Hongzhi Cui

Conversion reaction mechanisms of cubic bismuth phosphate Bi13.1POδ as cathode in lithium-ion batteries

AbstractnCompounds containing bismuth ions (Bi3+) as cathodes used in lithium-ion batteries based on chemical conversion reaction were supposed to be the most promising cathodes. They were considered to break through the storage capacity because a Bi atom could react with three Li+ ions and simultaneously transfer three electrons at a time during conversion reaction. In the paper, the cubic phase bismuth phosphate Bi13.1POδ as cathode used in lithium-ion batteries was proposed. The results showed that the crystalline Bi13.1POδ with sizes of 2–5xa0μm synthesized via hydrothermal method possessed excellent capacities and poor cycling stability. The initial discharge and charge capacities reached to 706 and 419 mAhxa0g−1 at current density of 39.06xa0mAxa0g−1. To improve the cycling stability of the cathode material, the chemical conversion process was focused on investigation. The elemental analyses indicated that the ratio of Bi:P ratio was decreased from 12.98 to 4.00, which suggests that about 8 Bi atoms participated in the reaction. Therefore, the capacitiesn of the material were very high. The reduced Bi transformed from the beginning isolated state to ribbon or plate one, and coated on the surface of the active materials, inhibiting further conversion reaction. Consequently, the cycling stability of the cathode material was less than the capacity performance.

Phase structure and electrochemical performance control of 0.5Li2MnO3 0.5LiNi1/3Co1/3Mn1/3O2 based on the concentration adjustment in a molten salt synthesis system

The lithium-rich layered 0.5Li2MnO3⋅0.5LiNi1/3Co1/3Mn1/3O2 material was simply prepared by the molten-salt method. Effect of reactant concentration on phase and electrochemical performance was systemically studied by the X-ray diffraction, the galvanostatical charge/discharge and the dQ/dV profile, respectively. It can be confirmed that the obtained phase is sensitive to the reactant concentration. The spinel structure LiMn2O4 or Li4Mn5O12 phase easily occurs, when reactant concentration is low during the molten salt synthesis of Lithium-rich cathode material. The 0.5Li2MnO3–0.5LiNi1/3Co1/3Mn1/3O2 material with partial Li4Mn5O12 phase shows the higher specific capacity, and delivers a initial discharge capacity of 191xa0mAh g−u20091 under a 20xa0mA g−u20091 current rate, and then increases to the maximum value of 250xa0mAhg−u20091. The discharge plateau of 2.5xa0V and the redox peaks at 2.55, 4.6xa0V give the electrochemical evidence of the existing Li4Mn5O12 phase, which also results in the higher specific capacity. Formation of partial Li4Mn5O12 phase reduces the initial discharge voltage, but mitigates the decay rate of voltage at the higher discharge current rate.Graphical Abstract

A simple synthesis and characterization of PbTe nano-particles

PbTe nanopowders with different morphology were prepared by a simple chemical synthesis. Similar cubic nanoparticles have been successfully synthesized by using Pb(NO3)2 and Na2TeO3 as the precursors, and NaBH4 as the reductant. The single PbTe phase is confirmed from XRD pattern, and obvious width of XRD peaks occur. The size of powders is distributed from 20nm to 70nm in a typical process according to observation from SEM and TEM images. Based on HRTEM observation, PbTe nanopowders with an amorphous layer show polyhedron feature. In different crystallization stages, there is different morphology due to competition between surface energy and crystal face energy. The globular, polyhedron and cubic particles belongs to different growth stages, respectively. Possible growth mechanisms of PbTe were also discussed.

Enhanced thermoelectric properties of Co1-x-yNix＋ySb3-xSnx materials

Co1−x−yNix+ySb3−xSnx polycrystals were fabricated by vacuum melting combined with hot-press sintering. The effect of alloying on the thermoelectric properties of unfilled skutterudite Co1−xNixSb3−xSnx was investigated. A leap of electrical conductivity from the Co0.93Ni0.07Sb2.93Sn0.07 sample to the Co0.88Ni0.12Sb2.88Sn0.12 sample occurs during the measurement of electrical conductivity, indicating the adjustment of band structure by proper alloying. The results show that alloying enhances the power factor of the materials. On the basis of alloying, the thermoelectric properties of Co0.88Ni0.12Sb2.88Sn0.12 are improved by Ni-doping. The thermal conductivities of Ni-doping samples have no reduction, but their power factors have obvious enhancement. The power factor of Co0.81Ni0.19Sb2.88Sn0.12 reaches 3.0 mW·m−1·K−2 by Ni doping. The dimensionless thermoelectric figure of merit reaches 0.55 at 773 K for the unfilled Co0.81Ni0.19 Sb2.88Sn0.12.