Although vanadium-containing phosphates with the NASICON-related structure are promising cathode materials for lithium-ion batteries, the issues of structural degradation associated with the complete extraction of Li+ and/or complete oxidation of vanadium remain unclear. Here, we present novel monoclinic (m-LVScP) and rhombohedral (r-LVScP) polymorphs of Li3VSc(PO4)(3) as model objects to study structural transformations occurring upon oxidation and reduction of vanadium cations. The structure of m-LVScP obtained by direct high-temperature synthesis belongs to the anti-NASICON type. Ion Li+ -> Na+ exchange from NASICON type Na3VSc(PO4)(3) leads to the formation of the rhombohedral polymorph of Li3VSc(PO4)(3) and is accompanied by a strong distortion of the NASICON type polyanion framework. The BVSE study of Li-3(V,Sc)(2)(PO4)(3) indicates faster diffusion of Li+ ions within the anti-NASICON framework; moreover, the activation energy of cation migration in the substituted phase m-Li3VSc(PO4)(3) is lower than that of the corresponding non-substituted vanadium and scandium phosphates. Carbon-coated m-LVScP and r-LVScP demonstrate a specific capacity up to similar to 175 mA h g(-1) which corresponds to a complete three-electron V2+/V3+/V4+/V5+ process within the voltage range of 1-4.65 V vs. Li/Li+, following a predominantly solid-solution mechanism, as shown by operando and ex situ powder X-ray diffraction. Electrochemical and chemical deintercalation of 2Li(+) per formula unit from m-LVScP and r-LVScP results in the formation of a short V5+ = O bond, revealed by V-51 NMR and Fourier-transformed infrared spectroscopy. This is accompanied by strong distortion of the frameworks, which impedes the complete reversibility of the phase transformations and leads to capacity degradation during long time cycling.

С 4 по 10 июля 2025 г. в Республике Бурятия (4–5 июля в г. Улан-Удэ, 6–10 июля на побережье оз. Байкал в с. Горячинск) прошла одна из крупнейших национальных профильных конференций – Всероссийская научная конференция с международным участием «ПЯТЫЙ БАЙКАЛЬСКИЙ МАТЕРИАЛОВЕДЧЕСКИЙ ФОРУМ» (БФМ-2025). Цели БМФ-2025 – осуществить анализ состояния научных исследований в области материаловедения и наметить стратегические направления их развития, способствовать преемственности поколений ученых-материаловедов и интеграции высшего образования, фундаментальной и прикладной науки. Основные задачи Форума – обсудить фундаментальные и прикладные проблемы материаловедения, представить последние достижения в данной области, выявить наиболее перспективные работы, в том числе проводимые молодыми учеными, способствовать творческому общению специалистов и ученых, углублению связей между учеными Сибирского региона и центральной России, стимулировать распространение научных знаний и повышение престижа науки.

Hybrid anode-less sodium metal batteries are a promising high-energy-density technology. Carbon-based electrodes have often been studied both as favorable substrates for sodium electrodeposition and as potential intercalation-type anode materials. However, the mechanism governing sodium plating morphology and its impact on performance remain poorly understood. In this study, we leveraged a combination of electrochemical methods, such as electrochemical impedance spectroscopy and distribution of relaxation time analysis, with ex situ scanning electron microscopy and in situ optical microscopy to shed light on sodium electroplating features. By carrying out the experiments across a wide range of current densities (from C/10 to C) and plating capacities (from 100 % to 400 % of the insertion capacity), we proposed a current-density-dependent mechanism for sodium electrodeposition on hard carbon. Key novelties include the identification of four distinct stages - insertion, nucleation, plating on hard carbon surface, and plating on sodium grains - with competing processes at high currents leading to altered morphologies and enhanced reversibility. Moreover, we demonstrated that by electroplating far beyond intercalation the reversible capacity of hard carbon could be tripled, highlighting a previously unreported performance gain. The results provide mechanistic insight into the behavior of sodium metal during plating, which can inform new strategies for controllable sodium electrodeposition in hybrid sodium-ion/ metal batteries with extended capacity and energy density.

The A(x)(Nb,M-III)(2)(PO4)(3) phosphates with NASICON-related structures have been the subject of intense study as potential hosts for the reversible intercalation of alkali metal ions due to their rigid polyanionic framework, which ensures rapid A(+) cation diffusion, and the ability of niobium to undergo the Nb5+/Nb4+/Nb3+ multielectron redox transitions. In this article, we have employed the sol-gel technique to synthesize the M0.5Nb1.5(PO4)(3) (M=Al, Cr, Sc) phosphates that lack an A-cation, and explored their structural features and electrochemical performance. We found a close similarity in the energy between the NASICON and anti-NASICON polymorphs, with a stability preference calculated by density functional theory being <0.6 kJ & centerdot;mol(-1). This results in a coherent intergrowth of domains from both polymorphs in the M0.5Nb1.5(PO4)(3) (M=Al, Cr, Sc) samples, as observed by X-ray powder diffraction and transmission electron microscopy. The bond valence site energy calculations revealed the emergence of a sodium ion migration barrier at the NASICON/anti-NASICON interface, which is significantly higher than either within the NASICON or anti-NASICON frameworks individually. The obtained M0.5Nb1.5(PO4)(3) (M=Al, Cr, Sc) phosphates demonstrate reversible sodium intercalation through niobium multielectron reactions rendering an initial capacity of 140-150 mAh & centerdot;g(-1), however, the hindered migration of alkali ions deteriorates their cycling performance. These findings contribute to our understanding of the stability of NASICON-related frameworks and their ability to accommodate alkali metal ions.

The NaNbTi(PO4)3 material with the NASICON structure (space group R3-c) was prepared by the Pechini-type technique followed by spark plasma sintering. XANES measurements revealed mixed-valence states of niobium (Nb5+/4+) and titanium (Ti4+/3+). The material exhibits reversible electrochemical intercalation of about 1.67 Na+ per formula unit at a C/10 rate, with a gradual decrease in capacity, which could be attributed to the mixing of Na+ and Ti3+ cations in the structure.

In solvothermal synthesis, LiMnPO 4 (LMP) forms smaller particles than LiFePO 4 (LFP). Besides, the particle size of LMP is much less dependent on the solvent type. These effects are primarily attributed to the stability of the particle dispersions.

The charge storage mechanism of hard carbon anode materials in sodium-ion batteries remains a highly debated topic. Although multiple models have been proposed, their accuracy is still limited, underscoring the need for a deeper investigation. Our study explores the processes behind charge storage using operando powder X-ray diffraction, ex situ small-angle and wide-angle X-ray scattering, operando Raman spectroscopy, and ex situ scanning transmission electron microscopy with integrated differential phase contrast imaging. We propose that the exceptional electrochemical performance of hard carbon compared to graphite can be attributed to its curvature-a unique microstructural feature that promotes a high density of defects with electron-withdrawing properties. To demonstrate the significant role of curvature in hard carbon performance, we computationally analyze sodium adsorption using density functional theory. Our experimental and computational findings provide empirical evidence of changes in curvature and the interlayer spacing during the charge-discharge cycle. By revisiting previous findings, we aim to address long-standing issues in understanding charge storage mechanism in hard carbon materials.

Increasing interest in sodium-ion batteries (SIBs) implementation leads to investigation and optimization of different sodium-based cathode materials. Sodium-iron phosphate-pyrophosphate Na4Fe3(PO4)2(P2O7) (NFPP) is a promising cathode material due to its low cost, safety, stability, non-toxicity and relatively high Fe3+/Fe2+ redox potential value. One of the significant problems related to synthesis of NFPP is formation of impurity phases-NaFePO4 and Na2FeP2O7, which leads to degradation of materials electrochemical performance. The correct identification and estimation of electrochemical activity of impurity phases is a crucial task for further development of synthetic routes for NFPP-based cathode materials. Herein we suggest a novel approach to identification and quantitative estimation of peculiar phase activity in multiphase NFPP-based cathode materials using electrochemical data. The approach is based on comparing experimentally obtained galvanostatic curves with model galvanostatic curves derived from quantitative phase analysis based on Rietveld refinement of the powder X-ray diffraction data. Implementation of such approach allowed us to distinguish the contribution of NFPP, NaFePO4 and Na2FeP2O7 phases into galvanostatic discharge curves profile. Furthermore, the conditions for synthesizing NFPP with optimal electrochemical properties were established, providing a pathway for the development of high-performance NFPP cathodes.

Phosphate-based cathode materials represent a major class of compounds used in the manufacturing of low-cost and safe lithium-ion batteries (LIBs). A significant challenge in this field is developing scalable and cost-effective synthesis routes that yield battery-grade materials meeting industrial standards. This study addresses this challenge by focusing on reagent selection for the hydrothermal synthesis of near-commercial-grade phosphate cathodes. Specifically, we used hematite-type iron oxide (alpha-Fe2O3) and pyrolusite-type manganese dioxide (beta-MnO2) as cost-effective and chemically stable sources of iron and manganese. We investigated phase evolution pathways by adjusting the reducing strength of complexing agents, including citric acid, ascorbic acid, oxalic acid, and ethylenediaminetetraacetic acid, as well as the reaction medium (water or ethylene glycol). This approach allowed us to identify crystallization routes leading to the formation of tavorite (LiFePO4(OH)), triphylite (LiFePO4), and lithiophilite (LiMnPO4). During hydrothermal treatment, the formation of LiFePO4 proceeded through sequential phase transformations from hematite to lipscombite and then triphylite. In addition, we showed that the synthesis conditions and phase transformation pathways were correlated with the resulting electrochemical properties, which explains the origin of the limited electrochemical activity. This study lays the groundwork for future research aimed at optimizing the production of high-performance phosphate-based cathode materials.

The development of stable solid electrolytes with fast ionic conductivity is essential for advancing all-solid-state metal-ion batteries, which provide higher energy density and improved safety compared to conventional metal-ion batteries. We present a combined theoretical and experimental study of NaGaPO4F, a new class of KTiOPO4-structured solid electrolytes. Electrochemical impedance spectroscopy measurements and large-scale machine learning-based molecular dynamics (MD) simulations reveal that the stoichiometric compound is a poor ionic conductor due to the relatively high formation energy of Na Frenkel pairs. However, quantum chemistry-based MD simulations uncover a mixed Na-ion diffusion mechanism involving single and concerted hopping, with an ultra-low activation barrier of 0.12-0.16 eV. The predicted room-temperature conductivity of similar to 0.01 S cm(-1) in the presence of extrinsic Na vacancies matches top superionic conductors. Our DFT calculations of dopant solubility indicate that aliovalent substitution of Na+ with Ba2+ and Ga3+ with Sn4+ is thermodynamically favorable, enabling the introduction of the required Na vacancy concentration and confirm the material's high oxidation potential. These results deepen the understanding of Na-ion conductivity in KTiOPO4-structured electrolytes.

Tungsten oxides and related compounds have been known as negative electrode materials for metal-ion batteries for decades. Despite their structural flexibility, most studies has largely focused on lithium-based energy storage systems. Here, we investigated KMxW2_xO6 (M = Ta, Nb, Ti, Cr, Al) oxides adopting a defect pyrochlore structure as intercalation-type anodes for potassium-ion batteries. Crystal structure, chemical composition, and thermal behavior of all representatives were comprehensively characterized. Electrochemical testing in K half-cells revealed average operating potentials of the considered pyrochlores to be in the range of-1.1-1.3 V vs. K+/ K, consistent with density functional theory predictions. The variation in the electrochemical performance among the KMxW2_xO6 was correlated with differences in electronic conductivity of M dopants, as validated by M density of states calculations. Through regression analysis of Rietveld-refined structural data, a strong linear dependence (rho =0.96) between the average intercalation potential of KMxW2_xO6 and the intrinsic parameters (ionic radius and electronegativity) of the M metal was established. This work not only advances fundamental understanding of tungsten-based oxygen-deficient pyrochlores but also paves the way for their development as potassium-ion intercalation hosts.

P2-Na-x[LiyMn1-y-z]O-2 (TM: Ni, Cu, Co, Fe) exhibits anionic redox reactions, and among these, the cost-effective Fe substitution has attracted significant attention to aid reasonable a promising material. However, we find that the dissolution and deposition of Fe present in the TM layer can cause detrimental effects, structural disintegration that affects capacity fading. Operando X-ray diffraction shows that the P2 phase of Na-0.6[Li0.15Fe0.15Mn0.7]O-2 is maintained during de/sodiation processes, and X-ray absorption analysis reveals the redox activity of Fe3+/Fe4+, Mn3+/Mn4+, and O2-/(O-2)(n-)redox pairs. Mossbauer spectroscopy provides insights into the behavior of Fe during de/sodiation, particularly in the two-electron oxidation process observed during charging, where the Fe3+/Fe4+ redox reaction simultaneously influences the oxidation of lattice oxygen, thereby aiding overall charge compensation during desodiation. These findings clarify the connection between this process and the redox activity of lattice oxygen. Additionally, Li-7 NMR is employed to analyze the migration of Li from the transition-metal layer to the Na layer, elucidating the anionic-redox-reaction mechanism. Notably, X-ray photoelectron spectroscopy and inductively coupled plasma-atomic emission spectroscopy analyses demonstrate Fe dissolution and subsequent deposition on the surface of anode, leading to capacity degradation and poor electrochemical performance. These findings underscore the significant impact of Fe dissolution and deposition on the performance of Na-0.6[Li0.15Fe0.15Mn0.7]O-2, highlighting the challenges associated with Fe doping in cathode materials for sodium-ion batteries.

The influence of electrolyte composition on the kinetics of electrocatalytic reactions was discussed in the seminal works of Frumkin. However, recent findings have reignited interest in the role of cations and pH in electrocatalysis, particularly in alkaline environments. Manganese oxides have attracted much attention as catalysts for both oxygen reduction and oxygen evolution reactions. In addition, some Mn oxides are promising materials for supercapacitors due to their high pseudocapacitance. In this work, we combine electrochemical measurements with microkinetic modeling to unveil the influence of pH and cation concentration on the interfacial recharging behavior of alpha-MnOOH, alpha-Mn2O3, and LaMnO3. Titration experiments revealed that the isoelectric point of manganese oxides is around 5, indicating that they are negatively charged in alkaline environments. Cyclic voltammetry showed that both OH- and Na+ concentrations influence the Mn(III)/Mn(IV) redox transition at the oxide-electrolyte interface, with distinct behaviors for alpha-MnOOH, alpha-Mn2O3, and LaMnO3. It is noteworthy that alpha-MnOOH exhibits two types of interfacial redox centers, protonated and cationic, which emphasize that the redox behavior is determined by ion-exchange equilibria.

Hydrothermal synthesis of LiFePO 4 without using the traditional three-fold lithium excess revealed unexpected alluaudite-triphylite phase transformation.

The NASICON-structured NaAlNb(PO4)3 phosphate was synthesized via Pechini sol-gel technique. Electrochemical measurements in sodium half-cells have disclosed that NaAlNb(PO4)3 can reversibly intercalate 2Na+ ions per formula unit owing to the Nb5+/Nb4+/Nb3+ multielectron redox processes, which was confirmed by the Nb K-edge XANES measurements. Differential thermal calorimetry has revealed an excellent thermal stability of the sodiated NaAlNb(PO4)3/C electrode material up to the point of electrolyte decomposition. E (vs. Na+/Na)/V 2.5 2.0 1.5 1.0 NaAlNb5+(PO4)3 + 2Na+ + 2e-(R) Na3AlNb3+(PO4)3 Nb5+/Nb4+ Nb4+/Nb3+ Capacity/mAh g-1 1.2 Normalized intensity (arbitrary units) 1.0 0.8 0.6 0.4 0.2 0.0 2 1 20 40 60 80 100 120 18950 18975 19000 19025 4 3 1 NaAlNb(PO4)3 2 Na3AlNb(PO4)3 3 Nb2O5 4 NbO2 Energy/eV

The precipitation method is an efficient, economically feasible, and reproducible synthetic route to cathode materials for lithium-ion batteries with attractive performance characteristics, in particular, lithium iron phosphate (LiFePO 4 ). This paper reviews the mechanisms of the key steps of the synthesis, namely, precipitation of iron phosphate FePO 4 followed by its sintering with a lithium-containing raw material to give the LiFePO 4 phase. The most probable interactions determining the kinetics of the precipitation process are considered using the data on the dissociation degree of the reacting components. The influence of the nature and concentrations of the commonly used sources of iron (FeSO 4 , FeCl 3 , Fe(NO 3 ) 3 ) and phosphorus (H 3 PO 4 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 ), as well as the precipitation conditions (pH, temperature) on the precipitation efficiency of FePO 4 is analyzed. The effect of the nature of the lithium-containing raw material (LiOH, Li 2 CO 3 , LiNO 3 ) and the sintering (calcination) temperature on the morphology, phase composition, and electrochemical properties of the resulting LiFePO 4 is discussed. The possibility is considered of obtaining spherical particles with high bulk density, which provides high specific and volumetric energy density of electrochemical cells. Based on the relationships established, optimal parameters for the synthesis of LiFePO 4 with preliminary FePO 4 precipitation step are proposed.

Because of the environmental benignity, abundance, and promising electrochemical properties of Ti-containing materials in batteries, these materials have been attracting the attention of the academic community. Herein, we report on KTiPO4F as a novel Ti-containing polyanionic negative electrode (anode) material with a robust framework structure, which is obtained via a facile hydrothermal synthesis route. A comprehensive analysis of the chemical composition, particle morphology, and electronic and crystal structure of KTiPO4F is performed using X-ray powder diffraction, electron microscopy, and spectroscopy methods. When tested against metallic K with a 1 M KPF6 electrolyte, the carbon-coated KTiPO4F reveals remarkable K-ion storage properties, delivering around 130 mA h g(-1) at 130 mA g(-1) with symmetric charge/discharge (1C rate) in the 0.001-3.0 V vs. K/K+ potential range with 97% capacity retention after 1000 cycles. This polyanion anode operates at an average potential of only 0.8 V vs. K/K(+)via a solid-solution-like de/insertion mechanism showing a cell volume change of 8.5% - the lowest value among modern benchmark electrode materials for potassium-ion batteries. A full symmetric K-ion KTiPO4F & Vert;KTiPO4F cell is for the first time assembled and tested. This work complements the available range of anode materials for K-ion batteries with a new polyanionic representative thus extending the development frontiers.

Sodium-ion batteries are a technology rapidly approaching widespread adoption, so studying the thermal stability and safety of their components is a pressing issue. In this work, we employed differential scanning calorimetry (DSC) and ex situ powder X-ray diffraction to study the thermal stability of several types of sodium-ion electrolytes (NaClO4 and NaPF6 solutions in PC, EC, DEC, and their mixtures) and various cathode and anode materials (Na3V2(PO4)3, Na3(VO)2(PO4)2F, β-NaVP2O7, and hard carbon) in combination with electrolytes. The obtained results indicate, first, the satisfactory thermal stability of liquid Na-ion electrolytes, which start to decompose only at 270~300 °C. Second, we observed that charged vanadium-based polyanionic cathodes, which appear to be very stable in the “dry” state, demonstrate an increase in decomposition enthalpy and a shift of the DSC peaks to lower temperatures when in contact with 1 M NaPF6 in the EC:DEC solution. However, the greatest thermal effect from the “electrode–electrolyte” interaction is demonstrated by the anode material: the heat of decomposition of the soaked electrode in the charged state is almost 40% higher than the sum of the decomposition enthalpies of the electrolyte and dry electrode separately.

The distribution of relaxation times (DRT) approach was used to analyze the electrochemical impedance spectra obtained for lithium-ion cells as a function of their state of charge as well as the cell preparation conditions. The cells were made using LiFePO4 cathodes with PEDOT:PSS binder and Li anodes. The following parameters were varied: the load of the active mass with LiFePO4, the presence or absence of carbon nanotubes, the presence or absence of the carbon coating of the current collector, die-pressing of the active mass, as well as artificial degradation of the binder using thermal treatment. The results support the view adopted in the literature that the DRT response of Li-ion cells involves 4 main regions attributed to (i) contact resistance between the particles of the active mass or the particles and the current collector; (ii) ionic resistance of the active layer including that of SEI on the surface of the electrodes; (iii) faradaic resistance of the electrochemical charge transfer at the surface of the active material, and (iv) solid-state diffusion/transport of Li+ ions in the particles of active material. Moreover, we identified yet another contribution to the DRT spectra related to the ionic conductivity of the binder and electrolyte in the active mass of the cathode.

The change in the composition of the electrolyte after life cycle testing (cycling) of lithium-ion batteries (LIBs) was studied. The cell with a nominal capacity of 22 A h was composed of a cathode based on nickel-rich layered lithium oxide LiNi0.6Mn0.2Co0.2O2 (NMC622) and an anode based on graphite. NMR and high-resolution mass spectrometry demonstrated the continuous decomposition of dimethyl carbonate and ethyl methyl carbonate, related to the disruption of the formation of protective surface layers on the graphite electrode. The degradation of the LIB is related to the formation of polyethylene oxide oligomers of various compositions as a result of the decomposition of the electrolyte components and the precipitation of the salt MeOCO2Li, which is poorly soluble in carbonate solvents, on the separator. A water content of more than 20 ppm in the electrolyte leads to the hydrolysis of the salt LiPF6 with the formation of HPO2F2 and HF. The presence of HF facilitates the dissolution of the components of the surface film at the graphite/electrolyte interface with the regeneration of H2O and the formation of a “fresh” surface on the graphite, which participates in the electrochemical decomposition of the carbonate solvents. Organophosphate C2H5O4P is formed upon the interaction of the electrolyte components with HF.