Practical Implementation of Magnetite-Based Conversion-Type Negative Electrodes via Electrochemical Prelithiation.

We report the performance of a conversion-type magnetite-decorated partially reduced graphene oxide (Fe3O4@PrGO) negative electrode material in full-cell configuration with LiNi0.8Co0.15Al0.05O2 (NCA) positive electrodes. To enable practical implementation of the conversion-type negative electrodes in full cells, the beneficial impact of electrochemical prelithiation on mitigating active lithium losses and improving cycle life is shown here for the first time in the literature. The initial Coulombic efficiency (ICE) of the full cells is improved from 70.8 to 91.2% by prelithiation of the negative electrode to 35% of its specific delithiation capacity. The prelithiation is shown to improve the surface passivation of the Fe3O4@PrGO electrodes, leading to less electrolyte reduction on their surface which is prominent from the significantly lowered accumulated Coulombic inefficiency values, lower polarization growth, and doubled capacity retention by the 100th cycle. The reduced surface reactions of the negative electrode by prelithiation also aids in reducing the extent of aging of the NCA positive electrode. Overall, the prelithiation leads to a longer cycle life, where a retained capacity of 60.4% was achieved for the prelithiated cells by the end of long-term cycling, which is 3 times higher than the capacity retention of the non-prelithiated cells. Results reported herein indicate for the first time that the electrochemical prelithiation of the Fe3O4@PrGO electrode is a promising approach for making conversion negative electrode materials more applicable in lithium-ion batteries.

A Continuous-flow Photocatalytic Reactor for the Precisely Controlled Deposition of Metallic Nanoparticles.

In this work, a novel photocatalytic reactor for the pulsed and controlled excitation of the photocatalyst and the precise deposition of metallic nanoparticles is developed. Guidelines for the replication of the reactor and its operation are provided in detail. Three different composite systems (Pt/graphene, Pt/TiO2, and Au/TiO2) with monodisperse and uniformly distributed particles are produced by this reactor, and the photodeposition mechanism, as well as the synthesis optimization strategy, are discussed. The synthesis methods and their technical aspects are described comprehensively. The role of the ultraviolet (UV) dose (in each excitation pulse) on the photodeposition process is investigated and the optimum values for each composite system are provided.

Homogeneous growth of TiO2-based nanotubes on nitrogen-doped reduced graphene oxide and its enhanced performance as a Li-ion battery anode.

The pursuit of a promising replacement candidate for graphite as a Li-ion battery anode, which can satisfy both engineering criteria and market needs has been the target of researchers for more than two decades. In this work, we have investigated the synergistic effect of nitrogen-doped reduced graphene oxide (NrGO) and nanotubular TiO2 to achieve high rate capabilities with high discharge capacities through a simple, one-step and scalable method. First, nanotubes of hydrogen titanate were hydrothermally grown on the surface of NrGO sheets, and then converted to a mixed phase of TiO2-B and anatase (TB) by thermal annealing. Specific surface area, thermal gravimetric, structural and morphological characterizations were performed on the synthesized product. Electrochemical properties were investigated by cyclic voltammetry and cyclic charge/discharge tests. The prepared anode showed high discharge capacity of 150 mAh g-1 at 1 C current rate after 50 cycles. The promising capacity of synthesized NrGO-TB was attributed to the unique and novel microstructure of NrGO-TB in which long nanotubes of TiO2 have been grown on the surface of NrGO sheets. Such architecture synergistically reduces the solid-state diffusion distance of Li+ and increases the electronic conductivity of the anode.

The effect of pH on the interlayer distances of elongated titanate nanotubes and their use as a Li-ion battery anode.

Titanate nanotubes are promising materials for Li-ion battery anodes because of their special morphology and high specific surface areas. These titanates provide high rate capability and low volume expansion upon lithiation. More importantly, their tubular structure helps the transport of ions through the crystal. In this study, we synthesized elongated titanate nanotubes and modified their interlayer distances by changing the pH (2-13). For the structural characterization XRD, BET, SEM and TEM techniques were used. In addition, the effect of interlayer distance on energy capacity and rate capability was investigated. The highest interlayer distance was obtained at pH 10 and with decreasing pH, the interlayer distance dropped until reaching a pH value of 4. Conversely, the specific surface area reached its maximum value of 204 m(2) g(-1) at a pH of 4. Different from anatase (TiO2), titanate nanotubes had broad peaks in cyclic voltammograms suggesting a pseudocapacitive behavior. The sloping profiles of potential-capacity results also supported the pseudocapacitive property. For the titanate nanotubes obtained at pH 10, an initial discharge capacity of 980 mAh g(-1) was achieved. More importantly, titanate nanotubes showed exceptional rate capabilities and the capacities stayed almost constant at high current rates because of their elongated structure. It was found that the interlayer distance and the elongated structure play an important role in the electrochemical performance of the material.