Nanda Gunawardhana

Synthesis, characterization and application for lithium-ion rechargeable batteries of hollow silica nanospheres

Hollow silica nanospheres with uniform size of about 30 nm have been successfully synthesized using a template of ABC triblock copolymer micelles of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS–PVP–PEO) with a core–shell–corona architecture. In this type of triblock copolymers, the PS block (core) works as a template of the void space of hollow silica, the PVP block (shell) acts as a reaction field for the sol–gel reaction of tetramethoxysilane (TMOS), and the PEO block (corona) stabilizes the polymer/silica composite particles. Use of polymers with different chain lengths of PS, PVP, and PEO led to hollow silica with tunable cavity size and wall thickness. The obtained hollow particles were thoroughly characterized by X-ray diffraction (XRD), thermal (TG/DTA) and nitrogen sorption analyses, infra-red (FT IR) and nuclear magnetic resonance (29Si MAS NMR) spectroscopies, and transmission electron microscopy (TEM). The efficiency of hollow silica nanospheres for lithium-ion rechargeable batteries is demonstrated for the first time. The hollow silica nanoparticles exhibited high cycle performance of up to 500 cycles in the lithium rechargeable batteries through the alloying/dealloying process. The tiny grain size of hollow nanospheres results in less volume expansion and/or contraction during charge/discharge cycles.

Micelle templated NiO hollow nanospheres as anode materials in lithium ion batteries

Nano-sized nickel oxide (NiO) hollow spheres of size 28 ± 2 nm have been synthesized by a soft-template self-assembly process. ABC triblock copolymeric micelles of poly(styrene-b-acrylic acid-b-ethylene oxide) (PS–PAA–PEO) with core–shell–corona architecture serve as an efficient colloidal-template for fabrication of NiO hollow nanospheres. In the above polymeric template, the PS block (core) acts as a template of hollow void space, the PAA block (shell) with negative charges serves as the reaction site for metal ion interactions, and the corona domain stabilizes organic/inorganic composite particles. The PS–PAA–PEO template micelles as well as the NiO hollow nanospheres were thoroughly characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermal analysis (TG/DTA), FTIR spectroscopy, and nitrogen adsorption/desorption analyses. The XRD and TEM techniques confirmed the hollow spherical morphology and phase purity of nickel oxide nanoparticles. The NiO hollow nanospheres were further investigated as anode materials for lithium ion rechargeable batteries for the first time. The nanostructured electrode delivers a high capacity of 393 mA h g−1 after 50 cycles of charge–discharge at a rate of 0.3 C. More importantly, the hollow spherical electrode maintains the structural integrity and excellent cycling stability even after subjecting to a high rate of 10 C (high current density). The high electrochemical performance is attributed to hollow void space coupled with a nanosized NiO shell domain that facilitates fast lithium diffusion kinetics.

Novel LaBO3 hollow nanospheres of size 34±2 nm templated by polymeric micelles.

Novel lanthanum borate (LaBO(3)) hollow nanospheres of size 34±2 nm have been reported for the first time by soft-template self-assembly process. Poly(styrene-b-acrylic acid-b-ethylene oxide) (PS-PAA-PEO) micelle with core-shell-corona architecture serves as an efficient soft template for fabrication of LaBO(3) hollow particles using sodium borohydride (NaBH(4)) and LaCl(3)⋅7H(2)O as the precursors. In this template, the PS block (core) acts as a template of the void space of hollow particle, the anionic PAA block (shell) serves as reaction field for metal ion interactions, and the PEO block (corona) stabilizes the polymer/lanthana composite particles. The PS-PAA-PEO micelles and the resulting LaBO(3) hollow nanospheres were thoroughly characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), X-ray diffraction, magic angle spinning-nuclear magnetic resonance ((11)B MAS NMR), energy dispersive X-ray analysis, thermal analyses, Fourier transform infra red spectroscopy, and nitrogen adsorption/desorption analyses. The nitrogen adsorption/desorption analyses and TEM observation of the hollow particles confirmed the presence of disordered mesopores in the LaBO(3) shell domain. The solid state (11)B MAS NMR spectra of LaBO(3) hollow nanospheres revealed that the shell part contains both trigonal and tetrahedral boron species. The LaBO(3) hollow particles were applied to anode materials in lithium-ion rechargeable batteries (LIBs). The hollow particles exhibited high coulombic efficiency and charge-discharge cycling capacities of up to 100 cycles in the LIBs.