Zipper‐Inspired SEI Film for Remarkably Enhancing the Stability of Li Metal Anode via Nucleation Barriers Controlled Weaving of Lithium Pits

The lithium dendrite, inducing short circuit and breaking solid electrolyte interphase (SEI) films, is deleterious to the stability of Li metal batteries due to the uncontrollable occurrence of miscellaneous stresses. In contrast to conventional suppression routes, herein a strategy is proposed via controlling SEI film broken regions to minimize releasing stress in terms of weaving lithium pits. Inspired by the principle of zippers, zipper‐like SEI films enable offering ordered pattern on the surface of Li anode via mechanical rolling. For the available cells, net‐like sewing/breaking patterns alternatively occur in Li plating/stripping. In the same electrolyte, a stable and dendrite‐free Li homogeneous growth is achieved.     

Electrokinetic Phenomena Enhanced Lithium‐Ion Transport in Leaky Film for Stable Lithium Metal Anodes

The application of lithium (Li) metal anodes in Li metal batteries has been hindered by growth of Li dendrites, which lead to short cycling life. Here a Li‐ion‐affinity leaky film as a protection layer is reported to promote a dendrite‐free Li metal anode. The leaky film induces electrokinetic phenomena to enhance Li‐ion transport, leading to a reduced Li‐ion concentration polarization and homogeneous Li‐ion distribution. As a result, the dendrite‐free Li metal anode during Li plating/stripping is demonstrated even at an extremely high deposition capacity (6 mAh cm^?2) and current density (40 mA cm^?2) with improved Coulombic efficiencies. A full cell battery with the leaky‐film protected Li metal as the anode and high‐areal‐capacity LiNi_0.8Co_0.1Mn_0.1O₂ (NCM‐811) (≈4.2 mAh cm^?2) or LiFePO₄ (≈3.8 mAh cm^?2) as the cathode shows improved cycling stability and capacity retention, even at lean electrolyte conditions.     

Tailoring Lithium Deposition via an SEI‐Functionalized Membrane Derived from LiF Decorated Layered Carbon Structure

Lithium (Li) metal is a key anode material for constructing next generation high energy density batteries. However, dendritic Li deposition and unstable solid electrolyte interphase (SEI) layers still prevent practical application of Li metal anodes. In this work, it is demonstrated that an uniform Li coating can be achieved in a lithium fluoride (LiF) decorated layered structure of stacked graphene (SG), leading to the formation of an SEI‐functionalized membrane that retards electron transfer by three orders of magnitude to avoid undesirable Li deposition on the top surface, and ameliorates Li⁺ ion migration to enable uniform and dendrite‐free Li deposition beneath such an interlayer. Surface chemistry analysis and density functional theory calculations demonstrate that these beneficial features arise from the formation of C–F_x surface components on the SG sheets during the Li coating process. Based on such an SEI‐functionalized membrane, stable cycling at high current densities up to 3 mA cm^?2 and Li plating capacities up to 4 mAh cm^?2 can be realized in LiPF₆/carbonate electrolytes. This work elucidates the promising strategy of modifying Li plating behavior through the SEI‐functionalized carbon structure, with significantly improved cycling stability of rechargeable Li metal anodes.     

Pristine or Highly Defective? Understanding the Role of Graphene Structure for Stable Lithium Metal Plating

The role of graphene host structure/chemistry in plating–stripping in lithium metal anodes employed for lithium metal batteries is first examined in this study. Structural and chemical defects are bad, since highly defective graphene promotes unstable solid electrolyte interphase (SEI) growth. This consumes the fluoroethylene carbonate (FEC) additive in the carbonate electrolyte and is correlated with rapid decay in Coulombic efficiency (CE) and formation of filament‐like Li dendrites. A unique flow‐aided sonication exfoliation method is employed to synthesize “defect‐free” graphene (df‐G), allowing for a direct performance comparison with conventional reduced graphene oxide (r‐GO). At cycle 1, the r‐GO is better electrochemically wetted by Li than df‐G, indicating that initially it is more lithiophilic. With cycling, the nucleation overpotential with r‐GO becomes higher than with df‐G, indicating less facile plating reactions. The df‐G yields state‐of‐the‐art electrochemical performance, with the post cycled metal surface being relatively smooth and dendrite‐free. Conversely, r‐GO templates have CE rapidly degrade from the onset, with extensive dendrites after cycling. Severe SEI growth and associated FEC depletion with r‐GO are further confirmed by electrochemical impedance analysis and surface science methods. A new design rule is provided for Li metal templates: An ideal host must be noncatalytic toward SEI formation.     

Uniform High Ionic Conducting Lithium Sulfide Protection Layer for Stable Lithium Metal Anode

Artificial solid‐electrolyte interphase (SEI) is one of the key approaches in addressing the low reversibility and dendritic growth problems of lithium metal anode, yet its current effect is still insufficient due to insufficient stability. Here, a new principle of “simultaneous high ionic conductivity and homogeneity” is proposed for stabilizing SEI and lithium metal anodes. Fabricated by a facile, environmentally friendly, and low‐cost lithium solid‐sulfur vapor reaction at elevated temperature, a designed lithium sulfide protective layer successfully maintains its protection function during cycling, which is confirmed by both simulations and experiments. Stable dendrite‐free cycling of lithium metal anode is realized even at a high areal capacity of 5 mAh cm^?2, and prototype Li–Li₄Ti₅O₁₂ cell with limited lithium also achieves 900 stable cycles. These findings give new insight into the ideal SEI composition and structure and provide new design strategies for stable lithium metal batteries.     

Enhanced Stability of Li Metal Anodes by Synergetic Control of Nucleation and the Solid Electrolyte Interphase

Use of a protective coating on a lithium metal anode (LMA) is an effective approach to enhance its coulombic efficiency and cycling stability. Here, a facile approach to produce uniform silver nanoparticle‐decorated LMA for high‐performance Li metal batteries (LMBs) is reported. This effective treatment can lead to well‐controlled nucleation and the formation of a stable solid electrolyte interphase (SEI). Ag nanoparticles embedded in the surface of Li anodes induce uniform Li plating/stripping morphologies with reduced overpotential. More importantly, cross‐linked lithium fluoride‐rich interphase formed during Ag⁺ reduction enables a highly stable SEI layer. Based on the Ag‐LiF decorated anodes, LMBs with LiNi_1/3Mn_1/3Co_1/3O₂ cathode (≈1.8 mAh cm^?2) can retain >80% capacity over 500 cycles. The similar approach can also be used to treat sodium metal anodes. Excellent stability (80% capacity retention in 10 000 cycles) is obtained for a Na||Na₃V₂(PO₄)₃ full cell using a Na‐Ag‐NaF/Na anode cycled in carbonate electrolyte. These results clearly indicate that synergetic control of the nucleation and SEI is an efficient approach to stabilize rechargeable metal batteries.     

Dendrite‐Suppressed Lithium Plating from a Liquid Electrolyte via Wetting of Li3N

Lithium metal is an ultimate anode material to provide the highest energy density for a given cathode by providing a higher capacity and cell voltage. However, lithium is not used as the anode in commercial lithium‐ion batteries because electrochemical dendrite formation and growth during charge can induce a cell short circuit that ignites the flammable liquid electrolyte. Plating of lithium through a bed of Li₃N particles is shown to transform dendrite growth into a 3D lithium network formed by wetting the particle surfaces; plating through a Li₃N particle is without dendrite nucleation. The Li₃N particles create a higher overpotential during Li deposition than that with dendrite growth in galvanostatic charge/discharge tests. The characteristic overpotential increase is correlated with the morphological changes and a more isotropic growth behavior. The Li₃N‐modified Li electrode shows a stable cycling performance at 0.5 and 1.0 mA cm^?2 for more than 100 cycles. The origin of the bonding responsible for wetting of the Li₃N particles by lithium and for plating through a Li₃N particle is discussed.     

Interface Engineering for Lithium Metal Anodes in Liquid Electrolyte

Interfacial chemistry between lithium metal anodes and electrolytes plays a vital role in regulating the Li plating/stripping behavior and improving the cycling performance of Li metal batteries. Constructing a stable solid electrolyte interphase (SEI) on Li metal anodes is now understood to be a requirement for progress in achieving feasible Li‐metal batteries. Recently, the application of novel analytical tools has led to a clearer understanding of composition and the fine structure of the SEI. This further promoted the development of interface engineering for stable Li metal anodes. In this review, the SEI formation mechanism, conceptual models, and the nature of the SEI are briefly summarized. Recent progress in probing the atomic structure of the SEI and elucidating the fundamental effect of interfacial stability on battery performance are emphasized. Multiple factors including current density, mechanical strength, operating temperature, and structure/composition homogeneity that affect the interfacial properties are comprehensively discussed. Moreover, strategies for designing stable Li‐metal/electrolyte interfaces are also reviewed. Finally, new insights and future directions associated with Li‐metal anode interfaces are proposed to inspire more revolutionary solutions toward commercialization of Li metal batteries.     

Recent Developments of the Lithium Metal Anode for Rechargeable Non‐Aqueous Batteries

Over the last 40 years, metallic lithium as an anode material has been of great interest owing to its high energy density. However, dendritic lithium growth causes serious safety issues. Awareness and understanding of the Li deposition and stripping processes have grown rapidly especially in recent years, and consequently, there have been many attempts to suppress the Li dendrites. Recent developments that have modified the electrolytes and the Li anode in order to inhibit the growth of Li dendrite and improve cycling performance are summarized. It has been shown that current density, solid‐electrolyte interphase (SEI) film, Li⁺ transference number, and shear modulus have significant impact on the growth behavior and the Coulombic efficiency. Various methods have been introduced to increase the surface area of the Li anode, enhance Li⁺ conductivity, form stable SEI film, and improve mechanical strength of electrolytes. These approaches are discussed in details, and the perspectives regarding the future use of Li anode are also outlined. It is hoped that this review will facilitate the future development of Li metal batteries.     

High Polarity Poly(vinylidene difluoride) Thin Coating for Dendrite‐Free and High‐Performance Lithium Metal Anodes

The high‐polarity β‐phase poly(vinylidene difluoride) (β‐PVDF), which has all trans conformation with F and H atoms located on the opposite sides of the polymer backbone, is demonstrated to be a promising artificial solid‐electrolyte interphase coating on both Cu and Li metal anodes for dendrite‐free Li deposition/stripping and enhanced cycling performance. A thin (≈4 µm) β‐PVDF coating on Cu enables uniform Li deposition/stripping at high current densities up to 5 mA cm^?2, Li‐plating capacity loadings of up to 4 mAh cm^?2, and excellent cycling stability over hundreds of cycles under practical conditions (1 mA cm^?2 with 2 mAh cm^?2). Full cells containing an LiFePO₄ cathode and an anode of either β‐PVDF coated Cu or Li also exhibit excellent cycling stability. The profound effects of the high‐polarity PVDF coating on dendrite suppression are attributed to the electronegative F‐rich interface that favors layer‐by‐layer Li deposition. This study offers a new strategy for the development of dendrite‐free metal anode technology.     

In Situ Generation of Artificial Solid‐Electrolyte Interphases on 3D Conducting Scaffolds for High‐Performance Lithium‐Metal Anodes

Rational structure design of the current collector along with further engineering of the solid‐electrolyte interphases (SEI) layer is one of the most promising strategies to achieve uniform Li deposition and inhibit uncontrolled growth of Li dendrites. Here, a Li₂S layer as an artificial SEI with high compositional uniformity and high lithium ion conductivity is in situ generated on the surface of the 3D porous Cu current collector to regulate homogeneous Li plating/stripping. Both simulations and experiments demonstrate that the Li₂S protective layer can passivate the porous Cu skeleton and balance the transport rate of lithium ions and electrons, thereby alleviating the agglomerated Li deposition at the top of the electrode or at the defect area of the SEI layer. As a result, the modified current collector exhibits long‐term cycling of 500 cycles at 1 mA cm^?2 and stable electrodeposition capabilities of 4 mAh cm^?2 at an ultrahigh current density of 4 mA cm^?2. Furthermore, full batteries (LiFePO₄ as cathode) paired with this designed 3D anode with only ≈200% extra lithium show superior stability and rate performance than the batteries paired with lithium foil (≈3000% extra lithium). These explorations provide new strategies for developing high‐performance Li metal anodes.     

SiO2 Hollow Nanosphere‐Based Composite Solid Electrolyte for Lithium Metal Batteries to Suppress Lithium Dendrite Growth and Enhance Cycle Life

The low Coulombic efficiency and serious security issues of lithium (Li) metal anode caused by uncontrollable Li dendrite growth have permanently prevented its practical application. A novel SiO₂ hollow nanosphere‐based composite solid electrolyte (SiSE) for Li metal batteries is reported. This hierarchical electrolyte is fabricated via in situ polymerizing the tripropylene gycol diacrylate (TPGDA) monomer in the presence of liquid electrolyte, which is absorbed in a SiO₂ hollow nanosphere layer. The polymerized TPGDA framework keeps the prepared SiSE in a quasi‐solid state without safety risks caused by electrolyte leakage, meanwhile the SiO₂ layer not only acts as a mechanics‐strong separator but also provides the SiSE with high room‐temperature ionic conductivity (1.74 × 10^?3 S cm^?1) due to the high pore volume (1.49 cm³ g^?1) and large liquid electrolyte uptake of SiO₂ hollow nanospheres. When the SiSE is in situ fabricated on the cathode and applied to LiFePO₄/SiSE/Li batteries, the obtained cells show a significant improvement in cycling stability, mainly attributed to the stable electrode/electrolyte interface and remarkable suppression for Li dendrite growth by the SiSE. This work can extend the application of hollow nanooxide and enable a safe, efficient operation of Li anode in next generation energy storage systems.     

Tailoring the Mechanical and Electrochemical Properties of an Artificial Interphase for High‐Performance Metallic Lithium Anode

Lithium metal is regarded as the “Holy Grail” of anode materials due to its low electrochemical potential and high theoretical capacity. Unfortunately, its unstable solid electrolyte interphase (SEI) leads to low Coulombic efficiency (CE) and serious safety issues. Herein, a hybrid nanoscale polymeric protective film with tunable composition and improved stiffness is developed by incorporating aluminum crosslinkers into the polymer chains. The Li plating/stripping process is regulated through the protective coating and the dendrite growth is effectively suppressed. Promisingly, the protected Li can deliver stable performance for more than 350 h with a cycling capacity of 2 mAh cm^?2 without a notable increase in overpotential. Moreover, a stable charge/discharge cycling in Li–O₂ batteries with the protected Li can be maintained for more than 600 h. This work provides guidance on the rational design of electrode interfaces and opens up new opportunities for the fabrication of next‐generation energy storage systems.     

Highly Stable Operation of Lithium Metal Batteries Enabled by the Formation of a Transient High‐Concentration Electrolyte Layer

Lithium (Li) metal has been extensively investigated as an anode for rechargeable battery applications due to its ultrahigh theoretical specific capacity and the lowest redox potential. However, significant challenges including dendrite growth and low Coulombic efficiency are still hindering the practical applications of rechargeable Li metal batteries. It is demonstrated that long‐term cycling of Li metal batteries can be realized by the formation of a transient high‐concentration electrolyte layer near the surface of Li metal anode during high rate discharge process. The highly concentrated Li⁺ ions in this transient layer will immediately be solvated by the available solvent molecules and facilitate the formation of a stable and flexible solid electrolyte interphase (SEI) layer composed of a poly(ethylene carbonate) framework integrated with other organic/inorganic lithium salts. This SEI layer largely suppresses the corrosion of Li metal anode attacked by free organic solvents and enables the long‐term operation of Li metal batteries. The fundamental findings in this work provide a new direction for the development of Li metal batteries that could be operated at high current densities for a wide range of applications.     

Coated Lithium Powder (CLiP) Electrodes for Lithium‐Metal Batteries

Safety issues caused by the metallic lithium inside a battery represent one of the main reasons for the lack of commercial availability of rechargeable lithium‐metal batteries. The advantage of anodes based on coated lithium powder (CLiP), compared to plain lithium foil, include the suppression of dendrite formation, as the local current density during stripping/plating is reduced due to the higher surface area. Another performance and safety advantage of lithium powder is the precisely controlled mass loading of the lithium anode during electrode preparation, giving the opportunity to avoid Li excess in the cell. As an additional benefit, the coating makes electrode manufacturing safer and eases handling. Here, electrodes based on coated lithium powder electrodes (CLiP) are introduced for application in lithium‐metal batteries. These electrodes are compared to lithium foil electrodes with respect to cycling stability, coulombic efficiency of lithium stripping/plating, overpotential, and morphology changes during cycling.     

Compact 3D Copper with Uniform Porous Structure Derived by Electrochemical Dealloying as Dendrite‐Free Lithium Metal Anode Current Collector

The development of lithium (Li) metal anodes Li metal batteries faces huge challenges such as uncontrolled Li dendrite growth and large volume change during Li plating/stripping, resulting in severe capacity decay and high safety hazards. A 3D porous copper (Cu) current collector as a host for Li deposition can effectively settle these problems. However, constructing a uniform and compact 3D porous Cu structure is still an enormous challenge. Herein, an electrochemical etching method for Cu–Zinc (Zn) alloy is reported to precisely engrave a 3D Cu structure with uniform, smooth, and compact porous network. Such a continuous structure endows 3D Cu excellent mechanical properties and high electrical conductivity. The uniform and smooth pores with a large internal surface area ensures well dispersed current density for homogeneous Li metal deposition and accommodation. A smooth and stable solid electrolyte interphase is formed and meanwhile Li dendrites and dead Li are effectively suppressed. The Li metal anode conceived 3D Cu current collector can stably cycle for 400 h under an Li plating/stripping capacity of 1 mA h cm^?2 and a current density of 1 mA cm^?2. The Li@3D Cu||LiFePO₄ full cells present excellent cycling and rate performances. The electrochemical dealloying is a robust method to construct 3D Cu current collectors for dendrite‐free Li metal anodes.     

A Coaxial‐Interweaved Hybrid Lithium Metal Anode for Long‐Lifespan Lithium Metal Batteries

Lithium (Li) metal is one of the most promising anode materials to construct next‐generation rechargeable batteries owing to its ultrahigh theoretical capacity and the lowest electrochemical potential. Unfortunately, practical application of Li metal batteries is severely hindered by short lifespan and safety concerns caused by Li dendrite growth during cycling. Herein, a coaxial‐interweaved hybrid Li metal anode is proposed for dendrite inhibition that significantly improves the cycling stability of Li metal batteries. The hybrid Li metal anode is fabricated by Li composition into a 3D interweaved scaffold, where each fiber of the interwoven scaffold is composed of a conductive skeleton and a coaxial lithiophilic layer modified on the surface. The coaxial‐interweaved structure endows the hybrid anode with favored Li affinity to guide uniform Li deposition, sufficient channels for ion transportation and electron conduction, and enhanced stability during Li plating and stripping. Consequently, the hybrid Li metal anode affords high Coulombic efficiency over 98.5% for 750 cycles with dendrite‐free morphologies in half cells and improved capacity retention of 80.1% after 100 cycles in LiFePO₄ full cells. The innovative coaxial‐interweaved hybrid Li metal anode demonstrates multiscale design strategy from lithiophilic modification to scaffold construction and promises the prospect of Li metal batteries for future applications.     

An Interconnected Channel‐Like Framework as Host for Lithium Metal Composite Anodes

Lithium (Li) metal anodes have long been counted on to meet the increasing demand for high energy, high‐power rechargeable battery systems but they have been plagued by uncontrollable plating, unstable solid electrolyte interphase (SEI) formation, and the resulting low Coulombic efficiency. These problems are even aggravated under commercial levels of current density and areal capacity testing conditions. In this work, the channel‐like structure of a carbonized eggplant (EP) as a stable “host” for Li metal melt infusion, is utilized. With further interphase modification of lithium fluoride (LiF), the as‐formed EP–LiF composite anode maintains ≈90% Li metal theoretical capacity and can successfully suppress dendrite growth and volume fluctuation during cycling. EP–LiF offers much improved symmetric cell and full‐cell cycling performance with lower and more stable overpotential under various areal capacity and elevated rate capability. Furthermore, carbonized EP serves as a light‐weight high‐performance current collector, achieving an average Coulombic efficiency ≈99.1% in ether‐based electrolytes with 2.2 mAh cm^?2 cycling areal capacity. The natural structure of carbonized EP will inspire further artificial designs of electrode frameworks for both Li anode and sulfur cathodes, enabling promising candidates for next‐generation high‐energy density batteries.     

Stable Lithium Electrodeposition at Ultra‐High Current Densities Enabled by 3D PMF/Li Composite Anode

Lithium metal batteries (LMBs) are promising candidates for next‐generation energy storage due to their high energy densities on both weight and volume bases. However, LMBs usually undergo uncontrollable lithium deposition, unstable solid electrolyte interphase, and volume expansion, which easily lead to low Coulombic efficiency, poor cycling performance, and even safety hazards, hindering their practical applications for more than forty years. These issues can be further exacerbated if operated at high current densities. Here a stable lithium metal battery enabled by 3D porous poly‐melamine‐formaldehyde (PMF)/Li composite anode is reported. PMF with a large number of polar groups (amine and triazine) can effectively homogenize Li‐ion concentration when these ions approach to the anode surface and thus achieve uniform Li deposition. Moreover, the 3D structured anode can serve as a Li host to mitigate the volume change during Li stripping and plating process. Galvanostatic measurements demonstrate that the 3D composite electrode can achieve high‐lithium Coulombic efficiency of 94.7% at an ultrahigh current density of 10 mA cm^?2 after 50 cycles with low hysteresis and smooth voltage plateaus. When coupled with Li₄Ti₅O₁₂, half‐cells show enhanced rate capabilities and Coulombic efficiencies, opening great opportunities for high‐energy batteries.     

Taming Interfacial Instability in Lithium–Oxygen Batteries: A Polymeric Ionic Liquid Electrolyte Solution

There is a growing concern about the cyclability and safety, in particular, of the high‐energy density lithium–metal batteries. This concern is even greater for Li–O₂ batteries because O₂ that is transported from the cathode to the anode compartment, can exacerbate side reactions and dendrite growth of the lithium metal anode. The key to solving this dilemma lays in tailoring the solid electrolyte interphase (SEI) formed on the lithium metal anode in Li–O₂ batteries. Here it is reported that a new electrolyte, formed from LiFSI as the salt and a mixture of tetraethylene glycol dimethyl ether and polymeric ionic liquid of P[C₅O₂N_MA,11]FSI as the solvent, can produce a stable electrode (both cathode and anode)|electrolyte interface in Li–O₂ batteries. Specifically, this new electrolyte, when in contact with lithium metal anodes, has the ability to produce a uniform SEI with high ionic conductivity for Li⁺ transport and desired mechanical property for suppression of dendritic lithium growth. Moreover, the electrolyte possesses a high oxidation tolerance that is very beneficial to the oxygen electrochemistry on the cathode of Li–O₂ batteries. As a result, enhanced reversibility and cycle life are realized for the resultant Li–O₂ batteries.