Effect of Clusters on [Li] Solvation and Transport in Mixed Organic Compound/Ionic Liquid Electrolytes under External Electric Fields

Highly efficient recognition of similar objects based on ionic robotic tactile sensors

Tactile sensing provides robots the ability of object recognition, fine operation, natural interaction, etc. However, in the actual scenario, robotic tactile recognition of similar objects still faces difficulties such as low efficiency and accuracy, resulting from a lack of high-performance sensors and intelligent recognition algorithms. In this paper, a flexible sensor combining a pyramidal microstructure with a gradient conformal ionic gel coating was demonstrated, exhibiting excellent signal-to-noise ratio (48 dB), low detection limit (1 Pa), high sensitivity (92.96 kPa-1), fast response time (55 ms), and outstanding stability over 15,000 compression-release cycles. Furthermore, a Pressure-Slip Dual-Branch Convolutional Neural Network (PSNet) architecture was proposed to separately extract hardness and texture features and perform feature fusion. In tactile experiments on different kinds of leaves, a recognition rate of 97.16% was achieved, and surpassed that of human hands recognition (72.5%). These researches showed the great potential in a broad application in bionic robots, intelligent prostheses, and precise human-computer interaction.

In Situ Species Analysis of a Lithium-Ion Battery Electrolyte Containing LiTFSI and Propylene Carbonate

In this study, we analyzed the species in a model electrolyte consisting of a lithium salt, lithium bis(trifluoromethane sulfone)imide (LiTFSI), and a widely used neutral solvent propylene carbonate (PC) with excess infrared (IR) spectroscopy, ab initio molecular dynamics simulations (AIMD), and quantum chemical calculations. Complexing species including the charged ones [Li+(PC)4, TFSI-, TFSI-(PC), TFSI-(PC)2, and Li(TFSI)2-] are identified in the electrolyte. Quantum chemical calculations show strong Li+···O(PC) interaction, which suggests that Li+ would transport in the mode of solvation-carriage. However, the interaction energy of each hydrogen bond in TFSI-(PC) is very weak, suggesting that TFSI- would transport in hopping mode. In addition, the concentration dependences of the relative population of the species were also derived, providing a scenario for the dissolving process of the salt in PC. These in-depth studies provide physical insights into the structural and interactive properties of the electrolyte of lithium-ion batteries.

Phase Separation and Ion Diffusion in Ionic Liquid, Organic Solvent, and Lithium Salt Electrolyte Mixtures

The highly desirable characteristics of ternary mixtures of ionic liquids, organic solvents, and metal salts make them a promising candidate for use in various electrothermal energy storage and conversion systems. In this study, using large-scale classical molecular dynamics simulations, we looked into 10 different ternary electrolyte mixtures using combinations of [EMIM]+, [BMIM]+, and [OMIM]+ cations with [NO3]-, [BF4]-, [PF6]-, [ClO4]-, [TFO]-, and [NTf2]- anions, tetraglyme, and Li salt to study the effect of ionic liquid composition on the phase behavior of ternary electrolyte mixtures. We uncovered that in these electrolytes, phase separation is mainly a function of pairwise binding energy of the constituents of the mixture. To corroborate this theory, several simulations are performed at various temperatures ranging from 260 to 500 K for each mixture, followed by calculating the binding energy of ionic liquid pairs using density functional theory. Our results verify that the transition temperature for the phase separation of each system is indeed a function of the pairwise binding energy of its ionic liquid pairs. It is also found that in some cases, the diffusion coefficient of the Li+ ions decreased even with the increase in the temperature, an effect that is attributed to the presence of condensed ionic domains in the electrolyte. This study provides a new insight for the design of multicomponent electrolyte mixtures for a wide range of energy applications.

Molecular Dynamics Simulation of the Influence of External Electric Fields on the Glass Transition Temperature of the Ionic Liquid 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide

We present the results of molecular dynamics simulations of the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C₂C₁im][NTf₂] in the presence of external electric fields (EEFs) of varying strengths to understand the effects of EEFs on the glass transition temperature T_g. We compute T_g with an automated and objective method and observe a depression in T_g when cooling the IL within an EEF above a critical strength. The effect is reversible, and glasses prepared with EEFs recover their original zero-field T_g when heated. By examining the dynamics and structure of the liquid phase, we find that the EEF lowers the activation energy for diffusion, reducing the energetic barrier for movement and consequently T_g. We show that the effect can be leveraged to drive an electrified nonvapor compression refrigeration cycle.

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.

Insights into Ionic Liquids: From Z-Bonds to Quasi-Liquids

Ionic liquids (ILs) hold great promise in the fields of green chemistry, environmental science, and sustainable technology due to their unique properties, such as a tailorable structure, the various types available, and their environmentally friendly features. On the basis of multiscale simulations and experimental characterizations, two unique features of ILs are as follows: (1) strong coupling interactions between the electrostatic forces and hydrogen bonds, namely in the Z-bond, and (2) the unique semiordered structure and properties of ultrathin films, specifically regarding the quasi-liquid. In accordance with the aforementioned theoretical findings, many cutting-edge applications have been proposed: for example, CO₂ capture and conversion, biomass conversion and utilization, and energy storage materials. Although substantial progress has been made recently in the field of ILs, considerable challenges remain in understanding the nature of and devising applications for ILs, especially in terms of e.g. in situ/real-time observation and highly precise multiscale simulations of the Z-bond and quasi-liquid. In this Perspective, we review recent developments and challenges for the IL research community and provide insights into the nature and function of ILs, which will facilitate future applications.

Continuous Energy Harvesting from Ubiquitous Humidity Gradients using Liquid-Infused Nanofluidics

Humidity-based power generation that converts internal energy of water molecules into electricity is an emerging approach for harvesting clean energy from nature. Here it is proposed that intrinsic gradient within a humidity field near sweating surfaces, such as rivers, soil, or animal skin, is a promising power resource when integrated with liquid-infused nanofluidics. Specifically, capillary-stabilized ionic liquid (IL, Omim⁺ Cl^- ) film is exposed to the above humidity field to create a sustained transmembrane water-content difference, which enables asymmetric ion-diffusion across the nanoconfined fluidics, facilitating long-term electricity generation with the power density of ≈12.11 µW cm^-2 . This high record is attributed to the nanoconfined IL that integrates van der Waals and electrostatic interactions to block movement of Omim⁺ clusters while allowing for directional diffusion of moisture-liberated Cl⁺ . This humidity gradient triggers large ion-diffusion flux for power generation indicates great potential of sweating surfaces considering that most of the earth is covered by water or soil.

Tracking the Micro-Heterogeneity and Hydrogen-Bonding Interactions in Hydroxyl-Functionalized Ionic Liquid Solutions: A Combined Experimental and Computational Study

Ionic liquids (ILs) are an important class of media that are usually used in combination with polar solvents to reduce costs and tune their physicochemical properties. In this regard, it is essential to understand the influence of adding solvents on the properties of ILs. In this work, the micro-heterogeneity and H-bonding interactions between a hydroxyl-functionalized IL, [HOEmim][TFSI], and acetonitrile (ACN) were investigated by attenuated total reflection Fourier transform infrared spectroscopy and molecular simulations. All studied IL-ACN mixtures were found to deviate from the ideal mixtures. The degree of deviations reaches the maximum at about x(ACN)=0.7 with the presence of both homogeneous clusters of pure IL/ACN and heterogeneous clusters of IL-ACN. With the addition of ACN to IL, the mixtures undergo the transformation from "ACN solvated in [HOEmim][TFSI]" to "[HOEmim][TFSI] solvated in ACN". It is found that the newly formed H-bonding interactions between the IL and ACN is the main factor that contributes to the red shifts of O-H, C₂ -H, C_4,5 -H, and C_alkyl -H of [HOEmim]⁺ cation, and the blue shifts of C-D, C≡N of ACN, and C-F, S=O of [TFSI]^- anion. These in-depth studies on the mixtures of hydroxyl-functionalized IL and acetonitrile would help to understand the micro-heterogeneity and H-bonding interactions of miscible solutions and shed light on exploring their applications.

Multicomponent Phase Separation in Ternary Mixture Ionic Liquid Electrolytes

We investigate the phase behavior of ternary mixtures of ionic liquid, organic solvent, and lithium salt by molecular dynamics simulations. We find that at room temperature, the electrolyte separates into distinct phases with specific compositions; an ion-rich domain that contains a fraction of solvent molecules and a second domain of pure solvent. The phase separation is shown to be entropy-driven and is independent of lithium salt concentration. Phase separation is only observed at microsecond time scales and greatly affects the transport properties of the electrolyte.