Electrolyte engineering via ether solvent fluorination for developing stable non-aqueous lithium metal batteries

Enhancing Anion-Selective Catalysis for Stable Lithium Metal Pouch Cells through Charge Separated COF Interlayer

Regulating the composition of solid-electrolyte-interphase (SEI) is the key to construct high-energy density lithium metal batteries. Here we report a selective catalysis anionic decomposition strategy to achieve a lithium fluoride (LiF)-rich SEI for stable lithium metal batteries. To accomplish this, the tris(4-aminophenyl) amine-pyromeletic dianhydride covalent organic frameworks (TP-COF) was adopted as an interlayer on lithium metal anode. The strong donor-acceptor unit structure of TP-COF induces local charge separation, resulting in electron depletion and thus boosting its affinity to FSI-. The strong interaction between TP-COF and FSI- lowers the lowest unoccupied molecular orbital (LUMO) energy level of FSI-, accelerating the decomposition of FSI- and generating a stable LiF-rich SEI. This feature facilitates rapid Li+ transfer and suppresses dendritic Li growth. Notably, we demonstrate a 6.5 Ah LiNi0.8Co0.1Mn0.1O2|TP-COF@Li pouch cell with high energy density (473.4 Wh kg-1) and excellent cycling stability (97.4 %, 95 cycles) under lean electrolyte 1.39 g Ah-1, high areal capacity 5.7 mAh cm-2, and high current density 2.7 mA cm-2. Our selective catalysis strategy opens a promising avenue toward the practical applications of high energy-density rechargeable batteries.

Trace Dual-Salt Electrolyte Additive Enabling a LiF-Rich Solid Electrolyte Interphase for High-Performance Lithium Metal Batteries

The composition and physiochemical properties of the solid electrolyte interphase (SEI) significantly impact the electrochemical cyclability of the Li metal. Here, we introduce a trace dual-salt electrolyte additive (TDEA) that accelerates LiF production from FEC decomposition and improves the LiF distribution, resulting in earlier LiF precipitation and the formation of a LiF-rich SEI on the Li anode. TDEA at a millimolar-level concentration was found to alter the morphology of deposited Li, suppress Li dendrite formation, and increase the cycling time and operating current density for Li anodes. Li∥NCM811 full cells using TDEA-based electrolytes exhibited approximately two times longer lifespan than those without additives. Additionally, the TDEA-based electrolytes enabled a high energy density of 347 Wh kg-1 for 500-mAh pouch cells, maintaining stable cycling over 180 cycles under stringent conditions (N/P = 1.26 and E/C = 2.2 g A h-1). Our findings suggest that the proposed TDEA strategy offers a promising path to achieving high-performance Li metal batteries.

Electrolyte Solvation Engineering Stabilizing Anode-Free Sodium Metal Battery With 4.0 V-Class Layered Oxide Cathode

Anode-free sodium metal batteries (AFSMBs) are regarded as the "ceiling" for current sodium-based batteries. However, their practical application is hindered by the unstable electrolyte and interfacial chemistry at the high-voltage cathode and anode-free side, especially under extreme temperature conditions. Here, an advanced electrolyte design strategy based on electrolyte solvation engineering is presented, which shapes a weakly solvating anion-stabilized (WSAS) electrolyte by balancing the interaction between the Na+-solvent and Na+-anion. The special interaction constructs rich contact ion pairs (CIPs) /aggregates (AGGs) clusters at the electrode/electrolyte interface during the dynamic solvation process which facilitates the formation of a uniform and stable interfacial layer, enabling highly stable cycling of 4.0 V-class layered oxide cathode from -40 °C to 60 °C and excellent reversibility of Na plating/stripping with an ultrahigh average CE of 99.89%. Ultimately, industrial multi-layer anode-free pouch cells using the WSAS electrolyte achieve 80% capacity remaining after 50 cycles and even deliver 74.3% capacity at -30 °C. This work takes a pivotal step for the further development of high-energy-density Na batteries.

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.

Molecular-docking electrolytes enable high-voltage lithium battery chemistries

Ideal rechargeable lithium battery electrolytes should promote the Faradaic reaction near the electrode surface while mitigating undesired side reactions. Yet, conventional electrolytes usually show sluggish kinetics and severe degradation due to their high desolvation energy and poor compatibility. Here we propose an electrolyte design strategy that overcomes the limitations associated with Li salt dissociation in non-coordinating solvents to enable fast, stable Li chemistries. The non-coordinating solvents are activated through favourable hydrogen bond interactions, specifically Fδ--Hδ+ or Hδ+-Oδ-, when blended with fluorinated benzenes or halide alkane compounds. These intermolecular interactions enable a dynamic Li+-solvent coordination process, thereby promoting the fast Li+ reaction kinetics and suppressing electrode side reactions. Utilizing this molecular-docking electrolyte design strategy, we have developed 25 electrolytes that demonstrate high Li plating/stripping Coulombic efficiencies and promising capacity retentions in both full cells and pouch cells. This work supports the use of the molecular-docking solvation mechanism for designing electrolytes with fast Li+ kinetics for high-voltage Li batteries.

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

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

Impact of Glyme Ether Chain Length on the Interphasial Stability of Lithium-Electrode in High-Capacity Lithium-Metal Battery

The realization of lithium-metal (Li) batteries faces challenges due to dendritic Li deposition causing internal short-circuit and low Coulombic efficiency. In this regard, the Li-deposition stability largely depends on the electrolyte, which reacts with Li to form a solid electrolyte interphase (SEI) with diverse physico-chemical properties, and dictates the interphasial kinetics. Therefore, optimizing the electrolyte for stability and performance remains pivotal. Hereof, glyme ethers are an emerging class of electrolytes, showing improved compatibility with metallic Li and enhanced stability in Li─Air and Li─Sulfur batteries. Yet, the criteria for selecting glyme solvents, particularly concerning Li deposition and dissolution processes, remain unclear. The SEI characteristics and Li deposition/dissolution processes are investigated in glyme-ether-based electrolytes with varying chain lengths, using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate (LiNO₃) salts under high capacity and limited electrolyte conditions. Longer glymes led to more homogeneous SEI, particularly pronounced with LiNO₃, minimizing surface roughness during stripping, and promoting compact Li deposits. Higher reductive stability, resulting in homogeneous interphasial properties, and slower kinetics due to high desolvation barrier and viscosity, underline stable Li growth in longer glymes. This study clarifies factors guiding the selection of glyme ether-based electrolytes in Li metal batteries, offering insights for next-generation energy storage systems.

Decreased Electrically and Increased Ionically Conducting Scaffolds for Long-Life, High-Rate and Deep-Capacity Lithium-Metal Anodes

Lithium (Li) metal batteries are deemed as promising next-generation power solutions but are hindered by the uncontrolled dendrite growth and infinite volume change of Li anodes. The extensively studied 3D scaffolds as solutions generally lead to undesired "top-growth" of Li due to their high electrical conductivity and the lack of ion-transporting pathways. Here, by reducing electrical conductivity and increasing the ionic conductivity of the scaffold, the deposition spot of Li to the bottom of the scaffold can be regulated, thus resulting in a safe bottom-up plating mode of the Li and dendrite-free Li deposition. The resulting symmetrical cells with these scaffolds, despite with a limited pre-plated Li capacity of 5 mAh cm-2, exhibit ultra-stable Li plating/stripping for over 1 year (11 000 h) at a high current density of 3 mA cm-2 and a high areal capacity of 3 mAh cm-2. Moreover, the full cells with these scaffolds further demonstrate high cycling stability under challenging conditions, including high cathode loading of 21.6 mg cm-2, low negative-to-positive ratio of 1.6, and limited electrolyte-to-capacity ratio of 4.2 g Ah-1.

A novel cathode interphase formation methodology by preferential adsorption of a borate-based electrolyte additive

The coupling of high-capacity cathodes and lithium metal anodes promises to be the next generation of high-energy-density batteries. However, the fast-structural degradations of the cathode and anode challenge their practical application. Herein, we synthesize an electrolyte additive, tris(2,2,3,3,3-pentafluoropropyl) borane (TPFPB), for ultra-stable lithium (Li) metal||Ni-rich layered oxide batteries. It can be preferentially adsorbed on the cathode surface to form a stable (B and F)-rich cathode electrolyte interface film, which greatly suppresses the electrolyte-cathode side reactions and improves the stability of the cathode. In addition, the electrophilicity of B atoms in TPFPB enhances the solubility of LiNO3 by 30 times in ester electrolyte to significantly improve the stability of the Li metal anode. Thus, the Li||Ni-rich layered oxide full batteries using TPFPB show high stability and an ultralong cycle life (up to 1500 cycles), which also present excellent performance even under high voltage (4.8 V), high areal mass loading (30 mg cm-2) and wide temperature range (-30∼60°C). The Li||LiNi0.9Co0.05Mn0.05O2 (NCM90) pouch cell using TPFPB with a capacity of 3.1 Ah reaches a high energy density of 420 Wh kg-1 at 0.1 C and presents outstanding cycling performance.

Super-Ionic Conductor Soft Filler Promotes Li+ Transport in Integrated Cathode-Electrolyte for Solid-State Battery at Room Temperature

Composite polymer solid electrolytes (CPEs), possessing good rigid flexible, are expected to be used in solid-state lithium-metal batteries. The integration of fillers into polymer matrices emerges as a dominant strategy to improve Li+ transport and form a Li+-conducting electrode-electrolyte interface. However, challenges arise as traditional fillers: 1) inorganic fillers, characterized by high interfacial energy, induce agglomeration; 2) organic fillers, with elevated crystallinity, impede intrinsic ionic conductivity, both severely hindering Li+ migration. Here, a concept of super-ionic conductor soft filler, utilizing a Li+ conductivity nanocellulose (Li-NC) as a model, is introduced which exhibits super-ionic conductivity. Li-NC anchors anions, and enhances Li+ transport speed, and assists in the integration of cathode-electrolyte electrodes for room temperature solid-state batteries. The tough dual-channel Li+ transport electrolyte (TDCT) with Li-NC and polyvinylidene fluoride (PVDF) demonstrates a high Li+ transfer number (0.79) due to the synergistic coordination mechanism in Li+ transport. Integrated electrodes' design enables stable performance in LiNi0.5Co0.2Mn0.3O2|Li cells, with 720 cycles at 0.5 C, and 88.8% capacity retention. Furthermore, the lifespan of Li|TDCT|Li cells over 4000 h and Li-rich Li1.2Ni0.13Co0.13Mn0.54O2|Li cells exhibits excellent performance, proving the practical application potential of soft filler for high energy density solid-state lithium-metal batteries at room temperature.

Chlorination Design for Highly Stable Electrolyte toward High Mass Loading and Long Cycle Life Sodium-Based Dual-Ion Battery

Sodium-based dual ion batteries (SDIBs) have garnered significant attention as novel energy storage devices offering the advantages of high-voltage and low-cost. Nonetheless, conventional electrolytes exhibit low resistance to oxidation and poor compatibility with electrode materials, resulting in rapid battery failure. In this study, for the first time, a chlorination design of electrolytes for SDIB, is proposed. Using ethyl methyl carbonate (EMC) as a representative, chlorine (Cl)-substituted EMC not only demonstrates increased oxidative stability ascribed to the electron-withdrawing characteristics of chlorine atom, electrolyte compatibility with both the cathode and anode is also greatly improved by forming Cl-containing interface layers. Consequently, a discharge capacity of 104.6 mAh g-1 within a voltage range of 3.0-5.0 V is achieved for Na||graphite SDIB that employs a high graphite cathode mass loading of 5.0 mg cm-2, along with almost no capacity decay after 900 cycles. Notably, the Na||graphite SDIB can be revived for an additional 900 cycles through the replacement of a fresh Na anode. As the mass loading of graphite cathode increased to 10 mg cm-2, Na||graphite SDIB is still capable of sustaining over 700 times with ≈100% capacity retention. These results mark the best outcome among reported SDIBs. This study corroborates the effectiveness of chlorination design in developing high-voltage electrolytes and attaining enduring cycle stability of Na-based energy storage devices.

Interface Engineering via Manipulating Solvation Chemistry for Liquid Lithium-Ion Batteries Operated≥100 °C

High-performance and temperature-resistant lithium-ion batteries (LIBs), which are able to operate at elevated temperatures (i.e., >60 °C) are highly demanded in various fields, especially in military or aerospace exploration. However, their applications were largely impeded by the poor electrochemical performance and unsatisfying safety issues, which were induced by the severe side reactions between electrolytes and electrodes at high temperatures. Herein, with the synergetic effects of solvation chemistry and functional additive in the elaborately designed weakly solvating electrolyte, a unique robust organic/inorganic hetero-interphase, composed of gradient F, B-rich inorganic components and homogeneously distributed Si-rich organic components, was successfully constructed on both cathodes and anodes, which would effectively inhibit the constant decomposition of electrolytes and dissolution of transition metal ions, thus highly enhancing the high-temperature electrochemical performance. As a result, both cathodes and anodes, without compromising their low-temperature performance, can operate at temperatures ≥100 °C, with excellent capacity retentions of 96.1 % after 500 cycles and 93.5 % after ≥200 cycles, respectively, at 80 °C. Ah-level LiCoO2||graphite full cells with a cut-off voltage of 4.3 V also exhibited superior temperature-resistance with a capacity retention of 89.9 % at temperature as high as 120 °C. Moreover, the fully charged pouch cells exhibited highly enhanced safety, demonstrating their potentials in practical applications at ultrahigh temperatures.

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.

Non-Fluorinated Ethers to Mitigate Electrode Surface Reactivity in High-Voltage NCM811-Li Batteries

Lithium (Li) metal batteries (LMBs) with nickel (Ni)-rich layered oxide cathodes exhibit twice the energy density of conventional Li-ion batteries. However, their lifespan is limited by severe side reactions caused by high electrode reactivity. Fluorinated solvent-based electrolytes can address this challenge, but they pose environmental and biological hazards. This work reports on the molecular engineering of fluorine (F)-free ethers to mitigate electrode surface reactivity in high-voltage Ni-rich LMBs. By merely extending the alkyl chains of traditional ethers, we effectively reduce the catalytic reactivity of the cathode towards the electrolyte at high voltages, which suppresses the oxidation decomposition of the electrolyte, microstructural defects and rock-salt phase formation in the cathode, and gas release issues. The high-voltage Ni-rich NCM811-Li battery delivers capacity retention of 80 % after 250 cycles with a high Coulombic efficiency of 99.85 %, even superior to that in carbonate electrolytes. Additionally, this strategy facilitates passivation of the Li anode by forming a robust solid-electrolyte interphase, boosting the Li reversibility to 99.11 % with a cycling life of 350 cycles, which outperforms conventional F-free ether electrolytes. Consequently, the lifespan of practical LMBs has been prolonged by over 100 % and 500 % compared to those in conventional carbonate- and ether-based electrolytes, respectively.

Rational Molecular Engineering via Electron Reconfiguration toward Robust Dual-Electrode/Electrolyte Interphases for High-Performance Lithium Metal Batteries

High-energy-density lithium-metal batteries (LMBs) coupling lithium-metal anodes and high-voltage cathodes are hindered by unstable electrode/electrolyte interphases (EEIs), which calls for the rational design of efficient additives. Herein, we analyze the effect of electron structure on the coordination ability and energy levels of the additive, from the aspects of intramolecular electron cloud density and electron delocalization, to reveal its mechanism on solvation structure, redox stability, as-formed EEI chemistry, and electrochemical performances. Furthermore, we propose an electron reconfiguration strategy for molecular engineering of additives, by taking sorbide nitrate (SN) additive as an example. The lone pair electron-rich group enables strong interaction with the Li ion to regulate solvation structure, and intramolecular electron delocalization yields further positive synergistic effects. The strong electron-withdrawing nitrate moiety decreases the electron cloud density of the ether-based backbone, improving the overall oxidation stability and cathode compatibility, anchoring it as a reliable cathode/electrolyte interface (CEI) framework for cathode integrity. In turn, the electron-donating bicyclic-ring-ether backbone breaks the inherent resonance structure of nitrate, facilitating its reducibility to form a N-contained and inorganic Li2O-rich solid electrolyte interface (SEI) for uniform Li deposition. Optimized physicochemical properties and interfacial biaffinity enable significantly improved electrochemical performance. High rate (10 C), low temperature (-25 °C), and long-term stability (2700 h) are achieved, and a 4.5 Ah level Li||NCM811 multilayer pouch cell under harsh conditions is realized with high energy density (462 W h/kg). The proof of concept of this work highlights that the rational ingenious molecular design based on electron structure regulation represents an energetic strategy to modulate the electrolyte and interphase stability, providing a realistic reference for electrolyte innovations and practical LMBs.

Interphase Engineering via Solvent Molecule Chemistry for Stable Lithium Metal Batteries

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

Chloro-Functionalized Ether-Based Electrolyte for High-Voltage and Stable Potassium-Ion Batteries

Ether-based electrolyte is beneficial to obtaining good low-temperature performance and high ionic conductivity in potassium ion batteries. However, the dilute ether-based electrolytes usually result in ion-solvent co-intercalation of graphite, poor cycling stability, and hard to withstand high voltage cathodes above 4.0 V. To address the aforementioned issues, an electron-withdrawing group (chloro-substitution) was introduced to regulate the solid-electrolyte interphase (SEI) and enhance the oxidative stability of ether-based electrolytes. The dilute (~0.91 M) chloro-functionalized ether-based electrolyte not only facilitates the formation of homogeneous dual halides-based SEI, but also effectively suppress aluminum corrosion at high voltage. Using this functionalized electrolyte, the K||graphite cell exhibits a stability of 700 cycles, the K||Prussian blue (PB) cell (4.3 V) delivers a stability of 500 cycles, and the PB||graphite full-cell reveals a long stability of 6000 cycles with a high average Coulombic efficiency of 99.98 %. Additionally, the PB||graphite full-cell can operate under a wide temperature range from -5 °C to 45 °C. This work highlights the positive impact of electrolyte functionalization on the electrochemical performance, providing a bright future of ether-based electrolytes application for long-lasting, wide-temperature, and high Coulombic efficiency PIBs and beyond.

Electrolyte Design for High-Voltage Lithium-Metal Batteries with Synthetic Sulfonamide-Based Solvent and Electrochemically Active Additives

Considering practical viability, Li-metal battery electrolytes should be formulated by tuning solvent composition similar to electrolyte systems for Li-ion batteries to enable the facile salt-dissociation, ion-conduction, and introduction of sacrificial additives for building stable electrode-electrolyte interfaces. Although 1,2-dimethoxyethane with a high-donor number enables the implementation of ionic compounds as effective interface modifiers, its ubiquitous usage is limited by its low-oxidation durability and high-volatility. Regulation of the solvation structure and construction of well-structured interfacial layers ensure the potential strength of electrolytes in both Li-metal and LiNi0.8Co0.1Mn0.1O2 (NCM811). This study reports the build-up of multilayer solid-electrolyte interphase by utilizing different electron-accepting tendencies of lithium difluoro(bisoxalato) phosphate (LiDFBP), lithium nitrate, and synthetic 1-((trifluoromethyl)sulfonyl)piperidine. Furthermore, a well-structured cathode-electrolyte interface from LiDFBP effectively addresses the issues with NCM811. The developed electrolyte based on a framework of highly- and weakly-solvating solvents with interface modifiers enables the operation of Li|NCM811 cells with a high areal capacity cathode (4.3 mAh cm-2) at 4.4 V versus Li/Li+.

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.

Air-Stable and Low-Cost High-Voltage Hydrated Eutectic Electrolyte for High-Performance Aqueous Aluminum-Ion Rechargeable Battery with Wide-Temperature Range

Aqueous aluminum-ion batteries (AAIBs) are considered as a promising alternative to lithium-ion batteries due to their large theoretical capacity, high safety, and low cost. However, the uneven deposition, hydrogen evolution reaction (HER), and corrosion during cycling impede the development of AAIBs, especially under a harsh environment. Here, a hydrated eutectic electrolyte (AATH40) composed of Al(OTf)3, acetonitrile (AN), triethyl phosphate (TEP), and H2O was designed to improve the electrochemical performance of AAIBs in a wide temperature range. The combination of molecular dynamics simulations and spectroscopy analysis reveals that AATH40 has a less-water-solvated structure [Al(AN)2(TEP)(OTf)2(H2O)]3+, which effectively inhibits side reactions, decreases the freezing point, and extends the electrochemical window of the electrolyte. Furthermore, the formation of a solid electrolyte interface, which effectively inhibits HER and corrosion, has been demonstrated by X-ray photoelectron spectroscopy, X-ray diffraction tests, and in situ differential electrochemical mass spectrometry. Additionally, operando synchrotron Fourier transform infrared spectroscopy and electrochemical quartz crystal microbalance with dissipation monitoring reveal a three-electron storage mechanism for the Al//polyaniline full cells. Consequently, AAIBs with this electrolyte exhibit improved cycling stability within the temperature range of -10-50 °C. This present study introduces a promising methodology for designing electrolytes suitable for low-cost, safe, and stable AAIBs over a wide temperature range.

Reduction-Tolerance Electrolyte Design for High-Energy Lithium Batteries

Lithium batteries employing Li or silicon (Si) anodes hold promise for the next-generation energy storage systems. However, their cycling behavior encounters rapid capacity degradation due to the vulnerability of solid electrolyte interphases (SEIs). Though anion-derived SEIs mitigate this degradation, the unavoidable reduction of solvents introduces heterogeneity to SEIs, leading to fractures during cycling. Here, we elucidate how the reductive stability of solvents, dominated by the electrophilicity (EPT) and coordination ability (CDA), delineates the SEI formed on Li or Si anodes. Solvents exhibiting lower EPT and CDA demonstrate enhanced tolerance to reduction, resulting in inorganic-rich SEIs with homogeneity. Guided by these criteria, we synthesized three promising solvents tailored for Li or Si anodes. The decomposition of these solvents is dictated by their EPTs under similar solvation structures, imparting distinct characteristics to SEIs and impacting battery performance. The optimized electrolyte, 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in N-Pyrrolidine-trifluoromethanesulfonamide (TFSPY), achieves 600 cycles of Si anodes with a capacity retention of 81 % (1910 mAh g-1). In anode-free Cu||LiNi0.5Co0.2Mn0.3O2 (NCM523) pouch cells, this electrolyte sustains over 100 cycles with an 82 % capacity retention. These findings illustrate that reducing solvent decomposition benefits SEI formation, offering valuable insights for the designing electrolytes in high-energy lithium batteries.

Ether-Based High-Voltage Lithium Metal Batteries: The Road to Commercialization

Ether-based high-voltage lithium metal batteries (HV-LMBs) are drawing growing interest due to their high compatibility with the Li metal anode. However, the commercialization of ether-based HV-LMBs still faces many challenges, including short cycle life, limited safety, and complex failure mechanisms. In this Review, we discuss recent progress achieved in ether-based electrolytes for HV-LMBs and propose a systematic design principle for the electrolyte based on three important parameters: electrochemical performance, safety, and industrial scalability. Finally, we summarize the challenges for the commercial application of ether-based HV-LMBs and suggest a roadmap for future development.

Facilitating Rapid Na+ Storage through MoWSe/C Heterostructure Construction and Synergistic Electrolyte Matching Strategy

The realization of sodium-ion devices with high-power density and long-cycle capability is challenging due to the difficulties of carrier diffusion and electrode fragmentation in transition metal selenide anodes. Herein, a Mo/W-based metal-organic framework is constructed by a one-step method through rational selection, after which MoWSe/C heterostructures with large angles are synthesized by a facile selenization/carbonization strategy. Through physical characterization and theoretical calculations, the synthesized MoWSe/C electrode delivers obvious structural advantages and excellent electrochemical performance in an ethylene glycol dimethyl ether electrolyte. Furthermore, the electrochemical vehicle mechanism of ions in the electrolyte is systematically revealed through comparative analyses. Resultantly, ether-based electrolytes advantageously construct stable solid electrolyte interfaces and avoid electrolyte decomposition. Based on the above benefits, the Na half-cell assembled with MoWSe/C electrodes demonstrated excellent rate capability and a high specific capacity of 347.3 mA h g-1 even after cycling 2000 cycles at 10 A g-1. Meanwhile, the constructed sodium-ion capacitor maintains ∼80% capacity retention after 11,000 ultralong cycles at a high-power density of 3800 W kg-1. The findings can broaden the mechanistic understanding of conversion anodes in different electrolytes and provide a reference for the structural design of anodes with high capacity, fast kinetics, and long-cycle stability.

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.

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.

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.

Recent progress in SEI engineering for boosting Li metal anodes

Lithium metal anodes (LMAs) are ideal anode candidates for achieving next-generation high-energy-density battery systems due to their high theoretical capacity (3680 mA h g-1) and low working potential (-3.04 V versus the standard hydrogen electrode). However, the non-ideal solid electrolyte interface (SEI) derived from electrolyte/electrode interfacial reactions plays a vital role in the lithium deposition/stripping process and battery cycling performance. The composition and morphology of a SEI, which is sensitive to the outside environment, make it difficult to characterize and understand. With the development of characterization techniques, the mechanism, composition, and structure of a SEI can be better understood. In this review, the mechanism formation, the structure model evolution, and the composition of a SEI are briefly presented. Moreover, the development of in situ characterization techniques in recent years is introduced to better understand a SEI followed by the properties of the SEI, which are beneficial to the battery performance. Furthermore, recent optimization strategies of the SEI including the improvement of intrinsic SEIs and construction of artificial SEIs are summarized. Finally, the current challenges and future perspectives of SEI research are summarized.

Weakly Solvating Few-Layer-Carbon Interface toward High Initial Coulombic Efficiency and Cyclability Hard Carbon Anodes

The carbonaceous anodes in sodium ion batteries suffer from low initial Coulombic efficiency (ICE) and poor cyclability due to rampant solid electrolyte interface (SEI) growth. The concept of the weakly solvating electrolyte (WSE) has been popularized for SEI regulation on the anode by adjusting the cation solvation structure. Nevertheless, the effects on the solvation sheath from the electrode/electrolyte interface are ignored in most WSE applications. In this work, we extend the WSE from the bulk electrolyte to the electrolyte/carbon interface. By recycling asphalt wastes into sp2 C enriched few-layer carbon on hard carbon, a weakly solvating interface is fabricated with lower adsorption energy to electrolyte solvent molecules than a pristine anode (-0.89 vs -1.08 eV for Na/diglyme). Accordingly, more anionic groups are attracted into the solvent-weakened solvation sheath during sodiation (2.30 vs 1.96 coordination number for PF6-). The anion-mediated contact ion pairs facilitate a thin, inorganic-rich SEI layer with a homogeneous distribution, which confers a high ICE of 97.9% and a high capacity of 335.6 mA h g-1 at 1 C (89.5% retention, 1000 cycles). The full battery also manifests an energy density of 209 W h kg-1. This interfacial design is applicable in both ether- and ester-based electrolytes, which is promising in cost-effective modification for carbonaceous electrodes.

Partially Ion-Paired Solvation Structure Design for Lithium-Sulfur Batteries under Extreme Operating Conditions

Achieving increased energy density under extreme operating conditions remains a major challenge in rechargeable batteries. Herein, we demonstrate an all-fluorinated ester-based electrolyte comprising partially fluorinated carboxylate and carbonate esters. This electrolyte exhibits temperature-resilient physicochemical properties and moderate ion-paired solvation, leading to a half solvent-separated and half contact-ion pair in a sole electrolyte. As a result, facile desolvation and preferential reduction of anions/fluorinated co-solvents for LiF-dominated interphases are achieved without compromising ionic conductivity (>1 mS cm-1 even at -40 °C). These advantageous features were found to apply to both lithium metal and sulfur-based electrodes even under extreme operating conditions, allowing stable cycling of Li || sulfurized polyacrylonitrile (SPAN) full cells with high SPAN loading (>3.5 mAh cm-2 ) and thin Li anode (50 μm) at -40, 23 and 50 °C. This work offers a promising path for designing temperature-resilient electrolytes to support high energy density Li metal batteries operating in extreme conditions.

Green Ether Electrolytes for Sustainable High-voltage Potassium Ion Batteries

Ether-based electrolytes are promising for secondary batteries due to their good compatibility with alkali metal anodes and high ionic conductivity. However, they suffer from poor oxidative stability and high toxicity, leading to severe electrolyte decomposition at high voltage and biosafety/environmental concerns when electrolyte leakage occurs. Here, we report a green ether solvent through a rational design of carbon-chain regulation to elicit steric hindrance, such a structure significantly reducing the solvent's biotoxicity and tuning the solvation structure of electrolytes. Notably, our solvent design is versatile, and an anion-dominated solvation structure is favored, facilitating a stable interphase formation on both the anode and cathode in potassium-ion batteries. Remarkably, the green ether-based electrolyte demonstrates excellent compatibility with K metal and graphite anode and a 4.2 V high-voltage cathode (200 cycles with average Coulombic efficiency of 99.64 %). This work points to a promising path toward the molecular design of green ether-based electrolytes for practical high-voltage potassium-ion batteries and other rechargeable batteries.

Operando Spatial Pressure Mapping Analysis for Prototype Lithium Metal Pouch Cells Under Practical Conditions

Monitoring and diagnosing the battery status in real-time are of utmost importance for clarifying failure mechanism, improving battery performance, and ensuring safety, particularly under fast charging conditions. Recently, advanced operando techniques have been developed to observe changes in the microstructures of lithium deposits using laboratory-scale cell designs, focusing on understanding the nature of Li metal electrodes. However, the macroscopic spatial inhomogeneity of lithium electroplating/stripping in the prototype pressurized pouch cells has not been measured in real-time under practical conditions. Herein, a new noninvasive operando technique, spatial pressure mapping analysis, is introduced to macroscopically and quantitatively measure spatial pressure changes in a pressurized pouch cell during cycling. Moreover, dynamic spatial changes in the macroscopic morphology of the lithium metal electrode are theoretically visualized by combining operando pressure mapping data with mechanical analyses of cell components. Additionally, under fast charging conditions, the direct correlation between abrupt capacity fading and sudden increases in spatial pressure distribution inhomogeneity is demonstrated through comparative analysis of pouch cells under various external pressures, electrolyte species, and electrolyte weight to cell capacity (e/c) ratios. This operando technique provides insights for assessing the current battery status and understanding the complex origin of cell degradation behavior in pressurized pouch cells.

Electron Delocalization Enables Sulfone-based Single-solvent Electrolyte for Lithium Metal Batteries

Li-metal batteries (LMB), although providing high energy density, face the grand challenge of identifying good electrolyte solvents for cycling. Common solvents are either only stable against lithium metal anode or only stable against LiNix Mny Co1-x-y O2 (NMC) cathode. There is significant effort trying to increase the cathode stability for ether electrolytes, which are in general stable against lithium metal anode. In comparison, there is much less effort trying to increase the anode stability of electrolytes that are stable against NMC cathode. One example is the sulfone-based electrolyte. It has good cathode stability but is hindered from practical application because of (1) high viscosity and poor wetting capability and (2) poor anode stability. Here, we solve these issues by modifying the sulfone molecules using resonance and electron withdrawing effect. The viscosity is significantly reduced by delocalizing the electrons through introducing additional oxygen on the molecular backbone and applying appropriate fluorination. The resulting molecule 2,2,2-trifluoroethyl mesylate (TFEM) has decreased Lewis basicity and less reactivity toward Li+ . The electrolyte based on TFEM as single solvent enables cycling of LMB under harsh conditions of low N/P ratio (21 mg/cm2 NMC811 and 50 μm Li) with 90 % capacity retention after 160 cycles at C/3 discharge rate.

A Radical Pathway and Stabilized Li Anode Enabled by Halide Quaternary Ammonium Electrolyte Additives for Lithium-Sulfur Batteries

Passivation of the sulfur cathode by insulating lithium sulfide restricts the reversibility and sulfur utilization of Li-S batteries. 3D nucleation of Li2 S enabled by radical conversion may significantly boost the redox kinetics. Electrolytes with high donor number (DN) solvents allow for tri-sulfur (S3 ⋅- ) radicals as intermediates, however, the catastrophic reactivity of such solvents with Li anodes pose a great challenge for their practical application. Here, we propose the use of quaternary ammonium salts as electrolyte additives, which can preserve the partial high-DN characteristics that trigger the S3 ⋅- radical pathway, and inhibit the growth of Li dendrites. Li-S batteries with tetrapropylammonium bromide (T3Br) electrolyte additive deliver the outstanding cycling stability (700 cycles at 1 C with a low-capacity decay rate of 0.049 % per cycle), and high capacity under a lean electrolyte of 5 μLelectrolyte  mgsulfur -1 . This work opens a new avenue for the development of electrolyte additives for Li-S batteries.

Fluorinated Carbamate-Based Electrolyte Enables Anion-Dominated Solid Electrolyte Interphase for Highly Reversible Li Metal Anode

Li metal is regarded as the most promising battery anode to boost energy density. However, being faced with the hostile compatibility between the Li anode and traditional carbonate electrolyte, its large-scale industrialization has been in a distressing circumstance due to severe dendrite growth caused by unsatisfying solid electrolyte interphase (SEI). With this regard, accurate control over the composition of the SEI is urgently desired to tackle the electrochemical and mechanical instability at the electrolyte/anode interface. Herein, we report a rationally designed fluorinated carbamate-based electrolyte employing LiNO3 as one of the main salts to induce the preferable anion decomposition to achieve a homogeneous and inorganic (LiF, Li3N, Li2O)-rich SEI. Thus, this electrolyte achieves a high Coulombic efficiency of 99% of the Li metal anode, a stable cycling over 1000 h for Li|Li symmetric cells, more than 100 cycles in 40-μm-thin Li|high-loading-NCM811 full batteries, and >50 cycles in Cu|LiFePO4 pouch cells, which is a promising electrolyte for highly reversible Li metal batteries.

Tuning the Li+ Solvation Structure by a "Bulky Coordinating" Strategy Enables Nonflammable Electrolyte for Ultrahigh Voltage Lithium Metal Batteries

In battery electrolyte design principles, tuning Li⁺ solvation structure is an effective way to connect electrolyte chemistry with interfacial chemistry. Although recent proposed solvation tuning strategies are able to improve battery cyclability, a comprehensive strategy for electrolyte design remains imperative. Here, we report a solvation tuning strategy by utilizing molecular steric effect to create a "bulky coordinating" structure. Based on this strategy, the designed electrolyte generates an inorganic-rich solid electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI), leading to excellent compatibility with both Li metal anodes and high-voltage cathodes. Under an ultrahigh voltage of 4.6 V, Li/NMC811 full-cells (N/P = 2.0) hold an 84.1% capacity retention over 150 cycles and industrial Li/NMC811 pouch cells realize an energy density of 495 Wh kg^-1. This study provides innovative insights into Li⁺ solvation tuning for electrolyte engineering and offers a promising path toward developing high-energy Li metal batteries.

A monofluoride ether-based electrolyte solution for fast-charging and low-temperature non-aqueous lithium metal batteries

The electrochemical stability window of the electrolyte solution limits the energy content of non-aqueous lithium metal batteries. In particular, although electrolytes comprising fluorinated solvents show good oxidation stability against high-voltage positive electrode active materials such as LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811), the ionic conductivity is adversely affected and, thus, the battery cycling performance at high current rates and low temperatures. To address these issues, here we report the design and synthesis of a monofluoride ether as an electrolyte solvent with Li-F and Li-O tridentate coordination chemistries. The monofluoro substituent (-CH₂F) in the solvent molecule, differently from the difluoro (-CHF₂) and trifluoro (-CF₃) counterparts, improves the electrolyte ionic conductivity without narrowing the oxidation stability. Indeed, the electrolyte solution with the monofluoride ether solvent demonstrates good compatibility with positive and negative electrodes in a wide range of temperatures (i.e., from -60 °C to +60 °C) and at high charge/discharge rates (e.g., at 17.5 mA cm^-2). Using this electrolyte solution, we assemble and test a 320 mAh Li||NCM811 multi-layer pouch cell, which delivers a specific energy of 426 Wh kg^-1 (based on the weight of the entire cell) and capacity retention of 80% after 200 cycles at 0.8/8 mA cm^-2 charge/discharge rate and 30 °C.