Pinjie Zhang

Micro/nano-complex-structure SiOx–PANI–Ag composites with homogeneously-embedded Si nanocrystals and nanopores as high-performance anodes for lithium ion batteries

The extremely large volume variation and poor electronic conductivity of Si anode materials for lithium ion batteries have seriously hampered their performances and practical applications. SiOx materials are regarded as ideal alternatives to high-capacity Si anode materials for Li-ion batteries, since the generated Li2O matrix from Li–SiOx reactions can effectively accommodate the large volume swing of Si. Furthermore, micron-sized particles with much smaller surface area always present higher initial coulombic efficiency and tap density than nanomaterials. Based on the above considerations, SiOx microparticles with homogeneously-embedded Si nanocrystals and nanopores were fabricated by magnesiothermic reduction in this work and were further modified by high-electronic-conductivity and flexible polyaniline (PANI)–Ag shell. Profiting from these favorable features, the obtained SiOx–PANI–Ag micron-composites exhibited better cycling performances (with a reversible capacity of 1149 mA h g−1 after 100 cycles), good initial coulombic efficiency and tap density in comparison with SiOx-based materials in other works. This study promotes us to exploit advanced Si- or Sn-based materials for Li ion batteries and preparing micro/nano complex structures for promising applications.

Surface coating of LiMn 2 O 4 spinel via in situ hydrolysis route: effect of the solution

Thin SiO2 shell consisting of nano-SiO2 particles can be deposited on to LiMn2O4 through the facile hydrolysis of tetraethoxysilane (TEOS) as a solution in either methanol or ethanol. The structure and surface morphologies of the modified and pristine materials were characterized by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The choice of solvent (methanol vs. ethanol) for TEOS hydrolysis has a profound effect on the physical and electrochemical properties of the resultant SiO2-coated LiMn2O4. Coated LiMn2O4 demonstrated an improved cycling ability compared to the uncoated counterpart. Moreover, samples coated using a TEOS–methanol solution showed better cycling ability in extended potential windows and at an elevated temperature than that coated using ethanol.

Uniform core–shell Cu6Sn5@C nanospheres with controllable synthesis and excellent lithium storage performances

Metallic tin (Sn) is one of the most promising alternatives to graphite anodes for lithium ion batteries due to its higher theoretical capacity, higher packing density and safer thermodynamic potential, while the huge volume transformation during repeated cycling leads to rapid pulverization and consequently poor capacity retention. This work provides an easy-to-control method to prepare uniform core–shell Cu6Sn5@C nanospheres in which Cu@Sn cores (40–50 nm in diameter) are well encapsulated by PANI-derived carbon layers with a thickness of ∼5 nm. The obtained Cu6Sn5@C exhibits an excellent cycling ability and good rate capabilities. Both the reversible capacity (518 mA h g−1) after 100 cycles and the initial coulombic efficiency (89.2%) are the highest values in Cu6Sn5-based materials. The impressive cycling performance is believed to result from the carbon coating that not only prevents particle agglomeration during the synthesis but also accommodates the vast structural transformation of the Cu6Sn5 nanocores during the electrochemical (de)lithiation process, so ensuring good ionic and electronic transport to the core. The effect of synthesis conditions on the composition are also investigated systematically.