In Situ Chemical Lithiation Transforms Diamond-Like Carbon into an Ultrastrong Ion Conductor for Dendrite-Free Lithium-Metal Anodes

Recent Progress of Advanced Functional Separators in Lithium Metal Batteries

As a representative in the post-lithium-ion batteries (LIBs) landscape, lithium metal batteries (LMBs) exhibit high-energy densities but suffer from low coulombic efficiencies and short cycling lifetimes due to dendrite formation and complex side reactions. Separator modification holds the most promise in overcoming these challenges because it utilizes the original elements of LMBs. In this review, separators designed to address critical issues in LMBs that are fatal to their destiny according to the target electrodes are focused on. On the lithium anode side, functional separators reduce dendrite propagation with a conductive lithiophilic layer and a uniform Li-ion channel or form a stable solid electrolyte interphase layer through the continuous release of active agents. The classification of functional separators solving the degradation stemming from the cathodes, which has often been overlooked, is summarized. Structural deterioration and the resulting leakage from cathode materials are suppressed by acidic impurity scavenging, transition metal ion capture, and polysulfide shuttle effect inhibition from functional separators. Furthermore, flame-retardant separators for preventing LMB safety issues and multifunctional separators are discussed. Further expansion of functional separators can be effectively utilized in other types of batteries, indicating that intensive and extensive research on functional separators is expected to continue in LIBs.

Lithiophilic Multichannel Layer to Simultaneously Control the Li-Ion Flux and Li Nucleation for Stable Lithium Metal Batteries

Although the Li metal has been gaining attention as a promising anode material for the next-generation high-energy-density rechargeable batteries owing to its high theoretical specific capacity (3860 mAh g-1), its practical use remains challenging owing to inherent issues related to Li nucleation and growth. This paper reports the fabrication of a lithiophilic multichannel layer (LML) that enables the simultaneous control of Li nucleation and growth in Li-metal batteries. The LML, composed of lithiophilic ceramic composite nanoparticles (Ag-plated Al2O3 particles), is fabricated using the electroless plating method. This LML provides numerous channels for a uniform Li-ion diffusion on a nonwoven separator. Furthermore, the lithiophilic Ag on the Li metal anode surface facing the LML induces a low overpotential during Li nucleation, resulting in a dense Li deposition. The LML enables the LiNi0.8Co0.1Mn0.1O2|| Li cells to maintain a capacity higher than 75% after 100 cycles, even at high charge/discharge rates of 5.0 C at a cutoff voltage of 4.4 V, and achieve an ultrahigh energy density of 1164 Wh kg-1. These results demonstrate that the LML is a promising solution enabling the application of Li metal as an anode material in the next-generation Li-ion batteries.

Coupling High Hardness and Zn Affinity in Amorphous-Crystalline Diamond for Stable Zn Metal Anodes

The highly reversible plating/stripping of Zn is plagued by dendrite growth and side reactions on metallic Zn anodes, retarding the commercial application of aqueous Zn-ion batteries. Herein, a distinctive nano dual-phase diamond (NDPD) comprised of an amorphous-crystalline heterostructure is developed to regulate Zn deposition and mechanically block dendrite growth. The rich amorphous-crystalline heterointerfaces in the NDPD endow modified Zn anodes with enhanced Zn affinity and result in homogeneous nucleation. In addition, the unparalleled hardness of the NDPD effectively overcomes the high growth stress of dendrites and mechanically impedes their proliferation. Moreover, the hydrophobic surfaces of the NDPD facilitate the desolvation of hydrate Zn2+ and prevent water-mediated side reactions. Consequently, the Zn@NDPD presents an ultrastable lifespan exceeding 3200 h at 5 mA cm-2 and 1 mAh cm-2. The practical application potential of Zn@NDPD is further demonstrated in full cells. This work exhibits the great significance of a chemical-mechanical synergistic anode modification strategy in constructing high-performance aqueous Zn-ion batteries.

Functionalized polyoxometalates enable fast ion transport in solid-state batteries at room temperature

The coupling of functionalized inorganic polyoxometalates with polymer electrolytes leads to considerably enhanced mechanical properties and faster ion transport (1.1 × 10-4 S cm-1) at room temperature. The assembled Li/Li symmetric cell displays excellent stability in a 3000 h cycling test and a Li/LiFePO4 cell exhibits superior cycling performance over 250 cycles.

Progress and Perspectives on Promising Covalent-Organic Frameworks (COFs) Materials for Energy Storage Capacity

In recent years, a new class of highly crystalline advanced permeable materials covalent-organic frameworks (COFs) have garnered a great deal of attention thanks to their remarkable properties, such as their large surface area, highly ordered pores and channels, and controllable crystalline structures. The lower physical stability and electrical conductivity, however, prevent them from being widely used in applications like photocatalytic activities and innovative energy storage and conversion devices. For this reason, many studies have focused on finding ways to improve upon these interesting materials while also minimizing their drawbacks. This review article begins with a brief introduction to the history and major milestones of COFs development before moving on to a comprehensive exploration of the various synthesis methods and recent successes and signposts of their potential applications in carbon dioxide (CO2 ) sequestration, supercapacitors (SCs), lithium-ion batteries (LIBs), and hydrogen production (H2 -energy). In conclusion, the difficulties and potential of future developing with highly efficient COFs ideas for photocatalytic as well as electrochemical energy storage applications are highlighted.

Upgrading the Separators Integrated with Desolvation and Selective Deposition toward the Stable Lithium Metal Batteries

A practical and effective approach to improve the cycle stability of high-energy density lithium metal batteries (LMBs) is to selectively regulate the growth of the lithium anode. The design of desolvation and lithiophilic structure have proved to be significant means to regulate the lithium deposition process. Here, a fluorinated polymer lithiophilic separator (LS) loaded with a metal-organic framework (MOF801) is designed, which facilitates the rapid transfer of Li+ within the separator owing to the MOF801-anchored PF6 - from the electrolyte, Li deposition is confined in the plane resulting from the polymer fiber layer rich in lithiophilic groups (C─F). The numerical simulation results confirm that LS induces a uniform electric field and Li+ concentration distribution. Visualization technology records the behavior of regular Li deposition in Li||Li and Li||Cu cells equipping LS. Therefore, LS exhibits an ultrahigh Li+ transference number (tLi + = 0.80) and a large exchange current density (j0 = 1.963 mA cm-2 ). LS guarantees the stable operation of Li||Li cells for over 1000 h. In addition, the LiNi0.8 Co0.1 Mn0.1 O2 ||Li cell equipped with LS exhibits superior rate and cycle performances owing to the formation of LiF-rich robust SEI layers. This study provides a way forward for dendrite-free Li anodes from the perspective of separator engineering.

Dendrite-Free Lithium Metal Anodes Enabled by an Ordered Conductive Ni-Based Catecholate Interlayer for Solid-State Lithium Batteries

The large-scale commercial application of Li metal batteries is hindered by uncontrolled Li dendrite growth. Most of the present interfacial engineering strategies in lithium metal batteries can only prolong the nucleation time of lithium dendrites but cannot prevent the growth of lithium dendrites in three-dimensional space. In this work, a nickel-based catecholate (Ni-CAT) conductive interlayer that can guide the orderly migration of lithium ions and inhibit the disordered deposition of lithium dendrites is successfully constructed between the solid electrolyte and lithium metal through a reasonable design. The experimental analysis proves that the Ni-CAT nanorod arrays with unique vertical structures are closely connected to the solid electrolyte, which can reduce the charge-transfer resistance at the interface and guide lithium ions to be preferentially deposited on the surface of the Ni-CAT intermediate layer through the conduction gradient. Hence, this structure effectively avoids the phenomenon of apical growth during lithium deposition. In addition, the rich pores and inherent nanochannels of Ni-CAT itself act as an "ion sieve", successfully inducing the uniform deposition of lithium metal, which greatly reduces the occurrence of dead lithium due to the loss of electrical contact of lithium during cycling. This strategy holds promise for solving the lithium dendrite problem.

Yttrium trifluoride doped polyacrylonitrile based carbon nanofibers as separator coating layer for high performance lithium-metal batteries

In this study, the yttrium trifluoride-doped polyacrylonitrile(PAN) based carbon nanofibers (YF₃-PAN-CNFs) are successfully designed and prepared through the electro-blow spinning and carbonization strategies. And the YF₃-PAN-CNFs acted as main materials of functional layer for modifying separator of lithium metal batteries are systematically studied and analyzed. The prepared CNFs have long-range ordered structures and high conductivity, which can extremely improve the transport of lithium ions and electrons during charge-discharge processes. The lithiophilic YF₃ nanoparticles formed in the carbonization process can endow enough active sites to produce alloying reaction with Li, which makes the plating/stripping of Li more uniform. For the assembled Li||lithium iron phosphate (LiFePO₄) battery, it still maintains a high specific discharge capacity of 137.1 mAh g^-1 after 500 cycles at 0.5 C, which there is almost no specific discharge capacity degradation after long cycle. The modified separator for the Li||Li symmetric battery can effectively suppress the growth of lithium dendrites and improve cycle stability. Meanwhile, based on the strong chemical bonding between YF₃ and lithium polysulfide combining the effectively physical confinement of the YF₃-PAN-CNFs coating layer, the "shuttle effect" of lithium polysulfide also can be greatly suppressed. Thus the assembled Li||S battery using the separator has excellent electrochemical performance. Therefore, the YF₃-PAN-CNFs modified separator will have a promising application prospect in lithium metal batteries even other high performance secondary batteries.

In Situ Separator Modification with an N-Rich Conjugated Microporous Polymer for the Effective Suppression of Polysulfide Shuttle and Li Dendrite Growth

Lithium-sulfur (Li-S) batteries are very promising high-energy-density electrochemical energy storage devices, but suffer from serious Li polysulfide (LiPS) shuttle and uncontrollable Li dendrite growth. Here, we show in situ polyolefin separator modification with an N-rich conjugated microporous polymer (NCMP) for advanced Li-S battery. In situ polymerization generates an ultrathin NCMP coating on the whole external surface and the internal surface of the separator, which is substantially different from the conventional approaches with thick coatings only on the external surface. The NCMP coating with abundant N-containing groups (-NH₂ and -N═), uniform nanopores (12.294 Å), and π-conjugated structure can simultaneously inhibit LiPS shuttle and regulate uniform nucleation and growth of Li dendrites. Consequently, the NCMP-based separator endows the Li-S battery with significantly enhanced cycling stability at high S loading (5.4 mg cm^-2), lean electrolyte (E/S = 6.3 μL mg^-1), and limited Li excess (50 μm).

Influence of nanoparticles on freezing inside container equipped with fins

With loading of different shapes of nanoparticles, the solidification speed can be changed which was scrutinized in current work. Although the nanoparticles dispersion can decline the heat capacity, the conduction mode can be improved with such technique and changing the styles of nano-powders can alter the strength of conduction. The velocity terms were neglected in freezing, thus, the main equations include two equations with unsteady form for scalars of solid fraction and temperature. Grid adaption with position of ice front has been considered in simulations utilizing FEM. The upper sinusoidal and inner rectangular walls maintain cold temperature and freezing starts from these regions. Adding nanomaterial can expedite the process around 15.75% (for m = 4.8) and 29.8% (for m = 8.6). Also, utilizing particles with shapes of blade form can augment the freezing rate around 16.69%. The efficacy of m on freezing process rises around 4% with elevate of concentration of nanoparticles.

A Dual Functional Artificial SEI Layer Based on a Facile Surface Chemistry for Stable Lithium Metal Anode

Solid electrolyte interphase (SEI) on a Li anode is critical to the interface stability and cycle life of Li metal batteries. On the one hand, components of SEI with the passivation effect can effectively hinder the interfacial side reactions to promote long-term cycling stability. On the other hand, SEI species that exhibit the active site effect can reduce the Li nucleation barrier and guide Li deposition homogeneously. However, strategies that only focus on a separated effect make it difficult to realize an ideal overall performance of a Li anode. Herein, a dual functional artificial SEI layer simultaneously combining the passivation effect and the active site effect is proposed and constructed via a facial surface chemistry method. Simultaneously, the formed LiF component effectively passivates the anode/electrolyte interface and contributes to the long-term stable cycling performance, while the Li-Mg solid solution alloy with the active site effect promotes the transmission of Li+ and guides homogeneous Li deposition with a low energy barrier. Benefiting from these advantages, the Li||Li cell with the modified anode performs with a lower nucleation overpotential of 2.3 mV, and an ultralong cycling lifetime of over 2000 h at the current density of 1 mA cm−2, while the Li||LiFePO4 full battery maintains a capacity retention of 84.6% at rate of 1 C after 300 cycles.

Alloy-Type Anodes for High-Performance Rechargeable Batteries

Alloy-type anodes are one of the most promising classes of next-generation anode materials due to their ultrahigh theoretical capacity (2-10 times that of graphite). However, current alloy-type anodes have several limitations: huge volume expansion, high tendency to fracture and disintegrate, an unstable solid-electrolyte interphase (SEI) layer, and low Coulombic efficiency. Efforts to overcome these challenges are ongoing. This Review details recent progress in the research of batteries based on alloy-type anodes and discusses the direction of their future development. We conclude that improvements in structural design, the introduction of a protective interface, and the selection of suitable electrolytes are the most effective ways to improve the performance of alloy-type anodes. Furthermore, future studies should direct more attention toward analyzing their synergistic promoting effect.

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.

Advances in the Development of Single-Atom Catalysts for High-Energy-Density Lithium-Sulfur Batteries

Although lithium-sulfur (Li-S) batteries are promising next-generation energy-storage systems, their practical applications are limited by the growth of Li dendrites and lithium polysulfide shuttling. These problems can be mitigated through the use of single-atom catalysts (SACs), which exhibit the advantages of maximal atom utilization efficiency (≈100%) and unique catalytic properties, thus effectively enhancing the performance of electrode materials in energy-storage devices. This review systematically summarizes the recent progress in SACs intended for use in Li-metal anodes, S cathodes, and separators, briefly introducing the operating principles of Li-S batteries, the action mechanisms of the corresponding SACs, and the fundamentals of SACs activity, and then comprehensively describes the main strategies for SACs synthesis. Subsequently, the applications of SACs and the principles of SACs operation in reinforced Li-S batteries as well as other metal-S batteries are individually illustrated, and the major challenges of SACs usage in Li-S batteries as well as future development directions are presented.

Sweetening Lithium Metal Interface by High Surface and Adhesive Energy Coating of Crystalline α-d-Glucose Film to Inhibit Dendrite Growth

The notorious growth of lithium (Li) dendrites and the instability of the solid electrolyte interface (SEI) during cycling make Li metal anodes unsuitable for use in commercial Li-ion batteries. Herein, the use of simple sugar coating (α-d-glucose) is demonstrated on top of Li metal to halt the growth of Li dendrites and stabilize the SEI. The α-d-glucose layer possesses high surface and adhesive energies toward Li, which promote the homogenous stripping and plating of Li ions on top of the Li metal. Density functional theory reveals that Li-ion diffusion within the α-d-glucose layer is governed by hopping around the bare sides of the O atoms and along the apparent passages formed by the glucose molecules. Stable cycling performance is achieved when combining α-d-glucose-coated Li (G|Li) anodes with sulfur- and LiFePO₄ -based cathodes in both LiTFSI (ether) and LiPF₆ (carbonate) electrolyte systems. A G|Li-based symmetrical cell operates at a current density of 1 mA cm^-2 and areal capacity of 1 mAh cm^-2 displays a stable overpotential profile for over 9 months (7000 h) of continuous charge/discharge cycling.

Superdry poly(vinylidene fluoride-co-hexafluoropropylene) coating on a lithium anode as a protective layer and separator for a high-performance lithium-oxygen battery

In this study, a dense polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) coating is fabricated on a lithium (Li) anode sheet, which acts as a synergistic protective layer and electrolyte separator for Li-oxygen (Li-O₂) batteries. This thin coating is dried through slow solvent evaporation and vacuum drying methods. The solvent-free, dense PVDF-HFP coating has a thickness of 45 µm and can absorb 62% of electrolyte. The battery containing the PVDF-HFP coating demonstrates a maximum peak power density of 3 mW cm^-2, significantly higher than that of the battery with the PVDF coating (0.8 mW cm^-2) but lower than that without coating (equipped with a commercial glass fiber separator, 7.3 mW cm^-2). However, the PVDF-HFP coating enables the Li-O₂ battery to reach a capacity of 4400 mA h g^-1, much higher than that without the coating (glass fiber separator, 850 mA h g^-1). The symmetric Li-Li cells further confirm steady and low overpotentials using the anode coating at a high current density of 1.0 mA cm^-2, indicating stable Li plating/stripping process. The PVDF-HFP-coated battery has a longer cycling lifetime (1700 h) than those with the PVDF coating (120 h) and a glass fiber separator (670 h). The Raman spectra show that there are lithium compounds (mainly lithium hydroxide) and residual PVDF-HFP on the aged anode surface. The dense PVDF-HFP coating on the Li anode plays dual roles: it creates a strong protective layer for stabilizing the solid-electrolyte interface (in the solid phase), and acts as a separator for modulating the Li metal deposition and stripping behaviors in liquid electrolyte.

A "Blockchain" Synergy in Conductive Polymer-Filled Metal-Organic Frameworks for Dendrite-Free Li Plating/Stripping with High Coulombic Efficiency

The performance of lithium-metal batteries is severely hampered by uncontrollable dendrite growth and volume expansion on the metal anodes. Inspired by the "blockchain" concept in data mining, here we utilize a conductive polymer-filled metal-organic framework (MOF) as the lithium host, in which polypyrrole (PPy) serves as the "chain" to interlink Li "blocks" stored in the MOF pores. While the N-rich PPy guides fast Li⁺ infiltration/extrusion and serves as the nucleation sites for isotropic Li growth, the MOF pores compartmentalize bulk Li deposition for 3D matrix Li storage, leading to low-barrier and dendrite-free Li plating/stripping with superb Coulombic efficiency. The as-fabricated lithium-metal anodes operate over 700 cycles at 5 mA cm^-2 in symmetric cells, and 800 cycles at 1 C in full cells with a per-cycle capacity loss of only 0.017 %. This work might open a new chapter for Li-metal anode construction by introducing the concept of "blockchain" management of Li plating/stripping.

Suppressing electrolyte-lithium metal reactivity via Li+-desolvation in uniform nano-porous separator

Lithium reactivity with electrolytes leads to their continuous consumption and dendrite growth, which constitute major obstacles to harnessing the tremendous energy of lithium-metal anode in a reversible manner. Considerable attention has been focused on inhibiting dendrite via interface and electrolyte engineering, while admitting electrolyte-lithium metal reactivity as a thermodynamic inevitability. Here, we report the effective suppression of such reactivity through a nano-porous separator. Calculation assisted by diversified characterizations reveals that the separator partially desolvates Li⁺ in confinement created by its uniform nanopores, and deactivates solvents for electrochemical reduction before Li⁰-deposition occurs. The consequence of such deactivation is realizing dendrite-free lithium-metal electrode, which even retaining its metallic lustre after long-term cycling in both Li-symmetric cell and high-voltage Li-metal battery with LiNi_0.6Mn_0.2Co_0.2O₂ as cathode. The discovery that a nano-structured separator alters both bulk and interfacial behaviors of electrolytes points us toward a new direction to harness lithium-metal as the most promising anode.

Lithium dendrite and parasitic reactions are two major challenges for lithium metal anode. Here, the authors show suppression of lithium-dendrite and elimination of continuous parasitic reactions by tuning the reduction kinetics of lithium-ion through a uniform nano-porous separator.

Strategies and challenges of carbon materials in the practical applications of lithium metal anode: a review

Lithium (Li) metal is strongly considered to be the ultimate anode for next-generation high-energy-density rechargeable batteries. Carbon materials and their composites with excellent structure tunability and properties have shown great potential applications in Li metal anodes.

Mechanistic Probing of Encapsulation and Confined Growth of Lithium Crystals in Carbonaceous Nanotubes

Encapsulation of lithium in the confined spaces within individual nanocapsules is intriguing and highly desirable for developing high-performance Li metal anodes. This work aims for a mechanistic understanding of Li encapsulation and its confined growth kinetics inside 1D enclosed spaces. To achieve this, amorphous carbon nanotubes are employed as a model host using in situ transmission electron microscopy. The carbon shells have dual roles, providing geometric/mechanical constraints and electron/ion transport channels, which profoundly alter the Li growth patterns. Li growth/dissolution takes place via atom addition/removal at the free surfaces through Li⁺ diffusion along the shells in the electric field direction, resulting in the formation of unusual Li structures, such as poly-crystalline nanowires and free-standing 2D ultrathin (1-2 nm) Li membranes. Such confined front-growth processes are dominated by Li {110} or {200} growing faces, distinct from the root growth of single-crystal Li dendrites outside the nanotubes. Controlled experiments show that high lithiophilicity/permeability, enabled by sufficient nitrogen/oxygen doping or pre-lithiation, is critical for the stable encapsulation of lithium inside carbonaceous nanocapsules. First-principles-based calculations reveal that N/O doping can reduce the diffusion barrier for Li⁺ penetration, and facilitate Li filling driven by energy minimization associated with the formation of low-energy Li/C interfaces.