A Coaxial‐Interweaved Hybrid Lithium Metal Anode for Long‐Lifespan Lithium Metal Batteries

Lithium (Li) metal is one of the most promising anode materials to construct next‐generation rechargeable batteries owing to its ultrahigh theoretical capacity and the lowest electrochemical potential. Unfortunately, practical application of Li metal batteries is severely hindered by short lifespan and safety concerns caused by Li dendrite growth during cycling. Herein, a coaxial‐interweaved hybrid Li metal anode is proposed for dendrite inhibition that significantly improves the cycling stability of Li metal batteries. The hybrid Li metal anode is fabricated by Li composition into a 3D interweaved scaffold, where each fiber of the interwoven scaffold is composed of a conductive skeleton and a coaxial lithiophilic layer modified on the surface. The coaxial‐interweaved structure endows the hybrid anode with favored Li affinity to guide uniform Li deposition, sufficient channels for ion transportation and electron conduction, and enhanced stability during Li plating and stripping. Consequently, the hybrid Li metal anode affords high Coulombic efficiency over 98.5% for 750 cycles with dendrite‐free morphologies in half cells and improved capacity retention of 80.1% after 100 cycles in LiFePO₄ full cells. The innovative coaxial‐interweaved hybrid Li metal anode demonstrates multiscale design strategy from lithiophilic modification to scaffold construction and promises the prospect of Li metal batteries for future applications.     

In Situ NMR Verification for Stacking Pressure-Induced Lithium Deposition and Dead Lithium in Anode-Free Lithium Metal Batteries

Anode-free lithium metal batteries have emerged as strong contenders for next-generation rechargeable batteries due to their ultra-high energy density. However, their safety and life span are insufficient because of the easy generation of dendrites and dead lithium during lithium plating and stripping. Understanding the formation mechanism for lithium dendrites and dead lithium is essential to further improve battery performance. By employing in situ solid-state nuclear magnetic resonance (NMR) spectroscopy, the influence of stacking pressure on dendritic behavior and dead lithium is systematically investigated. At 0.1 MPa, lithium dendrite is rapidly formed, followed by a linear increase of dead lithium. High stacking pressure not only causes lithium metal to fracture but also leads to form dendrites and dead lithium at the fracture site. At 0.5 MPa stacking pressure, the least quantity of dead lithium is attained, and the growth pattern of dead lithium is exponential growth. The exponential growth pattern is distinguished by the high growth of dead lithium early in the battery cycle and essentially no growth later in the cycle. As a result, it is believed that efficient suppression of dead lithium generation early in battery cycling can play a critical role in improving battery performance.     

Accurate Determination of Coulombic Efficiency for Lithium Metal Anodes and Lithium Metal Batteries

Lithium (Li) metal is an ideal anode material for high energy density batteries. However, the low Coulombic efficiency (CE) and the formation of dendrites during repeated plating and stripping processes have hindered its applications in rechargeable Li metal batteries. The accurate measurement of Li CE is a critical factor to predict the cycle life of Li metal batteries, but the measurement of Li CE is affected by various factors that often lead to conflicting values reported in the literature. Here, several parameters that affect the measurement of Li CE are investigated and a more accurate method of determining Li CE is proposed. It is also found that the capacity used for cycling greatly affects the stabilization cycles and the average CE. A higher cycling capacity leads to faster stabilization of Li anode and a higher average CE. With a proper operating protocol, the average Li CE can be increased from 99.0% to 99.5% at a high capacity of 6 mA h cm^?2 (which is suitable for practical applications) when a high‐concentration ether‐based electrolyte is used.     

Coated Lithium Powder (CLiP) Electrodes for Lithium‐Metal Batteries

Safety issues caused by the metallic lithium inside a battery represent one of the main reasons for the lack of commercial availability of rechargeable lithium‐metal batteries. The advantage of anodes based on coated lithium powder (CLiP), compared to plain lithium foil, include the suppression of dendrite formation, as the local current density during stripping/plating is reduced due to the higher surface area. Another performance and safety advantage of lithium powder is the precisely controlled mass loading of the lithium anode during electrode preparation, giving the opportunity to avoid Li excess in the cell. As an additional benefit, the coating makes electrode manufacturing safer and eases handling. Here, electrodes based on coated lithium powder electrodes (CLiP) are introduced for application in lithium‐metal batteries. These electrodes are compared to lithium foil electrodes with respect to cycling stability, coulombic efficiency of lithium stripping/plating, overpotential, and morphology changes during cycling.     

A Temperature‐Responsive Electrolyte Endowing Superior Safety Characteristic of Lithium Metal Batteries

Lithium metal batteries (LMBs) have attracted wide attention due to their high energy density. However, flammable organic carbonate electrolytes are associated with severe parasitic reactions and huge safety hazards for LMBs. Herein, a smart temperature‐responsive electrolyte is presented that demonstrates two distinct polymerization behaviors in LMBs. Through an anionic polymerization triggered by lithium metal, this electrolyte forms a favorable polymer protection layer on lithium anodes at ambient temperature, leading to a reversible Li plating/stripping behavior over 2000 h, and dendrite‐free morphology even under a current density of 10 mA cm^?2. On suffering from thermal abuse, this electrolyte can be rapidly transformed from liquid into solid by a thermal free radical polymerization, thus realizing significant improvements in safety performance without internal short‐circuit failures thus achieving safe operation even at a temperature of 150 °C. It is noted that no thermal runway occurs even at an extremely high temperature of 280 °C. It is believed that this study not only offers new valuable insights in interfacial chemistry of electrolytes, but also opens up new avenue to develop safe LMBs.     

Marginal Magnesium Doping for High‐Performance Lithium Metal Batteries

Due to unparalleled theoretical capacity and operation voltage, metallic Li is considered as the most attractive candidate for lithium‐ion battery anodes. However, Li metal electrodes suffer from uncontrolled dendrite growth and consequent interfacial instability, which result in an unacceptable level of performance in cycling stability and safety. Herein, it is reported that a marginal amount (1.5 at%) of magnesium (Mg) doping alters the surface properties of Li metal foil drastically in such a way that upon Li plating, a highly dense Li whisker layer is induced, instead of sharp dendrites, with enhanced interfacial stability and cycling performance. The effect of Mg doping is explained in terms of increased surface energy, which facilitates plating of Li onto the main surface over the existing whiskers. The present study offers a useful guideline for Li metal batteries, as it largely resolves the longstanding shortcoming of Li metal electrodes without significantly sacrificing their main advantages.     

Highly Stable Operation of Lithium Metal Batteries Enabled by the Formation of a Transient High‐Concentration Electrolyte Layer

Lithium (Li) metal has been extensively investigated as an anode for rechargeable battery applications due to its ultrahigh theoretical specific capacity and the lowest redox potential. However, significant challenges including dendrite growth and low Coulombic efficiency are still hindering the practical applications of rechargeable Li metal batteries. It is demonstrated that long‐term cycling of Li metal batteries can be realized by the formation of a transient high‐concentration electrolyte layer near the surface of Li metal anode during high rate discharge process. The highly concentrated Li⁺ ions in this transient layer will immediately be solvated by the available solvent molecules and facilitate the formation of a stable and flexible solid electrolyte interphase (SEI) layer composed of a poly(ethylene carbonate) framework integrated with other organic/inorganic lithium salts. This SEI layer largely suppresses the corrosion of Li metal anode attacked by free organic solvents and enables the long‐term operation of Li metal batteries. The fundamental findings in this work provide a new direction for the development of Li metal batteries that could be operated at high current densities for a wide range of applications.     

Vertically Aligned Lithiophilic CuO Nanosheets on a Cu Collector to Stabilize Lithium Deposition for Lithium Metal Batteries

Uncontrollable dendrite growth hinders the direct use of a lithium metal anode in batteries, even though it has the highest energy density of all anode materials. Achieving uniform lithium deposition is the key to solving this problem, but it is hard to be realized on a planar electrode surface. In this study, a thin lithiophilic layer consisting of vertically aligned CuO nanosheets directly grown on a planar Cu current collector is prepared by a simple wet chemical reaction. The lithiophilic nature of the CuO nanosheets reduces the polarization of the electrode, ensuring uniform Li nucleation and continuous smooth Li plating, which is difficult to realize on the normally used lithiophobic Cu current collector surface. The integration of the grown CuO arrays and the Cu current collector guarantees good electron transfer, and moreover, the vertically aligned channels between the CuO nanosheets guarantee fast ion diffusion and reduce the local current density. As a result, a high Columbic efficiency of 94% for 180 cycles at a current density of 1 mA cm^?2 and a prolonged lifespan of a symmetrical cell (700 h at 0.5 mA cm^?2) can be easily achieved, showing a simple but effective way to realize Li metal‐based anode stabilization.     

Lithium Difluorophosphate‐Based Dual‐Salt Low Concentration Electrolytes for Lithium Metal Batteries

The safety hazards and low Coulombic efficiency originating from the growth of lithium dendrites and decomposition of the electrolyte restrict the practical application of Li metal batteries (LMBs). Inspired by the low cost of low concentration electrolytes (LCEs) in industrial applications, dual‐salt LCEs employing 0.1 m Li difluorophosphate (LiDFP) and 0.4 m LiBOB/LiFSI/LiTFSI are proposed to construct a robust and conductive interphase on a Li metal anode. Compared with the conventional electrolyte using 1 m LiPF₆, the ionic conductivity of LCEs is reduced but the conductivity decrement of the separator immersed in LCEs is moderate, especially for the LiDFP–LiFSI and LiDFP–LiTFSI electrolytes. The accurate Coulombic efficiency (CE) of the Li||Cu cells increases from 83.3% (electrolyte using 1 m LiPF₆) to 97.6%, 94.5%, and 93.6% for LiDFP–LiBOB, LiDFP–LiFSI, and LiDFP–LiTFSI electrolytes, respectively. The capacity retention of Li||LiFePO₄ cells using the LiDFP–LiBOB electrolyte reaches 95.4% along with a CE over 99.8% after 300 cycles at a current density of 2.0 mA cm^?2 and the capacity reaches 103.7 mAh g^?1 at a current density of up to 16.0 mA cm^?2. This work provides a dual‐salt LCE for practical LMBs and presents a new perspective for the design of electrolytes for LMBs.     

Recent Developments of the Lithium Metal Anode for Rechargeable Non‐Aqueous Batteries

Over the last 40 years, metallic lithium as an anode material has been of great interest owing to its high energy density. However, dendritic lithium growth causes serious safety issues. Awareness and understanding of the Li deposition and stripping processes have grown rapidly especially in recent years, and consequently, there have been many attempts to suppress the Li dendrites. Recent developments that have modified the electrolytes and the Li anode in order to inhibit the growth of Li dendrite and improve cycling performance are summarized. It has been shown that current density, solid‐electrolyte interphase (SEI) film, Li⁺ transference number, and shear modulus have significant impact on the growth behavior and the Coulombic efficiency. Various methods have been introduced to increase the surface area of the Li anode, enhance Li⁺ conductivity, form stable SEI film, and improve mechanical strength of electrolytes. These approaches are discussed in details, and the perspectives regarding the future use of Li anode are also outlined. It is hoped that this review will facilitate the future development of Li metal batteries.     

Toward the Sustainable Lithium Metal Batteries with a New Electrolyte Solvation Chemistry

Herein, a new solvation strategy enabled by Mg(NO₃)₂ is introduced, which can be dissolved directly as Mg²⁺ and NO₃^? ions in the electrolyte to change the Li⁺ ion solvation structure and greatly increase interfacial stability in Li‐metal batteries (LMBs). This is the first report of introducing Mg(NO₃)₂ additives in an ester‐based electrolyte composed of ternary salts and binary ester solvents to stabilize LMBs. In particular, it is found that NO₃^? efficiently forms a stable solid electrolyte interphase through an electrochemical reduction reaction, along with the other multiple anion components in the electrolyte. The interaction between Li⁺ and NO₃^? and coordination between Mg²⁺ and the solvent molecules greatly decreases the number of solvent molecules surrounding the Li⁺, which leads to facile Li⁺ desolvation during plating. In addition, Mg²⁺ ions are reduced to Mg via a spontaneous chemical reaction on the Li metal surface and subsequently form a lithiophilic Li–Mg alloy, suppressing lithium dendritic growth. The unique solvation chemistry of Mg(NO₃)₂ enables long cycling stability and high efficiency of the Li‐metal anode and ensures an unprecedented lifespan for a practical pouch‐type LMB with high‐voltage Ni‐rich NCMA73 cathode even under constrained conditions.     

Magnetic Field–Suppressed Lithium Dendrite Growth for Stable Lithium‐Metal Batteries

Lithium metal is the most attractive anode material due to its extremely high specific capacity, minimum potential, and low density. However, uncontrollable growth of lithium dendrite results in severe safety and cycling stability concerns, which hinders the application in next generation secondary batteries. In this paper, a new and facile method imposing a magnetic field to lithium metal anodes is proposed. That is, the lithium ions suffering Lorentz force due to the electromagnetic fields are put into spiral motion causing magnetohydrodynamics (MHD) effect. This MHD effect can effectively promote mass transfer and uniform distribution of lithium ions to suppress the dendrite growth as well as obtain uniform and compact lithium deposition. The results show that the lithium metal electrodes within the magnetic field exhibit excellent cycling and rate performance in a symmetrical battery. Additionally, full batteries using limited lithium metal as anodes and commercial LiFePO₄ as cathodes show improved performance within the magnetic field. In summary, a new and facile strategy of suppressing lithium dendrites using the MHD effect by imposing a magnetic field is proposed, which may be generalized to other advanced alkali metal batteries.     

Temperature-Mediated Dynamic Lithium Loss and its Implications for High-Efficiency Lithium Metal Anodes

Lithium (Li) metal has been strongly regarded as the ultimate anode option for next-generation high-energy-density batteries. Nevertheless, the insufficient Coulombic efficiency induced by the extensive active Li loss largely hinders the practical operation of Li metal batteries under wide temperature range. Herein, the temperature-mediated dynamic growth of inactive Li from −20 to 60°C via titration gas chromatograph measurements is quantitatively decoupled. Combined X-ray photoelectronic spectroscopy, cryo-transmission electronic microscopy, and scanning electronic microscopy methods depicted that both solid electrolyte interphase (SEI) characteristics and Li deposition compactness can be profoundly manipulated by working temperature. The elevation of temperature is found to fundamentally aggravate the parasitic reactions and deteriorate the spatial uniformity of SEI, yet promote the lateral growth of Li by kinetic reason. The opposite effects of temperature on SEI properties and Li deposition compactness can properly explain the intricate temperature-dependent growth rates of SEI-Li⁺ and dead Li⁰ capacity loss observed under titration gas chromatograph measurements. Design implications towards more stable Li metal anodes with higher reversibility can thus be yielded.