High Energy Density Rechargeable Batteries Based on Li Metal Anodes. The Role of Unique Surface Chemistry Developed in Solutions Containing Fluorinated Organic Co-solvents

Reactive Solid Polymer Layer: From a Single Fluoropolymer to Divergent Fluorinated Interface

Controlling the structure and chemistry of solid electrolyte interphase (SEI) underpins the stability of electrolyte-electrode interface, and is crucial for advancing rechargeable lithium metal batteries (LMBs). Here, we utilized photo-controlled copolymerization to achieve the on-demand synthesis of fluorosulfonyl fluoropolymers as unprecedented artificial SEI layers on Li metal anodes. This work not only enables instant formation of a hybrid polymer-inorganic interphase that consists of a polymer-enriched top layer and a LiF-fortified bottom layer, originating from a single polymeric component, but also imparts various desirable physical properties (e.g., good mechanical strength and flexibility, high ion conductivity, low overpotential) to SEI via a single-to-divergent strategy. Model reactions and structural characterizations supported the formation of a divergent fluorinated interphase, which furnished prolonged stabilization of Li deposition, high coulombic efficiency and improved cycling behavior in electrochemical experiments. This work highlights the great potential of exploring reactive polymers as versatile coatings to stabilize Li metal anodes, providing a promising avenue to solve electrode-electrolyte interfacial problems for LMBs.

CF3-Substituted Ethylene Carbonates for High-Voltage/High-Energy Rechargeable Lithium Metal-LiNi0.8Co0.1Mn0.1O2 Batteries

The development of advanced liquid electrolytes for high-voltage/high-energy rechargeable Li metal batteries is an important strategy to attain an effective protective surface film on both the Li metal anode and the high-voltage composite cathode. Herein, we report a study of two CF3-substituted ethylene carbonates as components of the electrolyte solutions for Li metal|NCM811 cells. We evaluated trifluoromethyl ethylene carbonate (CF3-EC) and trans-ditrifluoromethylethylene carbonate Di-(CF3)-EC as cosolvents and additives to the electrolyte solutions. Using CF3-substituted ethylene carbonates as additives to a fluoroethylene carbonate (FEC)-based electrolyte solution enables improved capacity retention of high-power Li metal|NCM811 cells. The composition of the products from the transformations of CF3-EC and Di-(CF3)-EC in Li|NCM811 cells was studied by FTIR, XPS, and 19F NMR spectroscopy. We concluded that fluorinated Li alkyl carbonates are the main reaction products formed from these cyclic carbonates during the cycling of Li|NCM 811 cells, and fragmentation of the ring with the formation of CO2, CO, or olefins is not characteristic of CF3-substituted ethylene carbonates. The NCM 811 cathodes and Li metal anodes were characterized by X-ray diffraction, SEM, XPS, and FTIR spectroscopy. The role of CF3-substituted ethylene carbonate additives in stabilizing high energy density secondary batteries based on Li metal anodes was discussed. A bright horizon for developing sustainable rechargeable batteries with the highest possible energy density is demonstrated.

Template-Assisted Epitaxial Growth of Ordered SnO2 Nanorods Arrays with Different Hollow Structures for High-Performance Sodium Storage

Anode materials for sodium ion batteries (SIBs) are confronted with severe volume expansion and poor electrical conductivity. Construction of assembled structures featuring hollow interior and carbon material modification is considered as an efficient strategy to address the issues. Herein, a novel template-assisted epitaxial growth method, ingeniously exploiting lattice matching nature, is developed to fabricate hollow ordered architectures assembled by SnO2 nanorods. SnO2 nanorods growing along [100] direction can achieve lattice-matched epitaxial growth on (110) plane of α-Fe2O3. Driven by the lattice matching, different α-Fe2O3 templates possessing different crystal plane orientations enable distinct assembly modes of SnO2, and four kinds of hollow ordered SnO2@C nanorods arrays (HONAs) with different morphologies including disc, hexahedron, dodecahedron and tetrakaidecahedron (denoted as Di-, He-, Do-, and Te-SnO2@C) are achieved. Benefiting from the synergy of hollow structure, carbon coating and ordered assembly structure, good structural integrity and stability and enhanced electrical conductivity are realized, resulting in impressive sodium storage performances when utilized as SIB anodes. Specifically, Te-SnO2@C HONAs exhibit excellent rate capability (385.6 mAh·g-1 at 2.0 A·g-1) and remarkable cycling stability (355.4 mAh·g-1 after 2000 cycles at 1.0 A·g-1). This work provides a promising route for constructing advanced SIB anode materials through epitaxial growth for rational structural design.

Regulating Electrolyte Solvation Structures via Diluent-Solvent Interactions for Safe High-Voltage Lithium Metal Batteries

Local high concentration electrolytes (LHCEs) have been proved to be one of the most promising systems to stabilize both high voltage cathodes and Li metal anode for next-generation batteries. However, the solvation structures and interactions among different species in LHCEs are still convoluted, which bottlenecks the further breakthrough on electrolyte development. Here, it is demonstrated that the hydrogen bonding interaction between diluent and solvent is crucial for the construction of LHCEs and corresponding interphase chemistries. The 2,2,2-trifluoroethyl trifluoromethane sulfonate (TFSF) is selected as diluent with the solvent dimethoxy-ethane (DME) to prepare a non-flammable LHCE for high voltage LMBs. This is first find that the hydrogen bonding interaction between TFSF and DME solvent tailors the electrolyte solvation structures by weakening the coordination of DME molecules to Li+ cations and allows more participation of anions in the first solvation shell, leading to the formation of aggregates (AGGs) clusters which are conducive to generating inorganic solid/cathodic electrolyte interphases (SEI/CEIs). The proposed TFSF based LHCE enables the Li||NCM811 (LiNi0.8Mn0.1O2) batteries to realize >80% capacity retention with a high average Coulombic efficiency of 99.8% for 230 cycles under aggressive conditions (NCM811 cathode: 3.4 mAh cm-2, cut-off voltage: 4.4 V, and 20 µm Li foil).

Intrinsically Safe Lithium Metal Batteries Enabled by Thermo-Electrochemical Compatible In Situ Polymerized Solid-State Electrolytes

In situ polymerized solid-state electrolytes have attracted much attention due to high Li-ion conductivity, conformal interface contact, and low interface resistance, but are plagued by lithium dendrite, interface degradation, and inferior thermal stability, which thereby leads to limited lifespan and severe safety hazards for high-energy lithium metal batteries (LMBs). Herein, an in situ polymerized electrolyte is proposed by copolymerization of 1,3-dioxolane with 1,3,5-tri glycidyl isocyanurate (TGIC) as a cross-linking agent, which realizes a synergy of battery thermal safety and interface compatibility with Li anode. Functional TGIC enhances the electrolyte polymeric level. The unique carbon-formation mechanism facilitates flame retardancy and eliminates the battery fire risk. In the meantime, TGIC-derived inorganic-rich interphase inhibits interface side reactions and promotes uniform Li plating. Intrinsically safe LMBs with nonflammability and outstanding electrochemical performances under extreme temperatures (130 °C) are achieved. This functional polymer design shows a promising prospect for the development of safe LMBs.

The Role of the Molecular Encapsulation Effect in Stabilizing Hydrogen-Bond-Rich Gel-State Lithium Metal Batteries

Gel-state polymer electrolytes with superior mechanical properties, self-healing abilities and high Li+ transference numbers can be obtained by in situ polymerization of monomers with hydrogen-bonding moieties. However, it is overlooked that the active hydrogen atoms in hydrogen-bond donors experience displacement reactions with lithium metal in lithium metal batteries (LMBs), leading to corrosion of the lithium metal. Herein, it is discovered that the addition of hydrogen-bond acceptors to hydrogen-bond-rich gel-state electrolytes modulates the chemical activity of the active hydrogen atoms via the formation of hydrogen-bonded intermolecular interactions. The characterizations reveal that the added hydrogen-bond acceptors encapsulate the active hydrogen atoms to suppress the interfacial chemical corrosions of lithium metals, thereby enhancing the chemical stability of the polymer structure and interphase. With the employment of this strategy, a 1.1 Ah LiNi0.8Co0.1Mn0.1O2/Li metal pouch cell achieves stable cycling with 96.3 % capacity retention at 100 cycles. This new approach indicates a feasible path for achieving in situ polymerization of highly stable gel-state-based LMBs.

Fluorinated Co-Solvents Enable Excellent Performances of Practical Cells Comprising LixSiO-Graphite Composite Anodes and LiNi0.89Co0.05Mn0.05Al0.01O2 (NCMA) Cathodes

Li-ion batteries based on high specific capacity LixSiO-Graphite anodes and LiNi0.89Co0.05 Mn0.05Al0.01O2 (NCMA) cathodes may have numerous practical applications owing to high energy density without a necessary compromise on safety. SiO, which is an attractive Li insertion anode material, offers more cycling stability than Si and a higher capacity than graphite. Therefore, a new trend has emerged for developing composite C-Si anodes, possessing the excellent cyclability of graphite coupled with high capacity SiO. The composite structure described herein prevents the volume expansion of SiO and maintains the structural integrity during prolonged cycling. However, graphite electrodes suffer from exfoliation in propylene carbonate (PC) based electrolyte solutions, which avoids well known safety benefits related to a possible use of PC based electrolyte solutions in all kinds of Li batteries. Herein, it is reported that trifluoro propylene carbonate (TFPC) is compatible with graphite anodes. New electrolyte formulations are developed and tested containing fluorinated co-solvents and compared the performance of several electrolyte solutions, including conventional alkyl carbonates-based solutions in full Li-ion cells, which included LixSiO-Graphite anodes and LiNi0.89Co0.05Mn0.05Al0.01O2 (NCMA) cathodes. Cells with new electrolyte solutions developed herein demonstrated nearly twice capacity retention in prolonged cycling experiments compared to similar reference cells containing conventional electrolyte solutions.

Engineering a Dynamic Solvent-Phobic Liquid Electrolyte Interphase for Long-Life Lithium Metal Batteries

The heterogeneity, species diversity, and poor mechanical stability of solid electrolyte interphases (SEIs) in conventional carbonate electrolytes result in the irreversible exhaustion of lithium (Li) and electrolytes during cycling, hindering the practical applications of Li metal batteries (LMBs). Herein, this work proposes a solvent-phobic dynamic liquid electrolyte interphase (DLEI) on a Li metal (Li-PFbTHF (perfluoro-butyltetrahydrofuran)) surface that selectively transports salt and induces salt-derived SEI formation. The solvent-phobic DLEI with C-F-rich groups dramatically reduces the side reactions between Li, carbonate solvents, and humid air, forming a LiF/Li3PO4-rich SEI. In situ electrochemical impedance spectroscopy and Ab-initio molecular dynamics demonstrate that DLEI effectively stabilizes the interface between Li metal and the carbonate electrolyte. Specifically, the LiFePO4||Li-PFbTHF cells deliver 80.4% capacity retention after 1000 cycles at 1.0 C, excellent rate capacity (108.2 mAh g-1 at 5.0 C), and 90.2% capacity retention after 550 cycles at 1.0 C in full-cells (negative/positive (N/P) ratio of 8) with high LiFePO4 loadings (15.6 mg cm-2) in carbonate electrolyte. In addition, the 0.55 Ah pouch cell of 252.0 Wh kg-1 delivers stable cycling. Hence, this study provides an effective strategy for controlling salt-derived SEI to improve the cycling performances of carbonate-based LMBs.

Exploring the Optical and Energetic Properties of a Co(II)-Based Mixed Ligand MOF

Due to their remarkable properties, including remarkable porosity and extensive surface area, metal-organic frameworks (MOFs) are being investigated for various applications. Herein, we report the first Co(II)-based mixed ligand MOF, formulated Co4(HTrz)2(d-cam)2.5(μ-OH)3. Its 3D structure framework is composed of helical chains {[Co4(μ3-HTrz)4]8+}n connected by d-camphorate ligand building blocks and featured as an extended structure in an AB-AB fashion. The investigated compound displays a wide absorption range across the visible spectrum, characterized by an optical gap energy of 3.7 eV, indicating its semiconducting nature and efficient sunlight absorption capabilities across various wavelengths. The electrochemical performance demonstrated an excellent reversibility, cyclability, structural stability, as well as a specific capacity of up to 100 cycles at a scan rate of 0.1 mV·s-1 and a current density of 50 mA·g-1. Thus, it showcases its ability to retain the capacity over numerous charge-discharge cycles. Additionally, the investigated sample displayed an impressive rate capability during the Li-ion charge/discharge process. Therefore, the material's remarkable electrochemical properties can be ascribed to the synergistic effects of its large specific surface area of 348.294 m2·g-1 and well-defined pore size distribution of 20.448 Å, making it a promising candidate for high-performance Li-ion batteries.

Molecular Engineering toward Robust Solid Electrolyte Interphase for Lithium Metal Batteries

Lithium-metal batteries (LMBs) with high energy density are becoming increasingly important in global sustainability initiatives. However, uncontrollable dendrite seeds, inscrutable interfacial chemistry, and repetitively formed solid electrolyte interphase (SEI) have severely hindered the advancement of LMBs. Organic molecules have been ingeniously engineered to construct targeted SEI and effectively minimize the above issues. In this review, multiple organic molecules, including polymer, fluorinated molecules, and organosulfur, are comprehensively summarized and insights into how to construct the corresponding elastic, fluorine-rich, and organosulfur-containing SEIs are provided. A variety of meticulously selected cases are analyzed in depth to support the arguments of molecular design in SEI. Specifically, the evolution of organic molecules-derived SEI is discussed and corresponding design principles are proposed, which are beneficial in guiding researchers to understand and architect SEI based on organic molecules. This review provides a design guideline for constructing organic molecule-derived SEI and will inspire more researchers to concentrate on the exploitation of LMBs.

Solid Electrolyte Interphase Recombination on Graphene Nanoribbons for Lithium Anode

The practical application of lithium metal batteries is hindered by the lithium dendrite issue, which is seriously affected by the composition and structure of the solid electrolyte interphase (SEI). Modifying the SEI can regulate lithium dendrite formation and growth. Here, we experimentally realize a Li protective layer of LiTFSI-ether electrolyte induced a natural SEI grafted on graphene nanoribbons (SEI@GNRs) via their in situ reactions. The experimental results and theoretical calculations uncover that the 3D structure of SEI@GNRs can reduce the local current density and Li+ flux. The natural SEI in SEI@GNRs, especially the rich inorganic species of LiF, Li3N, and Li2S, decreases the Li+ nucleation overpotential, makes Li+ ion deposition and nucleation uniform, and isolates electron transport. Their synergetic effect suppresses Li dendrite formation and growth, increasing the electrochemical performance of lithium metal batteries. The design strategy is beneficial for the development of lithium metal batteries.

Dual-Salt Electrolyte Additive Enables High Moisture Tolerance and Favorable Electric Double Layer for Lithium Metal Battery

The carbonate electrolyte chemistry is a primary determinant for the development of high-voltage lithium metal batteries (LMBs). Unfortunately, their implementation is greatly plagued by sluggish electrode interfacial dynamics and insufficient electrolyte thermodynamic stability. Herein, lithium trifluoroacetate-lithium nitrate (LiTFA-LiNO3 ) dual-salt additive-reinforced carbonate electrolyte (LTFAN) is proposed for stabilizing high-voltage LMBs. We reveal that 1) the in situ generated inorganic-rich electrode-electrolyte interphase (EEI) enables rapid interfacial dynamics, 2) TFA- preferentially interacts with moisture over PF6 - to strengthen the moisture tolerance of designed electrolyte, and 3) NO3 - is found to be noticeably enriched at the cathode interface on charging, thus constructing Li+ -enriched, solvent-coordinated, thermodynamically favorable electric double layer (EDL). The superior moisture tolerance of LTFAN and the thermodynamically stable EDL constructed at cathode interface play a decisive role in upgrading the compatibility of carbonate electrolyte with high-voltage cathode. The LMBs with LTFAN realize 4.3 V-NCM523/4.4 V-NCM622 superior cycling reversibility and excellent rate capability, which is the leading level of documented records for carbonate electrode.

Enabling Stable and Low-Strain Lithium Plating/Stripping with 2D Layered Transition Metal Carbides by Forming Li-Zipped MXenes and a Li Halide-Rich Solid Electrolyte Interphase

Two-dimensional (2D) layered materials demonstrate prominent advantage in regulating lithium plating/stripping behavior by confining lithium diffusion/plating within interlayer gaps. However, achieving effective interlayer confined lithium diffusion/plating without compromising the stability of bulk-structural and the solid electrolyte interphase (SEI) remains a considerable challenge. This paper presents an electrochemical scissor and lithium zipper-driven protocol for realizing interlayer confined lithium plating with pretty-low strain and volume change. In this protocol, lithium serves as a "zipper" to reunite the adjacent MXene back to MAX-like phase to markedly enhance the structural stability, and a lithium halide-rich SEI is formed by electrochemically removing the terminals of halogenated MXenes to maintain the stability and rapid lithium ions diffusion of SEI. When the Ti3 C2 I2 serves as the host for lithium plating, the average coulomb efficiency exceeds 97.0 % after 320 lithium plating/stripping cycles in conventional ester electrolyte. Furthermore, a full cell comprising of LiNi0.8 Mn0.1 Co0.1 O2 and Ti3 C2 I2 @Li exhibits a capacity retention rate of 73.4 % after 200 cycles even under high cathode mass-loading (20 mg cm-2 ) and a low negative/positive capacity ratio of 1.4. Our findings advance the understanding of interlayer confined lithium plating in 2D layered materials and provide a new direction in regulating lithium and other metal plating/stripping behaviors.

Recent advances in electrolyte molecular design for alkali metal batteries

In response to societal developments and the growing demand for high-energy-density battery systems, alkali metal batteries (AMBs) have emerged as promising candidates for next-generation energy storage. Despite their high theoretical specific capacity and output voltage, AMBs face critical challenges related to high reactivity with electrolytes and unstable interphases. This review, from the perspective of electrolytes, analyzes AMB failure mechanisms, including interfacial side reactions, active materials loss, and metal dendrite growth. It then reviews recent advances in innovative electrolyte molecular designs, such as ether, ester, sulfone, sulfonamide, phosphate, and salt, aimed at overcoming the above-mentioned challenges. Finally, we propose the current molecular design principles and future promising directions that can help future precise electrolyte molecular design.

Gradual gradient distribution composite solid electrolyte for solid-state lithium metal batteries with ameliorated electrochemical performance

Composite solid electrolytes (CSEs) have emerged as promising contenders for tackling the safety concerns associated with lithium metal batteries and attaining elevated energy densities. Nonetheless, augmenting ion conductivity and curtailing the growth of lithium dendrites within the electrolyte remain pressing challenges. We have developed CSEs featuring a unique structure, in which Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is distributed in a gradient decline from the center to both sides (GCSE). This distinctive arrangement encompasses heightened polymer content at the edges, thereby enhancing the compatibility between CSEs and electrode materials. Concurrently, the escalated LLZTO content at the center functions to impede the proliferation of lithium dendrites. The uniform gradient distribution state facilitates the consistent and rapid transport of lithium ions. At room temperature, GCSE exhibits an ionic conductivity of 1.5 × 10-4 S cm-1, with stable constant current cycling of lithium for over 1200 h. Furthermore, CR2032 coin batteries with a LiFePO4 (LFP)|GCSE|Li configuration demonstrate excellent rate performance and cycling stability, yielding a discharge capacity of 120 mA h g-1 at 0.5C and retaining 90 % capacity after 200 cycles at 60 °C. Flexible solid electrolytes with gradient structures offer substantial advantages in dealing with ion conductivity and inhibition of lithium dendrites, thereby expected to propel the practical application of lithium metal batteries.

Constructing LiF-Dominated Interphases with Polymer Interwoven Outer Layer Enables Long-Term Cycling of Si Anodes

Constructing a robust solid electrolyte interphase (SEI) is extremely critical to developing high-energy-density silicon (Si)-based lithium-ion batteries. However, it is still elusive how to accurately manipulate the chemical composition and structure of the SEI layer. Herein, a LiF-dominated SEI film intertwined by a highly elastic polymer is achieved by regulating the defluorination mechanism of the fluorinated carbonate additive on the Si electrode surface. The experimental and computational results confirm that the decomposition route of trans-difluoroethylene carbonate (DFEC) molecules can be significantly altered in the presence of lithium difluoro(oxalato)borate (LiDFOB) additive. The induction of direct defluorination of DFEC step by LiDFOB, as opposed to the breaking of C-O bonds without LiDFOB addition, is crucial in ensuring the exclusive formation of LiF-dominated SEI and maintaining the cyclic structure of DFEC. The defluorinated DFEC easily polymerizes to form poly(vinylene carbonate), enhancing the elasticity of the SEI. The resulting LiF-dominated SEI film with a polymer interwoven outer layer shows enhanced ionic conductivity and mechanical stability, which can effectively accelerate electrode reaction kinetics and maintain the structural stability of the Si electrode. As a result, the Si electrode with the electrolyte containing the designed dual-additive exhibits superior cycling stability and excellent rate performance, delivering a high reversible capacity of 1487.3 mAh g-1 after 1000 cycles at 2 A g-1.

Unveiling the Role of Fluorination in Hexacyclic Coordinated Ether Electrolytes for High-Voltage Lithium Metal Batteries

Fluorinated ethers have become promising electrolyte solvent candidates for lithium metal batteries (LMBs) because they are endowed with high oxidative stability and high Coulombic efficiencies of lithium metal stripping/plating. Up to now, most reported fluorinated ether electrolytes are -CF3-based, and the influence of ion solvation in modifying degree of fluorination has not been well-elucidated. In this work, we synthesize a hexacyclic coordinated ether (1-methoxy-3-ethoxypropane, EMP) and its fluorinated ether counterparts with -CH2F (F1EMP), -CHF2 (F2EMP), or -CF3 (F3EMP) as terminal group. With lithium bis(fluorosulfonyl)imide as single salt, the solvation structure, Li-ion transport behavior, lithium deposition kinetics, and high-voltage stability of the electrolytes were systematically studied. Theoretical calculations and spectra reveal the gradually reduced solvating power from nonfluorinated EMP to fully fluorinated F3EMP, which leads to decreased ionic conductivity. In contrast, the weakly solvating fluorinated ethers possess higher Li+ transference number and exchange current density. Overall, partially fluorinated -CHF2 is demonstrated as the desired group. Further full cell testing using high-voltage (4.4 V) and high-loading (3.885 mAh cm-2) LiNi0.8Co0.1Mn0.1O2 cathode demonstrates that F2EMP electrolyte enables 80% capacity retention after 168 cycles under limited Li (50 μm) and lean electrolyte (5 mL Ah-1) conditions and 129 cycles under extremely lean electrolyte (1.8 mL Ah-1) and the anode-free conditions. This work deepens the fundamental understanding on the ion transport and interphase dynamics under various degrees of fluorination and provides a feasible approach toward the design of fluorinated ether electrolytes for practical high-voltage LMBs.

Designing an Air-Stable Interphase on Lithium Metal Anode to Improve Cycling Performance

The application of rechargeable lithium metal batteries is challenged by intractable issues of uncontrollable Li dendrite growth that result in poor cycle life and safety risks. In this work, an air-stable interphase is developed to protect the lithium metal anode (LMA) via a facile solution-based approach. The Ag-embedded fluoride-rich interphase not only creates abundant lithiophilic sites for homogenizing Li nucleation and growth but also resists severe air erosion to protect the LMA beneath and enable decent cycling stability. As a result, the Ag-F-rich interphase enables flat Li deposition on LMA, which is clearly observed in the operando Li plating experiments. Paired with a LiFePO4 cathode (11.8 mg cm-2), the Ag-F-rich interphase-modified LMA enables 300 stable cycles at 0.5 C, delivering a capacity retention ratio as high as 91.4%. Even after being exposed to air for 1 h, the modified LMA still runs smoothly for over 120 cycles with ignorable capacity decay, exhibiting great air stability. This work proves the concept of functionalizing the interphase on the LMA to enable good cycling performance even under severe air erosion.

Powering the Future: Unleashing the Potential of MXene-Based Dual-Functional Photoactive Cathodes in Photo-Rechargeable Zinc-Ion Capacitor

Dual-functional photo-rechargeable (photo-R) energy storage devices, which acquire stored energy from solar energy harvesting, are being developed to battle the current energy crisis. In this study, these findings on the photo-driven characteristics of MXene-based photocathodes in photo-R zinc-ion capacitors (ZICs) are presented. Along with the pristine Ti3 C2 Tx MXene, tellurium/Ti3 C2 Tx (Te/Ti3 C2 Tx ) hybrid nanostructure is synthesized via facile chemical vapor transport technique to examine them for photocathodes in ZICs. Interestingly, the evaluated self-powered photodetector devices using MXene-based samples revealed a pyro-phototronic behavior introduced into the samples, with higher desirability observed in Te/Ti3 C2 Tx . The photo-R ZICs results exhibited a capacitance enhancement of 50.86% for Te/Ti3 C2 Tx at two scan rates of 5 and 10 mV s-1 under illumination, compared to dark conditions. In contrast, a capacitance enhancement of 30.20% is obtained for the pristine Ti3 C2 Tx at only a 5 mV s-1 scan rate. Furthermore, both samples achieved photo-charging voltage responses of ≈960 mV, and photoconversion efficiencies of 0.01% (for Te/ Ti3 C2 Tx ) and 0.07% (for Ti3 C2 Tx ). These characteristics in MXene-based single photo-R ZICs are significant and considerable with the distinguished integrated photo-R supercapacitors with solar cells, or coupled energy-harvesting and energy-storing devices reported recently in the literature.

Li3Bi/Li2O layer with uniform built-in electric field distribution for dendrite free lithium metal batteries

Lithium metal batteries have garnered significant attention as a promising energy storage technology, offering high energy density and potential applications across various industries. However, the formation of lithium dendrites during battery cycling poses a considerable challenge, leading to performance degradation and safety hazards. This study aims to address this issue by investigating the effectiveness of a protective layer on the lithium metal surface in inhibiting dendrite growth. The hypothesis is that continuous lithium consumption during battery cycling is a primary contributor to dendrite formation. To test this hypothesis, a protective layer of Li3Bi/Li2O was applied to the lithium foil through immersion in a BiN3O9 solution. Experimental techniques including kelvin probe force microscopy (KPFM) and density functional theory (DFT) calculations were employed to analyze the structural and electronic properties of the Li3Bi/Li2O layer. The findings demonstrate successful doping of Bi into the Li coating, forming Bi-Bi and Bi-O bonds. KPFM measurements reveal a higher work function of Li3Bi/Li2O, indicating its potential as an effective protective layer. DFT calculations further support this observation by revealing a greater adsorption energy of lithium on the Li3Bi/Li2O layer compared to the bulk material. Charge density analysis suggests that the adsorption of Li atoms onto the Li3Bi/Li2O layer induces a redistribution of charge, resulting in increased electron availability on the surface and preventing electrode-electrolyte contact. This study provides insights into the role of the Li3Bi/Li2O protective layer in inhibiting dendrite growth in lithium metal batteries. By mitigating dendrite formation, the protective layer holds promise for enhancing battery performance and longevity. These findings contribute to the development of strategies for improving the stability and reliability of lithium metal batteries, facilitating their wider adoption in energy storage applications.

Domino Reactions Enabling Sulfur-Mediated Gradient Interphases for High-Energy Lithium Batteries

Silicon (Si)-based anodes are currently considered a feasible solution to improve the energy density of lithium-ion batteries owing to their sufficient specific capacity and natural abundance. However, Si-based anodes exhibit low electric conductivities and large volume changes during cycling, which could easily trigger continuous breakdown/reparation of the as-formed solid-electrolyte-interphase (SEI) layer, seriously hampering their practical application in current battery technology. To control the chemoelectrochemical instability of the conventional SEI layer, we herein propose the introduction of elemental sulfur into nonaqueous electrolytes, aiming to build a sulfur-mediated gradient interphase (SMGI) layer on Si-based anodes. The SMGI layer is generated through the domino reactions (i.e., electrochemical cascade reactions) involving the electrochemical reductions of elemental sulfur followed by nucleophilic substitutions of fluoroethylene carbonate, which endows the corresponding SEI layer with strong elasticity and chemomechanical stability and enables rapid transportation of Li+ ions. Consequently, the prototype Si||LiNi0.8Co0.1Mn0.1O2 cells attain a high-energy density of 622.2 W h kg-1 and a capacity retention of 88.8% after 100 cycles. Unlike previous attempts based on sophisticated chemical modifications of electrolyte components, this study opens a new avenue in interphase design for long-lived and high-energy rechargeable batteries.

Origin of dendrite-free lithium deposition in concentrated electrolytes

The electrolyte solvation structure and the solid-electrolyte interphase (SEI) formation are critical to dictate the morphology of lithium deposition in organic electrolytes. However, the link between the electrolyte solvation structure and SEI composition and its implications on lithium morphology evolution are poorly understood. Herein, we use a single-salt and single-solvent model electrolyte system to systematically study the correlation between the electrolyte solvation structure, SEI formation process and lithium deposition morphology. The mechanism of lithium deposition is thoroughly investigated using cryo-electron microscopy characterizations and computational simulations. It is observed that, in the high concentration electrolytes, concentrated Li⁺ and anion-dominated solvation structure initiate the uniform Li nucleation kinetically and favor the decomposition of anions rather than solvents, resulting in inorganic-rich amorphous SEI with high interface energy, which thermodynamically facilitates the formation of granular Li. On the contrary, solvent-dominated solvation structure in the low concentration electrolytes tends to exacerbate the solvolysis process, forming organic-rich mosaic SEI with low interface energy, which leads to aggregated whisker-like nucleation and growth. These results are helpful to tackle the long-standing question on the origin of lithium dendrite formation and guide the rational design of high-performance electrolytes for advanced lithium metal batteries.

A Review on Regulating Li+ Solvation Structures in Carbonate Electrolytes for Lithium Metal Batteries

Lithium metal batteries (LMBs) are considered promising candidates for next-generation battery systems due to their high energy density. However, commercialized carbonate electrolytes cannot be used in LMBs due to their poor compatibility with lithium metal anodes. While increasing cut-off voltage is an effective way to boost the energy density of LMBs, conventional ethylene carbonate-based electrolytes undergo a number of side reactions at high voltages. It is therefore critical to upgrade conventional carbonate electrolytes, the performance of which is highly influenced by the solvation structure of lithium ions (Li⁺ ). This review provides a comprehensive overview of the strategies to regulate the solvation structure of Li⁺ in carbonate electrolytes for LMBs by better understanding the science behind the Li⁺ solvation structure and Li⁺ behavior. Different strategies are systematically compared to help select better electrolytes for specific applications. The remaining scientific and technical problems are pointed out, and directions for future research on carbonate electrolytes for LMBs are proposed.

Strongly Solvating Ether Electrolytes for High-Voltage Lithium Metal Batteries

Ethers are promising electrolytes for lithium (Li) metal batteries (LMBs) because of their unique stability with Li metal. Although intensive research on designing anion-enriched electrolyte solvation structures has greatly improved their electrochemical stabilities, ether electrolytes are approaching an anodic bottleneck. Herein, we reveal the strong correlation between electrolyte solvation structure and oxidation stability. In contrast to previous designs of weakly solvating solvents for enhanced anion reactivities, the triglyme (G3)-based electrolyte with the largest Li⁺ solvation energy among different linear ethers demonstrates greatly improved stability on Ni-rich cathodes under an ultrahigh voltage of 4.7 V (93% capacity retention after 100 cycles). Ether electrolytes with a stronger Li⁺ solvating ability could greatly suppress deleterious oxidation side reactions by decreasing the lifetime of free labile ether molecules. This study provides critical insights into the dynamics of the solvation structure and its significant influence on the interfacial stability for future development of high-efficiency electrolytes for high-energy-density LMBs.

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.

Non-polar ether-based electrolyte solutions for stable high-voltage non-aqueous lithium metal batteries

The electrochemical instability of ether-based electrolyte solutions hinders their practical applications in high-voltage Li metal batteries. To circumvent this issue, here, we propose a dilution strategy to lose the Li⁺/solvent interaction and use the dilute non-aqueous electrolyte solution in high-voltage lithium metal batteries. We demonstrate that in a non-polar dipropyl ether (DPE)-based electrolyte solution with lithium bis(fluorosulfonyl) imide salt, the decomposition order of solvated species can be adjusted to promote the Li⁺/salt-derived anion clusters decomposition over free ether solvent molecules. This selective mechanism favors the formation of a robust cathode electrolyte interphase (CEI) and a solvent-deficient electric double-layer structure at the positive electrode interface. When the DPE-based electrolyte is tested in combination with a Li metal negative electrode (50 μm thick) and a LiNi_0.8Co_0.1Mn_0.1O₂-based positive electrode (3.3 mAh/cm²) in pouch cell configuration at 25 °C, a specific discharge capacity retention of about 74% after 150 cycles (0.33 and 1 mA/cm² charge and discharge, respectively) is obtained.

A New In Situ Prepared MOF-Natural Polymer Composite Electrolyte for Solid Lithium Metal Batteries with Superior High- Rate Capability and Long-Term Cycling Stability at Ultrahigh Current Density

Lithium metal batteries hold promise for energy storage applications but suffer from uncontrolled lithium dendrites. In this study, a new composite membrane based on modified natural polymer and ZIF-67 is designed and prepared by the in situ composite method for the first time. Among them, a modified natural polymer composed of lithium alginate (LA) and polyacrylamide (PAM) can be obtained by electrospinning. Importantly, the polar functional groups of natural polymers can interact by hydrogen bonding and MOFs can construct lithium-ion transport channels. Consequently, compared with LA-PAM electrolyte without MOF, the electrochemical stability window of ZIF-67-LA-PAM electrolyte becomes wider from 4.5 to 5.2 V, and the lithium-ion transference number (t_Li+ ) enhances from 0.326 to 0.627 at 30°C. It is worth noting that the symmetric cells with ZIF-67-LA-PAM have superior stable cycling performance at 40 and 100 mA cm^-2 , and a high rate at 10C and 20C for LFP cells. Besides, the cell with NCM811 high-voltage cathode can run stably for 400 cycles with an initial discharge capacity of 136.1 mAh g^-1 at 0.5C. This work provides an effective method for designing and preparing MOF-natural polymer composite electrolytes and exhibits an excellent application prospect in high-energy-density lithium metal batteries.

A Low-Concentration Electrolyte for High-Voltage Lithium-Metal Batteries: Fluorinated Solvation Shell and Low Salt Concentration Effect

Concentration of electrolyte has significant effects on performances of rechargeable batteries. Previous studies mainly focused on concentrated electrolytes. So far, only several recipes on low-concentration electrolytes were studied, performing enhanced performance in advanced rechargeable batteries. Here, based on common electrolyte components, a low-concentration electrolyte composed of 0.2 M lithium hexafluorophosphate (LiPF₆ ) solvated in fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) is employed for high-voltage Li metal battery. The synergistic working mechanisms of introducing fluorine-containing solvent in the solvated structure and low salt concentration effect are revealed, resulting in LiF-rich, uniform, and robust solid electrolyte interphase layer and fewer unfavorable decomposition products. As a result, this low-concentration electrolyte significantly enhances electrochemical performances of Li||Li symmetric cells and high-voltage LiCoO₂ ||Li batteries.

Thermally Stable Polymer-Rich Solid Electrolyte Interphase for Safe Lithium Metal Pouch Cells

Serious safety risks caused by the high reactivity of lithium metal against electrolytes severely hamper the practicability of lithium metal batteries. By introducing unique polymerization site and more fluoride substitution, we built an in situ formed polymer-rich solid electrolyte interphase upon lithium anode to improve battery safety. The fluorine-rich and hydrogen-free polymer exhibits high thermal stability, which effectively reduces the continuous exothermic reaction between electrolyte and anode/cathode. As a result, the critical temperature for thermal safety of 1.0 Ah lithium-LiNi_0.5 Co_0.2 Mn_0.3 O₂ pouch cell can be increased from 143.2 °C to 174.2 °C. The more dangerous "ignition" point of lithium metal batteries, the starting temperature of battery thermal runaway, has been dramatically raised from 240.0 °C to 338.0 °C. This work affords novel strategies upon electrolyte design, aiming to pave the way for high-energy-density and thermally safe lithium metal batteries.

Designer Cathode Additive for Stable Interphases on High-Energy Anodes

Rechargeable lithium-based batteries built with high-energy anode materials (e.g., silicon-based and silicon-derivative materials) are considered a feasible solution to satisfy the stringent requirements imposed by emerging markets, including electric vehicles and grid storage, due to their higher energy density compared to contemporary lithium-ion batteries. The robustness of the solid electrolyte interphase (SEI) layer on high-energy anodes is critical to achieve long-term and stable cycling performances of the batteries. Herein, we propose a new type of designer cathode additive (DCA), i.e., an ultrathin coating layer of elemental sulfur on the cathode, for the in situ formation of a thin and robust SEI layer on various types of high-energy anodes. The DCA elemental sulfur undergoes simultaneous oxidation and reduction paths, forming lithium alkyl sulfate (R-OSO₂OLi) and poly(ethylene oxide) (PEO)-like polymers on the anode surface. The as-formed R-OSO₂OLi/PEO-modified SEI layer has good lithium cation (Li⁺) permeability to facilitate fast ion transportation across the interphases and superior elasticity to adapt to large volume changes, which is particularly effective for improving the cycling efficiency of high-energy anodes (e.g., ca. 14-35% increase in capacity retention for the silicon-carbon composite (SiC) or silicon-tin alloy (Si-Sn)||LiFePO₄ cells). The present work opens a new avenue toward the practical deployment of high-energy rechargeable lithium-based batteries.

Rationally Designed Fluorinated Amide Additive Enables the Stable Operation of Lithium Metal Batteries by Regulating the Interfacial Chemistry

A fluorinated amide molecule with two functional segments, namely, an amide group with a high donor number to bind lithium ions and a fluorine chain to expel carbonate solvents and mediate the formation of LiF, was designed to regulate the interfacial chemistry. As expected, the additive preferably appears in the first solvation sheath of lithium ions and is electrochemically reduced on the anode, and thus an inorganic-rich solid electrolyte interphase is generated. The morphology of deposited lithium metal evolves from brittle dendrites into a granular shape. Consequently, the Li||LiFePO₄ cell shows an excellent capacity retention of 92.7% at a high rate of 5 C after 800 cycles. Besides, the Li||LiNi_0.8Co_0.1Mn_0.1O₂ cell succeeds to maintain 98.1% of the initial capacity after 100 cycles at 1 C. Our designing of N,N-diethyl- 2,3,3,3-tetrafluoropropionamide (denoted as DETFP) highlights the importance of a "high donor number" and may shed light on the design principles of electrolytes for high performance batteries.

Direct Detection of Lithium Exchange across the Solid Electrolyte Interphase by 7Li Chemical Exchange Saturation Transfer

Lithium metal anodes offer a huge leap in the energy density of batteries, yet their implementation is limited by solid electrolyte interphase (SEI) formation and dendrite deposition. A key challenge in developing electrolytes leading to the SEI with beneficial properties is the lack of experimental approaches for directly probing the ionic permeability of the SEI. Here, we introduce lithium chemical exchange saturation transfer (Li-CEST) as an efficient nuclear magnetic resonance (NMR) approach for detecting the otherwise invisible process of Li exchange across the metal–SEI interface. In Li-CEST, the properties of the undetectable SEI are encoded in the NMR signal of the metal resonance through their exchange process. We benefit from the high surface area of lithium dendrites and are able, for the first time, to detect exchange across solid phases through CEST. Analytical Bloch-McConnell models allow us to compare the SEI permeability formed in different electrolytes, making the presented Li-CEST approach a powerful tool for designing electrolytes for metal-based batteries.

A low-concentration all-fluorinated electrolyte for stable lithium metal batteries

A novel low-concentration all-fluorinated electrolyte was designed to stabilize lithium metal batteries with excellent wettability and safety.