Polymer-templated functional organic-inorganic nanocomposites for lithium ion batteries, capacitors and ferroelectric devices

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Jiang, Beibei
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Functional hybrid organic-inorganic nanocomposites, formed by integrating two or more materials at the nanoscale with complementary properties, offer the potential to achieve performance, functionality and architecture far beyond those of each constituent. Despite this, we lack a versatile approach to design hybrid nanocomposites with desired functions and properties while having a good control over the size, shape, and architecture of the resulting nanocomposites. In this thesis, we developed a versatile and robust polymer-templated approach for synthesizing organic-inorganic nanocomposites with controllable size, shape, morphology, and functionality. This viable polymer-templated approach enables the in-situ synthesis of inorganic nanocrystals with well-controlled size, shape, and functionality in the presence of some rationally designed polymer template by utilizing the interplay between the functional groups of polymer templates and the inorganic precursors. Two main targeted applications, namely, functional nanocomposites as electrodes for Lithium ion batteries (LIBs) and as dielectric materials for capacitors guide the polymer-templated strategy when designing the polymer templates and crafting hybrid organic-inorganic nanocomposites. The major achievements can be summarized as follows: First, a viable and robust in-situ synthesis of poly(vinylidene fluoride) (PVDF)-BaTiO3 nanocomposites composed of monodisperse ferroelectric BaTiO3 nanoparticles with tunable diameter directly and stably connected with ferroelectric PVDF was initiated by exploiting both the ability to synthesizing amphiphilic star-like poly(acrylic acid)-block-poly(vinylidene fluoride) (PAA-b-PVDF) diblock copolymers with well-defined molecular weight of each block as nanoreactors, and the strong coordination interaction between the precursors and hydrophilic PAA blocks. The resulting PVDF-BaTiO3 nanocomposites, with tunable PVDF/BaTiO3 volume ratio, displayed high dielectric constant and low dielectric loss, which is promising for applications in high energy density capacitors. In addition, these PVDF-functionalized BaTiO3 nanoparticles exhibited the ferroelectric tetragonal structure. Second, we extended this amphiphilic star-like diblock copolymer nanoreactor strategy to bottlebrush-like diblock copolymer and crafted ferroelectric PVDF-BaTiO3 nanocomposites composed of ferroelectric BaTiO3 nanorods with tunable diameter, length and aspect ratio stably connected with ferroelectric PVDF. The capability of systematically varying the size of BaTiO3 nanocrystals offers the potential to investigate the size and shape effects on the ferroelectric and dielectric properties of BaTiO3-based nanocomposites, thereby providing insight into the rational design of ferroelectric PVDF-BaTiO3 nanocomposites for practical applications. Third, we developed a facile and effective strategy for in-situ crafting ZnFe2O4/carbon nanocomposites comprising small-sized ZnFe2O4 nanoparticles embedded within the continuous carbon network through the pyrolysis of ZnFe2O4 precursors-containing polymer template PS@PAA core@shell nanospheres. The advantages of this strategy are threefold. First, the PS@PAA nanosphere template is synthesized by emulsion polymerization in one-step. Second, the pyrolysis leads to the formation of ZnFe2O4 nanoparticles. Third, in the meantime the pyrolysis also induced the carbonization of PS@PAA, forming continuous carbon network that encapsulates the formed ZnFe2O4 nanoparticles. The synergy of nanoscopic ZnFe2O4 particles and their hybridization with a continuous conductive carbon network contributes to excellent rate performance and prolonged cycling stability over several hundred cycles when the ZnFe2O4 (79.3 wt%)/carbon nanocomposites are investigated as anodes for lithium ion batteries (LIBs). We envision that this synthetic strategy is simple and robust, and can be readily extended for the preparation of other carbon hybridized electrode materials for high-performance LIBs. Finally, we crafted corn-like SnO2 nanocrystals, composed of hundreds of SnO2 nanoparticles (~5 nm) decorated along the cob with a large number of pores between SnO2 nanoparticles, using judiciously designed bottlebrush-like hydroxypropyl cellulose-graft-poly (acrylic acid) (HPC-g-PAA) as template and coated the corn-like SnO2 with a thin layer of protective polydopamine (PDA). The synergy of the corn-like nanostructures and the protective PDA coating enabled the excellent electrochemical performance for the PDA-coated corn-like SnO2 electrode, including the superior long-term cycling stability, high Sn→SnO2 reversibility, and excellent rate capability. We envisage that the bottlebrush-like polymer templating strategy is facile and robust, and can be readily extended to create a rich variety of other functional metal oxides and metal sulfides for high-performance LIBs. The bottom-up crafting of functional hybrid organic-inorganic nanocomposites offers new levels of tailorability to nanostructured materials and promises new opportunities for achieving exquisite control over the surface chemistry and properties of nanocomposites with engineered functionality for diverse applications in energy conversion and storage, catalysis, electronics, nanotechnology, and biotechnology.
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