Xuebu Hu

A ( LiFePO4 – AC ) ∕ Li4Ti5O12 Hybrid Battery Capacitor

In this work, we synthesized a composite cathode material containing LiFePO 4 and activated carbon (AC), which is abbreviated as LAC, by a solid-state reaction, and assembled a hybrid battery-capacitor LAC/Li 4 Ti 5 O 12 . The electrochemical performances of the hybrid battery-capacitor LAC/Li 4 Ti 5 O 12 were characterized by cyclic voltammograms, constant current charge-discharge, rate charge-discharge, and cycle performance testing. The results show the hybrid battery-capacitor LAC/Li 4 Ti 5 O 12 has advantages of the high rate capability of hybrid capacitor AC/Li 4 Ti 5 O 12 and the high capacity of battery LiFePO 4 /Li 4 Ti 5 O 12 . It is also proven that the hybrid battery-capacitor LAC/Li 4 Ti 5 O 12 is an energy storage device where the capacitor and the secondary battery coexist in one cell system.

Kinetic analysis of one-step solid-state reaction for Li4Ti5O12/C.

The kinetics of one-step solid-state reaction of Li(4)Ti(5)O(12)/C in a dynamic nitrogen atmosphere was first studied by means of thermogravimetric-differential thermal analysis technique at five different heating rates. According to the double equal-double steps method, the Li(4)Ti(5)O(12)/C solid-state reaction mechanism could be properly described as the Jander equation, which was a three-dimensional diffusion with spherical symmetry, and the reaction mechanism functions were listed as follows: f(α) = (3)/(2)(1 - α)(2/3)[1 - (1 - α)(1/3)](-1), G(α) = [1 - (1 - α)(1/3)](2). In FWO method, average activation energy, frequency factor, and reaction order were 284.40 kJ mol(-1), 2.51 × 10(18) min(-1), and 1.01, respectively. However, the corresponding values in FRL method were 271.70 kJ mol(-1), 1.00 × 10(17) min(-1), and 0.96, respectively. Moreover, the values of enthalpy of activation, Gibbs free energy of activation, and entropy of activation at the peak temperature were 272.06 kJ mol(-1), 240.16 kJ mol(-1), and 44.24 J mol(-1) K(-1), respectively.

New polytypes of LPSO structures in an Mg–Co–Y alloy

Abstract The magnesium alloys containing long-period stacking ordered (LPSO) structures exhibit excellent mechanical properties. Each LPSO structure is known to contain either AB′C′A or AB′C building block and feature its own stacking sequences. By atomic-scale high-angle annular dark field scanning transmission electron microscopy, we find the co-existence of AB′C′A and AB′C building block in a single LPSO structure of the as-cast Mg92Co2Y6 (at.%) alloy, leading to the formation of six new polytypes of the LPSO structures determined as 29H, 51R, 60H, 72R, 102R and 192R. The lattice parameter of each LPSO structure is derived as and (n presents the number of basal layers in a unit cell). The stacking sequences and the space groups of these newly identified LPSO structures are proposed based on the electron diffraction and atomic-scale aberration-corrected high-resolution images. A random distribution of Co/Y elements in the basal planes of AB′C′A and AB′C structural units is also observed and discussed.

Atomic imaging of the interface between M23C6-type carbide and matrix in a long-term ageing polycrystalline Ni-based superalloy

Besides the well-known cube-on-cube orientation relationship (OR) between M23C6 carbide and matrix, we have determined a new OR named as the twin-related OR in a long-term ageing Ni-based superalloy on the basis of the extensive and detailed electron diffraction analyses. Furthermore, by means of atomic-resolution high angle annular dark-field imaging technique which is implemented in the aberration-corrected scanning transmission electron microscope, we elucidated the interfacial characteristics between M23C6 and matrix for above two types of ORs. Taking into account of the interfacial characteristics, we propose that the twin-related OR possesses a higher total interfacial energy. Thus, its frequency of occurrence is lower than that of the cube-on-cube OR though both ORs are usually seen in the long-term ageing samples.

Promotional role of Li4Ti5O12 on SnO2-based materials electrochemical performances

SnO2-based materials consisting of core-shell structure (SnO2/C)@C microspheres and Li4Ti5O12/C composites were prepared via a hydrothermal method and solid-state reaction. The effects of Li4Ti5O12/C content on the electrochemical performances of SnO2-based materials were systematically studied. The results illustrate that the SnO2-based materials with Li4Ti5O12 show improved cycling performance and rate capability as compared to pure SnO2 and (SnO2/C)@C composites, which is attributed to the multi-functional roles of the electronic conductor carbon and the lithium ionic conductor Li4Ti5O12. Due to the presence of Li4Ti5O12, the significantly increased lithium-ion diffusion coefficient and Warburg impedance of SnO2-based anode materials lead to overall high lithium ionic conductivity. The “combined effect” of the electronic conductor and the lithium ionic conductor is an efficient way for the SnO2 anode to suppress volume expansion and improve electrochemical performances, especially rate capability.

Nano-Sn doped carbon-coated rutile TiO2 spheres as a high capacity anode for Li-ion battery

Nano-Sn doped carbon-coated rutile TiO2 spheres (C-NS/TiO2-1 and C-NS/TiO2-2) as an improved TiO2-based anode for Li-ion batteries were in situ fabricated. The physical characteristics of the C-NS/TiO2 spheres were tested by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Their electrochemical properties were characterized by cyclic voltammograms (CVs), electrochemical impedance spectra (EIS) and galvanostatic charge–discharge cycles. The results indicated that the as-prepared samples had particle sizes ranging from 1 to 5 μm and were composed of several small inner rutile TiO2 spheres, an outer mesoporous carbon coating layer and nano-Sn inhabited in the outer carbon layer. Their electronic conductivity was significantly enhanced owing to high electronic conductivity of the carbon layer and nano-Sn. Moreover, their reversibility capacity was also significantly improved due to the high specific capacity of nano-Sn. The C-NS/TiO2-1 and C-NS/TiO2-2 delivered a reversible capacity of 143.1 and 219.0 mA h g−1, respectively, after 200 cycles at a high current density of 500 mA g−1, which was increased by 52.0% and 132.6% compared to carbon-coated rutile TiO2 (C-TiO2).

A High Rate, High Capacity and Long Life (LiFePO4+AC)/Li4Ti5O12 Hybrid Battery-Supercapacitor

A hybrid battery-supercapacitor (LiFePO4+AC)/Li4Ti5O12 using a Li4Ti5O12 anode and a LiFePO4/activated carbon (AC) composite cathode was built. The electrochemical performances of the hybrid battery-supercapacitor (LiFePO4+AC)/Li4Ti5O12 were characterized by constant current charge-discharge, rate charge-discharge, electrochemical impedance spectra, internal resistance, leakage current, self-discharge and cycle performance testing. The results show that (LiFePO4+AC)/Li4Ti5O12 hybrid battery-supercapacitors have rapid charge-discharge performance, high energy density, long cycle life, low resistance, low leakage current and self-discharge rate, which meet the requirements of practical power supply and can be applied in auxiliary power supplies for hybrid electric vehicles. At 4C rate, the capacity loss of (LiFePO4+AC)/Li4Ti5O12 hybrid battery-supercapacitors in constant current mode is no more than 7.71% after 2000 cycles, and the capacity loss in constant current-constant voltage mode is no more than 4.51% after 1500 cycles.