Electrolytes For Lithium Batteries Research Articles

Concentration controlling of carboxylic ester-based electrolyte for low temperature lithium-ion batteries.

Low temperature has been a major challenge for lithium-ion batteries (LIBs) to maintain satisfied electrochemical performance, and the main reason is the deactivation of electrolyte with the decreasing temperature. To address this point, in present work, we develop a low-temperature resistant electrolyte which includes ethyl acetate (EA) and fluoroethylene carbonate (FEC) as solvent and lithium difluoro(oxalato)borate (LiDFOB) as the primary lithium salt. Due to the preferential decomposition of LiDFOB and FEC, a solid electrolyte interface rich in LiF is formed on the lithium metal anodes (LMAs) and lithium cobalt oxide (LCO) cathodes, contributing to higher stability and rapid desolvation of Li+ ions. The batteries with the optimized electrolyte can undergo cycling tests at -40 °C, with a capacity retention of 83.9 % after 200 cycles. Furthermore, the optimized electrolyte exhibits excellent compatibility with both LCO cathodes and graphite (Gr) anodes, enabling a Gr/LCO battery to maintain a capacity retention of 90.3 % after multiple cycles at -25 °C. This work proposes a cost-effective electrolyte that can activate potential LIBs in practical scenarios, especially in low-temperature environments.

Enhancing lithium-ion battery safety: Investigating the flame-retardant efficacy of bis(2,2,2-trifluoroethyl) carbonate during ethyl methyl carbonate combustion

Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a candidate fire suppressant for lithium-ion batteries (LIBs). The high flammability of the electrolyte is the reason behind the frequent fire incidents reported with LIBs. These incidents are due to various factors, such as a default in the conception of the battery or operational abuse. The flame-retardant effectiveness of BtFEC was investigated by measuring its effect on the oxidation of ethyl methyl carbonate (EMC), a common LIB electrolyte component. Laminar flame speed (LFS) measurements for EMC-BtFEC in air mixtures were carried out at 403 K, 1 atm, for equivalence ratios (ϕ) between 0.8 and 1.4, and with 0.5 % vol. BtFEC. Additional measurements were made at ϕ = 1.1 with BtFEC addition ranging from 0.1 up to 1.4 % vol. To further understand the combustion chemistry of the EMC-BtFEC system, ignition delay times (time at the maximum peak production of the excited radical OH*) and CO time histories were measured in a shock tube with temperatures ranging from 1217 to 1732 K, at near-atmospheric pressure (1.24–1.42 atm), and for three equivalence ratios (ϕ = 0.5, 1.0, and 2.0). These new results constitute an experimental database that was used to evaluate the performance of a model assembled for both BtFEC and EMC using previous work from our group. The updated, detailed chemical kinetics mechanism presented in this study consists of 237 species and 1630 reactions. Sensitivity, rate-of-production, and reaction pathway analyses permitted the oxidation of the BtFEC-EMC system to be described. A flame sensitivity analysis exhibited the significant effect from the reactions H + CF2O ⇆ HF + CFO and CF3 + H ⇆ CF2 + HF, which consume H radicals that are involved in the branching reaction H + O2⇆ OH + O, ultimately reducing the LFS. This study shows that improvements in the base fluorine chemistry are still necessary to obtain better agreement with the experiments, especially at the speciation level.

Maleic Anhydride and (Ethoxy)pentafluorocyclotriphosphazene as Electrolyte Additives for High-Voltage LiCoO2/Si-Graphite Lithium-Ion Batteries.

Anhydride additives including maleic anhydride and succinic anhydride are initially selected as additives in the commercial electrolytes for high-voltage lithium-ion batteries with a Si-based anode. The introduction of (ethoxy)pentafluorocyclotriphosphazene as a flame retardant realizes the nonflammability of electrolytes, and the conductivity of electrolytes exceeds 10 mS cm-1 at 25 °C. Maleic anhydride and (ethoxy)pentafluorocyclotriphosphazene jointly contribute to the exceptional performances of 4.45 V LiCoO2/Si-graphite pouch cells at 25 °C. The capacity retention at 1C of 300 cycles reaches 78%, and the discharge capacity ratio of 6C/1C is approximately 83%. These results suggest that this nonflammable electrolyte has good application prospect. Scanning electron microscopy and X-ray photoelectron spectroscopy measurements are implemented to analyze the interface properties of electrodes.

Construction of Ion-Conducting Channels with Surface-Functionalized Carbon Nanotubes in Gel/Solid Polymer Electrolytes for Lithium-Ion Batteries

Construction of Ion-Conducting Channels with Surface-Functionalized Carbon Nanotubes in Gel/Solid Polymer Electrolytes for Lithium-Ion Batteries

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.

Diagnostic Protocols for Evaluating the Degradation Mechanisms in Gel-Polymer Lithium Batteries.

Gel polymer electrolytes (GPEs) present a promising alternative to standard liquid electrolytes (LE) for Lithium-ion Batteries (LIBs) and Lithium Metal Batteries bridging the advantages of both liquid and solid polymer electrolytes. However, their cycle life still lags behind that of standard LIBs, and their degradation mechanisms remain poorly understood. A significant challenge is the need for specific diagnostic protocols to systematically study the degradation mechanisms of GPE-based cells. Challenges include the separation of cell components and effective washing, as well as the study of the solid electrolyte interfaces, all complicated by the semi-solid nature of GPEs. This paper provides a brief review of existing literature and proposes a comprehensive set of diagnostic tools for dismantling and evaluating the degradation of GPE-based LIBs. Finally, these methods and recommendations are applied to LiNi0.5Mn1.5O4 (LNMO)-graphite cells, revealing electrolyte oxidation as a major source of cell degradation.

Coordination of dissolved transition metals in pristine battery electrolyte solutions determined by NMR and EPR spectroscopy.

The solvation of dissolved transition metal ions in lithium-ion battery electrolytes is not well-characterised experimentally, although it is important for battery degradation mechanisms governed by metal dissolution, deposition, and reactivity in solution. This work identifies the coordinating species in the Mn2+ and Ni2+ solvation spheres in LiPF6/LiTFSI-carbonate electrolyte solutions by examining the electron-nuclear spin interactions, which are probed by pulsed EPR and paramagnetic NMR spectroscopy. These techniques investigate solvation in frozen electrolytes and in the liquid state at ambient temperature, respectively, also probing the bound states and dynamics of the complexes involving the ions. Mn2+ and Ni2+ are shown to primarily coordinate to ethylene carbonate (EC) in the first coordination sphere, while PF6- is found primarily in the second coordination sphere, although a degree of contact ion pairing does appear to occur, particularly in electrolytes with low EC concentrations. NMR results suggest that Mn2+ coordinates more strongly to PF6- than to TFSI-, while the opposite is true for Ni2+. This work provides a framework to experimentally determine the coordination spheres of paramagnetic metals in battery electrolyte solutions.

Design of High-Performance Formyl-Functionalized COF Aerogels as Quasi-Solid Lithium Battery Electrolyte by a Solvent Substitution Strategy.

Covalent organic framework (COF) aerogels with functional groups offer exceptional processability and functionality for various applications. These hierarchical porous materials combine the advantages of COFs with the benefits of aerogels, overcoming the limitations of conventional insoluble and nonfusible COF powders. However, achieving both high crystallinity and shape retention remains a challenge for functionalized COF aerogels. In this work, we develop a novel and general solvent substitution method for the one-step synthesis of formyl-functionalized COF aerogels without harsh vacuum conditions. These aerogels exhibit excellent processing capabilities, superior mechanical strength, and enhanced functionality. As a proof-of-concept, they were used in adsorption and lithium metal battery applications, significantly maximizing the structural advantages of COFs, e.g.: (i) the hierarchical porous structure is fully wetted by the electrolyte to form continuous transport channels; (ii) the polar groups, which are easier to be acquired, help in desolvation and transfer of Li+; (iii) the regular pore structures stabilize deposition of Li+ and inhibit the growth of lithium dendrites. These combined benefits contribute to a lighter battery with improved energy density and enhanced safety.

Fluorinated Linkers Enable High-Voltage Pyrrolidinium-based Dicationic Ionic Liquid Electrolytes.

Novel fluorinated, pyrrolidinium-based dicationic ionic liquids (FDILs) as high-performance electrolytes in energy storage devices have been prepared, displaying unprecedented electrochemical stabilities (up to 7 V); thermal stability (up to 370 °C) and ion transport (up to 1.45 mS cm‑1). FDILs were designed with a fluorinated ether linker and paired with TFSI/FSI counterions. To comprehensively asess the impact of the fluorinated spacer on their electrochemical, thermal, and physico-chemical properties, a comparison with their non-fluorinated counterparts was conducted. With a specific focus on their application as electrolytes in next-generation high-voltage lithium-ion batteries, the impact of the Li-salt on the characteristics of dicationic ILs was systematically evaluated. The incorporation of a fluorinated linker demonstrates significantly superior properties compared to their non-fluorinated counterparts, presenting a promising alternative towards next-generation high-voltage energy storage systems.

Computational simulation-assisted research on chloride solid electrolytes for lithium-ion batteries

Computational simulation-assisted research on chloride solid electrolytes for lithium-ion batteries

Application of Li6.4La3Zr1.45Ta0.5Mo0.05O12/PEO Composite Solid Electrolyte in High-Performance Lithium Batteries.

Replacing the flammable liquid electrolytes with solid ones has been considered to be the most effective way to improve the safety of the lithium batteries. However, the solid electrolytes often suffer from low ionic conductivity and poor rate capability due to their relatively stable molecular/atomic architectures. In this study, we report a composite solid electrolyte, in which polyethylene oxide (PEO) is the matrix and Li6.4La3Zr1.45Ta0.5Mo0.05O12 (LLZTMO) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) are the fillers. Ta/Mo co-doping can further promote the ion transport capacity in the electrolyte. The synthesized composite electrolytes exhibit high thermal stability (up to 413 °C) and good ionic conductivity (LLZTMO-PEO 2.00 × 10-4 S·cm-1, LLZTO-PEO 1.53 × 10-4 S·cm-1) at 35 °C. Compared with a pure PEO electrolyte, whose ionic conductivity is in the range of 10-7~10-6 S·cm-1, the ionic conductivity of composite solid electrolytes is greatly improved. The full cell assembled with LiFePO4 as the positive electrode exhibits excellent rate performance and good cycling stability, indicating that prepared solid electrolytes have great potential applications in lithium batteries.

Local charge redistribution enables single ionic conductor for fast charge solid Li battery

Solid polymer electrolytes (SPEs) have been regarded as hopeful candidate electrolyte for solid-state lithium battery. However, the low Li+ transference number and poor interface stability pose great challenges for the high rate capability of SPE. Herein, inspired from the density functional theory (DFT) calculations that local positive charge distribution can be regulated by introducing strong electron-withdrawing groups, which can selectively anchor TFSI−, largely enhance the Li+ transference number. As predicted, the obtained CPE-NO2 deliver a remarkable Li+ transference number of 0.91, equal to a single-ion conductor for Li+, largely high than that of the SPE (0.31), according well with the molecular dynamics (MD) simulations and pyridine complexation experiments. Furthermore, the PEO||Li interfacial stability, flame retardant ability, and mass transfer of Li+ in interface can also be largely enhanced by interfacial by-product, which are fast Li+ conductors according to TOF-SIMS results. Impressively, the Li|CPE-NO2|Li cell exhibit superior cyclability for 2200 h at 0.1 mA cm−2, and the solid LFP|CPE-NO2|Li battery delivers prominent capacity of 127.4 mAh g−1 at a high rate 5 C (12 mins). This work breaks the fast charge limitation of solid lithium battery, and provides a feasible approach for the construction of advanced solid electrolyte.

Ultraviolet-cured heat-resistant and stretchable gel polymer electrolytes for flexible and safe semi-solid lithium-ion batteries

Lithium-ion (Li-ion) batteries assembled with gel polymer electrolytes (GPEs) are predicted to increase battery energy density while maintaining battery safety. In this work, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is successfully used as a polymer matrix to prepare a new kind of GPE (PHHNT) by ultraviolet (UV) curing technology. The polymer network structure formed by photopolymerization technology significantly enhances the tensile properties of the electrolyte. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) improves the concentration and transport efficiency of lithium ions in the electrolyte as well as the ionic conductivity (1.22 × 10−3 S cm−1) of the GPEs. In addition, the unique tubular structure of the halloysite nanotube (HNT) and the opposite charges carried by the inner and outer surfaces provide additional channels for the lithium salt and facilitate its dissociation. This enhances the expedited movement of Li+ inside the electrolyte, while simultaneously improving the electrochemical and thermal durability of the electrolyte. The assembled LiFePO4 (LFP)/PHHNT/Li battery has an initial discharge-specific capacity of 140.5 mAhg−1 at a current density of 0.5C, showing a high capacity retention rate of 89 % after 120 cycles. The design of this composite material significantly improves the overall performance of the electrolyte and is more suitable for flexible and safe solid-state Li-ion batteries.

An Active Halide Catholyte Boosts the Extra Capacity for All-Solid-State Batteries.

Replacing flammable organic liquid electrolytes with nonflammable solid electrolytes (SEs) in lithium batteries is crucial for enhancing safety across various applications, including portable electronics, electric vehicles, and scalable energy storage. Since typical cathode materials do not possess superionic conductivity, Li-ion conduction in the cathode predominantly relies on incorporating a significant number of SEs as additives to form a composite cathode, which substantially compromises the energy density of solid-state lithium batteries. Here, a halide SE, Li3VCl6 is demonstrated, which not only exhibits a decent Li+ conductivity, but more importantly, delivers a highly reversible capacity of approximately 80 mAh g-1 with an average voltage of 3V versus Li+/Li. The ionic conductivity of Li3VCl6 experiences marginal fluctuations upon electrochemical lithiation/delithiation, as its prototypical solid-solution reaction results solely in a reduction of lithium vacancy. When combined with the traditional LiFePO4 cathode, the active Li3VCl6 catholyte enables an impressive capacity of 217.1 mAh g-1 LFP and about 50% increase in energy density compared with inactive catholytes. Harnessing the integrated mass of the catholyte-which can serve as an active material-presents an opportunity to boost the extra capacity, rendering it feasible in applications.

Solvation Structures and Transport Mechanisms of Cations in Water-in-Bisalt Electrolytes for High-Concentration Lithium-Ion Batteries Revealed by Molecular Dynamics Simulations.

The development of safe and cost-effective electrolytes for rechargeable batteries is currently underway. While water-based electrolytes hold promise, their restricted electrochemical stability window poses a challenge. Combining multiple ionic species emerges as a promising strategy to broaden this stability window and optimize Li-ion battery performance. This study focuses on dual-cation electrolytes, which blend lithium and potassium acetates to enhance the electrochemical characteristics of the solution at high concentrations. We investigated the solvation structure of each ion and its interactions on a molecular level. Our analysis reveals that ion clusters and aggregates are formed through shared acetate and water molecules at high salt concentrations. Furthermore, the residence time analyses of atom pairs indicate that cations diffuse in vehicular mode at low concentrations. In contrast, they switch to a structural mode at high concentrations due to diminishing water content. This study offers a comprehensive model for exploring diverse solvation structures of cations and gaining insights into their diffusion mechanisms within water-in-bisalt electrolytes for aqueous Li-ion batteries.

A Cu/MnOx Composite with Copper-Doping-Induced Oxygen Vacancies as a Cathode for Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries are anticipated to be the next generation of important energy storage devices to replace lithium-ion batteries due to the ongoing use of lithium resources and the safety hazards associated with organic electrolytes in lithium-ion batteries. Manganese-based compounds, including MnOx materials, have prominent places among the many zinc-ion battery cathode materials. Additionally, Cu doping can cause the creation of an oxygen vacancy, which increases the material's internal electric field and enhances cycle stability. MnOx also has great cyclic stability and promotes ion transport. At a current density of 0.2 A g-1, the Cu/MnOx nanocomposite obtained a high specific capacitance of 304.4 mAh g-1. In addition, Cu/MnOx nanocomposites showed A high specific capacity of 198.9 mAh g-1 after 1000 cycles at a current density of 0.5 A g-1. Therefore, Cu/MnOx nanocomposites are expected to be a strong contender for the next generation of zinc-ion battery cathode materials in high energy density storage systems.

Fluorine-Doped Li7La3Zr2O12 Fiber-Based Composite Electrolyte for Solid-State Lithium Batteries with Enhanced Electrochemical Performance.

Garnet-based electrolytes with high ionic conductivity and excellent stability against lithium metal anodes are promising for commercial applications in solid-state lithium batteries (SSLBs). However, the further development of SSLBs is inhibited by issues such as low ionic conductivity and uncontrolled lithium dendrite growth. Herein, we report the synthesis of fluorine-doped Li7La3Zr2O12 (LLZO-F0.2) fibers by electrospinning and the subsequent calcination at high temperatures. The solid composite electrolyte with LLZO-F0.2 exhibits an ionic conductivity of 5.37 × 10-4 S cm-1 and a high lithium-ion transference number of 0.61 at room temperature. Meanwhile, it exhibits lower resistance and more uniform lithium metal stripping and deposition in symmetric cells. The full cell with LiFePO4 cathode exhibits excellent rate capability and cycling stability for 800 cycles at 0.5 C with a discharge specific capacity retention of 97.7%. This fluorine-doped fibrous garnet-type electrolyte provides a viable option for preparing high-performance SSLBs.

Chemical hazard assessment toward safer electrolytes for lithium-ion batteries.

Commercialization of rechargeable lithium-ion (Li-ion) batteries has revolutionized the design of portable electronic devices and is facilitating the current transition to electric vehicles. The technological specifications of Li-ion batteries continue to evolve through the introduction of various high-risk liquid electrolyte chemicals, yet critical evaluation of the physical, environmental, and human health hazards of these substances is lacking. Using the GreenScreen for Safer Chemicals approach, we conducted a chemical hazard assessment (CHA) of 103 electrolyte chemicals categorized into seven chemical groups: salts, carbonates, esters, ethers, sulfoxides-sulfites-sulfones, overcharge protection additives, and flame-retardant additives. To minimize data gaps, we focused on six toxicity and hazard data sources, including three empirical and three nonempirical predictive data sources. Furthermore, we investigated the structural similarities among selected electrolyte chemicals using the ChemMine tool and the simplified molecular input line entry systeminputs from PubChem to evaluate whether chemicals with similar structures exhibit similar toxicity. The results demonstrate that salts, overcharge protection additives, and flame-retardant additives contain the most toxic components in the electrolyte solutions. Furthermore, carbonates, esters, and ethers account for most flammability hazards in Li-ion batteries. This study supports the complementary use of quantitative structure-activity relationship modelsto minimize data gaps and inconsistencies in CHA. Integr Environ Assess Manag 2024;00:1-14. © 2024 The Author(s). Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Insights into the LiMn2O4 Cathode Stability in Aqueous Electrolytes

Insights into the LiMn₂O₄ Cathode Stability in Aqueous Electrolytes

Analysis of polyanion single ion conductor based on preparation of gel electrolyte for lithium ion battery

Abstract This study achieved efficient preparation of polyanionic single ion conductors by selecting appropriate raw materials and controlling preparation conditions. The results show that the window stability of electrolytic gel with a wide ionic electrochemical conductor is 2-4.5 V and 0.74 lithium ion migration. Lithium iron phosphate battery (LFP) is the positive electrode, lithium metal is the negative electrode, and PVDF-HFP Pampsli ion is the electrolyte. When lithium salt is not added, the rated power of the battery is 125 mah·g-1, and the current density is 2 C. The battery has a range of more than 500 times. In the current high-density 5 C situation, it has a specific capacity of 100 mAh·g-1 and a stable cycling ability of over 300 cycles, while maintaining nearly 100% stable Colomb efficiency.