Gui-Liang Xu

Morphology-conserved transformation: synthesis of hierarchical mesoporous nanostructures of Mn2O3 and the nanostructural effects on Li-ion insertion/deinsertion properties

By means of morphology-conserved transformation, we have synthesized hierarchically structured Mn2O3 nanomaterials with different morphologies and pore structures. The key step of this method consists of the formation of a precursor containing the target materials interlaced with the judiciously chosen polyol-based organic molecules, which are subsequently knocked out to generate the final nanomaterials. In the present work, two kinds of precursor morphologies, oval-shaped and straw-sheaf-shaped, have been selectively prepared by hydrothermal treatment of different functional polyol molecules (oval-shape with fructose and straw-sheaf-shape with β-cyclodextrin) and potassium permanganate. Thermal decomposition of the precursors resulted in the formation of mesoporous Mn2O3 maintaining the original morphologies, as revealed by extensive characterization. These novel hierarchical nanostructures with different pore sizes/structures prompted us to examine their potential as anode materials for lithium ion batteries (LIBs). The electrochemical results with reference to LIBs show that both of our mesoporous Mn2O3 nanomaterials deliver high reversible capacities and excellent cycling stabilities at a current density of 200 mA g−1 compared to the commercial Mn2O3 nanoparticles. Moreover, the straw-sheaf-shaped Mn2O3 exhibits a higher specific capacity and a better cycling performance than the oval-shaped one, due to the relatively higher surface area and the peculiar nanostrip structure resulting in the reduced length for lithium ion diffusion. Morphology-conserved transformation yields two kinds of hierarchical mesoporous Mn2O3 nanomaterials with high capacities and cycling stabilities for lithium ion batteries.

A composite material of uniformly dispersed sulfur on reduced graphene oxide: Aqueous one-pot synthesis, characterization and excellent performance as the cathode in rechargeable lithium-sulfur batteries

AbstractSulfur-reduced graphene oxide composite (SGC) materials with uniformly dispersed sulfur on reduced graphene oxide sheets have been prepared by a simple aqueous one-pot synthesis method, in which the formation of the composite is achieved through the simultaneous oxidation of sulfide and reduction of graphene oxide. The synthesis process has been tracked ex situ by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy, which both confirm that the majority of graphene oxide has been reduced during the synthesis reaction. The sulfur contents in the SGC, determined by thermogravimetry and elementary analysis, have been adjusted in the range from 20.9 to 72.5 wt.%. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images reveal that most of the sulfur is uniformly dispersed on the reduced graphene oxide sheets, for which no sulfur in particulate form could be observed. The SGC materials have been tested as the cathode of rechargeable lithium-sulfur (Li-S) batteries, and demonstrated a high reversible capacity and good cycleability. The SGC-63.6%S can deliver a reversible capacity as high as 804 mA·h/g after 80 cycles of charge/discharge at a current density of 312 mA/g (ca. 0.186 C), and 440 mA·h/g after 500 cycles at 1250 mA/g (ca. 0.75 C).

Nanostructured Black Phosphorus/Ketjenblack–Multiwalled Carbon Nanotubes Composite as High Performance Anode Material for Sodium-Ion Batteries

Sodium-ion batteries are promising alternatives to lithium-ion batteries for large-scale applications. However, the low capacity and poor rate capability of existing anodes for sodium-ion batteries are bottlenecks for future developments. Here, we report a high performance nanostructured anode material for sodium-ion batteries that is fabricated by high energy ball milling to form black phosphorus/Ketjenblack-multiwalled carbon nanotubes (BPC) composite. With this strategy, the BPC composite with a high phosphorus content (70 wt %) could deliver a very high initial Coulombic efficiency (>90%) and high specific capacity with excellent cyclability at high rate of charge/discharge (∼1700 mAh g(-1) after 100 cycles at 1.3 A g(-1) based on the mass of P). In situ electrochemical impedance spectroscopy, synchrotron high energy X-ray diffraction, ex situ small/wide-angle X-ray scattering, high resolution transmission electronic microscopy, and nuclear magnetic resonance were further used to unravel its superior sodium storage performance. The scientific findings gained in this work are expected to serve as a guide for future design on high performance anode material for sodium-ion batteries.

Synthesis of single crystalline hexagonal nanobricks of LiNi1/3Co1/3Mn1/3O2 with high percentage of exposed {010} active facets as high rate performance cathode material for lithium-ion battery

Single crystalline LiNi1/3Co1/3Mn1/3O2 (LNCM) hexagonal nanobricks with a high percentage of exposed {010} facets are synthesized by using Ni1/3Co1/3Mn1/3(OH)2 hexagonal nanosheets as both template and precursor, and exhibit excellent high rate performance as a cathode of lithium ion batteries.

Facile synthesis of hierarchical micro/nanostructured MnO material and its excellent lithium storage property and high performance as anode in a MnO/LiNi0.5Mn1.5O4-δ lithium ion battery

Hierarchical micro/nanostructured MnO material is synthesized from a precursor of MnCO3 with olive shape that is obtained through a facile one-pot hydrothermal procedure. The hierarchical micro/nanostructured MnO is served as anode of lithium ion battery together with a cathode of spinel LiNi0.5Mn1.5O(4-δ) material, which is synthesized also from the precursor of MnCO3 with olive shape through a different calcination process. The structures and compositions of the as-prepared materials are characterized by TGA, XRD, BET, SEM, and TEM. Electrochemical tests of the MnO materials demonstrate that it exhibit excellent lithium storage property. The MnO material in a MnO/Li half cell can deliver a reversible capacity of 782.8 mAh g(-1) after 200 cycles at a rate of 0.13 C, and a stable discharge capacity of 350 mAh g(-1) at a high rate of 2.08 C. Based on the outstanding electrochemical property of the MnO material and the LiNi0.5Mn1.5O(4-δ) as well, the MnO/LiNi0.5Mn1.5O(4-δ) full cell has demonstrated a high discharge specific energy ca. 350 Wh kg(-1) after 30 cycles at 0.1 C with an average high working voltage at 3.5 V and a long cycle stability. It can release a discharge specific energy of 227 Wh kg(-1) after 300 cycles at a higher rate of 0.5 C. Even at a much higher rate of 20 C, the MnO/LiNi0.5Mn1.5O(4-δ) full cell can still deliver a discharge specific energy of 145.5 Wh kg(-1). The excellent lithium storage property of the MnO material and its high performance as anode in the MnO/LiNi0.5Mn1.5O(4-δ) lithium ion battery is mainly attributed to its hierarchical micro/nanostructure, which could buffer the volume change and shorten the diffusion length of Li(+) during the charge/discharge processes.

Porous Graphitic Carbon Loading Ultra High Sulfur as High-Performance Cathode of Rechargeable Lithium-Sulfur Batteries

Porous graphitic carbon of high specific surface area of 1416 m(2) g(-1) and high pore volume of 1.11 cm(3) g(-1) is prepared by using commercial CaCO3 nanoparticles as template and sucrose as carbon source followed by 1200 °C high-temperature calcination. Sulfur/porous graphitic carbon composites with ultra high sulfur loading of 88.9 wt % (88.9%S/PC) and lower sulfur loading of 60.8 wt % (60.8%S/PC) are both synthesized by a simple melt-diffusion strategy, and served as cathode of rechargeable lithium-sulfur batteries. In comparison with the 60.8%S/PC, the 88.9%S/PC exhibits higher overall discharge capacity of 649.4 mAh g(-1)(S-C), higher capacity retention of 84.6% and better coulombic efficiency of 97.4% after 50 cycles at a rate of 0.1C, which benefits from its remarkable specific capacity with such a high sulfur loading. Moreover, by using BP2000 to replace the conventional acetylene black conductive agent, the 88.9% S/PC can further improve its overall discharge capacity and high rate property. At a high rate of 4C, it can still deliver an overall discharge capacity of 387.2 mAh g(-1)(S-C). The porous structure, high specific surface area, high pore volume and high electronic conductivity that is originated from increased graphitization of the porous graphitic carbon can provide stable electronic and ionic transfer channel for sulfur/porous graphitic carbon composite with ultra high sulfur loading, and are ascribed to the excellent electrochemical performance of the 88.9%S/PC.

Low temperature deposition of α-Al2O3 thin films by sputtering using a Cr2O3 template

A description about low temperature deposition of a-Al2O3 thin films by sputtering was presented. Cr2O3 thin layer was used as a template. Nanoindentation was used to study the mechanical propertie ...

Hierarchical WO3 flowers comprising porous single-crystalline nanoplates show enhanced lithium storage and photocatalysis

We report a morphology-conserved transformation approach to successfully synthesize a unique porous WO3 nanoplate assembly, which is hierarchically structured like a flower, from an ammonium tungsten peroxo oxalate containing precursor. The resulting novel, multiple length scale architecture of WO3 and its formation process have been investigated by a series of microscopic, spectroscopic and other techniques. A possible growth mechanism was proposed on the basis of the experiments. When tested as a lithium ion battery anode, the porous WO3 nanoplate assembly showed high rate capacity and high cyclability. Not least, it has also exhibited high photocatalytic activities under visible light irradiation.Graphical abstract

Tuning the structure and property of nanostructured cathode materials of lithium ion and lithium sulfur batteries

A great deal of progresses has been made in the pursuit of high energy and high power battery devices in the past decades on account of the growing demand for clean and sustainable energy. The tremendous challenges in increasing the specific energy and power density of batteries lie mainly in the cathode materials. Lots of attempts have been made to improve the reversible capacity and rate capability of cathode materials for lithium ion batteries in the past few years. On the one hand, the rate capability of the cathode materials depends strongly on their surface structures, which determine the kinetics of lithium ion transportation and intercalation. Through tuning the surface structure of cathode materials, the density of channels for fast Li+ diffusion can be increased, and therefore enhance greatly the surface/interfacial transportation kinetics of lithium ions. On the other hand, the reversible capacity of the cathode materials of lithium ion batteries is in direct proportion to the number of electrons transferred, thus exploration of high capacity cathode materials beyond intercalation, such as sulfur cathodes, has been conducted extensively. The utilization efficiency of sulfur active materials, the reaction kinetics and trapping of soluble polysulfides depend also on the structure of sulfur cathodes. This review outlines recent developments in structure-tuning of the most appealing cathode materials, including layered lithium metal oxides, olivine structured LiFePO4, spinel LiMn2O4 and LiNi0.5Mn1.5O4, as well as sulfur cathodes. The structure-dependent properties of the cathode materials are summarized, mainly focusing on electrochemical performance, which can provide an in-depth understanding and rational design of high performance cathode materials. Further direction and perspectives of research in the present field are also addressed.

Insight into the Capacity Fading Mechanism of Amorphous Se2S5 Confined in Micro/Mesoporous Carbon Matrix in Ether-Based Electrolytes

In contrast to the stable cycle performance of space confined Se-based cathodes for lithium batteries in carbonate-based electrolytes, their common capacity fading in ether-based electrolytes has been paid less attention and not yet well-addressed so far. In this work, the lithiation/delithiation of amorphous Se2S5 confined in micro/mesoporous carbon (Se2S5/MPC) cathode was investigated by in situ X-ray near edge absorption spectroscopy (XANES) and theoretical calculations. The Se2S5/MPC composite was synthesized by a modified vaporization-condensation method to ensure a good encapsulation of Se2S5 into the pores of MPC host. In situ XANES results illustrated that the lithiation/delithiation reversibility of Se component was gradually decreased in ether-based electrolytes, leading to an aggravated formation of long-chain polyselenides during cycling and further capacity decay. Moreover, ab initio calculations revealed that the binding energy of polyselenides (Li2Sen) with carbon host is in an order of Li2Se6 > Li2Se4 > Li2Se. The insights into the failure mechanism of Se-based cathode gain in this work are expected to serve as a guide for future design on high performance Se-based cathodes.