Electrolytes For Rechargeable Lithium Batteries Research Articles

Opportunities for ionic liquid-based electrolytes in rechargeable lithium batteries

Opportunities for ionic liquid-based electrolytes in rechargeable lithium batteries

40 Years of Low-Temperature Electrolytes for Rechargeable Lithium Batteries.

Rechargeable lithium batteries are one of the most appropriate energy storage systems in our electrified society, as virtually all portable electronic devices and electric vehicles today rely on the chemical energy stored in them. However, sub-zero Celsius operation, especially below -20 °C, remains a huge challenge for lithium batteries and greatly limits their application in extreme environments. Slow Li+ diffusion and charge transfer kinetics have been identified as two main origins of the poor performance of RLBs under low-temperature conditions, both strongly associated with the liquid electrolyte that governs bulk and interfacial ion transport. In this review, we first analyze the low-temperature kinetic behavior and failure mechanism of lithium batteries from an electrolyte standpoint. We next trace the history of low-temperature electrolytes in the past 40 years (1983-2022), followed by a comprehensive summary of the research progress as well as introducing the state-of-the-art characterization and computational methods for revealing their underlying mechanisms. Finally, we provide some perspectives on future research of low-temperature electrolytes with particular emphasis on mechanism analysis and practical application.

Recent Development in Topological Polymer Electrolytes for Rechargeable Lithium Batteries

Solid polymer electrolytes (SPEs) are still being considered as a candidate to replace liquid electrolytes for high-safety and flexible lithium batteries due to their superiorities including light-weight, good flexibility, and shape versatility. However, inefficient ion transportation of linear polymer electrolytes is still the biggest challenge. To improve ion transport capacity, developing novel polymer electrolytes are supposed to be an effective strategy. Nonlinear topological structures such as hyperbranched, star-shaped, comb-like, and brush-like types have highly branched features. Compared with linear polymer electrolytes, topological polymer electrolytes possess more functional groups, lower crystallization, glass transition temperature, and better solubility. Especially, a large number of functional groups are beneficial to dissociation of lithium salt for improving the ion conductivity. Furthermore, topological polymers have strong design ability to meet the requirements of comprehensive performances of SPEs. In this review, the recent development in topological polymer electrolytes is summarized and their design thought is analyzed. Outlooks are also provided for the development of future SPEs. It is expected that this review can raise a strong interest in the structural design of advanced polymer electrolyte, which can give inspirations for future research on novel SPEs and promote the development of next-generation high-safety flexible energy storage devices.

High entropy liquid electrolytes for lithium batteries

High-entropy alloys/compounds have large configurational entropy by introducing multiple components, showing improved functional properties that exceed those of conventional materials. However, how increasing entropy impacts the thermodynamic/kinetic properties in liquids that are ambiguous. Here we show this strategy in liquid electrolytes for rechargeable lithium batteries, demonstrating the substantial impact of raising the entropy of electrolytes by introducing multiple salts. Unlike all liquid electrolytes so far reported, the participation of several anionic groups in this electrolyte induces a larger diversity in solvation structures, unexpectedly decreasing solvation strengths between lithium ions and solvents/anions, facilitating lithium-ion diffusivity and the formation of stable interphase passivation layers. In comparison to the single-salt electrolytes, a low-concentration dimethyl ether electrolyte with four salts shows an enhanced cycling stability and rate capability. These findings, rationalized by the fundamental relationship between entropy-dominated solvation structures and ion transport, bring forward high-entropy electrolytes as a composition-rich and unexplored space for lithium batteries and beyond.

Benchmarking the Safety Performance of Organic Electrolytes for Rechargeable Lithium Batteries: A Thermochemical Perspective

Developing nonflammable organic electrolytes has been regarded as one of the most valuable strategies for tackling the safety issues of rechargeable lithium batteries. However, a quantitative and precise evaluation of electrolyte safety remains challenging mostly because of the inconsistent measurement conditions and the lack of a basic reference system. In this work, we performed a benchmark study on the safety of organic electrolytes by characterizing with cone calorimetry the thermochemistry of various types of single-solvent electrolytes. An intrinsically safe organic electrolyte should show simultaneous low total heat release, low maximum heat release rate, long time to ignition, and short self-extinguishing time. Experimentally, a “cocktail” therapy combining polyfluorinated solvents and high-boiling point solvents is found to be the optimal choice for composing nonflammable electrolytes. Our results help to identify promising electrolyte components and shed light on the reasonable design of high-safety organic electrolytes for advanced rechargeable batteries.

Bis(fluorosulfonyl)imide-based electrolyte for rechargeable lithium batteries: A perspective

The inherent properties of non-aqueous electrolytes are highly associated with the identity of salt anions. To build highly conductive and chemically/electrochemically robust electrolytes for lithium-ion batteries (LIBs) and rechargeable lithium metal batteries (RLMBs), various kinds of weakly coordinating anions have been proposed as counterparts of lithium salts and ionic liquids. Among them, bis(fluorosulfonyl)imide anion ([N(SO2F)2]−, FSI−) has aroused special attention in battery field due to the unique physical, chemical, and electrochemical properties of the FSI-based electrolytes. Herein, an overview on the synthetic methodologies of the FSI-based salts (e.g., alkali metal salts, ionic liquids) is provided, and their applications in LIBs and RLMBs are also updated. Future directions on developing FSI-based and/or FSI-derived electrolytes are presented. The present work is anticipated to inspire the design and screening of new anions for battery use, particularly, those stemming from sulfonimide anions.

Polyethylene Oxide-Based Solid-State Composite Polymer Electrolytes for Rechargeable Lithium Batteries

Solid-state polymer electrolytes are considered to be the most promising electrolytes for next-generation high-energy rechargeable lithium batteries due to the advantages of high safety, good mecha...

A self-healing liquid metal anode with PEO-Based polymer electrolytes for rechargeable lithium batteries

Ga-Sn liquid metal material is demonstrated as a self-healing anode system due to its fluidity via operando synchrotron-based transmission X-ray microscopy and X-ray diffraction experiments. Cracks formed due to volume expansions can be recovered by the fluidity of the liquid metals. By incorporating with a poly(ethylene oxide) (PEO)-based electrolyte at 60 °C, the Ga-Sn anode shows a reversible lithium insertion and extraction process with a high initial discharge specific capacity of 682 mAh g − 1, followed by delivering a capacity of 462 mAh g − 1 in the second cycle at C/20 rate. Compared with its solid counterparts, the Ga-Sn liquid metal anode demonstrates a better capability to maintain its mechanical integrity and better contact with PEO solid electrolytes due to its advantageous features of the liquid. This study suggests a potential strategy to use liquid metal alloys with polymer solid electrolyte to solve the challenges in rechargeable lithium batteries.

Morphosynthesis of 3D Macroporous Garnet Frameworks and Perfusion of Polymer‐Stabilized Lithium Salts for Flexible Solid‐State Hybrid Electrolytes

AbstractSolid‐state lithium‐ion‐conducting membranes are emerging as a promising electrolyte for rechargeable lithium batteries. However, their reliable and scalable preparation still remain challenges, due to low room‐temperature ionic conductivity of solid polymer electrolytes and inherent brittleness of ceramic inorganic electrolytes. Herein, a simple and cost‐effective morphogenetic route is developed for fabricating hierarchically nanostructured 3D garnet‐type Li7La3Zr2O12 monoliths by using degreasing cotton as a template. Nanostructuring of 3D Li+‐conducting frameworks offers interconnected and continuous Li+‐transport pathways in a poly(ethylene oxide)‐based composite electrolyte. The as‐fabricated solid‐state composite electrolyte is flexible and exhibits an enhanced Li‐ion conductivity of 0.89 × 10−4 S cm−1 as well as a large stable electrochemical window up to 5.5 V versus Li/Li+. The symmetric lithium cell using the 3D‐architectured electrolyte shows good cycling stability at different current densities. Furthermore, the LiFePO4 (+) | hybrid electrolyte | Li (−) battery working at 30 °C exhibits outstanding rate capability and cyclability and delivers a high coulombic efficiency of nearly 100% at a current density of 0.2 C (1 C = 170 mA g−1). The present fabrication route is easy and effective and holds promise for scaled‐up production.

Recent Advancements in Polymer-Based Composite Electrolytes for Rechargeable Lithium Batteries

In recent years, lithium batteries using conventional organic liquid electrolytes have been found to possess a series of safety concerns. Because of this, solid polymer electrolytes, benefiting from shape versatility, flexibility, low-weight and low processing costs, are being investigated as promising candidates to replace currently available organic liquid electrolytes in lithium batteries. However, the inferior ion diffusion and poor mechanical performance of these promising solid polymer electrolytes remain a challenge. To resolve these challenges and improve overall comprehensive performance, polymers are being coordinated with other components, including liquid electrolytes, polymers and inorganic fillers, to form polymer-based composite electrolytes. In this review, recent advancements in polymer-based composite electrolytes including polymer/liquid hybrid electrolytes, polymer/polymer coordinating electrolytes and polymer/inorganic composite electrolytes are reviewed; exploring the benefits, synergistic mechanisms, design methods, and developments and outlooks for each individual composite strategy. This review will also provide discussions aimed toward presenting perspectives for the strategic design of polymer-based composite electrolytes as well as building a foundation for the future research and development of high-performance solid polymer electrolytes.

(Invited) Electrochemical Impedance Study of Lithium Cobalt Oxide Thin Film in Some Ionic Liquids

Aprotic ionic liquids have been investigated as the alternative electrolytes for rechargeable lithium batteries because of less inflammability, which is expected to improve safety of the batteries in case of accident. However, the battery performance using ionic liquid electrolytes has been reported to be inferior to that using conventional organic electrolytes since the viscosity of ionic liquids is generally higher than that of the organic electrolytes. The viscosity of electrolytes is considered to affect not only the mobility of lithium ion but also charge transfer at both anode and cathode reaction. Quantitative evaluation of the charge transfer rates of the active materials is often difficult in composite electrodes involving binders and conductive additives. In the present study, the charge transfer resistance of lithium cobalt oxide (LiCoO2) thin film was evaluated by electrochemical impedance measurements in different ionic liquids. LiCoO2 thin film was prepared by RF magnetron sputtering of LiCoO2 target with Ar on a gold substrate and then annealed in the air at 700°C. MPPTFSA, BMPTFSA, MOMMPTFSA, MPPFSA and MOMMPFSA (MPP+ = 1-methyl-1-propylpyrrolidinium, BMP+ = 1-butyl-1-methylpyrrolidinium, MOMMP+ = 1-methoxymethy-1-methylpyrrolidinium, TFSA– = bis(trifluoromethysulfonyl)amide and FSA–= bis(fluorosulfonyl)amide) containing 1 M LiTFSA or LiFSA were used as the electrolytes. 1 M LiTFSA / EC + DEC (1 : 1 vol%, EC = ethylene carbonate, DEC = diethyl carbonate) was also used as the electrolyte as a control. Lithium metal was used as a reference and counter electrode. An air-tight three electrode cell was assembled in a glovebox of dry Ar atmosphere. Electrochemical impedance measurements were conducted using PARTSTAT 2263 or 2273 with the ac amplitude of 5 mV-rms, and the frequency range from 2 Hz to 5 kHz at a constant potential of 4 V. Charge and discharge of the LiCoO2 thin film electrode was confirmed to be possible in the ionic liquid electrolytes by galvanostatic charge-discharge test at ±20 μA cm–2. A slightly distorted semi-circle was observed in the Nyquist plots for the ac impedance measurement of the LiCoO2 thin film electrode in each electrolyte. The charge transfer resistance was calculated by assuming a Randles-type equivalent circuit with an electrolyte resistance, constant phase element and charge transfer resistance. The charge transfer resistance decreased with an decrease in the viscosity of the electrolytes, suggesting the charge transfer process is affected by the dynamics of the electrolytes, as reported for Li+/Li reaction in an organic electrolyte[1]. The activation energy of the charge transfer resistance was larger than that of the viscosity of the electrolytes, implying the charge transfer process is related to not only the dynamics of the electrolytes but also the activation processes at the interface between the active material and the electrolytes. Reference [1] Y. Kato, T. Ishihara, Y. Uchimoto, and M. Wakihara, J. Phys. Chem. B, 108, 4794 (2004).

Unique electrochemical behavior of heterocyclic selenium–sulfur cathode materials in ether-based electrolytes for rechargeable lithium batteries

Mixed chalcogenide systems represent a new class of promising cathode materials for high performance rechargeable lithium batteries. Among them, heterocyclic selenium–sulfur (SexSy) cathodes, coupling the good conductivity of Se and high capacity of S, have attracted great attention in recent years. However, further research is still needed to better understand the lithiation/delithiation process of SexSy cathodes in ether-based electrolytes. Herein, SexSy-based composites with covalent Se–S bonds were prepared by infiltrating various proportions of S and Se powders into the mesoporous carbon microsphere (MCM) host at 500°C in vacuum. As cathodes for rechargeable lithium batteries, SexSy/MCM composites exhibit unique electrochemical behavior rather than a simple hybrid of Li–S and Li–Se batteries in ether-based electrolytes. The Se–S bonds in SexSy/MCM could anchor S during cycling, and effectively reduce the formation of long-chain polysulfides. As a result, the SexSy/MCM cathodes demonstrate superior overall electrochemical performance than Se/MCM or S/MCM. Moreover, Se/S ratio could also affect the electrochemical behavior of SexSy/MCM composites. The optimal Se2S5/MCM cathode delivers the best performance with a high reversible capacity of 796.4mAhg−1 at 0.5C over 100 cycles, and good rate capability of 688.8mAhg−1 at 5C. Especially, a superior coulombic efficiency of ~100% is achieved without addition of LiNO3. This work could help us to better understand the inherent synergistic mechanism behind SexSy cathodes for high performance rechargeable lithium batteries in ether-based electrolytes.

A capsule-type gelled polymer electrolyte for rechargeable lithium batteries

A capsule-type gelled polymer electrolyte (CGPE) was prepared by integrating trilayer PVDF/L-PMMA/PVDF fibrous membrane with CL-PMMA.

Effect of Lithium-Ion Concentration on Morphology and Ion Transport in Single-Ion-Conducting Block Copolymer Electrolytes

Single-ion-conducting polymers are ideal electrolytes for rechargeable lithium batteries as they eliminate salt concentration gradients and concomitant concentration overpotentials during battery cycling. Here we study the ionic conductivity and morphology of poly(ethylene oxide)-b-poly(styrenesulfonyllithium(trifluoromethylsulfonyl)imide) (PEO-b-PSLiTFSI) block copolymers with no added salt using ac impedance spectroscopy and small-angle X-ray scattering. The PEO molecular weight was held fixed at 5.0 kg mol–1, and that of PSLiTFSI was varied from 2.0 to 7.5 kg mol–1. The lithium ion concentration and block copolymer composition are intimately coupled in this system. At low temperatures, copolymers with PSLiTFSI block molecular weights ≤4.0 kg mol–1 exhibited microphase separation with crystalline PEO-rich microphases and lithium ions trapped in the form of ionic clusters in the glassy PSLiTFSI-rich microphases. At temperatures above the melting temperature of the PEO microphase, the lithium ions were released from the clusters, and a homogeneous disordered morphology was obtained. The ionic conductivity increased abruptly by several orders of magnitude at this transition. Block copolymers with PSLiTFSI block molecular weights ≥5.4 kg mol–1 were disordered at all temperatures, and the ionic conductivity was a smooth function of temperature. The transference numbers of these copolymers varied from 0.87 to 0.99. The relationship between ion transport and molecular structure in single-ion-conducting block copolymer electrolytes is qualitatively different from the well-studied case of block copolymers with added salt.

Deposition and Dissolution of Lithium through Lithium Phosphorus Oxynitride Thin Film in Some Ionic Liquids

Aprotic ionic liquids have been studied as alternative electrolytes for rechargeable lithium batteries because of non-volatility, which is expected to improve safety of the batteries. However, most of the organic cations giving room-temperature ionic liquids are instable against metallic lithium. In case of carbonate-based organic electrolytes, a passivation film, so called solid-electrolyte interphase (SEI) film, is known to form as a result of reductive decomposition of organic solvents. The SEI film is considered as a lithium ion conductor, though its nature has not been clarified yet. On the other hand, the reductive decomposition of the organic cations of ionic liquids hardly leads to formation of good SEI film. In the present study, electrochemical deposition and dissolution of lithium were investigated in some aprotic ionic liquids through a typical inorganic lithium ion conductor, lithium phosphorus oxynitraide (LiPON), thin film. Reversible deposition and dissolution of lithium were possible on a nickel electrode covered with LiPON thin film in bis(trifluoromethylsulfonyl)amide (TFSA–) based ionic liquids consisting of 1-butyl-1-methylpyrrolidinium (BMP+) and 1-ethyl-3-methyl imidazolium (EMI+). No cathodic current attributable to reductive decomposition of these cations was observed on the LiPON-coated electrodes, indicating that LiPON thin film acted as an artificial SEI film and that lithium ions were transported between the ionic liquids and LiPON. The deposition of lithium between the nickel electrode and LiPON thin film was confirmed by electrochemical quartz crystal microbalance (EQCM) measurements and X-ray photoelectron spectroscopy.

Plastic crystal–solid biopolymer electrolytes for rechargeable lithium batteries

In this paper, solid polymer electrolytes consisting of chitosan, lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) as a salt and succinonitrile as a plastic crystal are prepared by using the solution casting method. Electrochemical impedance spectroscopy is used to examine the ionic conductivity of the films at the temperature range of 303–383K. Chitosan–LiTFSI containing 50wt% succinonitrile exhibits high ionic conductivity at a room temperature of 0.4×10−3Scm−1, a high lithium ion transference number (0.598) and wide electrochemical window. The solid polymer electrolyte with LiFePO4 as a cathode displays a stable discharge capacity of 160mAhg−1 for up to 50 cycles at a current density of 17mAg−1. The results demonstrate the potential for the solid polymer electrolyte system to be used as an electrolyte in lithium rechargeable batteries.

Effects of SiO2 Nanoparticles and Diethyl Carbonate on the Electrochemical Properties of a Fibrous Nanocomposite Polymer Electrolyte for Rechargeable Lithium Batteries

In this study, a fibrous nanocomposite polymer electrolyte (NCPE) based on poly(vinylidene fluoride-co-hexafluoropropylene) was prepared through a electrospinning technology. Effects of SiO2 nanoparticles and diethyl carbonate (DEC) on the electrochemical properties of the fibrous NCPE are investigated by linear sweep voltammetry, cyclic voltammogram and electrochemical impedance spectroscopy. The electrolyte uptake and ionic conductivity of the fibrous NCPE are enhanced due to incorporation of SiO2 nanoparticles. Addition of DEC into the electrolyte promotes not only the electrochemical stability but also the ionic conductivity of the fibrous NCPE. The fibrous NCPE has a high ionic conductivity up to 3.48 × 10−3 S cm−1 at 25 °C when it (incorporated with 5 wt% SiO2) absorbs the electrolyte of 1 mol l−1 LiBF4/EMIBF4-DEC (2:1 in volume). It exhibits good lithium striping and depositing properties during cycling accompanying with a discounted thermally stable temperature of 148 °C. The Li/LiFePO4 cells using this NCPE membrane as separator exhibit good rate capability and cycling performance, suggesting its promising application in rechargeable lithium batteries.

Effects of synthesis conditions on the structural, stability and ion conducting properties of Li0.30(La0.50Ln0.50)0.567TiO3 (Ln=La, Pr, Nd) solid electrolytes for rechargeable lithium batteries

The structure, thermal stability, morphology and ion conductivity of titanium perovskites with the general formula Li3xLn2/3−xTiO3 (Ln=rare earth element; 3x=0.30) are studied in the context of their possible use as solid electrolyte materials for lithium ion batteries. Materials are prepared by a glycine–nitrate method using different sintering treatments, with a cation-disorder-induced structural transition from tetragonal to cubic symmetry, and are detected as quenching temperature increases. SEM images show that the average grain size increases with increasing sintering temperature and time. Slightly higher bulk conductivity values have been observed for quenched samples sintered at high temperature. Bulk conductivity decreases with the lanthanide ion size. A slight conductivity enhancement, always limited by grain boundaries, is observed for longer sintering times. TDX measurements of the electrolyte/cathode mixtures also show a good stability of the electrolytes in the temperature range of 30–1100°C.

Thermodynamics of Block Copolymers with and without Salt

Ion-containing block copolymers are of interest for applications such as electrolytes in rechargeable lithium batteries. The addition of salt to these materials is necessary to make them conductive; however, even small amounts of salt can have significant effects on the phase behavior of these materials and consequently on their ion-transport and mechanical properties. As a result, the effect of salt addition on block copolymer thermodynamics has been the subject of significant interest over the past decade. This feature article describes a comprehensive study of the thermodynamics of block copolymer/salt mixtures over a wide range of molecular weights, compositions, salt concentrations, and temperatures. The Flory-Huggins interaction parameter was determined by fitting small-angle X-ray scattering data of disordered systems to predictions based on the random phase approximation. Experiments on neat block copolymers revealed that the Flory-Huggins parameter is a strong function of chain length. Experiments on block copolymer/salt mixtures revealed a highly nonlinear dependence of the Flory-Huggins parameter on salt concentration. These findings are a significant departure from previous results and indicate the need for improved theories for describing thermodynamic interactions in neat and salt-containing block copolymers.

Block copolymer electrolytes for rechargeable lithium batteries

ABSTRACTIon‐conducting block copolymers (BCPs) have attracted significant interest as conducting materials in solid‐state lithium batteries. BCP self‐assembly offers promise for designing ordered materials with nanoscale domains. Such nanostructures provide a facile method for introducing sufficient mechanical stability into polymer electrolyte membranes, while maintaining the ionic conductivity at levels similar to corresponding solvent‐free homopolymer electrolytes. This ability to simultaneously control conductivity and mechanical integrity provides opportunities for the fabrication of sturdy, yet easily processable, solid‐state lithium batteries. In this review, we first introduce several fundamental studies of ion conduction in homopolymers for the understanding of ion transport in the conducting domain of BCP systems. Then, we summarize recent experimental studies of BCP electrolytes with respect to the effects of salt‐doping and morphology on ionic conductivity. Finally, we present some remaining challenges for BCP electrolytes and highlight several important areas for future research. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1–16