Porous SnO2 nanostructure with a high specific surface area for improved electrochemical performance.

Tin oxide (SnO2) has been attractive as an alternative to carbon-based anode materials because of its fairly high theoretical capacity during cycling. However, SnO2 has critical drawbacks, such as poor cycle stability caused by a large volumetric variation during the alloying/de-alloying reaction and low capacity at a high current density due to its low electrical conductivity. In this study, we synthesized a porous SnO2 nanostructure (n-SnO2) that has a high specific surface area as an anode active material using the Adams fusion method. From the Brunauer-Emmett-Teller analysis and transmission electron microscopy, the as-prepared SnO2 sample was found to have a mesoporous structure with a fairly high surface area of 122 m2 g-1 consisting of highly-crystalline nanoparticles with an average particle size of 5.5 nm. Compared to a commercial SnO2, n-SnO2 showed significantly improved electrochemical performance because of its increased specific surface area and short Li+ ion pathway. Furthermore, during 50 cycles at a high current density of 800 mA g-1, n-SnO2 exhibited a high initial capacity of 1024 mA h g-1 and enhanced retention of 53.6% compared to c-SnO2 (496 mA h g-1 and 23.5%).

Enhanced electrochemical performance of MoS2/graphene nanosheet nanocomposites.

Molybdenum disulfide (MoS2) is attractive as an anode material for next-generation batteries, because of its layered structure being favorable for the insertion/deinsertion of Li+ ions, and its fairly high theoretical capacity. However, since the MoS2 anode material has exhibited disadvantages, such as low electrical conductivity and poor cycling stability, to improve the electrochemical performance of MoS2 in this study, a nanocomposite structure consisting of MoS2 and GNS (MoS2/GNS) as an anode for LIBs was prepared, by controlling the weight ratios of MoS2/GNS. The X-ray diffraction patterns and electron microscopic analysis showed that the nanocomposite electrode structure consisted of well-formed MoS2 nanoparticles and GNS. Compared to MoS2-only, the MoS2/GNS composites exhibited high retention and improved capacity at high current densities. In particular, among these nanocomposite samples, MoS2/GNS(8 : 2) with an appropriate portion of GNS exhibited the best LIB performance, due to the lowest interfacial resistance and highest Li-ion diffusivity.

Facile one-pot synthesis of Ge/TiO2 nanocomposite structures with improved electrochemical performance.

Germanium (Ge) as an alternative to graphite exhibits a fairly high theoretical energy density and improved Li+ ion diffusivity. However, the seriously deteriorated electrochemical performance of Ge during cycling and the difficulty in the preparation of Ge-based nanostructures can hinder the utilization of Ge as an anode. Thus, in this study, a nanocomposite structure with Ge and TiO2 (Ge/TiO2) was synthesized using a facile one-pot method with different ratios of a Ge source with a dominant GeO2 phase and titanium isopropoxide. From X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy, the Ge/TiO2 nanocomposites were found to be spherical structures homogeneously consisting of the reduced Ge as an active material and amorphous TiO2 as a matrix. In particular, the Ge/TiO2 nanocomposite with an appropriate amount of TiO2 exhibited improved electrochemical properties, i.e., a coulombic efficiency of 97% and a retention of 61% for 100 cycles, compared to commercial Ge (a coulombic efficiency of 82% and a retention of 16%). This demonstrates that the amorphous TiO2 matrix could relieve a volumetric expansion of the Ge active material in the nanocomposite electrode generated during the cycling process.