Yuqing Qiao

Synthesis of micro/nano-structured Mn3O4 for supercapacitor electrode with excellent rate performance

Micro/nano-structured Mn3O4 with an open three-dimensional flower-like morphology were fabricated by a facile solvothermal approach using hexadecyltrimethylammonium bromide as a surfactant and CH3CH2OH as a solvent. The Mn3O4 microspheres were self-assembled by one-dimensional nanowires; in addition, a dandelion-structure formation mechanism of the Mn3O4 microspheres is discussed. The Mn3O4 microspheres used as a supercapacitor electrode in 1 mol L−1 Na2SO4 electrolyte have a specific capacitance value of 286 F g−1 at a low current density of 0.5 A g−1, and can still retain 80% (230 F g−1) and 73% specific capacitance (210 F g−1) when the current densities are increased ten-fold (5 A g−1) and twenty-fold (10 A g−1), respectively. In addition, the capacitance retention is 90% after 1000 cycles at a current density of 5 A g−1. In comparison with Mn3O4 synthesized in N,N-dimethylformamide solvent at 0.5 A g−1 and 5 A g−1, the specific capacitance obtained increased by 18.7% and 17.4%, respectively.

One-pot synthesized mesoporous Ni–Co hydroxide for high performance supercapacitors

AbstractMesoporous Ni(OH)2/Co(OH)2 electrode materials were synthesized via a simple one-pot procedure by combining homogeneous precipitation and stepwise precipitation method. The configuration of the porous Ni(OH)2/Co(OH)2 electrode materials synthesized provides 3D electron transmission channels through a high conductive Co(OH)2 distributed in the peripheral nanolayer of the composites, which is beneficial to rate capability and cycle stability. The Ni(OH)2/Co(OH)2 electrode materials have a specific surface area of 229xa0m2xa0g−1, which is approximately 40% higher than that of Ni(OH)2 (163xa0m2xa0g−1). Their specific capacitance is up to 1202 and 1022xa0Fxa0g−1 at the current densities of 10 and 20xa0Axa0g−1, respectively. Furthermore, the capacitance retention of the electrode materials at the current density of 10xa0Axa0g−1 is 98% after 5000xa0cycles. The synthesis method provides a novel simple route to fabricate heterostructure materials for capacitors with high electrochemical performance.n Graphical abstractᅟ

Synthesis of single-crystalline LiFePO4 with rhombus-like morphology

In this investigation, carbon-coated LiFePO4 cathode materials were synthesized with a facile hydrothermal method. The structure and electrochemical properties of the materials were investigated by X-ray diffraction (XRD), Roman, transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS), and electrochemical impedance spectroscopy (EIS). By adjusting the mixing concentration of starting materials, a single-crystalline LiFePO4 with an anisotropic rhombus morphology (Space Group: Pmnb No. 62) were successfully synthesized. In addition, the carbon coated on the surface of LiFePO4 material prepared has a lower ID/IG (0.80), which indicates an optimized carbon structure with an increased amount of sp2-type carbon. Electrochemical performance test shows that the carbon-coated LiFePO4 cathode materials have an initial discharge capacity of 146xa0mAhxa0g−1 at 0.2C.

Study on LiFe1 − xSmxPO4/C used as cathode materials for lithium-ion batteries with low Sm component

LiFe1u2009−u2009xSmxPO4/C cathode materials were synthesized though a facile hydrothermal method. Compared with high-temperature solid-phase sintering, the method can allow for the fabrication of low Sm content (2xa0%), a scarce and expensive rare earth element, while the presence of an optimized carbon coating with large amount of sp2-type carbon sharply increases the material’s electrochemical performance. The high-rate dischargeability at 5xa0C, as well as the exchange current density, can be increased by 21 and 86xa0%, respectively, which were attributed to the fine size and the large cell parameter a/c as much. It should be pointed out that the a/c value will be increased for the LiFePO4 Sm-doped papered by both of the two methods, while the mechanism is different: The value c is increased for the front and the value a is decreased for the latter, respectively.

Investigation on the Structure and Electrochemical Properties of La-Ce-Mg-Al-Ni Hydrogen Storage Alloy

Structure and electrochemical characteristics of La 0.96Ce 0.04Mg 0.15Al 0.05Ni 2.8 hydrogen storage alloy have been investigated. X-ray diffraction analyses reveal that the La 0.96Ce 0.04Mg 0.15Al 0.05Ni 2.8 hydrogen storage alloy consisted of a (La, Mg)Ni 3 phase with the rhombohedral PuNi 3-type structure and a LaNi 5 phase with the hexagonal CaCu 5-type structure. TEM shows that the alloy is multicrystal with a lattice space 0.187u2009nm. EDS analyse shows that the content of Mg is 3.48% (atom) which coincide well with the designed composition of the electrode alloy. Electrochemical investigations show that the maximum discharge capacity of the alloy electrode is 325u2009mAhu2009g −1. The alloy electrode has higher discharge capacity within the discharge current density span from 60u2009mAu2009g −1 to 300u2009mAu2009g −1. Electrochemical impedance spectroscopy measurements indicate that the charge transfer resistance <path id=x1D445 d=M627 18l-10 -26q-79 6 -116 27t-69 76q-41 71 -71 138q-13 29 -27.5 39t-42.5 10h-46l-27 -145q-13 -74 -2.5 -88.5t78.5 -20.5l-6 -28h-271l5 28q66 6 82.5 21.5t30.5 87.5l71 387q12 66 2 78.5t-77 19.5l8 28h233q102 0 147 -29q65 -43 65 -129q0 -69 -45.5 -117nt-115.5 -72q40 -86 66 -133q39 -68 65 -101q28 -37 73 -51zM491 483q0 67 -33.5 101t-91.5 34q-35 0 -51 -10q-13 -8 -20 -48l-45 -245h49q71 0 113 28q79 52 79 140z /> <path id=x54 d=M592 498l-30 -3q-13 63 -31 89q-13 19 -33.5 25.5t-75.5 6.5h-70v-493q0 -60 16 -75.5t86 -19.5v-28h-286v28q68 4 83.5 19.5t15.5 75.5v493h-62q-60 0 -83 -7t-33 -24q-12 -17 -32 -90h-29q10 116 12 180h20q10 -16 21 -20.5t34 -4.5h395q19 0 28.5 5t21.5 20h21nq2 -89 11 -177z /> on the alloy electrode surface and the calculated exchange current density I0 are 0.135u2009Ω and 1298u2009mAu2009g −1, respectively; the better eletrochemical reaction kinetic of the alloy electrode may be responsible for the better high-rate dischargeability.