Dendrite-Free Lithium Deposition via a Superfilling Mechanism for High-Performance Li-Metal Batteries

Interfacial chemistry in multivalent aqueous batteries: fundamentals, challenges, and advances

As one of the most promising electrochemical energy storage systems, aqueous batteries are attracting great interest due to their advantages of high safety, high sustainability, and low costs when compared with commercial lithium-ion batteries, showing great promise for grid-scale energy storage. This invited tutorial review aims to provide universal design principles to address the critical challenges at the electrode-electrolyte interfaces faced by various multivalent aqueous battery systems. Specifically, deposition regulation, ion flux homogenization, and solvation chemistry modulation are proposed as the key principles to tune the inter-component interactions in aqueous batteries, with corresponding interfacial design strategies and their underlying working mechanisms illustrated. In the end, we present a critical analysis on the remaining obstacles necessitated to overcome for the use of aqueous batteries under different practical conditions and provide future prospects towards further advancement of sustainable aqueous energy storage systems with high energy and long durability.

Advances in Functional Organosulfur-Based Mediators for Regulating Performance of Lithium Metal Batteries

Rechargeable lithium metal batteries (LMBs) are promising next-generation energy storage systems due to their high theoretical energy density. However, their practical applications are hindered by lithium dendrite growth and various intricate issues associated with the cathodes. These challenges can be mitigated by using organosulfur-based mediators (OSMs), which offer the advantages of abundance, tailorable structures, and unique functional adaptability. These features enable the rational design of targeted functionalities, enhance the interfacial stability of the lithium anode and cathode, and accelerate the redox kinetics of electrodes via alternative reaction pathways, thereby effectively improving the performance of LMBs. Unlike the extensively explored field of organosulfur cathode materials, OSMs have garnered little attention. This review systematically summarizes recent advancements in OSMs for various LMB systems, including lithium-sulfur, lithium-selenium, lithium-oxygen, lithium-intercalation cathode batteries, and other LMB systems. It briefly elucidates the operating principles of these LMB systems, the regulatory mechanisms of the corresponding OSMs, and the fundamentals of OSMs activity. Ultimately, strategic optimizations are proposed for designing novel OSMs, advanced mechanism investigation, expanded applications, and the development of safe battery systems, thereby providing directions to narrow the gap between rational modulation of organosulfur compounds and their practical implementation in batteries.

Perfluorinated Amines: Accelerating Lithium Electrodeposition by Tailoring Interfacial Structure and Modulated Solvation for High-Performance Batteries

Modulating interfacial electrochemistry represents a prevalent approach for mitigating lithium dendrite growth and enhancing battery performance. Nevertheless, while most additives exhibit inhibitory characteristics, the accelerating effects on interfacial electrochemistry have garnered limited attention. In this work, perfluoromorpholine (PFM) with facilitated kinetics is utilized to preferentially adsorb on the lithium metal interface. The PFM molecules disrupt the solvation structure of Li+ and enhance the migration of Li+. Combined with the benzotrifluoride, a synergistic acceleration-inhibition system is formed. The ab initio molecular dynamics (AIMD) and density functional theory (DFT) calculation of the loose outer solvation clusters and the key adsorption-deposition step supports the fast diffusion and stable interface electrochemistry with an accelerated filling mode with C─F and C─H groups. The approach induces the uniform lithium deposition. Excellent cycling performance is achieved in Li||Li symmetric cells, and even after 200 cycles in Li||NCM811 full cells, 80% of the capacity is retained. This work elucidates the accelerated electrochemical processes at the interface and expands the design strategies of acceleration fluorinated additives for lithium metal batteries.

Constructing static two-electron lithium-bromide battery

Despite their potential as conversion-type energy storage technologies, the performance of static lithium-bromide (SLB) batteries has remained stagnant for decades. Progress has been hindered by the intrinsic liquid-liquid redox mode and single-electron transfer of these batteries. Here, we developed a high-performance SLB battery based on the active bromine salt cathode and the two-electron transfer chemistry with a Br-/Br+ redox couple by electrolyte tailoring. The introduction of NO3- improved the reversible single-electron transition of Br-, and more impressively, the coordinated Cl- anions activated the Br+ conversion to provide an additional electron transfer. A voltage plateau was observed at 3.8 V, and the discharge capacity and energy density were increased by 142 and 159% compared to the one-electron reaction benchmark. This two-step conversion mechanism exhibited excellent stability, with the battery functioning for 1000 cycles. These performances already approach the state of the art of currently established Li-halogen batteries. We consider the established two-electron redox mechanism highly exemplary for diversified halogen batteries.

Bimetallic MOFs-Derived NiFe2O4/Fe2O3 Enabled Dendrite-free Lithium Metal Anodes with Ultra-High Area Capacity Based on An Intermittent Lithium Deposition Model

In practical operating conditions, the lithium deposition behavior is often influenced by multiple coupled factors and there is also a lack of comprehensive and long-term validation for dendrite suppression strategies. Our group previously proposed an intermittent lithiophilic model for high-performance three-dimensional (3D) composite lithium metal anode (LMA), however, the electrodeposition behavior was not discussed. To verify this model, this paper presents a modified 3D carbon cloth (CC) backbone by incorporating NiFe2O4/Fe2O3 (NFFO) nanoparticles derived from bimetallic NiFe-MOFs. Enhanced Li adsorption capacity and lithiophilic modulation were achieved by bimetallic MOFs-derivatives which prompted faster and more homogeneous Li deposition. The intermittent model was further verified in conjunction with the density functional theory (DFT) calculations and electrodeposition behaviors. As a result, the obtained Li-CC@NFFO||Li-CC@NFFO symmetric batteries exhibit prolonged lifespan and low hysteresis voltage even under ultra-high current and capacity conditions (5 mA cm-2, 10 mAh cm-2), what's more, the full battery coupled with a high mass loading (9 mg cm-2) of LiFePO4 cathode can be cycled at a high rate of 5 C, the capacity retention is up to 95.2 % before 700 cycles. This work is of great significance to understand the evolution of lithium dendrites on the 3D intermittent lithiophilic frameworks.

State-of-the-Art Two-Dimensional Metal Phosphides for High Performance Lithium-ion Batteries: Progress and Prospects

Lithium-ion batteries (LIBs) with high energy density, long cycle life and safety have earned recognition as outstanding energy storage devices, and have been used in extensive applications, such as portable electronics and new energy vehicles. However, traditional graphite anodes deliver low specific capacity and inferior rate performance, which is difficult to satisfy ever-increasing demands in LIBs. Very recently, two-dimensional metal phosphides (2D MPs) emerge as the cutting-edge materials in LIBs due to their overwhelming advantages including high theoretical capacity, excellent conductivity and short lithium diffusion pathway. This review summarizes the up-to-date advances of 2D MPs from typical structures, main synthesis methods and LIBs applications. The corresponding lithium storage mechanism, and relationship between 2D structure and lithium storage performance is deeply discussed to provide new enlightening insights in application of 2D materials for LIBs. Several potential challenges and inspiring outlooks are highlighted to provide guidance for future research and applications of 2D MPs.

Atomic Zincophilic Sites Regulating Microspace Electric Fields for Dendrite-Free Zinc Anode

Aqueous Zn metal batteries are promising candidates for large-scale energy storage due to their intrinsic advantages. However, Zn tends to deposit irregularly and forms dendrites driven by the uneven space electric field distribution near the Zn-electrolyte interphase. Herein it is demonstrated that trace addition of Co single atom anchored carbon (denoted as CoSA/C) in the electrolyte regulates the microspace electric field at the Zn-electrolyte interphase and unifies Zn deposition. Through preferential adsorption of CoSA/C on the Zn surface, the atomically dispersed Co-N3 with strong charge polarization effect can redistribute the local space electric field and regulate ion flux. Moreover, the dynamic adsorption/desorption of CoSA/C upon plating/stripping offers sustainable long-term regulation. Therefore, Zn||Zn symmetric cells with CoSA/C electrolyte additive deliver stable cycling up to 1600 h (corresponding to a cumulative plated capacity of 8 Ah cm-2 ) at a high current density of 10 mA cm-2 , demonstrating the sustainable feature of microspace electric field regulation at high current density and capacity.

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 (Li2 S 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||LiNi0.8 Co0.1 Mn0.1 O2 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.

Surface modification using heptafluorobutyric acid to produce highly stable Li metal anodes

The Li metal is an ideal anode material owing to its high theoretical specific capacity and low electrode potential. However, its high reactivity and dendritic growth in carbonate-based electrolytes limit its application. To address these issues, we propose a novel surface modification technique using heptafluorobutyric acid. In-situ spontaneous reaction between Li and the organic acid generates a lithiophilic interface of lithium heptafluorobutyrate for dendrite-free uniform Li deposition, which significantly improves the cycle stability (Li/Li symmetric cells >1200 h at 1.0 mA cm^-2) and Coulombic efficiency (>99.3%) in conventional carbonate-based electrolytes. This lithiophilic interface also enables full batteries to achieve 83.2% capacity retention over 300 cycles under realistic testing condition. Lithium heptafluorobutyrate interface acts as an electrical bridge for uniform lithium-ion flux between Li anode and plating Li, which minimizes the occurrence of tortuous lithium dendrites and lowers interface impedance.

Suppressing Local Dendrite Hotspots via Current Density Redistribution Using a Superlithiophilic Membrane for Stable Lithium Metal Anode

Li metal anode is considered as one of the most desirable candidates for next-generation battery due to its lowest electrochemical potential and high theoretical capacity. However, undesirable dendrite growth severely exacerbates the interfacial stability, thus damaging battery performance and bringing safety concerns. Here, an efficient strategy is proposed to stabilize Li metal anode by digesting dendrites sprout using a 3D flexible superlithiophilic membrane consisting of poly(vinylidene fluoride) (PVDF) and ZnCl₂ composite nanofibers (PZEM) as a protective layer. Both the experimental studies and theoretical calculations show the origin of superlithiophilicity ascribed to a strong interaction between ZnCl₂ and PVDF to form the ZnF bonds. The multifield physics calculation implies effective removal of local dendrite hotspots by PZEM via a more homogeneous Li⁺ flux. The PZEM-covered Li anode (PZEM@Li) exhibits superior Li deposition/stripping performance in a symmetric cell over 1100 cycles at a high current density of 5 mA cm^-2 . When paired with LiFePO₄ (LFP), PZEM@Li|LFP full cell remains stable over 1000 cycles at 2 C with a degradation rate of 0.0083% per cycle. This work offers a new route for efficient protection of Li metal anode for practical applications.

An Inorganic-Rich SEI Layer by the Catalyzed Reduction of LiNO3 Enabled by Surface-Abundant Hydrogen Bonding for Stable Lithium Metal Batteries

Lithium (Li) metal anodes (LMAs) are promising anode candidates for realizing high-energy-density batteries. However, the formation of unstable solid electrolyte interphase (SEI) layers on Li metal is harmful for stable Li cycling; hence, enhancing the physical/chemical properties of SEI layers is important for stabilizing LMAs. Herein, thiourea (TU, CH₄ N₂ S) is introduced as a new catalyzing agent for LiNO₃ reduction to form robust inorganic-rich SEI layers containing abundant Li₃ N. Due to the unique molecular structure of TU, the TU molecules adsorb on the Cu electrode by forming CuS bond and simultaneously form hydrogen bonding with other hydrogen bonds accepting species such as NO₃ ^- and TFSI^- through its NH bonds, leading to their catalyzed reduction and hence the formation of inorganic-rich SEI layer with abundant Li₃ N, LiF, and Li₂ S/Li₂ S₂ . Particularly, this TU-modified SEI layer shows a lower film resistance and better uniformity compared to the electrochemically and naturally formed SEI layers, enabling planar Li growth without any other material treatments and hence improving the cyclic stability in Li/Cu half-cells and Li@Cu/LiFePO₄  full-cells.

Regulation of Li+ Diffusion via an Engineered Separator to Realize a Homogeneous Lithium Microstructure in Advanced Li-Metal Batteries

Lithium metal, the most promising anode material, is receiving increasing interest owing to its high theoretical capacity (3860 mA h g^-1) and low negative potential (-3.04 V vs. standard hydrogen electrode). However, the uneven Li dissolution/deposition behavior causes a degraded cycle stability and safety issues, thus seriously restricting the application of Li-metal batteries (LMBs). Separator modification is one of the most versatile and feasible approaches to overcome this problem. In this study, polypropylene (PP) separators are prepared and coated with an inert hexagonal boron nitride (h-BN) layer, which can provide sufficient ion transport channels and physical protection. The h-BN@PP separator exhibits a remarkable effect on the regulation of the diffusion and nucleation of Li⁺ to realize a homogeneous Li microstructure, thereby reducing the voltage polarization and improving the cycle performance of the battery. All LMBs equipped with the modified separators exhibit excellent cycling stabilities. The Li|Li symmetric cell exhibits a stable cycling for over 2300 h with a polarization voltage of 13 mV. In conclusion, the modified h-BN@PP separator has significant potential for stabilizing various Li metal anodes, which strongly promotes the applications of advanced LMBs.

Electrolyte Regulation of Bio-Inspired Zincophilic Additive toward High-Performance Dendrite-Free Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries hold attractive potential for large-scale energy storage devices owing to their prominent electrochemical performance and high security. Nevertheless, the applications of aqueous electrolytes have generated various challenges, including uncontrolled dendrite growth and parasitic reactions, thereby deteriorating the Zn anode's stability. Herein, inspired by the superior affinity between Zn²⁺ and amino acid chains in the zinc finger protein, a cost-effective and green glycine additive is incorporated into aqueous electrolytes to stabilize the Zn anode. As confirmed by experimental characterizations and theoretical calculations, the glycine additives can not only reorganize the solvation sheaths of hydrated Zn²⁺ via partial substitution of coordinated H₂ O but also preferentially adsorb onto the Zn anode, thereby significantly restraining dendrite growth and interfacial side reactions. Accordingly, the Zn anode could realize a long lifespan of over 2000 h and enhanced reversibility (98.8%) in the glycine-containing electrolyte. Furthermore, the assembled Zn||α-MnO₂ full cells with glycine-modified electrolyte also delivers substantial capacity retention (82.3% after 1000 cycles at 2 A g^-1 ), showing promising application prospects. This innovative bio-inspired design concept would inject new vitality into the development of aqueous electrolytes.

Columnar Lithium Deposition Guided by Graphdiyne Nanowalls toward a Stable Lithium Metal Anode

Lithium metal is the most promising anode for lithium batteries, but the growth of lithium dendrites leads to rapid attenuation of battery capacity and a series of safety problems during the plating/stripping process. Utilization of carbon materials for improving the Li metal anode stability represents a feasible strategy; particularly, the high affinity for lithium endows graphdiyne (GDY) with a promising capability for stabilizing Li metal anodes. Herein, vertically aligned GDY nanowalls (NWs) were uniformly grown on a copper foil, which allowed for dendrite-free, columnar deposition of lithium, desired for a stable Li metal anode. The highly lithiophilic GDY NWs afforded plentiful and evenly distributed active sites for Li nucleation as well as uniform distribution of Li-ion flux for Li growth, resulting in smooth, columnar Li deposition. The resultant Li metal electrode based on the Cu-GDY NWs was able to cycle stably for 500 cycles at 1 mA cm^-2 and 2 mA h cm^-2 with a high Coulombic efficiency of 99.2% maintained. A symmetric battery assembled by lithium-loaded Cu-GDY NWs (Cu-GDY NWs@Li) showed a long lifespan over 1000 h at 1 mA cm^-2 and 1 mA h cm^-2. Furthermore, a full cell assembled by Cu-GDY NWs@Li and LiFePO₄ was able to cycle stably for 200 cycles at a high current of 5 C, indicating the potential applications in practical Li metal batteries at high rates. This work demonstrated great potential of GDY-based materials toward applications in Li metal batteries of high safety and high energy density.

Regulating Lithium Plating/Stripping Behavior by a Composite Polymer Electrolyte Endowed with Designated Ion Channels

The urgent demand for high energy and safety storage devices is pushing the development of lithium metal batteries. However, unstable solid electrolyte interface (SEI) formation and uncontrollable lithium dendrite growth are still huge challenges for the practical use of lithium metal batteries. Herein, a composite polymer electrolyte (CPE) endowed with designated ion channels is fabricated by constructing nanoscale Uio66-NH₂ layer, which has uniformly distributed pore structure to regulate reversible Li plating/stripping in lithium metal batteries. The regular channels within the Uio66-NH₂ layer work as an ion sieve to restrict larger TFSI^- anions inside its channels and extract Li⁺ across selectively, which result in a high Li-ion transference number ( t Li + ${t_{{\rm{L}}{{\rm{i}}^{\bm{ + }}}}}$ ) of 0.6. Moreover, CPE provides high ion conductivity (0.245 mS cm^-1 at room temperature) and expanded oxidation window (5.1 V) and forms a stable SEI layer. As a result, the assembled lithium metal batteries with CPE exhibit outstanding cyclic stability and capacity retention. The Li/CPE/Li symmetric cell continues plating/stripping over 500 h without short-circuiting. The Li/CPE/LFP cell delivers a reversible capacity of 149.3 mAh g^-1 with a capacity retention of 99% after 100 cycles.

Dual Structure-Material Design of Separators toward Dendrite-Free Lithium Metal Anodes

The practical applications of lithium metal anodes have been severely hindered by the Li dendrite issue. Herein, a dual structure-material design strategy was developed to fabricate a new type of separator using interconnected hollow porous polyacrylonitrile (PAN) nanofibers (HPPANF), which delivered controllable and dendrite-free Li depositions. The interconnected mesopores on HPPANF bridged the hollow interiors with the outside voids among the fibers, enabling outstanding electrolyte uptake capabilities for high ion conductivity, and nano-level wetted electrolyte/anode interface for uniform Li plating/stripping. In parallel, the HPPANF separator enriched with polar groups acted as an exceptional polymer-based solid-state electrolyte, providing 3D ion channels for the transport of Li ions. Benefiting from the dual structure-material design, the HPPANF separator induced uniform Li ion flux for dendrite-free Li depositions, which caused enhanced cycling stability (1300 h, 3 mA cm^-2 ). This work demonstrates a new method to stabilize Li metal anodes through rational separator design.

Constructing Bimetallic ZIF-Derived Zn,Co-Containing N-Doped Porous Carbon Nanocube as the Lithiophilic Host to Stabilize Li Metal Anodes in Li-O2 Batteries

Li metal, because of its ultrahigh theoretical capacity, has attracted extensive attention. However, uncontrollable dendritic Li formation and infinite electrode dimensional variation hinder application of Li anodes. Herein, Zn,Co bimetallic zeolitic imidazolate frameworks (ZIFs) were synthesized and further pyrolyzed to obtain Zn,Co-containing N-doped porous carbon nanocube (Zn/Co-N@PCN), which was further applied as lithiophilic host to construct the lithiated Zn/Co-N@PCN (Li-Zn/Co-N@PCN). Zn vapor produced many pores on the carbon framework during calcination process that could store enough Li and thus inhibit the huge electrode volume change. Additionally, there were abundant lithiophilic groups in Zn/Co-N@PCN, such as N- or Co/Zn-based species, which were beneficial to uniform Li deposition. Moreover, the stable and conductive carbon-based matrix could ensure superior and reproducible Li plating/stripping behavior in Zn/Co-N@PCN over cycling. As a result, the Li-Zn/Co-N@PCN anode showed a steady and high columbic efficiency of around 99.0 % for 600 cycles at 0.5 mA cm^-2 . The Li-Zn/Co-N@PCN-based Li-O₂ battery could continuously work beyond 200 cycles, superior to a cell with a Li-Cu anode. These results in this work provide a novel way for construction of the advanced Li-based anodes and the corresponding high-performance Li-O₂ batteries.

Advances in the Emerging Gradient Designs of Li Metal Hosts

Developing host has been recognized a potential countermeasure to circumvent the intrinsic drawbacks of Li metal anode (LMA), such as uncontrolled dendrite growth, unstable solid electrolyte interface, and infinite volume fluctuations. To realize proper Li accommodation, particularly bottom-up deposition of Li metal, gradient designs of host materials including lithiophilicity and/or conductivity have attracted a great deal of attention in recent years. However, a critical and specialized review on this quickly evolving topic is still absent. In this review, we attempt to comprehensively summarize and update the related advances in guiding Li nucleation and deposition. First, the fundamentals regarding Li deposition are discussed, with particular attention to the gradient design principles of host materials. Correspondingly, the progress of creating different gradients in terms of lithiophilicity, conductivity, and their hybrid is systematically reviewed. Finally, future challenges and perspective on the gradient design of advanced hosts towards practical LMAs are provided, which would provide a useful guidance for future studies.

Designing Anion-Derived Solid Electrolyte Interphase in a Siloxane-Based Electrolyte for Lithium-Metal Batteries

The rational electrolyte design with weak solvation is regarded as an effective way to regulate the electrolyte/electrode interface (SEI) that profoundly affects the performance of Li-metal batteries. Herein, we propose a newly developed siloxane-based weakly solvating electrolyte (SiBE) with contact ion pairs (CIPs) or aggregates (AGGs) dominating the solution structure, which enables the dendrite-free Li deposition and long cycle stability of Li-metal batteries. By altering the combination of Li salts, the SiBE leads to the formation of an inorganic anion-derived solid electrolyte interphase, which is highly stable and Li⁺-conductive. Based on SiBE, the Li||LiFePO₄ (LFP) full cell can stably cycle for 1000 cycles at a 2C rate with a capacity retention of 76.9%. Even with a limited Li-metal anode, it can maintain a capacity retention of 80% after 110 cycles with a high average Coulombic efficiency of 99.8%. This work reveals that siloxane can be a promising solvent to obtain weakly solvating electrolytes, which opens a new avenue for SEI composition regulation of Li-metal batteries.

Thermally Conductive AlN-Network Shield for Separators to Achieve Dendrite-Free Plating and Fast Li-Ion Transport toward Durable and High-Rate Lithium-Metal Anodes

Lithium-metal anodes suffer from inadequate rate and cycling performances for practical application mainly due to the harmful dendrite growth, especially at high currents. Herein a facile construction of the porous and robust network with thermally conductive AlN nanowires onto the commercial polypropylene separator by convenient vacuum filtration is reported. The so-constructed AlN-network shield provides a uniform thermal distribution to realize homogeneous Li deposition, super electrolyte-philic channels to enhance Li-ion transport, and also a physical barrier to resist dendrite piercing as the last fence. Consequently, the symmetric Li|Li cell presents an ultralong lifetime over 8000 h (20 mA cm^-2 , 3 mAh cm^-2 ) and over 1000 h even at an unprecedented high rate (80 mA cm^-2 , 80 mAh cm^-2 ), which is far surpassing the corresponding performances reported to date. The corresponding Li|LiFePO₄ cell delivers a high specific capacity of 84.3 mAh g^-1 at 10 C. This study demonstrates an efficient approach with great application potential toward durable and high-power Li-metal batteries and even beyond.

Lithiophilic Carbon Nanofiber/Graphene Nanosheet Composite Scaffold Prepared by a Scalable and Controllable Biofabrication Method for Ultrastable Dendrite-Free Lithium-Metal Anodes

Li metal is regarded as a promising anode for high-energy-density Li batteries, while the limited cycle life and fast capacity decay caused by notorious Li dendrite growth seriously impedes its application. Herein, a robust and highly lithiophilic bacterial cellulose-derived carbon nanofiber@reduced graphene oxide nanosheet (BC-CNF@rGO) composite scaffold is fabricated as a host for dendrite-free Li metal anode through an in situ biofabrication method. The abundant lithiophilic functional groups, conductive 3D network, and excellent mechanical property can effectively regulate uniform Li nucleation and deposition, enable fast reaction kinetics, and alleviate volume change. As a result, the BC-CNF@rGO skeleton achieves exceptional Li plating/stripping performance with a high average Coulombic efficiency of 98.3% over 800 cycles, and a long cycle life span of 5000 h at 2 mA cm^-2 @1 mAh cm^-2 with a low overpotential of ≈15 mV for lithium plating. Furthermore, full cells coupling BC-CNF@rGO-Li anode with LiFePO₄ cathode achieves an unprecedented cycling stability with a long cycle life of 3000 cycles at 1 C. This work sheds light on a promising material design and fabrication strategy for realizing high performance Li metal batteries.

In Situ Construction of Aramid Nanofiber Membrane on Li Anode as Artificial SEI Layer Achieving Ultra-High Stability

Achieving uniform Li deposition is vital for the construction of a safe but also efficient Li-metal anode for Li-metal batteries (LMBs). Herein, a facile coating strategy is used for forming an ultra-thin aramid nanofiber (ANF) membrane, with a network structure, on a Li anode (ANF-Li) as an artificial layer inhibiting Li dendrite's growth. The results show that under an ultra-high current density of 50 mA cm^-2 , the ANF-Li|ANF-Li symmetric cells can be kept stably cycled for a period exceeding 300 h. The ANF-Li|LiFePO₄ full cells exhibit a high-capacity retention of 80.1% after 1200 cycles at 1 C, showing a promising potential for LMBs application. Combined experimental results with theoretical calculations, the excellent performance of the ANF-Li anode is explored. Lithiophilic polar functional groups (CO, NH) appear in the surface and structure of ANF membrane, which offer high-concentration functional sites for the Li ions to realize an effective adhesion at the molecular level. This work also finds fiber-shaped lithium deposition for the first time. Furthermore, the nanoscale porosity of the ANF membrane not only provides fast pathways and channels for the diffusion of the electrolyte and Li transportation, but also eliminates the "weak links" of micron-scale Li dendrites penetrating the membrane.

An aqueous polyethylene oxide-based solid-state electrolyte with high voltage stability for dendrite-free lithium deposition via a self-healing electrostatic shield

Lithium metal batteries (LMBs) have attracted extensive attention for their ultrahigh energy density. However, the uncontrollable growth of Li-dendrites results in poor cyclability and potential safety risks, thus preventing their practical application. Herein, a flexible and cost-effective aqueous polyethylene oxide (PEO)-based solid-state electrolyte is prepared, which enables uniform and dendrite-free Li deposition by introducing Cs⁺ with an electrostatic shielding mechanism at high current densities. The self-assembly of PEO and bacterial cellulose by hydrogen bonding reduces the crystallinity of PEO and increases uniformly the distribution of lithium ions. With excellent flexibility and thermal stability, such a 3D polymer solid-state electrolyte exhibits an enhanced electrochemical stability window of 5.8 V versus Li/Li⁺ potential and a high ionic conductivity of 1.28 × 10^-4 S cm^-1 at 60 °C. The Li|BC-PEO-Cs⁺|Li symmetric cells operate stably for more than 1000 h. Furthermore, Li|BC-PEO-Cs⁺|LiFePO₄ (LFP) cells show remarkable enhancement in capacity (163.4 mA h g^-1 at 0.1 C), cycling stability (with a capacity retention of 96% after 500 cycles at 1 C) and high functionality and safety (withstanding folding and cutting) in practical applications.

Amidinothiourea as a new deposition-regulating additive for dendrite-free lithium metal anodes

Lithium (Li) dendrite growth seriously hinders the practical application of Li metal batteries. Here, we report molecular amidinothiourea (ATU) as a new electrolyte additive to regulate Li stripping/plating behaviors of Li metal anodes. The molecular ATU in the electrolyte can act as a shielding layer on the Li metal surface to suppress the decomposition of electrolytes as verified by XPS and adsorption energy calculation, which improves the electrochemical reversibility of the Li plating/stripping behaviors and inhibits lithium dendrite growth.

In situ surface-enhanced Raman spectroelectrochemistry reveals the molecular conformation of electrolyte additives in Li-ion batteries

We report the mechanism of rhodamine B (RhB) acting as an electrolyte additive in Li/graphite cells. We show that the cycle performance and rate capability of graphite are enhanced in carbonate-based electrolytes containing 0.2 wt% RhB. By using silica-encapsulated Au nanoparticles, in situ surface-enhanced Raman spectroscopy (SERS) is applied to study the graphite/electrolyte interface. We find that the adsorption orientation of RhB molecules on the surface of graphite can be modulated by the applied potential: vertical adsorption at higher potentials while horizontal adsorption takes place at lower potentials. This behavior effectively suppresses the electrolyte solvent decomposition, as well as electrode corrosion while improving the Li⁺ diffusion. This work shows that SERS is a powerful tool for interfacial analysis of battery systems and provides new ideas for rational design of electrolyte additives.

Confronting the Challenges in Lithium Anodes for Lithium Metal Batteries

With the low redox potential of -3.04 V (vs SHE) and ultrahigh theoretical capacity of 3862 mAh g-1 , lithium metal has been considered as promising anode material. However, lithium metal battery has ever suffered a trough in the past few decades due to its safety issues. Over the years, the limited energy density of the lithium-ion battery cannot meet the growing demands of the advanced energy storage devices. Therefore, lithium metal anodes receive renewed attention, which have the potential to achieve high-energy batteries. In this review, the history of the lithium anode is reviewed first. Then the failure mechanism of the lithium anode is analyzed, including dendrite, dead lithium, corrosion, and volume expansion of the lithium anode. Further, the strategies to alleviate the lithium anode issues in recent years are discussed emphatically. Eventually, remaining challenges of these strategies and possible research directions of lithium-anode modification are presented to inspire innovation of lithium anode.

Cobalt-Phthalocyanine-Derived Molecular Isolation Layer for Highly Stable Lithium Anode

The uneven consumption of anions during the lithium (Li) deposition process triggers a space charge effect that generates Li dendrites, seriously hindering the practical application of Li-metal batteries. We report on a cobalt phthalocyanine electrolyte additive with a planar molecular structure, which can be tightly adsorbed on the Li anode surface to form a dense molecular layer. Such a planar molecular layer cannot only complex with Li ions to reduce the space charge effect, but also suppress side reactions between the anode and the electrolyte, producing a stable solid electrolyte interphase composed of amorphous lithium fluoride (LiF) and lithium carbonate (LiCO₃ ), as verified by X-ray absorption near-edge spectroscopy. As a result, the Li|Li symmetric cell exhibits excellent cycling stability above 700 h under a high plating capacity of 3 mAh cm^-2 . Moreover, the assembled Li|lithium iron phosphate (LiFePO₄ , LFP) full-cell can also deliver excellent cycling over 200 cycles under lean electrolyte conditions (3 μL mg^-1 ).

Simultaneous Regulation on Solvation Shell and Electrode Interface for Dendrite-Free Zn Ion Batteries Achieved by a Low-Cost Glucose Additive

Dendrite growth and by-products in Zn metal aqueous batteries have impeded their development as promising energy storage devices. We utilize a low-cost additive, glucose, to modulate the typical ZnSO₄ electrolyte system for improving reversible plating/stripping on Zn anode for high-performance Zn ion batteries (ZIBs). Combing experimental characterizations and theoretical calculations, we show that the glucose in ZnSO₄ aqueous environment can simultaneously modulate solvation structure of Zn²⁺ and Zn anode-electrolyte interface. The electrolyte engineering can alternate one H₂ O molecule from the primary Zn²⁺ -6H₂ O solvation shell and restraining side reactions due to the decomposition of active water. Concomitantly, glucose molecules are inclined to absorb on the surface of Zn anode, suppressing the random growth of Zn dendrite. As a proof of concept, a symmetric cell and Zn-MnO₂ full cell with glucose electrolyte achieve boosted stability than that with pure ZnSO₄ electrolyte.

Stable Lithium-Carbon Composite Enabled by Dual-Salt Additives

Lithium metal is regarded as the ultimate negative electrode material for secondary batteries due to its high energy density. However, it suffers from poor cycling stability because of its high reactivity with liquid electrolytes. Therefore, continuous efforts have been put into improving the cycling Coulombic efficiency (CE) to extend the lifespan of the lithium metal negative electrode. Herein, we report that using dual-salt additives of LiPF₆ and LiNO₃ in an ether solvent-based electrolyte can significantly improve the cycling stability and rate capability of a Li-carbon (Li-CNT) composite. As a result, an average cycling CE as high as 99.30% was obtained for the Li-CNT at a current density of 2.5 mA cm^-2 and an negative electrode to positive electrode capacity (N/P) ratio of 2. The cycling stability and rate capability enhancement of the Li-CNT negative electrode could be attributed to the formation of a better solid electrolyte interphase layer that contains both inorganic components and organic polyether. The former component mainly originates from the decomposition of the LiNO₃ additive, while the latter comes from the LiPF₆-induced ring-opening polymerization of the ether solvent. This novel surface chemistry significantly improves the CE of Li negative electrode, revealing its importance for the practical application of lithium metal batteries.

A Fishing-Net-Like 3D Host for Robust and Ultrahigh-Rate Lithium Metal Anodes

Constructing an architectural host is demonstrated to be an effective strategy for long-life lithium metal anodes (LMAs). Herein, an integrated 3D host for stable and ultrahigh-rate LMAs is developed by a binary highly conductive network of 2D reduced graphene oxide (rGO) and 1D carbon nanofibers (CNF) anchored with 0D ultrasmall MgZnO nanoparticles (MgZnO/CNF-rGO). A facile net-fishing strategy is proposed to combine the rGO nanosheets with free-standing CNF matrix as interconnected paths for fast electron transport. Notably, serving as Li nucleation sites, the superlithiophilic MgZnO nanoparticles are uniformly distributed and tightly contacted with the conductive matrix without agglomeration due to the rGO confinement. Such a delicate nanoscale combination guarantees the effective transportation and uniform deposition of Li-ions in the inner surface of the host. The symmetric cell of Li@MgZnO/CNF-rGO exhibits a long lifespan above 1450 cycles under an ultrahigh current density of 50 mA cm^-2 with an areal capacity of 1.0 mAh cm^-2 . Impressively, it also delivers a high reversible capacity of 10 mAh cm^-2 at 50 mA cm^-2 . This work offers an avenue to promise the prospect for practical LMAs working under high rates and capacities.

Polycationic Polymer Layer for Air-Stable and Dendrite-Free Li Metal Anodes in Carbonate Electrolytes

The short cycle life and safety concerns caused by uncontrollable dendrite growth have severely hindered the commercialization of lithium metal batteries. Here, a polycationic and hydrophobic polymer protective layer fabricated by a scalable tape-casting method is developed to enable air-stable, dendrite-free, and highly efficient Li metal anodes. The polymeric cations of poly(diallyl dimethyl ammonium) (PDDA) provide an electrostatic shielding effect that unifies Li⁺ flux at the surface of the Li anode and promotes a homogeneous Li plating, while the bis(trifluoromethanesulfonyl)imide (TFSI) anions bring hydrophobic characteristics and improve moisture stability. The accumulated TFSI anions by the polycationic film also facilitate the formation of a stable solid electrolyte interphase (SEI). Steady Li plating/stripping in the carbonate electrolyte can be achieved under a high areal capacity of 10 mAh cm^-2 for 700 h with Li utilization efficiency up to 51.6%. LiNi_0.8 Mn_0.1 Co_0.1 O₂ and LiFePO₄ cells using the modified anode exhibit much improved electrochemical performance compared with the bare Li counterpart. Moreover, ultrasonic imaging shows no gas generation in the modified Li/LiFePO₄ pouch cell. Mechanism investigation demonstrates the stable SEI and homogeneous Li deposition derived by the polycationic layer.

Controlled Growth of Li Dendrite Induced by Periodic Ni Mesh for Ultrastable Lithium Metal Battery

The disordered dendritic growth of Li metal seriously hampers the practical application of lithium metal batteries. Great efforts are devoted to suppress the growth of dendrites, it is still necessary to explore measures of controlling dendritic growth and pave ways for normal cell operation in presence of dendrites. Herein, a modification technique of Li metal anode by a periodic Ni mesh with micrometer-sized grid is proposed for interfacial engineering. Periodic patterned Ni mesh is prepared using a novel laser direct-writing technique combined with selective electrodeposition process. The growth of Li dendrites is regulated under the effect of unique electric field distribution by the introduction of the Ni mesh. It is noteworthy that the controlled lateral growth of dendrites is successfully realized by the internal structure modification instead of any external electric or magnetic field as has been previously reported. The resultant anode exhibits a stable cycling performance with ultralow overpotential of 6-8 mV for over 1000 h at the current density of 0.5 mA cm^-2 . It also presents superior electrochemical performance when assembled against LiFePO₄ cathode into full cells, with an initial capacity of 133 mA h g^-1 and a stable cycling performance over 160 cycles.

Recent advances in research on anodes for safe and efficient lithium-metal batteries

The revival of lithium metal anodes (LMAs) makes it a potent influence on the battery research community in the recent years after the popularity of Li-ion batteries with graphite anodes. The main reason is due to the over ten-fold increase in the capacity of LMAs when compared with that obtained when using graphite, as well as the low redox potential of Li/Li⁺. However, the full potential of LMAs is heavily inhibited by several factors, such as dendrite growth, pulverization, side reactions, and volume changes. These adversities lower the cell's Coulombic efficiency dramatically if operated without massively excessive Li usage. In this review, we first introduce some of the most significant progresses made in the understandings of the charging/discharging processes at the anode. The importance of combining advanced characterization techniques with classical methods is highlighted. In particular, we aim to explore the hidden links between those studies for obtaining deeper insights. Two main categories of solutions to address common problems, namely, lithium-electrolyte interfacial engineering and three-dimensional hosting of Li, are subsequently illustrated, where each subsection takes a different methodological perspective to demonstrate the relevant state-of-the-art studies. Some interesting approaches to stop dendrites and a brief note on the practical aspects of lithium-metal batteries are provided, too. This review concludes with our essential discoveries from the current literature and valuable suggestions for future LMA research.

Porous BN Nanofibers Enable Long-Cycling Life Sodium Metal Batteries

Sodium metal anode, featuring high capacity, low voltage and earth abundance, is desirable for building advanced sodium-metal batteries. However, Na-ion deposition typically leads to morphological instability and notorious chemical reactivity between sodium and common electrolytes still limit its practical application. In this study, a porous BN nanofibers modified sodium metal (BN/Na) electrode is introduced for enhancing Na-ion deposition dynamics and stability. As a result, symmetrical BN/Na cells enable an impressive rate capability and markedly enhanced cycling durability over 600 h at 10 mA cm^-2 . Density functional theory simulations demonstrate BN could effectively improve Na-ion adsorption and diffusion kinetics simultaneously. Finite element simulation clearly reveals the intrinsic smoothing effect of BN upon multiple Na-ion plating/stripping cycles. Coupled with a Na₃ V₂ O₂ (PO₄ )₂ F/Ti₃ C₂ X cathode, sodium metal full cells offer an ultrastable capacity of 125/63 mA h g^-1 (≈420/240 Wh kg^-1 ) at 0.05/5 C rate over 500 cycles. These comprehensive analyses demonstrate the feasibility of BN/Na anode for the establishment of high-energy-density sodium-metal full batteries.

An asymmetric quasi-solid electrolyte for high-performance Li metal batteries

We propose an asymmetric quasi-solid electrolyte to regulate Li deposition and avoid Li dendrite formation. The thiourea in the electrolyte can absorb on the Li surface to induce Li deposition, change the propagative growth behavior of Li metal and eliminate dendritic formation, thereby ensuring excellent cycling stability and high specific capacity.

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.

Towards practical lithium-metal anodes

Lithium-ion batteries have had a tremendous impact on several sectors of our society; however, the intrinsic limitations of Li-ion chemistry limits their ability to meet the increasing demands of developing more advanced portable electronics, electric vehicles, and grid-scale energy storage systems. Therefore, battery chemistries beyond Li ions are being intensively investigated and need urgent breakthroughs toward commercial applications, wherein the use of metallic Li is one of the most intuitive choices. Despite several decades of oblivion due to safety concerns regarding the growth of Li dendrites, Li-metal anodes are now poised to be revived because of the advances in investigative tools and globally invested efforts. In this review, we first summarize the existing issues with regard to Li anodes and their underlying reasons and then highlight the recent progress made in the development of high-performance Li anodes. Finally, we propose the persisting challenges and opportunities toward the exploration of practical Li-metal anodes.