NaSICON electrolytes, such as Na1+xZr2(SiO4)(x)(PO4)(3-x) (NZSP), constitute promising candidates for solid-state battery (SSB) development. Research on such fast superionic conductors has primarily focused on two key phenomena acting specifically on Na+ ion migration: (i) the Na-concentration-driven modulation effect and (ii) the incidence of substitution. While numerous experimental and computational studies have established the fundamental role of concerted migration in ionic conduction, the precise influence of bottleneck size along with its dependence on NaSICON composition remains elusive. In view of participating in this research field and following an experimentally tested strategy, suggesting that the migration bottleneck can be expanded by partially substituting diffusing Na+ ions with larger-radius alkali elements, we investigated the impact of the introduction of such point defects (i.e. K+ or Cs+ replacing Na+) on structural and Na+ diffusion aspects in the NZSP crystal structure. A proof of concept of the interest linked to this unconventional doping approach has been searched for. Theoretical investigations relying on density functional theory (DFT) and subsequent kinetic Monte Carlo simulations were involved to unravel interrelations between the ionic radius of the substituting ion and bottleneck sizes, structural changes, diffusion pathways, and ionic conductivity features. Apart from an opening of the bottleneck along the migration path as a common feature, a clear differentiation between both kinds of substituents was evidenced on various aspects, K-NZSP outperforming the undoped counterpart and effectively enabling the maximization of ionic conductivity in these envisaged NaSICON-type matrices. Furthermore, the identification-emerging from this study-of a critical bottleneck size in such systems may contribute to provide a further key clue and lead to well thought-out crystal chemical engineering of improved materials for this research area.

Lithium-rich materials with anionic redox are promising candidates for high-energy-density positive electrodes. Manganese-based compounds like Li2MnO3 offer advantages, including low toxicity and abundant resources, but suffer from poor rate capability due to irreversible oxygen loss and structural transformation. Here, we study an O2-type layered oxide LiMn0.75O2, which shows significantly enhanced cycling stability, retaining 78% of its capacity after 140 cycles, with suppressed structural reorganization and more reversible oxygen redox. By combining electrochemical analysis with operando X-ray absorption spectroscopy (XAS) and pair distribution function measurements (PDF), we provide a detailed picture of the material's structural and redox evolution. The first charge differs markedly from subsequent cycles, combining partially reversible bulk oxygen redox, irreversible Li extraction from surface regions, and impurities with oxygen gas release. From the second cycle onward, the reversible bulk oxygen redox process becomes progressively activated. Besides, no clear evidence of short O-O dimers are observed in PDF, suggesting a limited degree of oxygen dimerization during the oxygen redox. Overall, this work showcases the high-capacity potential of Mn-based Li-rich materials, deepens understanding of their redox behavior, and underscores the power of PDF-based operando techniques in probing local structural changes during cycling.

An iron vanadate in the Li2O-Fe2O3-V2O5 ternary phase diagram was successfully synthesized by using β-Cu3Fe4(VO4)6 framework adaptivity. The three Cu2+ ions in Howardevansite β-Cu3Fe4(VO4)6 were substituted by 1.5 Li+ and 1.5 Fe3+ to form Li1.5Fe5.5(VO4)6. The structure was determined based on single-crystal X-ray diffraction data, which showed that it crystallizes in the triclinic P1̅ space group. The structure consists of zigzag chains formed of iron octahedra and distorted trigonal bipyramids running along the [10-1] direction and connected into a 3D framework by the VO4 tetrahedra. The framework can accommodate Li+ ions. Magnetic susceptibility revealed the presence of high spin Fe3+ ions in the material. Li1.5Fe5.5(VO4)6 was tested in electrochemistry and can reversibly insert up to 5.5 Li+ ions, with a theoretical capacity of 146 mA h/g, making it a suitable insertion positive electrode material. During galvanostatic discharge, a maximum capacity of 128 mA h/g and a reversible capacity of 78 mA h/g were obtained after 100 cycles at C/10.

Layered Na x MO2 sodium oxide positive electrode materials have experienced renewed interest owing to the current commercial attention on sodium-ion batteries. Although there are many attractive qualities of these materials, they suffer from serious shortcomings owing to Na+ ordering and transition-metal layer gliding that cause a plethora of voltage plateaus during cycling. The P2-layered Na2+x Ni2-x/2TeO6 (0 ≤ x ≤ 0.5) system provides a framework for investigating the effect of dual Na+ substitution into the sodium layer and the transition-metal layer of the structure and its effects on the electrochemical properties of the materials. A careful investigation into the synthesis and properties of these materials reveals that the sodium content used during material preparation has a drastic effect on the composition and electrochemical profile of these materials. The sodium substitution disrupts ordering within the transition-metal layer, thereby disrupting Na+ ordering in the adjacent sodium layers. Beyond a critical sodium concentration, the layer stacking shifts, and all voltage plateaus of the P2-Na2Ni2TeO6 material are no longer observed at 4.4 V versus Na+/Na. These results also question the common belief that additional sodium precursor is required when preparing layered sodium oxide cathodes, providing new guidelines for material synthesis and characterization.

Lithium‐rich materials with anionic redox are promising candidates for high‐energy‐density positive electrodes. Manganese‐based compounds like Li 2 MnO 3 offer advantages, including low toxicity and abundant resources, but suffer from poor rate capability due to irreversible oxygen loss and structural transformation. Here, we study an O2‐type layered oxide LiMn 0.75 O 2 , which shows significantly enhanced cycling stability, retaining 78% of its capacity after 140 cycles, with suppressed structural reorganization and more reversible oxygen redox. By combining electrochemical analysis with operando X‐ray absorption spectroscopy (XAS) and pair distribution function measurements (PDF), we provide a detailed picture of the material's structural and redox evolution. The first charge differs markedly from subsequent cycles, combining partially reversible bulk oxygen redox, irreversible Li extraction from surface regions, and impurities with oxygen gas release. From the second cycle onward, the reversible bulk oxygen redox process becomes progressively activated. Besides, no clear evidence of short O–O dimers are observed in PDF, suggesting a limited degree of oxygen dimerization during the oxygen redox. Overall, this work showcases the high‐capacity potential of Mn‐based Li‐rich materials, deepens understanding of their redox behavior, and underscores the power of PDF‐based operando techniques in probing local structural changes during cycling.

In this presentation 23 Na MAS NMR was used to probe the local structure, electronic structure and dynamics in several layered Na x MO 2 oxides for application in Na-ion batteries. Among them, P2-Na x CoO 2 appears to be a model material with a very specific phase diagram and unusual physical properties. 23 Na MAS NMR was used to characterize the changes in the electronic structure during Na deintercalation. 23 Na MAS was also used to characterize the local structure and dynamics versus temperature in several P2 or P3 Na x CoO 2 materials and P2-Na 1/2 VO 2 . In the latter, an increase of two orders of magnitude in its electronic conductivity has been observed at approximately 322 K and a structural transition has been found to occur simultaneously. At room temperature, high resolution powder diffraction and pair distribution function analysis reveal the triangular lattice formed by vanadium ions to be distorted by the formation of pseudo-trimers vanadium clusters. At 350 K, the mobility of the electronic charge carried by vanadium ions increases as evidenced by the increase in the electronic conductivity. The arrangement of sodium ordering in P2-Na 1/2 VO 2 , which maximizes sodium-sodium distances to lower electrostatic repulsions between alkali ions, is found to be unchanged across this transition, but the ionic mobility as observed by NMR, clearly change. Finally, the P2- Na 2+x Ni 2-x/2 TeO 6 (0 ≤ x ≤ 0.5) system provides a framework for investigating the effect of dual Na + substitution into the sodium layer and the transition-metal layer of the structure, and its effects on the electrochemical properties of the materials. The sodium substitution disrupts ordering within the transition-metal layer thereby disrupting Na + ordering in the adjacent sodium layers. Beyond a critical sodium concentration, the layer stacking shifts, and all voltage plateaus of the P2-Na 2 Ni 2 TeO 6 material are no longer observed. These results highlight how sodium ordering between the MO 2 layers and the electronic transport within the MO 2 layers are intimately correlated in Na x MO 2 type sodium layered oxides.

ABSTRACT High‐voltage cathodes such as LiMn1.5Ni0.5O4 (LNMO) offer promising energy density but suffer from interfacial degradation accelerated at elevated voltages and temperatures. Here, we present a comprehensive comparative study of three Li3PO4 coating methods (precipitation, sol–gel, and dry sol–gel routes) applied to commercial LNMO powders. Coating quality and intimacy are systematically assessed using a correlative, multitechnique approach including 7Li and 31P solid‐state NMR, X‐ray diffraction, and electrochemical testing. A key insight from this study is the use of ssNMR relaxation behavior as a sensitive probe of coating intimacy to the active phase. The methodology is validated on commercial LNMO and reproduced in a lab‐synthesized LNMO to demonstrate reproducibility across particle morphologies. Among all methods, the sol–gel route produced a uniform ∼20 nm coating with optimal surface contact, translating to improved rate capability and outstanding high‐temperature cycling stability (87% retention after 100 cycles at 50 °C compared to 29% for the non‐coated LNMO), while retaining rate capability. These findings establish a practical framework for designing robust interfacial coatings in high‐voltage lithium‐ion battery materials.

In our recent study, we demonstrated using Li-7 solid-state Nuclear Magnetic Resonance (ssNMR) and single-crystal X-ray diffraction that the cathode LiFeV2O7 possesses a defect associated with the positioning of vanadium atoms. We proposed that this defect could be the source of extra signals detected in the Li-7 spectra. In this context, we now apply density functional theory (DFT) calculations to assign the experimental signals observed in Li-7 NMR spectra of the pristine sample. The calculation results are in strong agreement with the experimental observations. DFT calculations are a useful tool to interpret the observed paramagnetic shifts and understand how the presence of disorder affects the spectra behavior through the spin-density transfer processes. Furthermore, we conducted a detailed study of the lithiated phase combining operando synchrotron powder X-ray diffraction (SPXRD) and DFT calculations. A noticeable volume expansion is observed through the first discharge cycle which likely contributes to the enhanced lithium dynamics in the bulk material, as supported by previously published ssNMR data. DFT calculations are used to model the lithiated phase and demonstrate that both iron and vanadium participate in the redox process. The unusual electronic structure of the V4+ exhibits a single electron on the 3d(xy) orbital perpendicular to the V-O-Li bond being a source of a negative Fermi contact shift observed in the Li-7 NMR of the lithiated phase.

Alkali transition-metal layered compounds usually contain only one type of alkali cation between the edge-shared octahedra layers. Herein, the ternary phase diagram A(2)Ni(2)TeO(6) (A = Li, Na, K) was explored through solid-state synthesis and new alkali-mixed compositions showing alternation of distinct alkali layers are obtained. Such intergrowth structures are synthesized either by a single high-temperature treatment from raw chemicals or through reaction between layered precursors, the latter involving a solid-state process triggered at moderate temperatures. The in-depth characterization of the multiple cationic orderings is performed by combining powder diffraction techniques (X-rays and neutrons), high-resolution transmission electron microscopy, and solid-state NMR spectroscopy. In addition to the Ni/Te honeycomb ordering, alternation of lithium layers with sodium or potassium layers is observed for compositions (Li/Na)(2)Ni2TeO6 or (Li/K)(2)Ni2TeO6, respectively. Crystal structure solving was achieved by stacking building blocks of the respective single alkali layered oxides and unveiled a complex out-of-plane ordering of honeycomb layers. Moreover, a solid-state reaction between Li2Ni2TeO6 and NaKNi2TeO6 enables preparation of the new phase Li similar to 1Na similar to 0.5K similar to 0.5Ni2TeO6, a unique example containing up to three alkali cations and exhibiting a more complex stacking with sodium and potassium cations occupying the same layer. This investigation confirms that the chemical versatility of layered alkali transition-metal compounds could also occur on the alkali layer. Following the research methodology described here, we revisit the crystal chemistry of alkali transition-metal layered materials by exploring alkali ion substitutions previously thought infeasible, in order to find new alkali-mixed compositions.

We report on single-phase NaxV2(PO4)3 compositions (1.5 ≤ x ≤ 2.5) of the Na super ionic conductor type, obtained from a straightforward synthesis route. Typically, chemically prepared c-Na2V2(PO4)3, obtained by annealing an equimolar mixture of Na3V2(PO4)3 and NaV2(PO4)3, exhibits a specific sodium-ion distribution (occupancy of the Na(1) site of only 0.66(4)), whereas that of the electrochemically obtained e-Na2V2(PO4)3 (from Na3V2(PO4)3) is close to 1. Unlike conventional Na3V2(PO4)3, when used as positive electrode materials in Na-ion batteries, the NaxV2(PO4)3 compositions lead to unusual single-phase Na+ extraction/insertion mechanisms with continuous voltage changes upon Na+ extraction/insertion. We demonstrate that the average equilibrium operating voltage observed upon Na+ deintercalation from single-phase Na2V2(PO4)3 is increased up to an average value of ~3.70 V versus Na+/Na (thanks to the activation of the V4+/V5+ redox couple) compared to 3.37 V versus Na+/Na in conventional Na3V2(PO4)3, thus leading to an increase in the theoretical energy density from 396.3 Wh kg–1 to 458.1 Wh kg–1. Electrochemical and chemical Na+ deintercalation from c-Na2V2(PO4)3 enables complete Na-ion extraction, increasing energy density. Single-phase NaxV2(PO4)3 compositions obtained by annealing mixtures of Na3V2(PO4)3 and NaV2(PO4)3 enable the complete electrochemical extraction of Na+ through the activation of the V4+/V5+ couple. This results in a substantial increase in the energy density of such Na super ionic conductor electrodes when used in sodium batteries.

The performance of the high voltage spinel LiNi0.5Mn1.5O4 (LNMO) in Li-ion batteries strongly depends on its synthesis conditions, actual Ni/Mn stoichiometry, and degree of ordering of Ni and Mn. Depending on the extent of this ordering, the spinel structure can be described in the conventional space group Fd3¯m as the non-substituted LiMn2O4 or, for the highly ordered phase, in the space group P4332. As previously reported in the literature, using neutron and electron diffraction, a qualitative description of the extent of ordering can be achieved and roughly related to the electrochemical performance of LNMO. To deeper characterize and understand this complex system, in this paper, we will show that Raman spectroscopy, and especially the characteristics of the band located at 160 cm−1 attributed for the first time to a twisting motion of octahedral entities, allow to estimate the degree of ordering in LNMO, whereas NMR spectroscopy allows to give a clear description of the local environments of Li, in relationship with the Ni/Mn stoichiometry and extent of ordering. Theoretical calculations were used to support the analysis and attribution of the Raman and NMR signals/spectra. These spectroscopic characterizations enabled in-depth insights into the complexity of LNMO in stoichiometry, degree of ordering, and purity versus the presence of rock-salt or layered oxides as defects or crystalline domains.

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One of the most promising and developed disruptive technology of energy storage for the future is all solid-state batteries. The NASICON phase LATP (Li1.3Al0.3Ti1.7(PO4)3) is widely studied especially thanks to its high ionic conductivity and mechanical strength. However, high temperature densification is required to obtain a dense and conductive material. Here we explore the fast sintering by Spark Plasma Sintering (SPS) of submicronic LATP particles, and the impact of the heating rate on the physico-chemical and transport properties of the pristine powder. High-speed rate for the sintering process induces particles’ growth, avoiding any reduction of titanium. The impurity AlPO4 plays a major role on the conductivity, depending on its content but also on its distribution within the composite, either as a coating (surface modification) or as crystalline particles within the grain boundaries. An intimate understanding of the ceramic composites was achieved using combination of advanced characterization techniques to get a multi-scale description of the material, from the pristine to the sintered states, from the surface to the bulk, and from the atomic long range to the local scales. Sharing these fundamental results is essential, with among other motivations, the spreading of our interpretation of complex spectroscopic results (Electronic Spin Resonance (ESR) spectroscopy, solid-state Nuclear Magnetic Resonance (NMR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS)), key for characterization of reactivities at interfaces in this work and in others.

In the last years, disordered rocksalt structure (DRS) materials were proposed as a positive electrode for lithium-ion batteries. In particular, the fluorinated DRS materials were proposed to be more stable upon cycling than pure oxide counterparts. These materials are mainly obtained by mechanosynthesis in order to incorporate a significant number of F ions and maintain a disordered structure. Since the local structural arrangement is crucial for battery application, we aim to monitor its evolution upon the synthesis of Li2MnO2F from two sets of precursors: Mn2O3, Li2O, and LiF or LiMnO2 and LiF. The synthesis progress was thus followed, by Li-7 and F-19 MAS NMR coupled to XRD to probe the structure at different scales. This allowed us to identify an optimal milling time to reach the final compounds. We show that they exhibit similar morphology (by SEM), medium- and short-range orders (by XRD, Li-7 and F-19 NMR, EXAFS), and average Mn oxidation degree (by XANES). The electrochemical performances of the two compounds are almost similar, with high specific capacities of 319 mAhg(-1) ("from LiMnO2") and 304 mAhg(-1) ("from Mn2O3") for the first charge to 4.8 V vs Li+/Li, proving their interest as post-NMC candidates as positive electrode materials.

One of the most promising and developed disruptive technology of energy storage for the future is all solid state batteries. The NASICON phase LATP (Li1.3Al0.3Ti1.7(PO4)3) is widely studied especially thanks to its high ionic conductivity and mechanical strength. However, high temperature densification is required to obtain a dense and conductive material. Here we explore the fast sintering by Spark Plasma Sintering (SPS) of submicronic LATP particles, and the impact of the heating rate on the physico-chemical and transport properties of the pristine powder. Combination of advanced characterization techniques was required to get a full (intimate) description of the material, from the pristine to the sintered states, from the surface to the bulk, and from the atomic long range to the local scales. Results thought firstly to be counterintuitive could be fully explained.

As the importance of developing low-cost and high capacity materials is emerging, Mn-based Na4MnV(PO4)3 positive electrode materials that allow multiredox reactions are in the spotlight for Na-ion batteries. The structure that gives highly reversible electrochemical reactions, when two Na+ (out of four) are de-inserted, deteriorates rapidly when the third Na+ is extracted at high voltage, resulting in poor cyclability. In this work, using synchrotron-based operando techniques, we perform long-range and local structural analyses to determine the origins of the rapid structural decay of Na4MnV(PO4)3 when the third Na+ is extracted. Operando XRD shows a significant change in the crystal structure (c parameter increases rapidly) as the occupancy of the Na (1) site decreases at high voltage. The local environments of Mn and V, monitored by operando XAS, remain rather symmetrical up to the extraction of two Na+, while both Mn and V show drastic local distortions when the third Na+ is extracted. These structural degradations are found to further progress when cycling to high voltage. This study presents important aspects of how local and long-range structure modifications can affect the electrochemical performance in multiredox NASICON materials.

The Na-ion battery technology appears as a reliable, sustainable and environmentally friendly alternative to the Li-ion one, especially for stationary energy storage. As for the Li-ion technology, safety aspect is of high importance to ensure large-scale development. In this work, we studied the thermal stability and decomposition mechanisms of carbon-coated Na3V2(PO4)2F3 and two fluorine-rich phases belonging to the solid-solution Na3V3+2-yV4+y(PO4)2F3-yOy (y = 0.07 and y = 0.12), that family of compounds being often considered among the most promising positive electrode materials for Na-ion batteries. This study shows the good thermal stability of these polyanionic materials and reveals that a low O2- for F- substitution has a very limited effect on the thermal stability of fully re-intercalated materials recovered in the discharged state of the battery, whereas it has a beneficial impact for highly de-intercalated ones, obtained by in-depth charges. Furthermore, whatever the state of charge and the oxygen content in NaxV2(PO4)2F3-yOy (1<=x<=3 and y = 0, 0.07 and 0.12), the thermal degradation leads, quite unexpectedly, to the formation of crystalline Na3V3+2(PO4)2F3 in addition to an amorphous phase. The fluorination of the partially oxygen for fluorine substituted material was clearly demonstrated by X-ray diffraction (XRD) and solid state nuclear magnetic resonance spectroscopy (NMR) on materials recovered after differential scanning calorimetry (DSC) analyses. The formation of a fully sodiated crystalline phase from the thermal degradation of the material obtained in charged states of the battery, with or without presence of electrolyte, was never reported before.

Alkali vanadium fluoride phosphates such as Tavorite LiVPO4F, Na3V2(PO4)2F3 and KTP-type KVPO4F are attractive materials for positive electrodes in rechargeable alkali-ion batteries. In such compounds, the presence of fluoride ions further increases the electrode's electrochemical potential compared to their phosphate counterparts such as Na3V2(PO4)3. Furthermore, the fluoride anions in these structures can be fully or partially substituted by oxide anions, leading to the formation of V4+=O vanadyl centres and a great number of mixed valence and mixed anion compositions. The oxygen substitution for fluorine has a considerable impact on the structural, electronic, and electrochemical properties of the resulting compounds. In this review, the similarities and peculiarities in the crystal structures, electronic structures, and electrochemical properties of the three analogous LiVPO4F–LiVPO4O, Na3V2(PO4)2F3–Na3V2(PO4)2FO2, and KVPO4F−KVPO4O material families will be compared in detail. Such a comparison is expected to provide an insightful understanding on the factors governing the structure and properties of vanadium oxyfluoride phosphates.

Among candidates at the positive electrode of the next generation of Li-ion technology and even beyond post Li-ion technology as all-solid-state batteries, spinel LiNi0.5Mn1.5O4 (LNMO) is one of the favorites. Nevertheless, before its integration into commercial systems, challenges still remain to be tackled, especially the stabilization of interfaces with the electrolyte (liquid or solid) at high voltage. In this work, a simple, fast, and cheap process is used to prepare a homogeneous coating of Al2O3 type to modify the surface of the spinel LNMO: the supercritical fluid chemical deposition (SFCD) route. This process is, to the best of our knowledge, used for the first time in the battery field. Significantly improved performance was demonstrated vs those of bare LNMO, especially at high rates and for highly loaded electrodes.

M-ion batteries (M = Li, Na, K ...) positive electrode materials most often operate through the reversible oxidation of transition-metal ions. In complex materials involving many transition metals or many redox centers, understanding the sequence in which they participate to the reaction is not trivial but is often necessary to explain the electrochemical properties. Mixed anion vanadium phosphates, such as KVPO4F0.5O0.5, are known to contain two different redox entities that are V3+O4F2 and V3+O5F "ionic" entities on the one hand and {V4+= O}O5 and {V4+=O}O4F "covalent" vanadyl-type units on the other hand. However, their participation to the redox mechanism occurring during the charge of this material has never been studied. Here, we use V K-edge X-ray absorption spectroscopy to unveil the redox mechanism of KVPO4F1-yOy (y = 0, 0.5, 1), performing data analysis via a chemometric approach. With XAS being very sensitive to the oxidation state and bond length, it was found that the ionic V3+- F units oxidize at a lower potential than the covalent {V4+=O} ones, which is surprising considering the high electronegativity of fluoride anions but is consistent with the redox potential observed for KVPO4F and KVOPO4. Further, ab initio calculations and ex situ X-ray diffraction analyses allowed an atomistic description of the redox mechanism with the sequential oxidation of the cis V site before the trans V site in KVPO4F upon charge. Finally, the complete atomically resolved redox mechanism of KVPO4F0.5O0.5 is proposed.