Improved electrochemical performance of silicon nitride film by hydrogen incorporation for lithium-ion battery anode

Effect of Rapid Thermal Annealing on Si-Based Dielectric Films Grown by ICP-CVD

Silicon nitride, silicon oxide, and silicon oxynitride thin films were deposited on the Si substrate by inductively coupled plasma chemical vapor deposition and annealed at 1100 °C for 3 min in an Ar environment. Silicon nitride and silicon oxide films deposited at ratios of the reactant flow rates of SiH4/N2 = 1.875 and SiH4/N2O = 3, respectively, were Si-rich, while Si excess for the oxynitride film (SiH4/N2/N2O = 3:2:2) was not found. Annealing resulted in a thickness decrease and structural transformation for SiOx and SiNx films. Nanocrystalline phases of Si as well as α- and β-Si3N4 were found in the annealed silicon nitride film. Compared to oxide and nitride films, the oxynitride film is the least susceptible to change during annealing. The relationship between the structure, composition, and optical properties of the Si-based films has been revealed. It has been shown that the calculated optical parameters (refractive index, extinction coefficient) reflect structural peculiarities of the as-deposited and annealed films.

Constructing a Stable Si-N-Enriched Interface Boosts Lithium Storage Kinetics in a Silicon-Based Anode

The stable operation of a SiOx anode largely depends on the intrinsic chemistry of the electrode/electrolyte interface; however, an unstable interface structure and undesirable parasitic reactions with the electrolyte of the SiOx anode often result in the formation of a fragile solid-electrolyte interphase (SEI) and serious capacity decay during the lithiation/delithiation process. Herein, a Si-N-enriched N-doped carbon coating is constructed on the surface of SiOx yolk-shell nanospheres (abbreviated as SiOx@NC) to optimize the SEI film. The two-dimensional covalently bound Si-N interface, on one hand, can suppress the interfacial reactivity of the SiOx anode to enable the formation of a thin SEI film with accelerated diffusion kinetics of ions and, on the other hand, acts as a Li+ conductor during the delithiation process, allowing Li+ to diffuse rapidly in the SiOx matrix, thereby improving the long-term cycling stability and rapid charge/discharge capability of the SiOx anode. A series of characterizations show that the interface charge-transfer barrier and the Li+ diffusion energy barrier through the SEI film are the main factors that determine the interfacial electrochemical behavior and lithium storage performance. This work clarifies the relationship between the SEI characteristics and the interfacial transfer dynamics and aims to offer a more basic basis for the screening of other electrode materials.

Stoichiometry-Controlled Reversible Lithiation Capacity in Nanostructured Silicon Nitrides Enabled by in Situ Conversion Reaction

In modern Li-based batteries, alloying anode materials have the potential to drastically improve the volumetric and specific energy storage capacity. For the past decade silicon has been viewed as a "Holy Grail" among these materials; however, severe stability issues limit its potential. Herein, we present amorphous substoichiometric silicon nitride (SiNx) as a convertible anode material, which allows overcoming the stability challenges associated with common alloying materials. Such material can be synthesized in a form of nanoparticles with seamlessly tunable chemical composition and particle size and, therefore, be used for the preparation of anodes for Li-based batteries directly through conventional slurry processing. Such SiNx materials were found to be capable of delivering high capacity that is controlled by the initial chemical composition of the nanoparticles. They exhibit an exceptional cycling stability, largely maintaining structural integrity of the nanoparticles and the complete electrodes, thus delivering stable electrochemical performance over the course of 1000 charge/discharge cycles. Such stability is achieved through the in situ conversion reaction, which was herein unambiguously confirmed by pair distribution function analysis of cycled SiNx nanoparticles revealing that active silicon domains and a stabilizing Li2SiN2 phase are formed in situ during the initial lithiation.

A novel electrochemical lung cancer biomarker cytokeratin 19 fragment antigen 21-1 immunosensor based on Si3N4/MoS2 incorporated MWCNTs and core-shell type magnetic nanoparticles

Lung cancer is one of deadliest and most life threatening cancer types. Cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) is a significant biomarker for the diagnosis of non-small cell lung cancer (NSCLC). Due to these reasons, a novel electrochemical immunosensor based on a silicon nitride (Si3N4)-molybdenum disulfide (MoS2) composite on multi-walled carbon nanotubes (Si3N4/MoS2-MWCNTs) as an electrochemical sensor platform and core-shell type magnetic mesoporous silica nanoparticles@gold nanoparticles (MMSNs@AuNPs) as a signal amplifier was presented for CYFRA21-1 detection in this study. Capture antibody (Ab1) immobilization on a Si3N4/MoS2-MWCNT modified glassy carbon electrode (Si3N4/MoS2-MWCNTs/GCE) was firstly successfully performed by stable electrostatic/ionic interactions between the -NH2 groups of the capture antibody and the polar groups of Si3N4/MoS2. Then, specific antibody-antigen interactions between the electrochemical sensor platform and the signal amplifier formed a novel voltammetric CYFRA21-1 immunosensor. The prepared composite materials and electrochemical sensor surfaces were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). A linearity range of 0.01-1.0 pg mL-1 and a low detection limit (LOD) of 2.00 fg mL-1 were also obtained for analytical applications. Thus, the proposed immunosensor based on Si3N4/MoS2-MWCNTs and MMSNs@AuNPs has great potential for medical diagnosis of lung cancer.

Freestanding symmetrical SiN/Si/SiN composite coated on carbon nanotube paper for a high-performance lithium-ion battery anode based on synergistic effects

Direct coating of Si on an elastic carbon nanotube (CNT) network effectively addresses the rapid capacity fading of the Si anode. However, this strategy is hindered by the low Si tap density (Si < 50 nm) since sufficient void space has to be left for accommodating the Si volume change. Also, the mechanical properties of the CNT network as the elastic buffer matrix degrade significantly caused by side reactions of CNT with electrolyte. This work presents a freestanding paper-like anode consisting of a symmetrical sandwich-structured SiN/Si/SiN composite grown on CNT paper. This anode works well (∼259 μA h cm⁻² under the current rate of 0.6C after 350 cycles, with a capacity retention of 73.8%) even when the CNT is filled by the composite without void space left for accommodating volume expansion. This is mainly due to the following synergistic effects: on one hand, the stress-compensation phenomenon in the symmetrical sandwich-structured composite balances the volume change-induced stress and thus the composite has a robust mechanical stability with an intact morphology during cycling. On the other hand, the intact composite avoids reaction of CNT with the electrolyte and thus the CNT retains excellent mechanical properties and serves well as the elastic buffer matrix. These two sides interact with each other, enabling the high anode performance.

This SiN/Si/SiN@CNT anode shows high reversible specific capacity without sacrificing cycling stability due to the synergistic effects.