Xianfeng Du

Graphene oxide sheets-induced growth of nanostructured Fe3O4 for a high-performance anode material of lithium ion batteries

Nanostructured Fe3O4 is intrinsically prone to aggregation, which hinders insertion and extraction of lithium ions. To overcome this problem, we adopt graphene oxide sheets (GOS) and induce growth of nanostructured Fe3O4 on the GOS in the presence of hexamethylenetetramine (HMT). During the synthetic process, GOS provides a template to regulate the growth of nanostructured Fe3O4 and the HMT is able to coordinate with Fe3+ and control its hydrolysis rate. After the annealing process, GOS is reduced to GS (graphene sheets), and Fe3O4/GS composite is obtained. In this hierarchical structure, GS is capable of enhancing the electronic transport of Fe3O4, and the Fe3O4/GS composite has superior electronic conductivity (106 S m−1). Benefitting from the uniform dispersion of the nanosized Fe3O4 on GS and the superior electronic conductivity, the obtained Fe3O4/GS exhibits prolonged cycling stability (1002 mA h g−1 after 175 cycles at a current density of 0.50 A g−1) and excellent rate capability (715, 647 and 535 mA h g−1 at 1.6, 3.2 and 5.0 A g−1, respectively).

Water-Free Titania-Bronze Thin Films With Superfast Lithium Ion Transport

Using pulsed laser deposition, TiO2 (-) B and its recently discovered variant Ca:TiO2 (-) B (CaTi5O11) are synthesized as highly crystalline thin films for the first time by a completely water-free process. Significant enhancement in the Li-ion battery performance is achieved by manipulating the crystal orientation of the films, used as anodes, with a demonstration of extraordinary structural stability under extreme conditions.

Double roles of aluminium ion on surface-modified spinel LiMn1.97Ti0.03O4

Spinel LiMn2O4 is one of the cathode active materials for the rechargeable lithium-ion batteries with the most potential, but suffers from a fast capacity fade when cycling at elevated temperatures (55 °C). Spinel LiMn1.97Ti0.03O4 coated with aluminum nitrate is heat-treated at various temperatures. The sample treated at low temperature (500 °C) exhibits porous Al2O3 layer coated on the surface, and little Al ion diffusing into the spinel structure. As for the sample treated at mid-temperature (700 °C), it exhibits double layers coated on the surface: the inner layer is LiAlxMn1.97−xTi0.03O4 solid solution and the outer layer is compact Al2O3 metal oxides. When the heat-treatment temperature increases to a high level (850 °C), nearly all the Al ion diffusing into the structure to form Al doped solid solution layer coated on the spinel. The relationship between the structure of the modified samples and their electrochemical properties is investigated. The galvanostatic charge–discharge results show that those surface-modified samples exhibit improved cycling performance compared to LiMn1.97Ti0.03O4; and the sample treated at mid-temperature delivers the best capacity retention, especially at 55 °C. The improved cycling performance is ascribed to the coated layers of Al2O3 and LiAlxMn1.97−xTi0.03O4 on the spinel particles. The Al2O3 layer could reduce the HF damage by scavenging of HF. While the LiAlxMn1.97−xTi0.03O4 layer could enhance the stability of the spinel structure due to the stronger Al–O bond; moreover, this coating layer having the same spinel structure with the LiMn1.97Ti0.03O4 core material would not hinder the lithium ion diffusion. The sample treated at mid-temperature has the double layers coated on the surface, and its Al2O3 coating becomes compact and thin which could effectively block the direct contact between the electrolyte and spinel particles as well as reduce the lithium ion diffusion distance in the inactive layer, leading to greatly improved capacity retention.

Microwave-Assisted Synthesis of SnO2@polypyrrole Nanotubes and Their Pyrolyzed Composite as Anode for Lithium-Ion Batteries

Tin dioxide (SnO2) as lithium-ion batteries (LIBs) anode has attracted numerous interests due to its huge Li(+) storage capacity. However, more than 300% volume variation of SnO2 during the charge/discharge process results in dramatic degradation of electrochemical performance and thus poor cyclic stability, which has hindered its application in LIBs. Here, a new strategy is proposed to suppress this volume change via anchoring mesoporous SnO2 on robust polypyrrole nanotubes (PPy NTs) to fabricate nanoarchitectured SnO2 composite. Benefiting from this nanoarchitecture design, the anode presents outstanding rate performance with a reversible specific capacity of about 770 mA h g(-1) at 2000 mA g(-1) and remarkable cyclability accompanied by a high specific capacity of about 790 mA h g(-1) at 200 mA g(-1) after 200 cycles.

One-step Preparation of Nanoarchitectured TiO2 on Porous Al as Integrated Anode for High-performance Lithium-ion Batteries.

Titanium dioxide (TiO2) is an attractive anode material for energy storage devices due to its low-volume-change and high safety. However, TiO2 anodes usually suffer from poor electrical and ionic conductivity, thus causing dramatic degradation of electrochemical performance at rapid charge/discharge rates, which has hindered its use in energy storage devices. Here, we present a novel strategy to address this main obstacle via using nanoarchitectured TiO2 anode consisting of mesoporous TiO2 wrapped in carbon on a tunnel-like etched aluminum substrate prepared by a simple one-step approach. As a result of this nanoarchitecture arrangement, the anode exhibits excellent rate performance and superior cyclability. A rate up to 100 C is achieved with a high specific capacity of about 95 mA h g−1, and without apparent decay after 8,000 cycles.

Low-Cost Al2O3 Coating Layer As a Preformed SEI on Natural Graphite Powder To Improve Coulombic Efficiency and High-Rate Cycling Stability of Lithium-Ion Batteries.

Coulombic efficiency especially in the first cycle, cycling stability, and high-rate performance are crucial factors for commercial Li-ion batteries (LIBs). To improve them, in this work, Al2O3-coated natural graphite powder was obtained through a low-cost and facile sol-gel method. Based on a comparison of various coated amounts, 0.5 mol % Al(NO3)3 (vs mole of graphite) could bring about a smooth Al2O3 coating layer with proper thickness, which could act as a preformed solid electrolyte interface (SEI) to reduce the regeneration of SEI and lithium-ions consumption during subsequent cycling. Furthermore, we examined the advantages of Al2O3 coating by relating energy levels in LIBs using density functional theory calculations. Owing to its proper bandgap and lithium-ion conduction ability, the coating layer performs the same function as a SEI does, preventing an electron from getting to the outer electrode surface and allowing lithium-ion transport. Therefore, as a preformed SEI, the Al2O3 coating layer reduces extra cathode consumption observed in commercial LIBs.

Effect of Doping Ions on Electrochemical Capacitance Properties of Polypyrrole Films

Abstract Conducting polypyrrole (PPy) films doped with p-toluenesulfonate (TOS−), ClO4−, and Cl− were electrochemically prepared, respectively. The electrochemical capacitance properties of the PPy films were investigated with cyclic voltammetry (CV), galvanostatical charge/discharge, and electrochemical impedance spectroscope (EIS) techniques. The morphology observation and structure analysis of PPy films were performed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that PPy-Cl and PPy-TOS were characterized with a highly porous and ordered structure, which led to their fast ion switch processes. Moreover, they exhibited a rectangle-like shape of voltammetry characteristics even at a scanning rate of 50 mV·s−1, a linear variation of the voltage with respect to time in the charge/discharge process, and almost ideal capacitance behavior in low frequency, even in deeply charged/discharged states in 1 mol·L−1 KCl solution. Furthermore, specific capacitance of PPy-Cl (polymerization charge of 2 mAh·cm−2) could reach 270 F·g−1 (scanning rate of 5 mV·s−1) or 175 F·g−1 (scanning rate of 200 mV·s−1) and its specific energy could reach 35.3 mWh·g−1. Moreover, with heavier doping ion (TOS−), PPy-TOS (polymerization charge of 2 mAh·cm−2) had a slightly smaller specific capacitance (146 F·g−1, scanning rate of 5 mV·s−1), but a very rapidly charge/discharge ability (specific capacitance of 123.6 F·g−1 at scanning rate of 200 mV·s−1) and its specific power could reach 10 W·g−1. In addition, both PPy-TOS and PPy-Cl had good cycleability. All of the above implied that the PPy-Cl and PPy-TOS were two kinds of promising electrode material for supercapacitors.

High rate capabilities of HF-etched SiOC anode materials derived from polymer for lithium-ion batteries

Polymer-derived silicon oxycarbide (SiOC) composites have recently attracted considerable attention because of their potential as high capacity electrode for rechargeable lithium ion batteries. However, low discharge capacity at large current densities hinders its practicality. In this work, SiOC compound as anode materials is synthesized by pyrolyzing polycarbosilane with a cyclic tetramethyl tetravinyl cyclotetrasiloxane, followed by etching with HF. The obtained SiOC delivers high reversible capacities of 321, 274 and 206 mA h g−1 and high capacity retention of 100%, 93.4% and 68% at current densities of 1000, 2000 and 4000 mA g−1 after 200 cycles, respectively. The excellent electrochemical properties can be attributed to the increased specific surface area, enlarged volume of nano-sized pores and F-doped silicon unit in the HF-etching process, which benefit the contact between active material and electrolyte, alleviate the volume change during discharge/charge process and raise the ionic conductivity.

Polypyrrole composites with carbon materials for supercapacitors

Supercapacitors fill the gap between batteries and conventional solid state and electrolytic capacitors. Polypyrrole (PPy) is a very important electrode material for supercapacitors. However, the repeated volume changes usually damage PPy structure and result in PPy poor stability during a long-term charging/discharging process. PPy/carbon material composites were prepared to overcome the defects of pure PPy electrodes, and significant enhancement for the specific capacitance, charging/discharging rate and electrodes stability was demonstrated thereafter. The development of composite electrodes based on PPy and carbon materials is reviewed in this paper.

Enhanced capacitance performance of Al2O3–TiO2 composite thin film via sol–gel using double chelators

Titanium dioxide (TiO2) is usually introduced into dielectric layer of aluminum electrolytic capacitor to enhance capacitance performance via forming Al2O3-TiO2 composite film. However, there is a big obstacle caused by high crystallization temperature of TiO2 to capacitance enhancement. In present work, a facile route was proposed to synthesize crystalline TiO2 with the size of 3-10 nm at room temperature using lactic acid (LA) and acetylacetone (Acac) as double chelators. After being introduced into the surface of etched aluminum foils as dielectric layer, TiO2 boosted the specific capacitance by about 24% compared to that without TiO2, and about 11% compared to that with TiO2 using lactic acid as only chelator.