ALD Al2O3-Coated TiO2 Nanotube Layers as Anodes for Lithium-Ion Batteries

Recent Progress of Self-Supported Metal Oxide Nano-Porous Arrays in Energy Storage Applications

The demand for high-performance and cost-effective energy storage solutions for mobile electronic devices and electric vehicles has been a driving force for technological advancements. Among the various options available, transitional metal oxides (TMOs) have emerged as a promising candidates due to their exceptional energy storage capabilities and affordability. In particular, TMO nanoporous arrays fabricated by electrochemical anodization technique demonstrate unrivaled advantages including large specific surface area, short ion transport paths, hollow structures that reduce bulk expansion of materials, and so on, which have garnered significant research attention in recent decades. However, there is a lack of comprehensive reviews that discuss the progress of anodized TMO nanoporous arrays and their applications in energy storage. Therefore, this review aims to provide a systematic detailed overview of recent advancements in understanding the ion storage mechanisms and behavior of self-organized anodic TMO nanoporous arrays in various energy storage devices, including alkali metal ion batteries, Mg/Al-ion batteries, Li/Na metal batteries, and supercapacitors. This review also explores modification strategies, redox mechanisms, and outlines future prospects for TMO nanoporous arrays in energy storage.

Sand-Fixation Model for Interface Engineering of Layered Titania and N/O-Doped Carbon Composites to Enhance Potassium/Sodium Storage

Layered titania (L-TiO2 ) holds great potential for potassium-ion batteries (PIBs) and sodium-ion batteries (SIBs) due to their high specific capacity. Synthesizing L-TiO2 functional materials for high-capacity and long cyclability battery remains challenging due to the unstable and poor conductivity of bare L-TiO2 . In nature, plant growth can stabilize land by preventing sands from dispersing following desertification. Inspired by nature's "sand-fixation model," Al3+ "seeds" are in situ grown on layered Ti3 C2 Tx "land." Subsequently, NH2 -MIL-101(Al) "plants" with Al as metal nodes are grown on the Ti3 C2 Tx "land" by self-assembly. After annealing and etching processes (similar to desertification), NH2 -MIL-101(Al) is transformed into interconnected N/O-doped carbon (MOF-NOC), which not only acts as a plant-like function to prevent the pulverization of L-TiO2 transformed from Ti3 C2 Tx but also improves the conductivity and stability of MOF-NOC@L-TiO2 . Al species are selected as seeds to improve interfacial compatibility and form intimate interface heterojunction. Systematic ex situ analysis discloses that the ions storage mechanism can be endowed by mixed contribution of non-Faradaic and Faradaic capacitance. Consequently, the MOF-NOC@L-TiO2 electrodes exhibit high interfacial capacitive charge storage and outstanding cycling performance. The interface engineering strategy inspired by "sand-fixation model" provides a reference for designing stable layered composites.

Ultra-thin graphene cube framework@TiO2 heterojunction as high-performance anode materials for lithium ion batteries

Here, we proposed a new strategy to build the integrated graphene cube (Gr) framework@TiO₂ composite to improve the ion transport kinetics and electrical conductivity of TiO₂ as a long-life and high-capacity anode for lithium ion batteries. Combined with the salt template method for ultra-thin framework, the distinct structure of Gr@TiO₂ shows an excellent electrochemical performance, e.g., initial coulombic efficiency (ICE), rate performance and specific capacity, due to the increased kinetics of lithium ions. Through this method, the integrity is dramatically improved and the pulverization and agglomeration of the anode after long-term cycles are restrained. The optimized Gr@TiO₂ displays a high stable reversible capacity of 179.5 mAh g^-1 after 4000 cycles at 1 A g^-1, excellent rate performance (125.5 mAh g^-1 at 5 A g^-1). Kinetic studies through Electrochemical Impedance Spectra, Galvanostatic Intermittent Titration Technique and Linear Sweep Voltammetry confirm that the electrical conductivity and ion transport kinetics are dramatically improved through the ultra-thin graphene cube framework as a heterojunction structure of Gr@TiO₂.

Advanced Atomic Layer Deposition Technologies for Micro-LEDs and VCSELs

In recent years, the process requirements of nano-devices have led to the gradual reduction in the scale of semiconductor devices, and the consequent non-negligible sidewall defects caused by etching. Since plasma-enhanced chemical vapor deposition can no longer provide sufficient step coverage, the characteristics of atomic layer deposition ALD technology are used to solve this problem. ALD utilizes self-limiting interactions between the precursor gas and the substrate surface. When the reactive gas forms a single layer of chemical adsorbed on the substrate surface, no reaction occurs between them and the growth thickness can be controlled. At the Å level, it can provide good step coverage. In this study, recent research on the ALD passivation on micro-light-emitting diodes and vertical cavity surface emitting lasers was reviewed and compared. Several passivation methods were demonstrated to lead to enhanced light efficiency, reduced leakage, and improved reliability.

Updated Insights into 3D Architecture Electrodes for Micropower Sources

Microbatteries (MBs) and microsupercapacitors (MSCs) are primary on-chip micropower sources that drive autonomous and stand-alone microelectronic devices for implementation of the Internet of Things (IoT). However, the performance of conventional MBs and MSCs is restricted by their 2D thin-film electrode design, and these devices struggle to satisfy the increasing IoT energy demands for high energy density, high power density, and long lifespan. The energy densities of MBs and MSCs can be improved significantly through adoption of a 2D thick-film electrode design; however, their power densities and lifespans deteriorate with increased electrode thickness. In contrast, 3D architecture electrodes offer remarkable opportunities to simultaneously improve MB and MSC energy density, power density, and lifespan. To date, various 3D architecture electrodes have been designed, fabricated, and investigated for MBs and MSCs. This review provides an update on the principal superiorities of 3D architecture electrodes over 2D thick-film electrodes in the context of improved MB and MSC energy density, power density, and lifespan. In addition, the most recent and representative progress in 3D architecture electrode development for MBs and MSCs is highlighted. Finally, present challenges are discussed and key perspectives for future research in this field are outlined.

Investigation of the influence of TiO2distribution on HA/TiO2composite wetting ability using the dispersant SDBS, high-temperature annealing, and ultrasonication

The use of composites such as hydroxyapatite (HA)/TiO₂in bioapplications has attracted increasing attention in recent years. Herein, for the enhancement wetting ability and biocompatibility, the HA/TiO₂composite was subjected to different treatments to improve nanoparticle (NP) distribution and surface energy with an aim of mitigating nanotoxicity concerns. The treatments included ultrasonication, high-temperature annealing, and addition of a dispersant and surfactant, sodium dodecylbenzenesulfonate (SDBS). Contact angle measurement tests revealed the effect of SDBS addition on the distribution of TiO₂NPs on the HA surface: a decrease in the contact angle and, thus, an increase in the wetting ability of the HA/TiO₂composite were observed. The combination of annealing and SDBS addition treatments allowed for guest TiO₂particles to be uniformly distributed on the surface of the host HA particles, showing a rapid conversion from a hydrophobic to superhydrophilic property.In vitroinvestigation suggested that the cell viabilities of annealed HA/TiO₂, SDBS-added HA/TiO₂, and SDBS-added and annealed HA/TiO₂reached 89.7%, 94.7%, and 95.8%, respectively, while those of HA and untreated HA/TiO₂were 80.3% and 86.9%, respectively. The modified composites exhibited lower cytotoxicities than the unmodified systems (HA and HA/TiO₂). Furthermore, the cell adhesion behavior of the composites was confirmed through actin-4',6-Diamidino-2-phenylindole (DAPI) staining, which showed negligible changes in the cytoskeleton architecture of the cells. This study confirmed that a modified HA/TiO₂composite has potential for bioapplications.

Atomic Layer Deposition of a Nanometer-Thick Li3PO4 Protective Layer on LiNi0.5Mn1.5O4 Films: Dream or Reality for Long-Term Cycling?

LiNi_0.5Mn_1.5O₄ (LNMO) is a promising 5V-class electrode for Li-ion batteries but suffers from manganese dissolution and electrolyte decomposition owing to the high working potential. An attractive solution to stabilize the surface chemistry consists in mastering the interface between the LNMO electrode and the liquid electrolyte with a surface protective layer made from the powerful surface deposition method. Here, we show that a 7400 nm thick sputtered LNMO film coated with a nanometer-thick lithium-ion-conductive Li₃PO₄ layer was deposited by the atomic layer deposition method. We demonstrate that this "material model system" can deliver a remarkable surface capacity (∼0.4 mAh cm^-2 at 1C) and exhibits improved cycling lifetime (×650%) compared to the nonprotected electrode. Nevertheless, we observe that mechanical failure occurs within the LNMO and Li₃PO₄ films when long-term cycling is performed. This in-depth study gives new insights regarding the mechanical degradation of LNMO electrodes upon charge/discharge cycling and reveals for the first time that the surface protective layer made from the ALD method is not sufficient for long-term stability applications.

Surface modification and functionalization of powder materials by atomic layer deposition: a review

Powder materials are a class of industrial materials with many important applications. In some circumstances, surface modification and functionalization of these materials are essential for achieving or enhancing their expected performances. However, effective and precise surface modification of powder materials remains a challenge due to a series of problems such as high surface area, diffusion limitation, and particle agglomeration. Atomic layer deposition (ALD) is a cutting-edge thin film coating technology traditionally used in the semiconductor industry. ALD enables layer by layer thin film growth by alternating saturated surface reactions between the gaseous precursors and the substrate. The self-limiting nature of ALD surface reaction offers angstrom level thickness control as well as exceptional film conformality on complex structures. With these advantages, ALD has become a powerful tool to effectively fabricate powder materials for applications in many areas other than microelectronics. This review focuses on the unique capability of ALD in surface engineering of powder materials, including recent advances in the design of ALD reactors for powder fabrication, and applications of ALD in areas such as stabilization of particles, catalysts, energetic materials, batteries, wave absorbing materials and medicine. We intend to show the versatility and efficacy of ALD in fabricating various kinds of powder materials, and help the readers gain insights into the principles, methods, and unique effects of powder fabrication by ALD.

Simple Approach: Heat Treatment to Improve the Electrochemical Performance of Commonly Used Anode Electrodes for Lithium-Ion Batteries

The lithium-ion battery (LIB) industry has been in high demand for simple and effective methods to improve the electrochemical performance of LIBs. Here, we treated three different widely studied anode electrodes (i.e., Li₄Ti₅O₁₂, TiO₂, and graphite) under vacuum at 250 °C, and compared their electrochemical performance with and without a 250 °C treatment. Without changing the composition of the fabricated electrodes, all of the 250 °C treated electrodes exhibited enhanced specific capacities, and the lithium-ion diffusion was improved in different degrees. By comparing the results of scanning electron microscopy (SEM) and energy-dispersive spectroscopy of the pristine and 250 °C treated electrodes, the 250 °C treatment improved the distribution of a polyvinylidene difluoride (PVDF) binder in the electrodes, resulting in a higher porosity of the 250 °C treated electrodes. The results of X-ray photoelectron spectrometry and SEM of the cycled electrodes confirmed that a uniform distribution of the PVDF binder from the 250 °C treatment played a positive role in the formation of a solid electrolyte interphase layer, thereby delivering higher capacities and capacity retentions than those of electrodes without heat treatment. The simplicity of this modification method provides considerable potential for building high-performance LIBs at a larger scale.

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.

TiO2 Nanotube Layers Decorated with Al2O3/MoS2/Al2O3 as Anode for Li-ion Microbatteries with Enhanced Cycling Stability

TiO₂ nanotube layers (TNTs) decorated with Al₂O₃/MoS₂/Al₂O₃ are investigated as a negative electrode for 3D Li-ion microbatteries. Homogenous nanosheets decoration of MoS₂, sandwiched between Al₂O₃ coatings within self-supporting TNTs was carried out using atomic layer deposition (ALD) process. The structure, morphology, and electrochemical performance of the Al₂O₃/MoS₂/Al₂O₃-decorated TNTs were studied using scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and chronopotentiometry. Al₂O₃/MoS₂/Al₂O₃-decorated TNTs deliver an areal capacity almost three times higher than that obtained for MoS₂-decorated TNTs and as-prepared TNTs after 100 cycles at 1C. Moreover, stable and high discharge capacity (414 µAh cm^-2) has been obtained after 200 cycles even at very fast kinetics (3C).

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.

A New Aspect of the Li Diffusion Enhancement Mechanism of Ultrathin Coating Layer on Electrode Materials

Atomic layer deposition (ALD) coating on active material particles has been widely considered as an effective and efficient strategy to improve the capacity and cycle life of lithium-ion batteries. One of the key roles of the ALD coating layer is to facilitate the Li ion transfer in electrode particles. Several recent studies demonstrated that an ALD coating layer could significantly improve the effective diffusion coefficients in cathode particles. As such, this enhanced transport property is generally believed to be a result of the higher conductivity of the coating layer itself when compared to that of active materials. However, since the fraction of ALD coating layer is very small, it is questionable that the ultrathin coating layer could lead to such a significant improvement of the diffusivity for the whole particle. Thus, we proposed a new hypothesis about the role of ALD coating layer on Li ion transportation. Due to the agglomeration of particles in an electrode, the surfaces of the particles are partially blocked, and, correspondingly, Li ion intercalation is not uniform over the whole surface. Herein, we propose that the ALD coating could provide a quick path to distribute Li ions over the whole particle surface and allow Li ions to spread uniformly and effectively, leading to improved effective diffusivity of the particles and their utilization. In this work, this hypothesis was validated by simulation and experimental study. It was proved that the particle with an optimal ALD coating thickness has the most uniform Li ion distribution, leading to an optimal discharge capacity. Along with the validation of the hypothesis, a parametric study was conducted by consideration of the flux area, particle size, and current density, which revealed the fundamental role of coating layer on charge transfer, Li ion diffusion, and corresponding battery performance.

Superior Electrochemical Performance of Thin-Film Thermoplastic Elastomer-Coated SnSb as an Anode for Li-ion Batteries

The high failure strain of thermoplastic elastomers (TPEs) is a very desirable feature for rechargeable Li-ion batteries by improving the lifetime of high specific capacity anode materials that undergo mechanical fractures induced by large volume variations. In this work, poly(styrene-b-2-hydroxyethyl acrylate) called PS-b-PHEA was synthesized by a nitroxide meditated polymerization method. Owing to the use of a specific polystyrene macroinitiator (SG1), a suitable TPE copolymer with long hydroxyethyl acrylate blocks to ensure good mechanical properties is obtained for the first time. We show that the electrochemical properties of the PS-b-PHEA-coated SnSb anode are drastically improved by suppressing the crack formation at the surface of the electrode. Indeed, electrochemical characterization revealed that a high and stable gravimetric capacity over 100 cycles could be achieved. Moreover, excellent capacity reversibility was achieved when cycled at multiple C-rates and fast kinetics confirming the strong protection role of the polymer. The advanced chemical and mechanical properties of PS-b-PHEA open up promising perspectives to significantly improve the electrochemical performance of all electrodes that are known to suffer from large volume variations.

Optical and Electrochemical Properties of Self-Organized TiO2 Nanotube Arrays From Anodized Ti-6Al-4V Alloy

Due to their high specific surface area and advanced properties, TiO₂ nanotubes (TiO₂ NTs) have a great significance for production and storage of energy. In this paper, TiO₂ NTs were synthesized from anodization of Ti-6Al-4V alloy at 60 V for 3 h in fluoride ethylene glycol electrolyte by varying the water content and further annealing treatment. The morphological, structural, optical and electrochemical performances of TiO₂ NTs were investigated by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), UV-Visible spectroscopy and electrochemical characterization techniques. By varying the water content in the solution, a honeycomb and porous structure was obtained at low water content and the presence of (α + β) phase in Ti-6Al-4V alloy caused not uniform etching. With an additional increase in water content, a nanotubular structure is formed in the (α + β) phases with different morphological parameters. The anatase TiO₂ NTs synthesized with 20 wt% H₂O shows an improvement in absorption band that extends into the visible region due the presence of vanadium oxide in the structure and the effective band gap energy (Eg) value of 2.25 eV. The TiO₂ NTs electrode also shows a good cycling performance, delivering a reversible capacity of 82 mAh.g⁻¹ (34 μAh.cm⁻².μm⁻¹) at 1C rate over 50 cycles.

TiO2 ALD Coating of Amorphous TiO2 Nanotube Layers: Inhibition of the Structural and Morphological Changes Due to Water Annealing

The present work presents a strategy to stabilize amorphous anodic self-organized TiO₂ nanotube layers against morphological changes and crystallization upon extensive water soaking. The growth of needle-like nanoparticles was observed on the outer and inner walls of amorphous nanotube layers after extensive water soakings, in line with the literature on water annealing. In contrary, when TiO₂ nanotube layers uniformly coated by thin TiO₂ using atomic layer deposition (ALD) were soaked in water, the growth rates of needle-like nanoparticles were substantially reduced. We investigated the soaking effects of ALD TiO₂ coatings with different thicknesses and deposition temperatures. Sufficiently thick TiO₂ coatings (≈8.4 nm) deposited at different ALD process temperatures efficiently hamper the reactions between water and F⁻ ions, maintain the amorphous state, and preserve the original tubular morphology. This work demonstrates the possibility of having robust amorphous 1D TiO₂ nanotube layers that are very stable in water. This is very practical for diverse biomedical applications that are accompanied by extensive contact with an aqueous environment.

Introducing nanodiamond into TiO2-based anode for improving the performance of lithium-ion batteries

In this work, we report a new type of anode consisting of mixed detonation nanodiamonds (DNDs) and titanium dioxide (TiO₂) hollow nanospheres (HNSs) for improving the specific capacity and cycle stability of lithium ion batteries (LIBs).

Biomass-Mediated Synthesis of Cu-Doped TiO2 Nanoparticles for Improved-Performance Lithium-Ion Batteries

Pure TiO₂ and Cu-doped TiO₂ nanoparticles are synthesized by the biomediated green approach using the Bengal gram bean extract. The extract containing biomolecules acts as capping agent, which helps to control the size of nanoparticles and inhibit the agglomeration of particles. Copper is doped in TiO₂ to enhance the electronic conductivity of TiO₂ and its electrochemical performance. The Cu-doped TiO₂ nanoparticle-based anode shows high specific capacitance, good cycling stability, and rate capability performance for its envisaged application in lithium-ion battery. Among pure TiO₂, 3% Cu-doped TiO₂, and 7% Cu-doped TiO₂ anode, the latter shows the highest capacity of 250 mAh g^-1 (97.6% capacity retention) after 100 cycles and more than 99% of coulombic efficiency at 0.5 A g^-1 current density. The improved electrochemical performance in the 7% Cu-doped TiO₂ is attributed to the synergetic effect between copper and titania. The results reveal that Cu-doped TiO₂ nanoparticles might be contributing to the enhanced electronic conductivity, providing an efficient pathway for fast electron transfer.