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Li L.,Nankai University | Peng Y.,Nankai University | Yang H.,Nankai University | Yang H.,Tianjin Key Laboratory of Metal and Molecule Based Material Chemistry
Electrochimica Acta | Year: 2013

Manganese phosphide anode material is successfully prepared by a high-temperature solid-phase synthesis process, and its phase structure changes during cycling are revealed in this work. The results derived from X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) combined with selection area electron diffraction (SAED) show that the prepared MnP powder has a single crystalline structure covered with an amorphous oxide layer. Galvanostatic charge/discharge test results indicate that in the voltage range between 0.01 V and 2.00 V at the current density of 50 mA g-1, the MnP anode delivers an initial lithiation and delithiation capacity of 1104 mAh g-1 and 870 mAh g-1, respectively. After 50 cycles, the retained capacity reaches 287 mAh g-1. XRD results indicate that the single crystalline MnP phase is transformed to an amorphous Li xMnyPz phase during the initial lithiation process. During the following cycles, the content of the MnP phase is gradually reduced, and the content of the amorphous LixMnyP z phase is continuously accumulated. The amorphous Li xMnyPz and Mn2P phases residued in the anode act as the buffer matrix for the MnP active material to suppress the decrease of the lithiation and delithiation capacity during cycling. This amorphous structure is believed to be responsible for the reversible lithiation and delithiation after decade cycles. © 2013 Elsevier Ltd. All rights reserved.

Wu W.,Nankai University | Liang Y.,Nankai University | Ma H.,Nankai University | Peng Y.,Nankai University | And 2 more authors.
Electrochimica Acta | Year: 2016

A SiO/graphite/amorphous carbon (SiO-C) hybrid anode with superior electrochemical performance is successfully realized by using a low-cost and simple method. Here, we apply a pretreatment of commercialized graphite by ball-milling to realize evenly dispersion of the components and good effect of carbon coating, thus resulting in excellent cycling stability. Specifically, the as-prepared sample shows a high reversible capacity of 850 mA h g-1 after 100 cycles at 100 mA g-1 and excellent rate capability of 730 mA h g-1 even at 500 mA h g-1. Additionally, a relatively high initial coulombic efficiency of 77% is delivered among SiO-based anode materials. High-resolution transmission electron microscope (HRTEM) technique is used to further visually verify the conversion behavior of SiO in the first cycle: scattered amorphous silicon particles with size about 5 nm and irreversible Li4SiO4 as the detected resultants. The result of electrochemical impedance spectroscopy (EIS) reveals that the polarization resistance (Rp) decreases with pre-treated graphite. This work presents a facile approach to prepare Si-based anode material for new generation lithium-ion batteries with high energy density and more insights into the conversion behavior of SiO. © 2015 Elsevier Ltd. All rights reserved.

Shi J.,Nankai University | Liang Y.,Nankai University | Li L.,Nankai University | Peng Y.,Nankai University | And 2 more authors.
Electrochimica Acta | Year: 2015

Silicon/lithium titanate (Si/Li2TiO3) nanocomposite is successfully prepared through the combination of a sol-gel approach with a high-temperature treatment as well as a high energy ball milling process. The structure and morphology of the composite are characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) analysis reveals Si particles are coated by the uniform disordered Li2TiO3 layer with a thickness of about 5 nm. The investigation in cycling performances demonstrates that Si/Li2TiO3 exhibits the improved cycling stability, with specific capacity of 471.0 mA h g-1 after 50 cycles and the capacity retention is 31.5%, much higher than pure Si. Compared with pure Si, Si/Li2TiO3 shows better rate-capability, a reversible capacity of 315.2 mA h g-1 at 0.8 A g-1 is maintained. The higher ionic conductivity of Li2TiO3 is responsible for the improved rate performance. In addition, the results derived from XRD, the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) indicate that lithium ions could react reversibly with Si, and electrochemically less active Li2TiO3 turns into the Li-Ti-O ternary phase, which acts as a buffer matrix in the Si/Li2TiO3 composite, thus improving the reversibility of electrode. © 2014 Elsevier Ltd. All rights reserved.

Zhang J.,Nankai University | Liang Y.,Nankai University | Zhou Q.,Nankai University | Peng Y.,Nankai University | And 2 more authors.
Journal of Power Sources | Year: 2015

(Graph Presented). A Si-Co-C composite material has been prepared by a simple high energy mechanical milling process (HEMM). The crystal structures and morphologies of the samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), indicating that silicon and cobalt elements uniformly distribute in graphite sheets. Electrochemical tests show that the initial discharge and charge capacities of the Si20Co10C70 composite are 1283.3 mAh g-1 and 1068.8 mAh g-1, respectively, with an initial coulombic efficiency of 83.3%. It maintains a reversible capacity of 620 mAh g-1 after 25 cycles and remains stable above 610 mAh g-1 after 50 cycles. The results of cyclic voltammetry (CV) prove that cobalt acts as an inactive matrix, and the result of electrochemical impedance spectroscopy (EIS) reveals that the polarization resistance (Rp) decreases after the Co addition. It is believed that uniform dispersed cobalt nanoparticles relieve the destruction of the graphite. Furthermore, the existence of carbon and cobalt not only restrains the agglomeration of Si particles, but also suppresses the volume expansion of Si. This extraordinary microstructure is believed to be responsible for the excellent electrochemical performance. © 2015 Elsevier B.V. All rights reserved.

Wei X.-H.,Nankai University | Yang L.-Y.,Nankai University | Liao S.-Y.,Nankai University | Zhang M.,Nankai University | And 6 more authors.
Dalton Transactions | Year: 2014

A series of metal-organic framework {Ln(BCPBA)(H2O)}n {Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5)}; {[Ln(BCPBA)(H 2O)](H2O)}n {Ln = Pr (6), Gd (7)} have been synthesized through the hydrothermal synthesis method. These compounds possess non-interpenetrating 3D networks with 10.1438 Å × 17.9149 Å rhombic channels along the [001] direction. The results of temperature-dependent magnetic susceptibility measurements indicate that compounds 4 and 7 exhibit LnIII⋯LnIII antiferromagnetic interactions, while compound 5 exhibits LnIII⋯LnIII ferromagnetic interactions. Frequency dependent out-of-phase signals were observed in alternating current (ac) magnetic susceptibility measurements which indicate that they have slow magnetic relaxation characteristics. The luminescent properties of 1, 2, 3, 4, and 5 are also discussed. Due to the good match between the lowest triplet state of the ligand and the resonant energy level of the lanthanide ion, compound 4 has longer fluorescence lifetime (τ1 = 400.0000 ms, τ2 = 1143.469 ms) and higher quantum yield (Φ = 42%) compared with other compounds. © 2014 the Partner Organisations.

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