Horizontal Growth of Lithium on Parallelly Aligned MXene Layers towards Dendrite‐Free Metallic Lithium Anodes

Although metallic lithium is an extremely promising anode for lithium‐based batteries due to its high theoretical capacity, the uncontrollable growth of lithium dendrites, in particular under deep stripping and plating, have stagnated its application. It is demonstrated that parallelly aligned MXene (Ti₃C₂T_x ) layers enable the efficient guiding of lithium nucleation and growth on the surface of 2D MXene nanosheets, giving rise to horizontal‐growth lithium anodes. Moreover, the inherent fluorine terminations in MXene afford a uniform and durable solid electrolyte interface with lithium fluoride at the anode/electrolyte interface, efficiently regulating electromigration of lithium ions. Thus, a dendrite‐free lithium anode with a long cycle life up to 900 h and excellent deep stripping–plating capabilities up to 35 mAh cm^?2 is achieved, which can further serve as an anode for a lithium metal battery, exhibiting high cycle stability up to 1000 cycles.     

Regulating Lithium Nucleation via CNTs Modifying Carbon Cloth Film for Stable Li Metal Anode

Li metal is demonstrated as one of the most promising anode materials for high energy density batteries. However, uncontrollable Li dendrite growth and repeated growth of solid electrolyte interface during the charge/discharge process lead to safety issues and capacity decay, preventing its practical application. To address these issues, an effective strategy is to realize uniform Li nucleation. Here, a stable lithium–scaffold composite electrode (CC/CNT@Li) is designed by melting of lithium metal into 3D interconnected lithiophilic carbon nanotube (CNT) on a porous carbon cloth (CC). The 3D interconnected CNTs successfully change the lithiophobic CC into lithiophilic nature, reducing the polarization of the electrode, ensuring homogenous Li nucleation and continuous smooth Li plating. The CNTs on the surface of CC provide adequate Li nucleation sites and reduce the areal current density to avoid Li dendrite growth. The 3D porous structure of CC/CNT offers enough free room for buffering the huge volume change during Li plating/stripping. The CC/CNT@Li composite anode exhibits dendrite‐free morphology and superior cycling performances over 500 h with low voltage hysteresis of 18, 23, and 71 mV at the current density of 1, 2, and 5 mA cm^?2, respectively.     

An Autotransferable g‐C3N4 Li+‐Modulating Layer toward Stable Lithium Anodes

Commercial deployment of lithium anodes has been severely impeded by the poor battery safety, unsatisfying cycling lifespan, and efficiency. Recently, building artificial interfacial layers over a lithium anode was regarded as an effective strategy to stabilize the electrode. However, the fabrications reported so far have mostly been conducted directly upon lithium foil, often requiring stringent reaction conditions with indispensable inert environment protection and highly specialized reagents due to the high reactivity of metallic lithium. Besides, the uneven lithium‐ion flux across the lithium surface should be more powerfully tailored via mighty interfacial layer materials. Herein, g‐C₃N₄ is employed as a Li⁺‐modulating material and a brand‐new autotransferable strategy to fabricate this interfacial layer for Li anodes without any inert atmosphere protection and limitation of chemical regents is developed. The g‐C₃N₄ film is filtrated on the separator in air using a common alcohol solution and then perfectly autotransferred to the lithium surface by electrolyte wetting during normal cell assembly. The abundant nitrogen species within g‐C₃N₄ nanosheets can form transient Li? N bonds to powerfully stabilize the lithium‐ion flux and thus enable a CE over 99% for 900 cycles and smooth deposition at high current densities and capacities, surpassing most previous works.     

Dendrite‐Free Lithium Anodes with Ultra‐Deep Stripping and Plating Properties Based on Vertically Oriented Lithium–Copper–Lithium Arrays

Although lithium metal is the best anode for lithium‐based batteries, the uncontrollable lithium dendrites especially under deep stripping and plating states hamper its practical applications. Here, a dendrite‐free lithium anode is developed based on vertically oriented lithium–copper–lithium arrays, which can be facilely produced via traditional rolling or repeated stacking approaches. Such vertically oriented arrays not only enable both the lithium‐ion flux and the electric field to be regulated, but also can act as a “dam” to guide the regular plating of lithium, thus efficiently buffering the volume change of the lithium anode upon cycling. As a consequence, the vertically oriented anode exhibits an excellent deep stripping and plating capability upto 50 mAh cm^?2, high rate capabilities (20 mA cm^?2), and long cycle life (2000 h). Based on this anode, a full lithium battery with a LiCoO₂ cathode delivers a good cycle life, holding great potential for practical lithium‐metal batteries with high energy densities.     

Ultrafine Silver Nanoparticles for Seeded Lithium Deposition toward Stable Lithium Metal Anode

To exploit the high energy density of the lithium (Li) metal battery, it is imperative to address the dendrite growth and interface instability of the anode. 3D hosts for Li metal are expected to suppress the growth of Li dendrites. Heterogeneous seeds are effective in guiding Li deposition and realizing spatial control over Li nucleation. Herein, this study shows that ultrafine silver (Ag) nanoparticles, which are synthesized via a novel rapid Joule heating method, can serve as nanoseeds to direct the deposition of Li within the 3D host materials, resolving the problems of the Li metal anode. By optimizing the Joule heating method, ultrafine Ag nanoparticles (≈40 nm) are homogeneously anchored on carbon nanofibers. The Ag nanoseeds effectively reduce the nucleation overpotential of Li and guide the Li deposition in the 3D carbon matrix uniformly, free from the dendrites. A stable and reversible Li metal anode is achieved in virtue of the Ag nanoseeds in the 3D substrate, showing a low overpotential (≈0.025 V) for a long cycle life. The ultrafine nanoseeds achieved by rapid Joule heating render uniform deposition of Li metal anode in 3D hosts, promising a safe and long‐life Li metal battery for high‐energy applications.     

A Triple‐Gradient Host for Long Cycling Lithium Metal Anodes at Ultrahigh Current Density

The viable Li metal anodes (LMAs) are still hampered by the safety concerns resulting from fast Li dendrite growth and huge volume expansion during cycling. Herein, carbon nanofiber matrix anchored with MgZnO nanoparticles (MgZnO/CNF) is developed as a flexible triple‐gradient host for long cycling LMAs. The superlithiophilic MgZnO nanoparticles significantly increase the wettability of CNF for fast and homogeneous infusion with molten Li. The in‐built potential and lithiophilic gradients constructed after an in situ lithiation of MgZnO and CNF enable nearly zero Li nucleation overpotential and homogeneous deposition of lithium at different scales. As such, the LMAs based on MgZnO/CNF achieve long cycling life and small overpotential even at a record‐high current density of 50 mA cm^?2 and a high areal capacity of 10 mAh cm^?2. A full cell paring with this designed LMA and LiFePO₄ exhibits a capacity retention up to 82% after 600 cycles at a high rate of 5 C. A Li‐ion capacitor also shows an impressive capacity retention of 84% at 5 A g^?1 after 10 000 cycles. Such a Li@MgZnO/CNF anode is a promising candidate for Li‐metal energy storage systems, especially working under ultrahigh current density.     

In Situ Formed Gradient Composite Solid Electrolyte Interphase Layer for Stable Lithium Metal Anodes

Lithium (Li) metal anode (LMA) is highly considered as a desirable anode material for next-generation rechargeable batteries because of its high specific capacity and the lowest reduction potential. However, uncontrollable growth of Li dendrites, large volume change, and unstable interfaces between LMA and electrolyte hinder its practical application. Herein, a novel in situ formed artificial gradient composite solid electrolyte interphase (GCSEI) layer for highly stable LMAs is proposed. The inner rigid inorganics (Li₂S and LiF) with high Li⁺ ion affinity and high electron tunneling barrier are beneficial to achieve homogeneous Li plating, while the flexible polymers (poly(ethylene oxide) and poly(vinylidene fluoride)) on the surface of GCSEI layer can accommodate the volume change. Furthermore, the GCSEI layer demonstrates fast Li⁺ ion transport capability and increased Li⁺ ion diffusion kinetics. Accordingly, the modified LMA enables excellent cycling stability (over 1000 h at 3 mA cm⁻²) in the symmetric cell using carbonate electrolyte, and the corresponding Li-GCSEI||LiNi_0.8Co_0.1Mn_0.1O₂ full cell demonstrates 83.4% capacity retention after 500 cycles. This work offers a new strategy for the design of dendrite-free LMAs for practical applications.     

Nanoarray Architecture of Ultra-Lithiophilic Metal Nitrides for Stable Lithium Metal Anodes

Lithium metal anode (LMA) is puzzled by the serious issues corresponding to infinite volume change and notorious lithium dendrite during long-term stripping/plating process. Herein, the transition metal nitrides array with outstanding lithiophilicity, including CoN, VN, and Ni₃N, are decorated onto carbon framework as “nests” to uniform Li nucleation and guide Li metal deposition. These transition metal nitrides with excellent conductivity can guarantee the fast electron transport, therefore maintain a stable interface for Li reduction. In addition, the designed multi-dimensional structure of metal nitride array decorated carbon framework can effectively regulate the growth of Li metal during the stripping/plating process. Of note, attributing to the lattice-matching between CoN and Li metal, the composite Li/CoN@CF anode exhibits ultra-stable cycling performance in symmetrical cells (over 4000 h@1 mA cm⁻² with 1 mAh cm⁻² and 1000h@20 mA cm⁻² with 20 mAh cm⁻²). The assembled full cells based on Li/CoN@CF composite anode, LiFePO₄ or S as cathodes, deliver excellent cycling stability and rate capability. This strategy provides an effective approach to develop a stable lithium metal anode for lithium metal batteries.     

Lithiophilic Cu‐CuO‐Ni Hybrid Structure: Advanced Current Collectors Toward Stable Lithium Metal Anodes

Metallic lithium (Li) is a promising anode material for next‐generation rechargeable batteries. However, the dendrite growth of Li and repeated formation of solid electrolyte interface during Li plating and stripping result in low Coulombic efficiency, internal short circuits, and capacity decay, hampering its practical application. In the development of stable Li metal anode, the current collector is recognized as a critical component to regulate Li plating. In this work, a lithiophilic Cu‐CuO‐Ni hybrid structure is synthesized as a current collector for Li metal anodes. The low overpotential of CuO for Li nucleation and the uniform Li⁺ ion flux induced by the formation of Cu nanowire arrays enable effective suppression of the growth of Li dendrites. Moreover, the surface Cu layer can act as a protective layer to enhance structural durability of the hybrid structure in long‐term running. As a result, the Cu‐CuO‐Ni hybrid structure achieves a Coulombic efficiency above 95% for more than 250 cycles at a current density of 1 mA cm^?2 and 580 h (290 cycles) stable repeated Li plating and stripping in a symmetric cell.     

Nanocellulose Modified Polyethylene Separators for Lithium Metal Batteries

Poor cycling stability and safety concerns regarding lithium (Li) metal anodes are two major issues preventing the commercialization of high‐energy density Li metal‐based batteries. Herein, a novel tri‐layer separator design that significantly enhances the cycling stability and safety of Li metal‐based batteries is presented. A thin, thermally stable, flexible, and hydrophilic cellulose nanofiber layer, produced using a straightforward paper‐making process, is directly laminated on each side of a plasma‐treated polyethylene (PE) separator. The 2.5 µm thick, mesoporous (≈20 nm average pore size) cellulose nanofiber layer stabilizes the Li metal anodes by generating a uniform Li⁺ flux toward the electrode through its homogenous nanochannels, leading to improved cycling stability. As the tri‐layer separator maintains its dimensional stability even at 200 °C when the internal PE layer is melted and blocks the ion transport through the separator, the separator also provides an effective thermal shutdown function. The present nanocellulose‐based tri‐layer separator design thus significantly facilitates the realization of high‐energy density Li metal‐based batteries.     

Stable Metal Anode enabled by Porous Lithium Foam with Superior Ion Accessibility

Lithium (Li) metal anodes have attracted much interest recently for high‐energy battery applications. However, low coulombic efficiency, infinite volume change, and severe dendrite formation limit their reliable implementation over a wide range. Here, an outstanding stability for a Li metal anode is revealed by designing a highly porous and hollow Li foam. This unique structure is capable of tackling many Li metal problems simultaneously: first, it assures uniform electrolyte distribution over the inner and outer electrode's surface; second, it reduces the local current density by providing a larger electroactive surface area; third, it can accommodate volume expansion and dissipate heat efficiently. Moreover, the structure shows superior stability compared to fully Li covered foam with low porosity, and bulky Li foil electrode counterparts. This Li foam exhibits small overpotential (≈25 mV at 4 mA cm^?2) and high cycling stability for 160 cycles at 4 mA cm^?2. Furthermore, when assembled, the porous Li metal as the anode with LiFePO₄ as the cathode for a full cell, the battery has a high‐rate performance of 138 mAh g^?1 at 0.2 C. The beneficial structure of the Li hollow foam is further studied through density functional theory simulations, which confirms that the porous structure has better charge mobility and more uniform Li deposition.     

Reviving Lithium‐Metal Anodes for Next‐Generation High‐Energy Batteries

Lithium‐metal batteries (LMBs), as one of the most promising next‐generation high‐energy‐density storage devices, are able to meet the rigid demands of new industries. However, the direct utilization of metallic lithium can induce harsh safety issues, inferior rate and cycle performance, or anode pulverization inside the cells. These drawbacks severely hinder the commercialization of LMBs. Here, an up‐to‐date review of the behavior of lithium ions upon deposition/dissolution, and the failure mechanisms of lithium‐metal anodes is presented. It has been shown that the primary causes consist of the growth of lithium dendrites due to large polarization and a strong electric field at the vicinity of the anode, the hyperactivity of metallic lithium, and hostless infinite volume changes upon cycling. The recent advances in liquid organic electrolyte (LOE) systems through modulating the local current density, anion depletion, lithium flux, the anode–electrolyte interface, or the mechanical strength of the interlayers are highlighted. Concrete strategies including tailoring the anode structures, optimizing the electrolytes, building artificial anode–electrolyte interfaces, and functionalizing the protective interlayers are summarized in detail. Furthermore, the challenges remaining in LOE systems are outlined, and the future perspectives of introducing solid‐state electrolytes to radically address safety issues are presented.     

Highly Stable Potassium Metal Anodes with Controllable Thickness and Area Capacity

K metal battery is a kind of high-energy-density storage device with economic advantages. However, due to the dendrite growth and difficult processing characteristics, it is difficult to prepare stable K metal anode with thin thickness and fixed area capacity, which severely limits its development. In this work, a multi-functional 3D skeleton (rGCA) is synthesized by simple vacuum filtration and thermal reduction, and K metal anodes with controllable thickness and area capacity (K content) can be fabricated by changing the raw material mass and graphene layer spacing of rGCA. Moreover, the graphene sheet layer of rGCA can relax stress and relieve volume expansion; carbon nanotubes can serve as the fast transport channel of electrons, reducing internal impedance and local current density; Ag nanoparticles can induce the uniform nucleation and deposition of K⁺. The K metal composite anodes (rGCA-K) based on the conductive skeleton can effectively suppress dendrites and exhibit excellent electrochemical performance in symmetric and full cells. The controllable fabrication process of stable K metal anode is expected to help K metal batteries move toward the stage of commercial production.     

Clay-Originated Two-Dimensional Holey Silica Separator for Dendrite-Free Lithium Metal Anode

Lithium metal anode is the ultimate choice to obtain next-generation high-energy-density lithium batteries, while the dendritic lithium growth owing to the unstable lithium anode/electrolyte interface largely limits its practical application. Separator is an important component in batteries and separator engineering is believed to be a tractable and effective way to address the above issue. Separators can play the role of ion redistributors to guide the transport of lithium ions and regulate the uniform electrodeposition of Li. The electrolyte wettability, thermal shrinkage resistance, and mechanical strength are of importance for separators. Here, clay-originated two-dimensional (2D) holey amorphous silica nanosheets (ASN) to develop a low-cost and eco-friendly inorganic separator is directly adopted. The ASN-based separator has higher porosity, better electrolyte wettability, much higher thermal resistance, larger lithium transference number, and ionic conductivity compared with commercial separator. The large amounts of holes and rich surface oxygen groups on the ASN guide the uniform distribution of lithium-ion flux. Consequently, the Li//Li cell with this separator shows stable lithium plating/stripping, and the corresponding Li//LiFePO₄, Li//LiCoO_2, and Li//NCM523 full cells also show high capacity, excellent rate performance, and outstanding cycling stability, which is much superior to that using the commercial separator.