Hailong Qiu

Synergetic Effects of Al3+ Doping and Graphene Modification on the Electrochemical Performance of V2O5 Cathode Materials

A series of V2O5-based cathode materials that include V2O5 and Al0.14 V2O5 nanoparticles, V2O5/reduced graphene oxide (RGO), and Al0.16 V2O5/RGO nanocomposites are prepared by a simple soft chemical method. XRD and Raman scattering show that the Al ions reside in the interlayer space of the materials. These doping ions strengthen the V−O bonds of the [VO5] unit and enhance the linkage of the [VO5] layers, which thus increases the structural stability of V2O5. SEM and TEM images show that the V2O5 nanoparticles construct a hybrid structure with RGO that enables fast electron transport in the electrode matrix. The electrochemical properties of the materials are studied by charge-discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Of all the materials tested, the one that contained both Al ions and RGO (Al0.16 V2O5/RGO) exhibited the highest discharge capacity, the best rate capability, and excellent capacity retention. The superior electrochemical performance is attributed to the synergetic effects of Al(3+) doping and RGO modification, which not only increase the structural stability of the V2O5 lattice but also improve the electrochemical kinetics of the material.

Improved Lithium-Ion and Sodium-Ion Storage Properties from Few-Layered WS2 Nanosheets Embedded in a Mesoporous CMK-3 Matrix

An integrated WS2 @CMK-3 nanocomposite has been prepared by a one-step hydrothermal method and then used as the anode material for lithium-ion and sodium-ion batteries. Ultrathin WS2 nanosheets have been successfully embedded into the ordered mesoporous carbon (CMK-3) framework. Owing to the few-layered nanostructure of WS2 , as well as the high electronic conductivity and the volume confinement effect of CMK-3, the material shows larger discharge capacity, better rate capability, and improved cycle stability than pristine WS2 . When tested in lithium-ion batteries, the material delivers a reversible capacity of 720 mA h g-1 after 100 cycles at a current density of 100 mA g-1 . A large discharge capacity of 307 mA h g-1 is obtained at a current density of 2 A g-1 . When used in sodium-ion batteries, the material exhibits a capacity of 333 mA h g-1 at 100 mA g-1 without capacity fading after 70 cycles. A discharge capacity of 230 mA h g-1 is obtained at 2 A g-1 . This excellent performance demonstrates that the WS2 @CMK-3 nanocomposite has great potential as a high-performance anode material for next-generation rechargeable batteries.

In situ growth of MnO2 nanosheets on activated carbon fibers: a low-cost electrode for high performance supercapacitors

MnO2 nanosheets were successfully grown in situ on the surface of activated carbon fibers (ACFs) via a facile microwave-assisted hydrothermal method. This environmentally-friendly approach displays the advantages of low temperature, short reaction time and low cost. A series of MnO2/ACFs composites with different MnO2 percentages were prepared and their electrochemical performance as an electrode for supercapacitors was investigated. The 63% MnO2 composite showed the optimal charge storage performance, remarkable rate ability, and excellent cycling capability. The enhanced electrochemical performance is attributed to the combination of good electrical conductivity of ACFs and high capacity of MnO2. This work provides a useful insight into the design and fabrication of hierarchical transition metal oxide and carbon material composite electrodes for potential applications in next generation energy storage systems.

Improved Cycle Stability and Rate Capability of Graphene Oxide Wrapped Tavorite LiFeSO4F as Cathode Material for Lithium-Ion Batteries

Tavorite LiFeSO4F has been regarded as a promising alternative to LiFePO4 due to its high Li ionic conductivity. To overcome the low electronic conductivity of LiFeSO4F, we prepared a graphene oxide (GO)/LiFeSO4F composite material by the solvothermal method. The GO wraps on the surface of LiFeSO4F and links the adjacent particles, thus providing an effective network for electrons transport. As a result, the electronic conductivity of the material is improved from 8.16 × 10(-11) S cm(-1) to 1.65 × 10(-4) S cm(-1). In addition, the GO depresses the side reactions of the electrode and electrolyte, promotes the charge transfer reactions at the electrode/electrolyte interface, and facilitates the lithium diffusion in the electrode. The GO-wrapped LiFeSO4F exhibits much better electrochemical performance than the pristine material. It showed a discharge capacity of 113.2 mAh g(-1) at the 0.1 C rate with 99% capacity retention after 100 cycles. In addition, the material is able to deliver 85.1, 73.4, and 30.3 mAh g(-1) at high current rates of 1 C, 2 C, and 10 C, respectively.

Copper-Doped Titanium Dioxide Bronze Nanowires with Superior High Rate Capability for Lithium Ion Batteries

Pristine and Cu-doped TiO2-B nanowires are synthesized by the microwave assisted hydrothermal method. The doped oxide exhibits a highly porous structure with a specific surface area of 160.7 m(2) g(-1). As evidenced by X-ray photoelectron spectroscopy and X-ray energy dispersive spectroscopy, around 2.0 atom % Cu(2+) cations are introduced into TiO2-B, which leads to not only a slightly expanded lattice network but also, more importantly, a modified electronic structure. The band gap of TiO2-B is reduced from 2.94 to 2.55 eV, resulting in enhanced electronic conductivity. Cyclic voltammetry and electrochemical impedance spectroscopy reveal improved electrochemical kinetic properties of TiO2-B due to the Cu doping. The doped nanowires show a specific capacity of 186.8 mAh g(-1) at the 10 C rate with a capacity retention of 64.3% after 2000 cycles. Remarkably, our material exhibits a specific capacity of 150 mAh g(-1) at the 60 C rate, substantiating its superior high rate capability for rechargeable lithium batteries.

Synthesis of graphene-wrapped ZnMn2O4 hollow microspheres as high performance anode materials for lithium ion batteries

Hollow microspheres of ZnMn2O4 wrapped by graphene have been successfully synthesized via a facile APS aided method. Characterization results certify that the reduced graphene sheets have been wrapped around the hollow ZnMn2O4 microspheres. Charge–discharge testing reveals that ZnMn2O4/RGO delivers superior electrochemical properties in terms of specific capacity, cycle stability (1082 mA h g−1 at 100 mA g−1 after 90 cycles) and high rate capability (580 mA h g−1 at 1 A g−1 after 150 cycles). The improved rate capability and cycling performance of the modified ZnMn2O4 microspheres are attributed to the incorporated RGO sheets’ perfect synergy collaborating with the hollow structures, which can provide higher electronic conductivity, a shorter Li+ diffusion path and also buffer the volume change during Li+ insertion and extraction.

Improved electrochemical properties of tavorite LiFeSO4F by surface coating with hydrophilic poly-dopamine via a self-polymerization process

Poly-dopamine coated Li1−xFeSO4F is prepared via a self-polymerization process. The material shows larger discharge capacities, better rate capability and longer cycle stability than the pristine LiFeSO4F. The improved electrochemical properties are attributed to the highly hydrophilic and elastic properties of poly-dopamine.

Self-Assembly of Antisite Defectless nano-LiFePO4@C/Reduced Graphene Oxide Microspheres for High-Performance Lithium-Ion Batteries

LiFePO4@C/rGO hierarchical microspheres with superior electrochemical activity and high tap density were first synthesized using a Fe-based single inorganic precursor (LiFePO4OH@RF/GO) obtained from a template-free self-assembly synthesis, following with direct calcination. The synthesis process requires no physical mixing step. The phase transformation path way from tavorite LiFePO4OH to olivine LiFePO4 upon calcination was determined by the in situ high temperature XRD technique. Benefitted from the unique structure of the material, these microspheres can be densely packed together, giving a high tap density of 1.3 g cm, and simultaneously, the defectless LiFePO4 primary nanocrystals modified with highly conductive surface carbon layer and ultrathin rGO provide good electronic and ionic kinetics for fast electron/Li ion transport. Lithium-ion batteries (LIBs), as one important technology for electric energy storage, have revolutionarily extend the battery life of portable electronic devices (e.g. smart phones, wearable devices, and laptop computers), and now stand as a promising candidate for high-power and long-life battery applications, typically for the electric transportation off the grid and the clean energy back-up and storage systems. [1-3] To date, olivine (e.g. LiFePO4), layer-type (e.g. LiNi1-x-yMnxCoyO2), and spinel (e.g. LiMn2O4) electrode materials are the three mostly used cathodes for high power LIBs. [1, 2, 4] Among them, LiFePO4 is more stable in thermodynamics and reaction kinetics than the other two owing to the presence of a robust polyanionic framework. [5-7] Moreover, LiFePO4 prevails in terms of natural abundance, cost, and environmental friendliness. The major issue to this material is the negative transport kinetics in both Li ion diffusion and electron delivery. Size tailoring, in conjunction with surface carbon (i.e. graphitic carbon, graphene, et al.) coatings to form LiFePO4/C nanocomposite is acknowledged as a technology of choice to alleviate this issue effectively. [6-9] However, when the particle size of LiFePO4/C is decreased down to nanoscale, thermodynamic instability and high risk of side reactions with the organic electrolyte become into new hazards needed to be faced with. [10] In addition, the processability and tap density (less than 1.0 g cm ) of the powders also require improvements when it comes to a practical point of view. [11] For that, small LiFePO4/C nanoparticles assembled into hierarchical architectures, ideally with a microsphere morphology, would naturally become more easily free-flowing and can be densely packed together, giving a higher tap density and hence a higher volumetric energy density. [12-14] Hydrothermal and solvothermal synthesis technologies or a combination of them are the methods commonly used to create LiFePO4/C microsphere with hierarchical architectures, the vast majority of which, however, required the use of instable and costly ferrous iron (Fe) salts as the raw material, and simultaneously a reducing agent and/or inert gas to avoid the oxidation of Fe ions during reactions. [13, 15] On top of that, most attempts to develop new routes, especially through ferric iron (Fe) based approaches, focused either on the “one-pot synthesis” or “in-situ carbon coating”, rather than considering both two concepts together. [12-14] Thus exploring a simpler synthesis scheme to produce LiFePO4/C microspheres with ideal structural features will be of great interest. In this communication, reduced GO-modified LiFePO4/C (i.e. LiFePO4@C/rGO) hierarchical microspheres were synthesized for the first time by a one-pot mixed-solvothermal process to form a ferric three-component precursor of LiFePO4OH@RF/GO, followed by direct calcination at high temperature, during which tedious physical mixing and grinding step can be totally avoided. The final LiFePO4@C/rGO microspheres created can be densely packed together, giving a high tap density of 1.3 g cm, and simultaneously, the small primary LiFePO4 nanoparticles (65 nm), in conjunction with the integrated carbonous conductive network can provide an adequate electrochemically available surface for enhancing the high-rate capability. The phase transformation mechanism from tavorite LiFePO4OH to the olivine LiFePO4 upon calcination was also determined by the in situ high temperature X-ray diffraction (XRD). [a] Dr. H. Wang, Dr. L. Liu, Prof. R. Wang, Dr. S. Jiang, L. Ni, H. Tang, Prof. Z. Zhang, Prof. S. Qiu State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, International Joint Research Laboratory of Nano-Micro Architecture Chemistry Jilin University Changchun 130012, P. R. China E-mail: zzhang@jlu.edu.cn [b] Dr. H. Wang, Dr. Z. Wang, J. Hu, Dr. H. Chen, Prof. F. Pan School of Advanced Materials Peking University Shenzhen Graduate School Shenzhen 518055, P. R. China E-mail: panfeng@pkusz.edu.cn [c] Dr. H. Qiu, Prof. Y. Wei, Prof. Z. Zhang Key Laboratory of Physics and Technology for Advanced Batteries (Ministry of Education) Jilin University Changchun 130012, P. R. China [d] Dr. X. Yan School of Chemistry and Materials Science Jiangsu Normal University Xuzhou 221116, P. R. China Supporting information for this article is given via a link at the end of the document. 10.1002/cssc.201800786 A cc ep te d M an us cr ip t ChemSusChem This article is protected by copyright. All rights reserved.LiFePO4 @C/reduced graphene oxide (rGO) hierarchical microspheres with superior electrochemical activity and a high tap density were first synthesized by using a Fe3+ -based single inorganic precursor (LiFePO4 OH@RF/GO; RF=resorcinol-formaldehyde, GO=graphene oxide) obtained from a template-free self-assembly synthesis followed by direct calcination. The synthetic process requires no physical mixing step. The phase transformation pathway from tavorite LiFePO4 OH to olivine LiFePO4 upon calcination was determined by means of the in situ high-temperature XRD technique. Benefitting from the unique structure of the material, these microspheres can be densely packed together, giving a high tap density of 1.3 g cm-3 , and simultaneously, defectless LiFePO4 primary nanocrystals modified with a highly conductive surface carbon layer and ultrathin rGO provide good electronic and ionic kinetics for fast electron/Li+ ion transport.