Interfacial Layers with Desolvation Function Induced Stable Deposition of Lithium Metal for Long-Cycling Lithium Metal Batteries

The unstable solid electrolyte interface (SEI) formed by uncontrollable electrolyte degradation, which leads to dendrite growth and Coulombic efficiency decay, hinders the development of Li metal anodes. A controllable desolvation process is essential for the formation of stable SEI and improved lithium metal deposition behavior. Here, we show a functional artificial interface protective layer comprised of chondroitin sulfate-reduced graphene oxide (CrG), on which polar functional groups are distributed to effectively reduce the energy barrier for desolvation of Li+ and effectively alienate solvent molecules to avoid solvent involvement in SEI formation, thus promoting the formation of a LiF-rich SEI. Consequently, stable Coulombic efficiencies of 98.4% were achieved after 500 cycles in a Li//Cu cell. Moreover, the LiFePO4 full cells achieve steady circulation (470 cycles at 80%, 1 C) with a negative/positive electrode capacity ratio of 2.87. Our multifunctional artificial interface protective layer provides a new way to advance Li metal batteries.

MgNiO2 as a Ceramic Additive To Improve the Durability of Lithium Metal Anode

Ceramic materials are the most popular additives to regulate the reinless interfacial reaction between lithium and the electrolyte by strengthening the SEI layer or tuning lithium deposition. Here, we propose an exceptional material, MgNiO2, abbreviated as MN, which can improve the durability of lithium metal anode. Since it is undecomposed up to 0 V vs Li/Li+, the MN's particles give some semiconductive characteristics to the SEI layer to tune the interfacial reactions. The addition of MgNiO2 in the protective films lowers interfacial resistance, which is responsible for the improved durability of Li|Cu cells: ∼210 cycles, which is 4 times longer than that of the control. Furthermore, this ceramic is used to modify the carbon film woven with carbon nanofibers (CNF @ MN). The cells with this modified 3-D host present excellent operational lives, as high as ∼2400 h in Li|Li symmetric cells and ∼280 cycles in the Li|NCM811 cells. Our approaches demonstrate that MN is an effective ceramic for stabilizing the lithium anode. It also indicates that the inert nature of the semiconductor to lithium is worth exploring thoroughly.

Vitrified Metal-Organic Framework Composite Electrolyte Enabling Dendrite-Free and Long-Lifespan Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (LMBs) are still plagued with low ionic conductivity and inferior interfacial contact, which hinder their practical implementation. Herein, a quasi-solid-state composite electrolyte, poly(1,3-dioxolane) (PDOL)/glassy ZIF-62 (PGZ) with fast ion transport and intimate interface contact, is fabricated via in situ polymerization. The in situ polymerization of DOL in an electrolyte matrix not only improves the exterior interface between electrolyte/electrode but also optimizes the inner interfaces among glassy particles, rendering PGZ as an uninterrupted ionic conductor. Moreover, PGZ inherits the superior ionic conductivity and the robust dendrite prohibition of glassy MOFs originating from their grain-boundary-free nature, isotropy, and abundant groups containing N species. As expected, our proposed PGZ exhibits a prominent ionic conductivity of 6.3 × 10-4 S cm-1 at 20 °C. Li|PGZ|LiFePO4 delivers an outstanding rate performance (103 mAh g-1 at 4C) and a stable cycling capacity (118 mAh g-1 at 1C over 1000 cycles). PGZ also presents excellent low-temperature cycling performance with 75 mAh g-1 for 480 cycles at -20 °C and excellent flame retardance. Even at a high loading of 12.1 mg cm-2, it can still discharge at 140 mAh g-1 for 100 cycles. Hence, PGZ prepared via in situ polymerization holds enormous prospects as a solid-state electrolyte for high-performance and safe LMBs.

Interphase Engineering via Solvent Molecule Chemistry for Stable Lithium Metal Batteries

Lithium metal battery has been regarded as promising next-generation battery system aiming for higher energy density. However, the lithium metal anode suffers severe side-reaction and dendrite issues. Its electrochemical performance is significantly dependant on the electrolyte components and solvation structure. Herein, a series of fluorinated ethers are synthesized with weak-solvation ability owing to the duple steric effect derived from the designed longer carbon chain and methine group. The electrolyte solvation structure rich in AGGs (97.96 %) enables remarkable CE of 99.71 % (25 °C) as well as high CE of 98.56 % even at -20 °C. Moreover, the lithium-sulfur battery exhibits excellent performance in a wide temperature range (-20 to 50 °C) ascribed to the modified interphase rich in LiF/LiO2. Furthermore, the pouch cell delivers superior energy density of 344.4 Wh kg-1 and maintains 80 % capacity retention after 50 cycles. The novel solvent design via molecule chemistry provides alternative strategy to adjust solvation structure and thus favors high-energy density lithium metal batteries.

Interfacial Spinel Local Interlocking Strategy Toward Structural Integrity in P3 Oxide Cathodes

P3-layered transition oxide cathodes have garnered considerable attention owing to their high initial capacity, rapid Na+ kinetics, and less energy consumption during the synthesis process. Despite these merits, their practical application is hindered by the substantial capacity degradation resulting from unfavorable structural transformations, Mn dissolution and migration. In this study, we systematically investigated the failure mechanisms of P3 cathodes, encompassing Mn dissolution, migration, and the irreversible P3-O3' phase transition, culminating in severe structural collapse. To address these challenges, we proposed an interfacial spinel local interlocking strategy utilizing P3/spinel intergrowth oxide as a proof-of-concept material. As a result, P3/spinel intergrowth oxide cathodes demonstrated enhanced cycling performance. The effectiveness of suppressing Mn migration and maintaining local structure of interfacial spinel local interlocking strategy was validated through depth-etching X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and in situ synchrotron-based X-ray diffraction. This interfacial spinel local interlocking engineering strategy presents a promising avenue for the development of advanced cathode materials for sodium-ion batteries.

Zn-based batteries for sustainable energy storage: strategies and mechanisms

Batteries play a pivotal role in various electrochemical energy storage systems, functioning as essential components to enhance energy utilization efficiency and expedite the realization of energy and environmental sustainability. Zn-based batteries have attracted increasing attention as a promising alternative to lithium-ion batteries owing to their cost effectiveness, enhanced intrinsic safety, and favorable electrochemical performance. In this context, substantial endeavors have been dedicated to crafting and advancing high-performance Zn-based batteries. However, some challenges, including limited discharging capacity, low operating voltage, low energy density, short cycle life, and complicated energy storage mechanism, need to be addressed in order to render large-scale practical applications. In this review, we comprehensively present recent advances in designing high-performance Zn-based batteries and in elucidating energy storage mechanisms. First, various redox mechanisms in Zn-based batteries are systematically summarized, including insertion-type, conversion-type, coordination-type, and catalysis-type mechanisms. Subsequently, the design strategies aiming at enhancing the electrochemical performance of Zn-based batteries are underscored, focusing on several aspects, including output voltage, capacity, energy density, and cycle life. Finally, challenges and future prospects of Zn-based batteries are discussed.

Interface engineering of Li6.75La3Zr1.75Ta0.25O12via in situ built LiI/ZnLix mixed buffer layer for solid-state lithium metal batteries

Garnet-type solid-state Li metal batteries (SSLMBs) are viewed as hopeful next-generation batteries due to their high energy density and safety. However, the major obstacle to the development of garnet-type SSLMBs is the lithiophobicity of Li6.75La3Zr1.75Ta0.25O12 (LLZTO), resulting in a large interfacial impedance. Herein, a LiI/ZnLix mixed ion/electron conductive buffer layer is constructed at the interface by an in situ reaction of molten Li metal with ZnI2 film. This mixed buffer layer ensures close contact between the Li metal and garnet, significantly reducing interfacial impedance. As a result, the Li symmetrical cell with the LiI/ZnLix buffer layer shows an interface impedance of 10.3 Ω cm2, much lower than that of the cell with bare LLZTO (1173.4 Ω cm2). The critical current density (CCD) is up to 2.3 mA cm-2, and the symmetric cells present a long cycle life of 2000 h at 0.1 mA cm-2 and 800 h at 1.0 mA cm-2. In addition, the full cells assembled with the LiFePO4 cathode show a capacity of 143.9 mA h g-1 after 200 cycles at 0.5C with a low-capacity decay of 0.021% per cycle. This work reveals a simple, feasible, and practical interface modification strategy for solid-state Li metal batteries.

An Ultrathin Composite Polymer Electrolyte Dual-Reinforced by a Polymer of Intrinsic Microporosity (PIM-1) and Poly(tetrafluoroethylene) (PTFE) Porous Membrane

The performances of solid-state polymer electrolytes are urgently required to be further improved for high energy density lithium metal batteries. Herein, a highly reinforced ultrathin composite polymer electrolyte (PLPP) is successfully fabricated in a large scale by densely filling the well-dispersed mixture of polyethylene oxide (PEO), Li-salt (LiTFSI) and a polymer of intrinsic microporosity (PIM-1) into porous poly(tetrafluoroethylene) (PTFE) matrix. Based on the macro-plus-micro synergistic enhancement of the PTFE with excellent mechanical properties and the soluble PIM-1 with suitable functional groups, the PLPP electrolyte exhibits excellent properties including mechanical stress, thermal stability, lithium-ion transference number, voltage window and ionic conductivity, which are all superior to the typical PEO/LiTFSI electrolytes. As a result, the Li/PLPP/Li symmetric cell can stably cycle for > 2000 h, and the LiFePO4/PLPP/Li full cell exhibits excellent rate performance (>10 C) and high cycling stability with an initial capacity of 158.8 mAh g-1 and a capacity retention of 78.8% after 300 cycles. In addition, the excellent mechanical properties as well as the wide voltage window reasonably result in the stable operation of full cells with either high-loading cathode up to 28.1 mg cm-2 or high voltage cathode with high energy density.

Highly Conductive Imidazolate Covalent Organic Frameworks with Ether Chains as Solid Electrolytes for Lithium Metal Batteries

Poly(ethylene oxide) (PEO)-based electrolytes are often used for Li+ conduction as they can dissociate the Li salts efficiently. However, high entanglement of the chains and lack of pathways for rapid ion diffusion limit their applications in advanced batteries. Recent developments in ionic covalent organic frameworks (iCOFs) showed that their highly ordered structures provide efficient pathways for Li+ transport, solving the limitations of traditional PEO-based electrolytes. Here, we present imidazolate COFs, PI-TMEFB-COFs, having methoxyethoxy chains, synthesized by Debus-Radziszewski multicomponent reactions and their ionized form, Li+@PI-TMEFB-COFs, showing a high Li+ conductivity of 8.81 mS cm-1 and a transference number of 0.974. The mechanism for such excellent electrochemical properties is that methoxyethoxy chains dissociate LiClO4, making free Li+, then those Li+ are transported through the imidazolate COFs' pores. The synthesized Li+@PI-TMEFB-COFs formed a stable interface with Li metal. Thus, employing Li+@PI-TMEFB-COFs as the solid electrolyte to assemble LiFePO4 batteries showed an initial discharge capacity of 119.2 mAh g-1 at 0.5 C, and 82.0 % capacity and 99.9 % Coulombic efficiency were maintained after 400 cycles. These results show that iCOFs with ether chains synthesized via multicomponent reactions can create a new chapter for making solid electrolytes for advanced rechargeable batteries.

Insight into the probability of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) as the functional electrolyte additive in lithium-sulfur batteries

Enhancing the flame retardancy of electrolytes and the stability of lithium anodes is of great significance to improve the safety performance of lithium-sulfur (Li-S) batteries. It is well known that the most commonly used ether based electrolyte solvents in Li-S batteries have a lower flash point and higher volatility than the ester electrolyte solvents in Li-ion batteries. Hence, lithium-sulfur batteries have greater safety risks than lithium-ion batteries. Herein, ethoxy(pentafluoro)cyclotriphosphazene (PFPN), which is commonly used as a flame retardant for ester electrolytes in lithium-ion batteries, is utilized as both a film-forming electrolyte additive and a flame retardant additive for the ether electrolyte to investigated its applicability in Li-S batteries. It is found that the ether electrolyte containing PFPN not only has good flame retardant properties and a wide potential window of about 5 V, but also can form a stable SEI film on the surface of a lithium anode. As a result, with the ether-based electrolyte containing 10 wt% PFPN, Li-Cu and Li-S batteries all delivered a stable cycling performance with a high coulombic Efficiency and a long-lifespan performance, which were all superior to the batteries using the ether-based electrolyte without PFPN. This study demonstrates an effective solution to solve the problems of flammable ether-based electrolytes and reactive lithium anodes, and it may contribute to the development of safe Li-S batteries.

Undercoordination Chemistry of Sulfur Electrocatalyst in Lithium-Sulfur Batteries

Undercoordination chemistry is an effective strategy to modulate the geometry-governed electronic structure and thereby regulate the activity of sulfur electrocatalysts. Efficient sulfur electrocatalysis is requisite to overcome the sluggish kinetics in lithium-sulfur (Li-S) batteries aroused by multi-electron transfer and multi-phase conversions. Recent advances unveil the great promise of undercoordination chemistry in facilitating and stabilizing sulfur electrochemistry, yet a related review with systematicness and perspectives is still missing. Herein, it is carefully combed through the recent progress of undercoordination chemistry in sulfur electrocatalysis. The typical material structures and operational strategies are elaborated, while the underlying working mechanism is also detailly introduced and generalized into polysulfide adsorption behaviors, polysulfide conversion kinetics, electron/ion transport, and dynamic reconstruction. Moreover, perspectives on the future development of undercoordination chemistry are further proposed.

Revitalization of Diluent Amide-Based Electrolyte for Building High-Voltage Lithium-Metal Batteries

Hitherto, highly concentrated electrolyte is the overarching strategy for revitalizing the usage of amide - in lithium-metal batteries (LMBs), which simultaneously mitigates the reactivity of amide toward Li and regulates uniform Li deposition via forming anion-solvated coordinate structure. However, it is undeniable that this would bring the cost burden for practical electrolyte preparation, which stimulates further electrolyte design toward tailoring anion-abundant Li+ solvation structure in stable amide electrolytes under a low salt content. Herein, a distinct method is conceived to design anions-enriched Li+ solvation structure in dilute amide-electrolyte (1 m Li-salt concentration) with the aid of integrating perfluoropolyethers (PFPE-MC) with anion-solvating ability and B/F-involved additives. The optimized electrolyte based on N,N-Dimethyltrifluoroacetamide (FDMAC) exhibits outstanding compatibility with Li and NCM622 cathode, facilitates uniform Li deposition along with robust solid electrolyte interphase (SEI) formation. Accordingly, both the lab-level LMB coin cell and practical pouch cell based on this dilute FDMAC electrolyte deliver remarkable performances with improved capacity and cyclability. This work pioneers the feasibility of diluted amide as electrolyte in LMB, and provides an innovative strategy for highly stable Li deposition via manipulating solvation structure within diluent electrolyte, impelling the electrolyte engineering development for practical high-energy LMBs.

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.

Molecular anchoring of free solvents for high-voltage and high-safety lithium metal batteries

Constraining the electrochemical reactivity of free solvent molecules is pivotal for developing high-voltage lithium metal batteries, especially for ether solvents with high Li metal compatibility but low oxidation stability ( <4.0 V vs Li+/Li). The typical high concentration electrolyte approach relies on nearly saturated Li+ coordination to ether molecules, which is confronted with severe side reactions under high voltages ( >4.4 V) and extensive exothermic reactions between Li metal and reactive anions. Herein, we propose a molecular anchoring approach to restrict the interfacial reactivity of free ether solvents in diluted electrolytes. The hydrogen-bonding interactions from the anchoring solvent effectively suppress excessive ether side reactions and enhances the stability of nickel rich cathodes at 4.7 V, despite the extremely low Li+/ether molar ratio (1:9) and the absence of typical anion-derived interphase. Furthermore, the exothermic processes under thermal abuse conditions are mitigated due to the reduced reactivity of anions, which effectively postpones the battery thermal runaway.

Bottom-Up Magnesium Deposition Induced by Paper-Based Triple-Gradient Scaffolds toward Flexible Magnesium Metal Batteries

The development of advanced magnesium metal batteries (MMBs) has been hindered by longstanding challenges, such as the inability to induce uniform magnesium (Mg) nucleation and the inefficient utilization of Mg foil. This study introduces a novel solution in the form of a flexible, lightweight, paper-based scaffold that incorporates gradient conductivity, magnesiophilicity, and pore size. This design is achieved through an industrially adaptable papermaking process in which the ratio of carboxylated multi-walled carbon nanotubes to softwood cellulose fibers is meticulously adjusted. The triple-gradient structure of the scaffold enables the regulation of Mg ion flux, promoting bottom-up Mg deposition. Owing to its high flexibility, low thickness, and reduced density, the scaffold has potential applications in flexible and wearable electronics. Accordingly, the triple-gradient electrodes exhibit stable operation for over 1200 h at 3 mA cm-2 /3 mAh cm-2 in symmetrical cells, markedly outperforming the non-gradient and metallic Mg alternatives. Notably, this study marks the first successful fabrication of a flexible MMB pouch full cell, achieving an impressive volumetric energy density of 244 Wh L-1 . The simplicity and scalability of the triple-gradient design, which uses readily available materials through an industrially compatible papermaking process, open new doors for the production of flexible, high-energy-density metal batteries.

Light-Assisted Lithium Metal Anode Enabled by In Situ Photoelectrochemical Engineering

Rechargeable battery devices with high energy density are highly demanded by the modern society. The use of lithium (Li) anodes is extremely attractive for future rechargeable battery devices. However, the notorious Li dendritic and instability of solid electrolyte interface (SEI) issues pose series of challenge for metal anodes. Here, based on the inspiration of in situ photoelectrochemical engineering, it is showed that a tailor-made composite photoanodes with good photoelectrochemical properties (Li affinity property and photocatalytic property) can significantly improve the electrochemical deposition behavior of Li anodes. The light-assisted Li anode is accommodated in the tailor-made current collector without uncontrollable Li dendrites. The as-prepared light-assisted Li metal anode can achieve the in situ stabilization of SEI layer under illumination. The corresponding in situ formation mechanism and photocatalytic mechanism of composite photoanodes are systematically investigated via DFT theoretical calculation, ex situ UV-vis and ex situ XPS characterization. It is worth mentioning that the as-prepared composite photoanodes can adapt to the ultra-high current density of 15 mA cm-2 and the cycle capacity of 15 mAh cm-2 under light, showing no dendritic morphology and low hysteresis voltage. This work is of great significance for the commercialization of new generation Li metal batteries.

A 3D Lithiophilic Host for Dendrite-Free Lithium Metal Anode via One-Step Carbonization of an Energetic Metal-Organic Framework

Low Coulombic efficiency (CE) and safety issues are huge problems that hinder the practical application of Li metal anodes. Constructing Li host structures decorated with functional species can restrain the growth of Li dendrites and alleviate the great volume change. Here, a 3D porous carbonaceous skeleton modified with rich lithiophilic groups (Zn, ZnO, and Zn(CN)2 ) is synthesized as a Li host via one-step carbonization of a triazole-containing metal-organic framework. The nano lithiophilic groups serve as preferred sites for Li nucleation and growth, regulating a uniform Li+ flux and uniform current density distribution. In addition, the 3D porous network functions as a Li reservoir that provides rich internal space to store Li, thus alleviating the volumetric expansion during Li plating/stripping process. Thanks to these component and structural merits, an ultra-low overpotential for Li deposition is achieved, together with high CE of over 99.5% for more than 500 cycles at 1 mA cm-2 and 1 mAh cm-2 in half cells. The symmetric cells exhibit a prolonged cycling of 900 h at 1 mA cm-2 . The full cells by coupling Zn/ZnO/Zn(CN)2 @C-Li anode with LiFePO4 cathode deliver a high capacity retention of 94.3% after 200 cycles at 1 C.

Diagnosing the Electrostatic Shielding Mechanism for Dendrite Suppression in Aqueous Zinc Batteries

Aqueous zinc electrolytes offer the potential for cheaper rechargeable batteries due to their safe compatibility with the high capacity metal anode; yet, they are stymied by irregular zinc deposition and consequent dendrite growth. Suppressing dendrite formation by tailoring the electrolyte is a proven approach from lithium batteries; yet, the underlying mechanistic understanding that guides such tailoring does not necessarily directly translate from one system to the other. Here, it is shown that the electrostatic shielding mechanism, a fundamental concept in electrolyte engineering for stable metal anodes, has different consequences for the plating morphology in aqueous zinc batteries. Operando electrochemical transmission electron microscopy is used to directly observe the zinc nucleation and growth under different electrolyte compositions and reveal that electrostatic shielding additive suppresses dendrites by inhibiting secondary zinc nucleation along the (100) edges of existing primary deposits and encouraging preferential deposition on the (002) faces, leading to a dense and block-like zinc morphology. The strong influence of the crystallography of Zn on the electrostatic shielding mechanism is further confirmed with Zn||Ti cells and density functional theory modeling. This work demonstrates the importance of considering the unique aspects of the aqueous zinc battery system when using concepts from other battery chemistries.

Insights into Nano- and Micro-Structured Scaffolds for Advanced Electrochemical Energy Storage

Adopting a nano- and micro-structuring approach to fully unleashing the genuine potential of electrode active material benefits in-depth understandings and research progress toward higher energy density electrochemical energy storage devices at all technology readiness levels. Due to various challenging issues, especially limited stability, nano- and micro-structured (NMS) electrodes undergo fast electrochemical performance degradation. The emerging NMS scaffold design is a pivotal aspect of many electrodes as it endows them with both robustness and electrochemical performance enhancement, even though it only occupies complementary and facilitating components for the main mechanism. However, extensive efforts are urgently needed toward optimizing the stereoscopic geometrical design of NMS scaffolds to minimize the volume ratio and maximize their functionality to fulfill the ever-increasing dependency and desire for energy power source supplies. This review will aim at highlighting these NMS scaffold design strategies, summarizing their corresponding strengths and challenges, and thereby outlining the potential solutions to resolve these challenges, design principles, and key perspectives for future research in this field. Therefore, this review will be one of the earliest reviews from this viewpoint.

Interconnected Three-Dimensional Porous Alginate-Based Gel Electrolytes for Lithium Metal Batteries

Lithium batteries have been widely used in our daily lives for their high energy density and long-term stability. However, their safety problems are of paramount concern for consumers, which restricts their scale applications. Gel polymer electrolytes (GPEs) compensate for the defects of liquid leakage and lower ionic conductivity of solid electrolytes, which have attracted a lot of attention. Herein, a 3D interconnected highly porous structural gel electrolyte was prepared with alginate dressing as a host material, poly(ethylene oxide) (PEO), and a commercial liquid electrolyte. With rich polar functional groups and (CH2-CH2-O) segments on the polymer matrix, the transportation of Li+ is faster and uniform; thus, the formations of lithium dendrite were significantly inhibited. The cycle stability of symmetrical Li||Li batteries with modified composite electrolytes (SAA) is greatly improved, and the overpotential remains stable after more than 1000 h. Meanwhile, under the same conditions, the cycle performance of batteries with unmodified electrolytes is inferior and overpotentials are nearly 1 V after 100 h. Additionally, the capacity retention of Li||LiFePO4 with SAA is more than 95% after 200 cycles, while those of the others declined sharply. The alginate dressing-based GPEs can greatly enhance the mechanical and thermal stability of PEO-based GPEs, which provides an environmentally friendly avenue for gel electrolytes' applications in lithium batteries.

Probing the Effectiveness in Stabilizing Lithium Metal Anodes through Functional Additives

A variety of electrolyte additives were comprehensively evaluated to understand their relative capability in stabilizing lithium metal anode. Although the Li||Cu test is an effective test to rule out ineffective additives, a reliable assessment of individual additives cannot be obtained just by a single evaluation method. Therefore, various methods must be combined to truly assess the stabilization of a lithium anode. Moreover, it was also discovered that a significant depletion of electrolytes occurred during the end-of-life of the lithium batteries, which partially contributed to the sudden failure of the lithium batteries during cycling. However, the main culprit of the sudden failure was identified as the significant increase in the resistance of the lithium metal anode. When used as an additive, cyclic fluorinated carbonates are the most effective in stabilizing the lithium anode and improving the cycling performance of lithium batteries among all the common additives. Despite its cost-effectiveness, the additive in the conventional electrolyte approach provides insufficient protection for lithium metal due to the complete consumption of the additive materials, which is necessary to repair the solid-electrolyte interphase (SEI). Therefore, it is suggested that a larger ratio (>15 wt %) of the SEI former should be employed to achieve effective lithium stabilization.

Electrolyte Design for Low-Temperature Li-Metal Batteries: Challenges and Prospects

Electrolyte design holds the greatest opportunity for the development of batteries that are capable of sub-zero temperature operation. To get the most energy storage out of the battery at low temperatures, improvements in electrolyte chemistry need to be coupled with optimized electrode materials and tailored electrolyte/electrode interphases. Herein, this review critically outlines electrolytes' limiting factors, including reduced ionic conductivity, large de-solvation energy, sluggish charge transfer, and slow Li-ion transportation across the electrolyte/electrode interphases, which affect the low-temperature performance of Li-metal batteries. Detailed theoretical derivations that explain the explicit influence of temperature on battery performance are presented to deepen understanding. Emerging improvement strategies from the aspects of electrolyte design and electrolyte/electrode interphase engineering are summarized and rigorously compared. Perspectives on future research are proposed to guide the ongoing exploration for better low-temperature Li-metal batteries.

Spatially isolating Li+ reduction from Li deposition via a Li22Sn5 alloy protective layer for advanced Li metal anodes

A Li alloy based artificial coating layer can improve the cyclic performance of Li metal anodes. However, the protective mechanism is not well clarified due to multiple components of the artificial layer and complicated interface in liquid electrolytes. Herein, a single-component Li22Sn5 alloy layer buffered Li anode is paired with a solid-state polymer electrolyte, where a metallic Sn film is sputtered onto the Li anode and the subsequent alloying reaction leads to the formation of a Li22Sn5 phase. During the striping/plating process, the thickness and composition of the Li-Sn alloy passivation layer remain unchanged. Meanwhile, Li+ ions are reduced on the top surface of the Li22Sn5 layer, then the reduced Li atoms immediately pass through the alloy layer, and finally dense Li deposition occurs beneath the protective layer, realizing spatial isolation of the electrochemical reduction of Li+ from Li nucleation/growth. This unique protection mechanism can principally avoid the formation of Li dendrites and efficiently mitigate irreversible reactions between the Li anode and the polymer electrolyte. The synergistic effects lead to a clean and flat surface of the protected Li electrode, enabling a prolonged cycle lifetime over 1300 h at 25 °C at 0.1 mA cm-2 and 0.1 mA h cm-2 in a configuration of symmetrical cells.

Directing (110) Oriented Lithium Deposition through High-flux Solid Electrolyte Interphase for Dendrite-free Lithium Metal Batteries

Controlling lithium (Li) electrocrystallization with preferred orientation is a promising strategy to realize highly reversible Li metal batteries (LMBs) but lack of facile regulation methods. Herein, we report a high-flux solid electrolyte interphase (SEI) strategy to direct (110) preferred Li deposition even on (200)-orientated Li substrate. Bravais rule and Curie-Wulff principle are expanded in Li electrocrystallization process to decouple the relationship between SEI engineering and preferred crystal orientation. Multi-spectroscopic techniques combined with dynamics analysis reveal that the high-flux CF3 Si(CH3 )3 (F3 ) induced SEI (F3 -SEI) with high LiF and -Si(CH3 )3 contents can ingeniously accelerate Li+ transport dynamics and ensure the sufficient Li+ concentration below SEI to direct Li (110) orientation. The induced Li (110) can in turn further promote the surface migration of Li atoms to avoid tip aggregation, resulting in a planar, dendrite-free morphology of Li. As a result, our F3 -SEI enables ultra-long stability of Li||Li symmetrical cells for more than 336 days. Furthermore, F3 -SEI modified Li can significantly enhance the cycle life of Li||LiFePO4 and Li||NCM811 coin and pouch full cells in practical conditions. Our crystallographic strategy for Li dendrite suppression paves a path to achieve reliable LMBs and may provide guidance for the preferred orientation of other metal crystals.

Photoelectrochemical Engineering for Light-Assisted Rechargeable Metal Batteries: Mechanism, Development, and Future

Rechargeable battery devices with high energy density are highly demanded by  our  modern society. The use of metal anodes is extremely attractive for future rechargeable battery devices. However, the notorious metal dendritic and instability of solid electrolyte interface issues pose a series of challenges for metal anodes. Recently, considering the indigestible dynamical behavior of metal anodes, photoelectrochemical engineering of light-assisted metal anodes have been rapidly developed since they efficiently utilize the integration and synergy of oriented crystal engineering and photocatalysis engineering, which provided a potential way to unlock the interface electrochemical mechanism and deposition reaction kinetics of metal anodes. This review starts with the fundamentals of photoelectrochemical engineering and follows with the state-of-art advance of photoelectrochemical engineering for light-assisted rechargeable metal batteries where photoelectrode materials, working principles, types, and practical applications are explained. The last section summarizes the major challenges and some invigorating perspectives for future research on light-assisted rechargeable metal batteries.

Plant Leaf-Inspired Separators with Hierarchical Structure and Exquisite Fluidic Channels for Dendrite-Free Lithium Metal Batteries

Lithium (Li) metal batteries are among the most promising devices for high energy storage applications but suffer from severe and irregular Li dendrite growth. Here, it is demonstrated that the issue can be well tackled by precisely designing the leaf-like membrane with hierarchical structure and exquisite fluidic channels. As a proof of concept, plant leaf-inspired membrane (PLIM) separators are prepared using natural attapulgite nanorods. The PLIM separators feature super-electrolyte-philicity, high thermal stability and high ion-selectivity. Thus, the separators can guide uniform and directed Li growth on the Li anode. The Li//PLIM//Li cell with limited Li anode shows high Coulombic efficiency and cycling stability over 1500 h with small overpotential and interface impedance. The Li//PLIM//S battery exhibits high initial capacity (1352 mAh g-1 ), cycling stability (0.019% capacity decay per cycle at 1 C over 500 cycles), rate performance (673 mAh g-1 at 4 C), and high operating temperature (65 °C). The separators can also effectively improve reversibility and cycling stability of the Li/Li cell and Li//LFP battery with carbonate-based electrolyte. As such, this work provides fresh insights into the design of bioinspired separators for dendrite-free metal batteries.

Radiation effects on lithium metal batteries

The radiation tolerance of energy storage batteries is a crucial index for universe exploration or nuclear rescue work, but there is no thorough investigation of Li metal batteries. Here, we systematically explore the energy storage behavior of Li metal batteries under gamma rays. Degradation of the performance of Li metal batteries under gamma radiation is linked to the active materials of the cathode, electrolyte, binder, and electrode interface. Specifically, gamma radiation triggers cation mixing in the cathode active material, which results in poor polarization and capacity. Ionization of solvent molecules in the electrolyte promotes decomposition of LiPF₆ along with its decomposition, and molecule chain breaking and cross-linking weaken the bonding ability of the binder, causing electrode cracking and reduced active material utilization. Additionally, deterioration of the electrode interface accelerates degradation of the Li metal anode and increases cell polarization, hastening the demise of Li metal batteries even more. This work provides significant theoretical and technical evidence for development of Li batteries in radiation environments.

An ionic liquid- and PEO-based ternary polymer electrolyte for lithium metal batteries: an advanced processing solvent-free approach for solid electrolyte processing

A processing solvent-free manufacturing process for cross-linked ternary solid polymer electrolytes (TSPEs) is presented. Ternary electrolytes (PEODA, Pyr₁₄TFSI, LiTFSI) with high ionic conductivities of >1 mS cm^-1 are obtained. It is shown that an increased LiTFSI content in the formulation (10 wt% to 30 wt%) decreases the risk of short-circuits by HSAL significantly. The practical areal capacity increases by more than a factor of 20 from 0.42 mA h cm^-2 to 8.80 mA h cm^-2 before a short-circuit occurs. With increasing Pyr₁₄TFSI content, the temperature dependency of the ionic conductivity changes from Vogel-Fulcher-Tammann to Arrhenius behavior, leading to activation energies for the ion conduction of 0.23 eV. In addition, high Coulombic efficiencies of 93% in Cu‖Li cells and limiting current densities of 0.46 mA cm^-2 in Li‖Li cells were obtained. Due to a temperature stability of >300 °C the electrolyte guarantees high safety in a broad window of conditions. In LFP‖Li cells, a high discharge capacity of 150 mA h g^-1 after 100 cycles at 60 °C was achieved.

Nucleophilic deposition behavior of metal anodes

Nucleophilic materials play important roles in the deposition behavior of high-energy-density metal batteries (Li, Na, K, Zn, and Ca), while the principle and determination method of nucleophilicity are lacking. In this review, we summarize the metal extraction/deposition process to find out the mechanism of nucleophilic deposition behavior. The key points of the most critical nucleophilic behavior were found by combining the potential change, thermodynamic analysis, and active metal deposition behavior. On this basis, the inductivity and affinity of the material have been determined by Gibbs free energy directly. Thus, the inducibility of most materials has been classified: (a) induced nuclei can reduce the overpotential of active metals; (b) not all materials can induce active metal deposition; (c) the induced reaction is not changeless. Based on these results, the influencing factors (temperature, mass, phase state, induced reaction product, and alloying reactions) were also taken into account during the choice of inducers for active metal deposition. Finally, the critical issues, challenges, and perspectives for further development of high-utilization metal electrodes were considered comprehensively.

Origin of Heterogeneous Stripping of Lithium in Liquid Electrolytes

Lithium metal batteries suffer from low cycle life. During discharge, parts of the lithium are not stripped reversibly and remain isolated from the current collector. This isolated lithium is trapped in the insulating remaining solid-electrolyte interphase (SEI) shell and contributes to the capacity loss. However, a fundamental understanding of why isolated lithium forms and how it can be mitigated is lacking. In this article, we perform a combined theoretical and experimental study to understand isolated lithium formation during stripping. We derive a thermodynamic consistent model of lithium dissolution and find that the interaction between lithium and SEI leads to locally preferred stripping and isolated lithium formation. Based on a cryogenic transmission electron microscopy (cryo TEM) setup, we reveal that these local effects are particularly pronounced at kinks of lithium whiskers. We find that lithium stripping can be heterogeneous both on a nanoscale and on a larger scale. Cryo TEM observations confirm our theoretical prediction that isolated lithium occurs less at higher stripping current densities. The origin of isolated lithium lies in local effects, such as heterogeneous SEI, stress fields, or the geometric shape of the deposits. We conclude that in order to mitigate isolated lithium, a uniform lithium morphology during plating and a homogeneous SEI are indispensable.

Engineering Li Metal Anode for Garnet-Based Solid-State Batteries

ConspectusThe past 30 years have witnessed the great achievements of Li-ion batteries (LIBs) based on a graphite anode and liquid organic electrolytes. Yet the limited energy density of a graphite anode and unavoidable safety risks caused by flammable liquid organic electrolytes hinder further developments of LIBs. To reach higher energy density, Li metal anodes (LMAs) with high capacity and low electrode potential are a promising choice. However, LMAs suffer from more serious safety concerns than the graphite anode in liquid LIBs. The dilemma of safety and energy density remains an inevitable obstacle in the way of LIBs.Solid-state batteries (SSBs) offer new opportunities to simultaneously achieve intrinsic safety and high energy density. Among all types of SSBs that are based on oxides, polymers, sulfides, or halides, garnet-type SSBs seem to be one of the most attractive choices due to garnet's merits in high ionic conductivities (10^-4-10^-3 S/cm at room temperature), wide electrochemical windows (0-6 V), and intrinsically high safety. However, garnet-type SSBs are faced with large interfacial impedance and short-circuit problems caused by Li dendrites. Recently, engineered Li metal anodes (ELMAs) have shown unique advantages in tackling interface issues and attracted extensive research interest.In this Account, we focus on fundamental understandings and provide an in-depth review of ELMAs in garnet-based SSBs. Considering the limited space, we mainly discuss the recent progress made in our groups. First, we introduce the design guidelines for ELMAs and emphasize the unique role of theoretical calculation in predicting and optimizing ELMAs. Then we discuss the interface compatibility of ELMAs with garnet SSEs in details. Specifically, we have demonstrated the advantages of ELMAs in enhancing interface contact and suppressing Li dendrite growth. Next, we attentively analyze the gaps between laboratory and practical applications. We strongly recommend establishing a unified testing standard, with a practically desired areal capacity per cycle (>3.0 mAh/cm²) and a precisely controlled Li capacity excess. Finally, novel chances to enhance ELMAs' processability and fabricate thin Li foils are highlighted. We believe that this Account will offer an insightful analysis of ELMAs' recent advancements and push forward their practical applications.

LiF-Rich Interfaces and HF Elimination Achieved by a Multifunctional Additive Enable High-Performance Li/LiNi0.8Co0.1Mn0.1O2 Batteries

Li-metal batteries (LMBs), especially in combination with high-energy-density Ni-rich materials, exhibit great potential for next-generation rechargeable Li batteries. Nevertheless, poor cathode-/anode-electrolyte interfaces (CEI/SEI) and hydrofluoric acid (HF) attack pose a threat to the electrochemical and safety performances of LMBs due to aggressive chemical and electrochemical reactivities of high-Ni materials, metallic Li, and carbonate-based electrolytes with the LiPF₆ salt. Herein, the carbonate electrolyte based on LiPF₆ is formulated by a multifunctional electrolyte additive pentafluorophenyl trifluoroacetate (PFTF) to adapt the Li/LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) battery. It is theoretically illustrated and experimentally revealed that HF elimination and the LiF-rich CEI/SEI films are successfully achieved via the chemical and electrochemical reactions of the PFTF additive. Significantly, the LiF-rich SEI film with high electrochemical kinetics facilitates Li homogeneous deposition and prevents dendritic Li from forming and growing. Benefiting from the collaborative protection of PFTF on the interfacial modification and HF capture, the capacity ratio of the Li/NCM811 battery is boosted by 22.4%, and the cycling stability of the symmetrical Li cell is expanded over 500 h. This provided strategy is conducive to the achievement of high-performance LMBs with Ni-rich materials by optimizing the electrolyte formula.

Low Concentration Sulfolane-Based Electrolyte for High Voltage Lithium Metal Batteries

Electrolyte engineering is crucial for the commercialization of lithium metal batteries. Here, lithium metal is stabilized in the highly reactive sulfolane-based electrolyte under low concentration (0.25 M) for the first time. Inorganic-polymer hybrid solid electrolyte interphase (SEI) with high ionic conductivity, low bonding with lithium and high flexibility enables dense chunky lithium deposition and high plating/stripping efficiency. Low concentration electrolyte (LCE) also enables excellent cycling stability of LiNi_0.5 Co_0.2 Mn_0.3 O₂ (NCM523)/Li cells at 1 C (90.7 % retention after 500 cycles) and 0.3 C (83.3 % retention after 1000 cycles). With a low N/P ratio (≈2), the capacity retention for NCM523/Li cells can achieve 94.3 % after 100 cycles at 0.3 C. Exploring the LCE is of paramount significance because it provides more possibilities of the lithium salt selections, especially reviving some lithium salts that are excluded before due to their low solubility. More importantly, LCE has the significant advantage of commercialization due to its cost-effectiveness.

Boron-Catalyzed Graphitization Carbon Layer Enabling LiMn0.8 Fe0.2 PO4 Cathode Superior Kinetics and Li-Storage Properties

The poor electrode kinetics and low conductivity of the LiMn_0.8 Fe_0.2 PO₄ cathode seriously impede its practical application. Here, an effective strategy of boron-catalyzed graphitization carbon coating layer is proposed to stabilize the nanostructure and improve the kinetic properties and Li-storage capability of LiMn_0.8 Fe_0.2 PO₄ nanocrystals for rechargeable lithium-ion batteries. The graphite-like BC₃ is derived from B-catalyzed graphitization coating layers, which can not only effectively maintain the dynamic stability of the LiMn_0.8 Fe_0.2 PO₄ nanostructure during cycling, but also plays an important role in enhancing the conductivity and Li⁺ migration kinetics of LiMn_0.8 Fe_0.2 PO₄ @B-C. The optimized LiMn_0.8 Fe_0.2 PO₄ @B-C exhibits the fastest intercalation/deintercalation kinetics, highest electrical conductivity (8.41 × 10^-2 S cm^-1 ), Li⁺ diffusion coefficient (6.17 × 10^-12 cm² s^-1 ), and Li-storage performance among three comparison samples (B-C0, B-C6, and B-C9). The highly reversible properties and structural stability of LiMn_0.8 Fe_0.2 PO₄ @B-C are further proved by operando XRD analysis. The B-catalyzed graphitization carbon coating strategy is expected to be an effective pathway to overcome the inherent drawbacks of the high-energy density LiMn_0.8 Fe_0.2 PO₄ cathode and to improve other cathode materials with low-conductivity and poor electrode kinetics for rechargeable second batteries.

Bifunctional Photoassisted Li-O2 Battery with Ultrahigh Rate-Cycling Performance Based on Siloxene Size Regulation

Directly integrating the bifunctional photoelectrode into Li-O2 batteries has been considered an effective way to reduce the overpotential and promote electric energy saving. However, more regular investigations on various bifunctional photocatalysts have still been desired for high-performance photoassisted Li-O2 batteries. Herein, a systematic exploration of various-sized siloxene photocatalysts affected by Li-O2 batteries has been introduced. Compared with the utilization of larger-sized siloxene nanosheets (SNSs), the photoassisted Li-O2 battery with a siloxene quantum dot (SQD) photoelectrode delivers a superior round-trip efficiency of 230% based on the highest discharge potential up to 3.72 V and lowest charge potential of 1.60 V and enables the maintenance of a long-term cycling life with only 13% efficiency attenuation after 200 cycles at 0.075 mA/cm2. Furthermore, this system exhibits a record-high rate-cycling performance (162% round-trip efficiency, even at 3 mA/cm2) and a high discharge capacity of 2212 mAh/g at 1 mA/cm2. These ground-breaking performances could be attributed to the synergistic effect of the photocatalytic and electrocatalytic activities of SQD photocatalysts with the ideal conduction band/valence band values, the abundant defective sites, and the stronger O2 and lower LiO2 adsorption strengths of SQD photocatalysts. These systematic research studies highlight the significance of SQD bifunctional photocatalysts and could be extended to other photocatalysts for further high-efficiency photoelectric conversion and storage.

Carbonized Polymer Dots with Controllable N, O Functional Groups as Electrolyte Additives to Achieve Stable Li Metal Batteries

Electrolyte additive is an effective strategy to inhibit the uncontrolled growth of Li dendrites for lithium metal batteries (LMBs). However, most of the additives are complex synthesis and prone to decompose in cycling. Herein, in order to guide the homogeneous deposition of Li⁺ , carbonized polymer dots (CPDs) as electrolyte additives are successfully designed and synthesized by microwave (M-CPDs) and hydrothermal (H-CPDs) approaches. The controllable functional groups containing N or O (especially pyridinic-N, pyrrolic-N, and carboxyl group) enable CPDs to keep stable in electrolytes for at least 3 months. Meanwhile, the clusters formed between CPDs and Li⁺ through electrostatic interaction effectively guide the uniform Li dispersion and limit the "tip effect" and dendrite formation. Moreover, as lithiophilic groups increase, the strong electrostatic interference for the solvation effect of Li⁺ in the electrolyte is formed, which induces faster Li⁺ diffusion/transfer. As expected, H-CPDs achieve the ultra-even Li⁺ transfer. The corresponding Li//LiFePO₄ full cell delivers a high capacity retention rate of 93.8% after 200 cycles, which is much higher than that of the cells without additives (61.2%) and with M-CPDs (83.7%) as additives. The strategy in this work provides a theoretical direction for CPDs as electrolyte additives used in energy storage devices.

Anchoring polysulfides via a CoS2/NC@1T MoS2 modified separator for high-performance lithium–sulfur batteries

CoS2/NC@1T MoS2 synthesized by a one-step hydrothermal method forms a unique hierarchical configuration with simultaneous internal and external modifications. A lithium–sulfur battery with a CoS2/NC@1T MoS2-PP separator shows superior cycling performance.

Regulation of Outer Solvation Shell Toward Superior Low-Temperature Aqueous Zinc-Ion Batteries

Aqueous Zn-ion batteries are well regarded among a next-generation energy-storage technology due to their low cost and high safety. However, the unstable stripping/plating process leading to severe dendrite growth under high current density and low temperature impede their practical application. Herein, it is demonstrated that the addition of 2-propanol can regulate the outer solvation shell structure of Zn²⁺ by replacing water molecules to establish a "eutectic solvation shell", which provides strong affinity with the Zn (101) crystalline plane and fast desolvation kinetics during the plating process, rendering homogeneous Zn deposition without dendrite formation. As a result, the Zn anode exhibits promising cycle stability over 500 h under an elevated current density of 15 mA cm^-2 and high depth of discharge of 51.2%. Furthermore, remarkable electrochemical performance is achieved in a 150 mAh Zn|V₂ O₅ pouch cell over 1000 cycles at low temperature of -20 °C. This work not only offers a new strategy to achieve excellent performance of aqueous Zn-ion batteries under harsh conditions, but also reveals electrolyte structure designs that can be applied in related energy storage and conversion fields.

Porous Metal Current Collectors for Alkali Metal Batteries

Alkali metals (i.e., Li, Na, and K) are promising anode materials for next-generation high-energy-density batteries due to their superior theoretical specific capacities and low electrochemical potentials. However, the uneven current and ion distribution on the anode surface probably induces undesirable dendrite growth, which leads to significant safety hazards and severely hinders the commercialization of alkali metal anodes. A smart and versatile strategy that can accommodate alkali metals into porous metal current collectors (PMCCs) has been well established to resolve the issues as well as to promote the practical applications of alkali metal anodes. Moreover, the proposal of PMCCs can meet the requirement of the dendrite-free battery fabrication industry, while the electrode material loading exactly needs the metal current collector component as well. Here, a systematic survey on advanced PMCCs for Li, Na, and K alkali metal anodes is presented, including their development timeline, categories, fabrication methods, and working mechanism. On this basis, some significant methodology advances to control pore structure, surface area, surface wettability, and mechanical properties are systematically summarized. Further, the existing issues and the development prospects of PMCCs to improve anode performance in alkali metal batteries are discussed.

Photoassisted High-Performance Lithium Anode Enabled by Oriented Crystal Planes

Lithium (Li) metal anodes are candidates for the next-generation high-performance lithium-ion batteries (LIBs). However, uncontrolable Li dendrite growth leads to safety issues and a low Coulombic efficiency (CE), which hinders the commercialization of Li metal batteries. Stable Li anodes based on the tailored plane deposition and photoassisted synergistic current collectors are currently the subject of research; however, there are few related studies. To suppress the growth of Li dendrites and achieve dense Li deposition, we design a low-cost customized-facet/photoassisted synergistic dendrite-free anode. The tailored (002) plane endows it with a nanorod array/microsphere composite structure and exhibits a strong affinity for Li, which effectively reduces the Li⁺ nucleation overpotential and promotes uniform Li deposition. Notably, during the photoassisted Li deposition/stripping process, due to electron-hole separation, a weakly charged layer is formed on the (002) surface and local charge carrier changes are induced, reducing the overpotential by 8.3 mV, enhancing the reaction kinetics, and resulting in a high CE of ∼99.3% for the 300th cycle at 2 mA cm^-2. This work is of great significance for the field of next-generation photoassisted Li metal anodes.

TiO2 nanotubular arrays decorated with ultrafine Ag nanoseeds enabling a stable and dendrite-free lithium metal anode

To exploit next-generation high-energy Li metal batteries, it is vitally important to settle the issue of dendrite growth accompanied by interfacial instability of the Li anode. Applying 3D current collectors as hosts for Li deposition emerges as a prospective strategy to achieve uniform Li nucleation and suppress Li dendrites. Herein, well-aligned and spaced TiO₂ nanotube arrays grown on Ti foil and surface decorated with dispersed Ag nanocrystals (Ag@TNTAs/Ti) were constructed and employed as a 3D host for regulating Li stripping/plating behaviors and suppressing Li dendrites, and also relieving volume fluctuation during repetitive Li plating/stripping. Uniform TiO₂ nanotubular structures with a large surface allow fast electron/ion transport and uniform local current density distribution, leading to homogeneous Li growth on the nanotube surface. Moreover, Ag nanocrystals and TiO₂ nanotubes have good Li affinity, which facilitates Li⁺ capture and reduces the Li nucleation barrier, achieving uniform nucleation and growth of Li metal over the 3D Ag@TNTAs/Ti host. As a result, the as-fabricated Ag@TNTAs/Ti electrode exhibits dendrite-free plating morphology and long-term cycle stability with coulombic efficiency maintained over 98.5% even after 1000 cycles at a current density of 1 mA cm^-2 and cycling capacity of 1 mA h cm^-2. In symmetric cells, the Ag@TNTAs/Ti-Li electrode shows a much lower hysteresis of 40 mV over an ultralong cycle period of 2600 h at a current density of 1 mA cm^-2 and cycling capacity of 1 mA h cm^-2. Moreover, the full cell with the Ag@TNTAs/Ti-Li anode and LiFePO₄ cathode achieves a high capacity of 155.2 mA h g^-1 at 0.5C and retains 77.9% capacity with an average CE of ≈99.7% over 200 cycles.

Combating Li metal deposits in all-solid-state battery via the piezoelectric and ferroelectric effects

All-solid-state Li-metal batteries (ASSLBs) are highly desirable, due to their inherent safety and high energy density; however, the irregular and uncontrolled growth of Li filaments is detrimental to interfacial stability and safety. Herein, we report on the incorporation of piezo-/ferroelectric BaTiO₃ (BTO) nanofibers into solid electrolytes and determination of electric-field distribution due to BTO inclusion that effectively regulates the nucleation and growth of Li dendrites. Theoretical simulations predict that the piezoelectric effect of BTO embedded in solid electrolyte reduces the driving force of dendrite growth at high curvatures, while its ferroelectricity reduces the overpotential, which helps to regularize Li deposition and Li⁺ flux. Polarization reversal of soft solid electrolytes was identified, confirming a regular deposition and morphology alteration of Li. As expected, the ASSLBs operating with LiFePO₄/Li and poly(ethylene oxide) (PEO)/garnet solid electrolyte containing 10% BTO additive showed a steady and long cycle life with a reversible capacity of 103.2 mAh g^-1 over 500 cycles at 1 C. Furthermore, the comparable cyclability and flexibility of the scalable pouch cells prepared and the successful validation in the sulfide electrolytes, demonstrating its universal and promising application for the integration of Li metal anodes in solid-state batteries.

Dual Vertically Aligned Electrode-Inspired High-Capacity Lithium Batteries

Lithium (Li) dendrite formation and poor Li⁺ transport kinetics under high-charging current densities and capacities inhibit the capabilities of Li metal batteries (LMBs). This study proposes a 3D conductive multichannel carbon framework (MCF) with homogeneously distributed vertical graphene nanowalls (VGWs@MCF) as a multifunctional host to efficiently regulate Li deposition and accelerate Li⁺ transport. A novel electrode for both Li|VGWs@MCF anode and LFP|VGWs@MCF (NCM₈₁₁ |VGWs@MCF) cathode is designed and fabricated using a dual vertically aligned architecture. This unique hierarchical structure provides ultrafast, continuous, and smooth electron transport channels; furthermore, it furnishes outstanding mechanical strength to support massive Li deposition at ultrahigh rates. As a result, the Li|VGWs@MCF anode exhibits outstanding cycling stability at ultrahigh currents and capacities (1000 h at 10 mA cm^-2 and 10 mAh cm^-2 , and 1000 h at 30 mA cm^-2 and 60 mAh cm^-2 ). Moreover, full cells made of such 3D anodes and freestanding LFP|VGWs@MCF (NCM₈₁₁ |VGWs@MCF) cathodes with conspicuous mass loading (45 mg cm^-2 for LFP and 35 mg cm^-2 for NCM₈₁₁ ) demonstrate excellent areal capacities (6.98 mAh cm^-2 for LFP and 5.6 mAh cm^-2 for NCM₈₁₁ ). This strategy proposes a promising direction for the development of high-energy-density practical Li batteries that combine safety, performance, and sustainability.

Pomegranate-Inspired Graphene Parcel Enables High-Performance Dendrite-Free Lithium Metal Anodes

Uncontrolled lithium dendrites seriously hinder the commercialization of lithium metal batteries in comparison to the durable lithium-ion batteries. Herein, inspired by squashy pomegranate structure, a novel loading strategy of metallic lithium (Li) is introduced to construct dendrite-free Li metal anodes through porous reduced graphene oxide/Au (PRGO/Au) composite microrods (MRs) as unique storage parcels. The abundant internal voids and robust host structure are capable of achieving high mass loading of Li metal and effectively alleviating the conceivable volume change during cycling, accompanied by the preferential selective plating/stripping of Li inside the graphene-based MRs with the embedded Au nanonuclei. As a result, the obtained PRGO/Au-Li anodes deliver a long-lifespan stable cycling up to 600 h with a high specific capacity of ≈2140 mA h g^-1 and voltage hysteresis as low as 20 mV in the absence of dendrites. The assembled full cells exhibit excellent rate capability and cycling stability. This work provides an alternative strategy to construct advanced high-energy-density lithium batteries via the unique 1D bioinspired graphene-based packaging strategy.

A Bioinspired Coating for Stabilizing Li Metal Batteries

With plenty of charges and rich functional groups, bovine serum albumin (BSA) protein provides effective transport for multiple metallic ions inside blood vessels. Inspired by the unique ionic transport function, we develop a BSA protein coating to stabilize Li anode, regulate Li⁺ transport, and resolve the Li dendrite growth for Li metal batteries (LMBs). The experimental and simulation studies demonstrate that the coating has strong interactions with Li metal, increases the wetting with electrolyte, reduces the electrolyte/Li side reactions, and significantly suppresses the Li dendrite formation. As a result, the BSA coating exhibits excellent stability in the electrolyte and improves the performance of Li|Cu and Li|Li cells as well as the LiFePO₄|Li batteries. This work reveals that LMBs can benefit from the biological function of BSA, i.e., special transport capability of metallic ions, and lays an important foundation in design of protein-based materials for effectively enhancing the electrochemical performance of energy storage systems.

Comonomer-Tuned Gel Electrolyte Enables Ultralong Cycle Life of Solid-State Lithium Metal Batteries

Rechargeable lithium metal batteries (LMBs) are considered the "holy grail" of energy storage systems. Unfortunately, uncontrollable dendritic lithium growth inherent in these batteries has prevented their practical applications. The benefits of solid-state electrolyte for LMBs are limited due to the common compromise between ionic conductivity and mechanical property. This work proposes a mechanism for simultaneous improvement in ionic conductivity and mechanical strength of gel polymer electrolyte (GPE) which is based on tunable cross-linked polymer network through adjusting monomer ratios. With increasing bisphenol A ethoxylate dimethacrylate (E2BADMA) and poly(ethylene glycol) diacrylate (PEGDA) mass ratios in GPE precursors, the formed polymer network experienced a composition evolution from a 3D cross-linked mono PEGDA network to triple PEGDA, E2BADMA, and PEGDA/E2BADMA networks and then to dual E2BADMA and PEGDA/E2BADMA networks, accompanied by the increase in both storage modulus (from 6 to 37 MPa) and ionic conductivity (from 0.06 to 0.44 mS cm^-1). As a result, the E2BADMA/PEGDA mass ratio of 2:1 facilitates the successful fabrication of a dual-network-supported GPE (PEEPL-12) with a mechanical strength of 37 MPa and superior electrochemical properties (a high ionic conductivity of 0.44 mS cm^-1 and a wide electrochemical stability window of 4.85 V vs Li/Li⁺). Such polymer electrolyte-based symmetric lithium metal batteries delivered a long cycle life (2000 h at 0.1 mA cm^-2 and 0.1 mAh cm^-2), and the Li|PEEPL-12|LiFePO₄ cell delivered a high capacity of 140 mAh g^-1 at the 100th cycle at the current density of 0.1 C (1 C = 170 mAh g^-1). A more thorough investigation indicated the formation of a stable solid electrolyte interphase layer on a lithium metal anode. These extraordinary features open up a venue for fabrication of advanced polymer electrolyte for long-cycle-life lithium metal batteries.

Operando Decoding of Surface Strain in Anode-Free Lithium Metal Batteries via Optical Fiber Sensor

With zero excess lithium, anode-free lithium metal batteries (AFLMBs) can deliver much higher energy density than that of traditional lithium metal batteries. However, AFLMBs are prone to suffer from rapid capacity loss and short life. Monitoring and analyzing the capacity decay of AFLMBs are of great importance for their future applications. It is known that the capacity fade mainly comes from the formation of solid electrolyte interphase species and dead lithium, which leads to irreversible volume expansion. Therefore, monitoring and distinguishing the irreversible volume expansion or reversible volume expansion are the key points to analyze the capacity fade of AFLMBs. Herein, an applicable technique based on optical fiber sensors to characterize and quantize the volume change of AFLMBs is developed. By attaching fiber Bragg grating (FBG) sensors onto the surface of the multilayered anode-free pouch cells, the strain evolution of the cells is successfully monitored and correlated with their electrochemical properties. It is found that the decline of surface strain fluctuation amplitude caused by the loss of active lithium is the leading indicator of battery failure. The proposed sensing technique has excellent multiplexing capability that can be considered as an elementary unit for capacity fade analysis in next-generation battery management system.

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.

Ionic Conductive and Highly-Stable Interface for Alkali Metal Anodes

Alkali metals are regarded as the most promising candidates for advanced anode for the next-generation batteries due to their high specific capacity, low electrochemical potential, and lightweight. However, critical problems of the alkali metal anodes, especially dendrite formation and interface stabilization, remain challenging to overcome. The solid electrolyte interphase (SEI) is a key factor affecting Li and Na deposition behavior and electrochemical performances. Herein, a facile and universal approach is successfully developed to fabricate ionic conductive interfaces for Li and Na metal anodes by modified atomic layer deposition (ALD). In this process, the Li metal (or Na metal) plays the role of Li (or Na) source without any additional Li (or Na) precursor during ALD. Moreover, the key questions about the influence of ALD deposition temperature on the compositions and structure of the coatings are addressed. The optimized ionic conductive coatings have significantly improved the electrochemical performances. In addition, the electrochemical phase-field model is performed to prove that the ionic conductive coating is very effective in promoting uniform electrodeposition. This approach is universal and can be potentially applied to other different metal anodes. At the same time, it can be extended to other types of coatings or other deposition techniques.