Sandwich-like, stacked ultrathin titanate nanosheets for ultrafast lithium storage

Graphene-doped silicon-carbon materials with multi-interface structures for lithium-ion battery anodes

The carbon nanomaterials are usually used to improve the electrical conductivity and stability of silicon (Si) anodes for lithium-ion batteries. However, the Si-based composites containing carbon nanomaterials generally show large specific surface area, leading to severe side reactions that generate large amounts of solid electrolyte interphase films. Herein, we embedded graphene oxide (GO) and silicon nanoparticles (Si NPs) uniformly in pitch matrix by solvent dispersion. The internally doped GO reduces the exposed surface and improves the electrical conductivity of the composite. Meanwhile, the multi-interface structures are constructed inside to limit the domains of Si NPs and improve the structural stability of the material. When evaluated as anodes, the Si/graphene/pitch-based carbon composite anode exhibits the outstanding electrochemical properties, delivering a reversible capacity of 820.8 mAh/g at 50 mA g-1, as well as a capacity retention of 93.6 % after 1000 cycles at 2 A/g. In addition, when assembled with the LiFePO4 cathode, the full cell exhibits an impressive capacity retention of 95 % after 100 cycles at 85 mA g-1. This work provides a valuable design concept for the development of Si/carbon anodes.

Simultaneous Enhancement of Lithium Transfer Kinetics and Structural Stability in Dual-Phase TiO2 Electrodes by Ruthenium Doping

Dual-phase TiO2 consisting of bronze and anatase phases is an attractive electrode material for fast-charging lithium-ion batteries due to the unique phase boundaries present. However, further enhancement of its lithium storage performance has been hindered by limited knowledge on the impact of cation doping as an efficient modification strategy. Here, the effects of Ru4+ doping on the dual-phase structure and the related lithium storage performance are demonstrated for the first time. Structural analysis reveals that an optimized doping ratio of Ru:Ti = 0.01:0.99 (1-RTO) is vital to maintain the dual-phase configuration because the further increment of Ru4+ fraction would compromise the crystallinity of the bronze phase. Various electrochemical tests and density functional theory calculations indicate that Ru4+ doping in 1-RTO enables more favorable lithium diffusion in the bulk for the bronze phase as compared to the undoped TiO2 (TO) counterpart, while lithium kinetics in the anatase phase are found to remain similar. Furthermore, Ru4+ doping leads to a better cycling stability for 1-RTO-based electrodes with a capacity retention of 82.1% after 1200 cycles at 8 C as compared to only 56.1% for TO-based electrodes. In situ X-ray diffraction reveals a reduced phase separation in the lithiated anatase phase, which is thought to stabilize the dual-phase architecture during extended cycling. The simultaneous enhancement of rate ability and cycling stability of dual-phase TiO2 enabled by Ru4+ doping provides a new strategy toward fast-charging lithium-ion batteries.

Nanostructured TiO2 Arrays for Energy Storage

Because of their extensive specific surface area, excellent charge transfer rate, superior chemical stability, low cost, and Earth abundance, nanostructured titanium dioxide (TiO₂) arrays have been thoroughly explored during the past few decades. The synthesis methods for TiO₂ nanoarrays, which mainly include hydrothermal/solvothermal processes, vapor-based approaches, templated growth, and top-down fabrication techniques, are summarized, and the mechanisms are also discussed. In order to improve their electrochemical performance, several attempts have been conducted to produce TiO₂ nanoarrays with morphologies and sizes that show tremendous promise for energy storage. This paper provides an overview of current developments in the research of TiO₂ nanostructured arrays. Initially, the morphological engineering of TiO₂ materials is discussed, with an emphasis on the various synthetic techniques and associated chemical and physical characteristics. We then give a brief overview of the most recent uses of TiO₂ nanoarrays in the manufacture of batteries and supercapacitors. This paper also highlights the emerging tendencies and difficulties of TiO₂ nanoarrays in different applications.

TiO2 as an Anode of High-Performance Lithium-Ion Batteries: A Comprehensive Review towards Practical Application

Lithium-ion batteries (LIBs) are undeniably the most promising system for storing electric energy for both portable and stationary devices. A wide range of materials for anodes is being investigated to mitigate the issues with conventional graphite anodes. Among them, TiO2 has attracted extensive focus as an anode candidate due to its green technology, low volume fluctuations (<4%), safety, and durability. In this review, the fabrication of different TiO2 nanostructures along with their electrochemical performance are presented. Different nanostructured TiO2 materials including 0D, 1D, 2D, and 3D are thoroughly discussed as well. More precisely, the breakthroughs and recent developments in different anodic oxidation processes have been explored to identify in detail the effects of anodization parameters on nanostructure morphology. Clear guidelines on the interconnected nature of electrochemical behaviors, nanostructure morphology, and tunable anodic constraints are provided in this review.

Mesoporous Single-Crystal Lithium Titanate Enabling Fast-Charging Li-Ion Batteries

There remain significant challenges in developing fast-charging materials for lithium-ion batteries (LIBs) due to sluggish ion diffusion kinetics and unfavorable electrolyte mass transportation in battery electrodes. In this work, a mesoporous single-crystalline lithium titanate (MSC-LTO) microrod that can realize exceptional fast charge/discharge performance and excellent long-term stability in LIBs is reported. The MSC-LTO microrods are featured with a single-crystalline structure and interconnected pores inside the entire single-crystalline body. These features not only shorten the lithium-ion diffusion distance but also allow for the penetration of electrolytes into the single-crystalline interior during battery cycling. Hence, the MSC-LTO microrods exhibit unprecedentedly high rate capability, achieving a specific discharge capacity of ≈174 mAh g^-1 at 10 C, which is very close to its theoretical capacity, and ≈169 mAh g^-1 at 50 C. More importantly, the porous single-crystalline microrods greatly mitigate the structure degradation during a long-term cycling test, offering ≈92% of the initial capacity after 10 000 cycles at 20 C. This work presents a novel strategy to engineer porous single-crystalline materials and paves a new venue for developing fast-charging materials for LIBs.

Photocatalysis and Li-Ion Battery Applications of {001} Faceted Anatase TiO2-Based Composites

Anatase TiO2 are the most widely used photocatalysts because of their unique electronic, optical and catalytic properties. Surface chemistry plays a very important role in the various applications of anatase TiO2 especially in the catalysis, photocatalysis, energy conversion and energy storage. Control of the surface structure by crystal facet engineering has become an important strategy for tuning and optimizing the physicochemical properties of TiO2. For anatase TiO2, the {001} crystal facets are the most reactive because they exhibit unique surface characteristics such as visible light responsiveness, dissociative adsorption, efficient charge separation capabilities and photocatalytic selectivity. In this review, a concise survey of the literature in the field of {001} dominated anatase TiO2 crystals and their composites is presented. To begin, the existing strategies for the synthesis of {001} dominated anatase TiO2 and their composites are discussed. These synthesis strategies include both fluorine-mediated and fluorine-free synthesis routes. Then, a detailed account of the effect of {001} facets on the physicochemical properties of TiO2 and their composites are reviewed, with a particular focus on photocatalysis and Li-ion batteries applications. Finally, an outlook is given on future strategies discussing the remaining challenges for the development of {001} dominated TiO2 nanomaterials and their potential applications.

Layered silicon carbide: a novel anode material for lithium ion batteries

The structural stability of carbon and the high theoretical capacity of silicon was the motivation for investigating the prospects of layered silicon carbide (SiC).

Ionic-liquid assisted architecture of amorphous nanoporous zinc-rich carbon-based microstars for lithium storage

Amorphous Zn-rich nitrogen-doped carbon-based microstars are synthesized using an ionic liquid-assisted method and annealing process. The microstars exhibit a high reversible capacity of 756 mA h g-1 and a capacity retention of 98% after 120 cycles at 0.5 A g-1 due to their large surface area, hierarchical nanopores, and uniform distribution of zinc and nitrogen.

Binder-Free Electrodes and Their Application for Li-Ion Batteries

Lithium-ion batteries (LIB) as energy supply and storage systems have been widely used in electronics, electric vehicles, and utility grids. However, there is an increasing demand to enhance the energy density of LIB. Therefore, the development of new electrode materials with high energy density becomes significant. Although many novel materials have been discovered, issues remain as (1) the weak interaction and interface problem between the binder and the active material (metal oxide, Si, Li, S, etc.), (2) large volume change, (3) low ion/electron conductivity, and (4) self-aggregation of active materials during charge and discharge processes. Currently, the binder-free electrode serves as a promising candidate to address the issues above. Firstly, the interface problem of the binder and active materials can be solved by fixing the active material directly to the conductive substrate. Secondly, the large volume expansion of active materials can be accommodated by the porosity of the binder-free electrode. Thirdly, the ion and electron conductivity can be enhanced by the close contact between the conductive substrate and the active material. Therefore, the binder-free electrode generally exhibits excellent electrochemical performances. The traditional manufacture process contains electrochemically inactive binders and conductive materials, which reduces the specific capacity and energy density of the active materials. When the binder and the conductive material are eliminated, the energy density of the battery can be largely improved. This review presents the preparation, application, and outlook of binder-free electrodes. First, different conductive substrates are introduced, which serve as carriers for the active materials. It is followed by the binder-free electrode fabrication method from the perspectives of chemistry, physics, and electricity. Subsequently, the application of the binder-free electrode in the field of the flexible battery is presented. Finally, the outlook in terms of these processing methods and the applications are provided.

Two-Dimensional Layered Ultrathin Carbon/TiO2 Nanosheet Composites for Superior Pseudocapacitive Lithium Storage

Intercalation of carbon nanosheets into two-dimensional (2D) inorganic materials could enhance their properties in terms of mechanics and electrochemistry, but sandwiching these two kinds of materials in an alternating sequence is a great challenge in synthesis. Herein, we report a novel strategy to construct TiO₂ nanosheets into 2D pillar-layer architectures by employing benzidine molecular assembly as pillars. Then, 2D carbon/TiO₂ nanosheet composite with a periodic interlayer distance of 1.1 nm was obtained following a polymerization and carbonization process. This method not only alleviates the strain arising from the torsion of binding during carbonization but also hinders the structural collapse of TiO₂ due to the intercalation of the carbon layer by rational control of annealing conditions. The composite material possesses a large carbon/TiO₂ interface, providing abundant active sites for ultrafast pseudocapacitive charge storage, thus displaying a superior high-rate performance with a specific capacity of 67.8 mAh g^-1 at a current density of 12.8 A g^-1 based on the total electrode and excellent cyclability with 87.4% capacity retention after 3000 cycles.

Classification of Spatially Confined Reactions and the Electrochemical Applications of Molybdenum-Based Nanocomposites

As a popular material synthesis method, spatially confined reactions have been gradually recognised for their excellent performance in the field of current materials synthesis. In recent years, molybdenum-based catalysts have gradually gained recognition due to high natural reserves of Mo, its low cost, and many other advantages, and they have wide applications in the area of functional materials, especially in topical areas such as batteries and electrocatalysts. In this context, spatially confined reactions have become widely to obtain various types of molybdenum-based electrode materials and electrocatalysts which result in an excellent morphology, structure, and performance. In this review, the concept of a spatially confined reaction system and the electrochemical application (electrode materials and electrocatalyst) of molybdenum-based materials synthesised in this way are comprehensively discussed. The current problems and future development and application of molybdenum-based materials are also discussed in this review.

Synthesis of Polyacetylene-like Modified Graphene Oxide Aerogel and Its Enhanced Electrical Properties

A graphene-based or carbon-based aerogel is a three-dimensional (3D) solid material in which the carbon atoms are arranged in a sheet-like nanostructure. In this study, we report the synthesis of low-density polymer-modified aerogel monoliths by 3D macroassemblies of graphene oxide sheets that exhibit significant internal surface areas (982 m2/g) and high electrical conductivity (∼0.1 to 1 × 102 S/cm). Different types of materials were prepared to obtain a single monolithic solid starting from a suspension of single-layer graphene oxide (GO) sheets and a polymer, made from the precursors 4-carboxybenzaldehyde and poly(vinyl alcohol). These materials were used to cross-link the individual sheets by covalent bonds, resulting in wet-gels that were supercritically dried and then, in some cases, thermally reduced to yield graphene aerogel composites. The average densities were approaching 15-20 mg/cm3. This approach allowed for the modulation of the distance between the sheets, pore dimension, surface area, and related properties. This specific GO/polymer ratio has suitable malleability, making it a viable conductive material for use in 3D printing; it also has other properties suitable for energy storage, catalysis, sensing and biosensing applications, bioelectronics, and superconductors.

Ti-Based Oxide Anode Materials for Advanced Electrochemical Energy Storage: Lithium/Sodium Ion Batteries and Hybrid Pseudocapacitors

Titanium-based oxides including TiO₂ and M-Ti-O compounds (M = Li, Nb, Na, etc.) family, exhibit advantageous structural dynamics (2D ion diffusion path, open and stable structure for ion accommodations) for practical applications in energy storage systems, such as lithium-ion batteries, sodium-ion batteries, and hybrid pseudocapacitors. Further, Ti-based oxides show high operating voltage relative to the deposition of alkali metal, ensuring full safety by avoiding the formation of lithium and sodium dendrites. On the other hand, high working potential prevents the decomposition of electrolyte, delivering excellent rate capability through the unique pseudocapacitive kinetics. Nevertheless, the intrinsic poor electrical conductivity and reaction dynamics limit further applications in energy storage devices. Recently, various work and in-depth understanding on the morphologies control, surface engineering, bulk-phase doping of Ti-based oxides, have been promoted to overcome these issues. Inspired by that, in this review, the authors summarize the fundamental issues, challenges and advances of Ti-based oxides in the applications of advanced electrochemical energy storage. Particularly, the authors focus on the progresses on the working mechanism and device applications from lithium-ion batteries to sodium-ion batteries, and then the hybrid pseudocapacitors. In addition, future perspectives for fundamental research and practical applications are discussed.

α-Ni(OH)2 Originated from Electro-Oxidation of NiSe2 Supported by Carbon Nanoarray on Carbon Cloth for Efficient Water Oxidation

Development of effective oxygen evolution reaction (OER) electrocatalysts has been intensively studied to improve water splitting efficiency and cost effectiveness in the last ten years. However, it is a big challenge to obtain highly efficient and durable OER electrocatalysts with overpotentials below 200 mV at 10 mA cm^-2 despite the efforts made to date. In this work, the successful synthesis of supersmall α-Ni(OH)₂ is reported through electro-oxidation of NiSe₂ loaded onto carbon nanoarrays. The obtained α-Ni(OH)₂ shows excellent activity and long-term stability for OER, with an overpotential of only 190 mV at the current density of 10 mA cm^-2 , which represents a highly efficient OER electrocatalyst. The excellent activity could be ascribed to the large electrochemical surface area provided by the carbon nanoarray, as well as the supersmall size (≈10 nm) of α-Ni(OH)₂ which possess a large number of active sites for the reaction. In addition, the phase evolution of α-Ni(OH)₂ from NiSe₂ during the electro-oxidation process was monitored with in situ X-ray absorption fine structure (XAFS) analysis.

Self-Reconstructed Formation of a One-Dimensional Hierarchical Porous Nanostructure Assembled by Ultrathin TiO2 Nanobelts for Fast and Stable Lithium Storage

Owing to their unique structural advantages, TiO₂ hierarchical nanostructures assembled by low-dimensional (LD) building blocks have been extensively used in the energy-storage/-conversion field. However, it is still a big challenge to produce such advanced structures by current synthetic techniques because of the harsh conditions needed to generate primary LD subunits. Herein, a novel one-dimensional (1D) TiO₂ hierarchical porous fibrous nanostructure constructed by TiO₂ nanobelts is synthesized by combining a room-temperature aqueous solution growth mechanism with the electrospinning technology. The nanobelt-constructed 1D hierarchical nanoarchitecture is evolves directly from the amorphous TiO₂/SiO₂ composite fibers in alkaline solutions at ambient conditions without any catalyst and other reactant. Benefiting from the unique structural features such as 1D nanoscale building blocks, large surface area, and numerous interconnected pores, as well as mixed phase anatase-TiO₂(B), the optimum 1D TiO₂ hierarchical porous nanostructure shows a remarkable high-rate performance when tested as an anode material for lithium-ion batteries (107 mA h g^-1 at ∼10 A g^-1) and can be used in a hybrid lithium-ion supercapacitor with very stable lithium-storage performance (a capacity retention of ∼80% after 3000 cycles at 2 A g^-1). The current work presents a scalable and cost-effective method for the synthesis of advanced TiO₂ hierarchical materials for high-power and stable energy-storage/-conversion devices.

Scalable 2D Mesoporous Silicon Nanosheets for High-Performance Lithium-Ion Battery Anode

Constructing unique mesoporous 2D Si nanostructures to shorten the lithium-ion diffusion pathway, facilitate interfacial charge transfer, and enlarge the electrode-electrolyte interface offers exciting opportunities in future high-performance lithium-ion batteries. However, simultaneous realization of 2D and mesoporous structures for Si material is quite difficult due to its non-van der Waals structure. Here, the coexistence of both mesoporous and 2D ultrathin nanosheets in the Si anodes and considerably high surface area (381.6 m² g^-1 ) are successfully achieved by a scalable and cost-efficient method. After being encapsulated with the homogeneous carbon layer, the Si/C nanocomposite anodes achieve outstanding reversible capacity, high cycle stability, and excellent rate capability. In particular, the reversible capacity reaches 1072.2 mA h g^-1 at 4 A g^-1 even after 500 cycles. The obvious enhancements can be attributed to the synergistic effect between the unique 2D mesoporous nanostructure and carbon capsulation. Furthermore, full-cell evaluations indicate that the unique Si/C nanostructures have a great potential in the next-generation lithium-ion battery. These findings not only greatly improve the electrochemical performances of Si anode, but also shine some light on designing the unique nanomaterials for various energy devices.

Direct Imprinting of Scalable, High-Performance Woodpile Electrodes for Three-Dimensional Lithium-Ion Nanobatteries

The trend of device downscaling drives a corresponding need for power source miniaturization. Though numerous microfabrication methods lead to successful creation of submillimeter-scale electrodes, scalable approaches that provide cost-effective nanoscale resolution for energy storage devices such as on-chip batteries remain elusive. Here, we report nanoimprint lithography (NIL) as a direct patterning technique to fabricate high-performance TiO₂ nanoelectrode arrays for lithium-ion batteries (LIBs) over relatively large areas. The critical electrode dimension is below 200 nm, which enables the structure to possess favorable rate capability even under discharging current densities as high as 5000 mA g^-1. In addition, by sequential imprinting, electrodes with three-dimensional (3D) woodpile architecture were readily made in a "stack-up" manner. The height of architecture can be easily controlled by the number of stacked layers while maintaining nearly constant surface-to-volume ratios. The result is a proportional increase of areal capacity with the number of layers. The structure-processing combination leads to efficient use of the material, and the resultant specific capacity (250.9 mAh g^-1) is among the highest reported. This work provides a simple yet effective strategy to fabricate nanobatteries and can be potentially extended to other electroactive materials.

Sb Nanoparticles Anchored on Nitrogen-Doped Amorphous Carbon-Coated Ultrathin CoSx Nanosheets for Excellent Performance in Lithium-Ion Batteries

Compared to single-component materials, hybrid materials with various components display superior electrochemical performance. In this work, two-dimensional CoS_x@NC@Sb nanosheets assembled by ultrathin CoS_x nanosheets (∼4 nm) and a thin layer of N-doped amorphous carbon (NC) combined with colloidlike Sb nanoparticles are designed and synthesized via a solvothermal route accompanied by a carbonization and Sb deposition procedure. If applied in lithium-ion batteries (LIBs), the hybrids exhibit a specific capacity of 960 mA h g^-1 at the 100th cycle at 0.1 A g^-1. Moreover, the reversible capacity still maintains at 494 mA h g^-1 after 500 cycles at a high rate of 10 A g^-1. All enhanced electrochemical properties of the hybrids are attributed to the synergistic effect of the two components and their unique structural features, which can effectively increase the electrical conductivity, shorten the pathway of Li⁺ diffusion, accommodate the volume variation, and inhibit the aggregation and pulverization of the electrode. We believe that the current work can provide a new strategy for designing and fabricating high-performance anode materials for LIBs.

Engineering 2D Nanofluidic Li-Ion Transport Channels for Superior Electrochemical Energy Storage

Rational surface engineering of 2D nanoarchitectures-based electrode materials is crucial as it may enable fast ion transport, abundant-surface-controlled energy storage, long-term structural integrity, and high-rate cycling performance. Here we developed the stacked ultrathin Co₃ O₄ nanosheets with surface functionalization (SUCNs-SF) converted from layered hydroxides with inheritance of included anion groups (OH^- , NO₃^- , CO₃^2- ). Such stacked structure establishes 2D nanofluidic channels offering extra lithium storage sites, accelerated Li-ion transport, and sufficient buffering space for volume change during electrochemical processes. Tested as an anode material, this unique nanoarchitecture delivers high specific capacity (1230 and 1011 mAh g^-1 at 0.2 and 1 A g^-1 , respectively), excellent rate performance, and long cycle capability (1500 cycles at 5 A g^-1 ). The demonstrated advantageous features by constructing 2D nanochannels in nonlayered materials may open up possibilities for designing high-power lithium ion batteries.

Structural Characterization of 2D Zirconomolybdate by Atomic Scale HAADF-STEM and XANES and Its Highly Stable Electrochemical Properties as a Li Battery Cathode

The structural determination of nanomaterials and their application in energy storage and transfer are of great importance. Herein, a layered zirconomolybdate with a two-dimensional structure was synthesized. Atomic resolution electron microscopy was utilized for direct visualization of the structure that was further confirmed by powder X-ray diffraction and X-ray absorption near-edge structure analyses. The structure of the molecular sheet was stable at a high temperature in an oxidative atmosphere. The electrochemical performance of the material was evaluated with a Li battery composed of the calcined material as a cathode. Li ions were reversibly inserted and extracted between the layers without collapse of the structure of the material. The electrochemical properties of the material were derived from the reversible redox activity of the Mo ions and Zr ions in the material as well as the flexibility of the molecular layer of the material.

TiO2-Based Nanomaterials for the Production of Hydrogen and the Development of Lithium-Ion Batteries

The photocatalytic activity of different titanium oxide nanowires containing gold (Au@TiO₂NWs), and gold-graphene (Au@TiO₂NWs-graphene), was evaluated by studying the reaction of hydrogen production by water splitting under UV-vis light. The composites showed high surface areas, with values above 300 m² per gram, even after the incorporation of gold and graphene on the surface of titanium oxide nanowires. The highest hydrogen production of Au@TiO₂NWs was 1436 μmol h^-1 g^-1, under irradiation at 400 nm, and with a gold loading of 10 wt %. This photocatalytic activity was 11.5 times greater than that shown by the unmodified TiO₂NWs. For the Au@TiO₂NWs-graphene composites, the highest hydrogen amount obtained was 1689 μmol h^-1 g^-1, at loadings of 10 and 1 wt % of gold and graphene, respectively. The photocatalytic activity of the gold-graphene compounds was 1.2 times greater than that shown by the titanium oxide catalysts and 13.5 times higher than the bare TiO₂NWs. Even at wavelengths greater than 500 nm, the compounds exhibited yields of hydrogen above 1000 μmol h^-1 g^-1, demonstrating the high catalytic activity of the compounds. In addition, TiO₂-based materials are of great interest for energy storage and conversion devices, in particular for rechargeable lithium ion batteries. TiO₂ has a significant advantage due to its low volume change (<4%) during the Li ion insertion/desertion process, short paths for fast lithium ion diffusion, and large exposed surface, offering more lithium insertion channels. However, the relatively low theoretical capacity and electrical conductivity of TiO₂ greatly hamper its practical application. In this work, free-standing electrodes composed by TiO₂NWs and carbon nanotubes, CNT@TiO₂NWs, were used as anode materials for Li-ion batteries. As a result, the electronic conductivity and mechanical properties of the composite were greatly improved and a good cycling performance was obtained in these batteries. This research shows the potential of TiO₂-based materials for the development of new catalysts for hydrogen production and energy storage systems.

High-Performance Li-Ion Capacitor Based on an Activated Carbon Cathode and Well-Dispersed Ultrafine TiO2 Nanoparticles Embedded in Mesoporous Carbon Nanofibers Anode

A novel Li-ion capacitor based on an activated carbon cathode and a well-dispersed ultrafine TiO₂ nanoparticles embedded in mesoporous carbon nanofibers (TiO₂@PCNFs) anode was reported. A series of TiO₂@PCNFs anode materials were prepared via a scalable electrospinning method followed by carbonization and a postetching method. The size of TiO₂ nanoparticles and the mesoporous structure of the TiO₂@PCNFs were tuned by varying amounts of tetraethyl orthosilicate (TEOS) to increase the energy density and power density of the LIC significantly. Such a subtle designed LIC displayed a high energy density of 67.4 Wh kg^-1 at a power density of 75 W kg^-1. Meanwhile, even when the power density was increased to 5 kW kg^-1, the energy density can still maintain 27.5 Wh kg^-1. Moreover, the LIC displayed a high capacitance retention of 80.5% after 10000 cycles at 10 A g^-1. The outstanding electrochemical performance can be contributed to the synergistic effect of the well-dispersed ultrafine TiO₂ nanoparticles, the abundant mesoporous structure, and the conductive carbon networks.

Bimolecular-induced hierarchical nanoporous LiTi2(PO4)3/C with superior high-rate and cycling performance

Carbon-coated hierarchical LiTi₂(PO₄)₃ was synthesized by a facile bimolecular (glucose and DMEA) assisted hydrothermal reaction and a solid-state reaction, and exhibits excellent high-rate and cycling performance.

TiO2 hollow spheres on reduced graphene oxide with high rate performance as anodes for lithium-ion batteries

Anatase TiO₂ anchored on graphene oxide (GO) can be synthesized through a one-step hydrothermal method.

Novel SiO2/H2Ti2O5·H2O-Nanochain Composite with High UV-Visible Photocatalytic Activity for Supertransparent Multifunctional Thin Films

In the current work, a peroxo titanium complex (PTC) solution was used as a novel water-soluble precursor to fabricate H₂Ti₂O₅·H₂O and the SiO₂/H₂Ti₂O₅·H₂O-nanochain composite at low temperature (90-100 °C). The average width of H₂Ti₂O₅·H₂O nanochains is 4.5 ± 1.5 nm. Under full-spectrum irradiation, the Si/Ti-nanochain composite showed good UV-visible light absorption and excellent photocatalytic activity, which is 2.8 times that of P25. In the composite, SiO₂ not only contributes to the formation of nanochains and improves the catalytic performance of H₂Ti₂O₅·H₂O but also reduces the refractive index of the complex. When coated on transparent organic substrates, the composite thin film exhibited excellent antireflective (as high as 99.3% on PC and 98.9% on PMMA) and self-cleaning properties. Pencil hardness, washing, and tape adhesion tests showed favorable adhesion-to-substrate and mechanical robustness of thin films, which make them extremely attractive for applications as highly transparent and self-cleaning thin films on lenses, photovoltaic cells, and windows of high-rise buildings.

Bioinspired Hierarchical Nanofibrous Silver-Nanoparticle/Anatase-Rutile-Titania Composite as an Anode Material for Lithium-Ion Batteries

A new bioinspired hierarchical nanofibrous silver-nanoparticle/anatase-rutile-titania (Ag-NP/A-R-titania) composite was fabricated by employing a natural cellulose substance (e.g., commercial laboratory cellulose filter paper) as the structural scaffold template, which was composed of anatase-phase titania (A-titania) nanotubes with rutile-phase titania (R-titania) nanoneedles grown on the surfaces and further silver nanoparticles (AgNPs) immobilized thereon. As it was employed as an anode material for lithium-ion batteries (LIBs), high reversible capacity, enhanced rate performance, and excellent cycling stability were achieved as compared with those of the corresponding cellulose-substance-derived nanotubular A-titania, R-titania, heterogeneous anatase/rutile titania (A-R-titania) composite, and commercial P25 powder. This benefited from its unique porous cross-linked three-dimensional structure inherited from the initial cellulose substance scaffold, which enhances the sufficient electrode/electrolyte contact, relieves the severe volume change upon cycling, and improves the amount of lithium-ion storage; moreover, the high loading content of the silver component in the composite improves the electrical conductivity of the electrode. The structural integrity of the composite was maintained upon long-term charge/discharge cycling, indicating its significant stability.

Hydrothermal etching fabrication of TiO2@graphene hollow structures: mutually independent exposed {001} and {101} facets nanocrystals and its synergistic photocaltalytic effects

Highly exposed facets TiO2 attracts enormous attention due to its excellent separation effect of photogenerated electron-hole pairs and induced high performance of photocatalytic activity. Herein, a novel hydrothermal etching reaction was used to synthesize graphene-wrapped TiO2 hollow core-shell structures. Different with the reported co-exposed facets TiO2 single crystal nanoparticles, the present TiO2 core layer is composed by the mutually independent exposed {001} and {101} facets nanocrystals. Combined with the reduced graphene oxide shell layer, this graphene-wrapped TiO2 hollow core-shell structures formed a Z-scheme photocatalytic system, which possess simultaneously the high charge-separation efficiency and strong redox ability. Additionally, the as-prepared samples show a higher absorption property for organic molecules and visible light due to the presence of graphene. All of these unique properties ensure the excellent photocatalytic activity for the graphene-wrapped TiO2 hollow structures in the synergistic photo-oxidation of organic molecules and photo-reduced of Cr(VI) process. The TiO2 core composed with mutually independent exposed {001} and {101} facets nanocrystals is propose to play an important role in the fabrication of this Z-scheme photocatalytic system. Fabrication of Z-scheme photocatalytic system based on this unique exposed facets TiO2 nanocrystals will provides a new insight into the design and fabrication of advanced photocatalytic materials.

Electrode materials with tailored facets for electrochemical energy storage

In recent years, the design and morphological control of crystals with tailored facets have become hot spots in the field of electrochemical energy storage devices. For electrode materials, morphologies play important roles in their activities because their shapes determine how many facets of specific orientation are exposed and therefore available for surface reactions. This review focuses on the strategies for crystal facet control and the unusual electrochemical properties of electrode materials bound by tailored facets. Here, electrode materials with tailored facets include transition metal oxides such as SnO₂, Co₃O₄, NiO, Cu₂O, and MnO₂, elementary substances such as Si and Au, and intercalation compounds such as Li₄Ti₅O₁₂, LiCoO₂, LiMn₂O₄, LiFePO₄, and Na_0.7MnO₂ for various applications of Li-ion batteries, aqueous rechargeable lithium batteries, Na-ion batteries, Li-O₂ batteries and supercapacitors. How these electrode materials with tailored facets affect their electrochemical properties is discussed. Finally, research opportunities as well as the challenges in this emerging research frontier are highlighted.

One-dimensional metal oxide-carbon hybrid nanostructures for electrochemical energy storage

Numerous metal oxides (MOs) have been considered as promising electrode materials for electrochemical energy storage devices, including lithium-ion batteries (LIBs) and electrochemical capacitors (ECs), because of their outstanding features such as high capacity/capacitance, low cost, as well as environmental friendliness. However, one major challenge for MO-based electrodes is the poor cycling stability derived from the large volume variation and intense mechanic strain, which are inevitably generated during repeated charge/discharge processes. Nanostructure engineering has proven to be one of the most effective strategies to improve the electrochemical performance of MO-based electrode materials. Among various nanostructures, one-dimensional (1D) metal oxide-carbon hybrid nanostructures might offer some solution for the challenging issues involved in bulk MO-based electrode materials for energy storage devices. Herein, we give an overview of the rational design, synthesis strategies and electrochemical properties of such 1D MO-carbon structures and highlight some of the latest advances in this niche area. It starts with a brief introduction to the development of nanostructured MO-based electrodes. We will then focus on the advanced synthesis and improved electrochemical performance of 1D MO-carbon nanostructures with different configurations, including MO-carbon composite nanowires, core-shell nanowires and hierarchical nanostructures. Lastly, we give some perspective on the current challenges and possible future research directions in this area.

Engineered nanomembranes for smart energy storage devices

This review presents recent progress in engineered tubular and planar nanomembranes for smart energy storage applications, especially related to the investigation of fundamental electrochemical kinetics.

An atomically thick titanium phosphate thin layer with enhancing electrochemical sensitivity toward Pb(ii)

An atomically thick titanium phosphate thin layer is synthesized and used for sensitive electrochemical detection for Pb(ii) with a high sensitivity and low limit of detection.

Preparation of 3D pompon-like titanate nanotube microspheres and their adsorption properties on cationic dyes

Hierarchical 3D pompon-like microspheres built with titanate nanotubes have been successfully synthesized by a simple hydrothermal method in the presence of CH₃COOH and H₂O₂.

Amorphous Ultrathin SnO2 Films by Atomic Layer Deposition on Graphene Network as Highly Stable Anodes for Lithium-Ion Batteries

Amorphous SnO2 (a-SnO2) thin films were conformally coated onto the surface of reduced graphene oxide (G) using atomic layer deposition (ALD). The electrochemical characteristics of the a-SnO2/G nanocomposites were then determined using cyclic voltammetry and galvanostatic charge/discharge curves. Because the SnO2 ALD films were ultrathin and amorphous, the impact of the large volume expansion of SnO2 upon cycling was greatly reduced. With as few as five formation cycles best reported in the literature, a-SnO2/G nanocomposites reached stable capacities of 800 mAh g(-1) at 100 mA g(-1) and 450 mAh g(-1) at 1000 mA g(-1). The capacity from a-SnO2 is higher than the bulk theoretical values. The extra capacity is attributed to additional interfacial charge storage resulting from the high surface area of the a-SnO2/G nanocomposites. These results demonstrate that metal oxide ALD on high surface area conducting carbon substrates can be used to fabricate high power and high capacity electrode materials for lithium-ion batteries.

Ultrathin Wrinkled N-Doped Carbon Nanotubes for Noble-Metal Loading and Oxygen Reduction Reaction

We describe the fabrication of ultrathin wrinkled N-doped carbon nanotubes by an in situ solid-state method. The positions of Co catalyst were first labeled by good-dispersion and highly loaded Au and Pt, indicating the most of Co are unsealed. The resultant unique nanoarchitecture, which exhibits the features of carbon nanotube and graphene with a combined effect of 1D and 2D carbon-based nanostructures, exhibited a superior ORR activity to carbon nanotubes and graphene. Moreover, the novel catalysts showed a better durability and higher tolerance to methanol crossover and poisoning effects than those of Pt/C.

Anatase TiO2 ultrathin nanobelts derived from room-temperature-synthesized titanates for fast and safe lithium storage

Lithium-ion batteries (LIBs) are promising energy storage devices for portable electronics, electric vehicles, and power-grid applications. It is highly desirable yet challenging to develop a simple and scalable method for constructions of sustainable materials for fast and safe LIBs. Herein, we exploit a novel and scalable route to synthesize ultrathin nanobelts of anatase TiO₂, which is resource abundant and is eligible for safe anodes in LIBs. The achieved ultrathin nanobelts demonstrate outstanding performances for lithium storage because of the unique nanoarchitecture and appropriate composition. Unlike conventional alkali-hydrothermal approaches to hydrogen titanates, the present room temperature alkaline-free wet chemistry strategy guarantees the ultrathin thickness for the resultant titanate nanobelts. The anatase TiO₂ ultrathin nanobelts were achieved simply by a subsequent calcination in air. The synthesis route is convenient for metal decoration and also for fabricating thin films of one/three dimensional arrays on various substrates at low temperatures, in absence of any seed layers.

Amine-Assisted Delamination of Nb2C MXene for Li-Ion Energy Storage Devices

2D Nb2CTx MXene flakes are produced using an amine-assisted delamination process. Upon mixing with carbon nanotubes and filtration, freestanding, flexible paper is produced. The latter exhibits high capacity and excellent stability when used as the electrode for Li-ion batteries and capacitors.

Two-dimensional wavelike spinel lithium titanate for fast lithium storage

Safe fast-charging lithium-ion batteries (LIBs) have huge potential market size on demand according to their shortened charging time for high-power devices. Zero-strain spinel Li4Ti5O12 is one of ideal candidates for safe high-power batteries owing to its good cycling performance, low cost and safety. However, the inherent insulating characteristic of LTO seriously limits its high-rate capability. In this work, we successfully synthesize novel wavelike spinel LTO nanosheets using a facile 'co-hydrolysis' method, which is superior to molten-salt approach and traditional solvothermal method in some respects. The unique 2D structures have single-crystal framework with shortened path for Li ion transport. As a result, the N-doped 2D wavelike LTO with 0.6 wt.% of 'carbon joint' not only exhibits exciting capacity of ~180 and ~150 mA h g(-1) for fast lithium storage at high discharge/charge rates of 1.7 and 8.5 A g(-1) (10C and 50C) respectively, but also shows excellent low-temperature performance at -20°C. In addition, the cost may be further decreased due to recycled functional reagents. This novel nanostructured 2D LTO anode material makes it possible to develop safe fast-charging high-power lithium ion batteries.

Synthesis of [111]- and {010}-faceted anatase TiO2 nanocrystals from tri-titanate nanosheets and their photocatalytic and DSSC performances

[111]- and {010}-faceted anatase nanocrystals with controllable crystal size and morphology were synthesized from tri-titanate H2Ti3O7 nanosheets by hydrothermal reaction. The nanostructures and the formation reaction mechanism of the obtained TiO2 nanocrystals were investigated using XRD, FE-SEM, and TEM. Furthermore, the photocatalytic and dye-sensitized solar cell (DSSC) performances of the synthesized anatase nanocrystals were also characterized. Two types of reactions occur in the formation process of the anatase nanocrystals. One is an in situ topochemical conversion reaction of the layered titanate structure to an anatase structure, and another is the dissolution-deposition reaction on the particle surface, which splits the formed nanosheet-like particles into small TiO2 nanocrystals. The surface photocatalytic activity and the DSSC performance of the anatase nanocrystals are dependent on the crystal facet exposed on the particle surface, which increases in the order of non-facet < [111]-facet < {010}-facet. The increasing order corresponds to the increasing order of the bandgap and energy level of the lowest valence band of the anatase nanocrystals. Furthermore, the facet of the anatase also affects the DSSC performance, which is enhanced in the order of non-facet < [111]-facet < {010}-facet.