Hierarchical Li electrochemistry using alloy-type anode for high-energy-density Li metal batteries

In Situ Forming a Black Phosphorene Mixed Ion/Electron Conductor Layer by External Pressure without Binder for Anode-Free Li Metal Batteries

Anode-free Li metal batteries are an excellent choice for developing the next generation of high-energy-density battery systems. However, due to poor chemical compatibility between the current collector and electrolyte interface, the Li electrodeposition on current collectors faces a huge challenge of rapid capacity degradation in anode-free Li metal batteries. Herein, a strategy for modifying an ultrathin black phosphorene (BP) mixed ion/electron conductor interface layer on the surface of a current collector by relying on pressure is proposed. The BP hybrid interface layer is formed in situ on the surface of the current collector solely by pressure compared with traditional current collector modification technology, and there is no powder shedding phenomenon in the absence of a binder. Moreover, the Cu-NCM811 cell matched with high mass loading cathodes exhibits excellent capacity retention and an average Coulombic efficiency of 99.1%. The relevant result has established the foundation for the development of long cycling anode-free Li metal batteries.

Rational design of an Ag@MOF functional separator for controlled lithium deposition and enhanced interfacial stability in lithium metal batteries

The increasing demand for high-energy-density batteries has driven intensive research into lithium metal batteries (LMBs) as promising alternatives to conventional lithium-ion batteries. Despite their ultrahigh theoretical capacity, lithium metal anodes (LMAs) suffer from uncontrolled dendrite growth, leading to safety hazards and irreversible capacity loss. Herein, we develop a functional separator based on a composite of Ag nanoparticles (NPs) and metal-organic frameworks (MOFs) to enhance LMA stability. The -NH2 groups in MOFs promote Li+ desolvation and transport, while Ag NPs induce the in-situ formation of a Li-Ag alloy interphase, effectively suppressing dendrite growth and improving interfacial lithiophilicity. As a result, the reversibility and Li plating/stripping kinetics of LMAs are significantly enhanced. The Li symmetric cells exhibit an ultralong lifespan of 2000 h at 0.2 mA cm-2 and 1000 h at 0.5 mA cm-2. Moreover, the Li||LiFePO4 full cell retains 93.3 % of its initial capacity after 2000 cycles at 1C and maintains 45 mAh g-1 even at an ultra-high rate of 15C.

Cocktail Effects in Boosting the Interfacial Ionic Conduction of the Garnet Solid-State Battery

The garnet-type Li7La3Zr2O12 electrolyte has gained a lot of attention due to its nonflammability, high ionic conductivity, and thermodynamic stability against lithium anodes. However, the large-scale application of solid garnet electrolytes is restricted by high interfacial resistance due to the poor wettability of metallic lithium and interfacial voids caused by sluggish lithium-ion transport during plating/stripping. Herein, we propose a three-dimensional (3D) composite lithium anode with high ionic and electronic conductivity by introducing a small amount of carbonized ZIF-8 powder into molten lithium, achieving compact contact with remarkably low interfacial resistance of 15.2 Ω cm2 due to the decreased surface tension of molten lithium. Aided by DFT calculations, we are able to confirm that the reaction products of Li3N, Li2O, Li-Zn alloy, and LiC6 have much lower interfacial formation energies with garnet electrolytes compared to that of the pure lithium anode. The lithiophobic Li3N and Li2O could impede lithium dendrite growth, provide rapid ionic transport, and thus prevent garnet reduction. In addition, the lithiophilic Li-Zn alloy and LiC6 accelerate lithium-ion migration, preventing the formation of voids at the interface. Thus, the so-called cocktail effects would occur to boost the electrochemical performance through synergistic interactions. The symmetric battery enabled with the composite lithium anode achieves an impressive CCD of 2.5 mA cm-2 and stable galvanostatic cycling for 350 h without short-circuiting at 0.5 mA cm-2. Moreover, the full cell paired with the LiFePO4 cathode delivers excellent cycling performance (LiFePO4, 86.2%@160th cycle@0.5 C). This article describes an integrated approach to develop safe and long-lasting solid-state batteries.

LiC6@Li as a Promising Substitution of Li Metal Counter Electrode for Low-Temperature Battery Evaluation

Li metal, as a counter electrode, is widely used for electrode materials evaluation in coin type half-cells. However, whether this configuration is suitable for different working conditions has often been neglected. Herein, the large resistance and high cathodic/anodic over-potential of Li metal at low temperature are highlighted, revealing its incompetence as counter electrode on cryogenic condition. In view of this, a novel LiC6@Li composite electrode is developed as a promising substitution for electrode materials evaluation. In the LiC6@Li electrode, Li+ de-intercalated from LiC6 preferentially due to the low interface resistance of LiC6, presenting a cathodic/anodic over-potential of 0.05 V (67 µA cm-2) at -20 °C, which is ten times lower than that of Li metal. Moreover, the rapid lithium replenishment into LiC6 from Li metal enables a stable potential of LiC6@Li. Consequently, the LiC6@Li-based half-cells enabled more precise evaluation of the Li+ storage potential and specific capacities of a series of electrode materials at low temperature. As an extension, KC8@K is also successfully prepared as a superior counter electrode to K metal. This work proposes a suitable counter electrode for more accurately evaluating electrode materials at subfreezing scenarios, demonstrating the necessity of specialized electrode evaluation systems for particular operating conditions.

From Promise to Practice: The Choice of Lithium Reservoir in Lithium Metal Batteries that Balances Cycling and Energy

Lithium metal batteries (LMBs) are inherently characterized by their high energy density, while the inventory loss of active lithium (Li) and the affected cyclability have been impeding the practical applications. Achieving a balance that simultaneously ensures long cycle life and high energy density is still a challenge. Here different LMB geometries are explored, specifically the anode-free, anode-less, and anode-rich configurations with different Li reservoirs in anode side, to address this trade-off. An engineered lithiophilic 3D pinchbeck alloy contributing to a suppressed Li inventory loss, a noticeably improved cyclability, and a higher energy density is also applied. By tuning the anode/cathode capacity ratio from anode-free to anode-rich of 0-3 using the 3D alloy substrate, from the perspective of balancing cyclability and energy density, a limited excess of Li reservoir (ratio 1-2) tentatively emerges as a more pragmatic choice. Despite a slight reduction in energy density, a significantly improved cycling stability is achieved. This optimized balance elevates battery efficiency and serves as a benchmark for evaluating the tangible effects of diverse architectures on LMB performance. The research underscores the importance of design choices in advancing LMB toward commercial viability, offering valuable insights into how it can be substantially improved for applications.

Robust and Antioxidative Quasi-Solid-State Polymer Electrolytes for Long-Cycling 4.6 V Lithium Metal Batteries

Quasi-solid-state polymer electrolytes (QSPEs) have been considered as one of the most promising electrolytes for high-safety high-energy-density lithium metal batteries (LMBs). However, their inadequate mechanical properties and instability under high voltages pose significant challenges for practical applications. Herein, robust and antioxidative QSPEs are developed based on a polymer-brush-based rigid supporting film (BC-g-PLiMTFSI-b-PPFEMA, BC: bacterial cellulose, PLiMTFSI: poly(lithium (3-methacryloyloxypropylsulfonyl) (trifluoromethylsulfonyl)imide), PPFEMA: poly(2-(perfluorohexyl)ethyl methacrylate)). The robust BC nanofibril backbone can produce a highly porous supporting structure with outstanding mechanical strength. More importantly, the PLiMTFSI-b-PPFEMA side-chains can not only obviously increase the conversion ratio of easily oxidized monomers in QSPEs, but also possess strong interaction with unstable electrolyte components. With such QSPEs as solid-state electrolytes, the Li/LiNi0.8Mn0.1Co0.1O2 full cell with a high cathode loading (20.3 mg cm-2) exhibits a specific discharge capacity of 200.7 mAh g-1 at 0.5 C and demonstrates a long lifespan of 137 cycles with a highly retained capacity of 170.7 mAh g-1 under a cut-off voltage of 4.5 V. More importantly, under a high cut-off voltage of 4.6 V, a high specific capacity of 147.0 mAh g-1 after 187 cycles can be retained for solid-state Li/LiCoO2 cells. This work provides a feasible development strategy of QSPEs for practical long-cycling high-voltage LMBs.

Topological Li-SbF3@Cu Alloying Anode for High-Energy-Density Li Metal Batteries

The ultrathin Lithium (Li) alloying anode (≤ 50 µm) plays a key role in advancing rechargeable Li metal batteries into practical use, especially because of the insurmountable difficulties in developing pure Li anode. Herein, a thickness-controllable (≈5.5-30 µm) and topological Li-SbF3@Cu anode with the embedded dual Li-based (Li3Sb and Li-Cu) alloys and outmost LiF-rich layer is prepared for high-energy-density Li metal batteries under high Li utilization. Upon cycling, the surface LiF-rich layer together with inner lithiophilic Li3Sb sites and ferroconcrete-like Li-Cu skeletons, synergistically regulates the Li deposition/dissolution behaviors and Li/electrolyte interface evolution. The assembled Li-SbF3@Cu symmetric cell can cycle stably over 1200 h at 1 mA cm-2/1 mAh cm-2, and realize an ultrahigh discharge/charge depth of 53.6% at 2 mA cm-2/3 mAh cm-2. Moreover, a full cell with a high-Li-capacity LiCoO2 cathode (3.8 mAh cm-2) delivers an energy density of 394.5 Wh kg-1 with impressive cycling reversibility at a low negative/positive electrode capacity (N/P) ratio of 1.5. All the findings provide a rewarding avenue toward the industrial application of high-Li-utilization alloying anodes for practical high-energy-density Li metal batteries.

In situ formed 3D hybrid framework of lithiophilic Li2Cu3Zn modified LixCu alloy nanowires towards a dendrite-free Li metal anode

Doping metallic Zn in Li-rich Li-Cu alloy leads to the formation of a hybrid built-in three-dimensional framework, i.e., lithiophilic Li2Cu3Zn and an electrochemically inert LixCu nanowire network, enabling a thin Li-Cu-Zn alloy electrode with significantly improved electrochemical performance.

The Crucial Role of Vacancy Concentration in Enabling Superatomic Diffusion in Lithium Intermetallics

Anode-free solid-state Li batteries promise significant increases in energy densities compared to current commercial batteries that rely on liquid electrolytes. Major challenges persist in controlling morphological evolution during the plating and stripping of lithium metal at the anode current collector. Elemental additives that alloy with lithium have been found to modify the plating and stripping behavior of lithium. Many alloying elements form intermetallics with lithium and the mobility of Li through these intermetallics is believed to have an important effect on morphological evolution. This study shows that Li transport coefficients through intermetallics span a wide range in values, with the B32 LiAl intermetallic predicted to have a Li tracer diffusion coefficient as high as 10-6 cm2/s at room temperature, which is 8 orders of magnitude larger than that of isostructural B32 LiZn. This work demonstrates the crucial role of vacancy concentration in controlling the mobility of Li atoms through intermetallics. While the migration barriers for Li-vacancy exchanges in both LiAl and LiZn are remarkably low, the superatomic conductivity in LiAl is shown to arise from the unique electronic structure of the B32 LiAl compound, which favors high concentrations of vacancies.

Fiber Optic Boltzmann Thermometry in a Doped Halide Double Perovskite for Dynamic Temperature Monitoring in Pouch Cell

Temperature evolution is critical in monitoring the status of Li-ion batteries (LIBs), however, it is a challenge to develop precise thermometry down to the nanoscale regime and instantly detect the internal temperature of pouch-type LIBs. Herein, a Boltzmann type luminescence thermometry is designed and prepared in halide double perovskite Cs2NaLuCl6:Yb/Er upconversion nanocrystals and further fabricate the flexible fluorescence polymer optical fiber (POF) sensor for their in situ and real-time temperature monitoring. The thermally enhanced upconversion luminescence of the nanocrystals thermometry ensures sensitive temperature sensing in a wide temperature range, and the POF sensor exhibits stable and repeatable responses to temperature with a deviation of ±0.13 at 30 °C. Through the implementation of fluorescence POF sensors into pouch cell, the dynamic thermal state inside the LIBs is instantaneously captured without affecting the normal operations during battery cycling. This work paves the way for fluorescence POF sensors assisting in battery thermal management and evaluating the performance of battery materials for further developing LIBs.

High-Elastic Flame-Retardant Polyacrylate-Based Gel Polymer Electrolyte by Dual-Phase Fluorination for Highly Stable Lithium-Metal Batteries

Lithium-metal batteries (LMBs) are emerging as promising energy storage devices due to their exceptional energy densities. However, uncontrolled lithium dendrite growth and the flammability of liquid electrolytes heavily hinder their widespread applications. To circumvent such issues, we develop a dual-phase fluorinated gel polymer electrolyte (TF-GPE), composed of a fluorinated framework polymerized by 2,2,2-trifluoroethyl acrylate and a fluorinated solvent with fluoroethylene carbonate. The resulting TF-GPE exhibits an impressive tensile elasticity and volumetric accommodations of repeated lithium deposition and stripping up to 4000 h. Additionally, TF-GPE demonstrates excellent flame retardancy by forming a dense fluorine-containing carbon layer. By analyzing the surface of cycled lithium metal, we reveal the formation of elastic solid electrolyte interphase structures with outer organic and inner LiF-rich inorganic layers, enabling stable cycling of 500 cycles with 80.5% capacity retention for solid-state LMBs at 1 C. Our work presents a promising approach to enhancing the stability of LMBs.

Regulating Interfacial Wettability for Fast Mass Transfer in Rechargeable Metal-Based Batteries

The interfacial wettability between electrodes and electrolytes could ensure sufficient physical contact and fast mass transfer at the gas-solid-liquid, solid-liquid, and solid-solid interfaces, which could improve the reaction kinetics and cycle stability of rechargeable metal-based batteries (RMBs). Herein, interfacial wettability engineering at multiphase interfaces is summarized from the electrolyte and electrode aspects to promote the interface reaction rate and durability of RMBs, which illustrates the revolution that is taking place in this field and thus provides inspiration for future developments in RMBs. Specifically, this review presents the principle of interfacial wettability at macro- and microscale and summarizes emerging applications concerning the interfacial wettability effect on mass transfer in RMBs. Moreover, deep insight into the future development of interfacial wettability is provided in the outlook. Therefore, this review not only provides insights into interfacial wettability engineering but also offers strategic guidance for wettability modification and optimization toward stable electrode-electrolyte interfaces for fast mass transfer in RMBs.

The nucleation and growth mechanism of spherical Li for advanced Li metal anodes - a review

Metallic lithium (Li) is known as the "Holy Grail" of anode materials in the research area of Li-based batteries. However, Li metal anodes (LMAs) are plagued by infinite volume changes and dendrite formation during operation. Spherical Li exhibits rounded surfaces, which effectively mitigates the short circuit risks associated with dendritic Li, and has the smallest specific surface area compared to other deposit morphologies, thus enabling less electrolyte consumption and higher Coulombic efficiency (CE). What's more, three-dimensional (3D) conductive frameworks have good mechanical robustness and flexibility to withstand the volume changes that occur during cycling. This review systematically depicts the theoretical models for Li deposition, the mechanisms and formation conditions of spherical Li, and the benefits of the Li deposition model as well as the advantages of combining Li spheres with 3D conductive frameworks based on our previous works. We hope that this review can inspire researchers in this filed to pave the way for advanced LMAs.

Enhancing Li Deposition Behavior through Valence Gradient-Assisted Iron Layer

Uncontrolled lithium (Li) dendrite formation presents major safety risks and challenges in the Li host design. A novel approach is introduced, using a valence gradient in iron nanoparticles (Fe0, Fe2+, Fe3+) to stabilize the anodes. An Fe0 component, with fast Li diffusion, ensures a steady supply of Li to Fe2+ and Fe3+ components, which have slower Li diffusion. This coordinated interplay between fast and slow diffusion uniformizes Li deposition near the substrate, effectively reducing the rate of dendrite growth. The as-prepared framework demonstrates uniform Li plating with a minimal hysteresis voltage after extensive cycling for 1200 h in symmetric cells. Integrated into a full cell with LiFePO4, it demonstrates outstanding cycling stability for almost 950 cycles with a capacity of 92.2 mA h g-1 at 1C with an ultralow N/P ratio of 1.19. This valence gradient design strategy broadens the design potential for transition-metal compounds in regulating Li deposition by mitigating interfacial Li+ behavior.

A modified separator based on ternary mixed-oxide for stable lithium metal batteries

Li metal batteries (LMBs) are among the most promising options for next-generation secondary batteries under the rapidly growing demand for high-energy-density electrochemical energy storage. However, the implementation of LMBs are hindered by major obstacles such as dentritic Li deposition and low cycling Coulombic efficiency. A practical functional separator is developed in this study, which consists of a Lewis acidic mixed oxide of ZrO2-SiO2-Al2O3 as a functional coating with anion anchoring ability to modulate ion transport in the vicinity of the Li metal anode, delivering a high Li+ transference number of 0.88 in carbonate electrolytes that suppresses dendrite formation. The strong Lewis acid sites in ZrO2-SiO2-Al2O3 originate from coordinatively unsaturated Zr4+ ions, which immobilize anions and reduce their decomposition rate. This significantly improves the chemical stability of the electrolyte and induces a more stable solid electrolyte interphase layer. The modified separator enables an anode-free cell containing a high-loading LiNi0.8Co0.1Mn0.1O2 cathode to present stable charge and discharge cycling for 150 cycles at 0.5C. By effectively suppressing Li dendrite growth and supporting the long-term operation of anode-free LMBs, this study offers a novel approach to rationally design mixed oxides with high Lewis acidity for functional separators.

Li2ZnCu3 Modified Cu Current Collector to Regulate Li Deposition

Rationally designing a current collector that can maintain low lithium (Li) porosity and smooth morphology while enduring high-loading Li deposition is crucial for realizing the high energy density of Li metal batteries, but it is still challengeable. Herein, a Li2ZnCu3 alloy-modified Cu foil is reported as a stable current collector to fulfill the stable high-loading Li deposition. Benefiting from the in situ alloying, the generated numerous Li2ZnCu3@Cu heterojunctions induce a homogeneous Li nucleation and dense growth even at an ultrahigh capacity of 12 mAh cm-2. Such a spatial structure endows the overall Li2ZnCu3@Cu electrode with the manipulated steric hindrance and outmost surface electric potential to suppress the side reactions during Li stripping and plating. The resultant Li||Li2ZnCu3@Cu asymmetric cell preserves an ultrahigh average Coulombic efficiency of 99.2 % at 3 mA cm-2/6 mAh cm-2 over 200 cycles. Moreover, the Li-Li2ZnCu3@Cu||LiFePO4 cell maintains a cycling stability of 87.5 % after 300 cycles. After coupling with the LiCoO2 cathode (4 mAh cm-2), the cell exhibits a high energy density of 407.4 Wh kg-1 with remarkable cycling reversibility at an N/P ratio of 3. All these findings present a doable way to realize the high-capacity, dendrite-free, and dense Li deposition for high-performance Li metal batteries.

In Situ Grown Li2Te Enhanced Lithium Metal Anode Interfacial Kinetics

Lithium metal anode (LMA) is expected to be the ideal anode material for future high-energy-density batteries, but regulating the complex electrolyte-anode interface remains a challenge. In this work, a stable Li2Te coating is formed on the surface of commercial copper mesh (LTCM) using a simple and quick method to improve lithium metal anode interfacial kinetics. Li2Te possesses a strong affinity for both Li+ and TFSI- anions, which reduces the lithium nucleation barrier and guides the formation of inorganic-rich SEI, accelerates the diffusion of Li+, and promotes the growth of lithium metal along the plane. The highly conductive Li2Te and Cu generated by in situ lithiation reaction together constitute an effective electron-conducting network, which synergistically enhances the interfacial kinetics and the cycling stability of LMA. As a result, the LTCM maintains high Coulombic efficiency (98%) even after 2200 cycles at 1 mA cm-2, whereas the symmetric cell has a long cycle life of over 5400 h at 1 mA cm-2. In addition, the full cells with LFP display a high capacity retention ratio (80%) after 480 cycles at 1 C and the corresponding pouch cell can cycle steadily more than 464 cycles at 1 C, which has good application prospects.

Interfacial Engineering Constructing TFSI- Ion-Sieve Protective Umbrella Guiding Li-Ion Selective Transport and Solid SEI Growth

A novel strategy is proposed by constructing TFSI- ion-sieve interlayer to guide Li-ion selective transport and solid SEI growth. The uniform MgF2 seeds on the fiber surface reacts rapidly with Li+ in electrolyte to form Mg and LiF dual functional sites for the first charging process. Benefiting from the high affinity of LiF, the TFSI- ions is enriched near the anode forming an ion-sieve interlayer, which acts as a protective umbrella and guides priority penetration of Li+ due to the coordination reaction with Li+ and thus homogenize the Li+ flux. While the Mg sites induce Li nucleation with its strong lithiophilicity and facilitate uniform Li plating on fiber surface. Furthermore, as raw material of LiF, the TFSI- enrichment on anode surface is contribute to increasing LiF content in SEI, achieving the stability enhancement and densification of SEI. Of greater importance, the excess Li+ can spread to the adjacent Mg sites for nucleation by means of ultralow Li+ migration barrier on LiF and Mg. The combination of the ion-sieve homogenization of Li+ flux in electrolyte and the uniformity of Li+ transport in LiF/Mg solid medium achieves the purpose of uniform Li metal plating/stripping.

Scalable Production of Thin and Durable Practical Li Metal Anode for High-Energy-Density Batteries

Utilization of thin Li metal is the ultimate pathway to achieving practical high-energy-density Li metal batteries (LMBs), but its practical implementation has been significantly impeded by formidable challenges of poor thinning processability, severe interphase instability and notorious dendritic Li growth. Here we report a practical thin (10-40 μm) Li/Mo/Li2Se with concurrently modulated interphase and mechanical properties, achieved via a scalable mechanical rolling process. The in situ generated Li2Se and Mo not only enhance the mechanical strength enabling the scalable fabrication of thin Li metal, but also promote homogeneous Li electrodeposition. Significantly, the Li/Mo/Li2Se demonstrates ultrahigh-rate performance (15 mA cm-2) and ultralong-lifespan cycling sustainability (2700 cycles) with exceptional anti-pulverization capability. The Li|LiFePO4 cells show substantially prolonged cyclability over 1200 cycles with an ultralow decay rate of ~0.01 % per cycle. Moreover, the Li|LiNi0.8Co0.1Mn0.1O2 pouch cells deliver enhanced cycling stability even under the extremely harsh conditions of low negative-to-positive-capacity (N/P) ratio of ~1.2 and lean electrolyte of ~0.95 g Ah-1, showing an exceptional energy density of 329.2 Wh kg-1. This work sheds light on facile pathway for scalable production of durable thin Li metal anode toward reliable practicability.

The Impact of Supersaturated Electrode on Heterogeneous Lithium Nucleation and Growth Dynamics

The concept of a lithiophilic electrode proves inadequate in describing carbon-based electrode materials due to their substantial mismatch in surface energy with lithium metal. However, their notable capacity for lithium chemisorption can increase active lithium concentration required for nucleation and growth, thereby enhancing the electrochemical performance of lithium metal anodes (LMAs). In this study, we elucidate the effects of the supersaturated electrode which has high active lithium capacity around equilibrium lithium potential on LMAs through an in-depth electrochemical comparison using two distinct carbon electrode platforms with differing carbon structures but similar two-dimensional morphologies. In the supersaturated electrode, both the dynamics and thermodynamic states involved in lithium nucleation and growth mechanisms are significantly improved, particularly under continuous current supply conditions. Furthermore, the chemical structures of the solid-electrolyte-interface layers (SEIs) are greatly influenced by the elevated surface lithium concentration environment, resulting in the formation of more conductive lithium-rich SEI layers. The improved dynamics and thermodynamics of surface lithium, coupled with the formation of enhanced SEI layers, contribute to higher power capabilities, enhanced Coulombic efficiencies, and improved cycling performances of LMAs. These results provide new insight into understanding the enhancements in heterogeneous lithium nucleation and growth kinetics on the supersaturated electrode.

Customizing Pore Structure and Lithiophilic Sites Dual-Gradient Free-Standing 3D Lithium-Based Anode to Enable Excellent Lithium Metal Batteries

Developing 3D hosts is one of the most promising strategies for putting forward the practical application of lithium(Li)-based anodes. However, the concentration polarization and uniform electric field of the traditional 3D hosts result in undesirable "top growth" of Li, reduced space utilization, and obnoxious dendrites. Herein, a novel dual-gradient 3D host (GDPL-3DH) simultaneously possessing gradient-distributed pore structure and lithiophilic sites is constructed by an electrospinning route. Under the synergistic effect of the gradient-distributed pore and lithiophilic sites, the GDPL-3DH exhibits the gradient-increased electrical conductivity from top to bottom. Also, Li is preferentially and uniformly deposited at the bottom of the GDPL-3DH with a typical "bottom-top" mode confirmed by the optical and SEM images, without Li dendrites. Consequently, an ultra-long lifespan of 5250 h of a symmetrical cell at 2 mA cm-2 with a fixed capacity of 2 mAh cm-2 is achieved. Also, the full cells based on the LiFePO4, S/C, and LiNi0.8Co0.1Mn0.1O2 cathodes all exhibit excellent performances. Specifically, the LiFePO4-based cell maintains a high capacity of 136.8 mAh g-1 after 700 cycles at 1 C (1 C = 170 mA g-1) with 94.7% capacity retention. The novel dual-gradient strategy broadens the perspective of regulating the mechanism of lithium deposition.

Defect-Mediated Formation of Oriented Phase Domains in a Lithium-Ion Insertion Electrode

The performance and robustness of electrodes are closely related to transformation-induced nanoscale structural heterogeneity during (de)lithiation. As a result, it is critical to understand at atomic scale the origin of such structural heterogeneity and ultimately control the transformation microstructure, which remains a formidable task. Here, by performing in situ studies on a model intercalation electrode material, anatase TiO2, we reveal that defects─both preexisting and as-formed during lithiation─can mediate the local anisotropic volume expansion direction, resulting in the formation of multiple differently oriented phase domains and eventually a network structure within the lithiated matrix. Our results indicate that such a mechanism operated by defects, if properly harnessed, could not only improve lithium transport kinetics but also facilitate strain accommodation and mitigate chemomechanical degradation. These findings provide insights into the connection of defects to the robustness and rate performance of electrodes, which help guide the development of advanced lithium-ion batteries via defect engineering.

Vacuum Evaporation Plating Enabling ≤ 10 µm Ultrathin Lithium Foils for Lithium Metal Batteries

Lithium (Li) metal is widely recognized as a viable candidate for anode material in future battery technologies due to its exceptional energy density. Nevertheless, the commercial Li foils in common use are too thick (≈100 µm), resulting in a waste of Li resources. Herein, by applying the vacuum evaporation plating technology, the ultra-thin Li foils (VELi) with high purity, strong adhesion, and thickness of less than 10 µm are successfully prepared. The manipulation of evaporation temperature allows for convenient regulation of the thickness of the fabricated Li film. This physical thinning method allows for fast, continuous, and highly accurate mass production. With a current density of 0.5 mA cm-2 for a plating amount of 0.5 mAh cm-2, VELi||VELi cells can stably cycle for 200 h. The maximum utilization of Li is already more than 25%. Furthermore, LiFePO4||VELi full cells present excellent cycling performance at 1 C (1 C = 155 mAh g-1) with a capacity retention rate of 90.56% after 240 cycles. VELi increases the utilization of active Li and significantly reduces the cost of Li usage while ensuring anode cycling and multiplication performance. Vacuum evaporation plating technology provides a feasible strategy for the practical application of ultra-thin Li anodes.

Recent Progress in Using Covalent Organic Frameworks to Stabilize Metal Anodes for Highly-Efficient Rechargeable Batteries

Alkali metals (e.g. Li, Na, and K) and multivalent metals (e.g. Zn, Mg, Ca, and Al) have become star anodes for developing high-energy-density rechargeable batteries due to their high theoretical capacity and excellent conductivity. However, the inevitable dendrites and unstable interfaces of metal anodes pose challenges to the safety and stability of batteries. To address these issues, covalent organic frameworks (COFs), as emerging materials, have been widely investigated due to their regular porous structure, flexible molecular design, and high specific surface area. In this minireview, we summarize the research progress of COFs in stabilizing metal anodes. First, we present the research origins of metal anodes and delve into their advantages and challenges as anodes based on the physical/chemical properties of alkali and multivalent metals. Then, special attention has been paid to the application of COFs in the host design of metal anodes, artificial solid electrolyte interfaces, electrolyte additives, solid-state electrolytes, and separator modifications. Finally, a new perspective is provided for the research of metal anodes from the molecular design, pore modulation, and synthesis of COFs.