Lithium Nitrate Regulated Sulfone Electrolytes for Lithium Metal Batteries

The electrolytes in lithium metal batteries have to be compatible with both lithium metal anodes and high voltage cathodes, and can be regulated by manipulating the solvation structure. Herein, to enhance the electrolyte stability, lithium nitrate (LiNO₃) and 1,1,2,2-tetrafuoroethyl-2′,2′,2′-trifuoroethyl(HFE) are introduced into the high-concentration sulfolane electrolyte to suppress Li dendrite growth and achieve a high Coulombic efficiency of >99 % for both the Li anode and LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes. Molecular dynamics simulations show that NO₃⁻ participates in the solvation sheath of lithium ions enabling more bis(trifluoromethanesulfonyl)imide anion (TFSI⁻) to coordinate with Li⁺ ions. Therefore, a robust LiN_xO_y−LiF-rich solid electrolyte interface (SEI) is formed on the Li surface, suppressing Li dendrite growth. The LiNO₃-containing sulfolane electrolyte can also support the highly aggressive LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathode, delivering a discharge capacity of 190.4 mAh g⁻¹ at 0.5 C for 200 cycles with a capacity retention rate of 99.5 %.     

Electrolytes for Rechargeable Lithium–Air Batteries

Lithium–air batteries are promising devices for electrochemical energy storage because of their ultrahigh energy density. However, it is still challenging to achieve practical Li–air batteries because of their severe capacity fading and poor rate capability. Electrolytes are the prime suspects for cell failure. In this Review, we focus on the opportunities and challenges of electrolytes for rechargeable Li–air batteries. A detailed summary of the reaction mechanisms, internal compositions, instability factors, selection criteria, and design ideas of the considered electrolytes is provided to obtain appropriate strategies to meet the battery requirements. In particular, ionic liquid (IL) electrolytes and solid‐state electrolytes show exciting opportunities to control both the high energy density and safety.     

Magnesocene‐Based Electrolytes: A New Class of Electrolytes for Magnesium Batteries

Unlike ferrocene, bis(η⁵‐cyclopentadienyl)magnesium (magnesocene, MgCp₂) is slightly dissociated in solvents, such as ethers, resulting in electrolyte solutions with low conductivity. MgCp₂/tetrahydrofuran solutions make possible reversible magnesium plating and stripping with low over‐potentials for many cycles. The Mg deposits appear with a cauliflower‐like morphology. IR and NMR spectroscopy confirm that the electrolyte is stable and not decomposed during prolonged cycling. The anodic stability limit is in the range of 1.5 V (at platinum) and 1.8 V versus Mg/Mg²⁺ (at stainless steel), which may be sufficient for low‐voltage cathode materials. MgCp₂ is a first example of a completely new class of halide‐free electrolytes, which may open up a new research direction for future magnesium metal and magnesium‐ion batteries.     

Achilles’ Heel of Lithium–Air Batteries: Lithium Carbonate

The lithium–air battery (LAB) is envisaged as an ultimate energy storage device because of its highest theoretical specific energy among all known batteries. However, parasitic reactions bring about vexing issues on the efficiency and longevity of the LAB, among which the formation and decomposition of lithium carbonate Li₂CO₃ is of paramount importance. The discovery of Li₂CO₃ as the main discharge product in carbonate‐based electrolytes once brought researchers to “the end of the idyll“ in the early 2010s. In the past few years, tremendous efforts have been made to understand the formation and decomposition mechanisms of Li₂CO₃, as well as to conceive novel chemical/material strategies to suppress the Li₂CO₃ formation and to facilitate the Li₂CO₃ decomposition. Moreover, the study on Li₂CO₃ in LABs is opening up a new research field in energy technology. Considering the rapid development and innumerous emerging issues, it is timely to recapitulate the current understandings, define the ambiguities and the scientific gaps, and discuss topics of high priority for future research, which is the aim of this Minireview.     

Superhalogens as Building Blocks of Halogen‐Free Electrolytes in Lithium‐Ion Batteries

Most electrolytes currently used in Li‐ion batteries contain halogens, which are toxic. In the search for halogen‐free electrolytes, we studied the electronic structure of the current electrolytes using first‐principles theory. The results showed that all current electrolytes are based on superhalogens, i.e., the vertical electron detachment energies of the moieties that make up the negative ions are larger than those of any halogen atom. Realizing that several superhalogens exist that do not contain a single halogen atom, we studied their potential as effective electrolytes by calculating not only the energy needed to remove a Li⁺ ion but also their affinity towards H₂O. Several halogen‐free electrolytes are identified among which Li(CB₁₁H₁₂) is shown to have the greatest potential.     

锂电池中的凝胶聚合物电解质

锂电池目前在人们生活中已经得到广泛应用,但是传统的液体电解质沸点低且易泄漏,容易引起锂枝晶生长和安全问题。凝胶聚合物电解质(GPEs)的状态介于液态电解质和固态电解质之间,不仅可以作为电解质,还可以作为隔膜,这样可以减少液体电解质的泄漏以及改善固体电解质的界面电阻。本文综述了锂电池中制备不同类型的GPEs的方法,如溶液浇铸法、相转化法、原位聚合法、UV(紫外)固化法和静电纺丝法等,重点总结了不同纤维基的GPEs(聚(偏二氟乙烯)(PVDF)、聚(偏二氟乙烯-共六氟丙烯)(PVDF- HFP)、聚甲基丙烯酸甲酯(PMMA)、聚丙烯腈(PAN)和聚间亚苯基间苯二甲酰胺(PMIA))在锂电池中的运用,并通过对不同基质的改性来改善电解质的离子电导率,阻碍锂枝晶的生长。最后,本文对锂电池中GPEs的未来发展前景进行了展望,讨论和提出的策略将为今后高性能锂电池的实际应用提供更多的途径。     

Solid‐State Electrolyte Anchored with a Carboxylated Azo Compound for All‐Solid‐State Lithium Batteries

Organic electrode materials are promising for green and sustainable lithium‐ion batteries. However, the high solubility of organic materials in the liquid electrolyte results in the shuttle reaction and fast capacity decay. Herein, azo compounds are firstly applied in all‐solid‐state lithium batteries (ASSLB) to suppress the dissolution challenge. Due to the high compatibility of azobenzene (AB) based compounds to Li₃PS₄ (LPS) solid electrolyte, the LPS solid electrolyte is used to prevent the dissolution and shuttle reaction of AB. To maintain the low interface resistance during the large volume change upon cycling, a carboxylate group is added into AB to provide 4‐(phenylazo) benzoic acid lithium salt (PBALS), which could bond with LPS solid electrolyte via the ionic bonding between oxygen in PBALS and lithium ion in LPS. The ionic bonding between the active material and solid electrolyte stabilizes the contact interface and enables the stable cycle life of PBALS in ASSLB.     

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.     

Lithium–Sulfur Batteries: Electrochemistry,Materials, and Prospects

With the increasing demand for efficient and economic energy storage, Li‐S batteries have become attractive candidates for the next‐generation high‐energy rechargeable Li batteries because of their high theoretical energy density and cost effectiveness. Starting from a brief history of Li‐S batteries, this Review introduces the electrochemistry of Li‐S batteries, and discusses issues resulting from the electrochemistry, such as the electroactivity and the polysulfide dissolution. To address these critical issues, recent advances in Li‐S batteries are summarized, including the S cathode, Li anode, electrolyte, and new designs of Li‐S batteries with a metallic Li‐free anode. Constructing S molecules confined in the conductive microporous carbon materials to improve the cyclability of Li‐S batteries serves as a prospective strategy for the industry in the future.     

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.     

Scalable Room‐Temperature Synthesis of Mesoporous Nanocrystalline ZnMn2O4 with Enhanced Lithium Storage Properties for Lithium‐Ion Batteries

In this work, we put forward a facile yet efficient room‐temperature synthetic methodology for the smart fabrication of mesoporous nanocrystalline ZnMn₂O₄ in macro‐quality from the birnessite‐type MnO₂ phase. A plausible reduction/ion exchange/re‐crystallization mechanism is tentatively proposed herein for the scalable synthesis of the spinel phase ZnMn₂O₄. When utilized as a high‐performance anode for advanced Li‐ion battery (LIB) application, the as‐synthesized nanocrystalline ZnMn₂O₄ delivered an excellent discharge capacity of approximately 1288 mAh g^?1 on the first cycle at a current density of 400 mA g^?1, and exhibited an outstanding cycling durability, rate capability, and coulombic efficiency, benefiting from its mesoporous and nanoscale structure, which strongly highlighted its great potential in next‐generation LIBs. Furthermore, the strategy developed here is very simple and of great importance for large‐scale industrial production.     

Methods for Optimizing Properties of Polymer Electrolytes Intended for Lithium Batteries

New plasticized polymer electrolytes, based on chlorinated derivatives of polyvinyl chloride, are studied by infrared and impedance spectroscopy. Morphological and electrochemical properties of the electrolytes depend on the nature of the lithium salt and liquid plasticizer and on the technology. Galvanostatic cycling data for lithium batteries based on Li-LiMn₂O₄ and Li-V₆O₁₃ and these electrolytes are presented.     

Synergistic Dual‐Additive Electrolyte Enables Practical Lithium‐Metal Batteries

A rechargeable Li metal anode coupled with a high‐voltage cathode is a promising approach to high‐energy‐density batteries exceeding 300 Wh kg^?1. Reported here is an advanced dual‐additive electrolyte containing a unique solvation structure and it comprises a tris(pentafluorophenyl)borane additive and LiNO₃ in a carbonate‐based electrolyte. This system generates a robust outer Li₂O solid electrolyte interface and F‐ and B‐containing conformal cathode electrolyte interphase. The resulting stable ion transport kinetics enables excellent cycling of Li/LiNi_0.8Mn_0.1Co_0.1O₂ for 140 cycles with 80 % capacity retention under highly challenging conditions (≈295.1 Wh kg^?1 at cell‐level). The electrolyte also exhibits high cycling stability for a 4.6 V LiCoO₂ (160 cycles with 89.8 % capacity retention) cathode and 4.95 V LiNi_0.5Mn_1.5O₄ cathode.     

锂/聚合物电解质电化学固/固界面的研究

综述了聚合物锂电池中锂/聚合物电解质电化学固/固界面的研究进展。通过与锂/液体电解质体系进行比较,简要介绍了在锂/聚合物电解质界面上发生的电化学反应、锂钝化层形成及其对界面反应的影响,并侧重讨论了传统电化学方法和谱学方法,特别是现场分析技术在电化学固/固界面研究中的应用。总结了锂/聚合物电解质界面的几种不同改善途径。     

An Artificial Lithium Protective Layer that Enables the Use of Acetonitrile‐Based Electrolytes in Lithium Metal Batteries

The resurgence of the lithium metal battery requires innovations in technology, including the use of non‐conventional liquid electrolytes. The inherent electrochemical potential of lithium metal (?3.04 V vs. SHE) inevitably limits its use in many solvents, such as acetonitrile, which could provide electrolytes with increased conductivity. The aim of this work is to produce an artificial passivation layer at the lithium metal/electrolyte interface that is electrochemically stable in acetonitrile‐based electrolytes. To produce such a stable interface, the lithium metal was immersed in fluoroethylene carbonate (FEC) to generate a passivation layer via the spontaneous decomposition of the solvent. With this passivation layer, the chemical stability of lithium metal is shown for the first time in 1 m LiPF₆ in acetonitrile.     

Fluorine and Lithium: Ideal Partners for High‐Performance Rechargeable Battery Electrolytes

Further enhancement in the energy densities of rechargeable lithium batteries calls for novel cell chemistry with advanced electrode materials that are compatible with suitable electrolytes without compromising the overall performance and safety, especially when considering high‐voltage applications. Significant advancements in cell chemistry based on traditional organic carbonate‐based electrolytes may be successfully achieved by introducing fluorine into the salt, solvent/cosolvent, or functional additive structure. The combination of the benefits from different constituents enables optimization of the electrolyte and battery chemistry toward specific, targeted applications. This Review aims to highlight key research activities and technical developments of fluorine‐based materials for aprotic non‐aqueous solvent‐based electrolytes and their components along with the related ongoing scientific challenges and limitations. Ionic liquid‐based electrolytes containing fluorine will not be considered in this Review.     

Solvated Graphene Frameworks as High‐Performance Anodes for Lithium‐Ion Batteries

A solvent‐exchange approach for the preparation of solvated graphene frameworks as high‐performance anode materials for lithium‐ion batteries is reported. The mechanically strong graphene frameworks exhibit unique hierarchical solvated porous networks and can be directly used as electrodes with a significantly improved electrochemical performance compared to unsolvated graphene frameworks, including very high reversible capacities, excellent rate capabilities, and superior cycling stabilities.     

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.