Ultrathin Anatase TiO2Nanosheets Embedded with TiO2-B Nanodomains for Lithium-Ion Storage: Capacity Enhancement by Phase Boundaries

Biphase-Interface Enhanced Sodium Storage and Accelerated Charge Transfer: Flower-Like Anatase/Bronze TiO2/C as an Advanced Anode Material for Na-Ion Batteries

Flower-like assembly of ultrathin nanosheets composed of anatase and bronze TiO₂ embedded in carbon is successfully synthesized by a simple solvothermal reaction, followed with a high-temperature annealing. As an anode material in sodium-ion batteries, this composite exhibits outstanding electrochemical performances. It delivers a reversible capacity of 120 mA h g^-1 over 6000 cycles at 10 C. Even at 100 C, there is still a capacity of 104 mA h g^-1. Besides carbon matrix and hierarchical structure, abundant interfaces between anatase and bronze greatly enhance the performance by offering additional sites for reversible Na⁺ storage and improving the charge-transfer kinetics. The interface enhancements are confirmed by discharge/charge profiles, rate performances, electrochemical impedance spectra, and first-principle calculations. These results offer a new pathway to upgrade the performances of anode materials in sodium-ion batteries.

Engineering the Surface/Interface Structures of Titanium Dioxide Micro and Nano Architectures towards Environmental and Electrochemical Applications

Titanium dioxide (TiO₂) materials have been intensively studied in the past years because of many varied applications. This mini review article focuses on TiO₂ micro and nano architectures with the prevalent crystal structures (anatase, rutile, brookite, and TiO₂(B)), and summarizes the major advances in the surface and interface engineering and applications in environmental and electrochemical applications. We analyze the advantages of surface/interface engineered TiO₂ micro and nano structures, and present the principles and growth mechanisms of TiO₂ nanostructures via different strategies, with an emphasis on rational control of the surface and interface structures. We further discuss the applications of TiO₂ micro and nano architectures in photocatalysis, lithium/sodium ion batteries, and Li-S batteries. Throughout the discussion, the relationship between the device performance and the surface/interface structures of TiO₂ micro and nano structures will be highlighted. Then, we discuss the phase transitions of TiO₂ nanostructures and possible strategies of improving the phase stability. The review concludes with a perspective on the current challenges and future research directions.

Enhancing Distorted Metal-Organic Framework-Derived ZnO as Anode Material for Lithium Storage by the Addition of Ag2S Quantum Dots

The lithium storage properties of the distorted metal-organic framework-derived nanosized ZnO@C are significantly improved by the introduction of Ag₂S quantum dots (QDs) during the processing of the material. In the thermal treatment, the Ag₂S QDs react to produce Ag nanoparticles and ZnS. The metal nanoparticles act to shorten electron pathways and improve the connectivity of the matrix, and the partial sulfidation of the ZnO surface improves the cycling stability of the material. The electrochemical properties of ZnO@C, Ag₂S QDs-treated ZnO@C, and the amorphous carbon in ZnO@C have been compared. The small weight ratio of Ag₂S QDs to ZnO@C at 1:180 shows the best performance in lithium storage. The exhibited specific capacities are improved and retained remarkably in the cycling at high current rates. At low current densities (200 mA g^-1), treatment of ZnO@C with Ag₂S QDs results in a 38% increase in the specific capacity.

Ultrafast-Charging and Long-Life Li-Ion Battery Anodes of TiO2-B and Anatase Dual-Phase Nanowires

Ideal lithium-ion batteries (LIBs) should possess a high power density, be charged extremely fast (e.g., 100C), and have a long service life. To achieve them all, all battery components, including anodes, cathodes, and electrolytes should have excellent structural and functional characteristics. The present work reports ultrafast-charging and long-life LIB anodes made from TiO₂-B/anatase dual-phase nanowires. The dual-phase nanowires are fabricated with anatase TiO₂ nanoparticles through a facile and cost-effective hydrothermal process, which can be easily scaled up for mass production. The anodes exhibit remarkable electrochemical performance with reversible capacities of ∼225, 172, and 140 mAh g^-1 at current rates of 1C, 10C, and 60C, respectively. They deliver exceptional capacity retention of not less than 126 and 93 mAh g^-1 after 1000 cycles at 60C and 100C, respectively, potentially worthwhile for high-power applications. These values are among the best when the high-rate capabilities are compared with the literature data for similar TiO₂-based anodes. The Ragone plot confirms both the exceptionally high energy and power densities of the devices prepared using the dual-phase nanowires. The electrochemical tests and operando Raman spectra present fast electrochemical kinetics for both Li⁺ and electron transports in the TiO₂ dual-phase nanowires than in anatase nanoparticles due to the excellent Li⁺ diffusion coefficient and electronic conductivity of nanowires.

Lithium titanate hydrates with superfast and stable cycling in lithium ion batteries

Lithium titanate and titanium dioxide are two best-known high-performance electrodes that can cycle around 10,000 times in aprotic lithium ion electrolytes. Here we show there exists more lithium titanate hydrates with superfast and stable cycling. That is, water promotes structural diversity and nanostructuring of compounds, but does not necessarily degrade electrochemical cycling stability or performance in aprotic electrolytes. As a lithium ion battery anode, our multi-phase lithium titanate hydrates show a specific capacity of about 130 mA h g⁻¹ at ~35 C (fully charged within ~100 s) and sustain more than 10,000 cycles with capacity fade of only 0.001% per cycle. In situ synchrotron diffraction reveals no 2-phase transformations, but a single solid-solution behavior during battery cycling. So instead of just a nanostructured intermediate to be calcined, lithium titanate hydrates can be the desirable final destination.

Water is usually not favorable in high-voltage window aprotic electrolytes. Here the authors discover some lithium titanate hydrates that allow superior power rate and ultralong cycle life in aprotic electrolytes.

TiO₂ Nanobelt@Co₉S₈ Composites as Promising Anode Materials for Lithium and Sodium Ion Batteries

TiO₂ anodes have attracted great attention due to their good cycling stability for lithium ion batteries and sodium ion batteries (LIBs and SIBs). Unfortunately, the low specific capacity and poor conductivity limit their practical application. The mixed phase TiO₂ nanobelt (anatase and TiO₂-B) based Co₉S₈ composites have been synthesized via the solvothermal reaction and subsequent calcination. During the formation process of hierarchical composites, glucose between TiO₂ nanobelts and Co₉S₈ serves as a linker to increase the nucleation and growth of sulfides on the surface of TiO₂ nanobelts. As anode materials for LIBs and SIBs, the composites combine the advantages of TiO₂ nanobelts with those of Co₉S₈ nanomaterials. The reversible specific capacity of TiO₂ nanobelt@Co₉S₈ composites is up to 889 and 387 mAh·g⁻¹ at 0.1 A·g⁻¹ after 100 cycles, respectively. The cooperation of excellent cycling stability of TiO₂ nanobelts and high capacities of Co₉S₈ nanoparticles leads to the good electrochemical performances of TiO₂ nanobelt@Co₉S₈ composites.

An Unprecedented Case: A Low Specific Surface Area Anatase/N-Doped Carbon Nanocomposite Derived from a New Single Source Precursor Affords Fast and Stable Lithium Storage

A nanocomposite of ultrafine anatase nanoparticles (<5 nm) embedded N-doped carbon (TiO₂-NPs/NC) with a relatively low specific surface area was successfully synthesized by in situ pyrolysis of a new and cheap single source precursor of (H₂en)₃[Ti₄(O₂)₄(Hcit)₂(cit)₂]·12H₂O (en = ethylenediamine and H₄cit = citric acid) under 550 °C and an inert atmosphere. The precursor in crystalline state was isolated from an aqueous solution containing of titanium butoxide, citric acid, hydrogen peroxide, and ethylenediamine and was characterized. The crystal structure was determined by X-ray single crystal diffraction. To our surprise, the low surface area TiO₂-NPs/NC exhibits a high specific capacity, superior rate capability, excellent cycle performance, and good processability as a negative material for rechargeable lithium-ion batteries (LIBs). A large reversible capacity of 360 and 125 mA h g^-1 and a high Coulombic efficiency (the average value is ∼99.8%) could be kept even after 1000 cycles under a current density of 0.3 and 6 A g^-1, respectively. An analysis of the voltammetric sweep data shows that the pseudocapacitive behavior occurred at the surface of the material and the lithium intercalation processes contribute to the total stored charge, resulting in the high capacity of the TiO₂-NPs/NC nanocomposite. The potentiostatic intermittent titration technique used to determine the lithium ion diffusion (D_Li+) suggested the TiO₂-NPs/NC nanocomposite displays a high D_Li+. In addition, the high electric conductivity provided by the NC substrate and the ultrafine anatase particles can mitigate the diffusion path for electrons and ions and tolerate higher strain, and thus effectively decrease pulverization and improve the rate and cycle performance. In particular, the observed superior lithium storage properties, resulting from the low surface area nanocomposite with ultrafine nanoparticles embedded NC substrate, are expected to have fundamental and practical implications for the preparation of high performance electrodes in LIBs or other cells.

Heterogeneous TiO2@Nb2O5 composite as a high-performance anode for lithium-ion batteries

Heterogeneous TiO₂@Nb₂O₅ composites, in which TiO₂ nanoparticles were evenly embedded on ultrathin Nb₂O₅ nanosheets, were used as anode materials for LIBs and demonstrated high capacities and excellent rate capability. For instance, this material displayed large capacities of 166.3 and 129.1 mA h g⁻¹ at current densities of 1 A g⁻¹ after 100 cycles and 5 A g⁻¹ after 300 cycles, respectively.

Efficient Lithium-Ion Storage by Hierarchical Core-Shell TiO2 Nanowires Decorated with MoO2 Quantum Dots Encapsulated in Carbon Nanosheets

Rational design and surface engineering are the key to synthesizing high-performance electrode materials for electrocatalysis and energy conversion and storage applications. Herein, a novel three-dimensional (3D) nanoarchitecture of TiO₂ nanowires decorated with MoO₂ quantum dots encapsulated in carbon nanosheets was successfully synthesized by a simple polymerization method. Such a hierarchical nanostructure can not only exhibit the synergistic effect of structural stability of a 1D TiO₂ substrate and high capacity of 0D MoO₂ quantum dots but also prevent the aggregation and oxidation of MoO₂. As a result, the novel 0D-1D-2D composite illustrates an initial discharge capacity of 470 mAh g^-1 at a high current density of 500 mA g^-1, especially a capacity retention of about 83% after 450 cycles. The present work highlights the designing strategy of nanoarchitectures containing high capacity materials for enhancing electrochemical performance of Ti-based materials.

Electrospinning preparation of oxygen-deficient nano TiO2-x/carbon fibre membrane as a self-standing high performance anode for Li-ion batteries

Improving the specific capacity and electronic conductivity of TiO₂ can boost its practical application as a promising anode material for lithium ion batteries. In this work, a three-dimensional networking oxygen-deficient nano TiO_2-x/carbon fibre membrane was achieved by combining the electrospinning process with a hot-press sintering method and directly used as a self-standing anode. With the synergistic effects of three-dimensional conductive networks, surface oxygen deficiency, high specific surface area and high porosity, binder-free and self-standing structure, etc., the nano TiO_2-x/carbon fibre membrane electrode displays a high electrochemical reaction kinetics and a high specific capacity. The reversible capacity could be jointly generated from porous carbon, full-lithiation of TiO₂ and interfacial lithium storage. At a current density of 100 mA g^-1, the reversible discharge capacity can reach 464 mA h g^-1. Even at 500 mA g^-1, the discharge capacity still remains at 312 mA h g^-1. Compared with pure carbon fibre and TiO₂ powder, the TiO_2-x/C fibre membrane electrode also exhibits an excellent cycle performance with a discharge capacity of 209 mA h g^-1 after 700 cycles at the current density of 300 mA g^-1, and the coulombic efficiency always remains at approximately 100%.

Electrospinning preparation of oxygen-deficient nano TiO2-x/carbon fibre membrane as a self-standing high performance anode for Li-ion batteries

Improving the specific capacity and electronic conductivity of TiO₂ can boost its practical application as a promising anode material for lithium ion batteries. In this work, a three-dimensional networking oxygen-deficient nano TiO_2-x/carbon fibre membrane was achieved by combining the electrospinning process with a hot-press sintering method and directly used as a self-standing anode. With the synergistic effects of three-dimensional conductive networks, surface oxygen deficiency, high specific surface area and high porosity, binder-free and self-standing structure, etc., the nano TiO_2-x/carbon fibre membrane electrode displays a high electrochemical reaction kinetics and a high specific capacity. The reversible capacity could be jointly generated from porous carbon, full-lithiation of TiO₂ and interfacial lithium storage. At a current density of 100 mA g^-1, the reversible discharge capacity can reach 464 mA h g^-1. Even at 500 mA g^-1, the discharge capacity still remains at 312 mA h g^-1. Compared with pure carbon fibre and TiO₂ powder, the TiO_2-x/C fibre membrane electrode also exhibits an excellent cycle performance with a discharge capacity of 209 mA h g^-1 after 700 cycles at the current density of 300 mA g^-1, and the coulombic efficiency always remains at approximately 100%.

Fabrication of Li4Ti5O12-TiO2 Nanosheets with Structural Defects as High-Rate and Long-Life Anodes for Lithium-Ion Batteries

Development of high-power lithium-ion batteries with high safety and durability has become a key challenge for practical applications of large-scale energy storage devices. Accordingly, we report here on a promising strategy to synthesize a high-rate and long-life Li4Ti5O12-TiO2 anode material. The novel material exhibits remarkable rate capability and long-term cycle stability. The specific capacities at 20 and 30 C (1 C = 175 mA g-1) reach 170.3 and 168.2 mA h g-1, respectively. Moreover, a capacity of up to 161.3 mA h g-1 is retained after 1000 cycles at 20 C, and the capacity retention ratio reaches up to 94.2%. The extraordinary rate performance of the Li4Ti5O12-TiO2 composite is attributed to the existence of oxygen vacancies and grain boundaries, significantly enhancing electrical conductivity and lithium insertion/extraction kinetics. Meanwhile, the pseudocapacitive effect is induced owing to the presence of abundant interfaces in the composite, which is beneficial to enhancing specific capacity and rate capability. Additionally, the ultrahigh capacity at low rates, greater than the theoretical value of spinel Li4Ti5O12, may be correlated to the lithium vacancies in 8a sites, increasing the extra docking sites of lithium ions.

Granadilla-Inspired Structure Design for Conversion/Alloy-Reaction Electrode with Integrated Lithium Storage Behaviors

Conversion/alloy-reaction electrode materials promise much higher energy density than the commonly used ones based on intercalation chemistries. However, the low electronic conductivity and, specially, the large volume expansion upon lithiation hinder their practical applications. Here, for the first time, a unique granadilla-inspired structure was designed to prepare the conversion/alloy-reaction anode of carbon coated tin/calcium tin oxide (C@void@Sn/CaSnO₃) ternary composite. The granadilla-inspired structure ensures the intimate contact between the Sn/CaSnO₃ nanoparticles and the carbon matrix, providing not only conductive networks for electron transport and a short distance for Li⁺ diffusion but also effective space for the electrode volume expansion toward conversion/alloy reaction. Moreover, the unique structure possesses abundant solid-solid interfaces between the three components as well as solid-liquid interfaces between nanoparticles and electrolyte, contributing to a large percent (58%) of interfacial charge (thus capacity). The integration of alloy-reaction, conversion-reaction, and interfacial lithium storage endows the hybrid electrode with a high capacity and long cycling life, holding great promise for next-generation high-capacity lithium-ion batteries.

Phase Separation Derived Core/Shell Structured Cu11 V6 O26 /V2 O5 Microspheres: First Synthesis and Excellent Lithium-Ion Anode Performance with Outstanding Capacity Self-Restoration

Novel amorphous vanadium oxide coated copper vanadium oxide (Cu₁₁ V₆ O₂₆ /V₂ O₅ ) microspheres with 3D hierarchical architecture have been successfully prepared via a microwave-assisted solution method and subsequent annealing induced phase separation process. Pure Cu₁₁ V₆ O₂₆ microspheres without V₂ O₅ coating are also obtained by an H₂ O₂ solution dissolving treatment. When evaluated as an anode material for lithium-ion batteries (LIBs), the as-synthesized hybrid exhibits large reversible capacity, excellent rate capability, and outstanding capacity self-recovery. Under the condition of high current density of 1 A g^-1 , the 3D hierarchical Cu₁₁ V₆ O₂₆ /V₂ O₅ hybrid maintains a reversible capacity of ≈1110 mA h g^-1 . Combined electrochemical analysis and high-resolution transmission electron microscopy observation during cycling reveals that the amorphous V₂ O₅ coating plays an important role on enhancing the electrochemical performances and capacity self-recovery, which provides an active amorphous protective layer and abundant grain interfaces for efficient inserting and extracting of Li-ion. As a result, this new copper vanadium oxide hybrid is proposed as a promising anode material for LIBs.

Walnut-like Porous Core/Shell TiO2 with Hybridized Phases Enabling Fast and Stable Lithium Storage

TiO₂ is a promising and safe anode material for lithium ion batteries (LIBs). However, its practical application has been plagued by its poor rate capability and cycling properties. Herein, we successfully demonstrate a novel structured TiO₂ anode with excellent rate capability and ultralong cycle life. The TiO₂ material reported here shows a walnut-like porous core/shell structure with hybridized anatase/amorphous phases. The effective synergy of the unique walnut-like porous core/shell structure, the phase hybridization with nanoscale coherent heterointerfaces, and the presence of minor carbon species endows the TiO₂ material with superior lithium storage properties in terms of high capacity (∼177 mA h g^-1 at 1 C, 1 C = 170 mA g^-1), good rate capability (62 mA h g^-1 at 100 C), and excellent cycling stability (∼83 mA h g^-1 was retained over 10 000 cycles at 10 C with a capacity decay of 0.002% per cycle).

Chestnut-Like TiO2@α-Fe2O3 Core-Shell Nanostructures with Abundant Interfaces for Efficient and Ultralong Life Lithium-Ion Storage

Transition metal oxides caused much attention owing to the scientific interests and potential applications in energy storage systems. In this study, a free-standing three-dimensional (3D) chestnut-like TiO₂@α-Fe₂O₃ core-shell nanostructure (TFN) is rationally synthesized and utilized as a carbon-free electrode for lithium-ion batteries (LIBs). Two new interfaces between anatase TiO₂ and α-Fe₂O₃ are observed and supposed to provide synergistic effect. The TiO₂ microsphere framework significantly improves the mechanical stability, while the α-Fe₂O₃ provides large capacity. The abundant boundary structures offer the possibility for interfacial lithium storage and electron transport. The as-prepared TFN delivers a high capacity of 820 mAh g^-1 even after 1000 continuous cycles with a Coulombic efficiency of ca. 99% at a current of 500 mA g^-1, which is better than the works reported previously. A thin gel-like SEI (solid electrolyte interphase) film and Fe⁰ phase yielded during charge/discharge cycling have been confirmed which makes it possible to alleviate the volumetric change and enhance the electronic conductivity. This confirmation is helpful for understanding the mechanism of lithium-ion storage in α-Fe₂O₃-based materials. The as-prepared free-standing TFN with excellent stability and high capacity can be an appropriate candidate for carbon-free anode material in LIBs.

Surfactant-assisted solvothermal synthesis of NiCo2O4 as an anode for lithium-ion batteries

The as-prepared NiCo₂O₄ nanoparticles through microemulsion-solvothermal growth and subsequent calcination in air exhibits excellent rate performance and cyclic stability.

Ligand-triggered electrostatic self-assembly of CdS nanosheet/Au nanocrystal nanocomposites for versatile photocatalytic redox applications

A facile and efficient ligand-triggered electrostatic self-assembly strategy has been developed to fabricate a series of Au/CdS nanosheet (Ns) (Au-CdS Ns) nanocomposites with varied weight addition ratios of Au nanoparticles (NPs) by judiciously utilizing the intrinsic surface charge properties of assembly units, through which uniform dispersion and controllable deposition of Au NPs on the CdS Ns were achieved. Versatile probe reactions including photocatalytic oxidation of an organic dye pollutant, selective photocatalytic reduction of aromatic nitro compounds and photocatalytic hydrogen production reactions under visible light irradiation and ambient conditions were used to systematically evaluate the photoredox performances of the as-assembled well-defined Au-CdS Ns nanocomposites. It was unveiled that the photoactivities of Au-CdS Ns nanocomposites strongly depend on the weight addition ratio of Au NPs and the addition of an excess amount of Au NPs is detrimental to the separation of photogenerated charge carriers from CdS Ns. With the optimum addition amount of Au NPs (1 wt%), it was found that spontaneous assembly of Au NPs on the CdS Ns remarkably prolonged the lifetime of the photogenerated charge carriers from CdS Ns under visible light irradiation, thus resulting in significantly enhanced photocatalytic redox activities of Au-CdS Ns nanocomposites compared with those of CdS Ns. The crucial role of Au NPs in the photoredox reactions as efficient electron traps rather than plasmonic sensitizers was determined. Moreover, predominant active species responsible for the photocatalytic process were unambiguously determined and a possible photocatalytic mechanism was elucidated. It is anticipated that our work could open up a new avenue to rationally prepare various 2D semiconductors-metal nanocomposites by utilizing such a simple and efficient self-assembly strategy for extensive photocatalytic applications in a myriad of fields.

Self-Templated Synthesis of Ultrathin Nanosheets Constructed TiO2 Hollow Spheres with High Electrochemical Properties

TiO2 is well-known nanomaterials and mostly used as solid nanoparticles, and normal hollow spheres for photocatalysts or electrode materials. In this study, a novel self-templated method is presented to successfully fabricate high-surface-area ultrathin nanosheets constructed TiO2 hollow spheres through the solvothermal treatment of the titanate-silicone composite particles combined with calcination. The uniquely structured hollow spheres exhibit excellent rate capability and good cycle stability even at a high current density of ≈10 C for the anode material of Li-ion battery.

New Approach to Create TiO2(B)/Carbon Core/Shell Nanotubes: Ideal Structure for Enhanced Lithium Ion Storage

To achieve uniform carbon coating on TiO2 nanomaterials, high temperature (>500 °C) annealing treatment is a necessity. However, the annealing treatment inevitably leads to the strong phase transformation from TiO2(B) with high lithium ion storage (LIS) capacity to anatase with low LIS one as well as the damage of nanostructures. Herein, we demonstrate a new approach to create TiO2(B)/carbon core/shell nanotubes (C@TBNTs) using a long-chain silane polymethylhydrosiloxane (PMHS) to bind the TBNTs by forming Si-O-Ti bonds. The key feature of this work is that the introduction of PMHS onto TBNTs can afford TBNTs with very high thermal stability at higher than 700 °C and inhibit the phase transformation from TiO2(B) to anatase. Such a high thermal property of PMHS-TBNTs makes them easily coated with highly graphitic carbon shell via CVD process at 700 °C. The as-prepared C@TBNTs deliver outstanding rate capability and electrochemical stability, i.e., reversible capacity above 250 mAh g(-1) at 10 C and a high specific capacity of 479.2 mAh g(-1) after 1000 cycles at 1 C. As far as we know, the LIS performance of our sample is the highest among the previously reported TiO2(B) anode materials.

Facial Synthesis of Three-Dimensional Cross-Linked Cage for High-Performance Lithium Storage

Silicon/C composite is a promising anode material for high-energy Li-ion batteries. However, synthesizing high-performance Si-based materials at large scale and low cost remains a huge challenge. Here, we for the first time report the preparation of an interconnected three-dimensional (3D) porous Si-hybrid architecture by using a spray drying method. In this unique structure, the highly robust C-CNT-RGO cages not only can improve the conductivity of the electrode and buffer the volume expansion but also suppress the Si nanoparticles aggregation. As a result, the 3D Si@po-C/CNT/RGO electrode achieves long-life cycling stability at high rates (a reversible capacity of 854.9 mA h g(-1) at 2 A g(-1) after 500 cycles and capacity decay less than 0.013% per cycle) and good rate capability (1454.7, 1198.8, 949.2, 597.8, and 150 mA h g(-1) at current densities of 1, 2, 4, 10, and 20 A g(-1), respectively). Moreover, this novel electrode could deliver high reversible capacities and long-life stabilities even with high mass loading density (764.9 mA h g(-1) at 1.0 mg cm(-2) after 500 cycles and 472.2 mA h g(-1) at 1.5 mg cm(-2) after 400 cycles, respectively). This cheap and scalable strategy can be extended to fabricate other materials with large volume expansion (Sn, Ge, transition-metal oxides) and 3D porous carbon for other potential applications.

Na2 Ti6 O13 Nanorods with Dominant Large Interlayer Spacing Exposed Facet for High-Performance Na-Ion Batteries

As the delegate of tunnel structure sodium titanates, Na2 Ti6 O13 nanorods with dominant large interlayer spacing exposed facet are prepared. The exposed large interlayers provide facile channels for Na(+) insertion and extraction when this material is used as anode for Na-ion batteries (NIBs). After an activation process, this NIB anode achieves a high specific capacity (a capacity of 172 mAh g(-1) at 0.1 A g(-1) ) and outstanding cycling stability (a capacity of 109 mAh g(-1) after 2800 cycles at 1 A g(-1) ), showing its promising application on large-scale energy storage systems. Furthermore, the electrochemical and structural characterization reveals that the expanded interlayer spacings should be in charge of the activation process, including the enhanced kinetics, the lowered apparent activation energy, and the increased capacity.

Carbon Quantum Dot Surface-Engineered VO2 Interwoven Nanowires: A Flexible Cathode Material for Lithium and Sodium Ion Batteries

The use of electrode materials in their powdery form requires binders and conductive additives for the fabrication of the cells, which leads to unsatisfactory energy storage performance. Recently, a new strategy to design flexible, binder-, and additive-free three-dimensional electrodes with nanoscale surface engineering has been exploited in boosting the storage performance of electrode materials. In this paper, we design a new type of free-standing carbon quantum dot coated VO2 interwoven nanowires through a simple fabrication process and demonstrate its potential to be used as cathode material for lithium and sodium ion batteries. The versatile carbon quantum dots that are vastly flexible for surface engineering serve the function of protecting the nanowire surface and play an important role in the diffusion of electrons. Also, the three-dimensional carbon cloth coated with VO2 interwoven nanowires assisted in the diffusion of ions through the inner and the outer surface. With this unique architecture, the carbon quantum dot nanosurface engineered VO2 electrode exhibited capacities of 420 and 328 mAh g(-1) at current density rate of 0.3 C for lithium and sodium storage, respectively. This work serves as a milestone for the potential replacement of lithium ion batteries and next generation postbatteries.

In situ plasmonic Ag nanoparticle anchored TiO2 nanotube arrays as visible-light-driven photocatalysts for enhanced water splitting

An ultrasonication-assisted in situ deposition strategy was utilised to uniformly decorate plasmonic Ag nanoparticles on vertically aligned TiO2 nanotube arrays (NTAs) to construct a Ag@TiO2 NTA composite. The Ag nanoparticles act as efficient surface plasmon resonance (SPR) photosensitizers to drive photocatalytic water splitting under visible light irradiation. The Ag nanoparticles were uniformly deposited on the surface and inside the highly oriented TiO2 nanotubes. The visible-light-driven hydrogen production activities of silver nanoparticle anchored TiO2 nanotube array photocatalysts were evaluated using methanol as a sacrificial reagent in water under a 500 W Xe lamp with a UV light cutoff filter (λ ≥ 420 nm). It was found that the hydrogen production rate of the Ag@TiO2 NTAs prepared with ultrasonication-assisted deposition for 5 min was approximately 15 times higher than that of its pristine TiO2 NTAs counterpart. The highly efficient photocatalytic hydrogen evolution is attributed to the SPR effect of Ag for enhanced visible light absorption and boosting the photogenerated electron-hole separation/transfer. This strategy is promising for the design and construction of high efficiency TiO2 based photocatalysts for solar energy conversion.

Engineering the surface of rutile TiO2 nanoparticles with quantum pits towards excellent lithium storage

Unique rutile TiO₂ nanoparticles with quantum pits have been successfully synthesized by a facile solution and subsequent thermal annealing method. The resultant rutile TiO₂ nanoparticles exhibit excellent lithium storage properties.

Chemically Lithiated TiO2 Heterostructured Nanosheet Anode with Excellent Rate Capability and Long Cycle Life for High-Performance Lithium-Ion Batteries

A new form of dual-phase heterostructured nanosheet comprised of oxygen-deficient TiO2/Li4Ti5O12 has been successfully synthesized and used as anode material for lithium ion batteries. With the three-dimensional (3D) Ti mesh as both the conducting substrate and the Ti(3+)/Ti(4+) source, blue anatase Ti(3+)/TiO2nanosheets were grown by a hydrothermal reaction. By controlling the chemical lithiation period of TiO2 nanosheets, a phase boundary was created between the TiO2 and the newly formed Li4Ti5O12, which contribute additional capacity benefiting from favorable charge separation between the two phase interfaces. Through further hydrogenation of the 3D TiO2/Li4Ti5O12 heterostructured nanosheets (denoted as H-TiO2/LTO HNS), an extraordinary rate performance with capacity of 174 mAh g(-1) at 200 C and outstanding long-term cycling stability with only an ∼6% decrease of its initial specific capacity after 6000 cycles were delivered. The heterostructured nanosheet morphology provides a short length of lithium diffusion and high electrode/electrolyte contact area, which could also explain the remarkable lithium storage performance. In addition, the full battery assembled based on the H-TiO2/LTO anode achieves high energy and power densities.

A Biomineralization Strategy for "Net"-Like Interconnected TiO2 Nanoparticles Conformably Covering Reduced Graphene Oxide with Reversible Interfacial Lithium Storage

A green and simple biomineralization-inspired method to create "net"-like interconnected TiO₂ nanoparticles conformably covering reduced graphene oxide (RGO) with high loading density is reported. This method uses polyamine as both the biomineralization agent and linker to manipulate the nucleation, growth, and crystallization of TiO₂ nanoparticles on the surface of graphene oxide. The obtained TiO₂/RGO composites demonstrate sub-10-nm TiO₂ nanoparticles with (001) facets, ultrathin thickness (10-12 nm), and a high surface area of 172 m² g^-1. When used as anode material for lithium ion batteries, the material displayed excellent rate capability and long cycle life; a capacity of 155 mAh g^-1 is obtained after 50 cycles at the rate of 5C (1C = 168 mA g^-1) and a specific capacity of 115 mAh g^-1 is retained after 2000 cycles at the rate of 25C, which is much higher than that of mechanically mixed TiO₂/graphene composites. Detailed discharge curve analysis reveals that the high rate and cycle performance are partly a result of the reversible interfacial lithium storage of materials, which might be attributed to the pores in the TiO₂ nets on the RGO and may provide a sufficient number of interfaces for accepting both electrons and lithium ions.

Tuning and understanding the phase interface of TiO₂ nanoparticles for more efficient lithium ion storage

We demonstrate that mixed-phase anatase-TiO2(B) nanoparticles can provide an interesting interphase interface with atomic-level contact for achieving more efficient Li ion storage with high capacity and cycle life. A novel lithium storage mode - "interfacial charge storage in allomorphs" (ICSA) - plays an important role in enhancing Li ion storage.