Integrated Gradient Cu Current Collector Enables Bottom-Up Li Growth for Li Metal Anodes: Role of Interfacial Structure

Taming Lithium Nucleation and Growth on Cu Current Collector by Electrochemical Activation of ZnF2 Layer

Lithium-metal anodes are essential for the advancement of next-generation batteries. However, their practical use is largely hindered by the uncontrollable growth of dendrites and intricate problems associated with fabricating anodes that meet capacity requirements. Here, it is demonstrated that an ultrathin ZnF2 layer deposited on the copper foil can produce a novel and efficient current collector to address these challenges. It is observed that ZnF2 can be transformed into LiZn alloy and LiF salt in one step by simple electrochemical activation. The resulting LiZn alloy exhibits high lithiophilicity, which reduces overpotential and promotes uniform lithium nucleation, while the LiF salt enhances the solid electrolyte interphase, ensuring uniform lithium growth. This synergistic effect led to a dendrite-free, densely packed lithium anode with an extended lifespan, achieving over 900 h in symmetric cells at a high current density of 3 mA cm-2 and a high cut-off capacity of 3 mAh cm-2. Furthermore, full cells utilizing the lithium anode (Li capacity of 6 mAh cm-2) paired with LiNi0.8Mn0.1Co0.1O2 cathodes (mass loading of 11.5 mg cm-2) demonstrates drastically improved rate capability and excellent cycling stability. This approach holds great promise for developing safer and more efficient lithium-metal-based batteries for future energy storage solutions.

Li2ZnCu3 Modified Cu Current Collector to Regulate Li Deposition

Rationally designing a current collector that can maintain low lithium (Li) porosity and smooth morphology while enduring high-loading Li deposition is crucial for realizing the high energy density of Li metal batteries, but it is still challengeable. Herein, a Li2ZnCu3 alloy-modified Cu foil is reported as a stable current collector to fulfill the stable high-loading Li deposition. Benefiting from the in situ alloying, the generated numerous Li2ZnCu3@Cu heterojunctions induce a homogeneous Li nucleation and dense growth even at an ultrahigh capacity of 12 mAh cm-2. Such a spatial structure endows the overall Li2ZnCu3@Cu electrode with the manipulated steric hindrance and outmost surface electric potential to suppress the side reactions during Li stripping and plating. The resultant Li||Li2ZnCu3@Cu asymmetric cell preserves an ultrahigh average Coulombic efficiency of 99.2 % at 3 mA cm-2/6 mAh cm-2 over 200 cycles. Moreover, the Li-Li2ZnCu3@Cu||LiFePO4 cell maintains a cycling stability of 87.5 % after 300 cycles. After coupling with the LiCoO2 cathode (4 mAh cm-2), the cell exhibits a high energy density of 407.4 Wh kg-1 with remarkable cycling reversibility at an N/P ratio of 3. All these findings present a doable way to realize the high-capacity, dendrite-free, and dense Li deposition for high-performance Li metal batteries.

Facile Electrodeposition Method for Constructing Li2S as Artificial Solid Electrolyte Interphase for High-Performance Li Metal Anode

Designing current collectors and constructing efficient artificial solid electrolyte interphase (SEI) layers are promising strategies for achieving dendrite-free Li deposition and practical applications in Li metal batteries (LMBs). Electrodeposition is advantageous for large-scale production and allows the direct formation of current collectors without binders, making them immediately usable as electrodes. In this study, an adherent Cu2S thin-layer on Cu foil is synthesized through anodic electrodeposition from a Na2S solution in a one-step process, followed by the generation of Li2S layers as artificial SEI layers via a conversion reaction (3DLi2S-Cu foil). The Li2S layers move from the 3D Cu surface to the deposited Li surface, facilitating uniform and dense Li deposition. The 3DLi2S-Cu foil structure demonstrates stable cycling performance over 350 cycles in an asymmetric cell, with a capacity of 1 mAh cm-2 at 1 mA cm-2. Moreover, symmetric cells with 5 mAh cm-2 of deposited Li exhibit a stable cycle life for over 1200 h. When paired with commercial LiFePO4 (LFP), the full cells show substantially enhanced cyclability, regardless of the amount of deposited Li. This study provides new insights into the construction of artificial SEIs for facilitating commercial applications.

Growing mulberry-like copper on copper current collector for stable lithium metal battery anodes

Due to the uncontrollable growth of lithium dendrites and the considerable volume change of lithium during cycling, the practical application of lithium metal batteries has stalled. The current collector with a 3D structure has been demonstrated to effectively inhibit the growth of lithium dendrites and mitigate the volume change of lithium, which can effectively promote the practical application of lithium metal batteries. The conventional electrodeposition method for constructing 3D structures on the surface of a copper current collector is prone to forming dendritic structures with sharp surfaces. However, the dendritic structure is susceptible to the tip effect, resulting in inhomogeneous lithium deposition. In this study, PAA molecules are adsorbed on the surface of copper to hinder and disperse its growth during electrodeposition, optimizing its growth mode. Thus, mulberry-like copper with a biomimetic structure is prepared on the surface of copper foil (M-CF). The mulberry structure not only provides additional electrochemically active sites and robust conductive frameworks for lithium deposition, it also efficiently mitigates the electric field concentration at the 3D structure's tip, optimizes lithium-ion transport flux, suppresses the growth of lithium dendrites. As a result, the M-CF anode is capable of stable Li plating/stripping over 500 cycles with a high average CE of 98.1 %. The assembled symmetrical battery is stably cycled over 1600 h at a low voltage hysteresis of 11 mV. The full cells paired with M-CF-Li-6 (Li: 6 mAh cm-2) anodes and LTO cathodes stably cycle more than 500 cycles, and the capacity retention rate is 95.3 %.

An integrated dual-gradient host facilitates oriented bottom-up lithium growth in lithium metal anodes

Integrated gradient hosts, composed of poorly conductive frameworks on copper current collectors, have been extensively explored for the development of Li metal anodes (LMAs). Despite their potential, high Li nucleation overpotentials and slow interface kinetics often lead to inferior performance. Herein, we combine electrospinning and electrodeposition to create an integrated gradient host, namely OPAN/rGO-Cu2O/Cu. This involves electrodeposition of graphene oxide onto copper foil, reacting in situ to form a lithiophilic rGO-Cu2O layer, which is then covered with an oxidized polyacrylonitrile (OPAN) nanofiber layer, establishing conductivity and lithiophilicity dual gradients. The insulating OPAN top layer blocks electron transmission to the surface and prevents Li deposition, while the lithiophilic rGO-Cu2O layer facilitates Li ion transport to the bottom and reduces the nucleation barrier, both of which promote uniform Li deposition from bottom to top. As a result, the battery achieves an average coulombic efficiency of 98.4% over 500 cycles at 1 mA cm-2, and the symmetric cell sustains an ultra-long cycle life of 1600 h with a minimal polarization voltage of 12 mV. When paired with a LiFePO4 cathode, the full cell demonstrates a capacity retention of 92.6% after 300 cycles at 1 C, with an average capacity decay rate of just 0.025% per cycle. This innovative approach offers a promising pathway for developing high-performance LMAs.

Oriented Structures for High Safety, Rate Capability, and Energy Density Lithium Metal Batteries

Lithium metal batteries (LMBs) have emerged in recent years as highly promising candidates for high-density energy storage systems. Despite their immense potential, mutual constraints arise when optimizing energy density, rate capability, and operational safety, which greatly hinder the commercialization of LMBs. The utilization of oriented structures in LMBs appears as a promising strategy to address three key performance barriers: 1) low efficiency of active material utilization at high surface loading, 2) easy formation of Li dendrites and damage to interfaces under high-rate cycling, and 3) low ionic conductivity of solid-state electrolytes in high safety LMBs. This review aims to holistically introduce the concept of oriented structures, provide criteria for quantifying the degree of orientation, and elucidate their systematic effects on the properties of materials and devices. Furthermore, a detailed categorization of oriented structures is proposed to offer more precise guidance for the design of LMBs. This review also provides a comprehensive summary of preparation techniques for oriented structures and delves into the mechanisms by which these can enhance the energy density, rate capability, and safety of LMBs. Finally, potential applications of oriented structures in LMBs and the crucial challenges that need to be addressed in this field are explored.

Advances in anode current collectors with a lithiophilic gradient for lithium metal batteries

The practical application of lithium metal batteries (LMBs) is inevitably associated with serious safety risks due to the uncontrolled growth of lithium dendrites. Thus, to inhibit the formation of lithium dendrites, many researchers have focused on constructing three-dimensional porous current collectors with a high specific surface area. However, the homogeneous structure of porous collectors does not effectively guide the deposition of lithium metal to the bottom, leading to a phenomenon known as "top-growth." Recently, the construction of 3D porous current collectors with a lithiophilic gradient has been widely reported and regarded as an effective approach to inhibit lithium top-growth, thus improving battery safety. In this review, we summarize the latest research progress on such anode current collector design strategies, including surface modification of different base materials, design of gradient structures, and field factors, emphasizing their lithium-affinity mechanism and the advantages and disadvantages of different collector designs. Finally, we provide a perspective on the future research directions and applications of gradient affinity current collectors.

Constructing Three-Dimensional Architectures to Design Advanced Copper-Based Current Collector Materials for Alkali Metal Batteries: From Nanoscale to Microscale

Alkali metals (Li, Na, and K) are deemed as the ideal anode materials for next-generation high-energy-density batteries because of their high theoretical specific capacity and low redox potentials. However, alkali metal anodes (AMAs) still face some challenges hindering their further applications, including uncontrollable dendrite growth and unstable solid electrolyte interphase during cycling, resulting in low Coulombic efficiency and inferior cycling performance. In this regard, designing 3D current collectors as hosts for AMAs is one of the most effective ways to address the above-mentioned problems, because their sufficient space could accommodate AMAs' volume expansion, and their high specific surface area could lower the local current density, leading to the uniform deposition of alkali metals. Herein, we review recent progress on the application of 3D Cu-based current collectors in stable and dendrite-free AMAs. The most widely used modification methods of 3D Cu-based current collectors are summarized. Furthermore, the relationships among methods of modification, structure and composition, and the electrochemical properties of AMAs using Cu-based current collectors, are systematically discussed. Finally, the challenges and prospects for future study and applications of Cu-based current collectors in high-performance alkali metal batteries are proposed.

Conformal 3D Li/Li13Sn5 Scaffolds Anodes for High-Areal Energy Density Flexible Lithium Metal Batteries

Achieving a high depth of discharge (DOD) in lithium metal anodes (LMAs) is crucial for developing high areal energy density batteries suitable for wearable electronics. Yet, the persistent growth of dendrites compromises battery performance, and the significant lithium consumption during pre-lithiation obstructs their broad application. Herein, A flexible 3D Li13Sn5 scaffold is designed by allowing molten lithium to infiltrate carbon cloth adorned with SnO2 nanocrystals. This design markedly curbs the troublesome dendrite growth, thanks to the uniform electric field distribution and swift Li+ diffusion dynamics. Additionally, with a minimal SnO2 nanocrystals loading (2 wt.%), only 0.6 wt.% of lithium is consumed during pre-lithiation. Insights from in situ optical microscope observations and COMSOL simulations reveal that lithium remains securely anchored within the scaffold, a result of the rapid mass/charge transfer and uniform electric field distribution. Consequently, this electrode achieves a remarkable DOD of 87.1% at 10 mA cm-2 for 40 mAh cm-2. Notably, when coupled with a polysulfide cathode, the constructed flexible Li/Li13Sn5@CC||Li2S6/SnO2@CC pouch cell delivers a high-areal capacity of 5.04 mAh cm-2 and an impressive areal-energy density of 10.6 mWh cm-2. The findings pave the way toward the development of high-performance LMAs, ideal for long-lasting wearable electronics.

Bottom-Up Magnesium Deposition Induced by Paper-Based Triple-Gradient Scaffolds toward Flexible Magnesium Metal Batteries

The development of advanced magnesium metal batteries (MMBs) has been hindered by longstanding challenges, such as the inability to induce uniform magnesium (Mg) nucleation and the inefficient utilization of Mg foil. This study introduces a novel solution in the form of a flexible, lightweight, paper-based scaffold that incorporates gradient conductivity, magnesiophilicity, and pore size. This design is achieved through an industrially adaptable papermaking process in which the ratio of carboxylated multi-walled carbon nanotubes to softwood cellulose fibers is meticulously adjusted. The triple-gradient structure of the scaffold enables the regulation of Mg ion flux, promoting bottom-up Mg deposition. Owing to its high flexibility, low thickness, and reduced density, the scaffold has potential applications in flexible and wearable electronics. Accordingly, the triple-gradient electrodes exhibit stable operation for over 1200 h at 3 mA cm-2 /3 mAh cm-2 in symmetrical cells, markedly outperforming the non-gradient and metallic Mg alternatives. Notably, this study marks the first successful fabrication of a flexible MMB pouch full cell, achieving an impressive volumetric energy density of 244 Wh L-1 . The simplicity and scalability of the triple-gradient design, which uses readily available materials through an industrially compatible papermaking process, open new doors for the production of flexible, high-energy-density metal batteries.

Sustainable release of LiNO3 in carbonate electrolytes for stable lithium metal anodes

LiNO3 is recognized as an effective additive, forming a dense, nitrogen-rich solid electrolyte interphase (SEI) on lithium's surface, which safeguards it from parasitic reactions. However, its use is limited due to the poor solubility in carbonate electrolytes. Herein, we introduce a bilayer separator designed to release LiNO3 sustainably. This continual release not only alters the chemistry of the SEI but also replenishes the additives that are depleted during battery cycling, thereby enhancing the durability of the modified interphase. This strategy effectively curtails Li dendrite formation, significantly enhancing the longevity of Li|LiFePO4 batteries, evidenced by an impressive 85% capacity retention after 800 cycles. This research offers a compelling remedy to the longstanding challenge of incorporating LiNO3 in carbonate electrolytes.

High-Areal Capacity, High-Rate Lithium Metal Anodes Enabled by Nitrogen-Doped Graphene Mesh

Hosts hold great prospects for addressing the dendrite growth and volume expansion of the Li metal anode, but Li dendrites are still observable under the conditions of high deposition capacity and/or high current density. Herein, a nitrogen-doped graphene mesh (NGM) is developed, which possesses a conductive and lithiophilic scaffold for efficient Li deposition. The abundant nanopores in NGM can not only provide sufficient room for Li deposition, but also speed up Li ion transport to achieve a high-rate capability. Moreover, the evenly distributed N dopants on the NGM can guide the uniform nucleation of Li so that to inhibit dendrite growth. As a result, the composite NGM@Li anode shows satisfactory electrochemical performances for Li-S batteries, including a high capacity of 600 mAh g-1 after 300 cycles at 1 C and a rate capacity of 438 mAh g-1 at 3 C. This work provides a new avenue for the fabrication of graphene-based hosts with large areal capacity and high-rate capability for Li metal batteries.

Stabilizing Lithium-Metal Host Anodes by Covalently Binding MgF2 Nanodots to Honeycomb Carbon Nanofibers

Constructing lithiophilic carbon hosts has been regarded as an effective strategy for inhibiting Li dendrite formation and mitigating the volume expansion of Li metal anodes. However, the limitation of lithiophilic carbon hosts by conventional surface decoration methods over long-term cycling hinders their practical application. In this work, a robust host composed of ultrafine MgF2 nanodots covalently bonded to honeycomb carbon nanofibers (MgF2/HCNFs) is created through an in situ solid-state reaction. The composite exhibits ultralight weight, excellent lithiophilicity, and structural stability, contributing to a significantly enhanced energy efficiency and lifespan of the battery. Specifically, the strong covalent bond not only prevents MgF2 nanodots from migrating and aggregating but also enhances the binding energy between Mg and Li during the molten Li infusion process. This allows for the effective and stable regulation of repeated Li plating/stripping. As a result, the MgF2/HCNF-Li electrode delivers a high Coulombic efficiency of 97% after 200 cycles, cycling stably for more than 2000 h. Furthermore, the full cells with a LiFePO4 cathode achieve a capacity retention of 85% after 500 cycles at 0.5C. This work provides a strategy to guide dendrite-free Li deposition patterns toward the development of high-performance Li metal batteries.