with improved rate capability, reduced overpotentials and high Coulombic efficiency (CE) of 99.5 %. Further, the moisture-assistant chlorinated separator is applied in energy-dense LMBs system, which allows for a stable and shuttle-free Li–S batteries with high sulfur utilization and chemically accelerated conversion kinetics. As a result, the dual-shield protected separator configuration synergistically fulfills high sulfur capacity of 1293.6 mAh g–1 at 0.1 C (1C = 1675 mA g−1), long-term Li–S cycle stability at 1 C and high-rate capability (582.2 mAh g–1 at 5 C). This contribution provides insights of implementing moisture-assistant chlorinated separator for Li anode protection and high-performance Li–S batteries.

Highly aligned lithiophilic electrospun nanofiber membrane for the multiscale suppression of Li dendrite growth

Using inorganic fibrous membranes as protective layers has yielded success in suppressing dendrite growth. However, conventional fibrous membranes usually have large voids and low affinity for Li, promoting inhomogeneous charge distribution and allowing some dendrites to grow. Herein, we introduce a highly aligned TiO2/SiO2 (A-TS) electrospun nanofiber membrane as a protective layer for the Li metal anode. The A-TS membrane is fabricated by a custom-made electrospinning system with an automatic fiber alignment collector that allows control of the fibers’ orientation. At the scale of the individual fibers, their high binding energies with Li can attract more “dead” Li by reacting with the SiO2 component of the composite, avoiding uncontrollable deposition on the metal anode. At the membrane scale, these highly ordered structures achieve homogeneous contact and charge distribution on the Li metal surface, leaving no vulnerable areas to nucleate dendrite formation. Additionally, the excellent mechanical and thermal stability properties of the A-TS membrane prevent any potential puncturing by dendrites or thermal runaway in a battery. Hence, an A-TS@Li anode exhibits stable cycling performance when used in both Li–S and Li–NCM811 batteries, highlighting significant reference values for the future design and development of high-energy-density metal-based battery systems.

An Ultra-Thin Crosslinked Carbonate Ester Electrolyte for 24 V Bipolar Lithium-Metal Batteries

Fabrication of an ultrathin solid electrolyte with high conductance is essential to achieve high energy density of solid-state batteries. As solid polymer electrolytes (SPEs) are characterized by good ductility, ease of manufacturing, and low cost, the current solvent-based casting pathway suffers from the difficulty in controlling the thickness. In addition, the low ionic conductivity and narrow electrochemical window of the polyether-type SPEs further hinder their practical applications. We fabricate an ultra-thin solid-polymer electrolyte by in situ polymerization of carbonate ester vinyl ethylene carbonate and poly(ethylene glycol) diacrylate using a porous polypropylene membrane as a support. The obtained solid electrolyte is of only 8 μm and possesses an unprecedented ionic conductance of 83.3 mS at room temperature. Furthermore, the electrolyte is compatible with Li metal and can suppress dendrite growth. An all-solid-state lithium battery based on LiFePO4 cathode can operate stably for over 150 cycles with 86% capacity retention. The non-fluidic nature of the electrolyte further enables the fabrication of an energy-dense 24 V bipolar pouch cell which demonstrates extreme flexibility and safety. No voltage drop is observed upon folding and cutting. This in situ polymerized ultra-thin electrolyte provides a promising platform for the fabrication of high-energy solid-state batteries and also a potential candidate for flexible batteries.

PBC@cellulose-filter paper separator design with efficient ion transport properties toward stabilized zinc-ion battery

The uneven pore structure and sluggish transport kinetics of the separator will accelerate the growth of dendrites and directly deteriorate the performance of zinc metal battery. Herein, we present a simple and unique interface engineering strategy to anchor persimmon branch carbon (PBC) material onto a cellulose-filter (CF) paper separator to address these issues. The novel PBC material demonstrates a hierarchical pore structure, uniform distribution of carbon dots, and rich N, and O functional groups, and an efficient ion transport modulator PBC@CF separator is designed to serve the dual function of promoting ions transfer and suppressing dendrite growth. Owing to the anchoring of PBC on CF and uniform filling of the surface interspace, the PBC modified separator not only greatly facilitates Zn2+ transport between the fiber-electrolyte interface, but also evenly redistributes the ion transport on the anode interface. As a result, highly reversible Zn plating/stripping is achieved in the symmetric Zn-Zn cell with the PBC@CF separator. Meanwhile, the modified Zn-LiFePO4 dual ion full battery can retain a specific capacity of 109.4 mAh g−1 after 200 cycles at 1 C with an excellent capacity retention of 86 %. The unique PBC material and facile separator engineering provide a new perspective to designing advanced separators for high-performance aqueous Zn dual ion full battery.

The Importance of Solid Electrolyte Interphase Formation on Metal Anodes for Next Generation Batteries

Alkali and alkaline earth metal anodes are gaining increasing research attention because they could provide high energy densities and theoretical specific capacities. Among them, lithium metal is the most investigated anode candidate for next generation batteries. However, due to some challenges, the commercialization of lithium metal anodes is still delayed. Reactions between lithium metal and the electrolyte lead to the formation of an inhomogeneous solid electrolyte interphase (SEI). Consequently, electrodissolution/-deposition of lithium is favored where the SEI is less resistive or cracked, resulting in high surface area lithium and dendrite growth. This does not only lower the coulombic efficiency (CE) and cell specific capacity but also causes safety issues due to an increased risk of short-circuits and thermal runaway.1,2 To enable increased safety in high energy batteries with lithium metal anodes an effective SEI is required to limit lithium dendrite growth. There is a variety of approaches to grow an effective SEI, such as the use of electrolyte additives, mechanical methods and chemical modification.3-5 Recently, alkaline earth metal anodes, such as magnesium or calcium, are also of considerable interest for next generation anodes. Their main advantage is the significantly lower susceptibility to dendrite formation, while still offering high theoretical specific capacities. However, their oxide passivation layer does not allow significant mobility for their divalent ions, leading to large overvoltage and slow reaction kinetics which hinders the cycling. Therefore, electrolytes which enable a non-passivating SEI have to be applied and additives are investigated on their ability to remove the oxide layers.6,7 Herein, we present a novel mechanochemical approach to form an effective SEI on the lithium metal surface by combining mechanical and chemical modification utilizing ionic liquids (ILs) prior to cell assembly. This method suppresses dendrite growth even at high current densities of 10 mA cm-2 in lithium metal batteries with liquid electrolytes. To further highlight the importance of surface treatment and SEI formation, we investigate electrolytes for calcium metal batteries as well as mechanical modification of calcium metal anodes. Acknowledgements: The authors would like to acknowledge financial support from the European Union through the Horizon 2020 framework program for research and innovation within the project “VIDICAT” (829145).

(Digital Presentation) H-BN Enhanced Gel Polymer Electrolyte for Solid State Li-Ion Batteries

In order to address safety concerns of conventional carbonate liquid electrolytes, porous gel polymer electrolytes (GPE) can effectively encapsulate the solution while providing good electrolyte-electrode contact. In this work, a GPE is incorporated with exfoliated 2D hexagonal boron nitride nanosheets (BNNS) as an effective and safe polymer electrolyte for Li-ion batteries. With a facile Dr. Blade approach combined with phase inversion, a high porosity and electrolyte uptake can be maintained while still acting as a stable film. Utilising a 15 wt.% binary polymer mixture of polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) doped with exfoliated BN flakes, the final GPE is not only more thermal stable but able to effectively suppress dendrite growth through multiple cycles with a high ionic conductivity of 3.03 x10-3 S/cm at ambient conditions. Cell performance with this GPE includes strong cycling performance while sustaining a high coulombic efficiency. Figure 1

Differentiating the dominant intrinsic kinetics for lithium dendrite growth under different circumstances by computational study

Although many works have been devoted to designing the dendrite-suppression lithium anodes through modifying the growth environments or electrode configurations, studies on their related intrinsic kinetics processes are still lacking. Using DFT calculations, the intrinsic kinetics processes to control the dendrite growth in different environments are investigated herein. Under different coverage concentrations and distributions of lithium, three types of competitive kinetics processes have been identified and defined as the two-dimensional (2D) accumulation, 2D dispersion, and 3D accumulation kinetics processes based on the near-neighboring interactions in the same layer. It was found that the dendrite-free condition can be realized under the natural growth processes based on the dominant 2D accumulation processes, but the dominant kinetics processes can be replaced by the 3D accumulation processes during the nonuniform deposition processes under the condition of moderate coverage concentration, leading to the formation of dendrites. Correspondingly, the suppression condition for the dendrite growth requires that the 2D dispersion kinetics processes can triumph over the 3D accumulation kinetics processes. Therefore, we employed the lithium-affinity molecules to illustrate how to adjust the 2D dispersion kinetics processes to suppress dendrite growth. These results provide microscopic guidance suppressing dendrite growth.

Dynamic Ionic Transport Actuated by Nanospinbar‐Dispersed Colloidal Electrolytes Toward Dendrite‐Free Electrodeposition

AbstractInhibiting uneven dendritic Li electroplating is crucial for the safe and stable cycling of Li metal batteries (LMBs). Homogeneous and fast Li+ transport towards the Li surface is required for uniform and dendrite‐free deposition. However, the traditional ionic transport of static liquid electrolytes involving electromigration and molecular diffusion can trigger a greater disparity in the Li concentration over the Li surface, leading to irregular dendrite growth. Here, a convective Li+ transfer for suppressing dendrite growth through magnetic nanospinbar (NSB)‐dispersed colloidal electrolytes is presented. An ultrahigh‐aspect‐ratio NSB consisting of a paramagnetic Fe3O4 nanoparticle array and silica outer coating is synthesized. Manipulating the external electromagnetic force can remotely control the rotation of individual NSBs without dispersion failure, thereby generating mesoscale turbulence inside the cells. Regardless of the electrolyte composition, rotating the NSB can reduce the Li+ diffusion layer thickness from the bulk and evenly redistribute the Li+ flux over the Li surface, thereby suppressing Li dendrite growth. The NSB‐dispersed electrolyte with advanced salt/solvent compositions demonstrates stable cycling of LMBs over 600 cycles with 70% capacity retention, thereby outperforming the NSB‐free cell.

Dendrite‐accelerated thermal runaway mechanisms of lithium metal pouch batteries

AbstractHigh‐energy‐density lithium metal batteries (LMBs) are widely accepted as promising next‐generation energy storage systems. However, the safety features of practical LMBs are rarely explored quantitatively. Herein, the thermal runaway behaviors of a 3.26 Ah (343 Wh kg−1) Li | LiNi0.5Co0.2Mn0.3O2 pouch cell in the whole life cycle are quantitatively investigated by extended volume‐accelerating rate calorimetry and differential scanning calorimetry. By thermal failure analyses on pristine cell with fresh Li metal, activated cell with once plated dendrites, and 20‐cycled cell with large quantities of dendrites and dead Li, dendrite‐accelerated thermal runaway mechanisms including reaction sequence and heat release contribution are reached. Suppressing dendrite growth and reducing the reactivity between Li metal anode and electrolyte at high temperature are effective strategies to enhance the safety performance of LMBs. These findings can largely enhance the understanding on the thermal runaway behaviors of Li metal pouch cells in practical working conditions.

Interfacial Engineering of Binder-Free Janus Separator with Ultra-Thin Multifunctional Layer for Simultaneous Enhancement of Both Metallic Li Anode and Sulfur Cathode.

Exploring a scalable strategy to fabricate a multifunctional separator is of great significance to overcome the challenges of lithium polysulfides (LiPSs) and dendritic growth in lithium-sulfur batteries (LSBs). Herein, a binder-free Janus separator is constructed by interfacial engineering. At the cathode interface, an ultra-thin covalent triazine piperazine film containing tailorable micropores and adsorption sites is decorated on polyacrylonitrile (PAN) membrane by in situ interfacial polymerization, building a triple barrier for LiPSs. The combination of steric hindrance and chemical adsorption reduces LiPS's migration by 81.85%. Meanwhile, at the anode interface, a fast-ionic conductor Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) is created on the surface of PANnanofiber by magnetron sputtering to suppress dendrite growth. Even though there is no binder between the ceramic layer and the fibrous separator, sputtering creates an inter-embedded structure that ensures no depowering after cycling. Furthermore, the PAN-based separator displays a high temperature tolerance of 180°C. Consequently, the cell delivers a high capacity of 1287.9 mAh g-1 at 0.5 C and stable cycling performance with an ultra-low capacity decay rate of 0.059% per cycle over 500 cycles. This work provides a scalable strategy for functionalizing separators to tackle the challenges in LSBs, which is binder-free, stripping-free, and essentially thickening-free.

Biomimetic Lipid‐Bilayer Anode Protection for Long Lifetime Aqueous Zinc‐Metal Batteries

AbstractThe practical application of rechargeable aqueous zinc batteries is impeded by dendrite growth, especially at high areal capacities and high current densities. Here, this challenge is addressed by proposing zinc perfluoro(2‐ethoxyethane)sulfonic (Zn(PES)2) as a zinc battery electrolyte. This new amphipathic zinc salt, with a hydrophobic perfluorinated tail, can form an anode protecting layer, in situ, with a biomimetic lipid‐bilayer structure. The layer limits the anode contact with free H2O and offers fast Zn2+ transport pathways, thereby effectively suppressing dendrite growth while maintaining high rate capability. A stable, Zn2+‐conductive fluorinated solid electrolyte interphase (SEI) is also formed, further enhancing zinc reversibility. The electrolyte enables unprecedented cycling stability with dendrite‐free zinc plating/stripping over 1600 h at 1 mA cm−2 at 2 mAh cm−2, and over 380 h under an even harsher condition of 2.5 mA cm−2 and 5 mAh cm−2. Full cell tests with a high‐loading VS2 cathode demonstrate good capacity retention of 78% after 1000 cycles at 1.5 mA cm−2. The idea of in situ formation of a biomimetic lipid‐bilayer anode protecting layer and fluorinated SEI opens a new route for engineering the electrode–electrolyte interface toward next‐generation aqueous zinc batteries with long lifetime and high areal capacities.

Anion Concentration Gradient-Assisted Construction of a Solid-Electrolyte Interphase for a Stable Zinc Metal Anode at High Rates.

Coulombic efficiency (CE) and cycle life of metal anodes (lithium, sodium, zinc) are limited by dendritic growth and side reactions in rechargeable metal batteries. Here, we proposed a concept for constructing an anion concentration gradient (ACG)-assisted solid-electrolyte interphase (SEI) for ultrahigh ionic conductivity on metal anodes, in which the SEI layer is fabricated through an in situ chemical reaction of the sulfonic acid polymer and zinc (Zn) metal. Owing to the driving force of the sulfonate concentration gradient and high bulky sulfonate concentration, a promoted Zn2+ ionic conductivity and inhibited anion diffusion in the SEI layer are realized, resulting in a significant suppression of dendrite growth and side reaction. The presence of ACG-SEI on the Zn metal enables stable Zn plating/stripping over 2000 h at a high current density of 20 mA cm-2 and a capacity of 5 mAh cm-2 in Zn/Zn symmetric cells, and moreover an improved cycling stability is also observed in Zn/MnO2 full cells and Zn/AC supercapacitors. The SEI layer containing anion concentration gradients for stable cycling of a metal anode sheds a new light on the fundamental understanding of cation plating/stripping on metal electrodes and technical advances of rechargeable metal batteries with remarkable performance under practical conditions.

Reversible and homogenous zinc deposition enabled by in-situ grown Cu particles on expanded graphite for dendrite-free and flexible zinc metal anodes

The rapid development of wearable electronics has boosted the exploration of flexible and safe energy storage devices, such as zinc ion batteries or capacitors; and suppressing the dendrite growth for Zn anode is essential for enhancing their performance. Addressing this, we report a dendrite-free and flexible Zn metal anode (Zn@Cu-Ps/EG) that is based on expanded graphite (EG) decorated with in-situ formed copper particles (Cu-Ps). In this material, the Cu-Ps act as zincophilic seeds that reduce zinc nucleation overpotential, while the EG substrate induces epitaxial electrodeposition of zinc for suppressing dendrite growth. Moreover, the Cu-Ps nail the graphite nanosheets tightly and enhance the mechanical strength and flexibility of the Cu-Ps/EG composite. Consequently, the Zn@Cu-Ps/EG anode exhibits a low Zn deposition overpotential of 142.8 mV and superior cycling performance over 3000 h upon cycling at 10.0 mA cm−2 and 10.0 mAh cm−2. A flexible Zn-ion capacitor equipped with this anode delivers excellent cycling performance for over 1600 cycles at 1.0 A g−1 and stable power output at various bending statuses. This work provides a new approach for designing advanced flexible and dendrite-free Zn metal anodes for energy storage applications.