Non-flammable liquid electrolytes for safe batteries

Effect of additives on the high-temperature performance of a sodium bis(oxalato)borate in trimethyl phosphate electrolyte in sodium-ion batteries

Sodium-ion batteries are a promising alternative to lithium-ion batteries due to their potential for lower cost and greater sustainability. However, achieving stable cycling performance, particularly at high mass-loadings and elevated temperatures, remains a challenge. The stable cycling of high mass-loading sodium-ion battery cells is here made possible by addition of prop-1-ene-1,3-sultone (PES) to a non-flammable and fluorine-free electrolyte solution of sodium bis(oxalato)borate (NaBOB) salt in triethyl phosphate (TEP). This study investigates the thermal stability and electrochemical performance of such electrolyte at 40 °C and 55 °C, contrasting their performance with base NaBOB in TEP with and without ethylene sulfate (DTD) additive and with a reference carbonate electrolyte of NaPF6 in ethylene carbonate:diethylene carbonate (EC:DEC). Nuclear Magnetic Resonance spectroscopy was used to reveal degradation products formed in the electrolyte following a 4-weeks storage at 55 °C. Results from galvanostatic cycling at 55 °C demonstrated comparable performance of NaBOB-TEP + PES electrolyte and the reference carbonate electrolyte. The internal cell resistance was initially lower when cells were cycled at 55 °C than at 40 °C for all studied electrolytes.

Modulating ion-dipole interactions in nonflammable phosphonate-based electrolyte for safe and stable sodium-ion pouch cells

Phosphonate-based electrolytes with the merits of low cost and intrinsic nonflammability are promising candidates to realize the safe operation of sodium-ion batteries. However, they generally suffer from poor interfacial chemistry because of the solvent-dominated solvation structure induced by the strong ion-dipole interactions between cations and phosphonate molecules. Herein, we report an electrolyte design strategy that selectively improves the competitive coordination of low-solvating-power molecules, achieving stable interfacial chemistry with a non-flammable, low-cost and fluorine-free electrolyte. By improving the ion-ion interaction between cation and anion, weakly coordinated molecules can enter the Na+ solvation shell, thereby promoting more adjustable and advantageous interfacial chemistry. As a result, the fluorine-free Prussian blue||hard carbon pouch cell, with a high cathode mass loading of ∼20 mg cm-2, reaches a high capacity retention with an energy density of over 221.7 Wh kg-1 based on electrode mass and 115.1 Wh kg-1 based on battery mass.

Boron Surface Treatment of Li7La3Zr2O12 Enabling Solid Composite Electrolytes for Li-Metal Battery Applications

Despite being promoted as a superior Li-ion conductor, lithium lanthanum zirconium oxide (LLZO) still suffers from a number of shortcomings when employed as an active ceramic filler in composite polymer-ceramic solid electrolytes for rechargeable all-solid-state lithium metal batteries. One of the main limitations is the detrimental presence of Li2CO3 on the surface of LLZO particles, restricting Li-ion transport at the polymer-ceramic interfaces. In this work, a facile way to improve this interface is presented, by purposely engineering the LLZO particle surfaces for a better compatibility with a PEO:LiTFSI solid polymer electrolyte matrix. It is shown that a surface treatment based on immersing LLZO particles in a boric acid solution can improve the LLZO surface chemistry, resulting in an enhancement in the ionic conductivity and cation transference number of the CPE with 20 wt % of boron-treated LLZO particles compared to the analogous CPE with non-treated LLZO. Ultimately, an improved cycling performance and stability in Li//LiFePO4 cells was also demonstrated for the modified material.

Designing Nonflammable Liquid Electrolytes for Safe Li-Ion Batteries

Li-ion batteries are essential technologies for electronic products in the daily life. However, serious fire safety concerns that are closely associated with the flammable liquid electrolyte remains a key challenge. Tremendous effort has been devoted to designing nonflammable liquid electrolytes. It is critical to gain comprehensive insights into nonflammability design and inspire more efficient approaches for building safer Li-ion batteries. This review presents current mechanistic understanding of safety issues and discusses state-of-the-art nonflammable liquid electrolytes design for Li-ion batteries based on molecule, solvation, and battery compatibility level. Various safety test methods are discussed for reliable safety risk evaluation. Finally, the challenges and perspectives of the nonflammability design for Li-ion electrolytes are summarized.

Solvate Complex LiAlCl4·SO2: Synthesis and Physical-Chemical Properties

This work describes the synthesis of the LiAlCl4·SO2 solvate complex and its properties. Its composition was determined using thermogravimetric analysis, Raman spectroscopy, and UV-vis spectroscopy. The specific ionic conductivity of LiAlCl4·SO2 is 4.7 × 10-2 S·cm-1. The dynamic viscosity is 19 cP at 25 °C, and the lithium transference number is 0.78. The melting point (+2.5 °C) and decomposition temperature (+60 °C) of LiAlCl4·SO2 were determined by simultaneous thermogravimetric analysis and differential scanning calorimetry. The structure of the solvate complex LiAlCl4·SO2 has been studied using a molecular dynamics method. A lithium cation is coordinated by one atom of Cl of the anion AlCl4- and one oxygen atom of SO2. The coordination number of lithium ions of LiAlCl4·SO2 is 4. The lithium cation is coordinated by three anions of AlCl4- and one molecule of SO2. Anion AlCl4- acts as a bridging ligand and binds different lithium cations.

Correlating Ionic Conductivity to Structure and Dynamics of Li-Ion Battery Electrolyte Systems: Raman Spectroscopy, Dielectric Relaxation Measurements, and Streak Camera Solvation Data Analysis

A correlation between ionic conductivity and electrolyte solution structure and dynamics was explored by performing electrolyte concentration- and temperature-dependent measurements of conductivity, viscosity, and dielectric relaxation (DR) in solutions of lithium bis(trifluoromethane)sulfonimide (LiTFSI) in triethylene glycol dimethyl ether (also known as triglyme, G3). In addition, an electrolyte concentration-dependent Raman spectroscopic study and ultrafast dynamic fluorescence Stokes shift measurements of solvation of a dissolved solute by employing a streak camera detection technique were carried out. Measured conductivities (σ) and the average DR times (⟨τDR⟩) were found to be partially decoupled from the solution viscosities (η) and obeyed the relation, σ or ⟨τDR⟩-1 ∝(η/T)-p, with p = 0.6-0.75 for σ and p = 0.2-0.45 for ⟨τDR⟩-1. Raman data indicated the formation of ion pairs and ionic aggregates in these solutions, while the measured glass transition temperature increased with LiTFSI concentration. Conductivities (σ) showed a nonlinear concentration dependence but increased linearly with the solution static dielectric constants (εs). The latter may be explained by considering the temperature effects on complex electrolyte species and the subsequent solution dielectric behavior. Interestingly, an inverse power-law dependence of σ on the measured DR or solvation time scales, σ ∝ (τx)-m, with m = 1.2-1.9, was observed. This dependence may be explained by considering that the same environmental friction regulates both the ion diffusion and the medium polarization relaxation. The control of a slow process (ion translation) by relatively faster medium dynamics (dipolar rotation), although quite fascinating for the present system, warrants further experimental scrutiny for other electrolyte systems relevant to battery applications.

From Lithium-Ion to Sodium-Ion Batteries for Sustainable Energy Storage: A Comprehensive Review on Recent Research Advancements and Perspectives

A significant turning point in the search for environmentally friendly energy storage options is the switch from lithium-ion to sodium-ion batteries. This review highlights the potential of sodium-ion battery (NIB) technology to address the environmental and financial issues related to lithium-ion systems by thoroughly examining recent developments in NIB technology. It is noted that sodium is more abundant and less expensive than lithium, NIBs have several benefits that could drastically lower the total cost of energy storage systems. In addition, this study examines new findings in important fields including electrolyte compositions, electrode materials, and battery performances of lithium-ion batteries (LIBs) and NIBs. The article highlights advancements in anode and cathode materials, with a focus on improving energy density, cycle stability, and rate capability of both LIBs and NIBs. The review also covers the advances made in comprehending the electrochemical mechanisms and special difficulties associated with NIBs, such as material degradation and sodium ion diffusion. Future research directions are discussed, with an emphasis on enhancing the scalability and commercial viability of sodium-ion technology over lithium on Electric Grid. Considering sustainability objectives and the integration of renewable energy sources, the review's assessment of sodium-ion batteries' possible effects on the future state of energy storage is included in its conclusion.

Nonflammable Ether and Phosphate-Based Liquid Electrolytes for Sodium-Ion Batteries

This study investigates a group of electrolytes containing NaPF6 or NaBF4 salts in phosphate- and ether-based solvents for high-mass loading sodium-ion batteries. It explores physicochemical properties such as ionic conductivity, dynamic viscosities, and nonflammability. The combination of experimental with computational studies reveals detailed insights into the physicochemical properties of the nonflammable liquid electrolytes. Diglyme-based electrolytes become nonflammable with 50 vol % phosphate solvents, while tetraglyme-based electrolytes require 70 vol %. The solvation structure has been investigated using NMR and is combined with computational studies to provide information about properties such as solvation structure, ionic conductivity, and viscosity. The molecular dynamic simulations confirm the enhanced solvation in diglyme-based liquid electrolytes observed experimentally by 23Na-NMR. Despite lacking sufficient electrochemical stability, this work provides a fundamental understanding of the solvation structure and physicochemical properties of a novel electrolyte system. This is an important contribution to be applied in future electrolyte design rationale.

Backscattering silicon spectrometer (BASIS): sixteen years in advanced materials characterization

Quasielastic neutron scattering (QENS) is an experimental technique that can measure parameters of mobility, such as diffusion jump rate and jump length, as well as localized relaxations of chemical species (molecules, ions, and segments) at atomic and nanometer length scales. Due to the high penetrative power of neutrons and their sensitivity to neutron scattering cross-section of chemical species, QENS can effectively probe mobility inside most bulk materials. This review focuses on QENS experiments performed using a neutron backscattering silicon spectrometer (BASIS) to explore the dynamics in various materials and understand their structure-property relationship. BASIS is a time-of-flight near-backscattering inverted geometry spectrometer with very high energy resolution (approximately 0.0035 meV of full width at half maximum), allowing measurements of dynamics on nano to picosecond timescales. The science areas studied with BASIS are diverse, with a focus on soft matter topics, including traditional biological and polymer science experiments, as well as measurements of fluids ranging from simple hydrocarbons and aqueous solutions to relatively complex room-temperature ionic liquids and deep-eutectic solvents, either in the bulk state or confined. Additionally, hydrogen confined in various materials is routinely measured on BASIS. Other topics successfully investigated at BASIS include quantum fluids, spin glasses, and magnetism. BASIS has been in the user program since 2007 at the Spallation Neutron Source of the Oak Ridge National Laboratory, an Office of Science User Facility supported by the U.S. Department of Energy. Over the past sixteen years, BASIS has contributed to various scientific disciplines, exploring the structure and dynamics of many chemical species and their fabrication for practical applications. A comprehensive review of BASIS contributions and capabilities would be an asset to the materials science community, providing insights into employing the neutron backscattering technique for advanced materials characterization.

Solvation Effect: The Cornerstone of High-Performance Battery Design for Commercialization-Driven Sodium Batteries

Sodium batteries (SBs) emerge as a potential candidate for large-scale energy storage and have become a hot topic in the past few decades. In the previous researches on electrolyte, designing electrolytes with the solvation theory has been the most promising direction is to improve the electrochemical performance of batteries through solvation theory. In general, the four essential factors for the commercial application of SBs, which are cost, low temperature performance, fast charge performance and safety. The solvent structure has significant impact on commercial applications. But so far, the solvation design of electrolyte and the practical application of sodium batteries have not been comprehensively summarized. This review first clarifies the process of Na+ solvation and the strategies for adjusting Na+ solvation. It is worth noting that the relationship between solvation theory and interface theory is pointed out. The cost, low temperature, fast charging, and safety issues of solvation are systematically summarized. The importance of the de-solvation step in low temperature and fast charging application is emphasized to help select better electrolytes for specific applications. Finally, new insights and potential solutions for electrolytes solvation related to SBs are proposed to stimulate revolutionary electrolyte chemistry for next generation SBs.

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.

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.

Structure and Properties of Na2S-SiS2-P2S5-NaPO3 Glassy Solid Electrolytes

In the development of sodium all-solid-state batteries (ASSBs), research efforts have focused on synthesizing highly conducting and electrochemically stable solid-state electrolytes. Glassy solid electrolytes (GSEs) have been considered very promising due to their tunable chemistry and resistance to dendrite growth. For these reasons, we focus here on the atomic-level structures and properties of GSEs in the compositional series (0.6-0.08y)Na2S + (0.4 + 0.08y)[(1 - y)[(1 - x)SiS2 + xPS5/2] + yNaPO3] (NaPSiSO). The mechanical moduli, glass transition temperatures, and temperature-dependent conductivity were determined and related to their short-range order structures that were determined using Raman, Fourier transform infrared, and 31P and 29Si magic angle spinning nuclear magnetic resonance spectroscopies. In addition, the conductivity activation energies were modeled using the Christensen-Martin-Anderson-Stuart model. These GSEs appear to be highly crystallization-resistant in the supercooled liquid region where no measurable crystallization below 450 °C could be observed in differential scanning calorimetry studies. Additionally, these GSEs were found to be highly conducting, with conductivities on the order of 10-5 (Ω cm)-1 at room temperature, and processable in the supercooled state without crystallization. For all these reasons, these NaPSiSO GSEs are considered to be highly competitive and easily processable candidate GSEs for enabling sodium ASSBs.

Glycerol Triacetate-Based Flame Retardant High-Temperature Electrolyte for the Lithium-Ion Battery

Rechargeable batteries that can operate at elevated temperatures (>70 °C) with high energy density are long-awaited for industrial applications including mining, grid stabilization, naval, aerospace, and medical devices. However, the safety, cycle life, energy density, and cost of the available high-temperature battery technologies remain an obstacle primarily owing to the limited electrolyte options available. We introduce a flame-retardant electrolyte that can enable stable battery cycling at 100 °C by incorporating triacetin into the electrolyte system. Triacetin has excellent chemical stability with lithium metal, and conventional cathode materials can effectively reduce parasitic reactions and promises a good battery performance at elevated temperatures. Our findings reveal that Li-metal half-cells can be made that have high energy density, high Coulombic efficiency, and good cycle life with triacetin-based electrolytes and three different cathode chemistries. Moreover, the nail penetration test in a commercial-scale pouch battery using this new electrolyte demonstrated suppressed heat generation when the cell was damaged and excellent safety when using the triacetin-based electrolyte.

Unraveling Propylene Oxide Formation in Alkali Metal Batteries

The increasing need for electrochemical energy storage drives the development of post-lithium battery systems. Among the most promising new battery types are sodium-based battery systems. However, like its lithium predecessor, sodium batteries suffer from various issues like parasitic side reactions, which lead to a loss of active sodium inventory, thus reducing the capacity over time. Some problems in sodium batteries arise from an unstable solid electrolyte interphase (SEI) reducing its protective power e. g., due to increased solubility of SEI components in sodium battery systems. While it is known that the electrolyte affects the SEI structure, the exact formation mechanism of the SEI is not yet fully understood. In this study, we follow the initial SEI formation on a piece of sodium metal submerged in propylene carbonate with and without the electrolyte salt sodium perchlorate. We combine X-ray photoelectron spectroscopy, gas chromatography, and density functional theory to unravel the sudden emergence of propylene oxide after adding sodium perchlorate to the electrolyte solvent. We identify the formation of a sodium chloride layer as a crucial step in forming propylene oxide by enabling precursors formed from propylene carbonate on the sodium metal surface to undergo a ring-closing reaction. Based on our combined theoretical and experimental approach, we identify changes in the electrolyte decomposition process, propose a reaction mechanism to form propylene oxide and discuss alternatives based on known synthesis routes.

Confining Ionic Liquids in Developing Quasi-Solid-State Electrolytes for Lithium Metal Batteries

The concept of confining ionic liquids (ILs) in developing quasi-solid-state electrolytes (QSSEs) has been proposed, where ILs are dispersed in polymer networks/backbones and/or filler/host pores, forming the so-called confinement, and great research progress and promising research results have been achieved. In this review, the progress and achievement in developing QSSEs using IL-confinement for lithium metal batteries (LMBs), together with advanced characterizations and simulations, were surveyed, summarized, and analyzed, where the influence of specific parameters, such as IL (type, content, etc.), substrate (type, structure, surface properties, etc.), confinement methods, and so on, was discussed. The confinement concept was further compared with the conventional one in other research areas. It indicates that the IL-confinement in QSSEs improves the performance of electrolytes, for example, increasing the ionic conductivity, widening the electrochemical window, and enhancing the cycle performance of the assembled cells, and being different from those in other areas, that is, the IL-confinement concept in the battery area is in a broad extent. Finally, insights into developing QSSEs in LMBs with the confinement strategy were provided to promote the development and application of QSSE LMBs.

Fluoroborate ionic liquids as sodium battery electrolytes

High-voltage sodium batteries are an appealing solution for economical energy storage applications. Currently available electrolyte materials have seen limited success in such applications therefore the identification of high-performing and safer alternatives is urgently required. Herein we synthesise six novel ionic liquids derived from two fluoroborate anions which have shown great promise in recent battery literature. This study reports for the first time the electrochemically applicable room-temperature ionic liquid (RTIL) N-ethyl-N,N,N-tris(2-(2-methoxyethoxy)ethyl)ammonium (tetrakis)hexafluoroisopropoxy borate ([N2(2O2O1)3][B(hfip)4]). The RTIL shows promising physical properties with a very low glass-transition at -73 °C and low viscosity. The RTIL exhibits an electrochemical window of 5.3 V on a glassy carbon substrate which enables high stability electrochemical cycling of sodium in a 3-electrode system. Of particular note is the strong passivation behaviour of [N2(2O2O1)3][B(hfip)4] on aluminium current-collector foil at potentials as high as 7 V (vs. Na+/Na) which is further improved with the addition of 50 mol% Na[FSI]. This study shows [B(hfip)4]- ionic liquids have the desired physical and electrochemical properties for high-voltage sodium electrolytes.

Pathways to Next-Generation Fire-Safe Alkali-Ion Batteries

High energy and power density alkali-ion (i.e., Li+ , Na+ , and K+ ) batteries (AIBs), especially lithium-ion batteries (LIBs), are being ubiquitously used for both large- and small-scale energy storage, and powering electric vehicles and electronics. However, the increasing LIB-triggered fires due to thermal runaways have continued to cause significant injuries and casualties as well as enormous economic losses. For this reason, to date, great efforts have been made to create reliable fire-safe AIBs through advanced materials design, thermal management, and fire safety characterization. In this review, the recent progress is highlighted in the battery design for better thermal stability and electrochemical performance, and state-of-the-art fire safety evaluation methods. The key challenges are also presented associated with the existing materials design, thermal management, and fire safety evaluation of AIBs. Future research opportunities are also proposed for the creation of next-generation fire-safe batteries to ensure their reliability in practical applications.

Ultra-Thin Lithium Silicide Interlayer for Solid-State Lithium-Metal Batteries

All-solid-state batteries with metallic lithium (Li_BCC ) anode and solid electrolyte (SE) are under active development. However, an unstable SE/Li_BCC interface due to electrochemical and mechanical instabilities hinders their operation. Herein, an ultra-thin nanoporous mixed ionic and electronic conductor (MIEC) interlayer (≈3.25 µm), which regulates Li_BCC deposition and stripping, serving as a 3D scaffold for Li⁰ ad-atom formation, Li_BCC nucleation, and long-range transport of ions and electrons at SE/Li_BCC interface is demonstrated. Consisting of lithium silicide and carbon nanotubes, the MIEC interlayer is thermodynamically stable against Li_BCC and highly lithiophilic. Moreover, its nanopores (<100 nm) confine the deposited Li_BCC to the size regime where Li_BCC exhibits "smaller is much softer" size-dependent plasticity governed by diffusive deformation mechanisms. The Li_BCC thus remains soft enough not to mechanically penetrate SE in contact. Upon further plating, Li_BCC grows in between the current collector and the MIEC interlayer, not directly contacting the SE. As a result, a full-cell having Li_3.75 Si-CNT/Li_BCC foil as an anode and LiNi_0.8 Co_0.1 Mn_0.1 O₂ as a cathode displays a high specific capacity of 207.8 mAh g^-1 , 92.0% initial Coulombic efficiency, 88.9% capacity retention after 200 cycles (Coulombic efficiency reaches 99.9% after tens of cycles), and excellent rate capability (76% at 5 C).

A self-healing polymerized-ionic-liquid-based polymer electrolyte enables a long lifespan and dendrite-free solid-state Li metal batteries at room temperature

The implementation of high-safety Li metal batteries (LMBs) needs more stable and safer electrolytes. The solid-state electrolytes (SSEs) with their advantageous properties stand out for this purpose. However, low Li/electrolyte interfacial instability and uncontrolled Li dendrites growth trigger unceasing breakage of the solid electrolyte interphase (SEI), leading to fast capacity degradation. In response to these shortcomings, a new type of polymer electrolyte with self-healing capacity is introduced by grafting ionic liquid chain units into the backbones of polymers, which inherits the chemical inertness against the Li anode, allowing high Li⁺ transport, wide electrochemical window, and self-healing traits. Benefiting from the strong external H-bonding interactions, the obtained polymer electrolyte can spontaneously reconstruct dendrite-induced defects and fatigue crack growth at the Li/electrolyte interface, and, in turn, help tailor Li deposition. Owing to the resilient Li/electrolyte interface and dendrite-free Li plating, the equipped Li|LFP batteries display a high initial specific capacity of 134.7 mA h g^-1, rendering a capacity retention of 91.2% after 206 cycles at room temperature. The new polymer electrolyte will undoubtedly bring inspiration for developing practical LMBs with highly improved safety and interfacial stability.

Advanced Nonflammable Organic Electrolyte Promises Safer Li-Metal Batteries: From Solvation Structure Perspectives

Batteries with a Li-metal anode have recently attracted extensive attention from the battery communities owing to their high energy density. However, severe dendrite growth hinders their practical applications. More seriously, when Li dendrites pierce the separators and trigger short circuit in a highly flammable organic electrolyte, the results would be catastrophic. Although the issues of growth of Li dendrites have been almost addressed by various methods, the highly flammable nature of conventional organic liquid electrolytes is still a lingering fear facing high-energy-density Li-metal batteries given the possibility of thermal runaway of the high-voltage cathode. Recently, various kinds of nonflammable liquid- or solid-state electrolytes have shown great potential toward safer Li-metal batteries with minimal detrimental effect on the battery performance or even enhanced electrochemical performance. In this review, recent advances in developing nonflammable electrolyte for high-energy-density Li-metal batteries including high-concentration electrolyte, localized high-concentration electrolyte, fluorinated electrolyte, ionic liquid electrolyte, and polymer electrolyte are summarized. Then, the solvation structure of different kinds of nonflammable liquid and polymer electrolytes are analyzed to provide insight into the mechanism for dendrite suppression and fire extinguishing. Finally, guidelines for future design of nonflammable electrolyte for safer Li-metal batteries are provided.

Effects of Difluoro(oxalato)borate-Based Ionic Liquid as Electrolyte Additive for Li-Ion Batteries

In this work, the use of N-methyl-N-propylpiperidinium difluoro(oxalato)borate Pip₁₃DFOB ionic liquid (IL), originally synthesized in our laboratory, as an additive for liquid electrolytes in lithium-ion batteries (LIBs), is proposed. The synthesized IL exhibits glass and melting transitions at -70.9 °C and 17.1 °C, respectively, and a thermal decomposition temperature over 230 °C. A mixture based on 1.0 M LiPF₆ in 1:1 v/v ethylene carbonate (EC): dimethyl carbonate (DMC) electrolyte solution (so called LP30) and the IL was prepared and tested in lithium metal cells versus two different commercially available carbonaceous electrodes, i.e., graphite (KS6) and graphene (GnP), and versus a high voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathode. A noticeable improvement was observed for Li|LNMO cells with an IL-added electrolyte, which exhibited a high specific capacity above 120 mAh g^-1 with a Coulombic efficiency above 93% throughout 200 cycles, while the efficiency fell below 80% after 80 cycles with the absence of IL. The results confirm that the IL is promising additive for the electrolyte, especially for a longer cycle life of high-voltage cells.

Synthesis and Behavior of Hexamethylenetetramine-Based Ionic Liquids as an Active Ingredient in Latent Curing Formulations with Ethylene Glycol for DGEBA

The paper presents the preparation of new ionic liquids based on hexamethylenetetramine with bis(trifluoromethanesulfonyl)imide and dicyanamide anion, which were characterized in detail in terms of their purity (Ion Chromatography) and thermal properties (Differential Scanning Calorimetry), as well as stability. The obtained substances were used to develop curing systems with ethylene glycol, which were successfully tested for their application with bisphenol A diglycidyl ether molecule. In addition, the curing process and its relationship to the structure of the ionic liquid are characterized in detail. The research showed that hexamethylenetetramine-based new ionic liquids can be successfully designed using well-known and simple synthetic methods-the Delepine reaction. Moreover, attention was paid to their stability, related limitations, and the application of hexamethylenetetramine-based ionic liquids in epoxy-curing systems.

Critical Review on cathode-electrolyte Interphase Toward High-Voltage Cathodes for Li-Ion Batteries

The thermal stability window of current commercial carbonate-based electrolytes is no longer sufficient to meet the ever-increasing cathode working voltage requirements of high energy density lithium-ion batteries. It is crucial to construct a robust cathode-electrolyte interphase (CEI) for high-voltage cathode electrodes to separate the electrolytes from the active cathode materials and thereby suppress the side reactions. Herein, this review presents a brief historic evolution of the mechanism of CEI formation and compositions, the state-of-art characterizations and modeling associated with CEI, and how to construct robust CEI from a practical electrolyte design perspective. The focus on electrolyte design is categorized into three parts: CEI-forming additives, anti-oxidation solvents, and lithium salts. Moreover, practical considerations for electrolyte design applications are proposed. This review will shed light on the future electrolyte design which enables aggressive high-voltage cathodes.

High-Energy Batteries: Beyond Lithium-Ion and Their Long Road to Commercialisation

Rechargeable batteries of high energy density and overall performance are becoming a critically important technology in the rapidly changing society of the twenty-first century. While lithium-ion batteries have so far been the dominant choice, numerous emerging applications call for higher capacity, better safety and lower costs while maintaining sufficient cyclability. The design space for potentially better alternatives is extremely large, with numerous new chemistries and architectures being simultaneously explored. These include other insertion ions (e.g. sodium and numerous multivalent ions), conversion electrode materials (e.g. silicon, metallic anodes, halides and chalcogens) and aqueous and solid electrolytes. However, each of these potential "beyond lithium-ion" alternatives faces numerous challenges that often lead to very poor cyclability, especially at the commercial cell level, while lithium-ion batteries continue to improve in performance and decrease in cost. This review examines fundamental principles to rationalise these numerous developments, and in each case, a brief overview is given on the advantages, advances, remaining challenges preventing cell-level implementation and the state-of-the-art of the solutions to these challenges. Finally, research and development results obtained in academia are compared to emerging commercial examples, as a commentary on the current and near-future viability of these "beyond lithium-ion" alternatives.

Do eco-friendly binders affect the electrochemical performance of MOF@CNT anodes in lithium-ion batteries?

We substituted an organic-based binder with a natural water-soluble binder (CMC) in the anode of a lithium-ion battery.

Electrolyte Engineering for High-Voltage Lithium Metal Batteries

High-voltage lithium metal batteries (HVLMBs) have been arguably regarded as the most prospective solution to ultrahigh-density energy storage devices beyond the reach of current technologies. Electrolyte, the only component inside the HVLMBs in contact with both aggressive cathode and Li anode, is expected to maintain stable electrode/electrolyte interfaces (EEIs) and facilitate reversible Li⁺ transference. Unfortunately, traditional electrolytes with narrow electrochemical windows fail to compromise the catalysis of high-voltage cathodes and infamous reactivity of the Li metal anode, which serves as a major contributor to detrimental electrochemical performance fading and thus impedes their practical applications. Developing stable electrolytes is vital for the further development of HVLMBs. However, optimization principles, design strategies, and future perspectives for the electrolytes of the HVLMBs have not been summarized in detail. This review first gives a systematical overview of recent progress in the improvement of traditional electrolytes and the design of novel electrolytes for the HVLMBs. Different strategies of conventional electrolyte modification, including high concentration electrolytes and CEI and SEI formation with additives, are covered. Novel electrolytes including fluorinated, ionic-liquid, sulfone, nitrile, and solid-state electrolytes are also outlined. In addition, theoretical studies and advanced characterization methods based on the electrolytes of the HVLMBs are probed to study the internal mechanism for ultrahigh stability at an extreme potential. It also foresees future research directions and perspectives for further development of electrolytes in the HVLMBs.