TiO2 Nanostructures as Anode Materials for Li/Na-Ion Batteries

Challenges and Strategies for Synthesizing High Performance Micro and Nanoscale High Entropy Oxide Materials

High-entropy oxide micro/nano materials (HEO MNMs) have shown broad application prospects and have become hot materials in recent years. This review comprehensively provides an overview of the latest developments and covers key aspects of HEO MNMs, by discussing design principles, computer-aided structural design, synthesis challenges and strategies, as well as application areas. The analysis of the synthesis process includes the role of high-throughput process in large-scale synthesis of HEOs MNMs, along with the effects of temperature elevation and undercooling on the formation of HEO MNMs. Additionally, the article summarizes the application of high-precision and in situ characterization devices in the field of HEO MNMs, offering robust support for related research. Finally, a brief introduction to the main applications of HEO MNMs is provided, emphasizing their key performances. This review offers valuable guidance for future research on HEO MNMs, outlining critical issues and challenges in the current field.

A rapid supercritical water approach for one-pot synthesis of a branched BiVO4/RGO composite as a Li-ion battery anode

The application of novel one-dimensional (1D) architectures in the field of energy storage has fascinated researchers for a long time. The fast-paced technological advancements require reliable rapid synthesis techniques for the development of various Multi-metal oxide (MMO) nanostructures. For the first time, we report the synthesis of a single-phase hierarchical one-dimensional (1D) branched BiVO4-Reduced Graphene Oxide (BVONB/RGO) nanocomposite with different weight percent variations of RGO starting from 6, 12, 24, and 26 wt% using the supercritical water method (SCW). The affirmation of the sample characteristics is done through various nano-characterization tools that help in establishing the monoclinic crystal structure, and nano branch morphology along with its physical, and thermal characteristics. Further, the electrochemical behavior evaluations of the fabricated coin cells provide insights into the well-known superior initial cycle capacity of around 810 mA h g-1, showing the superior ability of BVONB structures in storing lithium-ions (Li-ions). Meanwhile, an improved cyclic performance of the pure BVONB/RGO with 260 mA h g-1 is evident after 50 cycles. Finally, the reported rapid single-pot SCW approach has delivered promising results in establishing a material process technique for multimetal oxides and their RGO nanocomposites successfully.

Recent Advances and Challenges in Ti-Based Oxide Anodes for Superior Potassium Storage

Developing high-performance anodes is one of the most effective ways to improve the energy storage performances of potassium-ion batteries (PIBs). Among them, Ti-based oxides, including TiO2, K2Ti6O13, K2Ti4O9, K2Ti8O17, Li4Ti5O12, etc., as the intrinsic structural advantages, are of great interest for applications in PIBs. Despite numerous merits of Ti-based oxide anodes, such as fantastic chemical and thermal stability, a rich reserve of raw materials, non-toxic and environmentally friendly properties, etc., their poor electrical conductivity limits the energy storage applications in PIBs, which is the key challenge for these anodes. Although various modification projects are effectively used to improve their energy storage performances, there are still some related issues and problems that need to be addressed and solved. This review provides a comprehensive summary on the latest research progress of Ti-based oxide anodes for the application in PIBs. Besides the major impactful work and various performance improvement strategies, such as structural regulation, carbon modification, element doping, etc., some promising research directions, including effects of electrolytes and binders, MXene-derived TiO2-based anodes and application as a modifier, are outlined in this review. In addition, noteworthy research perspectives and future development challenges for Ti-based oxide anodes in PIBs are also proposed.

Toward Highly Stable Anode for Secondary Batteries: Employing TiO2 Shell as Elastic Buffering Marix for FeOx Nanoparticles

Transition metal oxides are considered promising anode materials for next-generation lithium-ion and sodium-ion batteries (LIBs and SIBs) because of their high theoretical capacities; however, their practical application is limited by the detrimental large volume expansion that occurs upon cycling. In this work, a rationally designed TiO₂ @Fe@FeO_x nanocomposite encapsulated by a TiO₂ shell with unique core-shell structure is synthesized and exhibits outstanding electrochemical performance as an anode in LIBs and SIBs. The nanocomposite exhibits a reversible capacity of 619.2 mAh g^-1 at 1 A g^-1 with a coulombic efficiency over 99.5% after 1000 cycles when used as a LIB anode. The nanocomposite also exhibits superior sodium storage performance (267 mAh g^-1 at 50 mA g^-1 , capacity retention of 65.4% after 1000 cycles at 200 mA g^-1 ). The TiO₂ shell serves as a strong conformal layer and soft matrix that can tolerate the volume expansion and maintain the structural integrity of the anode during discharging and charging. Moreover, the open active diffusion channels of the shell contribute to high ion diffusivity and improved ionic, and electronic diffusion. These findings indicate that adoption of TiO₂ coating is an effective strategy to optimize the electrochemical performance of transition metal oxide anode materials.

Graphene: Chemistry and Applications for Lithium-Ion Batteries

In the present era, different allotropes of carbon have been discovered, and graphene is the one among them that has contributed to many breakthroughs in research. It has been considered a promising candidate in the research and academic fields, as well as in industries, over the last decade. It has many properties to be explored, such as an enhanced specific surface area and beneficial thermal and electrical conductivities. Graphene is arranged as a 2D structure by organizing sp2 hybridized C with alternative single and double bonds, providing an extended conjugation combining hexagonal ring structures to form a honeycomb structure. The precious structure and outstanding characteristics are the major reason that modern industry relies heavily on graphene, and it is predominantly applied in electronic devices. Nowadays, lithium-ion batteries (LIBs) foremostly utilize graphene as an anode or a cathode, and are combined with polymers to use them as polymer electrolytes. After three decades of commercialization of the lithium-ion battery, it still leads in consumer electronic society due to its higher energy density, wider operating voltages, low self-discharge, noble high-temperature performance, and fewer maintenance requirements. In this review, we aim to give a brief review of the domination of graphene and its applications in LIBs.

Europium modified TiO2 as a high-rate long-cycle life anode material for lithium-ion batteries

Oxygen vacancies and Ti3+ were produced by Eu3+/Eu2+ doped TiO2, which features excellent rate performance and long-term stability.

Enhancing Lithium and Sodium Storage Properties of TiO2(B) Nanobelts by Doping with Nickel and Zinc

Nickel- and zinc-doped TiO2(B) nanobelts were synthesized using a hydrothermal technique. It was found that the incorporation of 5 at.% Ni into bronze TiO2 expanded the unit cell by 4%. Furthermore, Ni dopant induced the 3d energy levels within TiO2(B) band structure and oxygen defects, narrowing the band gap from 3.28 eV (undoped) to 2.70 eV. Oppositely, Zn entered restrictedly into TiO2(B), but nonetheless, improves its electronic properties (Eg is narrowed to 3.21 eV). The conductivity of nickel- (2.24 × 10-8 S·cm-1) and zinc-containing (3.29 × 10-9 S·cm-1) TiO2(B) exceeds that of unmodified TiO2(B) (1.05 × 10-10 S·cm-1). When tested for electrochemical storage, nickel-doped mesoporous TiO2(B) nanobelts exhibited improved electrochemical performance. For lithium batteries, a reversible capacity of 173 mAh·g-1 was reached after 100 cycles at the current load of 50 mA·g-1, whereas, for unmodified and Zn-doped samples, around 140 and 151 mAh·g-1 was obtained. Moreover, Ni doping enhanced the rate capability of TiO2(B) nanobelts (104 mAh·g-1 at a current density of 1.8 A·g-1). In terms of sodium storage, nickel-doped TiO2(B) nanobelts exhibited improved cycling with a stabilized reversible capacity of 97 mAh·g-1 over 50 cycles at the current load of 35 mA·g-1.

Oxygen-substituted borophene as a potential anode material for Li/Na-ion batteries: a first principles study

Two-dimensional graphene-like hexagonal borophene sheets (HBSs) have a thermodynamically unsteady configuration since boron has one electron less than the carbon in graphene. To overcome this problem, we proposed a novel 2D graphene-like HBS oxide (h-B3O) in theory, which is designed by substituting partial boron atoms in a HBS with oxygen atoms. Molecular dynamics simulations indicate that h-B3O has good thermal stability. Besides, we also explored the potential of h-B3O monolayers as anodes for Li-ion batteries (LIBs) and Na-ion batteries (NIBs) by using first-principles calculations. The results indicated that the h-B3O monolayer has high adsorption energies (-2.33/-1.70 eV for Li/Na), low diffusion barriers (0.67/0.42 eV for Li/Na) and suitable average open-circuit voltages (0.36/0.32 V for LIBs/NIBs). Particularly, h-B3O has a large theoretical specific capacity of 1161 mA h g-1 for LIBs. Thus, benefiting from these characteristics, the h-B3O monolayer is considered as a promising candidate for an anode material for LIBs/NIBs.

Ultrathin 2D Mesoporous TiO2 /rGO Heterostructure for High-Performance Lithium Storage

Lithium-ion batteries (LIBs) have been widely applied and studied as an effective energy supplement for a variety of electronic devices. Titanium dioxide (TiO₂ ), with a high theoretical capacity (335 mAh g^-1 ) and low volume expansion ratio upon lithiation, has been considered as one of the most promising anode materials for LIBs. However, the application of TiO₂ is hindered by its low electrical conductivity and slow ionic diffusion rate. Herein, a 2D ultrathin mesoporous TiO₂ /reduced graphene (rGO) heterostructure is fabricated via a layer-by-layer assembly process. The synergistic effect of ultrathin mesoporous TiO₂ and the rGO nanosheets significantly enhances the ionic diffusion and electron conductivity of the composite. The introduced 2D mesoporous heterostructure delivers a significantly improved capacity of 350 mAh g^-1 at a current density of 200 mA g^-1 and excellent cycling stability, with a capacity of 245 mAh g^-1 maintained over 1000 cycles at a high current density of 1 A g^-1 . The in situ transmission electron microscopy analysis indicates that the volume of the as-prepared 2D heterostructures changes slightly upon the insertion and extraction of Li⁺ , thus contributing to the enhanced long-cycle performance.

High Pseudocapacitance Boosts Ultrafast, High-Capacity Sodium Storage of 3D Graphene Foam-Encapsulated TiO2 Architecture

Anatase TiO₂ is an attractive anode for Li-ion batteries and Na-ion batteries because of its structural stability. However, the electrochemical capability of anatase TiO₂ is unsatisfactory due to its intrinsically low electrical conductivity and poor ion diffusivity at the electrode/electrolyte interface. We prepared 3D lightweight graphene aerogel-encapsulated anatase TiO₂, which exhibits a high reversible capacity (390 mA h g^-1 at 50 mA g^-1), a superior rate performance (164.9 mA h g^-1 at 5 A g^-1), and a long-term cycling capability (capacity retention of 86.8% after 7800 cycles). The major energy-storage mechanism is surface capacitance dominated, which favors a high capacity and fast Na⁺ uptake. The inherent features of 3D porous aerogels provide additional active reaction sites and facilitate fast charge diffusion and easy ion access. This will enable the development of 3D interconnected, graphene-based, high-capacity active materials for the development of next-generation energy-storage applications.

Comparative study of the implementation of tin and titanium oxide nanoparticles as electrodes materials in Li-ion batteries

Transition metal oxides potentially present higher specific capacities than the current anodes based on carbon, providing an increasing energy density as compared to commercial Li-ion batteries. However, many parameters could influence the performance of the batteries, which depend on the processing of the electrode materials leading to different surface properties, sizes or crystalline phases. In this work a comparative study of tin and titanium oxide nanoparticles synthesized by different methods, undoped or Li doped, used as single components or in mixed ratio, or alternatively forming a composite with graphene oxide have been tested demonstrating an enhancement in capacity with Li doping and better cyclability for mixed phases and composite anodes.

A stable TiO2–graphene nanocomposite anode with high rate capability for lithium-ion batteries

A rapid microwave hydrothermal process is adopted for the synthesis of titanium dioxide and reduced graphene oxide nanocomposites as high-performance anode materials for Li-ion batteries. With the assistance of hydrazine hydrate as a reducing agent, graphene oxide was reduced while TiO₂ nanoparticles were grown in situ on the nanosheets to obtain the nanocomposite material. The morphology of the nanocomposite obtained consisted of TiO₂ particles with a size of ∼100 nm, uniformly distributed on the reduced graphene oxide nanosheets. The as-prepared TiO₂–graphene nanocomposite was able to deliver a capacity of 250 mA h g⁻¹ ± 5% at 0.2C for more than 200 cycles with remarkably stable cycle life during the Li⁺ insertion/extraction process. In terms of high rate capability performance, the nanocomposite delivered discharge capacity of ca. 100 mA h g⁻¹ with >99% coulombic efficiency at C-rates of up to 20C. The enhanced electrochemical performance of the material in terms of high rate capability and cycling stability indicates that the as-developed TiO₂–rGO nanocomposites are promising electrode materials for future Li-ion batteries.

A rapid microwave hydrothermal process is adopted for the synthesis of titanium dioxide and reduced graphene oxide nanocomposites as high-performance anode materials for Li-ion batteries.

Interfacial Lattice-Strain-Driven Generation of Oxygen Vacancies in an Aerobic-Annealed TiO2 (B) Electrode

Oxygen vacancies play crucial roles in defining physical and chemical properties of materials to enhance the performances in electronics, solar cells, catalysis, sensors, and energy conversion and storage. Conventional approaches to incorporate oxygen defects mainly rely on reducing the oxygen partial pressure for the removal of product to change the equilibrium position. However, directly affecting reactants to shift the reaction toward generating oxygen vacancies is lacking and to fill this blank in synthetic methodology is very challenging. Here, a strategy is demonstrated to create oxygen vacancies through making the reaction energetically more favorable via applying interfacial strain on reactants by coating, using TiO₂ (B) as a model system. Geometrical phase analysis and density functional theory simulations verify that the formation energy of oxygen vacancies is largely decreased under external strain. Benefiting from these, the obtained oxygen-deficient TiO₂ (B) exhibits impressively high level of capacitive charge storage, e.g., ≈53% at 0.5 mV s^-1 , far surpassing the ≈31% of the unmodified counterpart. Meanwhile, the modified electrode shows significantly enhanced rate capability delivering a capacity of 112 mAh g^-1 at 20 C (≈6.7 A g^-1 ), ≈30% higher than air-annealed TiO₂ and comparable to vacuum-calcined TiO₂ . This work heralds a new paradigm of mechanical manipulation of materials through interfacial control for rational defect engineering.

Nitrogen-Doped TiO2-C Composite Nanofibers with High-Capacity and Long-Cycle Life as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped TiO₂-C composite nanofibers (TiO₂/N-C NFs) were manufactured by a convenient and green electrospinning technique in which urea acted as both the nitrogen source and a pore-forming agent. The TiO₂/N-C NFs exhibit a large specific surface area (213.04 m² g^-1) and a suitable nitrogen content (5.37 wt%). The large specific surface area can increase the contribution of the extrinsic pseudocapacitance, which greatly enhances the rate capability. Further, the diffusion coefficient of sodium ions (D _Na+) could be greatly improved by the incorporation of nitrogen atoms. Thus, the TiO₂/N-C NFs display excellent electrochemical properties in Na-ion batteries. A TiO₂/N-C NF anode delivers a high reversible discharge capacity of 265.8 mAh g^-1 at 0.05 A g^-1 and an outstanding long cycling performance even at a high current density (118.1 mAh g^-1) with almost no capacity decay at 5 A g^-1 over 2000 cycles. Therefore, this work sheds light on the application of TiO₂-based materials in sodium-ion batteries.

Nitrogen-Doped TiO2-C Composite Nanofibers with High-Capacity and Long-Cycle Life as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped TiO₂-C composite nanofibers (TiO₂/N-C NFs) were manufactured by a convenient and green electrospinning technique in which urea acted as both the nitrogen source and a pore-forming agent. The TiO₂/N-C NFs exhibit a large specific surface area (213.04 m² g^-1) and a suitable nitrogen content (5.37 wt%). The large specific surface area can increase the contribution of the extrinsic pseudocapacitance, which greatly enhances the rate capability. Further, the diffusion coefficient of sodium ions (D _Na+) could be greatly improved by the incorporation of nitrogen atoms. Thus, the TiO₂/N-C NFs display excellent electrochemical properties in Na-ion batteries. A TiO₂/N-C NF anode delivers a high reversible discharge capacity of 265.8 mAh g^-1 at 0.05 A g^-1 and an outstanding long cycling performance even at a high current density (118.1 mAh g^-1) with almost no capacity decay at 5 A g^-1 over 2000 cycles. Therefore, this work sheds light on the application of TiO₂-based materials in sodium-ion batteries.