Artificial Protection Film on Lithium Metal Anode toward Long-Cycle-Life Lithium-Oxygen Batteries

Design rules for liquid crystalline electrolytes for enabling dendrite-free lithium metal batteries

Dendrite-free electrodeposition of lithium metal is necessary for the adoption of high energy-density rechargeable lithium metal batteries. Here, we demonstrate a mechanism of using a liquid crystalline electrolyte to suppress dendrite growth with a lithium metal anode. A nematic liquid crystalline electrolyte modifies the kinetics of electrodeposition by introducing additional overpotential due to its bulk-distortion and anchoring free energy. By extending the phase-field model, we simulate the morphological evolution of the metal anode and explore the role of bulk-distortion and anchoring strengths on the electrodeposition process. We find that adsorption energy of liquid crystalline molecules on a lithium surface can be a good descriptor for the anchoring energy and obtain it using first-principles density functional theory calculations. Unlike other extrinsic mechanisms, we find that liquid crystals with high anchoring strengths can ensure smooth electrodeposition of lithium metal, thus paving the way for practical applications in rechargeable batteries based on metal anodes.

Not All Fluorination Is the Same: Unique Effects of Fluorine Functionalization of Ethylene Carbonate for Tuning Solid-Electrolyte Interphase in Li Metal Batteries

Li metal batteries (LMBs) are crucial for electrifying transportation and aviation. Engineering electrolytes to form desired solid-electrolyte interphase (SEI) is one of the most promising approaches to enable stable long-lasting LMBs. Among the liquid electrolytes explored, fluoroethylene carbonate (FEC) has seen great success in leading to desirable SEI properties for enabling stable cycling of LMBs. Given the many facets to desirable SEI properties, numerous descriptors and mechanisms have been proposed. To build a detailed mechanistic understanding, we analyze varying degrees of fluorination of the same prototype molecule, chosen to be ethylene carbonate (EC) to tease out the interfacial reactivity at the Li metal/electrolyte. Using density functional theory (DFT) calculations, we study the effect of mono-, di-, tri-, and tetra-fluorine substitutions of EC on its reactivity with Li surface facets in the presence and absence of Li salt. We find that the formation of LiF at the early stage of SEI formation, posited as a desirable SEI component, depends on the F-abstraction mechanism rather than the number of fluorine substitution. The best illustrations of this are cis- and trans-difluoro ECs, where F-abstraction is spontaneous with the trans case, while the cis case needs to overcome a nonzero energy barrier. Using a Pearson correlation map, we find that the extent of initial chemical decomposition quantified by the associated reaction free energy is linearly correlated with the charge transferred from the Li surface and the number of covalent-like bonds formed at the surface. The effect of salt and the surface facet have a much weaker role in determining the decompositions at the immediate electrolyte/electrode interfaces. Putting all of this together, we find that tetra-FEC could act as a high-performing SEI modifier as it leads to a more homogeneous, denser LiF-containing SEI. Using this methodology, future investigations will explore -CF₃ functionalization and other backbone molecules (linear carbonates).

In Situ Designing a Gradient Li+ Capture and Quasi-Spontaneous Diffusion Anode Protection Layer toward Long-Life Li-O2 Batteries

Lithium metal is the only anode material that can enable the Li-O₂ battery to realize its high theoretical energy density (≈3500 Wh kg^-1 ). However, the inherent uncontrolled dendrite growth and serious corrosion limitations of lithium metal anodes make it experience fast degradation and impede the practical application of Li-O₂ batteries. Herein, a multifunctional complementary LiF/F-doped carbon gradient protection layer on a lithium metal anode by one-step in situ reaction of molten Li with poly(tetrafluoroethylene) (PTFE) is developed. The abundant strong polar C-F bonds in the upper carbon can not only act as Li⁺ capture site to pre-uniform Li⁺ flux but also regulate the electron configuration of LiF to make Li⁺ quasi-spontaneously diffuse from carbon to LiF surface, avoiding the strong Li⁺ -adhesion-induced Li aggregation. For LiF, it can behave as fast Li⁺ conductor and homogenize the nucleation sites on lithium, as well as ensure firm connection with lithium. As a result, this well-designed protection layer endows the Li metal anode with dendrite-free plating/stripping and anticorrosion behavior both in ether-based and carbonate ester-based electrolytes. Even applied protected Li anodes in Li-O₂ batteries, its superiority can still be maintained, making the cell achieve stable cycling performance (180 cycles).

Ionic liquid assisted electrochemical coating zinc nanoparticles on carbon cloth as lithium dendrite suppressing host

The application of lithium metal anode with high specific capacity and energy density is limited by the volume expansion and pulverization caused by dendrite growth during cycle process. We propose a composite lithium anode by immersing molten lithium on the flexible three-dimensional (3D) carbon cloth scaffold with the zinc nanoparticles. The lithiophilic zinc nanoparticles layer of framework is synthesized by fast and easy electrochemical deposition from ionic liquid avoiding high temperature, high pressure and toxic reagent. The lithium is infused into the 3D lithiophilic framework, the composite anode is obtained. The steady network structure can confine the lithium and lead to Li dendrite restraining and reducing volume change due to the low interfacial resistance and reduce the effective current density, which induced the homogeneous Li growth. Benefiting from this, the Li infused 3D carbon cloth-Zn symmetric battery exhibits a low stripping/plating overpotential (~30 mV) and can be stable over 900 h at 1 mA cm^-2. The Li//LiFePO₄ battery delivers higher reversible capacity (140 mAh g^-1 at 2 C and 120 mAh g^-1 at 5 C) and stable cycling for 1500 and 2000 cycles than bare Li.

Li-CO2 and Na-CO2 Batteries: Toward Greener and Sustainable Electrical Energy Storage

Metal-CO₂ batteries, especially Li-CO₂ and Na-CO₂ batteries, offer a novel and attractive strategy for CO₂ capture as well as energy conversion and storage with high specific energy densities. However, some scientific issues and challenges existing restrict their practical applications. Here, recent progress of crucial reaction mechanisms on cathodes in Li-CO₂ and Na-CO₂ batteries are summarized. The detailed reaction pathways can be modified by operation conditions, electrolyte compositions, and catalysts. Besides, specific discussions from aspects of catalyst design, stability of electrolytes, and anode protection are presented. Perspectives of several innovative directions are also put forward. This review provides an intensive understanding of Li-CO₂ and Na-CO₂ batteries and gives a useful guideline for the practical development of metal-CO₂ batteries and even metal-air batteries.

A Facile Surface Preservation Strategy for the Lithium Anode for High-Performance Li-O2 Batteries

Protecting an anode from deterioration during charging/discharging has been seen as one of the key strategies in achieving high-performance lithium (Li)-O₂ batteries and other Li-metal batteries with a high energy density. Here, we describe a facile approach to prevent the Li anode from dendritic growth and chemical corrosion by constructing a SiO₂/GO hybrid thin layer on the surface. The uniform pore-preserving layer can conduct Li ions in the stripping/plating process, leading to an effective alleviation of the dendritic growth of Li by guiding the ion flux through the microstructure. Such a preservation technique significantly enhances the cell performance by enabling the Li-O₂ cell to cycle up to 348 times at 1 A·g^-1 with a capacity of 1000 mA·h·g^-1, which is several times the cycles of cells with pristine Li (58 cycles), Li-GO (166 cycles), and Li-SiO₂ (187 cycles). Moreover, the rate performance is improved, and the ultimate capacity of the cell is dramatically increased from 5400 to 25,200 mA·h·g^-1. This facile technology is robust and conforms to the Li surface, which demonstrates its potential applications in developing future high-performance and long lifespan Li batteries in a cost-effective fashion.

An Outlook on Low-Volume-Change Lithium Metal Anodes for Long-Life Batteries

Rechargeable Li metal batteries are one of the most attractive energy storage systems due to their high energy density. However, the hostless nature of Li, the excessive dendritic growth, and the accumulation of nonactive Li induce severe volume variation of Li anodes. The volume variation can give rise to a fracture of solid electrolyte interphase, continuous consumption of Li and electrolytes, low Coulombic efficiency, fast performance degradation, and finally short cycle life. This Outlook provides a comprehensive understanding of the origin and consequences of Li volume variation. Recent strategies to address this challenge are reviewed from liquid to gel to solid-state electrolyte systems. In the end, guidelines for structural design and fabrication suggestions for future long-life Li composite anodes are presented.

Stable Lithium Metal Anode Enabled by a Lithiophilic and Electron/Ion Conductive Framework

Li metal anode has been considered as the ideal anode for next-generation batteries due to its ultrahigh capacity and lowest electrochemical potential. However, its practical application is still impeded by low Coulombic efficiency, huge volume change, and safety hazards arising from Li dendrite growth. In this work, a three-dimensional (3D) structured highly stable Li metal anode is designed and easily preapred. Benefiting from the in situ reaction between Li metal and AlN, highly Li⁺ conductive Li₃N and lithiophilic LiAl alloy have been simultaneously formed and homogeneously distributed in the framework, in which Li metal is finely dispersed and embedded. The outstanding electron/ion mixed conductivity of Li₃N/LiAl and 3D composite structure with enhanced interfacial area significantly improve the electrode kinetics and suppress the volume change on cycling, while a lithiophilic effect of LiAl alloy and uniform distribution of Li ion flux inside the electrode avoid dendritic Li deposition. As a result, the proposed Li metal electrode exhibits exceptional electrochemical reversibility in both carbonate and ether-based electrolytes. Paired with LiFePO₄ and sulfurized polyacrylonitrile (S@pPAN) cathodes, the full cells deliver highly stable and long-term cycling performance. Therefore, the proposed strategy to fabricate Li metal anodes could promote the practical application of Li metal batteries.

Nitrogen-doped polymer nanofibers decorated with Co nanoparticles for uniform lithium nucleation/growth in lithium metal batteries

Lithium (Li) metal is deemed to be the most promising anode for new-generation lithium batteries due to its high specific capacity (3860 mA h g-1) and low redox potential (-3.04 V vs. SHE). However, Li dendritic formation during battery cycling results not only in poor performance, such as low coulombic efficiency and short cycling, but also serious safety risks such as fire and explosion. In this paper, we propose a novel interlayer with a 3D network which is rich in N-containing functional groups and Co nanoparticles to guide uniform Li nucleation/growth and thus relieve the Li dendritic formation. As a result, the as-designed composite delivers an ultra-long lifespan of 1500 h with a small and stable voltage profile of 38.1 mV for symmetric cells. The composite electrode also exhibits a prominent electrochemical performance in full cells with LiFePO4 as the cathode for lithium ion batteries (LIBs). Our findings provide strong support for inducing the uniform nucleation of Li by introducing lithiophilic sites, which is important for inhibiting Li dendritic formation.

Single-Atom Catalytic Materials for Advanced Battery Systems

Advanced battery systems with high energy density have attracted enormous research enthusiasm with potential for portable electronics, electrical vehicles, and grid-scale systems. To enhance the performance of conversion-type batteries, various catalytic materials are developed, including metals and transition-metal dichalcogenides (TMDs). Metals are highly conductive with catalytic effects, but bulk structures with low surface area result in low atom utilization, and high chemical reactivity induces unfavorable dendrite effects. TMDs present chemical adsorption with active species and catalytic activity promotes conversion processes, suppressing shuttle effect and improving energy density. But they suffer from inferior conductivity compared with metal, and limited sites mainly concentrate on edges and defects. Single-atom materials with atomic sizes, good conductivity, and individual sites are promising candidates for advanced batteries because of a large atom utilization, unsaturated coordination, and unique electronic structure. Single-atom sites with high activity chemically trap intermediates to suppress shuttle effects and facilitate electron transfer and redox reactions for achieving high capacity, rate capability, and conversion efficiency. Herein, single-atom catalytic electrodes design for advanced battery systems is addressed. Major challenges and promising strategies concerning electrochemical reactions, theoretical model, and in situ characterization are discussed to shed light on future research of single-atom material-based energy systems.

Two-Dimensional Transition Metal Chalcogenides for Alkali Metal Ions Storage

On the heels of exacerbating environmental concerns and ever-growing global energy demand, development of high-performance renewable energy-storage and -conversion devices has aroused great interest. The electrode materials, which are the critical components in electrochemical energy storage (EES) devices, largely determine the energy-storage properties, and the development of suitable active electrode materials is crucial to achieve efficient and environmentally friendly EES technologies albeit the challenges. Two-dimensional transition-metal chalcogenides (2D TMDs) are promising electrode materials in alkali metal ion batteries and supercapacitors because of ample interlayer space, large specific surface areas, fast ion-transfer kinetics, and large theoretical capacities achieved through intercalation and conversion reactions. However, they generally suffer from low electronic conductivities as well as substantial volume change and irreversible side reactions during the charge/discharge process, which result in poor cycling stability, poor rate performance, and low round-trip efficiency. In this Review, recent advances of 2D TMDs-based electrode materials for alkali metal-ion energy-storage devices with the focus on lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), high-energy lithium-sulfur (Li-S), and lithium-air (Li-O₂ ) batteries are described. The challenges and future directions of 2D TMDs-based electrode materials for high-performance LIBs, SIBs, PIBs, Li-S, and Li-O₂ batteries as well as emerging alkali metal-ion capacitors are also discussed.

Lithium-Oxygen Batteries and Related Systems: Potential, Status, and Future

The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO₂ emissions across many sectors of the world economy. Batteries are vital to this endeavor, whether used in electric vehicles, to store renewable electricity, or in aviation. Present lithium-ion technologies are preparing the public for this inevitable change, but their maximum theoretical specific capacity presents a limitation. Their high cost is another concern for commercial viability. Metal-air batteries have the highest theoretical energy density of all possible secondary battery technologies and could yield step changes in energy storage, if their practical difficulties could be overcome. The scope of this review is to provide an objective, comprehensive, and authoritative assessment of the intensive work invested in nonaqueous rechargeable metal-air batteries over the past few years, which identified the key problems and guides directions to solve them. We focus primarily on the challenges and outlook for Li-O₂ cells but include Na-O₂, K-O₂, and Mg-O₂ cells for comparison. Our review highlights the interdisciplinary nature of this field that involves a combination of materials chemistry, electrochemistry, computation, microscopy, spectroscopy, and surface science. The mechanisms of O₂ reduction and evolution are considered in the light of recent findings, along with developments in positive and negative electrodes, electrolytes, electrocatalysis on surfaces and in solution, and the degradative effect of singlet oxygen, which is typically formed in Li-O₂ cells.

Toward Stable Lithium Plating/Stripping by Successive Desolvation and Exclusive Transport of Li Ions

Li has been regarded as the most attractive anode for next-generation high-energy-density batteries due to its high specific capacity and low electrochemical potential. However, its low electrochemical potential leads to the side reaction of Li with the solvent of the electrolyte (the solvation of Li ions exacerbates the reaction). This adverse side reaction results in uneven Li distribution and deposition, low Coulombic efficiency, and the formation of Li dendrites. Herein, we demonstrate an efficient method for achieving successive desolvation and homogeneous distribution of Li ions by using a double-layer membrane. The first layer is designed to enable the desolvation of Li ions. The second layer with controllable and ordered nanopores is expected to facilitate the homogeneous and exclusive transport of Li ions. The efficiency of the double-layer membrane on desolvation and exclusive transport of Li ions is confirmed by theoretical calculations, the significantly enhanced Li-ion transference number, improved Coulombic efficiency, and the inhibition of Li dendrites. These results will deepen our understanding of the modulation of ions and pave a way to the next-generation high-energy-density Li-metal batteries.

Current Challenges and Routes Forward for Nonaqueous Lithium-Air Batteries

Nonaqueous lithium-air batteries have garnered considerable research interest over the past decade due to their extremely high theoretical energy densities and potentially low cost. Significant advances have been achieved both in the mechanistic understanding of the cell reactions and in the development of effective strategies to help realize a practical energy storage device. By drawing attention to reports published mainly within the past 8 years, this review provides an updated mechanistic picture of the lithium peroxide based cell reactions and highlights key remaining challenges, including those due to the parasitic processes occurring at the reaction product-electrolyte, product-cathode, electrolyte-cathode, and electrolyte-anode interfaces. We introduce the fundamental principles and critically evaluate the effectiveness of the different strategies that have been proposed to mitigate the various issues of this chemistry, which include the use of solid catalysts, redox mediators, solvating additives for oxygen reaction intermediates, gas separation membranes, etc. Recently established cell chemistries based on the superoxide, hydroxide, and oxide phases are also summarized and discussed.

Asymmetry in the Solvation-Desolvation Resistance for Li Metal Batteries

Li metal electrode is the ultimate choice use in Li ion batteries as high-energy storage systems. An obstacle to its practical realization is Li dendrite formation. In this study, the desolvation resistance of the Li metal electrode, which is strongly related to the inhibition of Li dendrite formation, is investigated. By applying a Laplace transform impedance technique, the desolvation/solvation resistances were successfully separated and analyzed in cells using liquid electrolytes containing different lithium salts, revealing asymmetry in the desolvation/solvation resistances of Li metal electrodes. The desolvation resistances, which supposedly require large amounts of energy derived from the strong interaction between Li⁺ ion and solvents, were smaller than the solvation resistances. It has also been revealed that the larger resistance in the desolvation process is effective for suppressing Li dendrite formation further.

Trace fluorinated-carbon-nanotube-induced lithium dendrite elimination for high-performance lithium-oxygen cells

Lithium metal has attracted considerable attention due to its ultrahigh theoretical capacity. Nevertheless, issues such as dendritic Li formation and instability of the Li metal/electrolyte interface still restrain its practical applications. In this work, we design a Li composite anode with fluorinated carbon nanotubes (FCNT) fabricated by a simple melting-soaking method. It was found that trace amounts of added FCNT (only 1.6 wt%) lead to a significant chemical/electrochemical stability of metallic Li. The obtained Li/FCNT composite electrode (LFCNT) exhibits much better stability in open air and electrolyte than bare Li. The LFCNT enables uniform plating/stripping of metallic Li, preventing the dendrite formation during repeated cycling. In situ optical microscopy observations confirm dendrite-free Li deposition with the mechanism clarified by density functional theory calculations. Compared with bare Li, the LFCNT shows a considerable improvement in rate capability, voltage hysteresis and cycle performance, sustaining stable cycling at a high current density of 3 mA cm^-2 or a capacity up to 5 mA h cm^-2. Li-O₂ cells with a LFCNT anode exhibit a long life of 135 cycles at a capacity of 1000 mA h g^-1, which is six-fold than that with the bare Li anode.

Inducing the Formation of In Situ Li3N-Rich SEI via Nanocomposite Plating of Mg3N2 with Lithium Enables High-Performance 3D Lithium-Metal Batteries

Lithium metals fit the growing demand of high-energy density rechargeable batteries because of their high specific capacity and low redox potential. However, the lithium-metal anodes are abandoned because of various defects. In this study, we apply composite plating into the protection of lithium-metal anodes. We confirmed that the Mg₃N₂ nanoparticle dispersed in the ether electrolyte can be easily composite-plated with lithium, resulting in a flat, dense, and dendrite-free lithium deposition layer during the electrodeposition process. In addition, the Mg₃N₂ plated in the lithium metal phase would react with lithium and then generate a Li₃N-rich solid electrolyte interphase (SEI) layer, mitigating continuous side reactions of the electrolyte on the Li metal. In addition, another product of the reaction is Mg which can work as lithiophilic sites in electrodeposition. The combined effect of the two fields can effectively improve the performance of lithium metal anodes. The Li₃N-rich SEI layer would grow well on the surface of the three-dimensional (3D) lithium anode by composite plating. Furthermore, composite plating with the Mg₃N₂-containing electrolyte is a viable route that can be used for various 3D current collectors easily with a small volume effect. Here, we show that the composite plating 3D lithium metal anode is successfully applied in the Li-S battery with a long lifetime.

Synergistic Effects of Inorganic-Organic Protective Layer for Robust Cycling Dendrite-Free Lithium Metal Batteries

The advantages in high theoretical capacity and low electrochemical potential have made Li metal one of the most promising anode materials satisfying the surging requirement of high energy density for the next-generation batteries. However, safety issues caused by the Li dendrite growth during cycling have greatly thwarted its application. Herein, a hybrid artificial protective layer, constructed by the one-step method through chemical reactions between Li metal and 1H,1H,1H,2H-perfluorodecyltrimethoxysilane, is demonstrated to guide Li deposition and protect lithium batteries from the destruction of Li dendrites. A synergistic effect of the inorganic and organic components in the protective layer significantly enhances the electrochemical performance of symmetric Li|Li and Li|LiFePO₄ cells. This work provides a facile, simple, and scalable method to design a hybrid artificial protective layer for long-lifespan Li metal batteries.

A Sustainable Solid Electrolyte Interphase for High-Energy-Density Lithium Metal Batteries Under Practical Conditions

High-energy-density Li metal batteries suffer from a short lifespan under practical conditions, such as limited lithium, high loading cathode, and lean electrolytes, owing to the absence of appropriate solid electrolyte interphase (SEI). Herein, a sustainable SEI was designed rationally by combining fluorinated co-solvents with sustained-release additives for practical challenges. The intrinsic uniformity of SEI and the constant supplements of building blocks of SEI jointly afford to sustainable SEI. Specific spatial distributions and abundant heterogeneous grain boundaries of LiF, LiN_x O_y , and Li₂ O effectively regulate uniformity of Li deposition. In a Li metal battery with an ultrathin Li anode (33 μm), a high-loading LiNi_0.5 Co_0.2 Mn_0.3 O₂ cathode (4.4 mAh cm^-2 ), and lean electrolytes (6.1 g Ah^-1 ), 83 % of initial capacity retains after 150 cycles. A pouch cell (3.5 Ah) demonstrated a specific energy of 340 Wh kg^-1 for 60 cycles with lean electrolytes (2.3 g Ah^-1 ).

Stable Lithium Anode of Li-O2 Batteries in a Wet Electrolyte Enabled by a High-Current Treatment

Rechargeable Li-air (O₂) batteries have attracted a great deal of attention because of their high theoretical energy density and been regarded as a promising next-generation energy storage technology. Among numerous obstacles to Li-air (O₂) batteries preventing their use in practical applications, water is a representative impurity for Li-air (O₂), which could hasten the deterioration of the anode and accelarate the premature death of cells. Here, we report an effective in situ high-current pretreatment process to enhance the cycling performance of Li-O₂ batteries in a wet tetraethylene glycol dimethyl ether-based electrolyte. With the help of certain levels of H₂O (from 100 to 2000 ppm) in the electrolyte, adequate Li₂O formed on the lithium anode surface after high-current pretreatment, which is necessary for a robust and uniform solid electrolyte interphase layer to protect Li metal during the long-term discharge-charge cycling process. This in situ high-current pretreatment method in a wet electrolyte is shown to be an effective approach for enhancing the cycling performance of Li-O₂ batteries with a stable Li metal anode and promoting the realization of practical Li-air batteries.

Novel Organophosphate-Derived Dual-Layered Interface Enabling Air-Stable and Dendrite-Free Lithium Metal Anode

Lithium (Li) metal, as a promising candidate for next-generation energy storage systems, suffers from an extremely unstable interface that is prone to crack, causing serious corrosion of Li metal and dendrite growth. To address this, a novel dual-layered interface on the Li metal anode is reported, which is featured with organics (COPO₃ , (CO)₂ PO₂ , and (CO)₃ PO) on the top and inorganics (Li₃ PO₄ ) at the bottom. The flexible organic layer with reduced Young's modulus (≈550 MPa) contributes to maintain structural integrity, while the rigid inorganic layer with improved Young's modulus of ≈12 GPa is beneficial to suppress the Li dendrite growth. Accordingly, the protected Li is stabilized to maintain successive electrodeposition over 800 cycles of plating/stripping process at a current density of 2 mA cm^-2 . Furthermore, the uniform dual-layered interface tends to prevent the corrosion of air to Li metal, exhibiting almost the same performance as the Li metal treated in the inert atmosphere.

Distinct Nanoscale Interphases and Morphology of Lithium Metal Electrodes Operating at Low Temperatures

While Li-ion batteries are known to fail at temperatures below -20 °C, very little is known regarding the low-temperature behavior of next-generation high-capacity electrode materials. The lithium metal anode is of particular interest for high-energy battery chemistries, but improved understanding of and control over its electrochemical and nanoscale interfacial behavior in diverse conditions is necessary. Here, we investigate lithium deposition/stripping, morphology evolution, and solid-electrolyte interphase (SEI) structure and properties down to -80 °C using an ether-based electrolyte (DOL/DME). As temperature is reduced, we find that the morphology of deposited lithium is significantly altered. Furthermore, cryogenic transmission electron microscopy coupled with vacuum-transfer X-ray photoelectron spectroscopy reveal that the SEI exhibits different structure, chemistry, thickness, and conductive properties at lower temperatures. These results show that Li is promising for batteries operating under extreme conditions, and the distinct nanoscale evolution of Li electrodes at different temperatures must be considered when designing high-energy 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.

Nano-SiO2 coating enabled uniform Na stripping/plating for dendrite-free and long-life sodium metal batteries

Metallic sodium, which has a suitable redox potential and high theoretical capacity, is regarded as an ideal anode material for rechargeable Na metal batteries. However, dendrite growth on sodium metal during cycling has seriously restricted its practical applications. Herein, we employed a low-cost and facile brushing method to fabricate a porous nano-SiO₂ coating, which can induce a relatively uniform distribution of Na⁺ flux and suppress the growth of Na dendrites. The nano-SiO₂ coating with high porosity can decrease the Na stripping/plating overpotential (<50 mV) over 400 cycles at 5 mA cm^-2. Moreover, when coupled with a Na₃V₂(PO₄)₃ (NVP) cathode, the Na with SiO₂ coating (Na@SiO₂) composite anode shows a favorable suitability in a full cell. Compared with the one with a bare Na anode, the full cell with the Na@SiO₂ anode delivers a 27.8% higher discharge capacity (94.6 vs. 74 mA h g^-1 at 1C) after 1000 cycles.

Self-Healable Solid Polymeric Electrolytes for Stable and Flexible Lithium Metal Batteries

The key issue holding back the application of solid polymeric electrolytes in high-energy density lithium metal batteries is the contradictory requirements of high ion conductivity and mechanical stability. In this work, self-healable solid polymeric electrolytes (SHSPEs) with rigid-flexible backbones and high ion conductivity are synthesized by a facile condensation polymerization approach. The all-solid Li metal full batteries based on the SHSPEs possess freely bending flexibility and stable cycling performance as a result of the more disciplined metal Li plating/stripping, which have great implications as long-lifespan energy sources compatible with other wearable devices.

Advanced Lithium Metal-Carbon Nanotube Composite Anode for High-Performance Lithium-Oxygen Batteries

The low Coulombic efficiency and hazardous dendrite growth hinder the adoption of lithium anode in high-energy density batteries. Herein, we report a lithium metal-carbon nanotube (Li-CNT) composite as an alternative to the long-term untamed lithium electrode to address the critical issues associated with the lithium anode in Li-O₂ batteries, where the lithium metal is impregnated in a porous carbon nanotube microsphere matrix (CNTm) and surface-passivated with a self-assembled monolayer of octadecylphosphonic acid as a tailor-designed solid electrolyte interphase (SEI). The high specific surface area of the Li-CNT composite reduces the local current density and thus suppresses the lithium dendrite formation upon cycling. Moreover, the tailor-designed SEI effectively separates the Li-CNT composite from the electrolyte solution and prevents the latter's further decomposition. When the Li-CNT composite anode is coupled with another CNTm-based O₂ cathode, the reversibility and cycle life of the resultant Li-O₂ batteries are drastically elevated.

High Current Enabled Stable Lithium Anode for Ultralong Cycling Life of Lithium-Oxygen Batteries

Rechargeable lithium-oxygen (Li-O₂) batteries (LOBs) with extremely high theoretical energy density have been regarded as a promising next-generation energy storage technology. However, the limited cycle life, undesirable corrosion, and safety hazards are seriously limiting the practical application of the lithium metal anode in LOBs. Here, we demonstrate a rational design of the Li-Al alloy (LiAl_x) anode that successfully achieves ultralong cycling life of LOBs with stable Li cycling. Through in situ high-current pretreatment technology, Al atoms accumulates, and a stable Al₂O₃-containing solid electrolyte interphase protective film formed on the LiAl_x anode surface to suppress side reactions and O₂ crossover. The cycling life of LOB with the protected LiAl_x anode increases to 667 cycles under a fixed capacity of 1000 mA h g^-1, as compared to 17 cycles without pretreatment. We believe that this in situ high-current pretreatment strategy presents a new vision to protect the lithium-containing alloy anodes, such as Li-Al, Li-Mg, Li-Sn, and Li-In alloys for stable and safe lithium metal batteries (Li-O₂ and Li-S batteries).

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.

High-Rate and Large-Capacity Lithium Metal Anode Enabled by Volume Conformal and Self-Healable Composite Polymer Electrolyte

The widespread implementation of lithium-metal batteries (LMBs) with Li metal anodes of high energy density has long been prevented due to the safety concern of dendrite-related failure. Here a solid-liquid hybrid electrolyte consisting of composite polymer electrolyte (CPE) soaked with liquid electrolyte is reported. The CPE membrane composes of self-healing polymer and Li+-conducting nanoparticles. The electrodeposited lithium metal in a uniform, smooth, and dense behavior is achieved using a hybrid electrolyte, rather than dendritic and pulverized structure for a conventional separator. The Li foil symmetric cells can deliver remarkable cycling performance at ultrahigh current density up to 20 mA cm-2 with an extremely low voltage hysteresis over 1500 cycles. A large areal capacity of 10 mAh cm-2 at 10 mA cm-2 could also be obtained. Furthermore, the Li|Li4Ti5O12 cells based on the hybrid electrolyte achieve a higher specific capacity and longer cycling life than those using conventional separators. The superior performances are mainly attributed to strong adhesion, volume conformity, and self-healing functionality of CPE, providing a novel approach and a significant step toward cost-effective and large-scalable LMBs.

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.

Nanocrevasse-Rich Carbon Fibers for Stable Lithium and Sodium Metal Anodes

Metallic lithium (Li) and sodium (Na) anodes have received great attention as ideal anodes to meet the needs for high energy density batteries due to their highest theoretical capacities. Although many approaches have successfully improved the performances of Li or Na metal anodes, many of these methods are difficult to scale up and thus cannot be applied in the production of batteries in practice. In this work, we introduce nanocrevasses in a carbon fiber scaffold which can facilitate the penetration of molten alkali metal into a carbon scaffold by enhancing its wettability for Li/Na metal. The resulting alkali metal/carbon composites exhibit stable long-term cycling over hundreds of cycles. The facile synthetic method is enabled for scalable production using recycled metal waste. Thus, the addition of nanocrevasses to carbon fiber as a scaffold for alkali metals can generate environmentally friendly and cost-effective composites for practical electrode applications.

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.

FeOOH Nanocubes Anchored on Carbon Ribbons for Use in Li/O2 Batteries

A composite of FeOOH nanocubes anchored on carbon ribbons has been synthesized and used as a cathode material for Li/O₂ batteries. Fe²⁺ ion-exchanged resin serves as a precursor for both FeOOH nanocubes and carbon ribbons, which are formed simultaneously. The as-prepared FeOOH cubes are proposed to have a core-shell structure, with FeOOH as the shell and Prussian blue as the core, based on information from XPS, TEM, and EDS mapping. As a cathode material for Li/O₂ batteries, FeOOH delivers a specific capacity of 14816 mA h g^-1 _cathode with a cycling stability of 67 cycles over 400 h. The high performance is related to the low overpotential of the oxygen reduction/evolution reaction on FeOOH. The cube structure, the supporting carbon ribbons, and the -OOH moieties all contribute to the low overpotential. The discharge product Li₂ O₂ can be efficiently decomposed in the FeOOH cathode after a charging process, leading to higher cycling stability. Its high activity and stability make FeOOH a good candidate for use in non-aqueous Li/O₂ batteries.

Atomic-Scale Direct Identification of Surface Variations in Cathode Oxides for Aqueous and Nonaqueous Lithium-Ion Batteries

The electrochemical (de)intercalation reactions of lithium ions are initiated at the electrode surface in contact with an electrolyte solution. Therefore, substantial structural degradation, which shortens the cycle life of cells, is frequently observed at the surface of cathode particles, including lithium-metal intermixing, phase transitions, and dissolution of lithium and transition metals into the electrolyte. Furthermore, in contrast to the strict restriction of moisture in lithium-ion cells with nonaqueous organic electrolytes, electrode materials in aqueous-electrolyte cells are under much more reactive environments with water and oxygen, thereby leading to serious surface chemical reactions on the cathode particles. The present article presents key results regarding structural and composition variations at the surface of oxide-based cathodes in both high-performance nonaqueous and recently proposed aqueous lithium-ion batteries; in particular, focusing on direct atomic-scale observations preformed by means of scanning transmission electron microscopy. Precise identification of surface degradation at the atomic level is thus emphasized because it can provide significant insights into overcoming the limitations of current lithium-ion batteries.

Vinyl Ethylene Carbonate as an Effective SEI-Forming Additive in Carbonate-Based Electrolyte for Lithium-Metal Anodes

We report the use of vinyl ethylene carbonate as a new solid electrolyte interface (SEI)-forming additive for Li-metal anodes in carbonate-based electrolyte, which has the advantages of both good storage performance and low price. Compared to the SEI formed in vinyl ethylene carbonate-free electrolyte, the SEI film formed in 10% vinyl ethylene carbonate electrolyte contains a higher relative content of polycarbonate species and a greater amount of decomposition products of LiPF₆ salt. Both components are expected to have positive effects on the passivation of Li-metal surface and the accommodation of volume changes of anode during cycling. Scanning electron microscopy images and COMSOL numerical simulation results further confirm that uniform Li deposition morphology can be achieved in the presence of vinyl ethylene carbonate additive. When cycling at the current density of 0.25 mA cm^-2 with a cycling capacity of 1.0 mAh cm^-2, the vinyl ethylene carbonate-contained Li-Cu cell exhibits a long life span of 816 h (100 cycles) and a relatively high Coulombic efficiency of 93.2%.

Improving the cyclability and capacity of Li-O2 batteries via low rate pre-activation

Simple low rate pre-activation effectively prolonged the cycle life of Li-O2 batteries with MWNT cathodes in a 1 M LiClO4/DMSO electrolyte from 55 to 290 cycles, and the ultimate capacity and rate performance were also significantly enhanced, attributed to reconstructed homogeneous and compact SEI layers on the Li anodes by pre-activation.