Halide Layer Cathodes for Compatible and Fast-Charged Halides-Based All-Solid-State Li Metal Batteries

Insertion-type compounds based on oxides and sulfides have been widely identified and well-studied as cathode materials in lithium-ion batteries. However, halides have rarely been used due to their high solubility in organic liquid electrolytes. Here, we reveal the insertion electrochemistry of VX₃ (X=Cl, Br, I) by introducing a compatible halide solid-state electrolyte with a wide electrochemical stability window. X-ray absorption near-edge structure analyses reveal a two-step lithiation process and the structural transition of typical VCl₃. Fast Li⁺ insertion/extraction in the layered VX₃ active materials and favorable interface guaranteed by the compatible electrode-electrolyte design enables high rate capability and stable operation of all-solid-state Li-VX₃ batteries. The findings from this study will contribute to developing intercalation insertion electrochemistry of halide materials and exploring novel electrode materials in viable energy storage systems.     

Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali‐Ion Batteries

We discuss here a unique flexible non‐carbonaceous layered host, namely, metal titanium niobates (M‐Ti‐niobate, M: Al³⁺, Pb²⁺, Sb³⁺, Ba²⁺, Mg²⁺), which can synergistically store both lithium ions and sodium ions via a simultaneous intercalation and alloying mechanisms. M‐Ti‐niobate is formed by ion exchange of the K⁺ ions, which are specifically located inside galleries between the layers formed by edge and corner sharing TiO₆ and NbO₆ octahedral units in the sol‐gel synthesized potassium titanium niobate (KTiNbO₅). Drastic volume changes (approximately 300–400 %) typically associated with an alloying mechanism of storage are completely tackled chemically by the unique chemical composition and structure of the M‐Ti‐niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50–75 % of total K⁺) in the M‐Ti‐niobate, an efficient alloying reaction takes place directly with ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M‐Ti‐niobate can be cycled over a wide voltage range (as low as 0.01 V) and displays remarkably stable Li⁺ and Na⁺ ion cyclability (>2 Li⁺/Na⁺ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms is also studied within the density functional theory (DFT) framework. DFT expectedly shows a very small variation in the volume of Al‐titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively support the occurrence of the alloying process of Li ions with the Al ions along with the intercalation process during discharge. The M‐Ti‐niobates studied here demonstrate a paradigm shift in chemical design of electrodes and will pave the way for the development of a multitude of improved electrodes for different battery chemistries.     

In situ spectroelectrochemical behaviour of nanocrystalline TiO2 thin films electrode fabricated by pulsed laser deposition

Nanocrystalline titanium oxide thin films have been successfully deposited on IT0 coated glass by pulsed laser ablation of metallic Ti target in 0₃/0₂ ambient gases. The intercalation of Li ions in the anatase TiO₂ film electrode is examined by cyclic voltammetry. The electrochromic behaviour of TiO₂ electrode is investigated byin-situ visible transmittance measurement, and two absorption bands at 420 and 650 nm are observed. The absorption falling and rising in color changing with excellent revisibility is relative to the insertion and deintercalation processes of Li ion. These results suggest that nanocrystalline titanium oxide films fabricated by pulsed laser deposition exhibit excellent spectroelectrochemical property. Project supported by the National Natural Science Foundation of China (Grant No. 29783001) and State Key Laboratory for Physical Chemistry of Solid Surface of Xiamen University (1997).     

Synergistic tuning of electrochemical surface area and surface Co3+ by oxygen plasma enhances the capacities of Co3O4 lithium–oxygen battery cathodes

Modifying electrochemical surface area (ECSA) and surface chemistry are promising approaches to enhance the capacities of oxygen cathodes for lithium–oxygen (Li–O₂) batteries. Although various chemical approaches have been successfully used to tune the cathode surface, versatile physical techniques including plasma etching etc. could be more effortless and effective than arduous chemical treatments. Herein, for the first time, we propose a facile oxygen plasma treatment to simultaneously etch and modify the surface of Co₃O₄ nanosheet arrays (NAs) cathode for Li–O₂ batteries. The oxygen plasma not only etches Co₃O₄ nanosheets to enhance the ECSA but also lowers the oxygen vacancy concentration to enable a Co³⁺-rich surface. In addition, the NA architecture enables the full exposure of oxygen vacancies and surface Co³⁺ that function as the catalytically active sites. Thus, the synergistic effects of enhanced ECSA, modest oxygen vacancy and high surface Co³⁺ achieve a significantly enhanced reversible capacity of 3.45 mAh/cm² for Co₃O₄ NAs. This work not only develops a promising high-capacity cathode for Li–O₂ batteries, but also provides a facile physical method to simultaneously tune the nanostructure and surface chemistry of energy storage materials.     

熔融盐法制备富氧空位TiO2纳米片及其光催化性能

氧空位缺陷对半导体材料性能的积极作用引起人们越来越多的关注。本文中,以TiCl4在三氟乙酸中的水解产物为前驱体,通过一步熔融盐法成功合成了具有富氧空位的蓝色TiO2纳米片。由于熔融盐低的氧分压,使前驱体在煅烧过程中消耗了TiO2中的晶格氧从而产生大量的氧空位和Ti3+。紫外-可见漫反射光谱测试表明,蓝色TiO2纳米片的带隙宽度减小至2.69eV,光吸收范围从紫外光区拓宽到可见光区。所制备的蓝色TiO2纳米片表现出优异的光催化活性,在全光谱照射下,对若丹明B的光降解速率是纯TiO2的47.3倍。同时,形成的晶格氟掺杂能有效地稳定氧空位,极大地提高了光生载流子的分离效率。本工作为在半导体氧化物材料内构建氧空位提供了新的思路。     

Enhancement of charge transfer rate at mixed morphology TiO2/graphene interface by Al3+

Applying conductive coatings on the surface of non-conductive materials can effectively reduce the hazards caused by static electricity during the production process. However, commercially available TiO₂ conductive powder relies on rare minerals and produces waste acids and bases. Therefore, we prepared Al-doped TiO₂/graphene composites, which combine the advantages of TiO₂ homojunction, ion doping, heterojunction, and rod morphology with excellent electrical conductivity (0.161 Ω·cm). In particular, the doping of Al³⁺ doubles its conductivity. This is due to the introduction of Al³⁺, which generates oxygen vacancies and so increases the carrier concentration. Furthermore, the introduction of Al³⁺ generates new conductive pathways (Al–O–C) and increases the content of highly electrochemically active oxygen-containing functional groups, leading to a significant enhancement of carrier transfer efficiency. Accordingly, the enhanced carrier concentration and transfer efficiency enhance the conductive properties of T-G-Al and provide new ideas for the preparation of conductive coatings.     

Tuning the layer structure of molybdenum trioxide towards high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) have attracted significant attentions because of low cost and high reliability. However, conventional ZIBs are severely limited by the development of high energy density cathode materials with reversible Zn²⁺ insertion/extraction. Herein, a conducting polymer intercalated MoO₃ (PMO) with extensively extended interlayer spacing is developed as a high-performance ZIBs cathode material. The interlayer spacing of PMO is prominently increased which results in an improved Zn²⁺ mobility during charge and discharge process. More significantly, the electrochemical results reveals that the intercalation of PANI facilitates the charge storage and reinforces the layered structure of MoO₃, leading to a high capacity and good cycling stability. DFT calculation further reveals the intercalation of PANI into MoO₃ significantly lower Zn²⁺ diffusion barrier. Benefit from these advantages, the ZIBs based on PMO electrode delivers a considerable capacity of 157 mAh/g at 0.5 A/g and ameliorative stability with 63.4% capacity retention after 1000 cycles.     

Oxidation in the γ phase of spinels containing iron II: Influence of defects on the oxidation kinetics and electrical properties

After a review of the distribution of vacancies in defect phases resulting from γFe₂O₃, the authors give several examples drawn from oxidation kinetics and electrical properties, where the vacancies play a basic part due to their concentration as well as their location. The decrease in chemical diffusion coefficient with increase in vacancy extent and the variation of the exponent from the pressure law with the extent of association are dependent on concentration, while the nature of the electron hopping between Fe²⁺ and Fe³⁺ ions is governed by the location of vacancies in the two types of sites in the spinel lattice.     

Boosting Fe Cationic Vacancies with Graphdiyne to Enhance Exceptional Pseudocapacitive Lithium Intercalation

Modulating the electronic structure of electrode materials at atomic level is the key to controlling electrodes with outstanding rate capability. On the basis of modulating the iron cationic vacancies (IV) and electronic structure of materials, we proposed the method of preparing graphdiyne/ferroferric oxide heterostructure (IV-GDY-FO) as anode materials. The goal is to motivate lithium-ion batteries (LIBs) toward ultra-high capacity, superior cyclic stability, and excellent rate performance. The graphdiyne is used as carriers to disperse Fe₃O₄ uniformly without agglomeration and induce high valence of Fe with reducing the energy in the system. The presence of Fe vacancy could regulate the charge distribution around vacancies and adjacent atoms, leading to facilitate electronic transportation, enlarge the lithium-ion diffusion, and decrease Li⁺ diffusion barriers, and thus displaying significant pseudocapacitive process and advantageous lithium-ion storage. The optimized electrode IV-GDY-FO reveals a capacity of 2084.1 mAh g⁻¹ at 0.1 C, superior cycle stability and rate performance with a high specific capacity of 1057.4 mAh g⁻¹ even at 10 C.     

Nb-doped rutile titanium dioxide nanorods for lithium-ion batteries

Rutile titanium dioxide is a promising negative electrode material for lithium-ion batteries due to low volume change on lithium-ion insertion, fast ion diffusion, and large surface area. However, the low theoretical capacity and conductivity of titanium dioxide has limited its application. In this work, rutile TiO₂ was synthesized using a batch hydrothermal method, and doped with Nb⁵⁺ (3.5 at%). <Potentiodynamic/galvanostatic > cycling in the range 1.0–3.0 V vs Li/Li⁺ was used to determine the Li-ion capacity of the doped and pristine TiO₂ material, and electrochemical cycling was used to measure the extent of conversion from the lithiated to de-lithiated state. The nanoscale structures of the pristine and doped materials were determined by powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller surface area measurements. Cycling in the range 1.0–3.0 V vs Li/Li⁺ showed that Nb⁵⁺ doping into the structure resulted in higher charge capacities. After 100 cycles at 100 mA g⁻¹, the Nb-doped rutile TiO₂ maintained a capacity of ca. 390 mAh g⁻¹, 64% higher than undoped TiO₂. For electrochemical cycling in the range 0.05–3.0 V vs Li/Li⁺, the introduction of Nb⁵⁺ resulted in a higher conversion of rutile TiO₂ from the lithiated to de-lithiated state. The higher capacity of the doped TiO₂ is shown to be mainly due to the smaller particle size, optimized surface area, and orientation of the nanorods.     

The Rechargeable Aluminum Battery: Opportunities and Challenges

Aluminum battery systems are considered as a system that could supplement current lithium batteries due to the low cost and high volumetric capacity of aluminum metal, and the high safety of the whole battery system. However, first the use of ionic liquid electrolytes leading to AlCl₄^? instead of Al³⁺, the different intercalation reagents, the sluggish solid diffusion process and the fast capacity fading during cycling in aluminum batteries all need to be thoroughly explored. To provide a good understanding of the opportunities and challenges of the newly emerging aluminum batteries, this Review discusses the reaction mechanisms and the difficulties caused by the trivalent reaction medium in electrolytes, electrodes, and electrode–electrolyte interfaces. It is hoped that the Review will stimulate scientists and engineers to develop more reliable aluminum batteries.     

Investigation of europium-ammonia intercalation compounds of titanium disulfide

EuNH₃ intercalation compounds of titanium disulfide have been synthesized from EuNH₃ solutions at −40 °C, characterized and studied using Mössbauer spectroscopy. These materials are at least initially mixedvalence compounds, with Eu²⁺ and Eu³⁺ probably occupying distinct sites. Europium occurs predominantly in the trivalent oxidation state. However, the nature of the intercalation products depends stongly upon the method of preparation as well as annealing time and temperature.     

Ammonium Ion Batteries: Material,Electrochemistry and Strategy

Ammonium-ion batteries (AIBs) have recently attracted increasing attention in the field of aqueous batteries owing to their high safety and fast diffusion kinetics. The NH₄⁺ storage mechanism is quite different from that of spherical metal ions (e.g. Li⁺, Na⁺, K⁺, Mg²⁺, and Zn²⁺) because of the formation of hydrogen bonds between NH₄⁺ and host materials. Although many materials have been proposed as electrode materials for AIBs, their performances hardly meet the requirement of future electrochemical energy storage devices. It is thus urgent to design and exploit advanced materials for AIBs. This review highlights the state-of-the-art research on AIBs. The insights into the basic configuration, operating mechanism and recent progress of electrode materials and corresponding electrolytes for AIBs have been comprehensively outlined. The electrode materials are classified and compared according to different NH₄⁺ storage behaviour in the structure. The challenges, design strategies and perspectives are also discussed for the future development of AIBs.     

Defect processes in MgAl2O4 spinel

In perfect normal MgAl₂O₄ spinel the Mg²⁺ ions occupy tetrahedral 8a sites and Al³⁺ ions occupy octahedral 16d sites. In reality some cations are exchanged between the cation sublattices forming pairs of antisite defects and thus a degree of “inversion”. Here atomic simulation is used to investigate the influence that antisite defects have on the populations of other intrinsic defects, those associated with Schottky and Frenkel reactions. One consequence is that the total magnesium interstitial concentration is increased substantially over the aluminium interstitial concentration and the magnesium vacancy concentration is increased over the aluminium vacancy concentration but to a much smaller extent. The split structures of isolated interstitial defects and the stability of various defect clusters are also discussed.     

Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO2 Using DRS,PL, and EPR

The electronic structure and photoactivation process in N‐doped TiO₂ is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat‐ and photoinduced N‐doped TiO₂ catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti³⁺ states are formed to enhance the optical absorption in the visible‐light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N‐doped TiO₂, the DRS absorption and PL emission in the visible spectral region of 450–700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N_s^.), oxygen vacancies with one electron (V_o^.), and Ti³⁺ ions are produced with light irradiation and the intensity of N_s^. species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO₂ corresponding to the main absorption band at 410 nm of N‐doped TiO₂, but oxygen vacancies and Ti³⁺ states as defects contribute to the visible‐light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N‐doped TiO₂ is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen‐vacancy‐related defects leads to quenching of paramagnetic N_s^. species but they stabilize the active nitrogen species N_s^?.     

In situ study of electrochromic properties of self-assembled TiO2 nanotubes

Electrochromical properties of anodic self-assembled nanotubes were investigated. It was found that amorphous titania nanotubes were able to insert H⁺ ions in a highly reversible manner. Coloration of the TiO₂ nanotubes occurred at potentials below ?0.5 V vs. Ag/AgCl in 1M (NH₄)₂SO₄ aqueous solution. The proton insertion reaction probably leads to the formation of a Ti³⁺/Ti⁴⁺ solid solution in the amorphous titania electrode, as was shown by the analysis of the derivative curve. The nanotubular titania electrode shows reasonable color efficiency when compared with other electrochromic materials and it is a promising candidate for the fabrication of low-cost interdigitated electrochromic devices.     

Does the valence state of an ion affect its diffusivity? Part I: Oxygen activity dependence of the diffusion of iron in alumina-doped MgO

To investigate whether a change in the valence state of tracer ions affects their diffusivity or not, the iron tracer diffusion in Al₂O₃-doped MgO, in which 0.5% of the cations were Al³⁺ ions, has been studied experimentally. Samples were prepared from high purity aluminum and magnesium nitrates using a chemical solution method and from powders of high purity Al₂O₃ and MgO. Because the concentration of the Al³⁺ dopant ions present in the samples was much larger than that of all other impurities, the concentration of the majority point defects, cation vacancies, was determined by the Al³⁺ concentration. Therefore, when changing the oxygen activity, the diffusivity of iron tracer ions can only be altered by changes in their valence state. Measurements of iron tracer diffusion coefficients were performed as a function of the oxygen activity at 1100 and 1200 °C. The experimental results indicate that the mean diffusivity of iron ions in Al₂O₃-doped MgO increases with increasing oxygen activity at both temperatures, suggesting that Fe³⁺ ions diffuse in Al₂O₃-doped MgO faster than Fe²⁺ ions.     

Redox Chemistry of Molybdenum Trioxide for Ultrafast Hydrogen‐Ion Storage

Hydrogen ions are ideal charge carriers for rechargeable batteries due to their small ionic radius and wide availability. However, little attention has been paid to hydrogen‐ion storage devices because they generally deliver relatively low Coulombic efficiency as a result of the hydrogen evolution reaction that occurs in an aqueous electrolyte. Herein, we successfully demonstrate that hydrogen ions can be electrochemically stored in an inorganic molybdenum trioxide (MoO₃) electrode with high Coulombic efficiency and stability. The as‐obtained electrode exhibits ultrafast hydrogen‐ion storage properties with a specific capacity of 88 mA hg^?1 at an ultrahigh rate of 100 C. The redox reaction mechanism of the MoO₃ electrode in the hydrogen‐ion cell was investigated in detail. The results reveal a conversion reaction of the MoO₃ electrode into H_0.88MoO₃ during the first hydrogen‐ion insertion process and reversible intercalation/deintercalation of hydrogen ions between H_0.88MoO₃ and H_0.12MoO₃ during the following cycles. This study reveals new opportunities for the development of high‐power energy storage devices with lightweight elements.     

Phosphorus-Doping-Induced Surface Vacancies of 3D Na2Ti3O7 Nanowire Arrays Enabling High-Rate and Long-Life Sodium Storage

Sodium-ion batteries have attracted interest as an alternative to lithium-ion batteries because of the abundance and cost effectiveness of sodium. However, suitable anode materials with high-rate and stable cycling performance are still needed to promote their practical application. Herein, three-dimensional Na₂Ti₃O₇ nanowire arrays with enriched surface vacancies endowed by phosphorus doping are reported. As anodes for sodium-ion batteries, they deliver a high specific capacity of 290 mA h g⁻¹at 0.2 C, good rate capability (50 mA h g⁻¹at 20 C), and stable cycling capability (98 % capacity retention over 3100 cycles at 20 C). The superior electrochemical performance is attributed to the synergistic effects of the nanowire arrays and phosphorus doping. The rational structure can provide convenient channels to facilitate ion/electron transport and improve the capacitive contributions. Moreover, the phosphorus-doping-induced surface vacancies not only provide more active sites but also improve the intrinsic electrical conductivity of Na₂Ti₃O₇, which will enable electrode materials with excellent sodium storage performance. This work may provide an effective strategy for the synthesis of other anode materials with fast electrochemical reaction kinetics and good sodium storage performance.     

Investigation of photocatalytic activity of metal-doped TiO2 nanoparticles prepared by Pechini method

M-doped TiO₂ (M = Ag²⁺, Al³⁺, Ce⁴⁺, Nb⁵⁺) with different dopant contents have been prepared by the Pechini method using titanium IV isopropoxide as precursor. The effect of doping concentration on the photocatalytic activity for methyl orange (MO) photodegradation was investigated using UV radiation. The photocatalysts were characterized by surface area, X-ray diffraction and UV–Vis diffuse reflectance spectroscopy. An increase in the photoactivity of TiO₂ nanoparticles was confirmed by MO photocatalytic degradation experiments, when the transition metal ions were incorporated into the semiconductor crystalline lattice, which could be attributed to an increase in the charge separation and reduction of e^?/h⁺ recombination as a function of the substitutional defect generated at very low levels.