Nitrogen-plasma doping of carbon film for a high-quality layered Si/C composite anode

Realizing fast-charging capability of silicon anode via ternary doping and structural disorder

Silicon (Si) is a potential fast-charging anode material for lithium-ion batteries (LIBs) due to its high energy density and suitable lithium insertion potential. However, the slow kinetics and significant volume changes during lithiation/delithiation hinder its practical application. High-entropy alloying of silicon enhances electronic conductivity and mitigates volume expansion, leading to improved rate performance. Nevertheless, the synergistic effects of high-entropy alloying and crystal structure on silicon-based anodes remain underexplored. Herein, a ternary doping alloy (Si-FeTiP) anode material with an amorphous structure was prepared via high-energy ball milling. The uniformly distributed microcrystalline phases of FeSi2 and TiP enhanced the electronic conductivity and structural stability of the Si anode. The local disordered structure of the amorphous silicon phase mitigates lithiation-induced stress, while the isotropic nature of the amorphous structure facilitates excellent Li+ diffusion kinetics in the Si-FeTiP composite. As a result, the Si-FeTiP anode exhibits an excellent rate capability of 658 mAh g-1 at 10 A g-1 and a capacity retention of 80.3 % after 500 cycles at 2 A g-1. This study enhances our understanding of how crystal structure influences ion transport and electrochemical performance. Furthermore, it provides valuable insights for the design of multivariate fast-charging silicon-based anode materials.

Graphene Oxide Nanosheets for Delivery of RNAi and Plant Immune Stimulation for Sustained Protection against Plant Viruses

Given the dearth of effective antiviral drugs, the exogenous delivery of dsRNA for RNAi against plant viral diseases holds great promise. Here, we present an effective delivery approach of dsRNA utilizing graphene oxide nanosheets (GONs) on mature plant leaves via a spray. Our method achieves rapid and sustained gene knockdown, reducing the level of the target gene to 46% by day 2, and continuously releases dsRNA for at least 6 days. The coupling of GONs with specific fragments of coat protein and replicase gene dsRNA exhibited a superior antiviral effect compared to specific fragments of RNA-dependent replicase and movement protein. The coupling of GONs with the specific fragment of the replicase gene even has 87.2% protection against TMV. Moreover, the nanocomplex GONs@dsRNA can also stimulate plant immunity through bursts of reactive oxygen species without harming growth. Overall, our findings present a robust and convenient tool for plant virus control.

Boron-doped three-dimensional porous carbon framework/carbon shell encapsulated silicon composites for high-performance lithium-ion battery anodes

Deleterious volumetric expansion and poor electrical conductivity seriously hinder the application of Si-based anode materials in lithium-ion batteries (LIBs). Herein, boron-doped three-dimensional (3D) porous carbon framework/carbon shell encapsulated silicon (B-3DCF/Si@C) hybrid composites are successfully prepared by two coating and thermal treatment processes. The presence of 3D porous carbon skeleton and carbon shell effectively improves the mechanical properties of the B-3DCF/Si@C electrode during the cycling process, ensures the stability of the electrical contacts of the silicon particles and stabilizes the solid electrolyte interface (SEI) layer, thus enhancing the electronic conductivity and ion migration efficiency of the anode. The developed B-3DCF/Si@C anode has a high reversible capacity, excellent cycling stability and outstanding rate performance. A reversible capacity of 1288.5 mAh/g is maintained after 600 cycles at a current density of 400 mA g-1. The improved electrochemical performance is demonstrated in a full cell using a LiFePO4-based cathode. This study presents a novel approach that not only mitigates the large volume expansion effects in LIB anode materials, but also provides a reference model for the preparation of porous composites with various functionalities.

Plasma-induced oxygen defects in titanium dioxide to address the long-term stability of pseudocapacitive MnO2 anode for lithium ion batteries

In this work, we developed Manganese and Titanium based oxide composites with oxygen defects (MnOx@aTiOy) via plasma processing as anodes of lithium ion batteries. By appropriately adjusting the defect concentration, the ion transport kinetics and electrical conductivity of the electrodes are significantly improved, showing stable capacity retention. Furthermore, the incremental capacity is further activated and long-term stable cycling performance is achieved, with a specific capacity of 829.5 mAh/g at 1 A/g after 2000 cycles. To scrutinize the lithium migration paths and energy barriers in MnO2 and Mn2O3, the density functional theory (DFT) calculations is performed to explore the lithium migration paths and energy barriers. Although the transformation of MnO2 into Mn2O3 through oxygen defects was initially surmised to inhibit Li ions along their standard routes, our results indicate quite the contrary. In fact, the composite's lithium diffusion rate saw a substantial increase. This can be accredited to the pronounced enhancement of conductivity and ion transport efficiency in the amorphous and porous TiOy.

Vanadium-Tailored Silicon Composite with Furthered Ion Diffusion Behaviors for Longevity Lithium-Ion Storage

As one of the promising anode materials, silicon has attracted much attention due to its high theoretical specific capacity (∼3579 mAh g^-1) and suitable lithium alloying voltage (0.1-0.4 V). Nevertheless, the enormous volume expansion (∼300%) in the process of lithium alloying has a great negative effect on its cyclic stability, which seriously restricts the large-scale industrial preparation of silicon anodes. Herein, we design a facile synthesis strategy combining vanadium doping and carbon coating to prepare a silicon-based composite (V-Si@C). The prepared V-Si@C composite does not merely show improved conductivity but also improved electrochemical kinetics, attributed to the enlarged lattice spacing by V doping. Additionally, the superiority of this doping strategy accompanied by microstructure change is embodied in the relieved volume changes during the repeated charging/discharging process. Notably, the initial capacity of the advanced V-Si@C electrode is 904 mAh g^-1 (1 A g^-1) and still holds at 1216 mAh g^-1 even after 600 cycles, showing superior electrochemical performance. This study offers an alternative direction for the large-scale preparation of high-performance silicon-based anodes.

Regulation of defects and nitrogen species on carbon nanotube by plasma-etching for peroxymonosulfate activation: Inducing non-radical/radical oxidation of organic contaminants

The structural defects and heteroatom dopants of carbonaceous materials play critical roles in their activation of peroxymonosulfate (PMS) for organic pollutants' removal. This study uses plasma-etching technology to control the levels of structural defects and nitrogen species in nitrogen-doped carbon nanotubes (N-CNTs) for excellent PMS activation. The vacancy defects, CO, pyrrolic N and graphitic N could be rationally designed by controlling the plasma-etching time. Obviously, the I_D/I_G (from 0.56 to 0.94) and CO contents (from 0.07 to 0.44 at%) of N-CNTs increase with rising etching time, exhibiting good linear positive correlations with phenol oxidation rates. Furthermore, through active species identification, quantitative structure-activity relationships analysis and theoretical calculations, vacancy defects (adsorbing PMS O1 site) and CO are confirmed to be the active sites for the generation of ¹O₂, which is major pathway (82%) for phenol degradation. While radicals induced by pyrrolic N and graphitic N adsorbing PMS O2 site are the minor pathway (18%). Overall, this study sheds new light on the crucial roles of defects and N species in inducing PMS non-radical/radical activation by carbocatalyst via efficiently controlled plasma-etching technology.

Strategies for Controlling or Releasing the Influence Due to the Volume Expansion of Silicon inside Si-C Composite Anode for High-Performance Lithium-Ion Batteries

Currently, silicon is considered among the foremost promising anode materials, due to its high capacity, abundant reserves, environmental friendliness, and low working potential. However, the huge volume changes in silicon anode materials can pulverize the material particles and result in the shedding of active materials and the continual rupturing of the solid electrolyte interface film, leading to a short cycle life and rapid capacity decay. Therefore, the practical application of silicon anode materials is hindered. However, carbon recombination may remedy this defect. In silicon/carbon composite anode materials, silicon provides ultra-high capacity, and carbon is used as a buffer, to relieve the volume expansion of silicon; thus, increasing the use of silicon-based anode materials. To ensure the future utilization of silicon as an anode material in lithium-ion batteries, this review considers the dampening effect on the volume expansion of silicon particles by the formation of carbon layers, cavities, and chemical bonds. Silicon-carbon composites are classified herein as coated core-shell structure, hollow core-shell structure, porous structure, and embedded structure. The above structures can adequately accommodate the Si volume expansion, buffer the mechanical stress, and ameliorate the interface/surface stability, with the potential for performance enhancement. Finally, a perspective on future studies on Si-C anodes is suggested. In the future, the rational design of high-capacity Si-C anodes for better lithium-ion batteries will narrow the gap between theoretical research and practical applications.

Durable silicon-carbon composites self-assembled from double-protected heterostructure for lithium-ion batteries

HYPOTHESIS

Silicon-carbon composites have been faced with the contact issues between silicon and carbon in the form of material aggregation and inferior dispersion, leading to electrode cracking or kinetic degradation during cycling. In addition to dispersion improvement from interfacial linkage between self-assembled Si nanoparticles (SiNPs) and carbon fibers (CNFs), the positive influences of high-content carboxymethyl cellulose(CMC) (25 wt%) and amorphous carbon are also expected, respectively after the second-step self-assembly and subsequently sintering.

EXPERIMENTS

A novel composite (i.e. Si-CNF@C) with the decoration of entire SiNPs in the framework of both CNFs and amorphous carbon was prepared via two-step electrostatic self-assembly followed by sintering. Such a composite with heterogeneous nanostructure was used as a lithium-ion battery anode without additional binders or conductive agents.

FINDINGS

SiNPs can be well protected with CNFs and amorphous carbon against the dispersion and contact problems under both effects of electrostatic attraction and chemical bonding. With the double-protected heterostructure, such a novel Si-CNF@C electrode exhibits highly reversible capacities of 1200 mAh g^-1, 982 mAh g^-1, and 849 mAh g^-1 after 100, 500, and 1000 cycles at 0.5 A g^-1, respectively. The long-term cycling stability with a capacity loss of 0.036% per cycle over 1000 cycles is comparable.

Three-dimensional flexible molybdenum oxynitride thin film as a high capacity anode for Li-ion batteries

With the fast development of flexible wearable electronics, mobile electronic equipment, electric tool and electric vehicles, high specific capacity, superior cycle stability and excellent fast-charge performance are required for lithium-ion batteries (LIBs). Nevertheless, commercial graphite with the limited theoretical capacity (372 mAh g^-1) and short lifespan is difficult to satisfy the requirements of the new generation of LIBs. In this work, the three-dimensional flexible molybdenum oxynitride (MNO) thin films with non-binder were prepared by magnetron sputtering approach. The charge transfer resistance and Li-ion diffusion coefficient were measured by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), and the results show that molybdenum nitride is helpful to increase the diffusion and electron transfer of Li-ion. The MNO thin film annealed at 300 °C with irregular aggregate matrix structure shows a discharge capacity of 413 mAh g^-1 after 180 cycles at 1 A g^-1. The outstanding rate performance and cycle stability suggest that these binder-free thin film electrodes, especially nitrides, offer great opportunity for energy storage systems with fast-charge capabilities.