Localized High-Concentration Sulfone Electrolytes for High-Efficiency Lithium-Metal Batteries

Constructing a Janus Catholyte/Cathode Structure: A New Strategy for Stable Zn-Organic Batteries

Organic materials are promising candidates for the electrodes of aqueous zinc-ion batteries due to their nonmetallic nature, environmental friendliness, and cost-effectiveness. However, they often suffer from significant dissolution during the charge-discharge process, which poses a major hurdle to their practical applications. Inspired by membrane-less organelles in cells, a simple and versatile strategy is proposed-constructing a Janus catholyte/cathode structured electrode based on liquid-liquid phase separation, in which redox-active organic molecules are confined in the liquid state within the activated carbon, thereby eliminating the volume effect and preventing their diffusion into the electrolyte. The customization of phase separation systems by leveraging the hydrophobicity/hydrophilicity differences of various anions is successfully demonstrated. This approach allows for precise regulation of ion cluster/coordination structures, enabling the confinement of active substances while ensuring efficient ion transport. Consequently, the as-constructed Zn||Janus catholyte/cathode cells exhibit superior reversible rate capacity (186 mA h g-1 at 5.0 A g-1) and remarkable cycling performance (retention of 72.5% after 12 000 cycles). The strategy in building Janus catholyte/cathode structured electrodes breaks free from the limitations imposed by traditional solid-state electrodes, offering tremendous opportunities for exploring diverse advanced battery systems.

Ether-Based Gel Polymer Electrolyte for High-Voltage Potassium Ion Batteries

Low-concentration ether electrolytes cannot efficiently achieve oxidation resistance and excellent interface behavior, resulting in severe electrolyte decomposition at a high voltage and ineffective electrode-electrolyte interphase. Herein, we utilize sandwich structure-like gel polymer electrolyte (GPE) to enhance the high voltage stability of potassium-ion batteries (PIBs). The GPE contact layer facilitates stable electrode-electrolyte interphase formation, and the GPE transport layer maintains good ionic transport, which enabled GPE to exhibit a wide electrochemical window and excellent electrochemical performance. In addition, Al corrosion under a high voltage is suppressed through the restriction of solvent molecules. Consequently, when using the designed GPE (based on 1 m), the K||graphite cell exhibits excellent cycling stability of 450 cycles with a capacity retention of 91%, and the K||FeFe-Prussian blue cell (2-4.2 V) delivers a high average Coulombic efficiency of 99.9% over 2200 cycles at 100 mA g-1. This study provides a promising path in the application of ether-based electrolytes in high-voltage and long-lasting PIBs.

Five Volts Lithium Batteries with Advanced Carbonate-Based Electrolytes: A Rational Design via a Trio-Functional Addon Materials

Lithium metal batteries paired with high-voltage LiNi0.5Mn1.5O4 (LNMO) cathodes are a promising energy storage source for achieving enhanced high energy density. Forming durable and robust solid-electrolyte interphase (SEI) and cathode-electrolyte interface (CEI) and the ability to withstand oxidation at high potentials are essential for long-lasting performance. Herein, advanced electrolytes are designed via trio-functional additives to carbonate-based electrolytes for 5 V Li||LNMO and graphite||LNMO cells achieving 88.3% capacity retention after 500 charge-discharge cycles. Theoretical calculations reveal that adding adiponitrile facilitates the presence of more hierarchical DFOB- and PF6 - dual anion structure in the solvation sheath, leading to a faster de-solvation of the Li cation. By combining both fluorine and nitrile additives, an efficient synergistic effect is obtained, generating robust thin inorganic SEI and CEI films, respectively. These films enhance microstructural stability; Li dendrite growth on the Li electrode is being suppressed at the anode side and transition-metals dissolution from the cathode is being mitigated, as evidenced by cryo-transmission electron microscopy and synchrotron studies.

The Polarity of Co-solvents Regulates the Charge Storage Mechanisms in Supercapacitors with Concentrated Electrolytes

Developing better energy storage devices depends on comprehending the underlying mechanisms involved in charge storage. With the continuous conception of new electrolytes, this task becomes progressively more urgent and complex. An example is the utilization of co-solvated concentrated solutions. While these show promising electrochemical responses, their dynamic properties (especially under confinement) and their relationships with performance are not fully understood. Here, we combined modified step potential electrochemical spectroscopy and quasielastic neutron scattering to investigate systems composed of activated mesoporous carbon (AMC) and concentrated solutions of lithium bis(trifluoromethanesulfonyl)imide in acetonitrile co-solvated with either toluene or acetone. We report that acetone does not impair surface-controlled mechanisms, contrary to the case with toluene, which competes with charged species to populate the AMC's pores without contributing to charge storage. In turn, toluene promotes a greater overall capacitance owing to Faradaic processes, which may be related to changes in the solvation structures under confinement.

In-Situ Polymerized High-Voltage Solid-State Lithium Metal Batteries with Dual-Reinforced Stable Interfaces

Solid polymer electrolytes (SPEs) represent a pivotal advance toward high-energy solid-state lithium metal batteries. However, inadequate interfacial contact remains a significant bottleneck, impeding scalability and application. Inadequate interfacial contact remains a significant bottleneck, impeding scalability and application. Recent efforts have focused on transforming liquid/solid interfaces into solid/solid ones through in situ polymerization, which shows potential especially in reducing interface impedance. Here, we designed high-voltage SSLMBs with dual-reinforced stable interfaces by combining interface modification with an in situ polymerization technology inspired by targeted effects in medicine. Theoretical calculations and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis demonstrate that tetramethylene sulfone (TMS) and bis(2,2,2-trifluoromethyl) carbonate (TFEC) exhibit selective adsorption at the interface of the LiNi0.8Co0.1Mn0.1O2 (NCM) cathode and Li anode, respectively. These compounds further decompose to form a stable cathode-electrolyte interface (CEI) film and a solid electrolyte interface (SEI) film, thereby simultaneously achieving a superior interface between the SPE and both the Li anode and NCM cathode. The developed Li||SPE||Li cell sustained cycling for more than 1000 h at 0.3 mA cm-2, and the NCM||SPE||Li cell also demonstrated an excellent capacity retention of 86.8% after 1000 cycles at 1 °C. This work will provide valuable insights for the rational design of high-voltage SSLMBs with stable interfaces, leveraging in situ polymerization as a cornerstone technology.

Design of Localized High-Concentration Electrolytes from the Perspective of Physicochemical Properties

The physicochemical properties of electrolytes profoundly impact the energy density, rate performance, and manufacturability of rechargeable lithium batteries. Localized high-concentration electrolytes (LHCEs), a novel electrolyte class, have attracted considerable interest, yet the impact of diluents on their physicochemical properties remains unclear, as most reports involve only a few samples. Here we prepared 345 electrolyte samples using 21 diluents and systematically investigated the effect of diluent type and content on the miscibility, density, viscosity, and ion conductivity of LHCEs. We found that the physicochemical properties of LHCEs are mainly affected by the diluents' density and viscosity, regardless of type. Notably, the ionic conductivity exhibits two typical variance trends, "volcano" and "descending," both correlating strongly with diluents' viscosity rather than dielectric constant, a parameter commonly employed in electrolyte design. This anomaly can be explained by the "plum pudding" solvation model, providing essential insights for developing lightweight, highly fluid, and conductive LHCEs.

Nonsolvating Fluoroaromatic Cosolvent Enabled Long-Term Cycling of High-Voltage Lithium-Ion Batteries with Organosulfur Electrolytes

The structure-activity relationships of nonsolvating cosolvents for organosulfur-based electrolyte systems were revealed. The performance of nonsolvating dilutant fluorobenzene (FB) was compared to various fluorinated ether dilutants in high-voltage electrolytes containing a concentration of 1.2 M LiPF6 dissolved in fluoroethylene carbonate (FEC), ethyl methyl sulfone (EMS), and the dilutant. In a high-voltage and high-loading LiNi0.8Mn0.1Co0.1O2 (NMC811) full cell configuration, the organosulfur-based electrolyte containing FB dilutant enabled superior electrochemical performance compared to the electrolytes using other nonsolvating fluorinated ether formulations. Moreover, the FB-containing electrolyte exhibited the highest ionic conductivity and lowest viscosity among all organosulfur-based electrolytes containing nonsolvating dilutant. These improvements are attributed to the enhanced physical properties of electrolyte and lithium-ion mobility. Furthermore, by employing first-principles simulations, the observed suppression of side reactions at high voltage is linked to FB's lower reactivity toward singlet dioxygen, which is likely produced at the NMC interface. Overall, FB is considered an excellent diluent that does not impede cell operation by mass decomposition at the cathode.

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.

Designer Anions for Better Rechargeable Lithium Batteries and Beyond

Non-aqueous electrolytes, generally consisting of metal salts and solvating media, are indispensable elements for building rechargeable batteries. As the major sources of ionic charges, the intrinsic characters of salt anions are of particular importance in determining the fundamental properties of bulk electrolyte, as well as the features of the resulting electrode-electrolyte interphases/interfaces. To cope with the increasing demand for better rechargeable batteries requested by emerging application domains, the structural design and modifications of salt anions are highly desired. Here, salt anions for lithium and other monovalent (e.g., sodium and potassium) and multivalent (e.g., magnesium, calcium, zinc, and aluminum) rechargeable batteries are outlined. Fundamental considerations on the design of salt anions are provided, particularly involving specific requirements imposed by different cell chemistries. Historical evolution and possible synthetic methodologies for metal salts with representative salt anions are reviewed. Recent advances in tailoring the anionic structures for rechargeable batteries are scrutinized, and due attention is paid to the paradigm shift from liquid to solid electrolytes, from intercalation to conversion/alloying-type electrodes, from lithium to other kinds of rechargeable batteries. The remaining challenges and key research directions in the development of robust salt anions are also discussed.

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

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

Upgrading Electrolyte Antioxidant Chemistry by Constructing Potential Scaling Relationship

Rational design of advanced electrolytes to improve the high-voltage capability has been attracting wide attention as one critical solution to enable next-generation high-energy-density batteries. However, the limited understanding of electrolyte antioxidant chemistry as well as the lack of valid quantization approaches have resulted in knowledge gap, which hinders the formulation of new electrolytes. Herein, we construct a standard curve based on representative solvation structures to quantify the oxidation stability of ether-based electrolytes, which reveals the linear correlation between the oxidation potential and the atomic charge of the least oxidation-resistant solvent. Dictated by the regularity between solvation composition and oxidation potential, a (Trifluoromethyl)cyclohexane-based localized high-concentration electrolyte dominated by anion-less solvation structures was designed to optimize the cycling performance of 4.5 V 30 μm-Li||3.8 mAh cm-2-LiCoO2 batteries, which maintained 80 % capacity retention even after 440 cycles. The consistency of experimental and computational results validates the proposed principles, offering a fundamental guideline to evaluate and design aggressive electrochemical systems.

Linear ether-based highly concentrated electrolytes for Li-sulfur batteries

Li-S batteries have attracted attention as next-generation rechargeable batteries owing to their high theoretical capacity and cost-effectiveness. Sparingly solvating electrolytes hold promise because they suppress the dissolution and shuttling of polysulfide intermediates to increase the coulombic efficiency and extend the cycle life. This study investigated the solubility of polysulfide (Li2S8) in a range of liquid electrolytes, including organic electrolytes, highly concentrated electrolytes, and ionic liquids. The Li2S8 solubility was well correlated with the donor number (DNNMR), estimated via23Na-NMR, and was lower than 100 mM_(elemental sulfur) in electrolytes with DNNMR < 14, regardless of the type of electrolyte. Highly concentrated electrolytes comprising lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and linear chain dialkyl ethers such as methyl propyl ether (MPE), n-butyl methyl ether (BME), and ethyl propyl ether (EPE) were studied as sparingly solvating electrolytes for Li-S batteries. Monomethyl ethers, such as BME, showed more pronounced Li-ion coordination and higher ionic conductivity, whereas the steric hindrance of the longer alkyl chains in EPE lowered the solvation number, enhanced ion association, and lowered the ionic conductivity despite the solvents having similar dielectric constants. The charge-discharge rate capabilities of Li-S cells with dialkyl ether-based electrolytes were more impressive than those of cells with a localized high-concentration electrolyte using sulfolane (SL) and hydrofluoroether (HFE), [Li(SL)2][TFSA]-2HFE. The higher rate performance was attributed to the superior Li-ion transport properties of the dialkyl ether-based electrolytes. A pouch-type cell using lightweight [Li(BME)3][TFSA] demonstrated an energy density exceeding 300 W h kg-1 under lean electrolyte conditions.

Cluster analysis as a tool for quantifying structure-transport properties in simulations of superconcentrated electrolyte

Using molecular dynamics simulations and graph-theory-based cluster analysis, we investigate the structure-transport properties of typical water-in-salt electrolytes. We demonstrate that ions exhibit distinct dynamics across different ionic clusters-namely, solvent-separated ion pairs (SSIPs), contact ion pairs (CIPs), and aggregates (AGGs). We assess the average proportions of various ionic species and their lifetimes. Our method reveals a dynamic decoupling of ion kinetics, with each species independently contributing to the overall molecular motion. This is evidenced by the fact that the total velocity autocorrelation function (VACF) and power spectrum can be expressed as a weighted sum of independent functions for each species. The experimental data on the ionic conductivity of the studied LiTFSI electrolytes align well with our theoretical predictions at various concentrations, based on the proportions and diffusion coefficients of free ions derived from our analysis. The insights gained into the solvation structures and dynamics of different ionic species enable us to elucidate the physical mechanisms driving ion transport in such superconcentrated electrolytes, providing a comprehensive framework for the future design and optimization of electrolytes.

Stabilization of lithium metal in concentrated electrolytes: effects of electrode potential and solid electrolyte interphase formation

Lithium (Li) metal negative electrodes have attracted wide attention for high-energy-density batteries. However, their low coulombic efficiency (CE) due to parasitic electrolyte reduction has been an alarming concern. Concentrated electrolytes are one of the promising concepts that can stabilize the Li metal/electrolyte interface, thus increasing the CE; however, its mechanism has remained controversial. In this work, we used a combination of LiN(SO2F)2 (LiFSI) and weakly solvating 1,2-diethoxyethane (DEE) as a model electrolyte to study how its liquid structure changes upon increasing salt concentration and how it is linked to the Li plating/stripping CE. Based on previous works, we focused on the Li electrode potential (ELi with reference to the redox potential of ferrocene) and solid-electrolyte-interphase (SEI) formation. Although ELi shows a different trend with DEE compared to conventional 1,2-dimethoxyethane (DME), which is accounted for by different ion-pair states of Li+ and FSI-, the ELi-CE plots overlap for both electrolytes, suggesting that ELi is one of the dominant factors of the CE. On the other hand, the extensive ion pairing results in the upward shift of the FSI- reduction potential, as demonstrated both experimentally and theoretically, which promotes the FSI--derived inorganic SEI. Both ELi and SEI contribute to increasing the Li plating/stripping CE.

Highly Stable Lithium Metal Batteries Enabled by Tuning the Molecular Polarity of Diluents in Localized High-Concentration Electrolytes

Electrolyte plays a crucial role in ensuring stable operation of lithium metal batteries (LMBs). Localized high-concentration electrolytes (LHCEs) have the potential to form a robust solid-electrolyte interphase (SEI) and mitigate Li dendrite growth, making them a highly promising electrolyte option. However, the principles governing the selection of diluents, a crucial component in LHCE, have not been clearly determined, hampering the advancement of such a type of electrolyte systems. Herein, the diluents from the perspective of molecular polarity are rationally designed and developed. A moderately fluorinated solvent, 1-(1,1,2,2-tetrafluoroethoxy)propane (TNE), is employed as a diluent to create a novel LHCE. The unique molecular structure of TNE enhances the intrinsic dipole moment, thereby altering solvent interactions and the coordination environment of Li-ions in LHCE. The achieved solvation structure not only enhances the bulk properties of LHCE, but also facilitates the formation of more stable anion-derived SEIs featured with a higher proportion of inorganic species. Consequently, the corresponding full cells of both Li||LiFePO4 and Li||LiNi0.8Co0.1Mn0.1O2 cells utilizing Li thin-film anodes exhibit extended long-term stability with significantly improved average Coulombic efficiency. This work offers new insights into the functions of diluents in LHCEs and provides direction for further optimizing the LHCEs for LMBs.

Development of Electrolytes under Lean Condition in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries stand out as one of the promising candidates for next-generation electrochemical energy storage technologies. A key requirement to realize high-specific-energy Li-S batteries is to implement low amount of electrolyte, often characterized by the electrolyte/sulfur (E/S) ratio. Low E/S ratio aggravates the known challenges for Li-S batteries and introduces new ones originated from the high concentration of polysulfides in limited electrolyte reservoir. In this review, the connections between the fundamental properties of electrolytes and the electrochemical/chemical reactions in Li-S batteries under lean electrolyte condition are elucidated. The emphasis is on how the solvating properties of the electrolyte affect the fate of polysulfides. Built upon the mechanistic analysis, different strategies to design lean electrolytes to improve the overall process of Li-S reactions and Li anode protection are discussed.

Scalable Customization of Crystallographic Plane Controllable Lithium Metal Anodes for Ultralong-Lasting Lithium Metal Batteries

A formidable challenge to achieve the practical applications of rechargeable lithium (Li) metal batteries (RLMBs) is to suppress the uncontrollable growth of Li dendrites. One of the most effective solutions is to fabricate Li metal anodes with specific crystal plane, but still lack of a simple and high-efficient approach. Herein, a facile and controllable way for the scalable customization of polished Li metal anodes with highly preferred (110) and (200) crystallographic orientation (donating as polished Li(110) and polished Li(200), respectively) by regulating the times of accumulative roll bonding, is reported. According to the inherent characteristics of polished Li(110)/Li(200), the influence of Li atomic structure on the electrochemical performance of RLMBs is deeply elucidated by combining theoretical calculations with relative experimental proofs. In particular, a polished Li(110) crystal plane is demonstrated to induce Li+ uniform deposition, promoting the formation of flat and dense Li deposits. Impressively, the polished Li(110)||LiFePO4 full cells exhibit unprecedented cycling stability with 10 000 cycles at 10 C almost without capacity degradation, indicating the great potential application prospect of such textured Li metal. More valuably, this work provides an important reference for low-cost, continued, and large-scale production of Li metal anodes with highly preferred crystal orientation through roll-to-roll manufacturability.

Flame-Retardant Nonaqueous Electrolytes for High-Safety Potassium-Ion Batteries

Potassium-ion batteries (PIBs) with conventional organic-based flammable electrolytes suffer from serious safety issues with a high risk of ignition and burning especially under harsh conditions, which significantly limits their widespread applications. Flame-retardant electrolytes (FREs) are considered as one of the most effective strategies to address these safety issues. Therefore, it's much necessary to summarize the challenges, recent progress, and design principles of flame-retardant nonaqueous electrolytes for PIBs to guide their development and future applications. In this review, an in-depth introduction and explanation of the origins of electrolyte flammability are first presented. Particularly, the state-of-the-art design principles of FREs for PIBs are extensively summarized and emphasized, including the electrolyte flame-retardant solvents/additives, highly concentrated electrolytes (HCEs), localized high-concentration electrolytes (LHCEs), ionic liquids-based electrolytes and solid-state electrolytes. Moreover, the advantages and drawbacks of each approach are systematically presented and discussed, following by proposed perspectives to guide the rational development of next-generation high-safety PIBs for practical applications.

A Temperature Self-Adaptive Electrolyte for Wide-Temperature Aqueous Zinc-Ion Batteries

The advancement of aqueous zinc-ion batteries (AZIBs) is often hampered by the dendritic zinc growth and the parasitic side reactions between the zinc anode and the aqueous electrolyte, especially under extreme temperature conditions. This study unveils the performance decay mechanism of zinc anodes in harsh environments, characterized by "dead zinc" at low temperatures and aggravated hydrogen evolution and adverse by-products at elevated temperatures. To address these issues, a temperature self-adaptive electrolyte (TSAE), founded on the competitive coordination principle of co-solvent and anions, is introduced. This electrolyte exhibits a dynamic solvation capability, engendering an inorganic-rich solid electrolyte interface (SEI) at low temperatures while an organic alkyl ether- and alkyl carbonate-containing SEI at elevated temperatures. The self-adaptability of the electrolyte significantly enhances the performance of the zinc anode across a broad temperature range. A Zn//Zn symmetrical cell, based on the TSAE, showcases reversible plating/stripping exceeding 16 800 h (>700 d) at room temperature under 1 mA cm-2 and 1 mAh cm-2, setting a record of lifespan. Furthermore, the TSAE enables stable operation of the zinc full batteries across an ultrawide temperature range of -35 to 75 °C. This work illuminates a pathway for optimizing AZIBs under extreme temperatures by fine-tuning the interfacial chemistry.

Sustainable Electrolytes: Design Principles and Recent Advances

Today, rechargeable batteries are omnipresent and essential for our existence. In order to improve the electrochemical performance of electric fields, the introduction of electrolytes with fluorine (F)-based inorganic elemental compositions is a direction of exploration. However, most fluorocarbons have a high global warming potential and ozone depletion potential, which do not meet the sustainability requirements of the battery industry. Therefore, developing sustainable electrolytes is a viable option for future battery development. Although researchers have made much progress in electrolyte optimization, little attention has been paid to developing low-toxic and safe electrolytes. This review aims to elucidate the design principles and recent advances in this direction for solvents and salts. It concludes with a summary and outlook on future research directions for the molecular design of green electrolytes for practical high-voltage rechargeable batteries.

Dual-Salts Localized High-Concentration Electrolyte for Li- and Mn-Rich High-Voltage Cathodes in Lithium Metal Batteries

Limited electrochemical stability windows of conventional carbonate-based electrolytes pose a challenge to support the Lithium (Li)- and manganese (Mn)-rich (LMR) high-voltage cathodes in rechargeable Li-metal batteries (LMBs). To address this issue, a novel localized high-concentration electrolyte (LHCE) composition incorporating LiPF6 and LiTFSI as dual-salts (D-LHCE), tailored for high-voltage (>4.6 Vvs.Li) operation of LMR cathodes in LMBs is introduced. 7Li nuclear magnetic resonance and Raman spectroscopy revealed the characteristics of the solvation structure of D-LHCE. The addition of LiPF6 provides stable Al-current-collector passivation while the addition of LiTFSI improves the stability of D-LHCE by producing a more robust cathode-electrolyte interphase (CEI) on LMR cathode and solid-electrolyte interphase (SEI) on Li-metal anode. As a result, LMR/Li cell, using the D-LHCE, achieved 72.5% capacity retention after 300 cycles, a significant improvement compared to the conventional electrolyte (21.9% after 100 cycles). The stabilities of LMR CEI and Li-metal SEI are systematically analyzed through combined applications of electrochemical impedance spectroscopy and distribution of relaxation times techniques. The results present that D-LHCE concept represents an effective strategy for designing next-generation electrolytes for high-energy and high-voltage LMB cells.

Adjusting Li+ Solvation Structures via Dipole-Dipole Interaction to Construct Inorganic-Rich Interphase for High-Performance Li Metal Batteries

Practical applications of lithium metal batteries are limited by unstable solid electrolyte interphase (SEI) and uncontrollable dendrite Li deposition. Regulating the solvation structure of Li+ via modifying electrolyte components enables optimizing the structure of the SEI and realizing dendrite-free Li deposition. In this work, it is found that the ionic-dipole interactions between the electron-deficient B atoms in lithium oxalyldifluoro borate (LiDFOB) and the O atoms in the DME solvent molecule can weaken the interaction between the DME molecule and Li+, accelerating the desolvation of Li+. On this basis, the ionic-dipole interactions facilitate the entry of abundant anions into the inner solvation sheath of Li+, which promotes the formation of inorganic-rich SEI. In addition, the interaction between DFOB- and DME molecules reduces the highest occupied molecular orbital energy level of DME molecules in electrolytes, which improves the oxidative stability of the electrolytes system. As a result, the Li||Li cells in LiDFOB-containing electrolytes exhibit an excellent cyclability of over 1800 h with a low overpotential of 18.2 mV, and the Li||LiFePO4 full cells display a high-capacity retention of 93.4% after 100 cycles with a high Coulombic efficiency of 99.3%.

Highly Solubilized Urea as Effective Proton Donor-Acceptors for Durable Zinc-Ion Storage Beyond Single-Anion Selection Criteria

Urea, as one of the most sustainable organic solutes, denies the high salt consumption in commercial electrolytes with its peculiar solubility in water. The bi-mixture of urea-H2O shows the eutectic feature for increased attention in aqueous Zn-ion electrochemical energy storage (AZEES) technologies. While the state-of-the-art aqueous electrolyte recipes are still pursuing the high-concentrated salt dosage with limited urea adoption and single-anion selection category. Here, a dual-anion urea-based (DAU) electrolyte composed of dual-Zn salts and urea-H2O-induced solutions is reported, contributing to a stable electric double-layer construction and in situ organic/inorganic SEI formation. The optimized ZT2S0.5-20U electrolytes show a high initial Coulombic efficiency of 93.2% and durable Zn-ion storage ≈4000 h regarding Zn//Cu and Zn//Zn stripping/plating procedures. The assembled Zn//activated carbon full cells maintain ≈100% capacitance over 50 000 cycles at 4 A g-1 in coin cell and ≈98% capacitance over 20 000 cycles at 1 A g-1 in pouch cell setups. A 12 × 12 cm2 pouch cell assembly illustrates the practicality of AZEES devices by designing the cheap, antifreezing, and nonflammable DAU electrolyte system coupling proton donor-acceptor molecule and multi-anion selection criteria, exterminating the critical technical barriers in commercialization.

Cation-Loaded Porous Mg2+-Zeolite Layer Direct Dendrite-Free Deposition toward Long-Life Lithium Metal Anodes

Lithium metal, with ultrahigh theoretical specific capacity, is considered as an ideal anode material for the lithium-ion batteries. However, its practical application is severely plagued by the uncontrolled formation of dendritic Li. Here, a cation-loaded porous Mg2+-Zeolite layer is proposed to enable the dendrite-free deposition on the surface of Li metal anode. The skeleton channels of zeolite provide the low coordinated Li+-solvation groups, leading to the faster desolvation process at the interface. Meanwhile, anions-involved solvation sheath induces a stable, inorganic-rich SEI, contributing to the uniform Li+ flux through the interface. Furthermore, the co-deposition of sustained release Mg2+ realizes a new faster migration pathway, which proactively facilitates the uniform diffusion of Li on the lithium substrate. The synergistic modulation of these kinetic processes facilitates the homogeneous Li plating/stripping behavior. Based on this synergistic mechanism, the high-efficiency deposition with cyclic longevity exceeding 2100 h is observed in the symmetric Li/Li cell with Mg2+-Zeolite modified anode at 1 mA cm-2. The pouch cell matched with LiFePO4 cathode fulfills a capacity retention of 88.4% after 100 cycles at a severe current density of 1 C charge/discharge. This synergistic protective mechanism can give new guidance for realizing the safe and high-performance Li metal batteries.

Localized High-Concentration Sulfone Electrolytes with High-Voltage Stability and Flame Retardancy for Ni-Rich Lithium Metal Batteries

The localized high-concentration electrolyte (LHCE) propels the advanced high-voltage battery system. Sulfone-based LHCE is a transformative direction compatible with high energy density and high safety. In this work, the application of lithium bis(trifluoromethanesulphonyl)imide and lithium bis(fluorosulfonyl)imide (LiFSI) in the LHCE system constructed from sulfolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is investigated. The addition of diluent causes an increase of contact ion pairs and ionic aggregates in the solvation cluster and an acceptable quantity of free solvent molecules. A small amount of LiFSI as an additive can synergistically decompose with TTE on the cathode and participate in the construction of both electrode interfaces. The designed electrolyte helps the Ni-rich system to cycle firmly at a high voltage of 4.5 V. Even with high mass load and lean electrolyte, it can keep a reversible specific capacity of 91.5% after 50 cycles. The constructed sulfone-based electrolyte system exhibits excellent thermal stability far beyond the commercial electrolytes. Further exploration of in-situ gelation has led to a quick conversion of the designed liquid electrolyte to the gel state, accompanied by preserved stability, which provides a direction for the synergistic development of LHCE with gel electrolytes.

Electrolyte Design Chart Reframed by Intermolecular Interactions for High-Performance Li-Ion Batteries

Developing advanced electrolytes has been regarded as a pivotal strategy for enhancing the electrochemical performance of batteries; however, the criteria for electrolyte design remain elusive. In this study, we present an electrolyte design chart reframed through intermolecular interactions. By combining systematic nuclear magnetic resonance, Fourier transform infrared measurements, molecular dynamics (MD) simulations, and machine-learning-assisted classifications, we establish semiquantitative correlations between electrolyte components and the electrochemical reversibility of electrolytes. We propose the equivalent increment of Li salt resulting from functional cosolvent and solvent-solvent interactions for effective electrolyte design and prediction. The controllable regulation of the electrolyte design chart by the properties of solvent-solvent interactions presents varying equivalent effects of increasing Li salt concentrations in different electrolyte systems. Based on this mechanism, we demonstrate highly reversible and nonflammable phosphate-based electrolytes for graphite||NCM811 full cells. The proposed electrolyte design chart, semiquantitatively determined by intermolecular interactions, provides the necessary experimental foundation and basis for the future rapid screening and prediction of electrolytes using machine-learning methods.

Weakly Coordinating Diluent Modulated Solvation Chemistry for High-Performance Sodium Metal Batteries

Diluents have been extensively employed to overcome the disadvantages of high viscosity and sluggish kinetics of high-concentration electrolytes, but generally do not change the pristine solvation structure. Herein, a weakly coordinating diluent, hexafluoroisopropyl methyl ether (HFME), is applied to regulate the coordination of Na+ with diglyme and anion and form a diluent-participated solvate. This unique solvation structure promotes the accelerated decomposition of anions and diluents, with the construction of robust inorganic-rich electrode-electrolyte interphases. In addition, the introduction of HFME reduces the desolvation energy of Na+, improves ionic conductivity, strengthens the antioxidant, and enhances the safety of the electrolyte. As a result, the assembled Na||Na symmetric cell achieves a stable cycle of over 1800 h. The cell of Na||P'2-Na0.67MnO2 delivers a high capacity retention of 87.3 % with a high average Coulombic efficiency of 99.7 % after 350 cycles. This work provides valuable insights into solvation chemistry for advanced electrolyte engineering.

Reaction Center Shifting in Partially Fluorinated Electrolytes for Robust Lithium Metal Battery

The strategic formulation of a compatible electrolyte plays a pivotal role in extending the longevity of lithium-metal batteries (LMBs). Here, we present findings on a partially fluorinated electrolyte distinguished by a subdued solvation affinity towards Li+ ions and a concentrated anion presence within the primary solvation layer. This distinctive solvation arrangement redirects the focal points of reactions from solvent molecules to anions, facilitating the predominant involvement of anions in the creation of a LiF-enriched solid-electrolyte interphase (SEI). Electrochemical assessments showcase effective Li+ transport kinetics, diminished overpotential polarization for Li nucleation (28 mV), and prolonged cycling durability in Li||Li cells employing the partially fluorinated electrolyte. When tested in Li||NCM811 cells, the designed electrolyte delivers a capacity retention of 89.30 % and exhibits a high average Coulombic efficiency of 99.80 % over 100 cycles with a charge-potential cut-off of 4.6 V vs. Li/Li+ under the current density of 0.4C. Furthermore, even at a current density of 1C, the cells maintain 81.90 % capacity retention and a high average Coulombic efficiency of 99.40 % after 180 cycles. This work underscores the significance of weak-solvation interaction in partially fluorinated electrolytes and highlights the crucial role of solvent structure in enabling the long-term stability and high-energy density of LMBs.

Rational Lithium Salt Molecule Tuning for Fast Charging/Discharging Lithium Metal Battery

The electrolytes for lithium metal batteries (LMBs) are plagued by a low Li+ transference number (T+) of conventional lithium salts and inability to form a stable solid electrolyte interphase (SEI). Here, we synthesized a self-folded lithium salt, lithium 2-[2-(2-methoxy ethoxy)ethoxy]ethanesulfonyl(trifluoromethanesulfonyl) imide (LiETFSI), and comparatively studied with its structure analogue, lithium 1,1,1-trifluoro-N-[2-[2-(2-methoxyethoxy)ethoxy)]ethyl]methanesulfonamide (LiFEA). The special anion chemistry imparts the following new characteristics: i) In both LiFEA and LiETFSI, the ethylene oxide moiety efficiently captures Li+, resulting in a self-folded structure and high T+ around 0.8. ii) For LiFEA, a Li-N bond (2.069 Å) is revealed by single crystal X-ray diffraction, indicating that the FEA anion possesses a high donor number (DN) and thus an intensive interphase "self-cleaning" function for an ultra-thin and compact SEI. iii) Starting from LiFEA, an electron-withdrawing sulfone group is introduced near the N atom. The distance of Li-N is tuned from 2.069 Å in LiFEA to 4.367 Å in LiETFSI. This alteration enhances ionic separation, achieves a more balanced DN, and tunes the self-cleaning intensity for a reinforced SEI. Consequently, the fast charging/discharging capability of LMBs is progressively improved. This rationally tuned anion chemistry reshapes the interactions among Li+, anions, and solvents, presenting new prospects for advanced LMBs.

An Ultralow-concentration and Moisture-resistant Electrolyte of Lithium Difluoro(oxalato)borate in Carbonate Solvents for Stable Cycling in Practical Lithium-ion Batteries

The electrolyte concentration not only impacts the battery performance but also affects the battery cost and manufacturing. Currently, most studies focus on high-concentration (>3 M) or localized high-concentration electrolytes (~1 M); however, the expensive lithium salt imposes a major concern. Most recently, ultralow concentration electrolytes (<0.3 M) have emerged as intriguing alternatives for battery applications, which feature low cost, low viscosity, and extreme-temperature operation. However, at such an early development stage, many works are urgently needed to further understand the electrolyte properties. Herein, we introduce an ultralow concentration electrolyte of 2 wt % (0.16 M) lithium difluoro(oxalato)borate (LiDFOB) in standard carbonate solvents. This electrolyte exhibits a record-low salt/solvent mass ratio reported to date, thus pointing to a superior low cost. Furthermore, this electrolyte is highly compatible with commercial Li-ion materials, forming stable and inorganic-rich interphases on the lithium cobalt oxide (LiCoO2) cathode and graphite anode. Consequently, the LiCoO2-graphite full cell demonstrates excellent cycling performance. Besides, this electrolyte is moisture-resistant and effectively suppresses the generation of hydrogen fluoride, which will markedly facilitate the battery assembly and recycling process under ambient conditions.

Electrolytes Design for Extending the Temperature Adaptability of Lithium-Ion Batteries: from Fundamentals to Strategies

With the continuously growing demand for wide-range applications, lithium-ion batteries (LIBs) are increasingly required to work under conditions that deviate from room temperature (RT). However, commercial electrolytes exhibit low thermal stability at high temperatures (HT) and poor dynamic properties at low temperatures (LT), hindering the operation of LIBs under extreme conditions. The bottleneck restricting the practical applications of LIBs has promoted researchers to pay more attention to developing a series of innovative electrolytes. This review primarily covers the design of electrolytes for LIBs from a temperature adaptability perspective. First, the fundamentals of electrolytes concerning temperature, including donor number (DN), dielectric constant, viscosity, conductivity, ionic transport, and theoretical calculations are elaborated. Second, prototypical examples, such as lithium salts, solvent structures, additives, and interfacial layers in both liquid and solid electrolytes, are presented to explain how these factors can affect the electrochemical behavior of LIBs at high or low temperatures. Meanwhile, the principles and limitations of electrolyte design are discussed under the corresponding temperature conditions. Finally, a summary and outlook regarding electrolytes design to extend the temperature adaptability of LIBs are proposed.

Compositionally Sequenced Interfacial Layers for High-Energy Li-Metal Batteries

Electrolyte additives with multiple functions enable the interfacial engineering of Li-metal batteries (LMBs). Owing to their unique reduction behavior, additives exhibit a high potential for electrode surface modification that increases the reversibility of Li-metal anodes by enabling the development of a hierarchical solid electrolyte interphase (SEI). This study confirms that an adequately designed SEI facilitates the homogeneous supply of Li+, nonlocalized Li deposition, and low electrolyte degradation in LMBs while enduring the volume fluctuation of Li-metal anodes on cycling. An in-depth analysis of interfacial engineering mechanisms reveals that multilayered SEI structures comprising mechanically robust LiF-rich species, electron-rich P-O species, and elastic polymeric species enabled the stable charge and discharge of LMBs. The polymeric outer SEI layer in the as-fabricated multilayered SEI could accommodate the volume fluctuation of Li-metal anodes, significantly enhancing the cycling stability Li||LiNi0.8Co0.1Mn0.1O2 full cells with an electrolyte amount of 3.6 g Ah-1 and an areal capacity of 3.2 mAh cm-2. Therefore, this study confirms the ability of interfacial layers formed by electrolyte additives and fluorinated solvents to advance the performance of LMBs and can open new frontiers in the fabrication of high-performance LMBs through electrolyte-formulation engineering.

Toward maximum energy density enabled by anode-free lithium metal batteries: Recent progress and perspective

Owing to the emergenceof energy storage and electric vehicles, the desire for safe high-energy-density energy storage devices has increased research interest in anode-free lithium metal batteries (AFLMBs). Unlike general lithium metal batteries (LMBs), in which excess Li exists to compensate for the irreversible loss of Li, only the current collector is employed as an anode and paired with a lithiated cathode in the fabrication of AFLMBs. Owing to their unique cell configuration, AFLMBs have attractive characteristics, including the highest energy density, safety, and cost-effectiveness. However, developing AFLMBs with extended cyclability remains an issue for practical applications because the high reactivity of Li with limited inventory causes severely low Coulombic efficiency (CE), poor cyclability, and dendrite growth. To address these issues, tremendous effort has been devoted to stabilizing Li metal anodes for AFLMBs. In this review, the importance and challenges of AFLMBs are highlighted. Then, diverse strategies, such as current collectors modification, advanced electrolytes, cathode engineering, and operation protocols are thoroughly reviewed. Finally, a future perspective on the strategy is provided for insight into the basis of future research. It is hoped that this review provides a comprehensive understanding by reviewing previous research and arousing more interest in this field.

Delineating the Impact of Transition-Metal Crossover on Solid-Electrolyte Interphase Formation with Ion Mass Spectrometry

Lithium-metal batteries (LMB) employing cobalt-free layered-oxide cathodes are a sustainable path forward to achieving high energy densities, but these cathodes exhibit substantial transition-metal dissolution during high-voltage cycling. While transition-metal crossover is recognized to disrupt solid-electrolyte interphase (SEI) formation on graphite anodes, experimental evidence is necessary to demonstrate this for lithium-metal anodes. In this work, advanced high-resolution 3D chemical analysis is conducted with time-of-flight secondary-ion mass spectrometry (TOF-SIMS) to establish spatial correlations between the transition metals and electrolyte decomposition products found on cycled lithium-metal anodes. Insights into the localization of various chemistries linked to crucial processes that define LMB performance, such as lithium deposition, SEI growth, and transition-metal deposition are deduced from a precise elemental and spatial analysis of the SEI. Heterogenous transition-metal deposition is found to perpetuate both heterogeneous SEI growth and lithium deposition on lithium-metal anodes. These correlations are confirmed across various lithium-metal anodes that are cycled with different cobalt-free cathodes and electrolytes. An advanced electrolyte that is stable to higher voltages is shown to minimize transition-metal crossover and its effects on lithium-metal anodes. Overall, these results highlight the importance of maintaining uniform SEI coverage on lithium-metal anodes, which is disrupted by transition-metal crossover during operation at high voltages.

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.

Regulating the Electrode-Electrolyte Interfaces of Lithium-High Nickel Batteries via a Multifunctional Additive

Lithium metal batteries with high nickel ternary (LiNixCoyMn1-x-yO2, x ≥ 0.8) as the cathode hold the promise to meet the demand of next-generation high energy density batteries. However, the unsatisfactory stability of electrode-electrolyte interfaces limits their practical applications. In this work, N-methyl-N-trimethylsilyltrifluoroacetamide (NMTFA) is suggested as a new functional electrolyte additive to stabilize the Li∥LiNi0.9Co0.05Mn0.05O2 chemistry by forming robust and effective electrode-electrolyte interphases, namely the anode-electrolyte interphase (AEI, or conventionally called SEI) and cathode-electrolyte interphase (CEI). The NMTFA-derived SEI/CEI greatly enhances the battery performance that a capacity retention of 82.1% after 200 cycles at 1C charge/discharge is achieved, significantly higher than that without NMTFA addition (52.5%). Moreover, the NMTFA also improves the thermal stability of the electrolyte and inhibits the hydrolysis of LiPF6. This work provides new clues for the optimization of electrolyte formulation for lithium-high nickel batteries through modulating interfaces.

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

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

Enabling an Inorganic-Rich Interface via Cationic Surfactant for High-Performance Lithium Metal Batteries

An anion-rich electric double layer (EDL) region is favorable for fabricating an inorganic-rich solid-electrolyte interphase (SEI) towards stable lithium metal anode in ester electrolyte. Herein, cetyltrimethylammonium bromide (CTAB), a cationic surfactant, is adopted to draw more anions into EDL by ionic interactions that shield the repelling force on anions during lithium plating. In situ electrochemical surface-enhanced Raman spectroscopy results combined with molecular dynamics simulations validate the enrichment of NO3-/FSI- anions in the EDL region due to the positively charged CTA+. In-depth analysis of SEI structure by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry results confirmed the formation of the inorganic-rich SEI, which helps improve the kinetics of Li+ transfer, lower the charge transfer activation energy, and homogenize Li deposition. As a result, the Li||Li symmetric cell in the designed electrolyte displays a prolongated cycling time from 500 to 1300 h compared to that in the blank electrolyte at 0.5 mA cm-2 with a capacity of 1 mAh cm-2. Moreover, Li||LiFePO4 and Li||LiCoO2 with a high cathode mass loading of > 10 mg cm-2 can be stably cycled over 180 cycles.

Enhancing Li-S Battery Performance with Limiting Li[N(SO2F)2] Content in a Sulfolane-Based Sparingly Solvating Electrolyte

By enhancing the stability of the lithium metal anode and mitigating the formation of lithium dendrites through electrolyte design, it becomes feasible to extend the lifespan of lithium-sulfur (Li-S) batteries. One widely accepted approach involves the utilization of Li[N(SO2F)2] (Li[FSA]), which holds promise in stabilizing the lithium anode by facilitating the formation of an inorganic-dominant solid electrolyte interface (SEI) film. However, the use of Li[FSA] encounters limitations due to inevitable side reactions between lithium polysulfides (LiPSs) and [FSA] anions. In this study, our focus lies in precisely controlling the composition of the SEI film and the morphology of the deposited lithium, as these two critical factors profoundly influence lithium reversibility. Specifically, by subjecting an initial charging process to an elevated temperature, we have achieved a significant enhancement in lithium reversibility. This improvement is accomplished through the employment of a LiPS sparingly solvating electrolyte with a restricted Li[FSA] content. Notably, these optimized conditions have resulted in an enhanced cycling performance in practical Li-S pouch cells. Our findings underscore the potential for improving the cycling performance of Li-S batteries, even when confronted with challenging constraints in electrolyte design.

Localized Medium Concentration Electrolyte with Fast Kinetics for Lithium Metal Batteries

Localized high-concentration electrolyte is widely acknowledged as a cutting-edge electrolyte for the lithium metal anode. However, the high fluorine content, either from high-concentration salts or from highly fluorinated diluents, results in significantly higher production costs and an increased environmental burden. Here, we have developed a novel electrolyte termed "Localized Medium-Concentration Electrolyte" (LMCE) to effectively address these issues. This LMCE is designed and produced by diluting a medium concentration (0.5 M-1.5 M) electrolyte which is incompatible with lithium metal anode before diluting. It has ultralow concentration (0.1 M) and demonstrates remarkable compatibility with lithium metal anode. Surprisingly, our LMCE, despite having an ultralow concentration (0.1 M), exhibits excellent kinetics in Li/Cu, Li/Li, LiFePO4 /Li, and NCM811/Li batteries. Additionally, LMCE effectively inhibits the corrosion of the Al current collector caused by LiTFSI salt under high voltage (>4 V) conditions. This groundbreaking LMCE design transforms the seemingly "incompatible" into the "compatible", opening up new avenues for exploring various electrolyte formulations, including all liquid electrolyte-based batteries.

Lithiophilic and Eco-Friendly Nano-Se Seeds Unlock Dendrite-Free and Anode-Free Li-Metal Batteries

A 3D host design for lithium (Li)-metal anodes can effectively accommodate volume changes and suppress Li dendrite growth; nonetheless, its practical applicability in energy-dense Li-metal batteries (LMBs) is plagued by excessive Li loading. Herein, we introduced eco- and human-friendly Se seeds into 3D carbon cloth (CC) to create a robust host for efficient Li deposition/stripping. The highly lithiophilic nano-Se endowed the Se-decorated CC (Se@CC) with perfect Li wettability for instantaneous Li infusion. At an optimal Li loading of 17 mg, the electrode delivered an unprecedentedly long life span of 5400 h with low overpotentials <36 mV at 1 mA cm-2/1 mAh cm-2 and 1500 h at 5 mA cm-2/5 mAh cm-2. Furthermore, the uniform Se distribution and strong Li-Se binding allowed for further reduction in Li loading to 2 mg via direct Li electrodeposition. The corresponding LiNi0.8Co0.1Mn0.1O2 (NCM811)-based full cell afforded a high capacity retention rate of 74.67% over 300 cycles at a low N/P ratio of 8.64. Finally, the initial anode-free LMB using a NCM811 cathode and a Se@CC anode current collector demonstrated a high electrode-level specific energy of 531 Wh kg-1 and consistently high CEs >99.7% over 200 cycles. This work highlights a high-performance host design with excellent tunability for practical high-energy-density LMBs.

Active Diluent-Anion Synergy Strategy Regulating Nonflammable Electrolytes for High-Efficiency Li Metal Batteries

High-energy Li metal batteries (LMBs) consisting of Li metal anodes and high-voltage cathodes are promising candidates of the next generation energy-storage systems owing to their ultrahigh energy density. However, it is still challenging to develop high-voltage nonflammable electrolytes with superior anode and cathode compatibility for LMBs. Here, we propose an active diluent-anion synergy strategy to achieve outstanding compatibility with Li metal anodes and high-voltage cathodes by using 1,2-difluorobenzene (DFB) with high activity for yielding LiF as an active diluent to regulate nonflammable dimethylacetamide (DMAC)-based localized high concentration electrolyte (LHCE-DFB). DFB and bis(fluorosulfonyl)imide (FSI- ) anion cooperate to construct robust LiF-rich solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), which effectively stabilize DMAC from intrinsic reactions with Li metal anode and enhance the interfacial stability of the Li metal anodes and LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) cathodes. LHCE-DFB enables ultrahigh Coulombic efficiency (98.7 %), dendrite-free, extremely stable and long-term cycling of Li metal anodes in Li || Cu cells and Li || Li cells. The fabricated NCM811 || Li cells with LHCE-DFB display remarkably enhanced long-term cycling stability and excellent rate capability. This work provides a promising active diluent-anion synergy strategy for designing high-voltage electrolytes for high-energy batteries.

Anion-Reinforced Solvating Ionic Liquid Electrolytes Enabling Stable High-Nickel Cathode in Lithium-Metal Batteries

Ionic liquid electrolytes (ILEs) are promising to develop high-safety and high-energy-density lithium-metal batteries (LMBs). Unfortunately, ILEs normally face the challenge of sluggish Li+ transport due to increased ions' clustering caused by Coulombic interactions. Here a type of anion-reinforced solvating ILEs (ASILEs) is discovered, which reduce ions' clustering by enhancing the anion-cation coordination and promoting more anions to enter the internal solvation sheath of Li+ to address this concern. The designed ASILEs, incorporating chlorinated hydrocarbons and two anions, bis(fluorosulfonyl) imide (FSI- ) and bis(trifluoromethanesulfonyl) imide (TFSI- ), aim to enhance Li+ transport ability, stabilize the interface of the high-nickel cathode material (LiNi0.8 Co0.1 Mn0.1 O2 , NCM811), and retain fire-retardant properties. With these ASILEs, the Li/NCM811 cell exhibits high initial specific capacity (203 mAh g-1 at 0.1 C), outstanding capacity retention (81.6% over 500 cycles at 1.0 C), and excellent average Coulombic efficiency (99.9% over 500 cycles at 1.0 C). Furthermore, an Ah-level Li/NCM811 pouch cell achieves a notable energy density of 386 Wh kg-1 , indicating the practical feasibility of this electrolyte. This research offers a practical solution and fundamental guidance for the rational design of advanced ILEs, enabling the development of high-safety and high-energy-density LMBs.

Ion Transport in (Localized) High Concentration Electrolytes for Li-Based Batteries

High concentration electrolytes (HCEs) and localized high concentration electrolytes (LHCEs) have emerged as promising candidates to enable higher energy density Li-ion batteries due to their advantageous interfacial properties that result from their unique solvent structures. Using electrophoretic NMR and electrochemical techniques, we characterize and report full transport properties, including the lithium transference numbers (t+) for electrolytes ranging from the conventional ∼1 M to HCE regimes as well as for LHCE systems. We find that compared to conventional electrolytes, t+ increases for HCEs; however the addition of diluents to LHCEs significantly decreases t+. Viscosity effects alone cannot explain this behavior. Using Onsager transport coefficients calculated from our experiments, we demonstrate that there is more positively correlated cation-cation motion in HCEs as well as fast cation-anion ligand exchange consistent with a concerted ion-hopping mechanism. The addition of diluents to LHCEs results in more anticorrelated motion indicating a disruption of concerted cation-hopping leading to low t+ in LHCEs.

Beyond LiF: Tailoring Li2O-Dominated Solid Electrolyte Interphase for Stable Lithium Metal Batteries

The components and structures of the solid-electrolyte interphase (SEI) are critical for stable cycling of lithium metal batteries (LMBs). LiF has been widely studied as the dominant component of SEI, but Li2O, which has a much lower diffusion barrier for Li+, has rarely been investigated as the dominant component of SEI. The effect of Li2O-dominated SEI on electrochemical performance still remains elusive. Herein, an ultrastrong coordinated cosolvation diluent, 2,3-difluoroethoxybenzene (DFEB), is designed to modulate solvation structure and tailor Li2O-dominated SEI for stable LMBs. In the DFEB-based LHCE (DFEB-LHCE), DFEB intensively participates in the first solvation shell and synergizes with FSI- to tailor an Li2O-dominated inorganic-rich SEI which is different from the LiF-dominated SEI formed in conventional LHCE. Benefiting from this special SEI architecture, a high Coulombic efficiency (CE) of 99.58% in Li||Cu half cells, stable voltage profiles, and dense and uniform lithium deposition, as well as effective inhibition of Li dendrite formation in the symmetrical cell, are achieved. More importantly, the DFEB-LHCE can be matched with various cathodes such as LFP, NCM811, and S cathodes, and the Li||LFP full cell using DFEB-LHCE possesses 85% capacity retention after 650 stable cycles with 99.9% CE. Especially the 1.5 Ah practical lithium metal pouch cell achieves an excellent capacity retention of 89% after 250 cycles with a superb average CE of 99.93%. This work unravels the superiority of the Li2O-dominated SEI and the feasibility of tailoring SEI components through modulation of solvation structures.

An Electrolyte with Less Space-Occupying Diluent at Cathode Inner Helmholtz Plane for Stable 4.6 V Lithium-Ion Batteries

Reasonably elevating the working voltage (≥4.4 V vs. Li/Li+ ) of the cathode is one of the efficient approaches to maximize the energy density of lithium-ion batteries (LIBs). As a preferred partner for high-voltage LIB systems, localized high-concentration electrolyte (LHCE), characterized by a stronger Li solvation structure, less free solvent, and robust electrode/electrolyte interphase has attracted much attention in academic circles. Herein, we systematically studied the role of the diluent in LHCE on the formation of the cathode electrolyte interphase (CEI) and elucidated that the existing anion-diluent pairing in the inner Helmholtz plane (IHP) results in an uneven CEI and subsequent battery degradation under high voltage. A m-fluorotoluene (mFT) diluent was further employed in the LHCE containing lithium difluoro(oxalato)borate (LiDFOB) to facilitate a uniform and rich-anion-derived CEI, since the weaker interaction of HmFT -BDFOB - , as compared to the HHhydrofluoroether -BDFOB - , reduces the influence of mFT in IHP or initial CEI formation. Consequently, the mFT-dominated LHCE propels the high-voltage performance of LIBs one step forward, endowing a 4.6 V-class 1.2-Ah graphite||LiNi0.8 Co0.1 Mn0.1 O2 pouch cells a 90.4 % capacity retention after 130 cycles. Our study thus describes a new index affecting the CEI formation and proposes novel strategies to deeply optimize the high-voltage LIBs.

Synergistic Cation Solvation Reorganization and Fluorinated Interphase for High Reversibility and Utilization of Zinc Metal Anode

Batteries based on zinc (Zn) chemistry offer a great opportunity for large-scale applications owing to their safety, cost-effectiveness, and environmental friendliness. However, the poor Zn reversibility and inhomogeneous electrodeposition have greatly impeded their practical implementation, stemming from water-related passivation/corrosion. Here, we present a multifunctional electrolyte comprising gamma-butyrolactone (GBL) and Zn(BF4)2·xH2O to resolve these intrinsic challenges. The systematic results confirm that water reactivity toward a Zn anode is minimized by forcing GBL solvents into the Zn2+ solvation shell and constructing a fluorinated interphase on the Zn anode surface via anion decomposition. Furthermore, NMR was selected as an auxiliary testing protocol to elevate and understand the role of electrolyte composition in building the interphase. The combined factors in synergy guarantee high Zn reversibility (average Coulombic efficiency is 99.74%), high areal capacity (55 mAh/cm2), and high Zn utilization (∼91%). Ultimately, these merits enable the Zn battery utilizing a VO2 cathode to operate smoothly over 5000 cycles with a low-capacity decay rate of ∼0.0083% per cycle and a 0.23 Ah VO2/Zn pouch cell to operate over 400 cycles with a capacity retention of 77.3%.

Protonation Stimulates the Layered to Rock Salt Phase Transition of Ni-Rich Sodium Cathodes

Protonation of oxide cathodes triggers surface transition metal dissolution and accelerates the performance degradation of Li-ion batteries. While strategies are developed to improve cathode material surface stability, little is known about the effects of protonation on bulk phase transitions in these cathode materials or their sodium-ion battery counterparts. Here, using NaNiO2 in electrolytes with different proton-generating levels as model systems, a holistic picture of the effect of incorporated protons is presented. Protonation of lattice oxygens stimulate transition metal migration to the alkaline layer and accelerates layered-rock-salt phase transition, which leads to bulk structure disintegration and anisotropic surface reconstruction layers formation. A cathode that undergoes severe protonation reactions attains a porous architecture corresponding to its multifold performance fade. This work reveals that interactions between electrolyte and cathode that result in protonation can dominate the structural reversibility/stability of bulk cathodes, and the insight sheds light for the development of future batteries.

Probing the Effectiveness in Stabilizing Lithium Metal Anodes through Functional Additives

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

Electrolyte Design for Lithium-Ion Batteries for Extreme Temperature Applications

With increasing energy storage demands across various applications, reliable batteries capable of performing in harsh environments, such as extreme temperatures, are crucial. However, current lithium-ion batteries (LIBs) exhibit limitations in both low and high-temperature performance, restricting their use in critical fields like defense, military, and aerospace. These challenges stem from the narrow operational temperature range and safety concerns of existing electrolyte systems. To enable LIBs to function effectively under extreme temperatures, the optimization and design of novel electrolytes are essential. Given the urgency for LIBs operating in extreme temperatures and the notable progress in this research field, a comprehensive and timely review is imperative. This article presents an overview of challenges associated with extreme temperature applications and strategies used to design electrolytes with enhanced performance. Additionally, the significance of understanding underlying electrolyte behavior mechanisms and the role of different electrolyte components in determining battery performance are emphasized. Last, future research directions and perspectives on electrolyte design for LIBs under extreme temperatures are discussed. Overall, this article offers valuable insights into the development of electrolytes for LIBs capable of reliable operation in extreme conditions.