An Armored Mixed Conductor Interphase on a Dendrite-Free Lithium-Metal Anode

Copper Nitride Nanowires Printed Li with Stable Cycling for Li Metal Batteries in Carbonate Electrolytes

The practical implementation of the lithium metal anode is hindered by obstacles such as Li dendrite growth, large volume changes, and poor lifespan. Here, copper nitride nanowires (Cu₃ N NWs) printed Li by a facile and low-cost roll-press method is reported, to operate in carbonate electrolytes for high-voltage cathode materials. Through one-step roll pressing, Cu₃ N NWs can be conformally printed onto the Li metal surface, and form a Li₃ N@Cu NWs layer on the Li metal. The Li₃ N@Cu NWs layer can assist homogeneous Li-ion flux with the 3D channel structure, as well as the high Li-ion conductivity of the Li₃ N. With those beneficial effects, the Li₃ N@Cu NWs layer can guide Li to deposit into a dense and planar structure without Li-dendrite growth. Li metal with Li₃ N@Cu NWs protection layer exhibits outstanding cycling performances even at a high current density of 5.0 mA cm^-2 with low overpotentials in Li symmetric cells. Furthermore, the stable cyclability and improved rate capability can be realized in a full cell using LiCoO₂ over 300 cycles. When decoupling the irreversible reactions of the cathode using Li₄ T_i5 O₁₂ , stable cycling performance over 1000 cycles can be achieved at a practical current density of ≈2 mA cm^-2 .

Fluorinated hybrid solid-electrolyte-interphase for dendrite-free lithium deposition

Lithium metal anodes have attracted extensive attention owing to their high theoretical specific capacity. However, the notorious reactivity of lithium prevents their practical applications, as evidenced by the undesired lithium dendrite growth and unstable solid electrolyte interphase formation. Here, we develop a facile, cost-effective and one-step approach to create an artificial lithium metal/electrolyte interphase by treating the lithium anode with a tin-containing electrolyte. As a result, an artificial solid electrolyte interphase composed of lithium fluoride, tin, and the tin-lithium alloy is formed, which not only ensures fast lithium-ion diffusion and suppresses lithium dendrite growth but also brings a synergistic effect of storing lithium via a reversible tin-lithium alloy formation and enabling lithium plating underneath it. With such an artificial solid electrolyte interphase, lithium symmetrical cells show outstanding plating/stripping cycles, and the full cell exhibits remarkably better cycling stability and capacity retention as well as capacity utilization at high rates compared to bare lithium.

Here the authors report a simple method to create a solid electrolyte interphase that is tightly anchored onto the surface of lithium metal anode. This artificial structure suppresses dead and dendrite Li and stores Li via formation of alloys, enabling impressive battery performance.

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.

Emerging interfacial chemistry of graphite anodes in lithium-ion batteries

Emerging interfacial chemistry of the graphite anode in today's lithium-ion batteries paves the way to next-generation, high-performance energy storage devices.

Developing high safety Li-metal anodes for future high-energy Li-metal batteries: strategies and perspectives

Developing high-safety Li-metal anodes (LMAs) are extremely important for the application of high-energy Li-metal batteries. The recently state-of-the-art technologies, strategies and perspectives for developing LMAs are comprehensively summarized in this review.

Conducting and Lithiophilic MXene/Graphene Framework for High-Capacity, Dendrite-Free Lithium-Metal Anodes

Li-metal anode is widely acknowledged as the ideal anode for high-energy-density batteries, but seriously hindered by the uncontrollable dendrite growth and infinite volume change. Toward this goal, suitable stable scaffolds for dendrite-free Li anodes with large current density (>5 mA cm^-2) and high Li loading (>90%) are highly in demand. Herein, a conductive and lithiophilic three-dimensional (3D) MXene/graphene (MG) framework is demonstrated for a dendrite-free Li-metal anode. Benefiting from its high surface area (259 m² g^-1) and lightweight nature with uniformly dispersed lithiophilic MXene nanosheets as Li nucleation sites, the as-formed 3D MG scaffold showcases an ultrahigh Li content (∼92% of the theoretical capacity), as well as strong capabilities in suppressing the Li-dendrite formation and accommodating the volume changes. Consequently, the MG-based electrode exhibits high Coulombic efficiencies (∼99%) with a record lifespan up to 2700 h and is stable for 230 cycles at an ultrahigh current density of 20 mA cm^-2. When coupled with Li₄Ti₅O₁₂ or sulfur, the MG-Li/Li₄Ti₅O₁₂ full-cell offers an enhanced capacity of 142 mAh g^-1 after 450 cycles, while the MG-Li/sulfur cell delivers an improved rate performance, implying the great potential of this 3D MG framework for building long-lifetime, high-energy-density batteries.

Self-Stabilized and Strongly Adhesive Supramolecular Polymer Protective Layer Enables Ultrahigh-Rate and Large-Capacity Lithium-Metal Anode

Constructing a solid electrolyte interface (SEI) is a highly effective approach to overcome the poor reversibility of lithium (Li) metal anodes. Herein, an adhesive and self-healable supramolecular copolymer, comprising of pendant poly(ethylene oxide) (PEO) segments and ureido-pyrimidinone (UPy) quadruple-hydrogen-bonding moieties, is developed as a protection layer of Li anode by a simple drop-coating. The protection performance of in-situ-formed LiPEO-UPy SEI layer is significantly enhanced owing to the strong binding and improved stability arising from a spontaneous reaction between UPy groups and Li metal. An ultrathin (approximately 70 nm) LiPEO-UPy layer can contribute to stable and dendrite-free cycling at a high areal capacity of 10 mAh cm^-2 at 5 mA cm^-2 for 1000 h. This coating together with the promising electrochemical performance offers a new strategy for the development of dendrite-free metal anodes.

Nonflammable and High-Voltage-Tolerated Polymer Electrolyte Achieving High Stability and Safety in 4.9 V-Class Lithium Metal Battery

High-voltage polymer electrolytes play important roles in achieving high-energy-density polymer electrolyte-based batteries, but the pace of progress moves slowly, since oxidation-resistant polymer electrolytes at high voltages are rarely obtained. Herein, we reported a nonflammable and high-voltage-tolerated polymer electrolyte (HVTPE) with extended voltage of 5.5 V. The obtained HVTPE has lower HOMO energy indicating a higher antioxidation ability, which avoids the decomposition and depletion of electrolyte near the cathode. Significantly, the HVTPE-based 4.45 V-class LiCoO₂ battery delivered a high capacity of 173.2 mA h g^-1 at 0.05 C. Using 4.9 V-class LiNi_0.5Mn_1.5O₄ as a cathode, the battery exhibited stable cycling performance. Moreover, HVTPE showed a high modulus of 2.3 GPa, which can efficiently restrain the penetration of Li dendrites, and desirable nonflammable feature, leading to the enhanced safety based on polymer electrolytes. The current work opens new avenues to realize high-voltage polymer electrolyte-based batteries with high safety.

Tuning Solid Electrolyte Interphase Layer Properties through the Integration of Conversion Reaction

The solid electrolyte interphase (SEI) layer plays an important role in altering the ion transport and modifying the structural evolution of the Li metal anode during repeated cycling. While the fundamental understanding of the SEI properties has been continuously advanced in recent years, effectively tuning the SEI components, especially the inorganic constituents, is still challenging. In this work, tungsten trioxide, WO₃, is found to promote the formation of inorganic salts, for example, LiF/Li₂CO₃ in SEI layers, thereby enhancing the SEI properties such as mechanical and chemical stabilities. Additionally, WO₃ is simultaneously reduced to electronic W nanoparticles during the electrochemical process, mitigating the formation of "dead" Li, which otherwise is completely wrapped by the accumulated insulating SEI layers. The possibility of WO₃ in catalyzing electrolyte decomposition, through favored reaction pathway, to produce robust SEI layers is discussed. This work provides new insights into the control of the SEI properties on Li metal surfaces.

Zinc anode-compatible in-situ solid electrolyte interphase via cation solvation modulation

The surface chemistry of solid electrolyte interphase is one of the critical factors that govern the cycling life of rechargeable batteries. However, this chemistry is less explored for zinc anodes, owing to their relatively high redox potential and limited choices in electrolyte. Here, we report the observation of a zinc fluoride-rich organic/inorganic hybrid solid electrolyte interphase on zinc anode, based on an acetamide-Zn(TFSI)₂ eutectic electrolyte. A combination of experimental and modeling investigations reveals that the presence of anion-complexing zinc species with markedly lowered decomposition energies contributes to the in situ formation of an interphase. The as-protected anode enables reversible (~100% Coulombic efficiency) and dendrite-free zinc plating/stripping even at high areal capacities (>2.5 mAh cm^‒2), endowed by the fast ion migration coupled with high mechanical strength of the protective interphase. With this interphasial design the assembled zinc batteries exhibit excellent cycling stability with negligible capacity loss at both low and high rates.

Zinc chemistry is not favourable to the formation of a solid electrolyte interphase as a result of its high redox potential. In a break with the traditional wisdom, the present authors realise ZnF₂-rich hybrid SEI on Zn anode via the modulation of cationic speciation in a eutectic electrolyte.

A fluorinated alloy-type interfacial layer enabled by metal fluoride nanoparticle modification for stabilizing Li metal anodes

Using highly dispersed metal fluoride nanoparticles to construct a uniform fluorinated alloy type interfacial layer on the surface of Li metal anodes is realized by an ex situ solution chemical modification method. The fluorinated alloy-type interfacial layer can effectively inhibit the growth of undesirable Li dendrites while enhancing the performance of Li metal anodes.

Constructing Ionic Gradient and Lithiophilic Interphase for High-Rate Li-Metal Anode

Li metal is the optimal choice as an anode due to its high theoretical capacity, but it suffers from severe dendrite growth, especially at high current rates. Here, an ionic gradient and lithiophilic inter-phase film is developed, which promises to produce a durable and high-rate Li-metal anode. The film, containing an ionic-conductive Li_0.33 La_0.56 TiO₃ nanofiber (NF) layer on the top and a thin lithiophilic Al₂ O₃ NF layer on the bottom, is fabricated with a sol-gel electrospinning method followed by sintering. During cycling, the top layer forms a spatially homogenous ionic field distribution over the anode, while the bottom layer reduces the driving force of Li-dendrite formation by decreasing the nucleation barrier, enabling dendrite-free plating-stripping behavior over 1000 h at a high current density of 5 mA cm^-2 . Remarkably, full cells of Li//LiNi_0.8 Co_0.15 Al_0.05 O₂ exhibit a high capacity of 133.3 mA h g^-1 at 5 C over 150 cycles, contributing a step forward for high-rate Li-metal anodes.

A 3D Lithiophilic Mo2 N-Modified Carbon Nanofiber Architecture for Dendrite-Free Lithium-Metal Anodes in a Full Cell

The pursuit for high-energy-density batteries has inspired the resurgence of metallic lithium (Li) as a promising anode, yet its practical viability is restricted by the uncontrollable Li dendrite growth and huge volume changes during repeated cycling. Herein, a new 3D framework configured with Mo₂ N-mofidied carbon nanofiber (CNF) architecture is established as a Li host via a facile fabrication method. The lithiophilic Mo₂ N acts as a homogeneously pre-planted seed with ultralow Li nucleation overpotential, thus spatially guiding a uniform Li nucleation and deposition in the matrix. The conductive CNF skeleton effectively homogenizes the current distribution and Li-ion flux, further suppressing Li-dendrite formation. As a result, the 3D hybrid Mo₂ N@CNF structure facilitates a dendrite-free morphology with greatly alleviated volume expansion, delivering a significantly improved Coulombic efficiency of ≈99.2% over 150 cycles at 4 mA cm^-2 . Symmetric cells with Mo₂ N@CNF substrates stably operate over 1500 h at 6 mA cm^-2 for 6 mA h cm^-2 . Furthermore, full cells paired with LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NMC811) cathodes in conventional carbonate electrolytes achieve a remarkable capacity retention of 90% over 150 cycles. This work sheds new light on the facile design of 3D lithiophilic hosts for dendrite-free lithium-metal anodes.

Lithium Metal Anode Materials Design: Interphase and Host

Abstract

Li metal is the ultimate anode choice due to its highest theoretical capacity and lowest electrode potential, but it is far from practical applications with its poor cycle lifetime. Recent research progresses show that materials designs of interphase and host structures for Li metal are two effective ways addressing the key issues of Li metal anodes. Despite the exciting improvement on Li metal cycling capability, problems still exist with these methodologies, such as the deficient long-time cycling stability of interphase materials and the accelerated Li corrosion for high surface area three-dimensional composite Li anodes. As a result, Coulombic efficiency of Li metal is still not sufficient for full-cell cycling. In the near future, an interphase protected three-dimensional composite Li metal anode, combined with high performance novel electrolytes might be the ultimate solution. Besides, nanoscale characterization technologies are also vital for guiding future Li metal anode designs.

Graphic Abstract

Early Lithium Plating Behavior in Confined Nanospace of 3D Lithiophilic Carbon Matrix for Stable Solid-State Lithium Metal Batteries

Considerable efforts are devoted to relieve the critical lithium dendritic and volume change problems in the lithium metal anode. Constructing uniform Li⁺ distribution and lithium "host" are shown to be the most promising strategies to drive practical lithium metal anode development. Herein, a uniform Li nucleation/growth behavior in a confined nanospace is verified by constructing vertical graphene on a 3D commercial copper mesh. The difference of solid-electrolyte interphase (SEI) composition and lithium growth behavior in the confined nanospace is further demonstrated by in-depth X-ray photoelectron spectrometer (XPS) and line-scan energy dispersive X-ray spectroscopic (EDS) methods. As a result, a high Columbic efficiency of 97% beyond 250 cycles at a current density of 2 mA cm^-2 and a prolonged lifespan of symmetrical cell (500 cycles at 5 mA cm^-2 ) can be easily achieved. More meaningfully, the solid-state lithium metal cell paired with the composite lithium anode and LiNi_0.5 Co_0.2 Mn_0.3 O₂ (NCM) as the cathode also demonstrate reduced polarization and extended cycle. The present confined nanospace-derived hybrid anode can further promote the development of future all solid-state lithium metal batteries.

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

Uncontrollable Li dendrite growth and low Coulombic efficiency severely hinder the application of lithium metal batteries. Although a lot of approaches have been developed to control Li deposition, most of them are based on inhibiting lithium deposition on protrusions, which can suppress Li dendrite growth at low current density, but is inefficient for practical battery applications, with high current density and large area capacity. Here, a novel leveling mechanism based on accelerating Li growth in concave fashion is proposed, which enables uniform and dendrite-free Li plating by simply adding thiourea into the electrolyte. The small thiourea molecules can be absorbed on the Li metal surface and promote Li growth with a superfilling effect. With 0.02 m thiourea added in the electrolyte, Li | Li symmetrical cells can be cycled over 1000 cycles at 5.0 mA cm^-2 , and a full cell with LiFePO₄ | Li configuration can even maintain 90% capacity after 650 cycles at 5.0 C. The superfilling effect is also verified by computational chemistry and numerical simulation, and can be expanded to a series of small chemicals using as electrolyte additives. It offers a new avenue to dendrite-free lithium deposition and may also be expanded to other battery chemistries.

Electrochemical Diagram of an Ultrathin Lithium Metal Anode in Pouch Cells

Lithium (Li) metal is regarded as a "Holy Grail" electrode for next-generation high-energy-density batteries. However, the electrochemical behavior of the Li anode under a practical working state is poorly understood, leading to a gap in the design strategy and the aim of efficient Li anodes. The electrochemical diagram to reveal failure mechanisms of ultrathin Li in pouch cells is demonstrated. The working mode of the Li metal anode ranging from 1.0 mA cm^-2 /1.0 mAh cm^-2 (28.0 mA/28.0 mAh) to 10.0 mA cm^-2 /10.0 mAh cm^-2 (280.0 mA/280.0 mAh) is investigated and divided into three categories: polarization, transition, and short-circuit zones. Powdering and the induced polarization are the main reasons for the failure of the Li electrode at small current density and capacity, while short-circuit occurs with the damage of the separator leading to safety concerns being dominant at large current and capacity. The electrochemical diagram is attributed from the distinctive plating/stripping behaviors of Li metal, accompanied by dendrites thickening and/or lengthening, and heterogeneous distribution of dendrites. A clear understanding in the electrochemical diagram of ultrathin Li is the primary step to rationally design an effective Li electrode and render a Li metal battery with high energy density, long lifespan, and enhanced safety.

Key Aspects of Lithium Metal Anodes for Lithium Metal Batteries

Rechargeable batteries are considered promising replacements for environmentally hazardous fossil fuel-based energy technologies. High-energy lithium-metal batteries have received tremendous attention for use in portable electronic devices and electric vehicles. However, the low Coulombic efficiency, short life cycle, huge volume expansion, uncontrolled dendrite growth, and endless interfacial reactions of the metallic lithium anode are major obstacles in their commercialization. Extensive research efforts have been devoted to address these issues and significant progress has been made by tuning electrolyte chemistry, designing electrode frameworks, discovering nanotechnology-based solutions, etc. This Review aims to provide a conceptual understanding of the current issues involved in using a lithium metal anode and to unveil its electrochemistry. The most recent advancements in lithium metal battery technology are outlined and suggestions for future research to develop a safe and stable lithium anode are presented.

Rational design of spontaneous reactions for protecting porous lithium electrodes in lithium-sulfur batteries

A rechargeable lithium anode requires a porous structure for a high capacity, and a stable electrode/electrolyte interface against dendrite formation and polysulfide crossover when used in a lithium-sulfur battery. Here, we design two simple steps of spontaneous reactions for protecting porous lithium electrodes. First, a reaction between molten lithium and sulfur-impregnated carbon nanofiber forms a fibrous network with a lithium shell and a carbon core. Second, we coat the surface of this porous lithium electrode with a composite of lithium bismuth alloys and lithium fluoride through another spontaneous reaction between lithium and bismuth trifluoride, solvated with phosphorous pentasulfide, which also polymerizes with lithium sulfide residual in the electrode to form a solid electrolyte layer. This protected porous lithium electrode enables stable operation of a lithium-sulfur battery with a sulfur loading of 10.2 mg cm-2 at 6.0 mA cm-2 for 200 cycles.

Anchoring an Artificial Protective Layer To Stabilize Potassium Metal Anode in Rechargeable K-O2 Batteries

Rechargeable potassium batteries, including the potassium-oxygen (K-O₂) battery, are deemed as promising low-cost energy storage solutions. Nevertheless, the chemical stability of the K metal anode remains problematic and hinders their development. In the K-O₂ battery, the electrolyte and dissolved oxygen tend to be reduced on the K metal anode, which consumes the active material continuously. Herein, an artificial protective layer is engineered on the K metal anode via a one-step method to mitigate side reactions induced by the solvent and reactive oxygen species. The chemical reaction between K and SbF₃ leads to an inorganic composite layer that consists of KF, Sb, and KSb _xF _y on the surface. This in situ synthesized layer effectively prevents K anode corrosion while maintaining good K⁺ ionic conductivity in K-O₂ batteries. Protection from O₂ and moisture also ensures battery safety. Improved anode life span and cycling performance (>30 days) are further demonstrated. This work introduces a novel strategy to stabilize the K anode for rechargeable potassium metal batteries.

Additive-Assisted Novel Dual-Salt Electrolyte Addresses Wide Temperature Operation of Lithium-Metal Batteries

In this study, self-synthesized lithium trifluoro(perfluoro-tert-butyloxyl)borate (LiTFPFB) is combined with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to formulate a novel 1 m dual-salt electrolyte, which contains lithium difluorophosphate (LiPO₂ F₂ ) additive and dominant carbonate solvents with low melting point and high boiling point. The addition of LiPO₂ F₂ into this novel dual-salt electrolyte dramatically improves cycleability and rate capability of a LiNi_0.5 Mn_0.3 Co_0.2 O₂ /Li (NMC/Li) battery, ranging from -40 to 90 °C. The NMC/Li batteries adopt a Li-metal anode with low thickness of 100 µm (even 50 µm) and a moderately high cathode mass loading level of 10 mg cm^-2 . For the first time, this paper provides valuable perspectives for developing practical lithium-metal batteries over a wide temperature range.

Bulk Nanostructured Materials Design for Fracture-Resistant Lithium Metal Anodes

Li metal is an ideal anode for next-generation batteries because of its high theoretical capacity and low potential. However, the unevenly distributed stress in Li metal anodes (LMAs) induced by volume fluctuation may cause the electrode to fracture easily, especially during high-rate plating/stripping processes. Here fracture-resistant LMAs using the concept of bulk nanostructured materials are designed via a metallurgical process. In bulk nanostructured Li (BNL), ionic conducting phases exist at grain boundaries, which promote Li⁺ transport. The refined Li grain size and precipitation hardening in BNL enhances the mechanical strength and fatigue endurance, alleviating the unevenly distributed stress and preventing electrode pulverization. Density functional theory is used to investigate the binding energy between Li and various kinds of oxides and SiO₂ is found to be optimal additive among screened oxides. BNL has 91% of the theoretical capacity of Li metal. In full cells with BNL anode, LiFePO₄ could deliver capacity of 90 mAh g^-1 at 10C, an order of magnitude higher than that in full cells with Li foil anode. This strategy is expected to pave the way for fracture-resistant LMAs in high-rate cycling with maximum capacity.

Surface Restraint Synthesis of an Organic-Inorganic Hybrid Layer for Dendrite-Free Lithium Metal Anode

Li metal is considered to be the most attractive anode for next-generation batteries because of its high specific capacity and low reduction potential. However, uncontrolled Li dendrite growth and low Coulombic efficiency cause severe capacity decay and safety issues. Here we propose a LiCl contained inorganic-organic hybrid layer on Li metal surface by a surface restraint dehalogenation reaction, which is highly uniform and features lithiophilic property as well as high ionic conductivity that can inhibit Li dendrite growth effectively. Consequently, the surface protected Li metal electrodes enable Li | Li symmetric cells to maintain a stable and low overpotential of 20 mV at a current density of 1 mA cm^-2 after cycling over 3000 h, and enable Li | LiFePO₄ pouch cell to decay only 0.05% in capacity per cycle at 5.0 C for 500 cycles, indicating excellent cycle stability and high rate capability. This work offers a simple and facile method to protect Li metal anode and promise a potential direction for industrialization of Li metal batteries.

In Situ Solid Electrolyte Interphase from Spray Quenching on Molten Li: A New Way to Construct High-Performance Lithium-Metal Anodes

Uncontrollable growth of Li dendrites and low utilization of active Li severely hinder its practical application. Construction of an artificial solid electrolyte interphase (SEI) on Li is demonstrated as one of the most effective ways to circumvent the above problems. Herein, a novel spray quenching method is developed in situ to fabricate an organic-inorganic composite SEI on Li metal. By spray quenching molten Li in a modified ether-based solution, a homogeneous and dense SEI consisting of organic matrix embedded with inorganic LiF and Li₃ N nanocrystallines (denoted as OIFN) is constructed on Li metal. Arising from high ionic conductivity and strong mechanical stability, the OIFN can not only effectively minimize the corrosion reaction of Li, but also greatly suppresses the dendrite growth. Accordingly, the OIFN-Li anode presents prominent electrochemical performance with an enhanced Coulombic efficiency of 98.15% for 200 cycles and a small hysteresis of <450 mV even at ultrahigh current density up to 10 mA cm^-2 . More importantly, during the full cell test with limited Li source, a high utilization of Li up to 40.5% is achieved for the OIFN-Li anode. The work provides a brand-new route to fabricate advanced SEI on alkali metal for high-performance alkali-metal batteries.