Mechanochemical reduction of clay minerals to porous silicon nanoflakes for high-performance lithium-ion battery anodes

Hierarchically porous silicon nanoflakes were synthesized from natural talc via a mechanochemical reduction method, which showed great potential in the scalable production of silicon nanoflakes due to the abundant precursor and facile strategy. The unique layered structure and chemical composition of talc enabled the formation of two-dimensional nanostructured silicon without any additional templates. As lithium-ion battery anodes, the silicon nanoflakes showed excellent electrochemical properties.

Carbon-Free Conversion of SiO2 to Si via Ultra-Rapid Alloy Formation: Toward the Sustainable Fabrication of Nanoporous Si for Lithium-Ion Batteries

Silicon has the potential to improve lithium-ion battery (LIB) performance substantially by replacing graphite as an anode. The sustainability of such a transformation, however, depends on the source of silicon and the nature of the manufacturing process. Today's silicon industry still overwhelmingly depends on the energy-intensive, high-temperature carbothermal reduction of silica─a process that adversely impacts the environment. Rather than use conventional thermoreduction alone to break Si-O bonds, we report the efficient conversion of SiO₂ directly to Mg₂Si by a microwave-induced Mg plasma within 2.5 min at merely 200 W under vacuum. The underlying mechanism is proposed, wherein electrons with enhanced kinetics function readily as the reductant while the "bombardment" from Mg cations and electrons promotes the fast nucleation of Mg₂Si. The 3D nanoporous (NP) Si is then fabricated by a facile thermal dealloying step. The resulting hierarchical NP Si anodes deliver stable, extended cycling with excellent rate capability in Li-ion half-cells, with capacities several times greater than graphite. The microwave-induced metal plasma (MIMP) concept can be applied just as efficiently to the synthesis of Mg₂Si from Si, and the chemistry should be extendable to the reduction of multiple metal(loid) oxides via their respective Mg alloys.

Encapsulation of Silicon Nano Powders via Electrospinning as Lithium Ion Battery Anode Materials

Silicon-containing polyester from tetramethoxysilane, ethylene glycol, and o-Phthalic anhydride were used as encapsulating materials for silicon nano powders (SiNP) via electrospinning, with Polyacrylonitrile (PAN) as spinning additives. In the correct quantities, SiNP could be well encapsulated in nano fibers (200-400 nm) using scanning electron microscopy (SEM). The encapsulating materials were then carbonized to a Si-O-C material at 755 °C (Si@C-SiNF-5 and Si@C-SiNF-10, with different SiNP content). Fiber structure and SiNP crystalline structure were reserved even after high-temperature treatment, as SEM and X-ray diffraction (XRD) verified. When used as lithium ion battery (LIB) anode materials, the cycling stability of SiNPs increased after encapsulation. The capacity of SiNPs decreased to ~10 mAh/g within 30 cycles, while those from Si@C-SiNF-5 and Si@C-SiNF-10 remained over 500 mAh/g at the 30th cycle. We also found that adequate SiNP content is necessary for good encapsulation and better cycling stability. In the anode from Si@C-SiNF-10 in which SiNPs were not well encapsulated, fibers were broken and pulverized as SEM confirmed; thus, its cycling stability is poorer than that from Si@C-SiNF-5.

The effect of prolonged holding time on the mechanical property and microstructural property of lithium disilicate glass-ceramic

Repeat firing produces uncertainty about stabilizing lithium disilicate glass-ceramic (LDGC) material properties, even though prolonged holding time can enhance the mechanical property of LDGC during a single firing cycle. However, the effect of prolonged holding time and repeat firing on the mechanical property and microstructure of LDGC is not fully understood. In the present study, three groups of LDGC material were created: (i) extension of holding time (7 vs. 14 vs. 28 min) at 780-800 °C; (ii) holding time extension (7 vs. 14 min) and dual sintering at 800-820 °C, respectively; (iii) dual sintering with prolonged holding time (7 vs. 14 min) at 820-840 °C. The nano-indenter test revealed that prolonged holding time (14 and 28 min) promoted the enhancement of LDGC hardness and Young's modulus. X-ray photoelectron spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed that prolonged holding time increased and stabilized LD phase in LDGC, as well as induced residual compressive stress. Scanning electron microscopy showed that prolonged holding time increased LD crystal grains homogeneously and facilitated LDGC to form dense interlocking structure without enlarging crystal size grains significantly. In contrast, LDGC that dual sintered alone at 820-840 °C possessed inferior mechanical properties, coupled with heterogeneous crystal phases, residual tensile stress, and melted crystals grains in the porous microstructure. Interestingly, these deteriorated properties of LDGC caused by dual sintering alone could be counteracted by prolonging the holding time. Nevertheless, the LDGC materials displayed an excellent biocompatibility throughout the study. This study identified that prolonged holding time during repeated firing cycles stabilized LD phase and crystal grain size of LDGC, thus enhanced the mechanical properties, which provided a new insight to extend the repeat fired restoration longevity of LDGC. Graphical abstract.

A Review on Recent Advances for Boosting Initial Coulombic Efficiency of Silicon Anodic Lithium Ion batteries

Rechargeable silicon anode lithium ion batteries (SLIBs) have attracted tremendous attention because of their merits, including a high theoretical capacity, low working potential, and abundant natural sources. The past decade has witnessed significant developments in terms of extending the lifespan and maintaining high capacities of SLIBs. However, the detrimental issue of low initial Coulombic efficiency (ICE) toward SLIBs is causing more and more attention in recent years because ICE value is a core index in full battery design that profoundly determines the utilization of active materials and the weight of an assembled battery. Herein, a comprehensive review is presented of recent advances in solutions for improving ICE of SLIBs. From design perspectives, the strategies for boosting ICE of silicon anodes are systematically categorized into several aspects covering structure regulation, prelithiation, interfacial design, binder design, and electrolyte additives. The merits and challenges of various approaches are highlighted and discussed in detail, which provides valuable insights into the rational design and development of state-of-the-art techniques to deal with the deteriorative issue of low ICE of SLIBs. Furthermore, conclusions and future promising research prospects for lifting ICE of SLIBs are proposed at the end of the review.

Silicon micron cages derived from a halloysite nanotube precursor and aluminum sacrificial template in molten AlCl3 as an anode for lithium-ion batteries

Porous nanostructures have been proposed a promising strategy to improve the electrochemical performance of Si materials as anodes of lithium-ion batteries (LIBs). However, expensive raw materials and the tedious preparation processes hinder their widespread adoption. In this work, silicon micron cages (SMCs) have been synthesized in molten AlCl₃ through using spherical aluminum particles as a sacrificial template, and the earth-abundant and low-cost natural halloysite clay as a precursor. The aluminum spheres (1–3 μm) not only act as a sacrificial template but also facilitate the formation of silicon branches, which connect together to form SMCs. As anodes for LIBs, the SMC electrode exhibits a high reversible capacity of 1977.5 mA h g⁻¹ after 50 cycles at a current density of 0.2 A g⁻¹, and 1035.1 mA h g⁻¹ after 300 cycles at a current density of 1.0 A g⁻¹. The improved electrochemical performance of SMCs could be ascribed to the micron cage structure, providing abundant buffering space and mesopores for Si expansion. This promising method is expected to offer a pathway towards the scalable application of Si-based anode materials in the next-generation LIB technology.

(1) Silicon micron cages (SMCs) was synthesized using natural halloysite as precursor. (2) The electrochemical performance of SMCs as anode materials of lithium-ion batteries can be improved for the micron cage structure.

When Silicon Materials Meet Natural Sources: Opportunities and Challenges for Low-Cost Lithium Storage

The manipulation of progressive lithium-ion batteries (LIBs) with high energy density, low cost, and long-term cycling stability is of high priority to meet the growing demands for next-generation energy storage devices. Silicon (Si) has been receiving marvelous attention as a promising anode material for rechargeable LIBs, due to its high theoretical gravimetric capacity and low cost. Si is the second most abundant element in the earth crust in the form of silicates, so it is the most cost-effective element as an anode material in next-generation LIBs. In this review, different natural sources such as rice husk, sugar cane bagasse, bamboo, reed plant, sand, halloysite, and different waste sources such as waste of the solar power industry, fly ash, straw ash, and other industrial waste that can give rise to different nanostructured Si are systematically summarized. In addition, different synthesis methods of fabricating nanostructured Si are reviewed as well as including magnesiothermic reduction, etching methods, ball milling, and chemical vapor deposition. The advantages and disadvantages of these kind of synthesis methods are discussed as well. Furthermore, the opportunities and challenges of nano-Si are also discussed.

Kirkendall effect modulated hollow red phosphorus nanospheres for high performance sodium-ion battery anodes

Kirkendall effect mediated hollow red phosphorus nanospheres in a mild molten salt reaction exhibit great sodium storage performance.

Synthesis of Porous Si/C Composite Nanosheets from Vermiculite with a Hierarchical Structure as a High-Performance Anode for Lithium-Ion Battery

Silicon nanosheets are fascinating anode materials for lithium-ion batteries because of their high specific capacities, structural stability, and fast kinetics in alloying/dealloying with Li. The nanosheets can be synthesized through chemical vapor deposition (CVD), topochemical reaction, and templating method. After coating with a carbon nanolayer, they exhibit enhanced electrochemical performance. However, it is challenging to synthesize ultrathin carbon-coated silicon nanosheets. In this work, porous silicon/carbon (pSi/C) composite nanosheets are synthesized by reducing the carbon-coated expanded vermiculite with metallic Al in the molten salts. The as-prepared pSi/C nanosheets retain the layered nanostructure of vermiculite, with a thickness of less than 50 nm. The carbon nanolayer serves as the diffusion barrier and mechanical support for the growth of mesoporous silicon nanosheets. The anode of pSi/C nanosheets achieves remarkable electrochemical performance, exhibiting a reversible capacity of 1837 mA h g^-1 at 4 A g^-1 and retaining 71.5% of the initial capacity after 500 cycles. The process can be extended to the synthesis of the pSi/C composite nanotube by using other carbon-coated silicate templates such as halloysite.

Formation of Si Hollow Structures as Promising Anode Materials through Reduction of Silica in AlCl3-NaCl Molten Salt

Hollow nanostructures are attractive for energy storage and conversion, drug delivery, and catalysis applications. Although these hollow nanostructures of compounds can be generated through the processes involving the well-established Kirkendall effect or ion exchange method, a similar process for the synthesis of the pure-substance one ( e. g., Si) remains elusive. Inspired by the above two methods, we introduce a continuous ultrathin carbon layer on the silica nano/microstructures (Stöber spheres, diatom frustules, sphere in sphere) as the stable reaction interface. With the layer as the diffusion mediator of the reactants, silica structures are successfully reduced into their porous silicon hollow counterparts with metal Al powder in AlCl₃-NaCl molten salt. The structures are composed of silicon nanocrystallites with sizes of 15-25 nm. The formation mechanism can be explained as an etching-reduction/nucleation-growth process. When used as the anode material, the silicon hollow structure from diatom frustules delivers specific capacities of 2179, 1988, 1798, 1505, 1240, and 974 mA h g^-1 at 0.5, 1, 2, 4, 6, and 8 A g^-1, respectively. After being prelithiated, it retains 80% of the initial capacity after 1100 cycles at 8 A g^-1. This work provides a general way to synthesize versatile silicon hollow structures for high-performance lithium ion batteries due to the existence of ample silica reactants and can be extended to the synthesis of hollow structures of other materials.

Mesoporous germanium nanoparticles synthesized in molten zinc chloride at low temperature as a high-performance anode for lithium-ion batteries

The mesoporous germanium nanoparticles are prepared by a “metathesis” reaction of magnesium germanide (Mg₂Ge) and zinc chloride (ZnCl₂), and they exhibit excellent electrochemical performance for Li-ion batteries.

Sonochemical synthesis of hydrogenated amorphous silicon nanoparticles from liquid trisilane at ambient temperature and pressure

Silicon nanoparticles (Si-NPs) are increasing in relevance in diverse fields of scientific and nanotechnological inquiry, where currently some of the most important areas of research involve energy storage and biomedical applications. The present article is concerned with a curious and scalable method for the preparation of discrete, unoxidized, hydrogenated, and amorphous Si-NPs of tunable size in the range of 1.5-50nm. Using ultrasound generated with a conventional ultrasonic horn, the "fusion" of Si-NPs is demonstrated at ambient temperature and pressure by sonicating solutions containing readily available, semiconductor-grade purity trisilane (Si₃H₈). The only requirement for the synthesis is that it be carried out in an inert atmosphere such as that of a N₂-filled glove box. Various spectroscopic techniques and electron microscopy images are used to show that the size of the Si-NPs can be controlled by varying the amplitude of the ultrasonic waves or the concentration of trisilane in the solution. Moreover, sustained ultrasonic irradiation is found to yield highly porous Si-NP agglomerates that may find use in applications requiring non-crystalline nanoscopic high specific surface area morphologies.

Structure-preserved 3D porous silicon/reduced graphene oxide materials as anodes for Li-ion batteries

3D porous networks are subject to be destroyed during electrode preparation. Structure-preserved 3D porous Si/rGO anode materials were synthesized by tuning pore size distribution and performed superior electrochemical properties.

Target-specific induced hyaluronic acid decorated silica fluorescent nanoparticles@polyaniline for bio-imaging guided near-infrared photothermal therapy

Heating properties of FNPs(Si/HA)@PANI nanoparticles could lead to new options for photothermal therapy guided by tumor targeted bioimaging to track treatment progress.

A scalable synthesis of N-doped Si nanoparticles for high-performance Li-ion batteries

N-doped Si nanoparticles were prepared synchronously using a nitridation process of Mg₂Si, which exhibited excellent electrochemical performance for lithium ion batteries.

Porous silicon nano-aggregate from silica fume as an anode for high-energy lithium-ion batteries

A porous silicon nano-aggregate (PSNA) has been synthesizedviaa solid-state reaction of silica fume and Mg₂Si. It delivers a high reversible specific capacity and significant cycling stability.

Solvothermal synthesis of a silicon hierarchical structure composed of 20 nm Si nanoparticles coated with carbon for high performance Li-ion battery anodes

A solvothermal synthesized silicon hierarchical structure shows a high electrochemical performance for Li-ion battery anodes after coating with a carbon layer.

Cu3Si@Si core-shell nanoparticles synthesized using a solid-state reaction and their performance as anode materials for lithium ion batteries

Cu3Si@Si core-shell nanoparticles with a Si shell coated over the Cu3Si core are synthesized by a solid-state reaction between CuCl and Si. The evaluation process of the core-shell structure shows a mechanism analogous to the Kirkendall effect. As anode materials for lithium ion batteries, Cu3Si@Si core-shell nanoparticles retained a capacity of 903.6 mA h g(-1) at the current density of 2 A g(-1) over 400 cycles.

Chemical synthesis of porous hierarchical Ge–Sn binary composites using metathesis reaction for rechargeable Li-ion batteries

A typical metathesis reaction is employed to prepare porous hierarchical Ge–Sn binary composites. As an anode for half/full LIBs, the Ge–Sn displays superior electrochemical performance.

Nanoporous silicon prepared through air-oxidation demagnesiation of Mg2Si and properties of its lithium ion batteries

Nanoporous silicon has been prepared through the air-oxidation demagnesiation of Mg₂Si at 600 °C for 10 hours (Mg₂Si + O₂ → Si + MgO), followed by HCl washing.

Synchronously synthesized Si@C composites through solvothermal oxidation of Mg2Si as lithium ion battery anode

Si@C composites have been synchronously synthesized by solvothermal oxidation of Mg₂Si at 650 °C.