A novel covalently grafted binder through in-situ polymerization for high-performance Si-based lithium-ion batteries

Advances and future perspectives on silicon-based anodes for lithium-ion batteries

Silicon (Si)-based anode has emerged as the most promising anode material for next-generation lithium-ion batteries (LIBs) due to its high specific capacity, suitable operating potential and abundant natural reserves. Nevertheless, the drastic volume effect of Si particles during lithiation/delithiation leads to particle pulverization, electrode structure collapse, and solid electrolyte interfacial (SEI) film instability, which results in a rapid reversible capacity degradation of Si-based anodes. It is essential to deeply analyze the failure mechanism of silicon-based electrodes and explore suitable improvement methods to achieve higher capacity retention. Herein, we systematically summarize the improvement strategies for Si-based anodes, including regulating material particle size, optimizing structure and composition, and exploring new binders, along with their enhancement mechanisms. In addition, the preparation of high-performance Si-based electrodes based on newly developed 3D printing technology in recent years is discussed. Lastly, several possible directions and emerging challenges for Si anode are presented to facilitate further improvement in practical applications. Overall, this review is expected to provide basic understanding and insights into the practical application of Si-based materials in next-generation LIBs negative electrodes.

Urea-Formaldehyde Strengthened by Polyvinyl Alcohol: Impact on Mulch Film Properties and Cucumber Cultivation

To address the problem of environmental pollution caused by the extensive use of low-density polyethylene (LDPE) mulch film, this study developed a novel sprayable mulch using natural fibers and biodegradable polymers. Urea-formaldehyde resin (UF), strengthened with polyvinyl alcohol (PVA), was used as a modifier to induce beneficial physicochemical structural changes in PVA-modified urea-formaldehyde (PUF) resins. Characterization of these resins was conducted using Fourier transformation infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Preparation of the biodegradable mulch was conducted using Xuan paper waste residue (XP) as an enhancer, with PUF as the auxiliary agent. The resulting film (PUF-XP) was examined for differences in thickness, morphological characterization, and rate of weight loss, and the effects of different covering films on cucumber growth, root development, soil temperature, and weed control were evaluated. Characterization reveals that when the PVA content was 4% (W4UF), the film had the lowest free formaldehyde content (0.26%) and highest elongation at break (5.70%). In addition, W4UF could easily undergo thermal degradation at 278.4 °C and possessed a close-knit, three-dimensional structural network. W4UF was then mixed with paper powder and water in various proportions to produce three mulch films (BioT1, BioT2, and BioT3) that demonstrated excellent water retention and heat preservation and inhibited weed growth by 68.8-96.8%. Compared to no mulching (NM), BioT1 increased both the specific root length and root density, as well as improved the plant height, stem diameter, and total biomass of the cucumbers by 43.5%, 34.1%, and 33.9%, respectively. Therefore, a mass ratio of paper powder, water, and W4UF of 1:30:2 produced a biodegradable mulch film that could be used as an alternative to LDPE, mitigating the environmental pollution rendered by synthetic plastic mulch films and offering the potential for a sustainable agricultural application.

Aqueous Binder with Self-Emulsifying Characteristics for Practical Si/C Anode in Lithium-Ion Batteries

Silicon/carbon (Si/C) materials have achieved commercial applications as a solution to the problems of large volume expansion and short lifespan of silicon-based anodes in lithium-ion batteries. However, the potential risk of structural fracture and localized differences in surface adsorption properties lead to difficulties in maintaining the structural integrity of Si/C anodes using conventional binders during repeated lithiation/delithiation. Herein, an aqueous binder (PVA-g-M) based on polyvinyl alcohol (PVA) grafted methacrylic acid (MAA) obtained by self-emulsifying emulsion polymerization is reported. The introduction of carboxyl groups of MAA enables PVA-g-M to form more hydrogen bonds, thereby enhancing both the cohesion of the binder film and its adhesion to silicon-based surface. Simultaneously, the methyl-containing segments of MAA can wet the carbon-based surface, thereby enhancing the adhesion of PVA-g-M to carbonaceous materials. In addition, the hydroxyl groups on both the PVA segments and the silicon surface can be esterified with the carboxyl groups during the heat treatment, thus further improving the bonding strength. As-prepared Si/C anodes with PVA-g-M binder can significantly inhibit the electrode volume expansion and maintain high structural integrity during cycling as well as form SEIs with high lithium fluoride content, showing excellent cycling stability (81.1 % capacity retention after 300 cycles).

Prefabrication of "Trinity" Functional Binary Layers on a Silicon Surface to Develop High-Performance Lithium-Ion Batteries

The silicon (Si) anode is widely recognized as the most prospective next-generation anode. To promote the application of Si electrodes, it is imperative to address persistent interface side reactions caused by the huge volume expansion of Si particles. Herein, we introduce beneficial groups of the optimized binder and electrolyte on the Si surface by a co-dissolution method, realizing a "trinity" functional layer composed of azodicarbonamide and 4-nitrobenzenesulfonyl fluoride (AN). The "trinity" functional AN interfacial layer induces beneficial reductive decomposition reactions of the electrolyte and forms a hybrid solid-electrolyte interphase (SEI) skin layer with uniformly distributed organic/inorganic components, which can enhance the mechanical strength of the overall electrode, restrain harmful electrolyte depletion reactions, and maintain efficient ion/electron transport. Hence, the optimized Si@AN11 electrode retains 1407.9 mAh g^-1 after 500 cycles and still delivers 1773.5 mAh g^-1 at 10 C. In stark contrast, Si anodes have almost no reserved capacity at the same test conditions. Besides, the LiNi_0.5Co_0.2Mn_0.3O₂//Si@AN11 full-cell maintains 141.2 mAh g^-1 after 350 cycles. This work demonstrates the potential of developing multiple composite artificial layers to modulate the SEI properties of various next-generation electrodes.

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.