Designing electrolytes and interphases for high-energy lithium batteries

An anisotropic strategy for developing polymer electrolytes endowing lithium metal batteries with electrochemo-mechanically stable interface

Developing versatile solid polymer electrolytes is a reasonable approach to achieving reliable lithium metal batteries but is still challenging due to the nonuniform lithium deposition associated with the sluggish Li+ kinetics and insufficient mechanical strength. Herein, the concept of developing anisotropic solid polymer electrolyte is realized via integrating polymer hosts with highly oriented polyacrylonitrile nanofibers modified by Li6.4La3Zr1.4Ta0.6O12 particles. The oriented composite structure is employed to homogenize Li+ flux, serving as a physical barrier to resist lithium dendrites, retarding the side reaction between the electrolyte and lithium, thus endowing a compatible interface for lithium negative electrode. Correspondingly, the Li | |LiFePO4 cells steadily operate over 1000 cycles, delivering durable capacity retention of 91% at 170 mA g-1. Furthermore, numerical modeling and density functional theory are combined to clarify the multiphysics interplay between the designed solid polymer electrolyte and lithium negative electrode. This work provides a perspective for constructing interface-friendly solid polymer electrolytes at an electrochemo-mechanical level.

Structural codes of organic electrode materials for rechargeable multivalent metal batteries

Rechargeable multivalent metal batteries (MMBs) are considered as promising alternatives to Li-ion and Pb-acid batteries for grid-scale energy storage applications due to the multi-electron redox capability of metal anodes. However, the conventional inorganic cathodes used in MMBs face challenges with the sluggish diffusivity and poor storage of charge-dense multivalent cations in their crystal lattice. Organic electrode materials (OEMs), on the other hand, offer several advantages as MMB cathodes, including flexible structural designability, high resource availability, sustainability, and a unique ion-coordination storage mechanism. This review explores the intrinsic connection between the structural features of OEMs and their charge storage performance, aiming to unveil key design principles for organic molecules used in various MMB applications. We begin with an overview of the fundamental aspects of different MMBs (i.e., Zn/Mg/Ca/Al batteries), covering electrolyte selection, metal stripping/plating electrochemistry, and the fundamentals of cathode operation. From a theoretical understanding of redox activities, we summarize the properties of different redox sites and correlate the electrochemical properties of OEMs with various structural factors. This analysis further leads to the introduction of critical design considerations for different types of OEMs. We then critically review a wide range of organic compounds for MMBs, from small organic molecules to redox-active polymers and covalent-organic frameworks, focusing on their structure-property relationships, key electrochemical parameters, and strengths and shortcomings for multivalent ion storage. Finally, we discuss the existing challenges and propose potential solutions for further advancing OEMs in MMBs.

High-performance aqueous copper-ion batteries based on iron hexacyanoferrate cathodes for enhanced energy storage

The integration of renewable energy sources, such as solar and wind, requires efficient energy storage systems. Aqueous batteries, with their safety, low cost, and flexibility, have gained attention as promising solutions for energy storage. In this study, we developed an aqueous copper-ion storage device based on an iron hexacyanoferrate (FeHCF) cathode, which offers high capacities of 190 mA h g-1 at 1 A g-1 and 102 mA h g-1 even at 3 A g-1, with a discharge plateau at 0.59 V vs. SHE and a low polarization voltage of 0.2 V. In situ XRD, Raman, and XPS characterization techniques show that copper-ion insertion induces structural changes in FeHCF, leading to a valence state transition between Fe2+ and Fe3+, with a partial conversion of Cu2+ to Cu+. To improve the working voltage, we replaced the Cu2+/Cu0 anode reaction with the lower potential Zn/Zn(OH)42- reaction, achieving an aqueous battery with a voltage range of 1.6-2.5 V. These findings highlight FeHCF-based aqueous batteries' potential for high-performance and safe energy storage.

Progress in Developing Polymer Electrolytes for Advanced Zn Batteries

Aqueous Zn batteries (ZBs) are promising candidates for large-scale energy storage, considering their intrinsically safe features, competitive cost, and environmental friendliness. However, the fascinating metallic Zn anode is subjected to severe issues, such as dendrite growth, hydrogen evolution, and corrosion. Additionally, traditional aqueous electrolytes' narrow electrochemical windows and temperature ranges further hinder the practical application of ZBs. Solid-state electrolytes, including solid polymer electrolytes and hydrogel electrolytes, offer distinct paths to mitigate these issues and simultaneously endow the ZBs with customizable functions such as flexibility, self-healing, anti-freezing, and regulated Zn deposition, etc, due to their tuneable structures. This review summarizes the latest progress in developing polymer electrolytes for ZBs, focusing on modifying the ionic conductivity, interfacial compatibility, Zn anode stability, electrochemical stability windows, and improving the environmental adaptability under harsh conditions. Although some achievements are obtained, many critical challenges still exist, and it is hoped to offer guidance for future research, accelerating the development and application of polymer electrolytes.

Nature-Inspired Separator with Thermal Sealing Reinforcement toward Sustainable Sodium-Ion Batteries

Sustainability serves as a predominant obstacle for advanced energy storage. Herein, we proposed biomass-based separator materials, with favorable flame retardancy, cost-effectiveness, potential sustainability, and excellent electrochemical performance. Specifically, the engineered hydroxyapatite (HAP) molecule incorporates solvent-friendly groups to establish enhanced ion transport channels. The resulting CF@HAP separator induces an orderly decomposition of the electrolyte, which could optimize the electrode/electrolyte interface layer and prevent dendrite growth, making the durable cycling process, let alone its great mechanical properties and potential versatility. The in-depth study clarifies its complicated interfacial chemistry, flame retardancy, and thermal control mechanisms, thus achieving a "thermally closed pore" behavior during the temperature regulation process. Furthermore, the CF@HAP separator achieves complete degradation in the soil naturally within 30 days. As-designed biomass-based separators could comprehensively improve electrochemical performance toward higher levels of reactivity, stability, and postlife self-degradability, further underscoring the promising prospects for sustainable energy storage systems.

Insights into the Electrolyte Hydrolysis and Its Impacts on the Interfacial Chemistry of a Li+-Intercalated Anode during High-Temperature Calendar Aging

Calendar aging occurring during high-temperature storage has long plagued practical realization of long-life, high-safety lithium-ion batteries (LIBs). Generally, the aging process is ascribed to the hydrolysis reaction of fluorine-containing electrolyte salt that generates hydrofluoric acid and chemically corrodes the anode surface. Nevertheless, the underlying mechanism about electrolyte degradation, HF generation and surface corrosion remains concealed for various electrolytes. In this work, we employed in situ liquid time-of-flight secondary ion mass spectroscopy to resolve the chemical evolution during high-temperature calendar aging in the bulk of the electrolyte and at the anode/electrolyte interface. Two conventional salts, LiPF6 and Li bis(fluorosulfonyl)imide (LiFSI), were employed for comparison. We identify that the high-temperature hydrolysis of LiPF6 preferentially occurs when the anion aggregates ([PF6+LiPF6]-) are attacked by trace H2O. HPO2F2, HF and LiF are generated and assist formation of an inorganics-rich solid electrolyte interphase (SEI), improving anode stability against parasitic reactions. The LiFSI-based electrolyte does not involve hydrolysis, which facilities the formation of an organics-rich SEI. Nevertheless, the SEI does not passivate the anode surface and could induce severe corrosions via electron tunneling at a high temperature. Our work offers original insights into rational design of electrolyte and interface for high-energy, long-calendar-life LIBs.

Revealing the roles of the solid-electrolyte interphase in designing stable, fast-charging, low-temperature Li-ion batteries

Designing the solid-electrolyte interphase (SEI) is critical for stable, fast-charging, low-temperature Li-ion batteries. Fostering a "fluorinated interphase," SEI enriched with LiF, has become a popular design strategy. Although LiF possesses low Li-ion conductivity, many studies have reported favorable battery performance with fluorinated SEIs. Such a contradiction suggests that optimizing SEI must extend beyond chemical composition design to consider spatial distributions of different chemical species. In this work, we demonstrate that the impact of a fluorinated SEI on battery performance should be evaluated on a case-by-case basis. Sufficiently passivating the anode surface without impeding Li-ion transport is key. We reveal that a fluorinated SEI containing excessive and dense LiF severely impedes Li-ion transport. In contrast, a fluorinated SEI with well-dispersed LiF (i.e., small LiF aggregates well mixed with other SEI components) is advantageous, presumably due to the enhanced Li-ion transport across heterointerfaces between LiF and other SEI components. An electrolyte, 1 M LiPF6 in 2-methyl tetrahydrofuran (2MeTHF), yields a fluorinated SEI with dispersed LiF. This electrolyte allows anodes of graphite, μSi/graphite composite, and pure Si to all deliver a stable Coulombic efficiency of 99.9% and excellent rate capability at low temperatures. Pouch cells containing layered cathodes also demonstrate impressive cycling stability over 1,000 cycles and exceptional rate capability down to -20 °C. Through experiments and theoretical modeling, we have identified a balanced SEI-based approach that achieves stable, fast-charging, low-temperature Li-ion batteries.

Sulfur defect engineering controls Li2S crystal orientation towards dendrite-free lithium metal batteries

Controlling nucleation and growth of Li is crucial to avoid dendrite formation for practical applications of lithium metal batteries. Li2S has been exemplified to promote Li transport, but its crystal orientation significantly influences the Li deposition behaviors. Here, we investigate the interactions between Li and various surface structures of Li2S, and reveal that the Li2S(111) plane exhibits the highest Li affinity and the lowest diffusion barrier, leading to dense Li deposition. Using sulfur defect engineering for Li2S crystal orientation control, we construct three-dimensional vertically oriented Li2S(111)@Cu nanorod arrays as a Li metal electrode substrate and identify a substrate-dependent Li nucleation process and a facet-dependent growth mode. Furthermore, we demonstrate the versatility of the Li2S(111)@Cu substrate when paired with two positive electrodes: achieving an initial discharge capacity of 138.8 mAh g-1 with 88% capacity retention after 400 cycles at 83.5 mA g-1 with LiFePO4, and an initial discharge capacity of 181 mAh g-1 with 80% capacity retention after 160 cycles at 60 mA g-1 with commercial LiNi0.8Co0.1Mn0.1O2 positive electrode (4 mAh cm-2).

Steric Coordinated Electrolytes for Fast-Charging and Low-Temperature Energy-Dense Lithium-Ion Batteries

Electrolytes are known as the dominant factors for fast-charging affordability and low-temperature capability of lithium-ion batteries (LIBs). Unfortunately, the current electrolytes can hardly simultaneously satisfy all the required characteristics, including sufficient ion transport, high oxidation/reduction interfacial stability, and fast de-solvation process over a wide-temperature range. Here, we report a solution by designing electrolyte solvents that coordinate with Li+ in steric configuration. The steric coordinated electrolytes (SCEs) can overcome the dilemma of quasi-planer coordinated ether electrolytes that has to be weakly coordinated with Li+ to avoid solvent co-intercalation towards graphite (Gr) anode, therefore enabling the merits including sufficiently dissociation of Li-salt with high ionic conductivity, low de-solvation energy, and forming electrode-electrolyte interphase with low energy barrier. As results, the SCEs with only single-salt and single-solvent (trimethoxymethane) achieve fast kinetics towards Gr anode and high oxidation stability. The LiNi0.8Co0.1Mn0.1O2 (NCM811)||Gr LIBs can reach 80% state of the charge in 6 min, and the Ah-level energy-dense pouch cells (4.5 V) retain 82.96% (500 cycles) and 85.94% (200 cycles) of initial capacities at room temperature and -20 °C, respectively. Our work deepens the fundamental understanding of Li-ion solvation structures and affords an effective approach to design sustainable fluro-free electrolytes for battery systems.

Fully Methylated Siloxane-Based Electrolyte for Practical Lithium Metal Batteries

Developing solvents with balanced physicochemical properties for high-voltage cathodes and lithium metal anodes is crucial for a sustainable and intelligent future. Herein, we report fully methylated tetramethyl-1,3-dimethoxydisiloxane (TMMS) as a single solvent for lithium metal batteries. We demonstrate that the fully methylated structure and Si-O bonds within TMMS can effectively elevate the dehydrogenation energy barrier, migrating the oxidation decomposition of the electrolyte. Additionally, the weak solvating power of TMMS favors the formation of an anion-rich solvation structure that induces the generation of an inorganic-rich electrode/electrolyte interphase layer at both the cathode and anode. Accordingly, the formulated electrolyte exhibits remarkable stability against high-voltage cathodes and lithium metal anodes. Notably, LiNi0.8Co0.1Mn0.1O2||Li (NCM811||Li) full cells with TMMS-based electrolytes realize a significant improvement in capacity retention compared with a dimethoxyethane-based electrolyte at both room temperature and 50 °C. This work provides insight into full methylation and the Si-O bond strategy and paves the way for the development of high-voltage lithium metal batteries.

Catalysis-Induced Highly-Stable Interface on Porous Silicon for High-Rate Lithium-Ion Batteries

Silicon stands as a key anode material in lithium-ion battery ascribing to its high energy density. Nevertheless, the poor rate performance and limited cycling life remain unresolved through conventional approaches that involve carbon composites or nanostructures, primarily due to the un-controllable effects arising from the substantial formation of a solid electrolyte interphase (SEI) during the cycling. Here, an ultra-thin and homogeneous Ti doping alumina oxide catalytic interface is meticulously applied on the porous Si through a synergistic etching and hydrolysis process. This defect-rich oxide interface promotes a selective adsorption of fluoroethylene carbonate, leading to a catalytic reaction that can be aptly described as "molecular concentration-in situ conversion". The resultant inorganic-rich SEI layer is electrochemical stable and favors ion-transport, particularly at high-rate cycling and high temperature. The robustly shielded porous Si, with a large surface area, achieves a high initial Coulombic efficiency of 84.7% and delivers exceptional high-rate performance at 25 A g-1 (692 mAh g-1) and a high Coulombic efficiency of 99.7% over 1000 cycles. The robust SEI constructed through a precious catalytic layer promises significant advantages for the fast development of silicon-based anode in fast-charging batteries.

Ductile Inorganic Solid Electrolytes for All-Solid-State Lithium Batteries

Solid electrolytes, as the core of all-solid-state batteries (ASSBs), play a crucial role in determining the kinetics of ion transport and the interface compatibility with cathodes and anodes, which can be subdivided into catholytes, bulk electrolytes, and anolytes based on their functional characteristics. Among various inorganic solid electrolytes, ductile solid electrolytes, distinguished from rigid oxide electrolytes, exhibit excellent ion transport properties even under cold pressing, thus holding greater promise for industrialization. However, the challenge lies in finding a ductile solid electrolyte that can simultaneously serve as catholyte, bulk electrolyte, and anolyte. Fortunately, due to the immobility of solid electrolytes, combining multiple types of solid electrolytes allows for leveraging their respective advantages. In this review, we discuss five types of solid electrolytes, sulfides, halides, nitrides, antiperovskite-type, and complex hydrides, and the challenges and superiorities for these electrolytes are also addressed. The impact of pressure on ASSBs has been systematically discussed. Furthermore, the suitability of electrolytes as the catholyte, bulk electrolyte, and anolyte is discussed based on their functional characteristics and physicochemical properties. This discussion aims to deepen our understanding of solid electrolytes, enabling us to harness the advantages of various types of solid electrolytes and develop practical, high-performance ASSBs.

Multitrack Boosted Hard Carbon Anodes: Innovative Paths and Advanced Performances in Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are emerging as a potential alternative to traditional lithium-ion batteries due to the abundant sodium resources. Carbon anodes, with their stable structure, wide availability, low cost, excellent conductivity, and tunable morphology and pore structure, exhibit outstanding performance in SIBs. This review summarizes the research progress of hard carbon anodes in SIBs, emphasizing the innovative paths and advanced performances achieved through multitrack optimization, including dimensional engineering, heteroatom doping, and microstructural tailoring. Each dimension of carbon material-0D, 1D, 2D, and 3D-offers unique advantages: 0D materials ensure uniform dispersion, 1D materials have short Na+ diffusion paths, 2D materials possess large specific surface areas, and 3D materials provide e-/Na+ conductive networks. Heteroatom doping with elements such as N, S, and P can tune electronic distribution, expand interlayer spacing of carbon, and induce Fermi level shifts, thereby enhancing sodium storage capability. In addition, defect engineering improves electrochemical performance by modifying graphitic crystal structure. Furthermore, suitable pore structure design, particularly closed pore structures, can increase capacity, minimizes side reactions, and suppress degradation. In future studies, optimizing morphology design, exploring heteroatom co-doping, and developing environmentally friendly, low-cost carbon anode methods will drive the application of high-performance and long cycle life SIBs.

Highly crystalline nanorods pyrene-based covalent organic framework artificial solid electrolyte interface accelerated interface Li+ regulation on lithium anode

The detrimental effects of heterogeneous Li deposition and aeolotropic Li dendrite propagation critically hamper its serviceability of Li metal batteries. The exploitation of neutral multifunctional porous polymer artificial SEI is imperative to modulate interfacial ionic transfer behavior. Herein, we propose a strategy based on dual-functional nanorod-shaped covalent organic frameworks (COF) to accelerate Li+ diffusion and mitigate lithium dendrite growth by creating an artificial solid electrolyte interface (SEI) layer. As anticipated, the immobilized high-polarity -OH and -CN- groups, along with the porous channel facilitates, facilitate uniform Li+ flux distribution and rapid Li+ migration. Additionally, the highly conjugated nature of the pyrene moiety not only enhances the plane π-π stacking crystallinity of TFDH-COF, but contributes positively to Li+ and repelling TFSI-. The combination of comprehensive ex-situ/in-situ characterizations and DFT calculations have unraveled the underlying mechanisms on the reductive Li mitigation energy barrier and enhancive Li+ transfer ability. In contrast with bare Li, the resultant TFDH-COF@Li electrode demonstrates the elevated reversibility of Li+ utilization, slight polarization, dendrite-free interface and prolonged cyclic performance in Li|Cu, Li|Li, and Li-based full cells operated at rigorous current densities. Those unswerving evidences enlighten the feasibility of engineering the neutrality COF layer to get rid of adverse disordered Li proliferation.

Highly efficient ionic actuators enabled by sliding ring molecule actuation

Ionic actuators with capability of electro-mechanical transduction are emerging as a useful platform for artificial intelligence and modern medical instruments. However, the insufficient ion transport inside material interfaces usually leads to limited energy transduction efficiency and energy density of actuators. Here, we report a polyrotaxane interface with adjustable ion transport based on sliding-ring effect for highly-efficient ionic actuators. The switch status of ion channels is synchronous with actuation strains, and energy barrier of interfacial ion transfer is reduced. As a result, the electro-mechanical transduction efficiency of actuators gets significantly improved. The as-delivered energy density of devices is stronger than that of mammalian skeletal muscle. Based on the high actuation performances, we demonstrate a fiber-shape soft actuator that can be directly injected into biological tissue just using syringe. The injectable actuator is promising for surgical navigation and physiological monitoring.

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.

Bridging Electrolyte Bulk and Interfacial Chemistry: Dynamic Protective Strategy Enable Ultra-Long Lifespan Aqueous Zinc Batteries

The main bottleneck of rechargeable aqueous zinc batteries (AZBs) is their limited cycle lifespans stemming from the unhealthy electrolyte bulk and fragile interface, especially in the absence of dynamic protection mechanism between them. To overcome this limitation, benefitting from their synergistic physical and chemical properties, chitin nanocrystals (ChNCs) are employed as superior colloid electrolyte to bridge electrolyte bulk and interfacial chemistry for ultra-long lifespan AZBs. This unique strategy not only enables continuous optimization of the electrolyte bulk and interfacial chemistry within the battery but also facilitates self-repairing of mechanical damage both internally and externally, thereby achieving comprehensive, persistent, and dynamic protection. As a result, the modified zinc (Zn) cells present high Zn plating/stripping coulombic efficiencies of 97.71 % ~99.81 % from 5 to 100 mA cm-2, and remarkably service lifespan up to 8,200 h (more than 11 months). Additionally, the Zn//MnO2 full cell exhibits a high capacity retention of 70.1 % after 3,000 cycles at 5 A g-1. This dynamic protective strategy to challenge aqueous Zn chemistry may open up a new avenue for building better AZBs and beyond.

Controlled Anodic Decomposition Pathway of Supramolecular Lithium Borate for Rationally Tuned Interphase Chemistry

The rational tailoring and molecular-level engineering of stable cathode-electrolyte interphases (CEIs) is paramount to advancing the performance of next-generation high-energy, layered nickel-rich oxide-based lithium metal batteries. However, developing well-tailored electrolyte additives with rationally controlled interfacial chemistry remains highly challenging. Here, two lithium borates: lithium (2-methoxy-15-crown-5)trifluoroborate (C-LiMCFB) and lithium (15-methoxy-2,5,8,11,14-pentaoxahexadecan)trifluoroborate (L-LiMCFB), incorporating cyclic 15-crown-5 (15C5) and linear pentaethylene glycol monomethyl ether (PEGME) as respective host groups tethered to the boron center are designed and synthesized. In C-LiMCFB, the supramolecular polydentate chelation/de-chelation of the 15C5 with Li+ can sequentially deactivate/activate the anodic decomposition of the C─O bonds, therefore leading to the controlled cleavage pathway of B─O and C─O bonds. The controlled interfacial chemistry leads to the formation of a uniform CEI layer, rich in lithium boron-oxygen clusters interwoven with LiF, on the NCM811 surface. This novel CEI configuration demonstrates an exceptional balance of mechanical robustness, adhesiveness, and toughness, providing highly desirable protection for the NCM811 cathode. The discovery of these novel supramolecular boron-based lithium salts not only unlocks supramolecular chemistry for rational electrolyte tuning but also provides a deeper understanding of the CEI formation mechanism in high-energy lithium metal batteries.

A Recyclable Inert Inorganic Framework Assisted Solid-State Electrolyte for Long-Life Aluminum Ion Batteries

The environmentally friendly and high-safety aluminum-ion batteries (AIBs) have attracted intense interest, but the extensive use of expensive EMIC-AlCl3 electrolyte, strong moisture sensitivity, and severe corrosion of the Al anode limit their commercial application. Herein, we develop a solid-state electrolyte (F-SSAF) with an AlF3 inert inorganic framework as the solid diluent, EMIC-AlCl3 as the electrolyte, and FEC@EMIC-AlCl3 (FIL) as the interface additive for solid-state AIBs (SSAIBs). The dissociation of Al2Cl7 - (AlCl3-AlCl4 -) into AlCl4 - is promoted by AlF3, which can facilitate the migration rate of AlCl4 - active ions and simultaneously mitigate the corrosion of the Al anode. The introduction of an AlF3 inert inorganic framework can also reduce the dosage of expensive EMIC-AlCl3 and alleviate the moisture sensitivity of EMIC-AlCl3. The FIL is introduced into the surfaces of both anode and cathode, thus in situ forming F-rich SEI and CEI films. The F-SSAF enables Al|F-SSAF|Al symmetric cells to achieve ultralong stable deposition and dissolution of Al up to 4000 h, and Al|F-SSAF|C full cells to achieve an unprecedented long cycle life of 10000 cycles with an average Coulombic efficiency of >99%. In addition, up to 80% of the AlF3 inert inorganic framework can be recycled. This work provides a simple yet substantial strategy for low-cost, long-life, and high-safety SSAIBs.

Coordination Topology Design in Anion-Rich Solvated Electrolytes for High-Voltage Lithium Metal Batteries

Electrolytes with anion-rich solvated structures are promising for high-voltage lithium metal batteries (LMBs) due to their good interfacial compatibility. Nevertheless, limited Li-ion transport of these electrolytes has hindered their high-rate application. Here we demonstrate that Li-ion transport in anion-rich solvated electrolytes could be facilitated by designing the coordination topology of anions in the solvation structure. Results show that, for a binary-anion electrolyte, equal-molar anions show the most expanded energy level distribution of solvation structures, thus reducing the Li-ion transport energy barrier, and resulting in a Li-ion conductivity even higher than that of the commercial carbonate electrolyte at a temperature range from -40 °C to 60 °C. More importantly, we identify a universal principle governing the Li-ion transport enhancement driven by anion configurations: only the combination of anions with multi-coordination sites shows facilitation in Li-ion transport, while the combination of centrosymmetric anions with the mono-coordination site harms it. The diversified anion-rich solvated structures also form stable interphases on the electrodes, enabling long-term cycling of 4.5 V LMBs at a high current density of 3.78 mA cm-2. Overall, our findings shine new light on developing practical electrolytes for energy-dense LMBs.

Stable Electrodeposition of Lithium Metal Driven by Interfacial Unsaturated Solvation Environments

The lithium (Li) dendrite and parasitic reactions are the two major challenges for the Li-metal anode, which is the most prominent anode for high-energy-density storage. However, in recent years, most studies have still focused on the increasingly complex design of electrolytes or solid electrolyte interfaces, and the essence of Li+ ion electrodeposition has been overlooked. Herein, we demonstrate a simple but useful strategy to control the Li solvation species in a classical electrolyte and promote its stable electrodeposition. In commonly used electrolytes consisting of ethylene carbonate (EC) and dimethyl carbonate, the first solvation shell of Li+ ions converts from EC-coordination-dominant to anion-diluent-dominant by simply reducing the EC content. Molecular simulations are performed to reveal that the latter solvation species could promote Li+ ions to become coordination-unsaturated in the electrical double layer and prefer to be reduced at the anode interface. Consequently, the simple tuning of local polarity around Li+ ions not only extends the cycling performance of the Li-metal anode significantly but also effectively suppresses Li-dendrite and parasitic reactions, which may inspire a rethinking of simple approaches for Li-metal anode challenges.

Lithium Deposition Mechanism under Different Thermal Conditions Unraveled via an Optimized Phase Field Model

As one of the most important physical fields for battery operation, the regulatory effect of temperature on the growth of lithium dendrites should be studied. In this paper, we develop an optimized phase field model to explore the effect of temperature on the growth of Li dendrites in Li metal batteries. We incorporated full lithium deposition kinetics, including atom diffusion and solid electrolyte interface restriction on interface kinetics, into the model and revealed their significance in determining the transformation of the lithium deposition morphology from moss-like to dendrite-like. We found that a high temperature or dispersed hot spots are more conducive to stable battery operation than a low temperature or concentrated hot spots due to the enhanced diffusion kinetics at the high temperature and the more uniform temperature distribution of dispersed hot spots. We believe our work can provide a useful tool for further exploring the thermal effect on stable lithium metal battery operation.

Development of PFAS-Free Locally Concentrated Ionic Liquid Electrolytes for High-Energy Lithium and Aluminum Metal Batteries

ConspectusLithium-ion batteries (LIBs) based on graphite anodes are a widely used state-of-the-art battery technology, but their energy density is approaching theoretical limits, prompting interest in lithium-metal batteries (LMBs) that can achieve higher energy density. In addition, the limited availability of lithium reserves raises supply concerns; therefore, research on postlithium metal batteries is underway. A major issue with these metal anodes, including lithium, is dendritic formation and insufficient reversibility, which leads to safety risks due to short circuits and the use of flammable electrolytes.Ionic liquid electrolytes (ILEs), composed of metal salts and ionic liquids, offer a safer alternative due to their nonflammable nature and high thermal stability. Moreover, they can enable high Coulombic efficiency (CE) for lithium metal anodes (LMAs) and allow reversible stripping/plating of various post-lithium metals for battery application, e.g., aluminum metal batteries (AMBs). Despite these advantages, ILEs suffer from high viscosity, which impairs ion transport and wettability. To resolve these challenges, researchers have developed locally concentrated ionic liquid electrolytes (LCILEs) by adding low-viscosity nonsolvating cosolvents, e.g., hydrofluoroether, to ILEs. These cosolvents do not coordinate with cationic charge carriers, thereby reducing viscosity and improving ion transport without compromising the compatibility of electrolytes with metal anodes. However, due to the inherent difference of molecular organic solvents and ionic liquids full of charged species, the most used nonsolvating cosolvents, i.e., hydrofluoroether, are less effective for ILEs with respect to concentrated electrolytes based on conventional organic solvents. Moreover, hydrofluoroether contains environmentally problematic -CF3 and/or -CF2- groups, i.e., per- and polyfluoroalkyl substances (PFAS), with their use subject to restrictions.In this Account, we provide an overview of the endeavors of our research group on the development of PFAS-free LCILEs for high-energy LMBs and AMBs. First, aromatic organic cations and aromatic less/nonfluorinated cosolvents are proposed to weaken the organic cation-anion interaction and strengthen the organic cation-cosolvent interaction, respectively. This is with consideration of the uncovered phase nanosegregation structure of LCILEs that effectively reduces the viscosity and promotes the Li+ transport ability with respect to the conventional nonaromatic organic cations and highly fluorinated PFAS cosolvents. Then, the effect of electrolyte components that do not coordinate to Li+, including organic cations and nonsolvating cosolvents, on the SEI composition and LMA reversibility is presented, which confirms the feasibility of reaching a high lithium stripping/plating CE up to 99.7% in the developed PFAS-free LCILEs. In the subsequent discussion on cathode compatibility, we present that in addition to LiFePO4 with high cyclability but inferior energy density, nickel-rich layered oxide and sulfurized polyacrylonitrile (SPAN) can be employed to construct high-energy LMBs for PFAS-free LCILEs with different anodic stability. Additionally, the feasible application of the LCILE strategy to promote the kinetics of AMBs relying on a different anode chemistry is demonstrated. Lastly, future research directions with an emphasis on nonsolvating component optimization, electrolyte dynamics, and electrode/electrolyte interphase formation are provided.

Dissolution, solvation and diffusion in low-temperature zinc electrolyte design

Aqueous zinc-based batteries have garnered the attention of the electrochemical energy storage community, but they suffer from electrolytes freezing and sluggish kinetics in cold environments. In this Review, we discuss the key parameters necessary for designing anti-freezing aqueous zinc electrolytes. We start with the fundamentals related to different zinc salts and their dissolution and solvation behaviours, by highlighting the effects of anions and additives on salt solubility, ion diffusion and freezing points. We then focus on the complex structures and energetics of cation-anion-solvent interaction. We also evaluate the prevailing strategies to improve the performance of electrolytes at low temperatures, with a discussion on the kinetics of plating and stripping of zinc anodes and charge storage in various cathode materials. Furthermore, we consider the current challenges and envisage future research directions in cold-resistant aqueous electrolyte formulations for zinc batteries.

Identifying the Role of Interfacial Long-Range Order in Regulating the Solid Electrolyte Interphase in Lithium Metal Batteries

The self-assembled monolayer (SAM) technique, known for its customizable molecular segments and active end groups, is widely recognized as a powerful tool for regulating the interfacial properties of high-energy-density lithium metal batteries. However, it remains unclear how the degree of long-range order in SAMs affects the solid electrolyte interphase (SEI). In this study, we precisely controlled the hydrolysis of silanes to construct monolayers with varying degrees of long-range order and investigated their effects on the SEI nanostructure and lithium anode performance. The results indicate that the degree of long-range order in SAMs significantly influences the decomposition kinetics of the carbon-fluorine bond in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), promoting the formation of a LiF-rich SEI and profoundly affecting the long-term stability of the highly sensitive anode during electrochemical processes. These findings provide new insights and directions for the molecular design of SAMs tailored for long-lasting lithium metal interfaces.

Modulating Interfacial Solvation via Ion Dipole Interactions for Low-Temperature and High-Voltage Lithium Batteries

Extending the stability of ether solvents is pivotal for developing low-temperature and high-voltage lithium batteries. Herein, we elucidate the oxidation behavior of tetrahydrofuran with ternary BF4 -, PF6 - and difluoro (oxalato) borate anions and the evolution of interfacial solvation environment. Combined in situ analyses and computations illustrate that the ion dipole interactions and the subsequent formation of ether-Li+-anion complexes in electrolyte rearrange the oxidation order of solvated species, which enhances the electrochemical stability of ether solvent. Furthermore, preferential absorption of anions on the surface of high-voltage cathode favors the formation of a solvent-deficient electric double layer and an anti-oxidation cathode electrolyte interphase, inhibiting the decomposition of tetrahydrofuran. Remarkably, the formulated electrolyte based on ternary anion and tetrahydrofuran solvent endows the LiNi0.8Co0.1Mn0.1O2 cathode with considerable rate capability of 5.0 C and high capacity retention of 93.12 % after 200 cycles. At a charging voltage of 4.5 V, the Li||LiNi0.8Co0.1Mn0.1O2 cells deliver Coulombic efficiency above 99 % at both 25 and -30 °C.

Localized High-Concentration Electrolyte for All-Carbon Rechargeable Dual-Ion Batteries with Durable Interfacial Chemistry

Lithium-based rechargeable dual-ion batteries (DIBs) based on graphite anode-cathode combinations have received much attention due to their high resource abundance and low cost. Currently, the practical realization of the batteries is hindered by easy oxidation of the electrolyte at the cathode interface, and solvent co-intercalation at the anode-electrolyte interface. Configuration of a "solvent-in-salt" electrolyte with a high concentration of Li salt is expected to stabilize the electrolyte chemistry versus both electrodes, yet inevitably reduces the mobility of the solvated working ions and increases the cost of the electrolyte. Herein, we propose to build a localized high-concentration electrolyte by adding hydrofluoroether as the diluent to reduce the salt content while improving the solvation structure, allowing more anions to enter the inner solvation sheath. The new electrolyte helps to form uniform and thin interfaces, with elevated contents of inorganic fluorides, on both electrodes, which effectively suppress electrolyte oxidation at the cathode and optimize electrolyte-electrode compatibility at the anode while facilitating charge transfer across the interface. Consequently, the DIBs with graphite as anode and cathode operate for 3000 cycles and retain a high-capacity retention of 95.7 %, highlighting the importance of stable interfacial chemistry in boosting the electrochemical performance of DIBs.

Unlocking Sulfide Solid-State Battery Longevity by the Paradigm of Dual-Functional Plastic Crystal

The utilization of sulfide-based solid electrolytes represents an attractive avenue for high safety and energy density all-solid-state batteries. However, the potential has been impeded by electrochemical and mechanical stability at the interface of oxide cathodes. Plastic crystals, a class of organic materials exhibiting remarkable elasticity, chemical stability, and ionic conductivity, have previously been underutilized due to their susceptibility to dissolution in liquid electrolytes. Nevertheless, their application in all-solid-state batteries presents a paradigm that could potentially overcome longstanding interface-related obstacles. This study presents a facile approach to enhancing the performance of sulfide-based solid-state batteries by utilizing nickel-rich oxide cathodes coated with ionically conductive plastic crystals. For employing plastically deformed succinonitrile as a metal ion ligand, it simultaneously supports mechanical stability and interfacial conduction, while LiDFOB establishes moderate ionic conductivity and a stable cathode electrolyte interphase (CEI). The synergistic effects of these mechanisms culminate in remarkable long-term performance metrics, with the capacity retaining 80% after 1529 cycles. Furthermore, this stability is maintained even when the areal capacity density is increased to a substantial 3.53 mA h cm-2. By combining electrochemical stability with mechanical plasticity, this approach opens possibilities for the development of long-lasting solid-state batteries suitable for practical applications.

Recent Advances on Characterization Techniques for the Composition-Structure-Property Relationships of Solid Electrolyte Interphase

The Solid Electrolyte Interphase (SEI) is a nanoscale thickness passivation layer that forms as a product of electrolyte decomposition through a combination of chemical and electrochemical reactions in the cell and evolves over time with charge/discharge cycling. The formation and stability of SEI directly determine the fundamental properties of the battery such as first coulombic efficiency (FCE), energy/power density, storage life, cycle life, and safety. The dynamic nature of SEI along with the presence of spatially inhomogeneous organic and inorganic components in SEI encompassing crystalline, amorphous, and polymeric nature distributed across the electrolyte to the electrolyte-electrode interface, highlights the need for advanced in situ/operando techniques to understand the formation and structure of these materials in creating a stable interface in real-world operating conditions. This perspective discusses the recent developments in interface-sensitive in situ/operando techniques, providing valuable insights and addressing the challenges of understanding the composition/structure/property of SEI and their correlations during the formation processes at spatio-temporal resolution across various length scales.

Garnet-Type Solid-State Electrolytes: Crystal-Phase Regulation and Interface Modification for Enhanced Lithium Metal Batteries

Due to their substantial energy density, rapid charging and discharging rates, and extended lifespan, lithium-ion batteries have attained broad application across various industries. However, their limited theoretical capacity struggles to meet the growing demand for battery capacity in consumer electronics, automotive, and aerospace applications. As a promising substitute, solid-state lithium-metal batteries (SSLBs) have emerged, utilizing a lithium-metal anode that boasts a significant theoretical specific capacity and non-flammable solid-state electrolytes (SSEs) to address energy density limitations and safety concerns. For SSLBs to attain large-scale commercial viability, SSEs require heightened ionic-conductivity, improved mechanical characteristics, and enhanced chemical and electrochemical stability. Furthermore, tackling the challenges related to interfacial contacts between SSEs and the lithium-metal anode is imperative. This review comprehensively overviews the primary methods used to prepare garnet SSEs and summarizes doping strategies for various sites on Li7La3Zr2O12 (LLZO) garnet SSEs, aiming to optimize the crystal phase to achieve more favorable properties in SSE applications. Additionally, it discusses strategies for modifying the interfacial contact between the lithium-metal anode and SSEs, classifying them into three areas: surface modification, interlayer-modification, and composite anodes. This review aims to serve as a valuable reference for future researchers working on high-performance garnet SSEs and effective interfacial-modification strategies.

Revealing the Dynamic Evolution of Electrolyte Configuration on the Cathode-Electrolyte Interface by Visualizing (De) Solvation Processes

Electrolyte engineering is crucial for improving cathode electrolyte interphase (CEI) to enhance the performance of lithium-ion batteries, especially at high charging cut-off voltages. However, typical electrolyte modification strategies always focus on the solvation structure in the bulk region, but consistently neglect the dynamic evolution of electrolyte solvation configuration at the cathode-electrolyte interface, which directly influences the CEI construction. Herein, we reveal an anti-synergy effect between Li+-solvation and interfacial electric field by visualizing the dynamic evolution of electrolyte solvation configuration at the cathode-electrolyte interface, which determines the concentration of interfacial solvated-Li+. The Li+ solvation in the charging process facilitates the construction of a concentrated (Li+-solvent/anion-rich) interface and anion-derived CEI, while the repulsive force derived from interfacial electric field induces the formation of a diluted (solvent-rich) interface and solvent-derived CEI. Modifying the electrochemical protocols and electrolyte formulation, we regulate the "inflection voltage" arising from the anti-synergy effect and prolong the lifetime of the concentrated interface, which further improves the functionality of CEI architecture.

Versatile Biopolymers for Advanced Lithium and Zinc Metal Batteries

Lithium (Li) and zinc (Zn) metals are emerging as promising anode materials for next-generation rechargeable metal batteries due to their excellent electronic conductivity and high theoretical capacities. However, issues such as uneven metal ion deposition and uncontrolled dendrite growth result in poor electrochemical stability, limited cycle life, and rapid capacity decay. Biopolymers, recognized for their abundance, cost-effectiveness, biodegradability, tunable structures, and adjustable properties, offer a compelling solution to these challenges. This review systematically and comprehensively examines biopolymers and their protective mechanisms for Li and Zn metal anodes. It begins with an overview of biopolymers, detailing key types, their structures, and properties. The review then explores recent advancements in the application of biopolymers as artificial solid electrolyte interphases, electrolyte additives, separators, and solid-state electrolytes, emphasizing how their structural properties enhance protection mechanisms and improve electrochemical performance. Finally, perspectives on current challenges and future research directions in this evolving field are provided.

Constructing an Artificial Interface as a Bifunctional Promoter for the Li Anode and the NCM Cathode in Lithium Metal Batteries

The bottleneck of Li metal batteries toward practical applications lies at inferior cyclability as well as Li dendrite issues. As a promising solution, an interface engineering strategy is proposed herein for the Li anode through constructing a hybrid artificial interface. It is assembled onto the Li anode using photocontrolled free radical polymerization (photo-CRP) of polyethylene glycol diacrylate-hexafluorobutyl methacrylate and hexafluorobutyl methacrylate-trifluoroethyl carbonate (PEGDA-HFMBA@HFMBA-FEMC or PH@HF layer). Among such hybrid interfaces, the interior layer of PEGDA-HFMBA exists as a protective shield with flexibility and fracture resistance, while the exterior layer of HFMBA-FEMC plays a role as a LiF reservoir to promote Li mass transfer and its even electrodeposition. In the meantime, some excess HFMBA and FEMC monomers further dissolve into the electrolyte as molecular additives, followed by in situ generation of a thin and robust LiF-rich cathode electrolyte interface (CEI). With the resulting Li anode, Li/NCM811 full cells showcase multifold cyclability amplification in comparison to cells using Bare-Li, covering durable cyclability with a capacity retention of 81.8% after 400 cycles. When the cutoff voltage is elevated to 4.5 V or the working temperature is elevated to 45 °C, the cells still maintain a stable operation for extending 300 cycles.

Super SEI-Forming Anion for Enhanced Interfacial Stability in Solid-State Lithium Metal Batteries

The extremely high chemical reactivity of lithium metal (Li°) electrodes and its enormous volume change during repetitive cycles cause continuous interfacial degradations in prevailing organic electrolytes, thus deteriorating the cycling performances of rechargeable lithium metal batteries (LMBs). Herein, departing from traditional wisdom on the design of electrolyte components, a super SEI-forming anion (SSA), as an efficient percussor for building stable interphases on Li° electrode, is proposed. Comprehensive investigations related to the unique anion chemistry of SSA reveal that the sulfonate and polyfluoroalkyl functionalities synergistically contribute to uniform spatial distributions of designer interfacial species, greatly improving the surface coverage property and conformal ability of the resulting interphases. Consequently, the incorporation of SSA leads to significant improvements in the cyclability of Li° electrode (exceeding 575 mAh cm-2 before failure) and the corresponding rechargeable Li°||LiFePO4 cells [a five-time increase in lifespan as compared to the benchmark cell with the popular SEI-forming anion bis(fluorosulfonyl)imide (FSI)]. The present work offers a paradigm shift to tame the notorious interfacial issues via upgraded anion chemistry, which can promote the practical development of rechargeable LMBs and other kinds of metal batteries.

Toward High-Energy-Density Initial-Anode-Free Lithium-Metal Batteries via Ultra-Thin Protective Ion-Transport-Promoting Interface Modification and Surface Prelithiation

Anode-free lithium-metal batteries (AFLMBs) are desirable candidates for achieving high-energy-density batteries, while severe active Li+ loss and uneven Li plating/stripping behavior impede their practical application. Herein, a trilaminar LS-Cu (LiCPON + Si/C-Cu) current collector is fabricated by radio frequency magnetron sputtering, including a Si/C hybrid lithiophilic layer and a supernatant carbon-incorporated lithium phosphorus oxynitride (LiCPON) solid-state electrolyte layer. Joint experimental and computational characterizations and simulations reveal that the LiCPON solid-state electrolyte layer can decompose into an in situ stout ion-transport-promoting protective layer, which can not only regulate homogeneous Li plating/stripping behavior but also inhibit the pulverization and deactivation of Si/C hybrid lithiophilic layer. When combined with surface prelithiated Li1.2Ni0.13Co0.13Mn0.54O2 (Preli-LRM) cathode, the Preli-LRM||LS-Cu full cell delivers 896.1 Wh kg-1 initially and retains 354.1 Wh kg-1 after 50 cycles. This strategy offers an innovative design of compensating for active Li+ loss and inducing uniform Li plating/stripping behavior simultaneously for the development of AFLMBs.

Anion-Dominated Solvation in Low-Concentration Electrolytes Promotes Inorganic-Rich Interphase Formation in Lithium Metal Batteries

While the formation of an inorganic-rich solid electrolyte interphase (SEI) plays a crucial role, the persistent challenge lies in the formation of an organic-rich SEI due to the high solvent ratio in low-concentration electrolytes (LCEs), which hinders the achievement of high-performance lithium metal batteries. Herein, by incorporating di-fluoroethylene carbonate (DFEC) as a non-solvating cosolvent, a solvation structure dominated by anions is introduced in the innovative LCE, leading to the creation of a durable and stable inorganic-rich SEI. Leveraging this electrolyte design, the Li||NCM83 cell demonstrates exceptional cycling stability, maintaining 82.85% of its capacity over 500 cycles at 1 C. Additionally, Li||NCM83 cell with a low N/P ratio (≈2.57) and reduced electrolyte volume (30 µL) retain 87.58% of its capacity after 150 cycles at 0.5 C. Direct molecular information is utilized to reveal a strong correlation between solvation structures and reduction sequences, proving the anion-dominate solvation structure can impedes the preferential reduction of solvents and constructs an inorganic-rich SEI. These findings shed light on the pivotal role of solvation structures in dictating SEI composition and battery performance, offering valuable insights for the design of advanced electrolytes for next-generation lithium metal batteries.

Electrodeposition of Polymer Networks as Conformal and Uniform Ultrathin Coatings

Natural systems, synthetic materials, and devices almost always feature interphases that control the flow of mass and energy or stabilize interfaces between incompatible materials. With technologies transitioning to non-planar and 3D mesoscale architectures, novel deposition methods for realizing ultrathin coatings and interphases are required. Polymer networks are of particular interest for their tunable chemical and physical properties combined with their structural integrity. Here, the electrodeposition of polymer networks (EPoN) is introduced as a general approach to uniformly coat non-planar conductive materials. Conceptually, EPoN utilizes electrochemically activated crosslinkers as polymer end groups to confine their network formation exclusively to the material surface upon charge transfer, yielding a passivating and self-limiting growth of conformal and uniform coatings with tunable submicron thickness on conductive materials. EPoN is found to result in thin functional films of various polymer backbones and side group chemistries as demonstrated for poly(ether) and poly(acrylamide) based polymers as solid electrolyte and thermally responsive interphases, respectively.

Wide Temperature Electrolytes for Lithium Batteries: Solvation Chemistry and Interfacial Reactions

Improving the wide-temperature operation of rechargeable batteries is crucial for boosting the adoption of electric vehicles and further advancing their application scope in harsh environments like deep ocean and space probes. Herein, recent advances in electrolyte solvation chemistry are critically summarized, aiming to address the long-standing challenge of notable energy diminution at sub-zero temperatures and rapid capacity degradation at elevated temperatures (>45°C). This review provides an in-depth analysis of the fundamental mechanisms governing the Li-ion transport process, illustrating how these insights have been effectively harnessed to synergize with high-capacity, high-rate electrodes. Another critical part highlights the interplay between solvation chemistry and interfacial reactions, as well as the stability of the resultant interphases, particularly in batteries employing ultrahigh-nickel layered oxides as cathodes and high-capacity Li/Si materials as anodes. The detailed examination reveals how these factors are pivotal in mitigating the rapid capacity fade, thereby ensuring a long cycle life, superior rate capability, and consistent high-/low-temperature performance. In the latter part, a comprehensive summary of in situ/operational analysis is presented. This holistic approach, encompassing innovative electrolyte design, interphase regulation, and advanced characterization, offers a comprehensive roadmap for advancing battery technology in extreme environmental conditions.

Screening of F-containing electrolyte additives and clarifying their decomposition routes for stable Li metal anodes

Constructing a LiF-rich solid electrolyte interphase (SEI) is a feasible strategy for inhibiting lithium (Li) dendrites of Li metal anodes (LMAs). However, selecting appropriate F-containing additives with efficient LiF contribution is still under active research. Herein, a series of fluorinated additives with diverse F/C molar ratios are investigated, and we demonstrate that the hexafluoroglutaric anhydride (F6-0) holds the best capability to derive the LiF-rich SEI in regular carbonate electrolytes (RCEs). To ameliorate the decomposition kinetics of the F6-0, LiNO3 (LNO) as an adjuvant is further introduced in the system. As a result, the reduction efficiency of F6-0 is increased to 91% under the F6-0/LNO synergistic effect, enabling the LMA with a uniform LiF-rich SEI in the RCE with merely 4 vol. % F6-0/LNO (F6L) addition. The LiNi0.8Co0.1Mn0.1O2||Li-20μm full-cell with the F6L also showcases better cycling and rate performances than the cases with other F-containing additives.

Electric pulses rejuvenate batteries

Dielectrophoresis allows "dead" material to recover its activity.

Sulfolane-Based Flame-Retardant Electrolyte for High-Voltage Sodium-Ion Batteries

Sodium-ion batteries hold great promise as next-generation energy storage systems. However, the high instability of the electrode/electrolyte interphase during cycling has seriously hindered the development of SIBs. In particular, an unstable cathode-electrolyte interphase (CEI) leads to successive electrolyte side reactions, transition metal leaching and rapid capacity decay, which tends to be exacerbated under high-voltage conditions. Therefore, constructing dense and stable CEIs are crucial for high-performance SIBs. This work reports localized high-concentration electrolyte by incorporating a highly oxidation-resistant sulfolane solvent with non-solvent diluent 1H, 1H, 5H-octafluoropentyl-1, 1, 2, 2-tetrafluoroethyl ether, which exhibited excellent oxidative stability and was able to form thin, dense and homogeneous CEI. The excellent CEI enabled the O3-type layered oxide cathode NaNi1/3Mn1/3Fe1/3O2 (NaNMF) to achieve stable cycling, with a capacity retention of 79.48% after 300 cycles at 1 C and 81.15% after 400 cycles at 2 C with a high charging voltage of 4.2 V. In addition, its nonflammable nature enhances the safety of SIBs. This work provides a viable pathway for the application of sulfolane-based electrolytes on SIBs and the design of next-generation high-voltage electrolytes.

Structural Regulation Enables High Interfacial Functionality for Ni-Rich Single-Crystalline Cathodes

Ni-rich single-crystalline layered cathodes have garnered significant attention due to their high energy density and thermal stability. However, they experience severe capacity degradation caused by lattice strain and interfacial side reactions during practical applications. In this study, an effective yttrium modification method is employed to stabilize the structure of Ni-rich single-crystalline LiNi0.83Mn0.05Co0.12O2 (SC-NMC83) to solve these issues. This innovative approach successfully immobilizes oxygen within the material, preventing crack formation while simultaneously broadening the diffusion path of Li+. The yttrium-modified sample (SC-NMC83-Y) exhibits a superior capacity retention compared to the SC-NMC83 sample, with values of 90% and 76.1% after 100 cycles, respectively. This work demonstrates the promising potential of a doping strategy for Ni-rich single-crystalline cathodes and paves a pathway for its practical implementation, such as all-solid-state batteries.

Sustainable synthesis of spongy-like porous carbon for supercapacitive energy storage systems towards pollution control

In this study, the fruit of Terminalia chebula, commonly known as chebulic myrobalan, is used as the precursor for carbon for its application in supercapacitors. The Terminalia chebula biomass-derived sponge-like porous carbon (TC-SPC) is synthesized using a facile and economical method of pyrolysis. TC-SPC thus obtained is subjected to XRD, FESEM, TEM, HRTEM, XPS, Raman spectroscopy, ATR-FTIR, and nitrogen adsorption-desorption analyses for their structural and chemical composition. The examination revealed that TC-SPC has a crystalline nature and a mesoporous and microporous structure accompanied by a disordered carbon framework that is doped with heteroatoms such as nitrogen and sulfur. Electrochemical studies are performed on TC-SPC using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. TC-SPC contributed a maximum specific capacitance of 145 F g-1 obtained at 1 A g-1. The cyclic stability of TC-SPC is significant with 10,000 cycles, maintaining the capacitance retention value of 96%. The results demonstrated that by turning the fruit of Terminalia chebula into an opulent product, a supercapacitor, TC-SPC generated from biomass has proven to be a potential candidate for energy storage application.

Electrolyte Superwetting and Electrode Friendly of Porous Membrane for Better Cycling Stability of Lithium Metal Batteries

Porous polymer membranes as separator plays important roles in separating cathode and anode, storing electrolytes, and transporting ions in energy storage devices. Here, an effective strategy is reported to prepare an electrolyte superwetting membrane, which shows good Li+ transport rate and uniformity, as well as electrode-friendly properties to afford the reduction and oxidation of electrodes. It thereby improves the cycle stability and safety of Li metal batteries. With the arrayed capillaries technique, a thin layer of polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) composite is uniformly coated on the surface and pores of polypropylene (PP) membrane with a total thickness of 30 µm. After treating it with n-butyllithium and LiNO3 in turn, a chemically inert membrane with efficient and uniform ion transport is prepared, and the cycle stability of Li||Li symmetric cells is up to 1500 h, 4 times higher than that of PP membrane. Moreover, the Li||LiFePO4 with as-prepared membranes achieve a higher capacity retention rate of 92% after 190 cycles at a current density of 3.6 mA cm-2 and a capacity of 3.6 mAh cm-2, and the Li||NCM721 batteries achieve a capacity retention rate of 71% after 600 cycles at a current density of 1.8 mA cm-2.

In-Depth Understanding of Interfacial Na+ Behaviors in Sodium Metal Anode: Migration, Desolvation, and Deposition

Interfacial Na+ behaviors of sodium (Na) anode severely threaten the stability of sodium-metal batteries (SMBs). This review systematically and in-depth discusses the current fundamental understanding of interfacial Na+ behaviors in SMBs including Na+ migration, desolvation, diffusion, nucleation, and deposition. The key influencing factors and optimization strategies of these behaviors are further summarized and discussed. More importantly, the high-energy-density anode-free sodium metal batteries (AFSMBs) are highlighted by addressing key issues in the areas of limited Na sources and irreversible Na loss. Simultaneously, recent advanced characterization techniques for deeper insights into interfacial Na+ deposition behavior and composition information of SEI film are spotlighted to provide guidance for the advancement of SMBs and AFSMBs. Finally, the prominent perspectives are presented to guide and promote the development of SMBs and AFSMBs.

Phosphorized 3D Current Collector for High-Energy Anode-Free Lithium Metal Batteries

The anode-free lithium metal battery (AF-LMB) demonstrates the emerging battery chemistry, exhibiting higher energy density than the existing lithium-ion battery and conventional LMB empirically. A systematic step-by-step while bottom-up calculation system is first developed to quantitatively depict the energy gap from theory to practice. The attainable high energy of AF-LMB necessitates a homogeneous Li+ flux on the anode side to achieve an improved Li reversibility against inventory loss. On such basis, a lithiophilic Cu3P-decorated 3D copper foil to promote dendrite-free lithium deposition is further reported. The phosphorized surface of high affinity toward Li+ incorporating the nanostructure of abundant nucleation sites synergistically regulates the Li nucleation/growth behavior, extending the cycling lifespan of high-loading AF-LMBs. The processed foil featuring lightweight and ultrathin merits further increases the energy density, both gravimetrically and volumetrically. This study provides a novel scheme for simultaneously realizing the uniform deposition of lithium and increasing the energy density of future AF-LMBs.

Aluminum Corrosion Chemistry in High-Voltage Lithium Metal Batteries with LiFSI-Based Ether Electrolytes

High-voltage Li metal batteries (LMBs) based on ether electrolytes hold potential for achieving high energy densities exceeding 500 Wh kg-1, but face challenges with electrolyte oxidative stability, particularly concerning aluminum (Al) current collector corrosion. However, the specific chemistry behind Al corrosion and its effect on electrolyte components remains unexplored. Here, our study delves into Al corrosion in the representative LiFSI-DME electrolyte system, revealing that low-concentration electrolytes exacerbate Al current collector corrosion and solvent decomposition. In contrast, high-concentration electrolytes mitigate these issues, enhancing long-term stability. Remarkably, LiFSI-0.7DME electrolyte demonstrates exceptional stability with up to 1000 cycles at high voltage without significant capacity decay. These findings offer crucial insights into Al corrosion mechanisms in ether-based electrolytes, advancing our comprehension of high-voltage LMBs and facilitating their development for practical applications.

Controlled Radical Copolymerization toward Tailored F/N Hybrid Polymers by Using Light-Driven Organocatalysis

Controlled radical copolymerizations present attractive avenues to obtain polymers with complicated compositions and sequences. In this work, we report the development of a visible-light-driven organocatalyzed controlled copolymerization of fluoroalkenes and acyclic N-vinylamides for the first time. The approach enables the on-demand synthesis of a broad scope of amide-functionalized main-chain fluoropolymers via novel fluorinated thiocarbamates, facilitating regulations over chemical compositions and alternating fractions by rationally selecting comonomer pairs and ratios. This method allows temporally controlled chain-growth by external light, and maintains high chain-end fidelity that promotes facile preparation of block sequences. Notably, the obtained F/N hybrid polymers, upon hydrolysis, afford free amino-substituted fluoropolymers versatile for post modifications toward various functionalities (e.g., amide, sulfonamide, carbamide, thiocarbamide). We further demonstrate the in situ formation of polymer networks with desirable properties as protective layers on lithium metal anodes, presenting a promising avenue for advancing lithium metal batteries.

Scaling-Free Cathodes: Enabling Electrochemical Extraction of High-Purity Nano-CaCO3 and -Mg(OH)2 in Seawater

For electrochemical application in seawater or brine, continuous scaling on cathodes will form insulation layers, making it nearly impossible to run an electrochemical reaction continuously. Herein, we report our discovery that a cathode consisting of conical nanobundle arrays with hydrophobic surfaces exhibits a unique scaling-free function. The hydrophobic surfaces will be covered with microbubbles created by electrolytic water splitting, which limits scale crystals from standing only on nanotips of conical nanobundles, and the bursting of large bubbles formed by the accumulation of microbubbles will cause a violent disturbance, removing scale crystals automatically from nanotips. Benefiting from the scaling-free properties of the cathode, high-purity nano-CaCO3 (98.9%) and nano-Mg(OH)2 (99.5%) were extracted from seawater. This novel scaling-free cathode is expected to eliminate the inherent limitations of electrochemical technology and open up a new route to seawater mining.

Extreme Fast Charging of Lithium Metal Batteries Enabled by a Molten-Salt-Derived Nanocrystal Interphase

The extreme fast charging performance of lithium metal batteries (LMBs) with a long life is an important focus in the development of next-generation battery technologies. The friable solid electrolyte interphase and dendritic lithium growth are major problems. The formation of an inorganic nanocrystal-dominant interphase produced by preimmersing the Li in molten lithium bis(fluorosulfonyl)imide that suppresses the overgrowth of the usual interphase is reported. Its high surface modulus combined with fast Li+ diffusivity enables a reversible dendrite-proof deposition under ultrahigh-rate conditions. It gives a record-breaking cumulative plating/stripping capacity of >240 000 mAh cm-2 at 30 mA cm-2@30 mAh cm-2 for a symmetric cell and an extreme fast charging performance at 6 C for 500 cycles for a Li||LiCoO2 full cell with a high-areal-capacity, thus expanding the use of LMBs to high-loading and power-intensive scenarios. Its usability both in roll-to-roll production and in different electrolytes indicating the scalable and industrial potential of this process for high-performance LMBs.