Plasma-Introduced Oxygen Defects Confined in Li4Ti5O12 Nanosheets for Boosting Lithium-Ion Diffusion

Oxalic acid-assisted preparation of LTO-carbon composite anode material for lithium-ion batteries

This study presents an oxalic acid-assisted method for synthesizing spinel-structured lithium titanate (Li4Ti5O12; LTO)/carbon composite materials. The Ag-doped LTO nanoparticles (NPs) are synthesized via flame spray pyrolysis (FSP). The synthesized material is used as a precursor for synthesizing the LTO-NP/C composite material with chitosan as a carbon source and oxalic acid as an additive. Oxalic acid improves the dissolution of chitosan in water as well as changes the composition and physical and chemical properties of the synthesized LTO-NP/C composite material. The oxalic acid/chitosan ratio can be optimized to improve the electrochemical performance of the LTO-NP/C composite material, and the electrode synthesized with a high mass loading ratio (5.44 mg cm-2) exhibits specific discharge capacities of 156.5 and 136 mAh g-1at 0.05 C- and 10 C-rate currents, respectively. Moreover, the synthesized composite LTO-NP/C composite material exhibits good cycling stability, and only 1.7% decrease in its specific capacity was observed after 200 charging-discharging cycles at 10 C-rate discharging current.

Quenching-Induced Defects Liberate the Latent Reversible Capacity of Lithium Titanate Anode

Interest in defect engineering for lithium-ion battery (LIB) materials is sparked by its ability to tailor electrical conductivity and introduce extra active sites for electrochemical reactions. However, harvesting excessive intrinsic defects in the bulk of the electrodes rather than near their surface remains a long-standing challenge. Here, a versatile strategy of quenching is demonstrated, which is exercised in lithium titanate (Li₄ Ti₅ O₁₂ , LTO), a renowned anode for LIBs, to achieve off-stoichiometry in the interior region. In situ synchrotron analysis and atomic-resolution microscopy reveal the enriched oxygen vacancies and cation redistribution after ice-water quenching, which can facilitate the native unextractable Li ions to participate in reversible cycling. The fabricated LTO anode delivers a sustained capacity of 202 mAh g^-1 in the 1.0-2.5 V range with excellent rate capability and overcomes the poor cycling stability seen in conventional defective electrodes. The feasibility of tuning the degree of structural defectiveness via quenching agents is also proven, which can open up an intriguing avenue of research to harness the intrinsic defects for improving the energy density of rechargeable batteries.

Ultrathin Carbon-Coated Porous TiNb2O7 Nanosheets as Anode Materials for Enhanced Lithium Storage

TiNb₂O₇ has been considered as a promising anode material for next-generation high power lithium ion batteries for its relatively high theoretical capacity, excellent safety and long cycle life. However, the unsatisfactory electrochemical kinetics resulting from the intrinsic sluggish electron transport and lithium ion diffusion of TiNb₂O₇ limit its wide application. Morphology controlling and carbon coating are two effective methods for improving the electrochemical performance of electrode materials. Herein, an ultrathin carbon-coated porous TiNb₂O₇ nanosheet (TNO@C) is successfully fabricated by a simple and effective approach. The distinctive sheet-like porous structure can shorten the transport path of ions/electrons and provide more active sites for electrochemical reaction. The introduction of nanolayer carbon can improve electronic conductivity and increase the specific surface area of the porous TiNb₂O₇ nanosheets. Based on the above synergistic effect, TiNb₂O₇@C delivers an initial discharge capacity of 250.6 mAh g^-1 under current density of 5C and can be maintained at 206.9 mAh g^-1 after 1000 cycles with a capacity retention of 82.6%, both of which are superior to that of pure TiNb₂O₇. These results well demonstrate that TiNb₂O₇@C is a promising anode material for lithium ion batteries.

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.

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.

An oxygen-deficient Li2ZnTi3O8 anode for high-performance lithium storage

The Li-storage mechanism of LZTO with oxygen vacancies has been revealed via experiments and first-principles calculations.

Introducing Oxygen Vacancies in Li4Ti5O12 via Hydrogen Reduction for High-Power Lithium-Ion Batteries

Li4Ti5O12 (LTO), known as a zero-strain material, is widely studied as the anode material for lithium-ion batteries owing to its high safety and long cycling stability. However, its low electronic conductivity and Li diffusion coefficient significantly deteriorate its high-rate performance. In this work, we proposed a facile approach to introduce oxygen vacancies into the commercialized LTO via thermal treatment under Ar/H2 (5%). The oxygen vacancy-containing LTO demonstrates much better performance than the sample before H2 treatment, especially at high current rates. Density functional theory calculation results suggest that increasing oxygen vacancy concentration could enhance the electronic conductivity and lower the diffusion barrier of Li+, giving rise to a fast electrochemical kinetic process and thus improved high-rate performance.

Recent progress of defect chemistry on 2D materials for advanced battery anodes

The rational design of anode materials plays a significant factor in harnessing energy storage. With an in-depth insight into the relationships and mechanisms that underlie the charge and discharge process of two-dimensional (2D) anode materials. The efficiency of rechargeable batteries has significantly been improved through the implementation of defect chemistry on anode materials. This mini review highlights the recent progress achieved in defect chemistry on 2D materials for advanced rechargeable battery electrodes, including vacancies, chemical functionalization, grain boundary, Stone Wales defects, holes and cracks, folding and wrinkling, layered von der Waals (vdW) heterostructure in 2D materials. The defect chemistry on 2D materials provides numerous features such as a more active adsorption sites, great adsorption energy, better ions-diffusion and therefore higher ion storage, which enhances the efficiency of the battery electrode.

The oxygen vacancy in Li-ion battery cathode materials

The substantial capacity gap between available anode and cathode materials for commercial Li-ion batteries (LiBs) remains, as of today, an unsolved problem. Oxygen vacancies (OVs) can promote Li-ion diffusion, reduce the charge transfer resistance, and improve the capacity and rate performance of LiBs. However, OVs can also lead to accelerated degradation of the cathode material structure, and from there, of the battery performance. Understanding the role of OVs for the performance of layered lithium transition metal oxides holds great promise and potential for the development of next generation cathode materials. This review summarises some of the most recent and exciting progress made on the understanding and control of OVs in cathode materials for Li-ion battery, focusing primarily on Li-rich layered oxides. Recent successes and residual unsolved challenges are presented and discussed to stimulate further interest and research in harnessing OVs towards next generation oxide-based cathode materials.

Recent Developments of Nanomaterials and Nanostructures for High-Rate Lithium Ion Batteries

Lithium ion batteries have been considered as a promising energy-storage solution, the performance of which depends on the electrochemical properties of each component, including cathode, anode, electrolyte and separator. Currently, fast charging is becoming an attractive research field due to the widespread application of batteries in electric vehicles, which are designated to replace conventional diesel automobiles in the future. In these batteries, rate capability, which is closely linked to the topology and morphology of electrode materials, is one of the determining parameters of interest. It has been revealed that nanotechnology is an exceptional tool in designing and preparing cathodes and anodes with outstanding electrochemical kinetics due to the well-known nanosizing effect. Nevertheless, the negative effects of applying nanomaterials in electrodes sometimes outweigh the benefits. To better understand the exact function of nanostructures in solid-state electrodes, herein, a comprehensive review is provided beginning with the fundamental theory of lithium ion transport in solids, which is then followed by a detailed analysis of several major factors affecting the migration of lithium ions in solid-state electrodes. The latest developments in characterisation techniques, based on either electrochemical or radiology methodologies, are covered as well. In addition, state-of-the-art research findings are provided to illustrate the effect of nanomaterials and nanostructures in promoting the rate performance of lithium ion batteries. Finally, several challenges and shortcomings of applying nanotechnology in fabricating high-rate lithium ion batteries are summarised.

Molybdenum-Suboxide Thin Films as Anode Layers in Planar Lithium Microbatteries

In this paper, we investigate the effects of operational conditions on structural, electronic and electrochemical properties on molybdenum suboxides (MoO3-δ) thin films. The films are prepared using pulsed-laser deposition by varying the deposition temperature (Ts), laser fluence (Φ), the partial oxygen pressure (PO2) and annealing temperature (Ta). We find that three classes of samples are obtained with different degrees of stoichiometric deviation without post-treatment: (i) amorphous MoO3-δ (δ < 0.05) (ii) nearly-stoichiometric samples (δ ≈ 0) and (iii) suboxides MoO3-δ (δ > 0.05). The suboxide films 0.05 ≤ δ ≤ 0.25 deposited on Au/Ti/SiO2/flexible-Si substrates with appropriate processing conditions show high electrochemical performance as an anode layer for lithium planar microbatteries. In the realm of simple synthesis, the MoO3-δ film deposited at 450 °C under oxygen pressure of 13 Pa is a mixture of α-MoO3 and Mo8O23 phases (15:85). The electrochemical test of the 0.15MoO3-0.85Mo8O23 film shows a specific capacity of 484 µAh cm−2 µm−1 after 100 cycles of charge-discharge at a constant current of 0.5 A cm−2 in the potential range 3.0-0.05 V.

Moderate oxygen-deficient Fe(III) oxide nanoplates for high performance symmetric supercapacitors

As a promising anode material for supercapacitors, Fe₂O₃ has been widely studied but still face the problem of low conductivity. Inducing oxygen vacancy (Vo) into Fe₂O₃ is a widely used approach to tune the conductivity to enhance its capacitive performance, but there is little research on the influence of Vo content. Herein, we report the effect of Vo in Fe₂O₃ nanoplates with various content. We tuned the Vo content by annealing at 200-500 °C. XPS and EPR were taken to characterize the Vo content, ranging from 11% to 26%. Electrochemical results show that FO-300 with 17% Vo has the highest capacity of 301 mAh g^-1, and the capacity of the highest Vo content's (26% Vo) is only 107 mAh g^-1. The symmetric supercapacitor based on FO-300 shows a considerably high energy density of 58.5 Wh kg^-1 at a power density of 9.32 kW kg^-1 and remains 84.6% after 12,000 cycles.

Defect Engineering on Electrode Materials for Rechargeable Batteries

The reasonable design of electrode materials for rechargeable batteries plays an important role in promoting the development of renewable energy technology. With the in-depth understanding of the mechanisms underlying electrode reactions and the rapid development of advanced technology, the performance of batteries has significantly been optimized through the introduction of defect engineering on electrode materials. A large number of coordination unsaturated sites can be exposed by defect construction in electrode materials, which play a crucial role in electrochemical reactions. Herein, recent advances regarding defect engineering in electrode materials for rechargeable batteries are systematically summarized, with a special focus on the application of metal-ion batteries, lithium-sulfur batteries, and metal-air batteries. The defects can not only effectively promote ion diffusion and charge transfer but also provide more storage/adsorption/active sites for guest ions and intermediate species, thus improving the performance of batteries. Moreover, the existing challenges and future development prospects are forecast, and the electrode materials are further optimized through defect engineering to promote the development of the battery industry.

Ti3+ Self-Doped Li4 Ti5 O12 Anchored on N-Doped Carbon Nanofiber Arrays for Ultrafast Lithium-Ion Storage

Omnibearing acceleration of charge/ion transfer in Li₄ Ti₅ O₁₂ (LTO) electrodes is of great significance to achieve advanced high-rate anodes in lithium-ion batteries. Here, a synergistic combination of hydrogenated LTO nanoparticles (H-LTO) and N-doped carbon fibers (NCFs) prepared by an electrodeposition-atomic layer deposition method is reported. Binder-free conductive NCFs skeletons are used as strong support for H-LTO, in which Ti³⁺ is self-doped along with oxygen vacancies in LTO lattice to realize enhanced intrinsic conductivity. Positive advantages including large surface area, boosted conductivity, and structural stability are obtained in the designed H-LTO@NCF electrode, which is demonstrated with preeminent high-rate capability (128 mAh g^-1 at 50 C) and long cycling life up to 10 000 cycles. The full battery assembled by H-LTO@NCFs anode and LiFePO₄ cathode also exhibits outstanding electrochemical performance revealing an encouraging application prospect. This work further demonstrates the effectiveness of self-doping of metal ions on reinforcing the high-rate charge/discharge capability of batteries.