Li+ solvation in pure, binary and ternary mixtures of organic carbonate electrolytes

Classical molecular dynamics (MD) simulations and quantum chemical density functional theory (DFT) calculations have been employed in the present study to investigate the solvation of lithium cations in pure organic carbonate solvents (ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC)) and their binary (EC-DMC, 1:1 molar composition) and ternary (EC-DMC-PC, 1:1:3 molar composition) mixtures. The results obtained by both methods indicate that the formation of complexes with four solvent molecules around Li+, exhibiting a strong local tetrahedral order, is the most favorable. However, the molecular dynamics simulations have revealed the existence of significant structural heterogeneities, extending up to a length scale which is more than five times the size of the first coordination shell radius. Due to these significant structural fluctuations in the bulk liquid phases, the use of larger size clusters in DFT calculations has been suggested. Contrary to the findings of the DFT calculations on small isolated clusters, the MD simulations have predicted a preference of Li+ to interact with DMC molecules within its first solvation shell and not with the highly polar EC and PC ones, in the binary and ternary mixtures. This behavior has been attributed to the local tetrahedral packing of the solvent molecules in the first solvation shell of Li+, which causes a cancellation of the individual molecular dipole vectors, and this effect seems to be more important in the cases where molecules of the same type are present. Due to these cancellation effects, the total dipole in the first solvation shell of Li+ increases when the local mole fraction of DMC is high

Fractionation of lignin using organic solvents: A combined experimental and theoretical study

Refining of industrial lignin to produce homogeneous fractions is essential for high-value applications. However, the understanding of key interactions between a variety of solvents with lignin polymer is still uncertain. In this work, single-step fractionation of industrial hardwood kraft lignin (HKL) using organic solvents of different polarities - ethanol, acetone, diethyl ether and hexane - was investigated by combining an experimental and theoretical approach. Experimental results revealed that higher polarity solvents (ethanol and acetone) exhibited higher solubility yield compared to moderate and low polarity solvents. The chemical differences between lignin fractions were proven by pyrolysis gas chromatography mass spectrometry and near infrared spectroscopy. Density functional theory (DFT) results indicated that ethanol presented higher interaction energy followed by acetone, diethyl ether and hexane, which was consistent with experimental findings. Hydrogen bond and non-covalent interaction results from DFT demonstrated that the predominant interaction was found for high polarity of ethanol over other solvents and gamma-OH in the lignin model is the key site.The authors gratefully acknowledge the European Commission for funding the InnoRenew project [Grant Agreement #739574] under the Horizon2020 Widespread-Teaming program, the Republic of Slovenia (investment funding from the Republic of Slovenia and the European Union European Regional Development Funds) and infrastructural ARRS program IO-0035. Additionally, O.G. is grateful for the financial support received from the University of the Basque Country (post-doctoral grant DOCREC18/29) and R.H. acknowledges to the Department of Education of the Basque Government (post-doctoral grant INGVTCL4-D00112-7)

Etude théorique et numérique de l'interaction des ions lithium dans les solvants carbonates et leurs mélanges

Due to the increasing global energy demand, eco-friendly and sustainable green resources including solar, or wind energies must be developed, in order to replace fossil fuels. These sources of energy are unfortunately discontinuous, being correlated with weather conditions and their availability is therefore strongly fluctuating in time. As a consequence, large-scale energy storage devices have become fundamental, to store energy on long time scales with a good environmental compatibility. Electrochemical energy conversion is the key mechanism for alternative power sources technological developments. Among these systems, Lithium-ion (Li+) batteries (LIBs) have demonstrated to be the most robust and efficient, and have become the prevalent technology for high-performance energy storage systems. These are widely used as the main energy source for popular applications, including laptops, cell phones and other electronic devices. The typical LIB consists of two (negative and positive) electrodes, separated by an electrolyte. This plays a very important role, transferring ions between the electrodes, therefore providing the electrical current. This thesis work focuses on the complex materials used as electrolytes in LIBs, which impact Li-ion transport properties, power densities and electrochemical performances. Usually, the electrolyte consists of Li-salts and mixtures of organic solvents, such as cyclic or linear carbonates. It is therefore indispensable to shed light on the most important structural (coordination) properties, and their implications on transport behaviour of Li+ ion in pure and mixed solvent compositions. We have performed a theoretical investigation based on combined density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations, and have focused on three carbonates, cyclic ethylene carbonate (EC) and propylene carbonate (PC), and linear dimethyl carbonate (DMC). DFT calculations have provided a detailed picture for the optimized structures of isolated carbonate molecules and Li+ ion, including pure clusters Li+(S)n (S=EC, PC, DMC and n=1-5), mixed binary clusters, Li+(S1)m(S2)n (S1, S2 =EC, PC, DMC, with m+n=4), and ternary clusters Li+(EC)l(DMC)m(PC)n with l+m+n=4. Pure solvent clusters were also studied including the effect of PF6- anion. We have investigated in details the structure of the coordination shell around Li+ for all cases. Our results show that clusters such as Li+(EC)4, Li+(DMC)4 and Li+(PC)3 are the most stable, according to Gibbs free energy values, in agreement with previous experimental and theoretical studies. The calculated Gibbs free energies of reactions in binary mixtures suggest that the addition of EC and PC molecules to the Li+-DMC clusters are more favourable than the addition of DMC to Li+-EC and Li+-PC clusters. In most of the cases, the substitution of solvent to binary mixtures are unfavourable. In the case of ternary mixtures, the DMC molecule cannot replace EC and PC, while PC can easily substitute both EC and DMC molecules. Our study shows that PC tends to substitute EC in the solvation shell. We have complemented our ab-initio studies by MD simulations of a Li-ion when immersed in the pure solvents and in particular solvents mixtures of interest for batteries applications, e.g. , EC:DMC (1:1) and EC:DMC:PC(1:1:3). MD is a very powerful tool and has allowed us to clarify the relevance of the cluster structures discovered by DFT when the ion is surrounded by bulk solvents. Indeed, DFT provides information about the most stable structures of isolated clusters but no information about their stability or multiplicity (entropy) when immersed in an infinite solvent environment. The MD data, together the DFT calculations have allowed us to give a very comprehensive picture of the local structure of solvent mixtures around Lithium ion, which substantially improve over previous work.En raison de l'augmentation de la demande d'énergie, ressources écologiques respectueux de l'environnement et durables (solaires, éoliennes) doivent être développées afin de remplacer les combustibles fossiles. Ces sources d'énergie sont discontinues, étant corrélés avec les conditions météorologiques et leur disponibilité est fluctuant dans le temps. En conséquence, les dispositifs de stockage d'énergie à grande échelle sont devenus incontournables, pour stocker l'énergie sur des échelles de temps longues avec une bonne compatibilité environnementale. La conversion d'énergie électrochimique est le mécanisme clé pour les développements technologiques des sources d'énergie alternatives. Parmi ces systèmes, les batteries Lithium-ion (LIB) ont démontré être les plus robustes et efficaces et sont devenus la technologie courante pour les systèmes de stockage d'énergie de haute performance. Ils sont largement utilisés comme sources d'énergie primaire pour des applications populaires (ordinateurs portables, téléphones cellulaires, et autres). La LIB typique est constitué de deux électrodes, séparés par un électrolyte. Celui-ci joue un rôle très important dans le transfert des ions entre les électrodes fournissant la courante électrique. Ce travail de thèse porte sur les matériaux complexes utilisés comme électrolytes dans les LIB, qui ont un impact sur les propriétés de transport du ion Li et les performances électrochimiques. Habituellement l'électrolyte est constitué de sels de Li et de mélanges de solvants organiques, tels que les carbonates cycliques ou linéaires. Il est donc indispensable de clarifier les propriétés structurelles les plus importantes, et leurs implications sur le transport des ions Li+ dans des solvants purs et mixtes. Nous avons effectué une étude théorique basée sur la théorie du fonctionnelle densité (DFT) et la dynamique moléculaire (MD), et nous avons consideré des carbonates cyclique (carbonate d'éthylène, EC, et carbonate de propylène, PC) et le carbonate de diméthyle, DMC, linéaire. Les calculs DFT ont fourni une image détaillée des structures optimisées de molécules de carbonate et le ion Li+, y compris les groupes pures Li+(S)n (S =EC,PC,DMC et n=1-5), groupes mixtes binaires, Li+(S1)m(S2)n (S1,S2=EC,PC,DMC, m+n=4), et ternaires Li+(EC)l(DMC)m(PC)n (l+m+n=4). L'effet de l'anion PF6 a également été étudié. Nous avons aussi étudié la structure de la couche de coordination autour du Li+, dans tous les cas. Nos résultats montrent que les complexes Li+(EC)4, Li+(DMC)4 et Li+(PC)3 sont les plus stables, selon les valeurs de l'énergie libre de Gibbs, en accord avec les études précédentes. Les énergies libres de réactions calculés pour les mélanges binaires suggèrent que l'ajout de molécules EC et PC aux clusters Li+ -DMC sont plus favorables que l'addition de DMC aux amas Li+-EC et Li+-PC. Dans la plupart des cas, la substitution de solvant aux mélanges binaires sont défavorables. Dans le cas de mélanges ternaires, la molécule DMC ne peut pas remplacer EC et PC, tandis que PC peut facilement remplacer EC et DMC. Notre étude montre que PC tend à substituer EC dans la couche de solvation. Nous avons complété nos études ab-initio par des simulations MD d'une ion Li immergé dans les solvants purs et dans des mélanges de solvants d'intérêt pour les batteries, EC:DMC(1: 1) et EC:DMC:PC(1:1:3). MD est un outil très puissant et nous a permis de clarifier la pertinence des structures découvertes par DFT lorsque le ion est entouré par des solvants mélangés. En effet,la DFT fournit des informations sur les structures les plus stables de groupes isolés, mais aucune information sur leur stabilité ou de la multiplicité (entropie) lorsqu'il est immergé dans un environnement solvant infinie. Les données MD, ainsi que les calculs DFT nous ont permis de donner une image très complète de la structure locale de mélanges de solvants autour le ion lithium, sensiblement amélioré par rapport aux travaux précédents

Etude théorique et numérique de l'interaction des ions lithium dans les solvants carbonates et leurs mélanges

Due to the increasing global energy demand, eco-friendly and sustainable green resources including solar, or wind energies must be developed, in order to replace fossil fuels. These sources of energy are unfortunately discontinuous, being correlated with weather conditions and their availability is therefore strongly fluctuating in time. As a consequence, large-scale energy storage devices have become fundamental, to store energy on long time scales with a good environmental compatibility. Electrochemical energy conversion is the key mechanism for alternative power sources technological developments. Among these systems, Lithium-ion (Li+) batteries (LIBs) have demonstrated to be the most robust and efficient, and have become the prevalent technology for high-performance energy storage systems. These are widely used as the main energy source for popular applications, including laptops, cell phones and other electronic devices. The typical LIB consists of two (negative and positive) electrodes, separated by an electrolyte. This plays a very important role, transferring ions between the electrodes, therefore providing the electrical current. This thesis work focuses on the complex materials used as electrolytes in LIBs, which impact Li-ion transport properties, power densities and electrochemical performances. Usually, the electrolyte consists of Li-salts and mixtures of organic solvents, such as cyclic or linear carbonates. It is therefore indispensable to shed light on the most important structural (coordination) properties, and their implications on transport behaviour of Li+ ion in pure and mixed solvent compositions. We have performed a theoretical investigation based on combined density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations, and have focused on three carbonates, cyclic ethylene carbonate (EC) and propylene carbonate (PC), and linear dimethyl carbonate (DMC). DFT calculations have provided a detailed picture for the optimized structures of isolated carbonate molecules and Li+ ion, including pure clusters Li+(S)n (S=EC, PC, DMC and n=1-5), mixed binary clusters, Li+(S1)m(S2)n (S1, S2 =EC, PC, DMC, with m+n=4), and ternary clusters Li+(EC)l(DMC)m(PC)n with l+m+n=4. Pure solvent clusters were also studied including the effect of PF6- anion. We have investigated in details the structure of the coordination shell around Li+ for all cases. Our results show that clusters such as Li+(EC)4, Li+(DMC)4 and Li+(PC)3 are the most stable, according to Gibbs free energy values, in agreement with previous experimental and theoretical studies. The calculated Gibbs free energies of reactions in binary mixtures suggest that the addition of EC and PC molecules to the Li+-DMC clusters are more favourable than the addition of DMC to Li+-EC and Li+-PC clusters. In most of the cases, the substitution of solvent to binary mixtures are unfavourable. In the case of ternary mixtures, the DMC molecule cannot replace EC and PC, while PC can easily substitute both EC and DMC molecules. Our study shows that PC tends to substitute EC in the solvation shell. We have complemented our ab-initio studies by MD simulations of a Li-ion when immersed in the pure solvents and in particular solvents mixtures of interest for batteries applications, e.g. , EC:DMC (1:1) and EC:DMC:PC(1:1:3). MD is a very powerful tool and has allowed us to clarify the relevance of the cluster structures discovered by DFT when the ion is surrounded by bulk solvents. Indeed, DFT provides information about the most stable structures of isolated clusters but no information about their stability or multiplicity (entropy) when immersed in an infinite solvent environment. The MD data, together the DFT calculations have allowed us to give a very comprehensive picture of the local structure of solvent mixtures around Lithium ion, which substantially improve over previous work.En raison de l'augmentation de la demande d'énergie, ressources écologiques respectueux de l'environnement et durables (solaires, éoliennes) doivent être développées afin de remplacer les combustibles fossiles. Ces sources d'énergie sont discontinues, étant corrélés avec les conditions météorologiques et leur disponibilité est fluctuant dans le temps. En conséquence, les dispositifs de stockage d'énergie à grande échelle sont devenus incontournables, pour stocker l'énergie sur des échelles de temps longues avec une bonne compatibilité environnementale. La conversion d'énergie électrochimique est le mécanisme clé pour les développements technologiques des sources d'énergie alternatives. Parmi ces systèmes, les batteries Lithium-ion (LIB) ont démontré être les plus robustes et efficaces et sont devenus la technologie courante pour les systèmes de stockage d'énergie de haute performance. Ils sont largement utilisés comme sources d'énergie primaire pour des applications populaires (ordinateurs portables, téléphones cellulaires, et autres). La LIB typique est constitué de deux électrodes, séparés par un électrolyte. Celui-ci joue un rôle très important dans le transfert des ions entre les électrodes fournissant la courante électrique. Ce travail de thèse porte sur les matériaux complexes utilisés comme électrolytes dans les LIB, qui ont un impact sur les propriétés de transport du ion Li et les performances électrochimiques. Habituellement l'électrolyte est constitué de sels de Li et de mélanges de solvants organiques, tels que les carbonates cycliques ou linéaires. Il est donc indispensable de clarifier les propriétés structurelles les plus importantes, et leurs implications sur le transport des ions Li+ dans des solvants purs et mixtes. Nous avons effectué une étude théorique basée sur la théorie du fonctionnelle densité (DFT) et la dynamique moléculaire (MD), et nous avons consideré des carbonates cyclique (carbonate d'éthylène, EC, et carbonate de propylène, PC) et le carbonate de diméthyle, DMC, linéaire. Les calculs DFT ont fourni une image détaillée des structures optimisées de molécules de carbonate et le ion Li+, y compris les groupes pures Li+(S)n (S =EC,PC,DMC et n=1-5), groupes mixtes binaires, Li+(S1)m(S2)n (S1,S2=EC,PC,DMC, m+n=4), et ternaires Li+(EC)l(DMC)m(PC)n (l+m+n=4). L'effet de l'anion PF6 a également été étudié. Nous avons aussi étudié la structure de la couche de coordination autour du Li+, dans tous les cas. Nos résultats montrent que les complexes Li+(EC)4, Li+(DMC)4 et Li+(PC)3 sont les plus stables, selon les valeurs de l'énergie libre de Gibbs, en accord avec les études précédentes. Les énergies libres de réactions calculés pour les mélanges binaires suggèrent que l'ajout de molécules EC et PC aux clusters Li+ -DMC sont plus favorables que l'addition de DMC aux amas Li+-EC et Li+-PC. Dans la plupart des cas, la substitution de solvant aux mélanges binaires sont défavorables. Dans le cas de mélanges ternaires, la molécule DMC ne peut pas remplacer EC et PC, tandis que PC peut facilement remplacer EC et DMC. Notre étude montre que PC tend à substituer EC dans la couche de solvation. Nous avons complété nos études ab-initio par des simulations MD d'une ion Li immergé dans les solvants purs et dans des mélanges de solvants d'intérêt pour les batteries, EC:DMC(1: 1) et EC:DMC:PC(1:1:3). MD est un outil très puissant et nous a permis de clarifier la pertinence des structures découvertes par DFT lorsque le ion est entouré par des solvants mélangés. En effet,la DFT fournit des informations sur les structures les plus stables de groupes isolés, mais aucune information sur leur stabilité ou de la multiplicité (entropie) lorsqu'il est immergé dans un environnement solvant infinie. Les données MD, ainsi que les calculs DFT nous ont permis de donner une image très complète de la structure locale de mélanges de solvants autour le ion lithium, sensiblement amélioré par rapport aux travaux précédents

Stabilità della cellulosa nel cluster di acqua- approfondimento della teoria del funzionale della densità e della spettroscopia infrarossa

A conference abstract from NIRItalia online 2021 in English and Italian.The authors gratefully acknowledge the European Commission for funding the InnoRenew project (grant agreement #739574) under the Horizon2020 Widespread-Teaming program and the Republic of Slovenia (investment funding of the Republic of Slovenia and the European Union European Regional Development Fund)

Revealing of supercritical water gasification process of lignin by reactive force field molecular dynamics simulations

Gasification with supercritical water is an efficient process that can be used for the valorization of biomass. Lignin is the second most abundant biopolymer in biomass and its conversion is fundamental for future energy and value-added chemicals. In this paper, the supercritical water gasification process of lignin by employing reactive force field molecular dynamics simulations (ReaxFF MD) was investigated. Guaiacyl glycerol-β-guaiacyl ether (GGE) was considered as a lignin model to evaluate the reaction mechanism and identify the components at different temperatures from 1000 K to 5000 K. The obtained results revealed that the reactions and breaking of the lignin model started at 2000 K. At the primary stage of the reaction at 2000 K the β-O-4 bond tends to break into several compounds, forming mainly guaiacol and 1,3-benzodioxole. In particular, 1,3-benzodioxole undergoes dissociation and forms cyclopentene-based ketones. Afterward, dealkylation reaction occurred through hydroxyl radicals of water to form methanol, formaldehyde and methane. Above 2500 K, H2, CO and CO2 are predominantly formed in which water molecules contributed hydrogen and oxygen for their formation. Understanding the detailed reactive mechanism of lignin’s gasification is important for efficient energy conversion of biomass

Solvent and Salt Effect on Lithium Ion Solvation and Contact Ion Pair Formation in Organic Carbonates: A Quantum Chemical Perspective

Quantum chemical calculations have been employed to investigate the solvation of lithium cations in ethylene carbonate/propylene carbonate and propylene carbonate/dimethyl carbonate mixed electrolytes. The impact of the presence of the counteranion on the solvation of Li⁺ in pure propylene carbonate and dimethyl carbonate was also studied. The calculations revealed small free-energy changes for the transitions between different preferred structures in mixed solvents. This implies that transitions between distinct local arrangements can take place in the mixtures. The addition of dimethyl carbonate causes a significant increase of the dipole moment of solvation clusters, indicating important molecular-scale modifications when dimethyl carbonate is used as a co-solvent. The presence of an anion in the solvation shell of Li⁺ modifies the intermolecular structure comprising four carbonate molecules in dilute solutions, allowing only two carbonate molecules to coordinate to Li⁺. The bidentate complexation of Li⁺ with the anion’s electron donor atoms, however, maintains the local tetrahedral structure on interatomic length scales. The neutralization of the solvation shell of Li⁺ due to contact ion pair formation and the consequent implications on the underlying mechanisms provide a rational explanation for the ionic conductivity drop of electrolyte solutions at high salt concentrations