Niobium Tungsten Oxide Research Articles

High-performance electrochromic devices composed of niobium tungsten oxide films

Electrochromic technology plays a pivotal role in various industries, offering significant benefits in energy efficiency and sustainability. By efficiently modulating sunlight, it reduces dependence on traditional climate control systems, thus decreasing overall energy consumption. Among electrochromic materials, tungsten oxide (WO3) is highly favored for its outstanding stability and superior optical modulation amplitude. However, the escalating demands of commercial applications necessitate enhancements in electrochromic performance, achievable through doping or composite designs. This study investigates the electrochromic characteristics of novel niobium tungsten oxide (Nb18W16O93) thin films, employing a gel electrolyte and examining their structural, optical, and electrochemical attributes. Compared to pure WO3, the Nb18W16O93-based electrochromic device exhibited a significant optical modulation of 55.1% in the visible spectrum and 31.3% in the near-infrared region. The gel-based device not only provides safety benefits over liquid electrolytes by mitigating leakage risks but also features rapid switching response times, with a coloration duration of 3.9 s and a bleaching interval of 3.6 s. Moreover, the device showcases exceptional long-term stability, retaining a ΔT of nearly 72% after 10,000 cycles.

The chemo-mechanics of initiation of crack advance in Niobium Tungsten Oxide single crystals due to delithiation

Niobium tungsten oxide (NWO) micron-sized single crystals show promise as the active particles in the anodes of lithium ion batteries due to their fast charge/discharge and high storage capabilities. Within the “block” phases such as Nb16W5O55, Nb14W3O44 and the HNb2O5 polymorph, Li ion diffusion occurs in a unidirectional manner along a single axis of the crystal and lithiation/delithiation results in significant length changes in this direction. A chemo-mechanics analysis is developed for delithiation of an NWO “block” phase single crystal that contains a pre-existing flaw in the form of a through-thickness edge crack. Galvanostatic delithiation occurs by the flux of Li ions through the free ends of the crystal and also through the faces of the crack, with concomitant shrinkage of the surface layer over a depth equal to that of the crack. The induced tensile stress in the surface layer can be of sufficient magnitude to advance the crack in the NWO crystal, consistent with recent experimental observations for Nb14W3O44. A 2D full-field finite element version of the chemo-mechanics model is used to explore the sensitivity of cracking to crack length, delithiation rate of the anode, diffusivity of Li ions within the NWO single crystal storage particle and to the kinetics of Li ion transfer across the particle surface-electrolyte interface. Additionally, a simplified, lumped parameter model is developed by assuming that the Li ion occupancy is spatially uniform in a surface layer that extends to a depth of the pre-existing crack, and has a spatially uniform but different value than that of the underlying core of the particle. This simplified model can be expressed as a set of first order differential equations in time and gives the main features of delithiation and the associated transient stress state in the single crystal. Both the full model and the lumped parameter version predict that crack advance from a pre-existing defect is triggered by a high delithiation rate, consistent with the experimental literature.

Nanofilms based on superstructured niobium tungsten oxide have high dual-functional potential for electrochromism and energy storage

Niobium-tungsten oxide represents a novel type of bimetallic cathode electrochromic material. The superstructure is capable of accommodating a greater number of ions, which has been a hot material for research in recent years. In this paper, composite niobium-tungsten oxide materials were prepared on fluorine-doped tin oxide (FTO) substrates using the sol–gel spin-coating method. The particle size, band gap and response time of the electrochromic films were improved by regulating the film annealing temperature. As the annealing temperature was increased, the particle size of the Nb18W16O93 film increased from 7.54 nm to 31.8 nm. Concurrently the band gap decreased, which enhanced the electrical conductivity of the material. The electrochemical and optical measurements show that the film has excellent properties, and by choosing the appropriate annealing temperature, the coloring efficiency reaches 55.3 cm2 C−1 from 34.1 cm2 C−1, the switching time reaches tc = 4.3 s, tb = 3.5 s, and the energy storage capacity reaches 21.086 mF cm−2 at a surface current density of 0.05 mA cm−2. The present work demonstrates that adjusting the annealing temperature can enhance the electrochromic and energy storage performance of the proposed films, which have for the potential to be utilized in electrochromic bifunctional applications.

Mechanochemically Enabled Metastable Niobium Tungsten Oxides.

Metastable compounds have greatly expanded the synthesizable compositions of solid-state materials and have attracted enormous amounts of attention in recent years. Especially, mechanochemically enabled metastable materials synthesis has been very successful in realizing cation-disordered materials with highly simple crystal structures, such as rock salts. Application of the same strategy for other structural types, especially for non-close-packed structures, is peculiarly underexplored. Niobium tungsten oxides (NbWOs), a class of materials that have been under the spotlight because of their diverse structural varieties and promising electrochemical and thermoelectric properties, are ideally suited to fill such a knowledge gap. In this work, we develop a new series of metastable NbWOs and realize one with a fully cation-disordered structure. Furthermore, we find that metastable NbWOs transform to a cation-disordered cubic structure when applied as a Li-ion battery anode, highlighting an intriguing non-close-packed-close-packed conversion process, as evidenced in various physicochemical characterizations, in terms of diffraction, electronic, and vibrational structures. Finally, by comparing the cation-disordered NbWO with other trending cation-disordered oxides, we raise a few key structural features for cation disorder and suggest a few possible research opportunities for this field.

Porous Nb4W7O31 microspheres with a mixed crystal structure for high-performance Li+ storage

Niobium-tungsten oxides with tungsten bronze and confined ReO3 crystal structures are prospective anode candidates for lithium-ion batteries since the multi-electron transfer per niobium/tungsten offers large specific capacities. To combine the merits of the two structures, porous Nb4W7O31 microspheres constructed by nanorods are synthesized based on a facile solvothermal method. This new material contains different tungsten bronze structures and 4 × 4 ReO3-type blocks confined by tungsten bronze matrices, generating plenty of pentagonal and quadrangular tunnels for Li+ storage, as confirmed by spherical-aberration-corrected scanning transmission electron microscopy. Such structural mixing enables three-dimensionally uniform and small lattice expansion/shrinkage during lithiation/delithiation, leading to good structural and cyclic stability (95.2% capacity retention over 1,500 cycles at 10C). The large interlayer spacing (~3.95 Å), coupled with the abundant pentagonal/quadrangular tunnels, results in ultra-high Li+ diffusion coefficients (1.24 × 10-11 cm2 s-1 during lithiation and 1.09 × 10-10 cm2 s-1 during delithiation) and high rate capability (10C vs. 0.1C capacity retention percentage of 47.6%). Nb4W7O31 further exhibits a large reversible capacity (252 mAh g-1 at 0.1C), high first-cycle Coulombic efficiency (88.4% at 0.1C), and safe operating potential (~1.66 V vs. Li/Li+). This comprehensive study demonstrates that the porous Nb4W7O31 microspheres are very promising anode materials for future use in high-performance Li+ storage.

Tailoring the Wadsley–Roth crystallographic shear structures for high-power lithium-ion batteries

A tailored Wadsley–Roth crystallographic shear structure containing inspiring domains with tetrahedron, tetrahedron-free and large-size blocks in the lattice of novel titanium niobium tungsten oxide for high-power lithium-ion batteries.

Introducing a Novel Light Scattering Technique for Visualising Operando State-of-Charge Changes Within Individual Active Particles and Across the Electrode

In our presentation we will demonstrate the application of a recently developed operando optical microscopy technique to mechanistic studies of lithium-ion battery electrodes and active material characterisation. Our technique probes state-of-charge (SoC) changes in the active particles within the electrode during battery operation, based on the intensity variation of scattered light across each active particle. This enables detailed spatially resolved data on an individual particle level to be utilised for furthering mechanistic understanding of battery capability and degradation, and it also allows global statistics to be established for the optimisation and screening of new electrode materials. The technique is agnostic to the underlying battery chemistry, so in principle can be applied to study any battery electrode.In this talk, we will demonstrate how our technique can be used in the study of two key dynamic processes, solid-state ion transport and mechanical degradation. The ability to quantify ion transport during battery operation helps to provide insights into how lithium-ion dynamics affect the (de)lithiation mechanisms and degradation mechanisms of battery electrodes, which is crucial to improving their electrochemical performance. Using lithium cobalt oxide (LCO) as a case study, we will show how ion-transport mechanisms can be deduced by observing moving phase boundaries within particles during cycling.We will then demonstrate how local SoC changes within Ni-rich nickel manganese cobalt oxide (NMC) active particles can be visualised during operation, and how the intra-particle ion gradients identified can be used to determine the mechanistic origins of first-cycle capacity losses. Building on this, we will highlight how variation in the rates of (dis)charge between a population of active particles could be used to characterise the performance of new electrode compositions.In addition, we will highlight how lithium-ion concentration gradients can also be identified in high-rate niobium tungsten oxide (NWO) anode materials during initial lithiation and under initial rapid delithiation conditions and demonstrate how this can lead to particle cracking. Expanding on this, we illustrate how the proportion of cracked particles within an electrode can be quantified and then monitored over successive cycles as a potential metric for screening the stability of new electrode materials.

Enabling Extreme Low-Temperature (≤ -100°C) Battery Cycling with Niobium Tungsten Oxides Electrode and Tailored Electrolytes.

The degradation of current Li-ion batteries (LIBs) hinders their use in electronic devices, electric vehicles, and other applications at low temperatures, particularly in extreme environments like the polar regions and outer space. This study presents a pseudocapacitive-type niobium tungsten oxides (NbWO) electrode material combined with tailored electrolytes, enabling extreme low-temperature battery cycling for the first time. The synthesized NbWO material exhibits analogous structural properties to previous studies. Its homogenous atom distribution can further facilitate Li+ diffusion, while its pseudocapacitive Li+ storage mechanism enables faster Li+ reactions. Notably, the NbWO electrode material exhibits remarkable battery performance even at -60 and -100°C, showcasing capacities of ≈90 and ≈75mAhg-1 , respectively. The electrolytes, which have demonstrated favorable Li+ transport attributes at low temperatures in the earlier investigations, now enable extreme low-temperature battery operations, a feat not achievable with either NbWO or the electrolytes independently. Moreover, the outcomes extend to -120°C and encompass a pouch-type cell configuration at -100°C, albeit with reduced performance. This study highlights the potential of NbWO for developing batteries for their use in extremely frigid environments.

Regulating the local coordination model of homologous and heterogeneous niobium tungsten oxides toward ultrafast lithium storage

Intercalation-type niobium tungsten oxide anodes show potential for use in high-power-density lithium-ion batteries (LIBs). Lithium activation barriers are vital factors determining the rate performance of niobium tungsten oxides. Lithium activation barriers located in the crystallographic shear plane are the highest in the entire block structure, as the rate-limiting factor for Li+ diffusion in the Wadsley–Roth crystallographic shear structure of niobium tungsten oxides. Nb(W)O6 octahedrons are distorted by introducing Nb18W8O69 (Nb18) into Nb16W5O55 (Nb16) to form heterogeneous composite structures. This distortion induces metal–oxygen bond lengthening in Nb16/Nb18, increasing the interspace between the edge-sharing octahedrons and thereby reducing the highest lithium activation barriers in the Nb16/Nb18 crystallographic shear plane and mitigating volume expansion. Nb16/Nb18 has an extraordinary rate capacity of 85 mA h g−1 at 100 C and structural stability with 86.3% capacity retention of its highest value at 100 C after 1000 cycles, with a high volumetric energy density of 647 W h L−1 at 134930 W L−1. Nb16/Nb18//LiCoO2 have a high energy density of 158 W h kg−1 at 12480 W kg−1. Thus, a new approach is proposed to improve the rate performance of niobium-based oxides with Wadsley–Roth crystallographic shear structure by employing homologous and heterogeneous composites.

Low Temperature Niobium Tungsten Oxides as Anodes for Fast Charging Li-Ion Batteries

The development of fast-charging Li-ion batteries is one of the important steps in building electric vehicles that need high power and fast charging. The reduction in the particle size to the nanometre length scale drastically improves the charging rate by increasing the surface area but lowers the volumetric energy density and can potentially result in more rapid degradation of the electrolyte via electrode-catalysed reactions. Recent reports show that niobium tungsten oxides (NbWOs) with µm sized particles serve as good anode materials for Li-ion batteries having high volumetric capacity with good cyclability at high rates while avoiding solid electrolyte interphase formation (SEI). The high rate performance of NbWOs is attributed to the topochemical charge storage mechanism that exhibits (i) minimal, highly reversible structural changes during the charge-discharge cycles, (ii) high Li-ion diffusion coefficients due to the presence of fast conducting tunnels, and (iii) high electronic conductivity upon lithiation.1,2 The NbWOs are known to crystallize into two families of different crystal structures depending on the composition and synthesis conditions. The NbWOs phases can either have tungsten bronze-type structures or block-type structures (commonly referred to as Wadsley-Roth phases). Different NbWO phases are reported in the literature3 which could serve as potential anode materials with better performance.In this work, a series of new NbWO phases have been synthesized at reduced annealing temperatures and the structure of these phases has been established using X-ray and neutron diffraction data. The electrochemical properties of NbWO/Li half cells were examined through a series of galvanostatic (dis)charge tests at varying current rates ranging from 0.2 C to 20 C. The NbWO phases delivers a high reversible capacity of 200 and 130 mAh/g at 0.2C and 10 C respectively vs. Li metal. Here we use operando powder X-ray diffraction to investigate the structural changes occurring at the anode during the charge-discharge process in the newly synthesised NbWO phases. Reference s : 1 K. J. Griffith, K. M. Wiaderek, G. Cibin, L. E. Marbella and C. P. Grey, Nature, 2018, 559, 556–563.2 C. P. Koçer, K. J. Griffith, C. P. Grey and A. J. Morris, Chem. Mater., 2020, 32, 3980–3989.3 N. C. Stephenson, Acta Crystallogr. Sect. B Struct. Crystallogr. Cryst. Chem., 1968, 24, 637–653. Figure 1

Lithium-Ion Diffusivity Increases with Block Size in Niobium Tungsten Oxide Shear Structures

Nb16W5O55 emerged as a high-rate anode material for Li-ion batteries in 2018 (Griffith et al.,Nature 2018, 559 (7715), 556–563). This exciting discovery ignited research in Wadsley-Roth (W-R) compounds, but systematic experimental studies have not focused on how to tune material chemistry and structure to achieve desirable properties for energy storage applications. In this work, we systematically investigate how structure and composition influences capacity, Li-ion diffusivity, charge-discharge profiles, and capacity loss in a series of niobium tungsten oxide W-R compounds: (3×4)-Nb12WO33, (4×4)-Nb14W3O44, and (4×5)-Nb16W5O55. Potentiostatic intermittent titration (PITT) data confirmed that Li-ion diffusivity increases with block size, which can be attributed to an increasing number of tunnels for Li-ion diffusion. The small (3×4)-Nb12WO33 block size compound with preferential W ordering on tetrahedral sites exhibits single electron redox and, therefore, the smallest measured capacity despite having the largest theoretical capacity. This observation signals that introducing cation disorder (W occupancy at the octahedral sites in the block center) is a viable strategy to access multi-electron redox behavior in (3×4) Nb12WO33. The asymmetric block size compounds (i.e., (3×4) and (4×5) blocks) exhibit the greatest capacity loss after the first cycle, possibly due to Li-ion trapping at a unique low energy pocket site along the shear plane. Finally, the slope of the charge-discharge profile increases with increasing block size, likely because the total number of energy-equivalent Li-ion binding sites also increases. This unfavorable characteristic prohibits the large block sizes from delivering constant power at a fixed C-rate more so than the smaller block sizes. Based on these findings, we discuss design principles for Li-ion insertion hosts made from W-R materials.

Nickel-doped Nb18W16O93 nanowires with improved electrochemical properties for lithium-ion battery anodes

Recently, niobium tungsten oxide nanowires have been reported to be a promising anode material for lithium-ion batteries (LiBs). This material has demonstrated high theoretical capacity, significant structural stability, high power density, and environmental friendliness. Nonetheless, its low electronic conductivity is a significant drawback that needs to be addressed. More so, it is desirable to enhance its electrochemical performance to meet the needs of current energy applications. In this study, pristine and nickel-doped (Ni = 1 wt%, 3 wt%, 5 wt%) niobium tungsten oxide nanowires were fabricated using the electrospinning technique, followed by annealing. The effect of nickel doping content on the morphology, structure, and electrochemical performance of niobium tungsten oxide nanowires was investigated. The XRD results show that the Ni doping expanded the unit cell and enhanced the lithium-ion diffusion in the Nb18W16O93 nanowires. The electrochemical test results indicate that the 3 wt% nickel-doped condition exhibits remarkable capacity retention of 93.1% over 500 cycles at a high current rate of 5 C. Furthermore, the Ni doping significantly enhanced the electronic conductivity compared to the pristine Nb18W16O93 nanowires. The results obtained from the CV test also show that Ni doping lowered the polarization and increased the lithium-ion diffusion coefficient.

Effect of Synthetic Conditions on the Structure and Properties of Nb14W3O44 Anode for Lithium‐Ion Batteries

AbstractNiobium tungsten oxide is a potential replacement for graphite in fast‐charge lithium‐ion batteries due to its high rate performance and high stability. Herein, Nb14W3O44 anode was synthesized by hydrothermal reaction of niobium oxalate and ammonium tungstate and sequent calcination of niobium tungsten oxide precursors. Compared with the traditional solid‐state method, the particle size and calcination time of Nb14W3O44 obtained by the modified method are greatly reduced. Through orthogonal experiments, the optimal synthesis conditions were determined, and it was found that hydrothermal conditions have an important influence on the particle size of the final product, while the calcination temperature and time greatly affect the purity of the product and thus influence its specific capacity during cycles.

Controlled synthesis of 3D urchinlike niobium tungsten oxide nanostructure for fast hydrogen ion storage

The shear crystal structure through metal doping can effectively promote the transport speed of ions and electrons in metal oxides, which has important dynamic significance for the design of high-performance energy storage materials. Herein, a 3D urchinlike niobium tungsten oxide (NWO) nanostructure as an efficient hydrogen ion storage material is reported for the first time, which exhibits a capacity of 88mAh g−1 at 20 °C (1 °C = 100 mA g−1). The large specific capacity of the 3D urchinlike NWO nanostructure is ascribed to the reversible reaction of a great quantity of W6+, W5+ and W4+ in the process of protonation and deprotonation processes. In addition, hydrogen ions can still be stored in large and stable quantities, even at rates as high as 100 °C (75 mAh g−1 at 100 °C). The improvement of hydrogen ion storage properties is arising from an optimized morphology of niobium tungsten oxide via tuning of the crystal structure. The high specific superficial area 3D urchinlike shape with rich one-dimensional nanostructures significantly shortens charge-carrier transport distances, ensuring rapid interfacial electronics movement to polish up ion storage kinetics. Consequently, this crystallographic shear structure strategy to boost hydrogen ion storage capacity may be universal and is likely to pave the way toward highly capacity hydrogen ion energy storage systems.

High‐Performance Aqueous Zn2+/Al3+ Electrochromic Batteries based on Niobium Tungsten Oxides

AbstractElectrochromic energy storage devices (EESDs) are incorporating electrochromic and energy storage functions, which can visually display energy storage levels in real‐time to promote the next generation of transparent battery development. However, their performances are still limited for practical applications. Herein, a self‐powered EESD based on complex niobium tungsten oxide is designed using aqueous Zn2+ and hybrid Zn2+/Mn+ (Mn+ = Al3+, Mg2+, and K+) electrolytes. The results reveal that the use of Zn2+/Al3+ hybrid electrolyte achieves superior electrochromic performances including a short self‐coloring time, high optical contrast, and excellent cyclic stability. Furthermore, it is also found that the self‐coloring process is accompanied by a high discharged capacity of niobium tungsten oxide, with high optical modulation in the Zn2+/Al3+ hybrid electrolyte. The detailed mechanism on the performances of EESD using various electrolytes is systematically studied. This work provides a simple and effective strategy for an aqueous and self‐powered EESD with high optical contrast and good cycle stability.

Structure–Property Relationships in High-Rate Anode Materials Based on Niobium Tungsten Oxide Shear Structures

Nb16W5O55 emerged as a high-rate anode material for Li-ion batteries in 2018 [Griffith et al., Nature2018, 559 (7715), 556–563]. This exciting discovery ignited research in Wadsley–Roth (W–R) compounds, but systematic experimental studies have not focused on how to tune material chemistry and structure to achieve desirable properties for energy storage applications. In this work, we systematically investigate how structure and composition influences capacity, Li-ion diffusivity, charge–discharge profiles, and capacity loss in a series of niobium tungsten oxide W–R compounds: (3 × 4)-Nb12WO33, (4 × 4)-Nb14W3O44, and (4 × 5)-Nb16W5O55. Potentiostatic intermittent titration (PITT) data confirmed that Li-ion diffusivity increases with block size, which can be attributed to an increasing number of tunnels for Li-ion diffusion. The small (3 × 4)-Nb12WO33 block size compound with preferential W ordering on tetrahedral sites exhibits single electron redox and, therefore, the smallest measured capacity despite having the largest theoretical capacity. This observation signals that introducing cation disorder (W occupancy at the octahedral sites in the block center) is a viable strategy to assess multi-electron redox behavior in (3 × 4) Nb12WO33. The asymmetric block size compounds [i.e., (3 × 4) and (4 × 5) blocks] exhibit the greatest capacity loss after the first cycle, possibly due to Li-ion trapping at a unique low energy pocket site along the shear plane. Finally, the slope of the charge–discharge profile increases with increasing block size, likely because the total number of energy-equivalent Li-ion binding sites also increases. This unfavorable characteristic prohibits the large block sizes from delivering constant power at a fixed C-rate more so than the smaller block sizes. Based on these findings, we discuss design principles for Li-ion insertion hosts made from W–R materials.

New Superionic Memory Devices Can Provide Clues to the Human Memory Structure and to Consciousness

Since the work of Penrose and Hameroff the possibility is discussed that the location of human memory and consciousness could be connected with tubulin microtubules. If one would use superionic nano-materials rolled up to microtubules with an electrolyte inside the formed channels mediating fast ionic exchange of protons respectively lithium ions, it seems to be possible to write into such materials whole image arrays (pictures) under the action of the complex electromagnetic spectrum that composes these images. The same material and architecture may be recommended for super-computers. Especially microtubules with a protofilament number of 13 are the most important to note. We connected such microtubules before with Fibonacci nets composed of 13 sub-cells that were helically rolled up to deliver suitable channels. Our recent Fibonacci analysis of Wadsley-Roth shear phases such as niobium tungsten oxide , exhibiting channels for ultra-fast lithium-ion diffusion, suggests to use these materials, besides super-battery main application, in form of nanorods or microtubules as effectively working superionic memory devices for computers that work ultra-fast with the complex effectiveness of human brains. Finally, we pose the question, whether dark matter, ever connected with ultrafast movement of ordinary matter, may be responsible for synchronization between interactions of human brains and consciousness.

Superior Volumetric Capability Dual‐Ion Batteries Enabled by A Microsize Niobium Tungsten Oxide Anode

AbstractDual‐ion batteries (DIBs) have gained great attention due to their advantages of high operating voltage and low cost. However, the overall performance of the reported DIBs falls far below expectation. In particular, electrode materials with rapid‐charging kinetics and high volumetric packing densities are still in short supply. Herein, a holistic design of the DIB is proposed by using a Wadsley–Roth phase niobium tungsten oxide as the anode, which possesses facile ion transport tunnels and ultrahigh electrode density to deliver superior volumetric performance (521.5 Ah L−1 at 0.2 C and 154.3 Ah L−1 at 60 C), and choosing graphite as the cathode. Benefiting from the respective advantages of this novel anode and the graphite cathode, the as‐built DIB full cell exhibits high volumetric and excellent rate performance (137.7 Ah L−1 at 1 C and 79.2 Ah L−1 at 5 C), and long‐term cyclic stability (1000 cycles at 5 C with negligible capacity attenuation). More impressively, such cells can deliver a high volumetric energy density (422.7 Wh L−1) and power density (8.3 kW L−1) . Furthermore, the comprehensive charge storage chemistry of this DIB is elaborated by operando electrochemical characterizations, and this assembly of flexible pouch cells shows its practical prospects.

Niobium Tungsten Oxides for Electrochromic Devices with Long-Term Stability.

There is a keen interest in the use of electrochromic materials because they can regulate light and heat, thereby reducing the cooling and heating energy. However, the long response time, short cycle life, and high power consumption of an electrochromic film hinder its development. Here, we report an electrochromic material of complex niobium tungsten oxides. The Nb18W16O93 thin films in the voltage range of 0 to -1.5 V show good redox kinetics with the coloration time of 4.7 s and bleaching time of 4.0 s, respectively. The electrochromic device based on the Nb18W16O93 thin film has an optical modulation of 53.1% at a wavelength of 633 nm, with the coloration efficiency of ∼46.57 cm2 C-1. An excellent electrochemical stability of 78.1% retention after 8000 cycles is also achieved. These good performances are due to the fast and stable Li-ion intercalation/extraction in the open framework of Nb18W16O93 with multiple ion positions. Our work provides a strategy for electrochromic materials with fast response time and good cycle stability.

Fibonacci Stoichiometry and Superb Performance of Nb<sub>16</sub>W<sub>5</sub>O<sub>55</sub> and Related Super-Battery Materials

In this contribution, two important crystallographic concepts for the formation of a series of block structures associated with channeling have been compared: chemical twinning and crystallographic shear. Twin planes respectively shear planes besides formed channels serve as a sink for charge carriers or, when the oxidation state of metal ions can be reduced, as a reservoir for intercalated lithium. In this way, Wadsley-Roth shear phases such as niobium tungsten oxide exhibit channels for ultra-fast lithium-ion diffusion. They are in focus as anode material for super-batteries, superb in terms of energy respectively power density, charging time, cycle life and safety. It should be noted that the transition metal to oxygen ratio TM/O = 21/55 of the title compound is a Fibonacci number quotient. Also, the crystal lattice can be traced back to Fibonacci geometry. When replacing only 0.0213 tungsten atoms in the formula with less expensive titanium, a TM/O ratio of 0.381966 =ϕ2 can be adapted besides an average valence electron concentration of 2⋅ϕ-2, where represents the most irrational number of the golden mean. The additional disorder caused by even such small titanium replacement and accompanied oxygen vacancies could fasten up the already high lithium diffusion further. Ultrasonic treatment may be applied besides thermal cycling to prepare phase-pure of the highest electrochemical performance. A replacement of oxygen by some fluorine atoms is an obvious synthesis possibility, but the higher binding energy expected between lithium and fluorine in contrast to oxygen may rather hinder than promote lithium diffusion.