We present a method to derive implicit solvent models of electrolyte solutions from all-atom descriptions; providing analytical expressions of the thermodynamic and structural properties of the ions consistent with the underlying explicit solvent representation. Effective potentials between ions in solution are calculated to perform perturbation theory calculations, in order to derive the best possible description in terms of charged hard spheres. Applying this method to NaCl solutions yields excellent agreement with the all-atom model, provided ion association is taken into account.
Tasker type III polar terminations of ionic crystals carry a net surface charge as well as a dipole moment and are fundamentally unstable. In contact with electrolytes, such polar surfaces can be stabilized by adsorption of counter ions from solution to form electric double layers (EDLs). In a previous work (J. Chem. Phys 147, 104702 (2017)) we reported on a classical force field based molecular dynamics study of a prototype model system namely a NaCl(111) slab interfaced with an aqueous NaCl solution on both sides. A serious hurdle in the simulation is that the finite width of the slab admits…
The nature of variations of ultrasonic wave velocity(v) and attenuation constant(α) with the concentration(c) in aqueous solutions of NaCl, KCl and CsCl are investigated at room temperature(250C) at 1MHz and 2 MHz wave frequency. Fourier Spectrum Pulse-Echo (FSPE) technique is used to achieve better accuracy in measurement, particularly for α measurement. In NaCl and KCl abrupt changes in the values of v and α are noticed at particular solution concentrations whereas, for CsCl almost smooth variation in v is observed over the whole concentration range for both of the frequencies 1 and 2 MHz . …
Studying the freezing of saltwater on a molecular level is of fundamental importance for improving freeze desalination techniques. Here, we investigate the freezing process of NaCl solutions using a combination of x-ray diffraction and molecular dynamics simulations (MD) for different salt-water concentrations, ranging from seawater conditions to saturation. A linear superposition model reproduces well the brine rejection due to hexagonal ice Ih formation and allows us to quantify the fraction of ice and brine. Furthermore, upon cooling at T = 233 K we observe the formation of NaCl$\cdot$2H$_2…
Austenitic Fe-30Mn-1C (FeMnC) is a prospective biodegradable implant material combining high mechanical integrity with adequate corrosion rates. The fast solidified TWIP alloy, its constituents and 316L stainless steel were electrochemically analysed in various electrolytes at 37 °C under laminar flow. Potentiodynamic polarization tests were conducted in Trisbuffered simulated body fluid (SBF), in Tris-buffered saline (TBS) and in 150 mM - 0.15 mM NaCl solutions (pH 7.6, 10, 5, 2) to study initial corrosion stages. Active dissolution of FeMnC is revealed in all electrolytes and is discussed on…
In this work, we examine metal electrode-ionomer electrolyte systems at high voltage / negative surface charge and at high pH to assess factors that influence hydrogen production efficiency. We simulate the hydrogen evolution electrode interface investigated experimentally in Bates et al., Journal of Physical Chemistry C, 2015 using a combination of first principles calculations and classical molecular dynamics. With this detailed molecular information, we explore the hypotheses posed in Bates et al. In particular we examine the response of the system to increased bias voltage and oxide covera…
MultiDK: A Multiple Descriptor Multiple Kernel Approach for Molecular Discovery and Its Application to The Discovery of Organic Flow Battery Electrolytes
我们提出了一个多描述符多内核（MultiDK）的方法，有效的分子发现使用机器学习。我们表明，MultiDK方法提高了分子性质预测的速度和准确性。我们将该方法应用于发现用于水性氧化还原液流电池的电解质分子。使用\emph{multiple-type - as opposed to single-type - descriptors}，可以获得用于机器学习的更多相关特征。遵循“群众智慧”的原则，多类型描述符的组合显著提高了预测性能。此外，MultiDK可以利用分子结构和性能关系之间的不规则性比线性回归方法更好地采用多个内核-一组输入描述符的一个以上的核函数。多个核分别由一组二进制描述符和一组非二进制描述符的Tanimoto相似性函数和线性核组成。使用MultiDK，我们实现了$r^2 = 0.92$的平均性能与一组分子的溶解度预测。我们还扩展了MultiDK来预测pH依赖的溶解度，并将其应用于具有可电离官能团的醌分子的溶解度估计，作为液流电池电解质的强有力的候选者。
Study of Interfacial Tension between an Organic Solvent and Aqueous Electrolyte Solutions Using Electrostatic Dissipative Particle Dynamics Simulations
The Association of Zn$^{2+}$-SO$_4^{2-}$ and Mg$^{2+}$-SO$_4^{2-}$ in Aqueous MgSO$_4$/ZnSO$_4$ Hybrid Electrolytes: Insights from All-Atom Molecular Dynamics Simulations Molecular Dynamics Simulations
A precise understanding of solvation is essential for rational search and design of electrolytes that can meet performance demands in Li-ion and beyond Li-ion batteries. In the context of Li-O$_2$ batteries, ion pairing is decisive in determining battery capacity via the solution mediated discharge mechanism without compromising heavily on electrolyte stability. We argue that models based on coordination numbers of the counterion in the first solvation shell are inadequate at describing the extent of ion pairing, especially at higher salt concentrations, and are often not consistent with exper…
Terahertz-induced local-field dynamics and transient birefringence in aqueous electrolytes
University of Paderborn（帕德博恩大学）；Center for Advanced Systems Understanding (CASUS)（先进系统理解中心）；Helmholtz-Zentrum Dresden-Rossendorf（德累斯顿-罗斯多夫亥姆霍兹中心）；Technische Universität Dresden（德累斯顿工业大学）
Li+ transport within a solid electrolyte interphase (SEI) in lithium ion batteries has challenged molecular dynamics (MD) studies due to limited compositional control of that layer. In recent years, experiments and ab initio simulations have identified dilithium ethylene dicarbonate (Li2EDC) as the dominant component of SEI layers. Here, we adopt a parameterized, non-polarizable MD force field for Li2EDC to study transport characteristics of Li+ in this model SEI layer at moderate temperatures. The observed correlations are consistent with recent MD results using a polarizable force field, sug…
In this work, we report the results from molecular dynamics simulations of lithium salt-ionic liquid electrolytes (ILEs) based either on the symmetric bis[(trifluoromethyl)sulfonyl]imide ($\text{TFSI}^-$) anion or its asymmetric analog 2,2,2-(trifluoromethyl)sulfonyl-N-cyanoamide ($\text{TFSAM}^-$). Relating lithium's coordination environment to anion mean residence times and diffusion constants confirms the remarkable transport behaviour of the $\text{TFSAM}^-$-based ILEs that has been observed in recent experiments: For increased salt doping, the lithium ions must compete for the more attrac…
Lithium chloride LiCl is widely used as a prototype system to study the strongly dissociated 1-1 electrolyte solution. Here, we combined experimental measurements and classical molecular dynamics simulations to study the ion conduction in this system. Ionic conductivities were reported at both 20$^\circ$C and 50$^\circ$C from experiments and compared to results from molecular dynamics simulations. The main finding of this work is that transference numbers of Li$^+$ and Cl$^-$ become comparable at high concentration. This phenomenon is independent of the force fields employed in the simulation …
Grand-canonical molecular dynamics simulations powered by a hybrid 4D nonequilibrium MD/MC method: Implementation in LAMMPS and applications to electrolyte solutions
Seemingly unrelated experiments such as electrolyte transport through nanotubes, nano-scale electrochemistry, NMR relaxometry and Surface Force Balance measurements, all probe electrical fluctuations: of the electric current, the charge and polarization, the field gradient (for quadrupolar nuclei) and the coupled mass/charge densities. The fluctuations of such various observables arise from the same underlying microscopic dynamics of the ions and solvent molecules. In principle, the relevant length and time scales of these dynamics are encoded in the dynamic structure factors. However modellin…
We present an extensive molecular dynamics (MD) simulation study of poly(ethylene oxide) (PEO) based densely cross-linked polymers, focussing on structural properties as well as the systems dynamics in the presence of lithium salt. Motivated by experimental findings for networks with short PEO strands we employ a combination of LiTFSI (Lithium bis(trifluoromethanesulfonyl)imide) and LiDFOB (Lithium difluoro(oxalato)borate). Recently, it has been shown that such multi-salt systems outperform classical single salt systems (Shaji et al., Energy Storage Materials, 2022, 44, 263). To analyse the mi…
Molecular dynamics simulations are a powerful tool to study diffusion processes in battery electrolyte and electrode materials. From a single molecular dynamics simulation many properties relevant to diffusion can be obtained, including the diffusion path, attempt frequency, activation energies, and collective diffusion processes. These detailed diffusion properties provide a thorough understanding of diffusion in solid electrolytes, and provides direction for the design of improved solid electrolyte materials. Here a thorough analysis methodology is developed, and applied to DFT MD simulation…
Extracting a nitrile-centered, ether-assisted motif hierarchy for lithium-battery electrolyte design from billion-scale molecular space
University of Science and Technology of China（中国科学技术大学）；Suzhou Institute for Advanced Research, University of Science and Technology of China（中国科学技术大学苏州高等研究院）；Suzhou Big Data & AI Research and Engineering Center（苏州大数据与人工智能研究与工程中心）；Contemporary Amperex Technology Co. Limited（宁德时代新能源科技股份有限公司）；AI for Science Institute（人工智能科学研究所）
Many key industrial processes, from electricity production, conversion and storage to electrocatalysis or electrochemistry in general, rely on physical mechanisms occurring at the interface between a metallic electrode and an electrolyte solution, summarized by the concept of electric double layer, with the accumulation/depletion of electrons on the metal side and of ions on the liquid side. While electrostatic interactions play an essential role on the structure, thermodynamics, dynamics and reactivity of electrode-electrolyte interfaces, these properties also crucially depend on the nature o…
Nuclear magnetic resonance relaxometry represents a powerful tool for extracting dynamic information. Yet, obtaining links to molecular motion is challenging for many ions that relax through the quadrupolar mechanism, which is mediated by electric field gradient fluctuations and lacks a detailed microscopic description. For sodium ions in aqueous electrolytes, we combine ab initio calculations to account for electron cloud effects with classical molecular dynamics to sample long-time fluctuations, and obtain relaxation rates in good agreement with experiments over broad concentration and tempe…
Molecular interpretability of the bulk electrochemical impedance of concentrated electrolytes
Yusuf Hamied Department of Chemistry, University of Cambridge（剑桥大学尤素夫·哈米德化学系）；Department of Chemistry, Durham University（杜伦大学化学系）；Sorbonne Université, CNRS, Physical Chemistry of Electrolytes and Interfacial Nanosystems (PHENIX)（索邦大学，法国国家科学研究中心，电解质和界面纳米系统物理化学（PHENIX））；Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459（电化学储能网络（RS2E），FR CNRS 3459）
Employing recent advances in response theory and nonequilibrium ensemble reweighting, we study the dynamic and static correlations that give rise to an electric field-dependent ionic conductivity in electrolyte solutions. We consider solutions modeled with both implicit and explicit solvents, with different dielectric properties, and at multiple concentrations. Implicit solvent models at low concentrations and small dielectric constants exhibit strongly field-dependent conductivities. We compared these results to the Onsager-Wilson theory of the Wien effect, which provides a qualitatively cons…
Identification of Solid-Electrolyte Interphase Species by Joint Characterization of Li-ion Battery Chemistry by Mass Spectrometry and Electro-Chemical Reaction Networks
Bakar Institute of Digital Materials for the Planet, University of California at Berkeley（加州大学伯克利分校巴克数字材料星球研究所）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Department of Materials Science and Engineering, University of California at Berkeley（加州大学伯克利分校材料科学与工程系）；Université de Rouen Normandie, INSA Rouen Normandie, Université de Caen Normandie, ENSICAEN, CNRS, Institut CARMeN UMR 6064（鲁昂诺曼底大学、鲁昂国立应用科学学院、卡昂诺曼底大学、ENSICAEN、法国国家科学研究中心CARMeN联合研究所）；TotalEnergies OneTech, TotalEnergies Research & Technology Gonfreville（道达尔能源OneTech、道达尔能源贡夫勒维尔研究与技术部）；Saft, Corporate Research（萨博公司企业研究部）；International Joint Laboratory-Complex Matrices Molecular Characterization (iC2MC)（国际联合实验室-复杂基体分子表征）；TotalEnergies OneTech Belgium（道达尔能源OneTech比利时）；TotalEnergies EP Research & Technology（道达尔能源勘探与生产研究与技术部）；Universite de Pau et des Pays de l’Adour, CNRS, IPREM（波城与阿杜尔地区大学、法国国家科学研究中心IPREM）
The distribution of ions at the air/water interface plays a decisive role in many natural processes. It is generally understood that polarizable ions with low charge density are surface-active, implying they sit on top of the water surface. Here, we revise this established hypothesis by combining surface-specific heterodyne-detected vibrational sum-frequency generation with neural network-assisted ab initio molecular dynamics simulations. Our results directly demonstrate that ions in typical electrolyte solutions are, in fact, located in a subsurface region leading to a stratification of such …
