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

Surfactant regulated Core-Double-Shell NF@NiO nanosheets matrix as integrated anodes for Lithium-Ion batteries

The direct oxidation of three-dimensional nickel foam (3D NF) to nickel oxide (NiO) as integrated anode material for lithium-ion batteries (LIBs) has attracted significant attention towards achieving high-areal-capacity and high-energy density LIBs. However, the rate capability of such monolithic NiO in LIBs usually falls off rapidly due to the poor electrical conductivity that hindered its ionic transport kinetics. Herein, to ease the ionic transport constrains, a surfactant-regulated strategy is developed for preparing in-situ core-double-shell architecture that consists of core nickel skeleton, dense nickel oxide shell and porous nickel oxide nanosheets (NS) shell as anode materials for LIBs. Among the three employed surfactants including cationic surfactant, anionic surfactant and nonionic surfactant, the anionic surfactant (sodium dodecyl sulfate, SDS) modulated anode denoted SDS-NF@NiONS exhibits ultrahigh reversible areal capacity of 8.64 mAh cm-2@ 0.4 mA cm-2, and excellent rate areal capacity of 5.20 mAh cm-2 @ 3.0 mA cm-2, which did not only show the best ever reported NiO-based high-areal-capacity based electrodes, but also demonstrate impressive performance in practical full cell LIBs. In addition, in-situ Raman and kinetic analyses confirm the mechanism of Li-ion storage and facile ionic transport kinetics in this proposed design.

Selenium-Doped Amorphous Black Phosphorus@TiO2/C Heterostructures for High-Performance Li/Na/K Ion Batteries

Heterostructures have been confirmed to demonstrate better electrochemical performance than their individual building blocks, which is not only attributed to the complementary advantages of diverse materials but also to various synergistic effects, such as increased active sites at the heterointerfaces, enhanced kinetics from a built-in electric field, stable structure due to physical or chemical bonding, etc. However, constructing a desired heterostructure remains greatly challenging owing to the mismatch of crystal structures, atomic spacings, and reaction mechanisms between different electrode materials. In this study, an amorphous heterostructure composed of Se-doped black phosphorus and metal-organic framework (MOF)-derived TiO₂/C (Se-BP@TiO₂/C) was successfully fabricated using a simple Se-assisted ball-milling method. In addition to the inherent advantages of heterostructures, the novel material also had considerable free volume in the amorphous domains, which not only buffered the volume change of active materials during cycles but also provided space and interconnected channels for ion diffusion. When used as anode materials for Li/Na/K ion batteries, the Se-BP@TiO₂/C achieved high specific capacities, good cyclability, and fast rate capability. This work opens up a new route to design amorphous heterostructure electrodes for high-performance battery systems.

Recent Development of Flexible and Stretchable Supercapacitors Using Transition Metal Compounds as Electrode Materials

Flexible and stretchable supercapacitors (FS-SCs) are promising energy storage devices for wearable electronics due to their versatile flexibility/stretchability, long cycle life, high power density, and safety. Transition metal compounds (TMCs) can deliver a high capacitance and energy density when applied as pseudocapacitive or battery-like electrode materials owing to their large theoretical capacitance and faradaic charge-storage mechanism. The recent development of TMCs (metal oxides/hydroxides, phosphides, sulfides, nitrides, and selenides) as electrode materials for FS-SCs are discussed here. First, fundamental energy-storage mechanisms of distinct TMCs, various flexible and stretchable substrates, and electrolytes for FS-SCs are presented. Then, the electrochemical performance and features of TMC-based electrodes for FS-SCs are categorically analyzed. The gravimetric, areal, and volumetric energy density of SC using TMC electrodes are summarized in Ragone plots. More importantly, several recent design strategies for achieving high-performance TMC-based electrodes are highlighted, including material composition, current collector design, nanostructure design, doping/intercalation, defect engineering, phase control, valence tuning, and surface coating. Integrated systems that combine wearable electronics with FS-SCs are introduced. Finally, a summary and outlook on TMCs as electrodes for FS-SCs are provided.

Phase evolution and structural modulation during in situ lithiation of MoS2, WS2 and graphite in TEM

Li-ion batteries function by Li intercalating into and through the layered electrode materials. Intercalation is a solid-state interaction resulting in the formation of new phases. The new observations presented here reveal that at the nanoscale the intercalation mechanism is fundamentally different from the existing models and is actually driven by nonuniform phase distributions rather than the localized Li concentration: the lithiation process is a 'distribution-dependent' phenomena. Direct structure imaging of 2H and 1T dual-phase microstructures in lithiated MoS2 and WS2 along with the localized chemical segregation has been demonstrated in the current study. Li, a perennial challenge for the TEM, is detected and imaged using a low-dose, direct-electron detection camera on an aberration-corrected TEM and confirmed by image simulation. This study shows the presence of fully lithiated nanoscale domains of 2D host matrix in the vicinity of Li-lean regions. This confirms the nanoscale phase formation followed by Oswald ripening, where the less-stable smaller domains dissolves at the expense of the larger and more stable phases.

Revealing the Phase-Transition Dynamics and Mechanism in a Spinel Li4Ti5O12 Anode Material through in Situ Electron Microscopy

Spinel Li₄Ti₅O₁₂ is considered as a promising anode material for long-life lithium-ion batteries because of the negligible volumetric variation during the insertion and extraction of Li ions. Phase transition is an inevitable process during the migration of Li ions, and the transition process and mechanism need detailed investigation down to the atomic scale. In this study, we investigated the behavior and mechanism on the phase transition of Li₄Ti₅O₁₂ through in situ transmission electron microscopy (TEM). It has been found that the spinel-structured Li₄Ti₅O₁₂ was gradually transformed to a rock salt structure under electron beam irradiation. A sharp interface with an epitaxial relationship was observed between the transformed rock salt phase and the parent spinel phase. Furthermore, the heterostructure with different crystal structures of Li₄Ti₅O₁₂ has been precisely tailored with electron beam irradiation. Our detailed in situ TEM results and theoretical calculations led to unprecedented level on the understanding of phase-transition mechanism in Li₄Ti₅O₁₂. This study demonstrates a possible approach to precisely engineer the crystal structure of materials and to realize a well-designed heterostructure in electrode materials.

An In situ Raman study of intermediate adsorption engineering by high-index facet control during the hydrogen evolution reaction

An in situ Raman study of the mechanism of HER catalytic performance enhanced by high-index facets on Ti@TiO₂ nanosheets.

Hierarchical TiO2-x nanoarchitectures on Ti foils as binder-free anodes for hybrid Li-ion capacitors

Hybrid Li-ion capacitor (LIC) draws more attention as novel energy storage device owing to its high power density and high energy density. Designing three-dimensional electrode materials is beneficial for improving electrochemical performance of LICs. Herein, an improved hydrothermal method combined with an ion-exchange reaction is used to manufacture oxygen vacancies (OVs)-doping TiO₂ (TiO_2-x) nanowires/nanosheets (NWS) on Ti-foil. Then TiCl₄ treatment is performed to form TiO_2-x NWS/nanocrystallines (NWSC). These-obtained hierarchical nanoarchitectures assumes enrich electro-active sites and contact areas, which can improve electron transference and structural stability. The TiO_2-x NWSC is used as binder-free anode for Li-ion battery and achieves high specific capacity (300 mAh g^-1 at 0.1 A g^-1), excellent rate capability (102 mAh g^-1 at 5 A g^-1) and long cycle stability (44% after 1000 cycles at 1 A g^-1). LICs assembled with a TiO_2-x NWSC anode and an activated carbon cathode have an energy density of 44.2 W h kg^-1 at the power density of 150 W kg^-1. Therefore, the TiO_2-x NWSC is a potential candidate for high energy and high power electrochemical energy storage devices.

Co3 O4 @Cu-Based Conductive Metal-Organic Framework Core-Shell Nanowire Electrocatalysts Enable Efficient Low-Overall-Potential Water Splitting

In the work reported herein, the electrocatalytic properties of Co₃ O₄ in hydrogen and oxygen evolution reactions have been significantly enhanced by coating a shell layer of a copper-based metal-organic framework on Co₃ O₄ porous nanowire arrays and using the products as high-performance bifunctional electrocatalysts for overall water splitting. The coating of the copper-based metal-organic framework resulted in the hybridization of the copper-embedded protective carbon shell layer with Co₃ O₄ to create a strong Cu-O-Co bonding interaction for efficient hydrogen adsorption. The hybridization also led to electronically induced oxygen defects and nitrogen doping to effectively enhance the electrical conductivity of Co₃ O₄ . The optimal as-prepared core-shell hybrid material displayed excellent overall-water-splitting catalytic activity that required overall voltages of 1.45 and 1.57 V to reach onset and a current density of 10 mA cm^-2 , respectively. This is the first report to highlight the relevance of hybridizing MOF-based co-catalysts to boost the electrocatalytic performance of nonprecious transition-metal oxides.

Achieving High-Energy Full-Cell Lithium-Storage Performance by Coupling High-Capacity V2O3 with Low-Potential Ni2P Anode

To optimize the potential window and maximize the utilization of the capacity of both negative and positive electrodes, rational design of electrode materials are critically important in full-cell construction of rechargeable batteries. In this work, we propose and fabricate a carbon-confined V₂O₃/Ni₂P/C composite structure for excellent performance lithium ion batteries by taking advantage of the high capacity of V₂O₃ and low potential of Ni₂P. The full cell constructed with V₂O₃/Ni₂P/C as anode and commercial LiMn₂O₄ as cathode offers a record high energy density of 361.5 Wh kg^-1 and excellent cycle stability, outperforming the state-of-the-art work reported in literature.

Synthesis and Progress of New Oxygen-Vacant Electrode Materials for High-Energy Rechargeable Battery Applications

During the last few years, a great amount of oxygen-vacant materials have been synthetized and applied as electrodes for electrochemical storage. The presence of oxygen vacancies leads to an increase in the conductivity and the diffusion coefficient; consequently, the controllable synthesis of oxygen vacancy plays an important role in improving the electrochemical performance, including achieving high specific capacitance, high power density, high energy density, and good cycling stability of the electrode materials for batteries. This review mainly focuses on research progress in the preparation of oxygen-vacant nanostructures and the application of materials with oxygen vacancies in various batteries (such as lithium-ion, lithium-oxygen, and sodium-ion batteries). Challenges related to and opportunities for oxygen-vacant materials are also provided.

Three-dimensional porous microspheres comprising hollow Fe2O3 nanorods/CNT building blocks with superior electrochemical performance for lithium ion batteries

It is highly desirable to develop anode materials with rational architectures for lithium ion batteries to achieve high-performance electrochemical properties. In this study, three-dimensional porous composite microspheres comprising hollow Fe2O3 nanorods/carbon nanotube (CNT) building blocks are successfully constructed by direct deposition and further thermal transformation of beta-FeOOH nanorods on CNT porous microspheres. The CNT porous microsphere, which is prepared by a spray pyrolysis, provides ample sites for the direct growth of beta-FeOOH nanorods. During the further oxidation process, the beta-FeOOH nanorods are transformed into hollow Fe2O3 nanorods as a result of dehydroxylation and lattice shrinkage, resulting in the formation of hollow Fe2O3 nanorods/CNT porous microspheres. Such a hierarchical structure of composite microspheres not only facilitates electrolyte accessibility but also offers conductive networks for electrons during electrochemical reactions. Accordingly, the electrodes exhibit a high discharge capacity of 1307 mA h g-1 after 300 cycles at a current density of 1 A g-1; this is associated with an excellent capacity retention of 84%, which is calculated from the initial cycle. In addition, the composite delivers a discharge capacity of 703 mA h g-1 at a current density of 15 A g-1.

Interface-engineered Li4Ti5O12-TiO2 dual-phase nanoparticles and CNT additive for supercapacitor-like high-power Li-ion battery applications

The single-pot synthesis of dual-phase spinel-Li₄Ti₅O₁₂ and anatase-TiO₂ (LTO-TiO₂) nanoparticles over all the phase fractions ranging from pure LTO to pure TiO₂ is conducted. Carrying out the process over the complete range enabled the identification of a unique weight ratio of 85:15 (LTO:TiO₂), providing the best combination of capacity, rate capability and cycling stability. We show that for this composition dual-phase nanoparticles have a predominant interfacial orientation of (111)_LTO∣∣(004)_TiO2 , while it is (111)_LTO∣∣(101)_TiO2 for other compositions. This study therefore shows that the dual-phase interface with these specific orientations gives the best performance. The synergistic combination of dual-phase nanoparticles with multi-wall carbon nanotubes improves the performance further. This results in an electrode with supercapacitor-like rate capability delivering high discharge capacities of 174, 127, 119, 110, 101 and 91 mAh g^-1 at specific currents of 2000, 6000, 12 000, 18 000, 24 000 and 30 000 mA g^-1, respectively. A discharge capacity of 174 mAh g^-1 at a specific current of 2000 mA g^-1 with only 0.005% capacity loss per cycle over 3000 cycles is demonstrated. At current densities of 6000, 12 000 and 24 000 mA g^-1, stable cycling is obtained for 1500 cycles. The present work enables nano-engineered interfaces in LTO-TiO₂ dual-phase nanoparticles with an electrochemical performance that is better than its individual components, opening up the potential for high-power Li-ion battery applications.

Enhanced lithium storage performance of porous exfoliated carbon fibers via anchored nickel nanoparticles

Herein, flexible carbon fiber cloth (CFC) is modified by embedding Ni nanoparticles via a thermal reduction strategy, and it is used as a suitable anode material for lithium-ion batteries. Benefitting from the elemental interaction between Ni and carbon, the Ni-embedded CFC displayed higher lithium storage properties than pristine CFC and Ni-free porous CFC.

Herein, flexible carbon fiber cloth (CFC) is modified by embedding Ni nanoparticles via a thermal reduction strategy, and it is used as a suitable anode material for lithium-ion batteries.

Enhancement of Electrochemical Performance by the Oxygen Vacancies in Hematite as Anode Material for Lithium-Ion Batteries

The application of hematite in lithium-ion batteries (LIBs) has been severely limited because of its poor cycling stability and rate performance. To solve this problem, hematite nanoparticles with oxygen vacancies have been rationally designed by a facile sol-gel method and a sequential carbon-thermic reduction process. Thanks to the existence of oxygen vacancies, the electrochemical performance of the as-obtained hematite nanoparticles is greatly enhancing. When used as the anode material in LIBs, it can deliver a reversible capacity of 1252 mAh g^-1 at 2 C after 400 cycles. Meanwhile, the as-obtained hematite nanoparticles also exhibit excellent rate performance as compared to its counterparts. This method not only provides a new approach for the development of hematite with enhanced electrochemical performance but also sheds new light on the synthesis of other kinds of metal oxides with oxygen vacancies.

High-Temperature Stable Anatase Titanium Oxide Nanofibers for Lithium-Ion Battery Anodes

Control of the crystal structure of electrochemically active materials is an important approach to fabricating high-performance electrodes for lithium-ion batteries (LIBs). Here, we report a methodology for controlling the crystal structure of TiO₂ nanofibers by adding aluminum isopropoxide to a common sol-gel precursor solution utilized to create TiO₂ nanofibers. The introduction of aluminum cations impedes the phase transformation of electrospun TiO₂ nanofibers from the anatase to the rutile phase, which inevitably occurs in the typical annealing process utilized for the formation of TiO₂ crystals. As a result, high-temperature stable anatase TiO₂ nanofibers were created in which the crystal structure was well-maintained even at high annealing temperatures of up to 700 °C. Finally, the resulting anatase TiO₂ nanofibers were utilized to prepare LIB anodes, and their electrochemical performance was compared to pristine TiO₂ nanofibers that contain both anatase and rutile phases. Compared to the electrode prepared with pristine TiO₂ nanofibers, the electrode prepared with anatase TiO₂ nanofibers exhibited excellent electrochemical performances such as an initial Coulombic efficiency of 83.9%, a capacity retention of 89.5% after 100 cycles, and a rate capability of 48.5% at a current density of 10 C (1 C = 200 mA g^-1).

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.

Ultrafine TiO2 Confined in Porous-Nitrogen-Doped Carbon from Metal-Organic Frameworks for High-Performance Lithium Sulfur Batteries

Ultrafine TiO₂ confined in porous-nitrogen-doped carbon is synthesized from a single metal-organic framework precursor. As a novel interlayer for lithium-sulfur batteries, the TiO₂@NC composite can act as both a high efficiency lithium polysulfide barrier to suppress the side reactions and an additional current collector to enhance the polysulfide redox reactions. The lithium-sulfur battery with a TiO₂@NC interlayer delivers a high reversible capacity of 1460 mAh g^-1 at 0.2 C and capacity retention of 71% even after 500 cycles with high rate capability.

Study of counter electrodes as an effective controlling factor of crystal orientation of TiO2 nanoarrays used as the anode in lithium-ion batteries

The morphology, crystal orientation, and Li ion electrochemical performance of TNAs strongly depend on the counter electrode.

Chromium-Modified Li4Ti5O12 with a Synergistic Effect of Bulk Doping, Surface Coating, and Size Reducing

Bulk doping, surface coating, and size reducing are three strategies for improving the electrochemical properties of Li4Ti5O12 (LTO). In this work, chromium (Cr)-modified LTO with a synergistic effect of bulk doping, surface coating, and size reducing is synthesized by a facile sol-gel method. X-ray diffraction (XRD) and Raman analysis prove that Cr dopes into the LTO bulk lattice, which effectively inhibits the generation of TiO2 impurities. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) verifies the surface coating of Li2CrO4 on the LTO surface, which decreases impedance of the LTO electrode. More importantly, the size of LTO particles can be significantly reduced from submicroscale to nanoscale as a result of the protection of the Li2CrO4 surface layer and the suppression from Cr atoms on the long-range order in the LTO lattice. As anode material, Li4-xCr3xTi5-2xO12 (x = 0.1) delivers a reversible capacity of 141 mAh g(-1) at 10 °C, and over 155 mAh g(-1) at 1 °C after 1000 cycles. Therefore, the Cr-modified Li4Ti5O12 prepared via a sol-gel method has potential for applications in high-power, long-life lithium-ion batteries.

Three-Dimensional Branched TiO2 Architectures in Controllable Bloom for Advanced Lithium-Ion Batteries

Three-dimensional branched TiO2 architectures (3D BTA) with controllable morphologies were synthesized via a facile template-free one-pot solvothermal route. The volume ratio of deionized water (DI water) and diethylene glycol in solvothermal process is key to the formation of 3D BTA assembled by nanowire-coated TiO2 dendrites, which combines the advantages of 3D hierarchical structure and 1D nanoscale building blocks. Benefiting from such unique structural features, the BTA in full bloom achieved significantly increased specific surface areas and shortened Li(+) ion/electrons diffusion pathway. The lithium-ion batteries based on BTA in full bloom exhibited remarkably enhanced reversible specific capacity and rate performance, attributing to the high contact area with the electrolyte and the short solid state diffusion pathway for Li(+) ion/electrons promoting lithium insertion and extraction.