Ionic‐Liquid–Nanoparticle Hybrid Electrolytes: Applications in Lithium Metal Batteries

Development of rechargeable lithium metal battery (LMB) remains a challenge because of uneven lithium deposition during repeated cycles of charge and discharge. Ionic liquids have received intensive scientific interest as electrolytes because of their exceptional thermal and electrochemical stabilities. Ionic liquid and ionic‐liquid–nanoparticle hybrid electrolytes based on 1‐methy‐3‐propylimidazolium (IM) and 1‐methy‐3‐propylpiperidinium (PP) have been synthesized and their ionic conductivity, electrochemical stability, mechanical properties, and ability to promote stable Li electrodeposition investigated. PP‐based electrolytes were found to be more conductive and substantially more efficient in suppressing dendrite formation on cycled lithium anodes; as little as 11 wt % PP‐IL in a PC‐LiTFSI host produces more than a ten‐fold increase in cell lifetime. Both PP‐ and IM‐based nanoparticle hybrid electrolytes provide up to 10 000‐fold improvements in cell lifetime than anticipated based on their mechanical modulus alone. Galvanostatic cycling measurements in Li/Li₄Ti₅O₁₂ half cells using IL–nanoparticle hybrid electrolytes reveal more than 500 cycles of trouble‐free operation and enhanced rate capability.     

Critical challenges and progress of solid garnet electrolytes for all-solid-state batteries

Significant safety problems and poor cyclic stability of conventional lithium-ion batteries, which based on organic liquid electrolytes, hinder their practical application, while all-solid-state batteries (ASSBs) are considered the most promising candidates to replace traditional lithium-ion batteries. As a critical component of ASSBs, solid-state electrolytes play an essential role in ion transport properties and stability. At present, the solid garnet electrolyte is considered as one of the most promising electrolytes because of its excellent performance. However, it still faces many challenges in ionic conductivity, air stability, electrode/electrolyte interface, and lithium dendrites. Therefore, this review is concerned about the up-to-date progress and challenges which will greatly influence the large-scale application of solid garnet electrolytes. Firstly, various ways to improve the ionic conductivity of solid garnet electrolytes are comprehensively summarized. Then, the stability of solid garnet electrolytes in the air is carefully discussed. Secondly, the latest progress in interface engineering between anode/cathode and solid garnet electrolytes treated by different methods is reported. The formation mechanism and influencing factors of lithium dendrites in the solid garnet electrolyte are systematically focused on. Finally, the development and innovation of composite solid garnet electrolytes and 3D garnet electrolytes are summarized in detail. Some important characterization techniques for studying the aforementioned problems are also summarized. Based on the current development of solid garnet electrolytes and solid-state batteries, further challenges and perspectives are presented.     

锂离子电池非水电解质锂盐的研究进展

新型电解质锂盐主要包括含螯合硼阴离子、螯合磷阴离子、全氟膦阴离子、烷基磺酸阴离子、全氟烷基、亚胺基的有机锂盐及有机铝酸锂盐.本文综述了近年来在新型电解质锂盐研究与探索方面的成果,介绍了锂离子电池电解质锂盐的合成方法、组成与结构、化学和电化学性能及其与结构的关系,并阐述今后电解质锂盐研究的可能发展方向及研究方法.     

Conductance behavior of electrolytes in 3-methylsulfolane at 25°C

3-Methylsulfolane is evaluated as an electrolytic solvent utilizing conductance techniques. Conductance data for triisoamylbutylammonium tetraphenylborate and iodide, NaBPh₄, KBPh₄, NaSCN, KSCN, NaI, and KI were analyzed by the Fuoss-Shedlovsky, Fuoss-Onsager, expanded Pitts, and Fuoss-Hsia treatments. Assocation decreases in the order thiocyanates > iodides > tetraphenylborates. These conductance data at 25°C agree with those obtained in previous investigations of 3-methylsulfolane at 30°C and sulfolane.     

Ionic‐Liquid‐Based Polymer Electrolytes for Battery Applications

The advent of solid‐state polymer electrolytes for application in lithium batteries took place more than four decades ago when the ability of polyethylene oxide (PEO) to dissolve suitable lithium salts was demonstrated. Since then, many modifications of this basic system have been proposed and tested, involving the addition of conventional, carbonate‐based electrolytes, low molecular weight polymers, ceramic fillers, and others. This Review focuses on ternary polymer electrolytes, that is, ion‐conducting systems consisting of a polymer incorporating two salts, one bearing the lithium cation and the other introducing additional anions capable of plasticizing the polymer chains. Assessing the state of the research field of solid‐state, ternary polymer electrolytes, while giving background on the whole field of polymer electrolytes, this Review is expected to stimulate new thoughts and ideas on the challenges and opportunities of lithium‐metal batteries.     

硅氧烷基聚合物电解质*

聚合物锂离子电池的核心技术是研制高离子传导率、适宜机械性能以及化学和电化学性能稳定的聚合物电解质材料。在众多寻求高性能聚合物电解质的研究工作中,由于硅氧烷基聚合物电解质具有灵活多样的分子结构设计、易于合成实施、优异的电化学性能和室温电导率等特点,一直是人们关注的热点领域。本文综述了近年来新型硅氧烷基聚合物电解质的设计与合成的研究工作,重点介绍了采用聚硅氧烷嵌段、接枝聚合物通过共混、互穿网络结构、交联网络结构以及无机-有机复合等方法开展的相关聚合物电解质的研究工作。同时也介绍了聚硅氧烷电解质的研究方法和基于聚硅氧烷电解质的应用研究进展。     

Highly Stable Lithium Metal Batteries Enabled by Regulating the Solvation of Lithium Ions in Nonaqueous Electrolytes

Safe and rechargeable lithium metal batteries have been difficult to achieve because of the formation of lithium dendrites. Herein an emerging electrolyte based on a simple solvation strategy is proposed for highly stable lithium metal anodes in both coin and pouch cells. Fluoroethylene carbonate (FEC) and lithium nitrate (LiNO₃) were concurrently introduced into an electrolyte, thus altering the solvation sheath of lithium ions, and forming a uniform solid electrolyte interphase (SEI), with an abundance of LiF and LiN_xO_y on a working lithium metal anode with dendrite‐free lithium deposition. Ultrahigh Coulombic efficiency (99.96 %) and long lifespans (1000 cycles) were achieved when the FEC/LiNO₃ electrolyte was applied in working batteries. The solvation chemistry of electrolyte was further explored by molecular dynamics simulations and first‐principles calculations. This work provides insight into understanding the critical role of the solvation of lithium ions in forming the SEI and delivering an effective route to optimize electrolytes for safe lithium metal batteries.     

Interfacial Evolution of Lithium Dendrites and Their Solid Electrolyte Interphase Shells of Quasi-Solid-State Lithium-Metal Batteries

Unstable electrode/solid-state electrolyte interfaces and internal lithium dendrite penetration hamper the applications of solid-state lithium-metal batteries (SSLMBs), and the underlying mechanisms are not well understood. Herein, in situ optical microscopy provides insights into the lithium plating/stripping processes in a gel polymer electrolyte and reveals its dynamic evolution. Spherical lithium deposits evolve into moss-like and branch-shaped lithium dendrites with increasing current densities. Remarkably, the on-site-formed solid electrolyte interphase (SEI) shell on the lithium dendrite is distinctly captured after lithium stripping. Inducing an on-site-formed SEI shell with an enhanced modulus to wrap the lithium precipitation densely and uniformly can regulate dendrite-free behaviors. An in-depth understanding of lithium dendrite evolution and its functional SEI shell will aid in the optimization of SSLMBs.     

Interfacial Evolution of Lithium Dendrites and Their Solid Electrolyte Interphase Shells of Quasi‐Solid‐State Lithium‐Metal Batteries

Unstable electrode/solid‐state electrolyte interfaces and internal lithium dendrite penetration hamper the applications of solid‐state lithium‐metal batteries (SSLMBs), and the underlying mechanisms are not well understood. Herein, in situ optical microscopy provides insights into the lithium plating/stripping processes in a gel polymer electrolyte and reveals its dynamic evolution. Spherical lithium deposits evolve into moss‐like and branch‐shaped lithium dendrites with increasing current densities. Remarkably, the on‐site‐formed solid electrolyte interphase (SEI) shell on the lithium dendrite is distinctly captured after lithium stripping. Inducing an on‐site‐formed SEI shell with an enhanced modulus to wrap the lithium precipitation densely and uniformly can regulate dendrite‐free behaviors. An in‐depth understanding of lithium dendrite evolution and its functional SEI shell will aid in the optimization of SSLMBs.     

Novel siloxane polymers as polymer electrolytes for high energy density lithium batteries

A variety of disubstituted (double-comb) polysiloxane polymers have been prepared containing linear, branched, and cyclic oligoethyleneoxide units, –(OCH₂CH₂)_n–, in the side chains and as part of the siloxane backbone. Copolymers, using mixtures of linear ethylene oxide side chains, were also synthesized. These polymers were doped with LiN(SO₂CF₃)₂ (LiTFSI, 1) and conductivities of the polymer-salt complexes were determined as a function of temperature and doping level. The maximum conductivity of these polymers at 25 ° C was 2.99 ×10^–4, for a copolymer containing equimolar amounts of side chains with n = 5 and 6.     

Novel zinc ion conducting polymer gel electrolytes based on ionic liquids

We report novel zinc ion conducting polymer gel electrolytes (PGEs) based on non-volatile room temperature ionic liquids. The PGEs consist of an ionic liquid, with a zinc salt dissolved in it, blended with a polymer matrix, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). The resultant electrolyte membranes are freestanding, translucent, flexible and elastic, with excellent mechanical integrity and strength. They possess exceptional thermal stability, exhibit essentially no weight loss under dynamic vacuum or upon heating to 200 °C, and remain the same gel phase in wide temperature ranges, with ionic conductivities on the order of 10⁻³ S/cm at room temperature, 10⁻⁴ S/cm at −20 °C and 4–5 × 10⁻³ S/cm at 80 °C. Electrochemical tests show that zinc ions are mobile in the membranes and zinc metal is capable of dissolution into and deposition from the membranes. The membranes also exhibit wide electrochemical stability windows. The results of this study demonstrate the promise of developing PGEs based on ionic liquids for potential application in next-generation non-aqueous zinc battery systems.     

Gel polymer electrolytes prepared with porous membranes based on an acrylonitrile/methyl methacrylate copolymer

Porous membranes based on acrylonitrile/methyl methacrylate copolymer were prepared by a phase‐inversion method. Microstructures of the porous membranes were controlled through the variation of the evaporation drying time before immersion in a nonsolvent bath. Gel polymer electrolytes were prepared from these porous membranes via soaking in an organic electrolyte solution. They encapsulated the electrolyte solution well without solvent leakage and maintained good mechanical properties that allowed the preparation of thin films (～23 μm). These systems showed acceptable ionic conductivity values (>6.0 × 10^?4 S/cm) at room temperature and sufficient electrochemical stability over 4.4 V that allowed applications in lithium‐ion polymer batteries. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1496–1502, 2002     

Recent advances in solid-state polymer electrolytes and innovative ionic liquids based polymer electrolyte systems

Solid polymer electrolytes are a promising alternative to widely used liquid carbonate electrolytes to deliver next-generation lithium-ion batteries with improved safety. However, the limited ionic conductivity and high interfacial resistance with electrodes limit their widespread use. This review aims to give an overview of the recent research on performance aspects and strategies of solid polymer electrolytes, including ionic conductivity, lithium transference number, design flexibility, scale-up, and integration of ionic liquids with a focus on safety.     

锂离子电池液体电解质与电极相容性的研究进展

随着锂离子电池商业化的不断发展,提高电池在室温及高温下的循环性和安全性已经引起了人们的高度重视.改善电解质与电极的相容性,提高电极表面钝化膜的稳定性是提高电池综合性能的有效途径.本文介绍了在优化电解质组成以及改善电解质与电极的相容性方面的研究进展,讨论了电解质各组分在电极上的作用机理.     

Rational Design of an Ionic Liquid‐Based Electrolyte with High Ionic Conductivity Towards Safe Lithium/Lithium‐Ion Batteries

It is a very urgent and important task to improve the safety and high‐temperature performance of lithium/lithium‐ion batteries (LIBs). Here, a novel ionic liquid, 1‐(2‐ethoxyethyl)‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR_1(2o2)TFSI), was designed and synthesized, and then mixed with dimethyl carbonate (DMC) as appropriate solvent and LiTFSI lithium salt to produce an electrolyte with high ionic conductivity for safe LIBs. Various characterizations and tests show that the highly flexible ether group could markedly reduce the viscosity and provide coordination sites for Li‐ion, and the DMC could reduce the viscosity and effectively enhance the Li‐ion transport rate and transference number. The electrolyte exhibits excellent electrochemical performance in Li/LiFeO₄ cells at room temperature as well as at a high temperature of 60 °C. More importantly, with the addition of DMC, the IL‐based electrolyte remains nonflammable and appropriate DMC can effectively inhibit the growth of lithium dendrites. Our present work may provide an attractive and promising strategy for high performance and safety of both lithium and lithium‐ion batteries.     

Li[B(OCH2CF3)4]: Synthesis,Characterization and Electrochemical Application as a Conducting Salt for LiSB Batteries

A new Li salt with views to success in electrolytes is synthesized in excellent yields from lithium borohydride with excess 2,2,2‐trifluorethanol (HOTfe) in toluene and at least two equivalents of 1,2‐dimethoxyethane (DME). The salt Li[B(OTfe)₄] is obtained in multigram scale without impurities, as long as DME is present during the reaction. It is characterized by heteronuclear magnetic resonance and vibrational spectroscopy (IR and Raman), has high thermal stability (T_{decomposition}>271 °C, DSC) and shows long‐term stability in water. The concentration‐dependent electrical conductivity of Li[B(OTfe)₄] is measured in water, acetone, EC/DMC, EC/DMC/DME, ethyl acetate and THF at RT In DME (0.8 mol L ^?1) it is 3.9 mS cm^?1, which is satisfactory for the use in lithium‐sulfur batteries (LiSB). Cyclic voltammetry confirms the electrochemical stability of Li[B(OTfe)₄] in a potential range of 0 to 4.8 V vs. Li/Li⁺. The performance of Li[B(OTfe)₄] as conducting salt in a 0.2 mol L ^?1 solution in 1:1 wt % DME/DOL is investigated in LiSB test cells. After the 40th cycle, 86 % of the capacity remains, with a coulombic efficiency of around 97 % for each cycle. This indicates a considerable performance improvement for LiSB, if compared to the standard Li[NTf₂]/DOL/DME electrolyte system.