1,3-Dimethyl-2-imidazolidinone: an ideal electrolyte solvent for high-performance Li–O2 battery with pretreated Li anode

Crown Ether Electrolyte Induced Li2O2 Amorphization for Low Polarization and Long Lifespan Li-O2 Batteries

Lithium-oxygen batteries possess an extremely high theoretical energy density, rendering them a prime candidate for next-generation secondary batteries. However, they still face multiple problems such as huge charge polarization and poor life, which lay a significant gap between laboratory research and commercial applications. In this work, we adopt 15-crown-5 ether (C15) as solvent to regulate the generation of discharge products in lithium-oxygen batteries. The coronal structure endows C15 with strong affinity to Li+, firmly stabilizes the intermediate LiO2 and discharge product Li2O2. Thus, the crystalline Li2O2 is amorphized into easily decomposable amorphous products. The lithium-oxygen batteries assembled with 0.5 M C15 electrolyte show an increased discharge capacity from 4.0 mAh cm-2 to 5.7 mAh cm-2 and a low charge overpotential of 0.88 V during the whole lifespan at 0.05 mA cm-2. The batteries with 1 M C15 electrolyte can cycle stably for 140 cycles. Furthermore, the amorphous characteristic of Li2O2 product is preserved when matched with redox mediators such as LiI, with the charge polarization further decreasing to 0.74 V over a cycle life of 190 cycles. This provides new possibilities for electrolyte design to promote Li2O2 amorphization and reduce charge overpotential in lithium-oxygen batteries.

Enhancing the Stability of Metallic Li Anodes for Aprotic Li-O2 Batteries with Dual-Anion Electrolytes

Despite the impressive specific capacity of Li-O2 batteries, challenges persist, particularly with lithium metal anode (LMA). These include dendritic growth and unstable solid electrolyte interface (SEI) layers, which become more pronounced in an oxygen-rich environment, a typical operation scenario for Li-O2 batteries. Herein, utilizing a hybrid dual anion electrolyte (DAE) strategy, which incorporates both inorganic LiNO3 and organic Li[(FSO2)(C2F5SO2)N] (LiFPFSI) salts, the dendritic growth is evidently inhibited by creating a "concrete-like" SEI structure. Simultaneously, it fosters the development of a fluorine-rich SEI layer. Consequently, a robust, compact, and stable barrier is formed, adeptly suppressing side reactions between LMA and the electrolyte, particularly those relevant to dissolved O2. The practicality and efficiency of this DAE strategy are validated across a variety of battery types including Li/Li, Li/Cu, and notably Li-O2 batteries, which showcased significantly improved reversibility and durability. These results underscore the important role of multifunctional salts in interphase engineering for LMA, which could lead to advancements in Li-O2 batteries.

Lithium ion Speciation in Cyclic Solvents: Impact of Anion Charge Delocalization and Solvent Polarizability

The increasing demand for lithium batteries has triggered the search for safer and more efficient electrolytes. Insights into the atomistic description of electrolytes are critical for relating microscopic and macroscopic (physicochemical) properties. Previous studies have shown that the type of lithium salt and solvent used in the electrolyte influences its performance by dictating the speciation of the ionic components in the system. Here, we investigate the molecular origins of ion association in lithium-based electrolytes as a function of anion charge delocalization and solvent chemical identity. To this end, a family of cyano-based lithium salts in organic solvents, having a cyclic structure and containing carbonyl groups, was investigated using a combination of linear infrared spectroscopy and ab initio computations. Our results show that the formation of contact-ion pairs (CIPs) is more favorable in organic solvents containing either ester or carbonate groups and in lithium salts with an anion having low charge delocalization than in an amide/urea solvent and an anion with large charge delocalization. Ab initio computations attribute the degree of CIP formation to the energetics of the process, which is largely influenced by the chemical nature of the lithium ion solvation shell. At the molecular level, atomic charge analysis reveals that CIP formation is directly related to the ability of the solvent molecule to rearrange its electronic density upon coordination to the lithium ion. Overall, these findings emphasize the importance of local interactions in determining the nature of ion-molecule interactions and provide a molecular framework for explaining lithium ion speciation in the design of new electrolytes.

Revitalization of Diluent Amide-Based Electrolyte for Building High-Voltage Lithium-Metal Batteries

Hitherto, highly concentrated electrolyte is the overarching strategy for revitalizing the usage of amide - in lithium-metal batteries (LMBs), which simultaneously mitigates the reactivity of amide toward Li and regulates uniform Li deposition via forming anion-solvated coordinate structure. However, it is undeniable that this would bring the cost burden for practical electrolyte preparation, which stimulates further electrolyte design toward tailoring anion-abundant Li+ solvation structure in stable amide electrolytes under a low salt content. Herein, a distinct method is conceived to design anions-enriched Li+ solvation structure in dilute amide-electrolyte (1 m Li-salt concentration) with the aid of integrating perfluoropolyethers (PFPE-MC) with anion-solvating ability and B/F-involved additives. The optimized electrolyte based on N,N-Dimethyltrifluoroacetamide (FDMAC) exhibits outstanding compatibility with Li and NCM622 cathode, facilitates uniform Li deposition along with robust solid electrolyte interphase (SEI) formation. Accordingly, both the lab-level LMB coin cell and practical pouch cell based on this dilute FDMAC electrolyte deliver remarkable performances with improved capacity and cyclability. This work pioneers the feasibility of diluted amide as electrolyte in LMB, and provides an innovative strategy for highly stable Li deposition via manipulating solvation structure within diluent electrolyte, impelling the electrolyte engineering development for practical high-energy LMBs.

An artificial interfacial layer with biomimetic ionic channels towards highly stable Li metal anodes

Lithium (Li) metal with low electrochemical potential and high theoretical capacity is a promising anode material for next-generation batteries. However, the low reversibility and safety problems caused by the notorious dendrite growth significantly impede the development of high-energy-density lithium metal batteries (LMBs). Here, to enable a dendrite-free and highly reversible Li metal anode (LMA), we develop a cytomembrane-inspired artificial layer (CAL) with biomimetic ionic channels using a scalable spread coating method. The negatively charged CAL with uniform intraparticle and interparticle ionic channels facilitates the Li-ion transport and redistributes the Li-ion flux, contributing to stable and homogeneous Li stripping and plating. Furthermore, a robust underneath transition layer with abundant lithiophilic inorganic components is in-situ formed through the transformation of CAL during cycling, which promotes Li-ion diffusion and suppresses the continuous side reactions with the electrolyte. Additionally, the resulting cytomembrane-inspired artificial Janus layer (CAJL) displays an ultrahigh Young's modulus (≥10.7 GPa) to inhibit the dendrite growth. Consequently, the CAJL-protected LMA (Li@CAJL) is stably cycled with a high areal capacity of 10 mAh cm^-2 at a high current density of 10 mA cm^-2. More importantly, the effective CAJL modification realizes the stable operation of a practical 429.2 Wh kg^-1 lithium-sulfur (Li-S) pouch cell using a low electrolyte/sulfur (E/S) ratio of 3 μL mg^-1. The facile yet effective protection strategy of LMAs can promote the practical application of LMBs.

Applying Classical, Ab Initio, and Machine-Learning Molecular Dynamics Simulations to the Liquid Electrolyte for Rechargeable Batteries

Rechargeable batteries have become indispensable implements in our daily life and are considered a promising technology to construct sustainable energy systems in the future. The liquid electrolyte is one of the most important parts of a battery and is extremely critical in stabilizing the electrode-electrolyte interfaces and constructing safe and long-life-span batteries. Tremendous efforts have been devoted to developing new electrolyte solvents, salts, additives, and recipes, where molecular dynamics (MD) simulations play an increasingly important role in exploring electrolyte structures, physicochemical properties such as ionic conductivity, and interfacial reaction mechanisms. This review affords an overview of applying MD simulations in the study of liquid electrolytes for rechargeable batteries. First, the fundamentals and recent theoretical progress in three-class MD simulations are summarized, including classical, ab initio, and machine-learning MD simulations (section 2). Next, the application of MD simulations to the exploration of liquid electrolytes, including probing bulk and interfacial structures (section 3), deriving macroscopic properties such as ionic conductivity and dielectric constant of electrolytes (section 4), and revealing the electrode-electrolyte interfacial reaction mechanisms (section 5), are sequentially presented. Finally, a general conclusion and an insightful perspective on current challenges and future directions in applying MD simulations to liquid electrolytes are provided. Machine-learning technologies are highlighted to figure out these challenging issues facing MD simulations and electrolyte research and promote the rational design of advanced electrolytes for next-generation rechargeable batteries.