Litao Yan

Nanoscale Engineering of Heterostructured Anode Materials for Boosting Lithium-Ion Storage

Rechargeable lithium-ion batteries (LIBs), as one of the most important electrochemical energy-storage devices, currently provide the dominant power source for a range of devices, including portable electronic devices and electric vehicles, due to their high energy and power densities. The interest in exploring new electrode materials for LIBs has been drastically increasing due to the surging demands for clean energy. However, the challenging issues essential to the development of electrode materials are their low lithium capacity, poor rate ability, and low cycling stability, which strongly limit their practical applications. Recent remarkable advances in material science and nanotechnology enable rational design of heterostructured nanomaterials with optimized composition and fine nanostructure, providing new opportunities for enhancing electrochemical performance. Here, the progress as to how to design new types of heterostructured anode materials for enhancing LIBs is reviewed, in the terms of capacity, rate ability, and cycling stability: i) carbon-nanomaterials-supported heterostructured anode materials; ii) conducting-polymer-coated electrode materials; iii) inorganic transition-metal compounds with core@shell structures; and iv) combined strategies to novel heterostructures. By applying different strategies, nanoscale heterostructured anode materials with reduced size, large surfaces area, enhanced electronic conductivity, structural stability, and fast electron and ion transport, are explored for boosting LIBs in terms of high capacity, long cycling lifespan, and high rate durability. Finally, the challenges and perspectives of future materials design for high-performance LIB anodes are considered. The strategies discussed here not only provide promising electrode materials for energy storage, but also offer opportunities in being extended for making a variety of novel heterostructured nanomaterials for practical renewable energy applications.

Facile synthesis of hierarchical MoS2–carbon microspheres as a robust anode for lithium ion batteries

Molybdenum disulfide (MoS2) may be a promising alternative for lithium ion batteries (LIBs) because it offers a unique layered crystal structure with a large and tunable distance between layers. This enables the anticipated excellent rate and cycling stability because they can promote the reversible lithium ion intercalation and de-intercalation without huge volume change which consequently prevents the pulverization of active materials during repeated charge and discharge processes. Herein, we prepared hierarchical MoS2–carbon (MoS2–C) microspheres via a continuous and scalable ultrasonic nebulization assisted route. The structure, composition, and electrochemical properties are investigated in detail. The MoS2–C microspheres consist of few-layer MoS2 nanosheets bridged by carbon, which separates the exfoliated MoS2 layers and prevents their aggregation and restacking, thus leading to improved kinetic, enhanced conductivity and structural integrity. The novel architecture offers additional merits such as overall large size and high packing density, which promotes their practical applications. The MoS2–C microspheres have been demonstrated with excellent electrochemical performances in terms of low resistance, high capacity even at large current density, stable cycling performance, etc. The electrodes exhibited 800 mA h g−1 at 1000 mA g−1 over 170 cycles. At a higher current density of 3200 mA g−1, a capacity of 730 mA h g−1 can be also maintained. The MoS2–C microspheres are practically applicable not only because of the continuous and large scale synthesis via the current strategy, but also the possess a robust and integrated architecture which ensures the excellent electrochemical properties.

Ultrafine Nb2O5 Nanocrystal Coating on Reduced Graphene Oxide as Anode Material for High Performance Sodium Ion Battery

Ultrafine niobium oxide nanocrystals/reduced graphene oxide (Nb2O5 NCs/rGO) was demonstrated as a promising anode material for sodium ion battery with high rate performance and high cycle durability. Nb2O5 NCs/rGO was synthesized by controllable hydrolysis of niobium ethoxide and followed by heat treatment at 450 °C in flowing forming gas. Transmission electron microscopy images showed that Nb2O5 NCs with average particle size of 3 nm were uniformly deposited on rGO sheets and voids among Nb2O5 NCs existed. The architecture of ultrafine Nb2O5 NCs anchored on a highly conductive rGO network can not only enhance charge transfer and buffer the volume change during sodiation/desodiation process but also provide more active surface area for sodium ion storage, resulting in superior rate and cycle performance. Ex situ XPS analysis revealed that the sodium ion storage mechanism in Nb2O5 could be accompanied by Nb(5+)/Nb(4+) redox reaction and the ultrafine Nb2O5 NCs provide more surface area to accomplish the redox reaction.

Titanium Oxynitride Nanoparticles Anchored on Carbon Nanotubes as Energy Storage Materials

Sub-8 nm titanium oxynitride (TiON) nanoparticles were uniformly formed on the surface of carbon nanotubes (CNTs) by annealing amorphous TiO2 (a-TiO2) conformally coated CNTs (CNTs/a-TiO2) at 600 °C in ammonia gas. The novel CNTs/TiON nanocomposite was systematically characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy imaging (HRTEM), scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDX), and X-ray photoelectron spectroscopy (XPS). The results show that Ti, O, and N are homogeneously distributed in TiON nanoparticles. The specific capacitance of CNTs/TiON exhibits 187 F g(-1) at a current density of 0.5 A g(-1), which is much higher than that of CNTs (33.4 F g(-1)) and CNTs/TiO2 (83.4 F g(-1)) obtained by annealing CNTs/a-TiO2 at 450 °C in nitrogen gas. CNTs/TiON also exhibits enhanced cycle durability, which enables it to be considered as a promising candidate for supercapacitors.

La0.8Sr0.2MnO3-Based Perovskite Nanoparticles with the A-Site Deficiency as High Performance Bifunctional Oxygen Catalyst in Alkaline Solution

Perovskite (La0.8Sr0.2)1-xMn1-xIrxO3 (x = 0 (LSM) and 0.05 (LSMI)) nanoparticles with particle size of 20-50 nm are prepared by the polymer-assisted chemical solution method and demonstrated as high performance bifunctional oxygen catalyst in alkaline solution. As compared with LSM, LSMI with the A-site deficiency and the B-site iridium (Ir)-doping has a larger lattice, lower valence state of transition metal, and weaker metal-OH bonding; therefore, it increases the concentration of oxygen vacancy and enhances both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). LSMI exhibits superior ORR performance with only 30 mV onset potential difference from the commercial Pt/C catalyst and significant enhancement in electrocatalytic activity in the OER process, resulting in the best oxygen electrode material among all the reported perovskite oxides. LSMI also exhibits high durability for both ORR (only 18 mV negative shift for the half-wave potential compared with the initial ORR) and OER process with 10% decay. The electrochemical results indicate that the A-site deficiency and Ir-doping in perovskite oxides could be promising catalysts for the applications in fuel cells, metal-air batteries, and solar fuel synthesis.

Niobium-doped titanium dioxide on a functionalized carbon supported palladium catalyst for enhanced ethanol electro-oxidation

Pd nanoparticles anchored on Nb-doped TiO2 with functionalized carbon support (denoted as Pd/Nb–TiO2–C) is synthesized through a controllable hydrolysis and impregnation method. The as-synthesized catalyst is characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Pd nanoparticles exhibit a uniform distribution with an average particle size of 3 nm. The electrochemical performance is tested by cyclic voltammetry (CV) and chronoamperometry (CA). Compared with Pd supported by functionalized carbon (Pd/C), Pd/Nb–TiO2–C demonstrates 15.7% higher metallic Pd content, 23% higher electrochemical active surface area, 75% higher current density in ethanol electro-oxidation, 5% higher durability, and better tolerance of carbonaceous species. The performance enhancement is attributed to the increased conductivity from Nb-doping and the synergistic effect between Pd and TiO2.