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Na‐ion batteries based on abundant and sustainable materials might become one of the leading alternative technologies especially suitable for large‐scale stationary storage. Various (mixed)phosphate framework materials are attracting much interest mainly due to their high structural stability and diversity. In this study, we report on the successful synthesis of mixed phosphate‐pyrophosphate Na7V4(PO4)(P2O7)4, Na4Fe3(PO4)2P2O7, and Na4Mn3(PO4)2P2O7. The electrochemical properties of these materials are comprehensively characterized in different organic and aqueous electrolytes. The findings reveal that Na7V4(PO4)(P2O7)4 and Na4Fe3(PO4)2P2O7 exhibit very good cycling performance and rate capability in organic solvent‐based electrolytes. However, their performance deteriorates significantly even in 'water‐in‐salt' aqueous electrolytes due to the rapid electrochemical degradation. Na4Mn3(PO4)2P2O7 demonstrates limited electrochemical activity in organic electrolytes and virtually no activity in 'water‐in‐salt' electrolytes, likely due to degradation processes resulting in blocking interphasial layers on electrode particles. These results underscore the need for further research to optimize the performance of these materials and identify potential strategies for enhancing their stability and activity in different electrolytes. [ABSTRACT FROM AUTHOR]

Due to their stability and structural freedom, NASICON-structured materials such as NaTi2(PO4)3 show a lot of promise as active electrode materials for aqueous batteries and deionization cells. However, due to their low intrinsic electronic conductivity, they must usually be composited with carbon to form suitable electrodes for power applications. In this work, two series of NaTi2(PO4)3–carbon composite structures were successfully prepared by different approaches: postsynthetic pyrolytic treatment of citric acid and surface polymerized dopamine. The latter route allows for a superior carbon loading control and yields more uniform and continuous particle coatings. The homogeneity of the polydopamine derived core–shell carbon layer is supported by FTIR, TEM, and XPS analysis. Combustion elemental analysis also indicates significant nitrogen doping in the final carbonaceous structure. The galvanostatic charge and discharge cycling results show similar initial capacities and their retention, but at only half of the carbon loading in polydopamine derived samples. The overall results indicate that careful nanostructure engineering could yield materials with superior properties and stability suitable for various electrochemical applications such as aqueous Na-ion batteries and deionization cells. [ABSTRACT FROM AUTHOR]

In this work, the electronic structure and properties of NASICON-structured A4V2(PO4)3, where A = Li, Na, K were studied using hybrid density functional theory calculations. The symmetries were analyzed using a group theoretical approach, and the band structures were examined by the atom and orbital projected density of states analyses. Li4V2(PO4)3 and Na4V2(PO4)3 adopted monoclinic structures with the C 2 space group and averaged vanadium oxidation states of V + 2.5 in the ground state, whereas K4V2(PO4)3 adopted a monoclinic structure with the C 2 space group and mixed vanadium oxidation states V + 2 /V + 3 in the ground state. The mixed oxidation state is the least stable state in Na4V2(PO4)3 and Li4V2(PO4)3. Symmetry increases in Li4V2(PO4)3 and Na4V2(PO4)3 led to the appearance of a metallic state that was independent of the vanadium oxidation states (except for the averaged oxidation state R 32 Na4V2(PO4)3). On the other hand, K4V2(PO4)3 retained a small band gap in all studied configurations. These results might provide valuable guidance for crystallography and electronic structure investigations for this important class of materials. [ABSTRACT FROM AUTHOR]

Aqueous Na-ion batteries are deemed to be among the most suitable candidates for future large-scale stationary energy storage systems. However, there are still a number of problems to be solved before their full potential can be utilized such as instability of the aqueous electrolyte/electrode interface towards electrolyte decomposition, chemical dissolution, and other side reactions. The mechanism of electrochemically induced degradation in NASICON-structured NaTi2(PO4)3 is studied in detail using various chemical and electrochemical techniques. The results unambiguously show that irreversible capacity fade, especially severe at low charging rates, is an electrochemically induced chemical dissolution of the active material. The oxygen reduction induced self-discharge reaction leading to a local pH increase is indicated as the main culprit for the material degradation and capacity loss during charge–discharge cycling. Although the degradation products form an insoluble Ti-rich interphasial layer similar to non-aqueous solid-electrolyte interphases, in this case it is shown to be insufficient for providing even kinetic stability of the electrochemical interface. Artificial protective layers applied using atomic layer deposition of Al2O3 directly on the electrode surface are shown to be a simple and scalable approach to significantly stabilize the electrodes towards oxygen attack and limit the rate of negative electrode degradation. The new understanding of irreversible degradation and its mitigation techniques presented in this work offer a pathway to viable and scalable strategies that enable and exploit the high-performance potential of this and many other aqueous battery materials. [ABSTRACT FROM AUTHOR]

Aqueous Na-ion based batteries are considered promising candidates for replacing Li-ion technologies, especially in the area of stationary energy storage. Research and development of novel electrode materials remain a central research effort in this field. NASICON-structured NaTi2(PO4)3 phosphate framework has attracted a great deal of attention and remains the most studied negative electrode material for aqueous Na-ion batteries. The active material preparation and carbon composite property tailoring play a critical role in the electrode materials engineering process which governs the performance of an entire electrochemical system. We present a study of a series of aqueous sol-gel synthesized NaTi2(PO4)3--carbon composites using three different solgel approaches and three distinct pyrolysis/calcination strategies. The structural and morphological analysis shows that both the sol-gel route as well as the thermal treatment strategy have significant effects on active material purity and degree of crystallinity as well as the content and properties of the carbonaceous phase. Electrochemical investigations of these composites also show strong effects of the materials structure and carbon matrix morphology on the electrochemical performance and degradation of these materials when employed as aqueous Na-ion battery negative electrodes. [ABSTRACT FROM AUTHOR]

Sodium Super Ionic Conductor (NASICON) structured phosphate framework compounds represent a very attractive class of materials for their use as Na-ion battery electrodes. A series of NASICON-structured NaxTi2(PO4)3 compounds corresponding to varying degrees of sodiation (x = 1–4) have been investigated using high-level hybrid density functional theory calculations using the Linear Combination of Atomic Orbitals and Gaussian-type basis set formalism together with hybrid B1WC and HSE06 exchange–correlation functionals. Using primitive cells of NaxTi2(PO4)3 compounds with different stoichiometry, sodium sublattice structure and titanium oxidation states are constructed and analyzed using group theoretical symmetry considerations. The existence of mixed titanium oxidation states for x = 4 (Ti2+/Ti3+) and x = 2 (Ti3+/Ti4+) and a single oxidation state for x = 1 (Ti4+) and x = 3 (Ti3+) has been demonstrated. The results show a necessary set of symmetry reductions taking place due to the highest possible sodium/vacancy and titanium charge ordering with changing x. For each composition, an electroneutrality condition for the oxidation states of all atoms was applied which led to the discovery of several energy minima corresponding to different electronic configurations as identified by different Ti magnetic moments. An interesting relation between the bulk electronic properties of NaxTi2(PO4)3 compounds and the variation of sodium content was also found. In addition to sodium and titanium oxidation state charge ordering, the existence of large differences between the origin and the size of the band gap is shown. The band gap changes from the 4.05 eV 2p–3d gap in Na1Ti2(PO4)3 to the 0.59 eV 3d–3d gap in Na4Ti(PO4)3 with extra states due to mixed titanium valence. These results serve as an important electronic structure benchmark for further studies of such polyanion materials and help to explain some important properties of these systems relevant to battery applications. [ABSTRACT FROM AUTHOR]

The indications of peculiar multiferroic behavior of dimethylammonium metal-formate perovskite frameworks raised important questions about the origin of the structural phase transition, structural phases and dipolar dynamics in these compounds. Here we provide answers on some of these phenomena by presenting a comprehensive experimental and theoretical study of the [(CH3)2NH2][Zn(HCOO)3] framework. Broadband dielectric spectroscopy assisted by molecular dynamics simulations allows us to probe the dipolar relaxation dynamics in both structural phases on an extensive time scale. The results of dielectric spectroscopy are complemented by non-linear dielectric susceptibility, electric field dependent and ultrasonic experiments. Contrary to a prevailing notion, we clearly demonstrate that the [(CH3)2NH2][Zn(HCOO)3] perovskite is not a relaxor material and raise serious doubts about its proper ferroelectric nature. [ABSTRACT FROM AUTHOR]

Electrolyte and electrode materials used in lithium-ion batteries have been studied separately to a great extent, however the structural and dynamical properties of the electrolyte–electrode interface still remain largely unexplored despite its critical role in governing battery performance. Using molecular dynamics simulations, we examine the structural reorganization of solvent molecules (cyclic ethylene carbonate : linear dimethyl carbonate 1 : 1 molar ratio doped with 1 M LiPF6) in the vicinity of graphite electrodes with varying surface charge densities (σ). The interfacial structure is found to be sensitive to the molecular geometry and polarity of each solvent molecule as well as the surface structure and charge distribution of the negative electrode. We also evaluated the potential difference across the electrolyte–electrode interface, which exhibits a nearly linear variation with respect to σ up until the onset of Li+ ion accumulation onto the graphite edges from the electrolyte. In addition, well-tempered metadynamics simulations are employed to predict the free-energy barriers to Li+ ion transport through the relatively dense interfacial layer, along with analysis of the Li+ solvation sheath structure. Quantitative analysis of the molecular arrangements at the electrolyte–electrode interface will help better understand and describe electrolyte decomposition, especially in the early stages of solid-electrolyte-interphase (SEI) formation. Moreover, the computational framework presented in this work offers a means to explore the effects of solvent composition, electrode surface modification, and operating temperature on the interfacial structure and properties, which may further assist in efforts to engineer the electrolyte–electrode interface leading to a SEI layer that optimizes battery performance. [ABSTRACT FROM AUTHOR]

AMP and its blends are an attractive solvent for CO2 capture, but the underlying reaction mechanisms still remain uncertain. We attempt to elucidate the factors enhancing bicarbonate production in aqueous AMP as compared to MEA which, like most other primary amines, preferentially forms carbamate. According to our predicted reaction energies, AMP and MEA exhibit similar thermodynamic favorability for bicarbonate versus carbamate formation; moreover, the conversion of carbamate to bicarbonate also does not appear more favorable kinetically in aqueous AMP compared to MEA. Ab initio molecular dynamics simulations, however, demonstrate that bicarbonate formation tends to be kinetically more probable in aqueous AMP while carbamate is more likely to form in aqueous MEA. Analysis of the solvation structure and dynamics shows that the enhanced interaction between N and H2O may hinder CO2 accessibility while facilitating the AMP + H2O → AMPH+ + OH− reaction, relative to the MEA case. This study highlights the importance of not only thermodynamic but also kinetic factors in describing CO2 capture by aqueous amines. [ABSTRACT FROM AUTHOR]

Na-ion batteries are deemed to be promising candidates for the future sustainable stationary energy storage systems. However, there is still a number of issues to be solved before their full potential could be utilized. In addition to finding suitable electrode materials there are also issues related to the stability of the aqueous electrolyte/electrode interface. Some of our recent contributions in terms of understanding and enabling of phosphate framework materials for the use in aqueous Na-ion batteries will be reviewed. The thermodynamic limitations in terms of phase formation, electrochemical stability issues and the origin of these effects in NASICON-structured Na1+2xMnTi2-x(PO4)3 (0.0 < x < 1.5) and Na3-xV2-xTix(PO4)3 (0.0 < x < 1.0) and several other phosphates systems as potential cathode materials for aqueous Na-ion batteries will be covered and discussed in detail [1-4]. [ABSTRACT FROM AUTHOR]

We study the temperature-dependent dynamical processes of a Si10H16 cluster and obtain a blue shift of the Si-Si vibrational modes with transverse acoustic character and a red shift of the other vibrational modes with increasing temperature. We link this behavior to the bond length expansion and the varying sign of the Grüneisen parameter. We further present a computational approach able to extract the vibron-vibron coupling strength in clusters or molecules. Our approach is based on ab initio Born-Oppenheimer molecular dynamics and a projection formalism able to deliver the individual vibron occupation numbers. From the Fourier transform of the vibron energy autocorrelation function, we obtain the coupling strength of each vibron to the most strongly coupled vibronic states. We find the vibron-vibron coupling strength up to 2.5 THz with a moderate increase of about 5% when increasing the temperature from 50 to 150 K. [ABSTRACT FROM AUTHOR]

Abstract: From a fundamental point of view, the family of compounds known as phosphorus oxoacids is among the most intriguing proton conducting systems. Two of its members, phosphoric (H3PO4) and phosphonic (H3PO3) acid, show the highest known intrinsic proton conductivities. However, little is known about the last member, phosphinic acid (H3PO2), that completes this series and could provide a fundamental insight into the relationship between proton transport and the other properties of the hydrogen bond network. Here we present the results of a proton conductivity and diffusion study of molten nominally dry phosphinic acid (H3PO2) by 1H PFG-NMR (Pulsed Magnetic Field Gradient Nuclear Magnetic Resonance) and AC impedance spectroscopy. While the general features of proton transport in H3PO2 share some similarities to those of H3PO4 and H3PO3, there are also important differences between these systems. The intrinsic conductivity is found to arise primarily, from the vehicular diffusion of protonic charge carriers that form as a result of the relatively high degree of self-dissociation (~3.5–4.75%). Nevertheless, the experimentally measured diffusion coefficients of the exchangeable protons are ~10% higher than the molecular diffusion coefficients, and assuming that the correlations in the structural diffusion of protonic charge carriers are slightly higher (Haven ratio in the range of ~2–3.5), this results in ~21–38% of the total conductivity coming from structural diffusion. [Copyright &y& Elsevier]

Due to their stability and structural freedom, NASICON-structured materials such as NaTi 2 (PO 4 ) 3 show a lot of promise as active electrode materials for aqueous batteries and deionization cells. However, due to their low intrinsic electronic conductivity, they must usually be composited with carbon to form suitable electrodes for power applications. In this work, two series of NaTi 2 (PO 4 ) 3 -carbon composite structures were successfully prepared by different approaches: postsynthetic pyrolytic treatment of citric acid and surface polymerized dopamine. The latter route allows for a superior carbon loading control and yields more uniform and continuous particle coatings. The homogeneity of the polydopamine derived core-shell carbon layer is supported by FTIR, TEM, and XPS analysis. Combustion elemental analysis also indicates significant nitrogen doping in the final carbonaceous structure. The galvanostatic charge and discharge cycling results show similar initial capacities and their retention, but at only half of the carbon loading in polydopamine derived samples. The overall results indicate that careful nanostructure engineering could yield materials with superior properties and stability suitable for various electrochemical applications such as aqueous Na-ion batteries and deionization cells., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)