Ion-dependent electrochemical behavior in shear-structured tungsten oxides

As representative extended planar defects, crystallographic shear (CS) planes, namely Wadsley defects, play an important role in modifying the physical and chemical properties of metal oxides. Although these special structures have been intensively investigated for high-rate anode materials and catalysts, it is still experimentally unclear how the CS planes form and propagate at the atomic scale. Here, the CS plane evolution in monoclinic WO3 is directly imaged via in situ scanning transmission electron microscope. It is found that the CS planes nucleate preferentially at the edge step defects and proceed by the cooperative migration of WO6 octahedrons along particular crystallographic orientations, passing through a series of intermediate states. The local reconstruction of atomic columns tends to form (102) CS planes featured with four edge-sharing octahedrons in preference to the (103) planes, which matches well with the theoretical calculations. Associated with the structure evolution, the sample undergoes a semiconductor-to-metal transition. In addition, the controlled growth of CS planes and V-shaped CS structures can be achieved by artificial defects for the first time. These findings enable an atomic-scale understanding of CS structure evolution dynamics.

Polaron interaction energies in reduced tungsten trioxide

Strain energy between parallel {001} crystallographic shear planes in the tungsten trioxide structure

Because of the technological importance of perovskite-based oxides, numerous pathways towards new structures have been developed, including ordering at the A and/or B cation sites of the perovskite (ABO3) structure, vacancy ordering at the anion site, the intergrowth of perovskite and related structures, and the formation of hexagonal perovskite polytypes. However, it has been generally accepted that crystallographic shear (CS) structures cannot be realized in perovskites. CS planes commonly occur in anion-deficient oxides derived from the ReO3 or rutile (TiO2) structures, which are based on metal-centered octahedra. Arrangement of the CS planes at different periodicities generates a homologous series. Some of the well-known examples of CS structures are MnO3n 1, MnO3n 2 (M=Mo, W), TinO2n 1, and the block structures of Nb2O5 and its Ti-containing derivatives. [2–6] The shear operation is such that along the CS plane the octahedra share edges or faces, instead of corners or edges as in the basic structure. The ReO3 structure is based on the same threedimensional framework of corner-sharing BO6 octahedra found in the perovskite structure, but the 12-coordinate A cation sites of the perovskite structure are empty in ReO3. Usually, the presence of A cations in perovskites favors point defects in the anion sites (in a random or ordered arrangement), leading to a lower coordination number for the B cations, and prevents the elimination of anion point defects by a shear operation. Herein, we report the occurrence of CS structures in perovskite-based “Pb2Fe2O5” for the first time. We also describe the general crystallographic mechanism of CS-plane formation in a perovskite framework with the A sites filled by cations bearing a lone 6s electron pair, which involves the elimination of O vacancies by the shear operation and the relaxation of the structure at the CS plane. We discuss the role of the lone electron pair in directing structure formation, as well as the relationship between the crystallographic orientation of the CS plane and the chemical composition. The discovery of this mechanism opens up new possibilities for the design of novel perovskite-based compounds containing A cations with a lone 6s electron pair. “Pb2Fe2O5” (or “PbFeO2.5”) is expected to be an aniondeficient perovskite of the brownmillerite (Ca2AlFeO5) type; however, its structure has not yet been determined. Because of the complexity of the structure and the prevalence of domain fragmentation, the only road to solving the structure is by transmission electron microscopy (TEM). The brighter reflections in the electron diffraction (ED) patterns of “Pb2Fe2O5” (Figure 1a) reveal a perovskite sublattice with a parameter ap 3.9 < (p denotes the perovskite subcell). Linear arrays of satellite reflections associated with each basic reciprocal lattice node are typical for periodic CS planes. The displacement vector for the CS planes was deduced from the ED patterns as R= 1/2 [110]p+ 1/ 3 [001]p by measuring the fractional shifts hR for the satellite reflections (Figure 1b). 11][*] Closer inspection of the [010]* ED pattern reveals the incommensurate character of the modulation. The monoclinic unit-cell parameters (denoted by

Factors affecting the structure and orientation of the crystallographic shear (CS) planes in anion-deficient perovskites were investigated using the (Pb(1-z)Sr(z))(1-x)Fe(1+x)O(3-y) perovskites as a model system. The isovalent substitution of Sr(2+) for Pb(2+) highlights the influence of the A cation electronic structure because these cations exhibit very close ionic radii. Two compositional ranges have been identified in the system: 0.05 ≤ z ≤ 0.2, where the CS plane orientation gradually varies but stays close to (203)p, and 0.3 ≤ z ≤ 0.45 with (101)p CS planes. The incommensurately modulated structure of Pb0.792Sr0.168Fe1.040O2.529 was refined from neutron powder diffraction data using the (3 + 1)D approach (space group X2/m(α0γ), X = (1/2, 1/2, 1/2, 1/2), a = 3.9512(1) Å, b = 3.9483(1) Å, c = 3.9165(1) Å, β = 93.268(2)°, q = 0.0879(1)a* + 0.1276(1)c*, RF = 0.023, RP = 0.029, and T = 900 K). A comparison of the compounds with different CS planes indicates that the orientation of the CS planes is governed mainly by the stereochemical activity of the lone-electron-pair cations inside the perovskite blocks.

Extended vacuum annealing of rutile ${\mathrm{TiO}}_{2}(110)$ produces macroscopic and nanoscopic changes in the surface morphology. These result from the ordering of oxygen ${\mathrm{v}\mathrm{a}\mathrm{c}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}/\mathrm{T}\mathrm{i}}^{n+}$ interstitials in bulk ${\mathrm{TiO}}_{2}$ into crystallographic shear (CS) planes. We have employed low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) to identify the surface termination of CS planes produced in the bulk. The directions of the planar defects along the surface indicate the {132} series of shear planes dominate the STM images, which is also supported by the LEED results. The spacing between planes gradually varies across the surface suggesting that a series of Magn\'eli phases are formed. LEED patterns confirm the coexistence of both relatively large areas of a single phase and a continuum of separations between planes. Formation of CS planes also leads to extensive facetting of the crystal, which is visible to the naked eye as a rippled surface finish. Some Ca segregation is observed during CS plane formation; however, when removed the CS planes remain, indicating they are not significantly stabilized by the Ca.

PbMnO 2.75—a high-pressure phase having a new type of crystallographic shear structure derived from perovskite

The thermoelectric properties of Magnèli phase titanium oxides TinO2n−1 (n=2,3,…) have been investigated, paying special attention to how the thermoelectric performance can be altered by changing the microstructure. Dense polycrystalline specimens with nominal composition of TiO2−x (x=0.05, 0.10, 0.15, and 0.20) prepared by conventional hot-pressing are all identified to be one of the Magnèli phases, in which crystallographic shear planes are regularly introduced according to the oxygen deficiency. Electrical conduction is n-type for all specimens and the carrier concentration increases with the increase in the oxygen deficiency. The values of lattice thermal conductivity, on the other hand, decrease with the increase in the oxygen deficiency, which can be attributed to phonon scattering at the crystallographic shear plane. The largest value of thermoelectric figure of merit Z, 1.6×10−4 K−1 was obtained at 773 K for the hot-pressed specimen of TiO1.90.

Advanced additives have become a key strategy for pushing the practical limits of lithium-ion batteries (LIBs) by tuning not only electrode materials but the entire cell structure. Instead of being passive bystanders, modern additives are intentionally designed to participate in electrochemical reactions, buffer mechanical stress, regulate ion and electron transport, and form robust interphases. This review offers a comprehensive overview of how additives are used in anodes, electrolytes, and cathodes to improve energy density, rate capability, cycle life, and overall safety. We explain how tailored additives can stabilize active materials that undergo significant volume changes, facilitate the formation of thin, stable, and conductive interphases, and enhance Li⁺ solvation and transport, thereby mitigating lithium plating and side reactions. Special attention is given to multifunctional additives that provide structural reinforcement, redox activity, and interface engineering, along with the interplay between bulk modifications and surface design strategies. Finally, we discuss ongoing challenges, including compatibility with high-voltage chemistries, scalability, and performance in practical cell formats, and we propose future directions for data-driven, rational additive development. By viewing additives as active, designable components of the entire battery system, this review aims to support the development of advanced LIBs with improved durability, safety, and performance under real-world conditions. • Modern additives play an active role in electrochemical reactions, surpassing traditional passive functions. • Multifunctional additives enhance structural integrity, exhibit redox activity, and stabilize interfaces. • Customized additives enhance energy density, improve rate capability, extend cycle life, and increase battery safety. • Data-driven design strategies facilitate the rational integration of both bulk and surface modifications for the effective development of high-voltage LIBs.

Crystallographic shear in WO 3· xNb 2O 5 ( x = 0.03–0.09)

Exploring resource‐abundant and high‐performance anode materials for sodium‐ion batteries remains a critical challenge in current research. For example, the practical applications of sodium‐ion batteries are restricted by the severe volume variation of active materials on the anode, which often results in irreversible capacity loss and poor cycling performance. Utilizing the different redox potential of metals is shown to be an effective way to alleviating volume changes. Here, we demonstrate that SnS/SnSb‐nanoparticle‐decorated carbon nanofibers (SnS/SnSb@C) prepared via vulcanization are a promising candidate as the anode material for sodium‐ion batteries. The resultant SnS/SnSb@C composites show an impressive electrochemical performance, featuring a large discharge capacity (1028 mAh g−1 at 50 mA g−1), rate capability (159 mAh g−1 at 2 A g−1), and excellent cycling stability (270 mAh g−1 at 200 mA g−1 after 200 cycles). The different sodiation/desodiation potential of Sn and Sb in the SnS/SnSb@C composite helps to alleviate the volume expansion during cycling, and the defects within carbon nanofibers caused by sulfur doping further promote fast ion and electron transport in sodium‐ion batteries.

Crystal structures of V nO 2 n−1 (2≤ n≤7)

Nitrogen‐doped porous carbon derived from various polymer precursors receives great attention for applications in supercapacitor electrodes due to its high specific area and fast ion transportation within the electrodes. The porous structure with high content of nitrogen atoms enhances the wettability and accelerates the diffusion of ions inside free‐standing electrodes. These electrodes are fabricated by carbonization of nitrogen‐rich carbon precursors such as polyimide and polyaniline. However, the porous structure and the high degree of nitrogen doping within electrodes are hard to maintain during the carbonization process. Herein, it is demonstrated that a new synthetic approach—nonsolvent‐induced phase separation method—can prepare melamine‐assisted polyimide sheet followed by carbonization process as nitrogen‐rich supercapacitor electrodes with high porosity. A symmetric supercapacitor composed of the above‐mentioned free‐standing electrodes exhibits a specific capacitance of 176 F g−1 at 1 A g−1 (rate capability of 152 A g−1 at 5 A g−1) and long lifetime over 10 000 cycles with 99.2% capacitance retention. Also, the supercapacitor shows a high energy density of 6.3 W h kg−1 and power density of 1.25 kW kg−1. In conclusion the nitrogen‐doped porous carbon sheet improves the energy density of a supercapacitor in comparison to electrodes prepared by conventional methods.

Due to its high working voltage (4.7 V vs. Li/Li+ for Ni2+/Ni4+ redox couple), high theoretical capacity (147 mAh/g), and inherent cyclic stability (no Jahn-Teller distortion from Mn3+), LiNi0.5Mn1.5O4 is a promising cathode material for the practical application in high energy density lithium ion batteries [1-3]. The cation ordering, the degree of presence of Mn3+ in the spinel structure, is regarded as an important factor influencing the electrochemical properties of LiNi0.5Mn1.5O4 [4, 5]. With a simply strategy of cooling rate, the degree of ordering in disordered spinel LiNi0.5Mn1.5O4-δ structure is controlled at 0.5 oC/min for slow cooled spinel and at 5 oC/min for fast cooled spinel. From XRD and FTIR analyses and charge/discharge profiles, it is confirmed that the fast cooled spinel develops more disordered structure than the slow cooled spinel, retaining more oxygen vacancies and more abundant Mn3+. Moreover, through in situ XRD analysis, the more disordered spinel follows the extended solid-solution reaction in favor of Li+transport, which results in an improved rate capability. But, the local structure information of interesting atoms without a destructive interference which can arise from long-range structural order is highly related to the electrochemical performance. Therefore, the examination in local structural variations of interesting atoms is essential for understanding their electrochemical properties. In this work, we investigate local structural changes in the vicinity of Mn and Ni cations at various C-rates by using ex situ XAS analysis and quantify the structural changes by fitting a theoretical model to the extended X-ray absorption fine structure data. This finding will propose that a change of structural distortion can be another platform to understand the enhanced Li+transport in the disordered spinel and offer valuable guidance for developing LiNi0.5Mn1.5O4, a promising cathode material with high rate capability for next generation rechargeable batteries. More detailed discussion will be presented at the 2016 IMLB meeting. [1]. X. Liu, D. Li et al., J. Alloys Compd.,2014, 609, 54-59. [2]. X.-W. Gao, Y.-F. Deng et al., J. Mater, Chem. A.,2015, 3, 404-411. [3]. H. Xia, Y.S. Meng et al., J. Electrochem. Soc., 2007, 154, A737-A743. [4]. M. Kunduraci and G.G Amatucci, J. Electrochem. Soc.,2006, 153, A1345-A1352 [5]. L. Wang, H. Li et al., Solid State Ionics., 2011, 193, 32-38

As the Li ion batteries industry moves towards high-nickel cathode materials owing to their high energy density, improved rate capability and extended working voltage, the challenges associated with these cathode materials, such as structural instability and electrochemical degradation, become increasingly prominent. Surface modification is one of the most effective ways to mitigate these problems by forming a protective layer and inhibiting transition metal dissolution. Herein, we reported a novel, highly efficient, solvent-free approach to dry coating high-nickel NMC (Lithium nickel manganese cobalt oxides) cathode materials with ultrafine fumed nano Al2O3 (10 nm). The resulting coating layer exhibits remarkable robustness via the strong van der Waals force between Al2O3 and the NMC host, which could effectively mitigate the side reaction of the high-nickel NMC cathode during cycling and thereby significantly improving the cycle performance and the rate capability of the NMC cathode materials (maintained stable at 1C over 100 cycles). We found the uniform surface coating could alleviate the mechanical fracture of NMC particles. Although the Al2O3 is electrochemically insulating, there are still some uniform porous spaces remaining on the surface of the NMC particles, serving as the fast li ion transfer pathways, which benefit the good rate capability. Moreover, the introduction of extra Al2O3 does not affect the capacity of the cathode due to the small amount (only 1%), it shows similar initial capacity at 0.1C compared with the uncoated NMC. The protection mechanism of the Al2O3 dry coated cathode surface is further revealed through electrochemical impedance spectroscopy (EIS) measurements conducted on the coated and uncoated electrode. In conclusion, the rapid dry coating process could effectively enhance the performance of the high-nickel NMC cathode materials and holds the promise to be scalable up to large-scale continuous processes which could be very desirable for industrial manufacturing.