Nitrogen Rich Carbon Coated TiO2 Nanoparticles as Anode for High Performance Lithium-ion Battery

Spontaneous redox reaction-mediated interfacial charge transfer in titanium dioxide/graphene oxide nanoanodes for rapid and durable lithium storage

Titanium dioxide (TiO2) anodes show significant advantages in ion storage owing to their low cost, abundant sources, and small volume change during cycling. However, their intrinsic low electronic conductivity and sluggish ion diffusion coefficient restrict the application of TiO2 anodes, especially at high current densities. The construction of a covalently-bonded interface in TiO2-based composite anodes is an effective approach to solve these issues. Covalent bonds are usually formed in situ during materials synthesis processes, such as high-energy ball milling, solvothermal reactions, plasma-assisted thermal treatment, and addition of a linking agent for covalent coupling. In this study, we demonstrate that a spontaneous redox reaction between defective TiO2 powder and an oxidative graphene oxide (GO) substate can be used to form interfacial covalent bonds in composites. Different structural characterization techniques confirmed the formation of interfacial covalent bonds. Electrochemical measurements on an optimized sample showed that a specific capacity of 281.3 mA h g-1 after 200 cycles can be achieved at a current density of 1 C (1 C = 168 mA g-1). Even at a high rate of 50 C, the electrode maintained a reversible capacity of 97.0 mA h g-1. The good lithium storage performance of the electrode is a result of the uniquely designed composite electrodes with strong interfacial chemical bonds.

Ultrafast and Stable Lithium Storage Enabled by the Electric Field Effect in Layer-Structured Tablet-Like NH4TiOF3 Mesocrystals

Design and synthesis of advanced electrode materials with fast and stable ion storage are of importance for energy storage applications. Herein, we propose that introducing the heterogeneous interface in layer-structured mesocrystals is an efficient way to greatly improve the rate capability and cycle stability of lithium-ion battery (LIB) devices. NH₄TiOF₃ mesocrystals were employed as a typical model system to demonstrate the idea. The NH₄TiOF₃ mesocrystals were obtained via the hydrothermal reaction, and the NH₄TiOF₃/TiO₂ interfaces were generated through calcining at different temperatures under an argon atmosphere. Phase composition, microstructure, and chemical analyses show that the as-prepared NH₄TiOF₃ mesocrystals possess "tablet-like" morphology, and the formation of the NH₄TiOF₃/TiO₂ interface can be controlled by the calcination temperature. When evaluated as the anode for LIBs, the optimized sample (NH₄TiOF₃ calcined at 250 °C, NTF-250) shows excellent, fast, and stable lithium storage properties. Specifically, the NTF-250 electrode holds a reversible capacity of 159.5 mA h g^-1 after 200 cycles at 0.2 A g^-1. At a high current density of 20 A g^-1, the electrode still maintains a reversible capacity of 89.6 mA h g^-1 and reaches a reversible capacity of 128.6 mA h g^-1 at a current density of 1 A g^-1 after 2000 cycles. Theoretical and experimental studies show that the synergistic effects of the heterogeneous NH₄TiOF₃/anatase TiO₂ interface in the layer-structured NH₄TiOF₃ mesocrystals lead to the upgraded electrochemical properties. Especially, the local build-in electric field induced by the nonuniform distribution of charge across the NH₄TiOF₃/anatase TiO₂ interface facilitates the charge transport during the charging and discharging cycling. The current electrode design strategy paves a new way in boosting stable ion storage and thus is of great interest in energy storage and conversion.

An oriented laterally-growing NiCo2O4 nanowire array on a Fe2O3 microdisc as a high-capacity and excellent rate-performance secondary battery anode

A novel hierarchical composite consisting of an ordered NiCo2O4 nanowire array growing on the lateral side of a Fe2O3 microdisc is presented, which was confirmed by X-ray holography technology on a synchrotron radiation station. The composite-based Li-ion battery anode exhibits a high capacity of 1528 mA h g-1 after 200 cycles at 0.2C, a recoverable rate-performance after repeated tests, and robust mechanical properties.

A uniform few-layered carbon coating derived from self-assembled carboxylate monolayers capable of promoting the rate properties and durability of commercial TiO2

The poor cyclability and rate property of commercial TiO₂ (c-TiO₂) hinder its utilization in lithium-ion batteries (LIBs). Coating carbon is one of the ways to ameliorate the electrochemical performance. However, how to effectively form a uniform thin carbon coating is still a challenge. On the basis of the strong interaction of the TiO₂ surface with carboxyl groups, herein a new tactic to achieve uniform and thin carbon layers on the c-TiO₂ particles was proposed. When mixing c-TiO₂ with citric acid containing carboxyl groups in deionized water, the high-affinity adsorption of TiO₂ for carboxyl groups resulted in self-assembled carboxylate monolayers on the surface of TiO₂ which evolved into a uniform few-layered amorphous carbon coating during carbonizing at 750 °C. The product derived from the mixture of c-TiO₂ and citric acid with a mass ratio of 1 : 0.3 exhibits the optimal performance, revealing a high specific capacity (256.6 mA h g⁻¹ after 50 cycles at 0.1 A g⁻¹) and outstanding cycling stability (retaining a capacity of 160.0 mA h g⁻¹ after 1000 cycles at 0.5 A g⁻¹). The greatly enhanced capacity and cyclability correlate with the uniform few-layered carbon coating which not only ameliorates the electronic conductivity of c-TiO₂ but also avoids the reduction in ionic conductivity caused by thick carbon layers and redundant carbon.

The uniform and thin carbon-coating formed on c-TiO₂ particles by virtue of the high-affinity adsorption of TiO₂ for carboxyl groups results in superior rate and cycling performance.

Niobium-Based Oxides Toward Advanced Electrochemical Energy Storage: Recent Advances and Challenges

Niobium-based oxides including Nb₂ O₅ , TiNb_x O_2+2.5x compounds, M-Nb-O (M = Cr, Ga, Fe, Zr, Mg, etc.) family, etc., as the unique structural merit (e.g., quasi-2D network for Li-ion incorporation, open and stable Wadsley- Roth shear crystal structure), are of great interest for applications in energy storage systems such as Li/Na-ion batteries and hybrid supercapacitors. Most of these Nb-based oxides show high operating voltage (>1.0 V vs Li⁺ /Li) that can suppress the formation of solid electrolyte interface film and lithium dendrites, ensuring the safety of working batteries. Outstanding rate capability is impressive, which can be derived from their fast intercalation pseudocapacitive kinetics. However, the intrinsic poor electrical conductivity hinders their energy storage applications. Various strategies including structure optimization, surface engineering, and carbon modification are effectively used to overcome the issues. This review provides a comprehensive summary on the latest progress of Nb-based oxides for advanced electrochemical energy storage applications. Major impactful work is outlined, promising research directions, and various performance-optimizing strategies, as well as the energy storage mechanisms investigated by combining theoretical calculations and various electrochemical characterization techniques. In addition, challenges and perspectives for future research and commercial applications are also presented.

3D ordered mesoporous TiO2@CMK-3 nanostructure for sodium-ion batteries with long-term and high-rate performance

Sodium ion battery is abundant in resources and costs low, making it very competitive in the large-scale energy storage devices. The anatase TiO₂ electrode material with insertion/extraction mechanism shows stable cycling performance, which is more in line with the technical requirements of large-scale energy storage batteries. To improve the electrical conductivity and stability of the TiO₂ electrode materials, we have synthesized anatase TiO₂ and CMK-3 composite. TiO₂ nanoparticles were deposited on the surface of CMK-3 by hydrothermal reaction, and the anode material of the SIBs with 3D network structure was prepared. With the CMK-3, the structure stability, conductivity and reaction kinetics of TiO₂@CMK-3 composite is improved. The electrochemical behavior is dominated by pseudocapacitance, which gives the material excellent high-rate performance. It delivers a reversible specific capacity of 186.3 mA h g^-1 after 100 cycles at the current density of 50 mA g^-1, 124.5 mA h g^-1 after 500 long-term cycles, meanwhile it shows an outstanding rate performance, a reversible specific capacity of 105.9 mA h g^-1 at 1600 mA g^-1, 177.3 mA h g^-1 when the current density drops to 50 mA g^-1.

Constructing Three-Dimensional Porous Carbon Framework Embedded with FeSe2 Nanoparticles as an Anode Material for Rechargeable Batteries

Metal selenides have caused widespread concern due to their high theoretical capacities and appropriate working potential; however, they suffer from large volume variation during cycling and low electrical conductivity, which limit their practical applications. In this article, a three-dimensional (3D) porous carbon framework embedded with homogeneous FeSe₂ nanoparticles (3D porous FeSe₂/C composite) was synthesized by a facile calcined approach, following a selenized method without a template. As the uniformity of FeSe₂ nanoparticles and 3D porous structure are beneficial to accommodate volume stress upon cycling and shorten electrons/ions transport path, associated with carbon as a buffer matrix for increasing conductivity, the 3D porous FeSe₂/C composite displays excellent electrochemical properties with high reversible capacities of 798.4 and 455.0 mA h g^-1 for lithium-ion batteries and sodium-ion batteries, respectively, when the current density is 100 mA g^-1 after 100 cycles. In addition, the as-prepared composite exhibits good cycling stability as compared to bare FeSe₂ nanoparticles. Therefore, the facile synthetic strategy in the current work provides a new perspective in constructing a high-performance anode.

Flexible TiO2 /SiO2 /C Film Anodes for Lithium-Ion Batteries

Flexible TiO₂ /SiO₂ /C films are prepared by using an electrospinning approach and used as self-supporting electrodes for lithium-ion batteries (LIBs), which exhibit excellent high-rate capability with a capacity of 115.5 mAh g^-1 at 8 A g^-1 (9.8 C rate) and good storage performance. The LIBs also show high long-term cycling stability of 700 cycles at 200 mA g^-1 with a capacity of 380.1 mAh g^-1 and a high capacity retention of 88.3 %. Thus, the TiO₂ /SiO₂ /C films have the potential to serve as electrodes for flexible LIBs, owing to their flexibility and excellent electrochemical performance.

Free-anchored Nb2O5@graphene networks for ultrafast-stable lithium storage

Orthorhombic Nb₂O₅ (T-Nb₂O₅) has structural merit but poor electrical conductivity, limiting their applications in energy storage. Although graphene is frequently adopted to effectively improve its electrochemical properties, the ordinary modified methods cannot meet the growing demands for high-performance. Here, we demonstrate that different graphene modified routes play a vital role in affecting the electrochemical performances of T-Nb₂O₅. By only manual shaking within one minute, Nb₂O₅ nano-particles can be rapidly adsorbed onto graphene, then the free-anchored T-Nb₂O₅@graphene three-dimensional networks can be successfully prepared based on hydrogel method. As for the application in lithium-ion batteries, it performs outstanding rate character (129 mA h g^-1 (25C rate), 110 mA h g^-1 (50C rate) and 90 mA h g^-1 (100C rate), correspond to 79%, 67% and 55% capacity of 0.5C rate, respectively) and excellent long-term cycling feature (∼70% capacity retention after 20000 cycles). Moreover, it still maintains similar ultrafast-stable lithium storage performances when Cu foil is substituted by Al foil as current collector. In addition, relevant kinetics mechanisms are also expounded. This work provides a versatile strategy for the preparation of graphene modified Nb₂O₅ or other types of nanoparticles.