Highly Ordered TiO2 Microcones with High Rate Performance for Enhanced Lithium-Ion Storage

Titanium dioxide-based anode materials for lithium-ion batteries: structure and synthesis

Lithium-ion batteries (LIBs) have high energy density, long life, good safety, and environmental friendliness, and have been widely used in large-scale energy storage and mobile electronic devices. As a cheap and non-toxic anode material for LIBs, titanium dioxide (TiO2) has a good application prospect. However, its poor electrical conductivity leads to unsatisfactory electrochemical performance, which limits its large-scale application. In this review, the structure of three TiO2 polymorphs which are widely investigated are briefly described, then the preparation and electrochemical performance of TiO2 with different morphologies, such as nanoparticles, nanowires, nanotubes, and nanospheres, and the related research on the TiO2 composite materials with carbon, silicon, and metal materials are discussed. Finally, the development trend of TiO2-based anode materials for LIBs has been briefly prospected.

Dual Doping of Titania for Enhanced Na Storage Performance

The sluggish sodium-ion diffusion kinetics and low electronic conductivity have severely restricted the development of the TiO₂ anode for sodium-ion batteries. Defect engineering, such as single-heteroatom doping and oxygen vacancies, has proven to be effective methods to improve the conductivity of TiO₂, but a comprehensive understanding of the synergistic effect of dual-heteroatom doping and oxygen vacancies on the sodium storage performance of TiO₂ is still lacking. Herein, we design a synergistic strategy of dual doping via the in situ doping and hydrogenation treatment to improve conductivity and cycling stability of TiO₂. Experiments and theoretical calculations together revealed that N and C doping reduces the band gap of TiO₂, while the presence of oxygen vacancies efficiently accelerates the diffusion of sodium ions. Thus N, C, and oxygen vacancies with high concentration co-doped TiO₂, resulting in extraordinary high-rate performance, significant stable cycling, and long-term cyclability of up to 10,000 cycles. The synthesis strategy of dual doping proposed here emphasizes the importance of defect engineering in improving material conductivity and electrode cycling stability for possible practical applications in the near future.

The Use of Anodic Oxides in Practical and Sustainable Devices for Energy Conversion and Storage

This review addresses the main contributions of anodic oxide films synthesized and designed to overcome the current limitations of practical applications in energy conversion and storage devices. We present some strategies adopted to improve the efficiency, stability, and overall performance of these sustainable technologies operating via photo, photoelectrochemical, and electrochemical processes. The facile and scalable synthesis with strict control of the properties combined with the low-cost, high surface area, chemical stability, and unidirectional orientation of these nanostructures make the anodized oxides attractive for these applications. Assuming different functionalities, TiO2-NT is the widely explored anodic oxide in dye-sensitized solar cells, PEC water-splitting systems, fuel cells, supercapacitors, and batteries. However, other nanostructured anodic films based on WO3, CuxO, ZnO, NiO, SnO, Fe2O3, ZrO2, Nb2O5, and Ta2O5 are also explored and act as the respective active layers in several devices. The use of AAO as a structural material to guide the synthesis is also reported. Although in the development stage, the proof-of-concept of these devices demonstrates the feasibility of using the anodic oxide as a component and opens up new perspectives for the industrial and commercial utilization of these technologies.

Spring-roll-like Ti3C2 MXene/carbon-coated Fe3O4 composite as a long-life Li-ion storage material

Fe₃O₄ is a promising anode material for Li-ion batteries because of its high theoretical capacity, low cost, and natural abundance.

Binder-free SnO2–TiO2 composite anode with high durability for lithium-ion batteries

A SnO₂–TiO₂ electrode was prepared via anodization and subsequent anodic potential shock for a binder-free anode for lithium-ion battery applications. Perpendicularly oriented TiO₂ microcones are formed by anodization; SnO₂, originating in a Na₂SnO₃ precursor, is then deposited in the valleys between the microcones and in their hollow cores by anodic potential shock. This sequence is confirmed by SEM and TEM analyses and EDS element mapping. The SnO₂–TiO₂ binder-free anode is evaluated for its C-rate performance and long-term cyclability in a half-cell measurement apparatus. The SnO₂–TiO₂ anode exhibits a higher specific capacity than the one with pristine TiO₂ microcones and shows excellent capacity recovery during the rate capability test. The SnO₂–TiO₂ microcone structure shows no deterioration caused by the breakdown of electrode materials over 300 cycles. The charge/discharge capacity is at least double that of the TiO₂ microcone material in a long-term cycling evaluation.

A binder-free SnO₂–TiO₂ composite, where SnO₂ is encapsulated into hollow TiO₂, is designed for inhibiting performance degradation for a stable LIB anode.

Evidence for Fast Lithium-Ion Diffusion and Charge-Transfer Reactions in Amorphous TiO x Nanotubes: Insights for High-Rate Electrochemical Energy Storage

The charge-storage kinetics of amorphous TiO _x nanotube electrodes formed by anodizing three-dimensional porous Ti scaffolds are reported. The resultant electrodes demonstrated not only superior storage capacities and rate capability to anatase TiO _x nanotube electrodes but also improved areal capacities (324 μAh cm^-2 at 50 μA cm^-2 and 182 μAh cm^-2 at 5 mA cm^-2) and cycling stability (over 2000 cycles) over previously reported TiO _x nanotube electrodes using planar current collectors. Amorphous TiO _x exhibits very different electrochemical storage behavior from its anatase counterpart as the majority of its storage capacity can be attributed to capacitive-like processes with more than 74 and 95% relative contributions being attained at 0.05 and 1 mV s^-1, respectively. The kinetic analysis revealed that the insertion/extraction process of Li⁺ in amorphous TiO _x is significantly faster than in anatase structure and controlled by both solid-state diffusion and interfacial charge-transfer kinetics. It is concluded that the large capacitive contribution in amorphous TiO _x originates from its highly defective and loosely packed structure and lack of long-range ordering, which facilitate not only a significantly faster Li⁺ diffusion process (diffusion coefficients of 2 × 10^-14 to 3 × 10^-13 cm² s^-1) but also more facile interfacial charge-transfer kinetics than anatase TiO _x.

RGO-Coated TiO2 Microcones for High-Rate Lithium-Ion Batteries

Reduced graphene oxide (RGO)-coated TiO₂ microcones have been synthesized via simple anodization and cyclic voltammetry for use in lithium-ion batteries (LIBs). Microcones had a perpendicularly oriented hollow core, an anatase structure, and a high surface area, allowing higher capacity than other nanosized TiO₂ structures. TiO₂ has low electrical conductivity, leading to the limitation of fast charging and high capacity; however, this was improved by the application of an RGO coating in this work. As anode materials of LIB, the obtained RGO microcone showed a capacity of 157 mAh g^-1 at 10C (fully charged within ∼360 s) and sustained 1000 cycles with only 0.02% capacity fading per cycle. The capacity was 1.5 times higher than that of conventional microcone. We speculated that the decrease in the charge-transfer resistance (R _ct) played a crucial role in increasing the capacity with fast charging.

Photoelectrocatalytic effect of unbalanced RF magnetron sputtered TiO2 thin film on ITO-coated patterned SiO2 nanocone arrays

Highly increased photocurrent response of unbalanced RF magnetron sputtered TiO₂ thin film on ITO-coated patterned SiO₂ nanocone arrays.

Li4 Ti5 O12 Anode: Structural Design from Material to Electrode and the Construction of Energy Storage Devices

Spinel Li₄ Ti₅ O₁₂ , known as a zero-strain material, is capable to be a competent anode material for promising applications in state-of-art electrochemical energy storage devices (EESDs). Compared with commercial graphite, spinel Li₄ Ti₅ O₁₂ offers a high operating potential of ∼1.55 V vs Li/Li⁺ , negligible volume expansion during Li⁺ intercalation process and excellent thermal stability, leading to high safety and favorable cyclability. Despite the merits of Li₄ Ti₅ O₁₂ been presented, there still remains the issue of Li₄ Ti₅ O₁₂ suffering from poor electronic conductivity, manifesting disadvantageous rate performance. Typically, a material modification process of Li₄ Ti₅ O₁₂ will be proposed to overcome such an issue. However, the previous reports have made few investigations and achievements to analyze the subsequent processes after a material modification process. In this review, we attempt to put considerable interest in complete device design and assembly process with its material structure design (or modification process), electrode structure design and device construction design. Moreover, we have systematically concluded a series of representative design schemes, which can be divided into three major categories involving: (1) nanostructures design, conductive material coating process and doping process on material level; (2) self-supporting or flexible electrode structure design on electrode level; (3) rational assembling of lithium ion full cell or lithium ion capacitor on device level. We believe that these rational designs can give an advanced performance for Li₄ Ti₅ O₁₂ -based energy storage device and deliver a deep inspiration.

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).

Graphene oxide hydrogel as a restricted-area nanoreactor for synthesis of 3D graphene-supported ultrafine TiO2 nanorod nanocomposites for high-rate lithium-ion battery anodes

Three-dimensional graphene-supported TiO₂ nanorod nanocomposites (3D GS-TNR) are prepared using graphene oxide hydrogel as a restricted-area nanoreactor in the hydrothermal process, in which well-distributed TiO₂ nanorods with a width of approximately 5 nm and length of 30 nm are conformally embedded in the 3D interconnected graphene network. The 3D graphene oxide not only works as a restricted-area nanoreactor to constrain the size, distribution and morphology of the TiO₂; it also work as a highly interconnected conducting network to facilitate electrochemical reactions and maintain good structural integration when the nanocomposites are used as anode materials in lithium-ion batteries. Benefiting from the nanostructure, the 3D GS-TNR nanocomposites show high capacity and excellent long-term cycling capability at high current rates. The 3D GS-TNR composites deliver a high initial charge capacity of 280 mAh g^-1 at 0.2 C and maintain a reversible capacity of 115 mAh g^-1, with a capacity retention of 83% at 20 C after 1000 cycles. Meanwhile, compared with that of previously reported TiO₂-based materials, the 3D GS-TNR nanocomposites show much better performance, including higher capacity, better rate capability and long-term cycling stability.

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%.