In this study, silicon oxycarbide (SiOC) is selected as the base polymer to derive a SiOC ceramic (PDC) matrix, and four transition metals M (M = Ni, Mo, Co, and Zr) are individually introduced into the SiOC base to form various SiOC/M systems. SiOC‐Ni, SiOC‐MoC
This study focuses on the early stage of polymer‐derived SiOC ceramic conversion. We demonstrate that the perceived SiOC phase separation is nonexistent. Instead, SiO2and free carbon clusters form first and then carbothermal reduction sets in to induce SiOC formation. Such fundamental understanding is supported by both synchrotron X‐ray diffraction study and reactive force field simulation. This work for the first time unifies the understanding of atomic evolution process of polysiloxane‐based polymer to ceramic conversion.
more » « less- Award ID(s):
- 2024546
- PAR ID:
- 10442596
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 106
- Issue:
- 5
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- p. 2737-2743
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract x , and SiOC‐CoSix are obtained by pyrolysis at 1100°C, whereas SiOC‐ZrOx forms upon pyrolysis at 1400°C. The selected SiOC/M systems encompass four different types of phase separation pathways—pure metal, metal carbide, metal silicide, and metal oxide (SiC‐SiO2‐C‐Ni, SiC‐SiO2‐C‐MoCx , SiC‐SiO2‐C‐CoSix , and SiC‐SiO2‐C‐ZrOx ). The driving force for crystallization has been analyzed using a Gibbs free energy minimization method and phase fractions of these different PDC systems are calculated based on the lever rule. This work also reveals the energetics related to the quaternary systems and provides guidance to synthesizing metal‐containing PDCs with desired phase contents. In addition, we have examined the broad applicability of the phase content prediction method for a variety of other SiOC/M systems. -
more » « less
Abstract Amorphous silicon oxycarbides are known to be an effective anode material for lithium‐ion batteries. Despite their exceptional properties and high charge capacities, however, their practical uses are limited by their significant first‐cycle loss, considerable hysteresis, and low cyclic ability. Comparatively, SiOC/metal oxide materials have demonstrated increased rate capability and cyclic stability. This study utilized a liquid precursor‐derived ceramic method to modify SiOC with titanium (IV) butoxide precursor to synthesize SiOC/TiOxCy. X‐ray diffractograms confirmed the amorphous nature of SiOC/TiOxCy. The elemental composition and bonding properties were investigated using X‐ray photoelectron spectroscopy, and electron microscopy was used to explore morphological features. In the first cycle, the reversible capacity of pyrolyzed SiOC/TiOxCywas 520 mAh g−1, which then increased to 736 mAh g−1for the 1200°C annealed SiOC/TiOxCydue to the increased free carbon network and TiC conductive phases. The irreversible capacity of the first cycle was 568 mAh g−1, which was lower than the annealed SiOC irreversible capacity of 695 mAh g−1. Interestingly, the rate stability of the pyrolyzed SiOC/TiOxCyperformed more stability than the annealed sample. Localized carbothermal reactions between amorphous SiOC/TiOxCyand free carbon at annealing temperatures resulted in loss of structure stability.
-
Transition metal dichalcogenides (TMDs) such as the WS2 have been widely studied as potential electrode materials for lithium-ion batteries (LIB) owing to TMDs’ layered morphology and reversible conversion reaction with the alkali metals between 0 to 2 V (v/s Li/Li+) potentials. However, works involving TMD materials as electrodes for sodium- (NIBs) and potassium-ion batteries (KIBs) are relatively few, mainly due to poor electrode performance arising from significant volume changes and pulverization by the larger size alkali-metal ions. Here, we show that Na+ and K+ cyclability in WS2 TMD is improved by introducing WS2 nanosheets in a chemically and mechanically robust matrix comprising precursor-derived ceramic (PDC) silicon oxycarbide (SiOC) material. The WS2/SiOC composite in fibermat morphology was achieved via electrospinning followed by thermolysis of a polymer solution consisting of a polysiloxane (precursor to SiOC) dispersed with exfoliated WS2 nanosheets. The composite electrode was successfully tested in Na-ion and K-ion half-cells as a working electrode, which rendered the first cycle charge capacity of 474.88 mAh g−1 and 218.91 mAh g−1, respectively. The synergistic effect of the composite electrode leads to higher capacity and improved coulombic efficiency compared to the neat WS2 and neat SiOC materials in these cells.more » « less
-
more » « less
A facile and novel processable method to synthesize the Ni nanoparticles (Ni NPs) by tailoring their size in the matrix of the silicon oxycarbide (SiOC) ceramic system is reported. This method is based on polymer‐derived ceramics (PDCs), instead of the conventional powder route. The specific structural characteristics and magnetic properties of the various Ni NPs/SiOC composites as a function of carbon content are systematically investigated. The magnetic properties are experimentally investigated as a function of NP size and measurement temperature. It is demonstrated that the change in the size of Ni NPs (average from ≈4 to ≈ 19 nm) determines the magnetic nature of superparamagnetism. Zero‐field‐cooled (ZFC) and field‐cooled (FC) magnetization studies under magnetic fields of 100 Oe are performed. The saturated
M versusH (M –H ) loops (saturation magnetization) increase and the coercivity decreases with the size reduction of Ni NPs. It is an indicator of the presence of superparamagnetic behavior and single‐domain NP for ceramic materials. -
more » « less
Ni-SiOC nanocomposites maintain crystal-amorphous dual-phase nanostructures after high-temperature annealing at different temperatures (600 °C, 800 °C and 1000 °C), while the feature sizes of crystal Ni and amorphous SiOC increase with the annealing temperature. Corresponding to the dual-phase nanostructures, Ni-SiOC nanocomposites exhibit a high strength and good plastic flow stability. In this study, we conducted a He implantation in Ni-SiOC nanocomposites at 300 °C by in-situ transmission electron microscope (TEM) irradiation test. In-situ TEM irradiation revealed that both crystal Ni and amorphous SiOC maintain stability under He irradiation. The 600 °C annealed sample presents a better He irradiation resistance, as manifested by a smaller He-bubble size and lower density. Both the grain boundary and crystal-amorphous phase boundary act as a sink to absorb He and irradiation-induced defects in the Ni matrix. More importantly, amorphous SiOC ceramic is immune to He irradiation damage, contributing to the He irradiation resistance of Ni alloy.
