Co-synthesis and Electrochemical Investigation of the Nitrogen-Doped Carbon Layer with Metallic Nano Beads on the SiOx Anode for Lithium Secondary Batteries

The high theoretical capacity (∼2000 mAh g-1) of silicon suboxide (SiOx, with 1 < x < 2) can solve the energy density issue of the graphite anode in Li-ion batteries. In addition, it has an advantage in terms of volume expansion or side reactions compared to pure Si or Li metals, which are considered as next-generation anode materials. However, the loading content of SiOx is limited in commercial anodes because of its low cycle stability and initial coulombic efficiency. In this study, a nitrogen-doped carbon layer with Cu beads (N-C/Cu) derived from copper phthalocyanine (CuPc) is applied to a SiOx electrode to improve its electrochemical performance. The SiOx electrode is simultaneously coated with a Cu- and N-doped carbon layer using CuPc. N-C/Cu synergistically enhances the electric conductivity of the electrode, thus improving its electrochemical performance. The SiOx/N-C/Cu composite has better cyclability and higher capacity (1095.5 mAh g-1) than the uncoated electrode, even after 200 cycles in the 0.5 C condition. In full-cell cycling with NCM811 cathodes, the SiOx (60 wt % of SiOx, with a n/p ratio of 1.1) and graphite-mixed (7.8 wt % of SiOx, with a n/p ratio of 1.1) anodes also show improved electrochemical performances in the same conditions.

Energy Landscapes for Lithium Incorporation and Diffusion in Multidomain Silicon Suboxide Anode Materials

In-depth understanding of the lithium interaction characteristics within multidomain silicon suboxide is indispensable for optimizing the electrochemical performance of silicon suboxide anode materials for lithium-ion batteries. In this study, we investigate the domain-dependent thermodynamic and kinetic properties of lithium atoms within systematically designed multidomain silicon suboxide models composed of Si, SiO2, and Si/SiO2 interface by performing a series of computational simulations combined with a unique tomography-like sampling scheme. We find that the Si/SiO2 interfacial region exhibits preferential thermodynamics and kinetics for lithiation and can serve as a critical lithium transport channel during charge-discharge cycles, while the SiO2 domain is likely to be excluded from lithiation due to its high resistance to lithium diffusion. Consequently, a significant fraction of lithium is expected to be trapped at the Si/SiO2 interface during the discharge process, which ultimately contributes to a low initial Coulombic efficiency. This theoretical understanding suggests that the formation of continuously connected lithium-transportable Si/SiO2 interfacial channels surrounding the Si domains, along with a well-structured shallow SiO2 framework through the use of appropriate synthesis methods, is essential for maximizing the electrochemical performance of silicon suboxide anode materials.

Embedding Atomically Dispersed Iron Sites in Nitrogen-Doped Carbon Frameworks-Wrapped Silicon Suboxide for Superior Lithium Storage

Silicon suboxide (SiO_x ) has attracted widespread interest as Li-ion battery (LIB) anodes. However, its undesirable electronic conductivity and apparent volume effect during cycling impede its practical applications. Herein, sustainable rice husks (RHs)-derived SiO₂ are chosen as a feedstock to design SiO_x /iron-nitrogen co-doped carbon (Fe-N-C) materials. Using a facile electrospray-carbonization strategy, SiO_x nanoparticles (NPs) are encapsulated in the nitrogen-doped carbon (N-C) frameworks decorating atomically dispersed iron sites. Systematic characterizations including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) verify the existence of Fe single atoms and typical coordination environment. Benefiting from its structural and compositional merits, the SiO_x /Fe-N-C anode delivers significantly improved discharge capacity of 799.1 mAh g^-1 , rate capability, and exceptional durability, compared with pure SiO₂ and SiO_x /N-C, which has been revealed by the density functional theory (DFT) calculations. Additionally, the electrochemical tests and in situ X-ray diffraction (XRD) analysis reveal the oxidation of Li_x Si phase and the storage mechanism. The synthetic strategy is universal for the design and synthesis of metal single atoms/clusters dispersed N-C frameworks encapsulated SiO_x NPs. Meanwhile, this work provides impressive insights into developing various LIB anode materials suffering from inferior conductivity and huge volume fluctuations.

Oxygen Content-Controllable Synthesis of Non-Stoichiometric Silicon Suboxide Nanoparticles by Electrochemical Anodization

A facile route to producing non-stoichiometric silicon suboxide nanoparticles (SiO_x NPs, 0 < x < 1) with an adjustable oxygen content is proposed. The process is based on electrochemical anodization involving the application of a strong electric field near the surface of a Si electrode to directly convert the Si electrode into SiO_x NPs. The difference in ion mobility between oxygen species (O²⁻ and OH⁻), formed during anodization, causes the production of non-stoichiometric SiO_x on the surface of the Si while, simultaneously, fluoride ions in the electrolyte solution etch the formed SiO_x layer, generating NPs under the intense electric field. The adjustment of the applied voltage and anodization temperature alters the oxygen content and the size of the SiO_x NPs, respectively, allowing the characteristics of the NPs to be readily controlled. The proposed approach can be applied for mass production of SiO_x NPs and is highly promising in the field of batteries and optoelectronics.

Fabrication of Periodic Nanostructures on Silicon Suboxide Films with Plasmonic Near-Field Ablation Induced by Low-Fluence Femtosecond Laser Pulses

Silicon suboxide (SiO_x, x ≈ 1) is a substoichiometric silicon oxide with a large refractive index and optical absorption coefficient that oxidizes to silica (SiO₂) by annealing in air at ~1000 °C. We demonstrate that nanostructures with a groove period of 200-330 nm can be formed in air on a silicon suboxide film with 800 nm, 100 fs, and 10 Hz laser pulses at a fluence an order of magnitude lower than that needed for glass materials such as fused silica and borosilicate glass. Experimental results show that high-density electrons can be produced with low-fluence femtosecond laser pulses, and plasmonic near-fields are subsequently excited to create nanostructures on the surface because silicon suboxide has a larger optical absorption coefficient than glass. Calculations using a model target reproduce the observed groove periods well and explain the mechanism of the nanostructure formation.

Pulsed laser-induced formation of silica nanogrids

Silica grids with micron to sub-micron mesh sizes and wire diameters of 50 nm are fabricated on fused silica substrates. They are formed by single-pulse structured excimer laser irradiation of a UV-absorbing silicon suboxide (SiOx) coating through the transparent substrate. A polydimethylsiloxane (PDMS) superstrate (cover layer) coated on top of the SiOx film prior to laser exposure serves as confinement for controlled laser-induced structure formation. At sufficiently high laser fluence, this process leads to grids consisting of a periodic loop network connected to the substrate at regular positions. By an additional high-temperature annealing, the residual SiOx is oxidized, and a pure SiO2 grid is obtained.

PACS

81.07.-b; 81.07.Gf; 81.65.Cf.