Solvation Stability Research Articles

Exploring the solubility and intermolecular interactions of biologically significant amino acids l-serine and L-cysteine in binary mixtures of H2O + DMF, H2O + DMSO and H2O + ACN in temperature range from T = 288.15 K to 308.15 K

In the presented work, a study on the solubility and intermolecular interactions of l-serine and L-cysteine was carried out in binary mixtures of H2O + dimethylformamide (DMF), H2O + dimethylsulfoxide (DMSO), and H2O + acetonitrile (ACN) in the temperature range of T = 288.15 K to 308.15 K. l-serine exhibited the highest solubility in water, while L-cysteine was more soluble in water-DMF. The solvation process was assessed through standard Gibbs energy calculations, indicating the solvation stability order: water-ACN > water-DMSO > water-DMF for l-serine, and water-DMF > water-DMSO > water-ACN for L-cysteine. This study also explored the influence of these amino acids on solvent–solvent interactions, revealing changes in chemical entropies and self-association patterns within the binary solvent mixtures.

A Comprehensive Study of the Parameters Affecting Magnesium Plating/Stripping Kinetics in Rechargeable Mg Batteries

Beyond the lithium ion battery (LIB) technology, alkali and alkaline earth metal (Li, Na, Mg, Ca etc.) anodes boost the prospect of next generation battery chemistry through their highly promising theoretical specific capacities.1,2 Mg metal anode based battery is thus one of the strong contenders for sustainable and alternative rechargeable battery systems, with its natural abundance and eco-friendly resources.3 Despite the first proof-of-concept of a Mg battery established back in 2000,4 its complete rechargeability still remains elusive due to the lack of suitable conventional electrolytes and low mobility of Mg2+ ions in typical intercalation cathodes. Although potentially safer than Li metal (less prone to dendritic growth), reversible Mg electrodeposition in non-aqueous liquid electrolytes is a challenge due to poor salt solubility and formation of ionically blocking surface passivation films.5,6 The study of the interphase between a Mg metal anode and electrolyte is therefore of critical worth as it can dictate stability and reversibility for a particular electrode/electrolyte combination.7 In this work, we explore the role of various parameters, including electrolyte composition, concentration, solvent and substrate nature (various metals and carbon based substrates) and their impact on Mg plating/stripping kinetics and coulombic efficiency. The deposit morphology was investigated via ex situ scanning electron microscopy (SEM) and the reductive stability of the electrolytes was studied by cyclic voltammetry (CV), X-ray Photoelectron Spectroscopy (XPS) and electrochemical quartz crystal microbalance (EQCM). Overall, a comprehensive discussion about the relationship between cation solvation structure, composition and stability of passivation layer (if any) and the degree of reversibility of Mg electrodeposition will be presented. Keywords: Beyond LIB chemistry, metal anode, magnesium, EQCM, plating/stripping.

Structures of 18-crown-6/Cs+ complexes in aqueous solutions by wide angle X-ray scattering and density functional theory

• The oxygen atoms of 18-crown-6 and the hydrogen atoms of water molecule form strong hydrogen bonds in aqueous solution. • Cs + is located directly above the 18-crown-6 ring plane, about 1.15 Å from the centroid of 18-crown-6. • The higher the concentration of CsCl, the lower the complexation percentage of 18-crown-6 to Cs + . • Cs + complexing with 18-crown-6 mainly hydrates with four water molecules. Wide angle X-ray scattering (WAXS) and density functional theory (DFT) were employed to study the structures of aqueous 18-crown-6/CsCl solutions with CsCl concentrations of 0.25, 0.50 and 1.00 mol·L -1 . The empirical potential structure refinement (EPSR) modelling was adopted to get the pair distribution functions (PDFs), coordination numbers ( CN ), coordination number distributions (CND), angle distribution functions (ADFs), independent gradient model (IGM) and spatial density functions (SDFs) for the 18-crown-6 hydration, the complexation of 18-crown-6 and Cs + , the hydration of 18-crown-6/Cs + complex, and the association of Cl - and 18-crown-6/Cs + complex. Judging from the distance and orientation of water molecules, and the IGM between 18-crown-6 and water molecules, the oxygen atoms of 18-crown-6 (Oc) and the hydrogen atoms of water molecules (Hw) form strong hydrogen bonds, and these water molecules were distributed on both sides of the 18-crown-6 ring plane. However, the hydrogen atoms of 18-crown-6 (Hc) hardly form hydrogen bonds with the oxygen atoms of water molecules (Ow). Cs + is located directly above the 18-crown-6 ring plane of 0.35 to 2.05 Å away from the centroid of 18-crown-6, and forms 18-crown-6/Cs + complex with six Oc at r Cs + - O c = 3.06 Å. When the concentrations of CsCl are 0.25, 0.50 and 1.00 mol·L -1 , the complexation percentage of 18-crown-6 to Cs + are about 100%, 58% and 54%, respectively. No classic 2:1 “sandwich” 18-crown-6/Cs + complex structure was found in the solutions we surveyed. Both interaction energies and solvation stability energies reveal that the hydrates of 18-crown-6/Cs + complexes were formed in aqueous solutions. Cs + uncomplexed with 18-crown-6 hydrates with eight water molecules in aqueous solution, while Cs + can also hydrate with about four water molecules when it complexes with 18-crown-6. The results of atomic pair distances, the dipole distance of water molecules, the SDF and the IGM indicate that although water molecules can be located on both sides of the 18-crown-6 ring plane when the hydrates are formed, they hydrate with Cs + on the side where Cs + only existed. Cs + of 18-crown-6/Cs + complex associates with Cl - with the r Cs + - Cl - = 3.79 Å by electrostatic attraction.

Structure, Diffusion, and Stability of Lithium Salts in Aprotic Dimethyl Sulfoxide and Acetonitrile Electrolytes

The development of lithium batteries, including lithium-ion batteries and lithium-air batteries, is the key technological breakthrough in the field of renewable energy storage. However, to date, it is still challenging to design a lithium battery with both high specific power and stability. Specifically, the solvation structure and thermodynamic stability of various electrolytes, mostly Li salts and aprotic solvents, have not been systematically studied from an atomic viewpoint. In this paper, we studied the solution chemistry of three most common inorganic Li salts (LiClO4, LiBF4, and LiPF6) and O2 in two aprotic (dimethyl sulfoxide (DMSO) and acetonitrile (CH3CN)) solvents. The Born–Oppenheimer molecular dynamics simulations and enhanced free energy samplings are employed to obtain their solvation structures, diffusion coefficients, and stability performances at room temperature. As a result, the tetrahedral Li(DMSO)4+ and Li(CH3CN)4+ are obtained as the stable solvation shells of Li+ in DMSO and CH3CN solvents, respectively. Among the three inorganic Li salts, the stability performances are found in the order of LiClO4 > LiBF4 > LiPF6 in both DMSO and CH3CN solvents. Compared with CH3CN, DMSO provides a more stable environment for the long-term usage of Li salts for that increases the energetic barriers of the degradation reactions of solvated Li+ components. However, DMSO shows a weaker ability (than CH3CN) to transport the main redox species (solvated Li+ and O2) in the electrolyte, which limits the discharging and charging rate in the batteries.

Structural Insights into the Highly Solvating System of Axitinib via Binary and Ternary Solvates

Axitinib is a well-known model in crystal engineering, exhibiting a high tendency to form various solvates, and more than 70 kinds of solvates have been reported. Therefore, it is a challenge to elucidate the effect of solvents on the crystallization of Axitinib and develop the polymorph or solvate landscape of Axitinib. Here, we illustrate an uncommon and complicated solvation behavior of Axitinib from the structural analysis and theoretical characterization. The structures of two new ternary solvates and five binary solvates are reported for the first time. Experimental and theoretical calculation and studies on phase transition are performed to rationalize and understand the formation of solvates and the transformation of polymorphisms. Crystal structure analysis and molecular properties reveal that shape, size, the hydrogen bond donor of the solvents, and the chance to lower crystal free energy are the main factors to drive solvates. Three sets of isostructural binary solvate are distinguished and calculated quantitatively to prove that the intermolecular interactions, strong hydrogen bond donor, CH−π, and orientation force control the classification results of binary solvates. Stability of solvates is found to be associated with the intermolecular interaction energies of solvent molecules with surrounding molecules. The polymorphic behavior of the desolventized product is attributed to the two-dimensional isostructurality between form IV and solvate.

Quasi-solid electrolytes with tailored lithium solvation for fast-charging lithium metal batteries

Using quasi-solid electrolytes (QSEs) can make lithium metal batteries (LMBs) considerably safer. However, formulating QSEs with rate capabilities rivaling those of liquid electrolytes is extremely difficult. Herein, we develop a QSE characterized by safety, high conductivity above 2 × 10 −3 S cm −1 , and high lithium-ion transference number ( t Li + ) above 0.8. Computations and experiments reveal that these characteristics are achieved by adjusting the Li + solvation through a weak interaction with the polymer skeleton and strong coordination with NO 3 − . The further inclusion of fluoroethylene carbonate leads to the formation of a Li 3 N- and LiF-rich solid electrolyte interphase on the lithium metal. Consequently, QSE-based LMBs are capable of fast charging and high-power density, as well as stable and long cycling. By adjusting Li + solvation and lithium metal stability, this work rationally develops QSEs for fast-charging LMBs. • Quasi-solid electrolyte prepared with high-donor-number solvent and LiNO 3 • In-depth investigations on lithium solvation and ion transport by atomic simulations • Fast-charging lithium metal battery based on the QSE • Safe, flexible, and non-flammable pouch-type lithium metal battery Zhou et al. design a quasi-solid electrolyte with tailored lithium solvation and diffusion for fast-charging lithium metal batteries. The impact of the high-donor number solvent and LiNO 3 on solvation and charge-transfer mechanisms is studied experimentally and computationally.

Rationalizing the Formation of Belinostat Solvates with Experimental Screening and Computational Predictions

Belinostat is a histone deacetylase inhibitor for the treatment of refractory T-cell lymphoma. Our study found that the tendency to form solvates of belinostat with hydrogen-bond acceptor type solvents was obvious based on the COSMO-RS model. Motivated by the prediction results, we investigated eight novel solvates, with 1,4-dioxane, tetrahydrofuran, furan, 3-picoline, cyclopentanone, 1-methyl-2-pyrrolidinone, and dimethyl sulfoxide/water as guest molecules, obtained by different crystallization methods. The obtained solid forms were thoroughly characterized with various analytical techniques, namely, powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermal analysis. The thermal stability order of solvates was S3PC > S′Diox > SNMP > SCP > SFuran > STHF > SDiox > SDMSO/H2O, and a strong correlation between the boiling points of solvents and the crystal lattice energy with the thermal stability of solvates was observed. Additionally, six crystal structures of five solvates and the reported Form I were successfully determined from single-crystal X-ray diffraction data. The results revealed that the belinostat molecule adopted flexible conformations in different crystal structures; meanwhile, the formation of belinostat solvate was mainly driven by the belinostat–solvent intermolecular interactions and the improved packing efficiency due to the introduction of solvent molecules.

Various Molecular Arrangements Leading to Different Desolvation Rates: Research on the Stability of 2,7‐Dibromo‐9H‐carbazole Solvates

AbstractThe stability of solvates is very important in the field of crystal engineering. Molecular interaction and packing mode are important factors affecting the stability of solvates. In this study, 2,7‐dibromo‐9H‐carbazole is selected as the model compound to investigate the influence of molecular stacking mode on the stability of solvates. An anhydrous form and five solvates of 2,7‐dibromo‐9H‐carbazole are obtained by recrystallization. The desolvation phenomena of the five solvates are studied by thermogravimetric analysis, hot stage microscope, and infrared spectroscopy and it is found that the stability of the solvates is N,N‐dimethylacetamide solvate > dimethyl sulfoxide solvate > N,N‐dimethylformamide solvate > dioxane solvate > acetonitrile solvate. Crystal structures are analyzed by single crystal X‐ray diffraction and Hirshfeld surface analysis is also applied to analyze the intermolecular interactions in the crystals. The results show that the stability of the five solvates is related to the packing modes of the molecules in the crystal. It is suggested that the solute molecules and solvent molecules in the unstable solvates are arranged in the interlayer mode, while they are arranged in a staggered mode in stable solvates.

Unifying the Clustering Kinetics of Lithium Polysulfides with the Nucleation Behavior of Li2S in Lithium-Sulfur Batteries.

Within the lithium-sulfur (Li-S) battery, a wide variety of soluble lithium polysulfide intermediates form during operation. Under lean-electrolyte or low-temperature conditions, the solution coordination of polysulfides dynamically shifts to highly clustered states, which is subsequently accompanied by inhibited electrochemical kinetics. In fact, it has been shown that the tendency for polysulfides to strongly aggregate is one of the dominant kinetically limiting obstacles towards achieving adequate utilization of active material under such conditions. While this association has been noted before, it is not explicitly understood what mechanism intrinsic to polysulfide clustering curtails the electrochemical utilization of active material, particularly during the conversion to insoluble Li2S. Here, we perform a series of investigations to unify and link the kinetic constraints that arise from polysulfide clustering to the nucleation and growth behavior of Li2S. We find that there is a drastic decrease in polysulfide diffusion coefficient arising from the advent of clustering, and that this decline functionally matches that seen for the nucleation and growth rate constants for Li2S deposition. Additionally, it is found that there is a less favorable minimization of energy during Li2S nucleation, arising from the altered solvation stability of polysulfide clusters. This knowledge expands our understanding of the Li-S materials chemistry and the primary factors dictating the electrochemical behavior.

Flexible cationic side chains for enhancing the hydroxide ion conductivity of olefinic-type copolymer-based anion exchange membranes: An experimental and theoretical study

The performance of anion exchange membranes (AEMs) is closely related to their cationic groups, hydration degree, and nano-phase morphology. Here, mono- (and di-) quaternary ammonium, pyrrolidinium, and imidazolium cation-based AEMs were synthesized by one-step photo-polymerization. Through combination of experimental and molecular dynamics (MD) approaches, the effects of mono- (and di-) cationic functional groups on the properties of the AEMs, in terms of physicochemical, electrochemical properties, and alkaline stability were comprehensively investigated. It was concluded by the experimental data that AEMs with di-cations exhibit better water uptake, swelling ratio, alkaline stability, and higher ionic conductivity than those with mono-cations. Furthermore, mathematical models of the synthesized AEMs were established for MD simulations, and the calculated radial distribution function and mean square displacements between cationic functional groups, hydroxide ions, and water molecules obtained using the simulated molecular trajectories were examined for the solvation, transport properties, and alkaline stability of AEMs, which are in good qualitative agreement with the experimental results.

Atomic Insights into the Fundamental Interactions in Lithium Battery Electrolytes.

ConspectusBuilding high-energy-density batteries is urgently demanded in contemporary society because of the continuous increase in global energy consumption and the quick upgrade of electronic devices, which promotes the use of high-capacity lithium metal anodes and high-voltage cathodes. Achieving a stable interface between electrolytes and highly reactive electrodes is a prerequisite to constructing a safe and powerful battery, in which electrolyte regulation plays a decisive role and largely determines the long-term and rate performances. The bulk and interfacial properties of electrolytes are directly determined by the fundamental interactions and the as-derived microstructures in electrolytes. Different from experimental trial-and-error approaches, the rational bottom-up design of electrolytes based on a comprehensive and deep understanding of the fundamental interactions between electrolyte compositions and the structure-function relationship is highly expected to accelerate breaking through the bottleneck in current technology and realizing next-generation Li batteries.In this Account, we afford an overview of our recent attempts toward rational electrolyte design for safe Li batteries based on a comprehensive understanding of the cation-solvent, cation-anion, and anion-solvent interactions in electrolytes. The formation of cation-solvent complexes decreases the reductive stability but increases the oxidative stability of solvent molecules according to frontier molecular orbital theory, whereas the introduction of anions into the Li+ solvation shell has the opposite function in regulating solvent stability compared with cations. The competitive coordination of anions and solvent molecules with cations directly determines the salt solubility in electrolytes and the formation of ion pairs and aggregates, which widely exist in high-concentration electrolytes and stabilize Li metal anodes. An easy and effective route to dissolve lithium nitrate in ester electrolytes is accordingly proposed. Although anions are hardly solvated in routine solvents, solvents with a high acceptor number or an exposed positive charge site are highly expected to enhance the anion-solvent interaction. The solvation of anions will have a strong influence on electrolytes, including regulating the electrolyte solvation structure and stability, increasing the cation transference number, and promoting salt dissociation. The emerging Li bond theory and big-data approaches, combined with first-principles calculations and experimental characterizations, are also expected to promote rational electrolyte design with much reduced time and expense.Collectively, with a comprehensive and deep understanding of the fundamental interactions in electrolytes and the structure-function relationship, bottom-up engineering of Li battery electrolytes is expected to be achieved, accelerating the applications of safe high-energy-density Li batteries. The general principles demonstrated in Li batteries are also supposed to be applicable to other battery systems and even universal electrochemistry in solutions, including fuel cells and various electrocatalyses.

Crystal structure and physical stability of ginsenoside compound-K solvates

Through systematic investigation on the structure of and thermal/hygroscopic experiments on GCK solvates, superior physical stabilities of the hemihydrate and monohydrate are demonstrated.

Monitoring the solvation process and stability of Eu2+ in an ionic liquid by in situ luminescence analysis

Abstract Ionic liquids (ILs) offer the remarkable possibility of the direct synthesis of Eu2+-doped nanophosphors in solution, under atmospheric conditions, without the necessity of a high-temperature post-synthetic reduction from its trivalent oxidation state. This work uses for the first time in situ luminescence measurements for monitoring the solvation process of Eu2+ from the solid salt to the IL and its stability against oxidation under atmospheric conditions. Upon the addition of EuBr2 to 1-butyl-3-methyl-imidazolium tetrafluoroborate, the formation of the solvation shell is detected by the shift of the emission band at approximately 24 100 cm−1 assigned to the 5d→4f electronic transitions of Eu2+ within EuBr2 to approximately 22 000 cm−1, assigned to Eu2+ within BminBF4, tracking the time-dependent influence of the Eu2+ coordination environment on the crystal field splitting of its d orbitals. Even though the solubility of EuBr2 was demonstrated to be improved by reducing the concentration and increasing the temperature to 60°C, the performance of reactions at room temperature is recommended for future synthesis of Eu2+ materials in ILs due to the slight oxidation to Eu3+ observed upon heating.

Computational analysis of carbohydrate recognition based on hybrid QM/MM modeling: a case study of norovirus capsid protein in complex with Lewis antigen.

Norovirus is a major pathogen of nonbacterial acute gastroenteritis in humans and animals. Carbohydrate recognition between norovirus capsid proteins and Lewis antigens is considered to play a critical role in initiating infection of eukaryotic cells. In this article, we first report a detailed atomistic simulation study of the norovirus capsid protein in complex with the Lewis antigen based on ab initio QM/MM combined with MD-FEP simulations. To understand the mechanistic details of ligand binding, we analyzed and compared the carbohydrate recognition mechanism of the wild-type P domain protein with a mutant protein. Small structural differences between two capsid proteins are observed on the weak interaction site of residue 389, which is located on the solvent exposed surface of the P domain. To further clarify affinity differences in ligand binding, we directly evaluated free energy changes of the ligand binding process. Although the mutant protein loses its interaction energy with the Lewis antigen, this small amount of energy penalty is compensated for by an increase in the solvation stability, which is induced by structural reorganization at the ligand binding site on the protein surface. As a sum of these opposite energy components, the mutant P domain obtains a slightly enhanced binding affinity for the Lewis antigen. The present computational study clearly demonstrated that a detailed free energy balance of the interaction energy between the capsid protein and the surrounding aqueous solvent is the mechanistic basis of carbohydrate recognition in the norovirus capsid protein.

Solubility of d-Element Salts in Organic and Aqueous–Organic Solvents: VI.1 Structure and Thermal Stability of Cadmium Iodide and Bromide Solvates with Dimethylacetamide and Dimethylformamide

Five solvates, [CdBr2(DMF)] n , [CdBr2(DMA)] n , [CdI2(DMF)] n , [Cd(DMF)6][Cd2I6], and {[Cd(DMA)6][Cd5I12] n } m , were isolated from the ternary systems CdX2–L–H2O (X = Br, I; L = N,N-dimethylacetamide, N,N-dimethylformamide) and characterized by the X-ray single crystal analysis. The structures of the first three solvates is similar to each other in structures and represent a one-dimensional polymer chain, the fourth solvate has the discrete structure containing [Cd(DMF)6]2+ and [Cd2I6]2– ions, and the fifth solvate contains discrete [Cd(DMA)6]2+ cations and the polymer anionic fragment [Cd5I12] n 2n–.

Solid-State Characterization and Insight into Transformations and Stability of Apatinib Mesylate Solvates

Two types of solvates for the anti-angiogenesis drug apatinib mesylate (ATM) were obtained and their crystal structures were determined by single-crystal X-ray diffraction. The properties of these solvates were fully characterized by powder X-ray diffraction, dynamic vapor sorption, differential scanning calorimetry, and thermogravimetric analysis. Experimental and theoretical studies were performed on the solvates to understand the phase transitions induced by heat and humidity. An irreversible humidity-induced single-crystal-to-single-crystal (SCTSC) transformation from ethanol solvate (type II) to monohydrate (type I) was elucidated. Stability of these solvates, including moisture-dependent and thermal stability, was studied. The comprehensive investigation of the solvates and hydrate provided essential knowledge about quality control of the important drug.

Exploration of the solvation behaviour of ascorbic acid in aqueous solutions of 1,2,4-triazolium based ionic liquid

In order to analyze the extent of solvation behaviour and stability of ascorbic acid (AA) in water or aqueous ionic liquid (IL) solutions, the knowledge of their thermodynamic properties is prerequisite which gives an appropriate idea about interactions involved in solutions. In addition, experimental and derived thermodynamic data is essential in effective process and product design involving these systems. In this report, we studied the volumetric and acoustic properties of AA in aqueous solution of synthesized IL, [HxTzm][CF3SO3] i.e. (1-Hexyl-4-(4-sulfobutyl)-1H-1,2,4-triazol-4-ium trifluoromethanesulfonate) in temperature range of (293.15–328.15) K and at atmospheric pressure. Further, the experimentally measured thermodynamic properties were used to calculate apparent molar and partial molar properties, which elucidate the solvation behaviour of AA in presence of studied IL. Further, on the basis of the structural interaction model, various type of interactions which is stirring between AA and IL have been discussed in terms of partial molar properties at infinite dilution, transfer parameters and pair and triplet interaction coefficients.

Thermal and Electrochemical Stability of Tetraglyme–Magnesium Bis(trifluoromethanesulfonyl)amide Complex: Electric Field Effect of Divalent Cation on Solvate Stability

Phase behavior of binary mixtures of tetraglyme (G4) and Mg[TFSA]2 (TFSA: bis(trifluoromethanesulfonyl)amide) was investigated. In a 1:1 molar ratio, G4 and Mg[TFSA]2 formed a stable complex with a melting point of 137 °C. X-ray crystallography of a single crystal of the complex grown from a G4-Mg[TFSA]2 binary mixture revealed that the G4 molecule wraps around Mg2+ to form a complex [Mg(G4)]2+ cation, and the two [TFSA]− anions also participate in the Mg2+ coordination in the crystal. The thermal stability of [Mg(G4)][TFSA]2 was examined by thermogravimetry, and it was found that the complex is stable up to 250 °C. Above 250 °C, desolvation of the Mg2+ ion takes place and G4 evaporates. On the other hand, the weight loss starts at around 140 °C in solutions containing excess G4 (n > 1 in Mg[TFSA]2:G4 = 1:n) due to the evaporation of free (uncoordinated) G4. The suppression of G4 volatility in the [Mg(G4)][TFSA]2 complex is attributed to strong electrostatic and induction interactions between divalent Mg2...

High Throughput Approach to Accelerate Electrolyte Discovery for Batteries

Increasing demand of high energy density and high capacity batteries require development beyond Li-ion technology and innovations in electrodes and electrolytes, alike. An approach to achieve energy density higher than the existing Li-ion batteries is to replace monovalent Li ion by multivalent ions such as Mg, Ca. The ability of Mg batteries to provide much higher volumetric capacity, particularly on the anode side where the Mg metal can theoretically provide 3833 mA h/cc as compared to the Li counterpart graphite (∼ 800 mA h/cc) at a lower cost makes the technology an attractive candidate for future batteries. However, development and commercialization of Mg batteries require not only improved electrode discovery and development but also novel electrolytes, which are compatible with the Mg metal as conventional electrolytes fail to penetrate the Mg metal passivation layer. Thus a fundamental understanding of molecular level properties of these electrolytes is required to improve the electrochemical stability and the charge transfer properties. An automatic High-throughput infrastructure has been constructed for the electrolyte genome project supported by the US Joint Center for Energy Storage Research (JCESR)2. In this work, we present classical molecular dynamics simulations coupled with ab initio calculations for Mg salts in various solvents. We uncover a novel effect between concentration dependent ion pair formation and anion stability at reducing potential, e.g., at the metal anode1. We elucidate systematic correlations between molecular level interactions and composite electrolyte properties, such as electrochemical stability, solvation structure, and dynamics. We find that Mg electrolytes are highly prone to ion pair formation, even at modest concentrations, for a wide range of solvents with different dielectric constants, which have implications for dynamics as well as charge transfer. Specifically, we observe that, at Mg metal potentials, the ion pair undergoes partial reduction at the Mg cation center (Mg2+ → Mg+), which competes with the charge transfer mechanism and can activate the anion to render it susceptible to decomposition. Specifically, TFSI− exhibits a significant bond weakening while paired with the transient, partially reduced Mg+. Furthermore, we observe that higher order glymes as well as DMSO improve the solubility of Mg salts, but only the longer glyme chains reduce the dynamics of the ions in solution. This information provides critical design metrics for future electrolytes as it elucidates a close connection between bulk solvation and cathodic stability as well as the dynamics of the salt.

(Invited) Insights into Solvation, Dynamics and Stability of Electrolytes for the Design of Novel Multivalent Systems from Coupled Molecular Dynamics and First-Principles Modeling

Within the Joint Center for Energy Storage (JCESR) we have developed a high-throughput infrastructure for the automated calculation of molecular properties with a focus on battery electrolytes. Computational screening techniques have been found to be an effective alternative to the trial and error of experimentation for discovery of new materials. Using this infrastructure, we have computed the ionization potential (IP) and electron affinities (EA) of 16,000 molecules relevant to electrolytes targeting both multivalent intercalation as well as non-aqueous redox flow systems. For some potential multi-valent electrolytes we use classical molecular dynamics simulations coupled with ab initio calculations for Mg salts in various solvents. We uncover a novel effect between concentration dependent ion pair formation and anion stability at reducing potential, e.g., at the metal anode1. We elucidate systematic correlations between molecular level interactions and composite electrolyte properties, such as electrochemical stability, solvation structure, and dynamics. Specifically, we find that multivalent electrolytes are highly prone to ion pair formation, even at modest concentrations, for a wide range of solvents with different dielectric constants, which have implications for dynamics as well as charge transfer. For example, at Mg metal potentials, the ion pair undergoes partial reduction at the Mg cation center (Mg2+→Mg+), which competes with the charge transfer mechanism and can activate the anion to render it susceptible to decomposition. Specifically, TFSI− exhibits a significant bond weakening while paired with the transient, partially reduced Mg+. This information provides critical design metrics for future electrolytes as it elucidates a close connection between bulk solvation and cathodic stability as well as the dynamics of the salt. We use our previous insights to design for new Mg electrolyte anions with the aim to stabilize the electrolyte during possible ion pair formation and charge transfer reactions. Through comprehensive calculations using both first-principles as well as well-benchmarked classical molecular dynamics, we proposed 16 new electrolyte salts. Based on successive property evaluation such as electrochemical stability window, chemical decomposition and hydrolysis vulnerability we down-select 4 potential new anions for Mg electrolytes.