Nanosized Si Particles Research Articles

Controllable Synthesis of Hollow Dodecahedral Si@C Core-Shell Structures for Ultrastable Lithium-Ion Batteries.

Silicon (Si) has attracted considerable attention as a promising alternative to graphite in lithium-ion batteries (LIBs) because of its high theoretical capacity and voltage. However, the durability and cycling stability of Si-based composites have emerged as major obstacles to their widespread adoption as LIBs anode materials. To tackle these challenges, a hollow core-shell dodecahedra structure of a Si-based composite (HD-Si@C) is developed through a novel double-layer in situ growth approach. This innovative design ensures that the nano-sized Si particles are evenly distributed within a hollow carbon shell, effectively addressing issues like Si fragmentation, volume expansion, and detachment from the carbon layer during cycles. The HD-Si@C composite demonstrates remarkable structural integrity as a LIBs anode, resulting in exceptional electrochemical performance and promising practical applications, as evidenced by tests in pouch-type full cells. Notably, the composite shows outstanding cycling stability, retaining 85% of its initial capacity (713 mAh g-1) even after 3000 cycles at a high current rate of 5000mA g-1. Additionally, the material achieves a gravimetric energy density of 369Wh kg-1, showcasing its potential for efficient energy storage solutions. This research signifies a significant step toward realizing the practical utilization of Si-based materials in the next generation of LIBs.

Facile synthesis of nano-si/graphite-carbon anode through microwave-induced carbothermal shock for lithium-ion batteries

We present a cost-effective synthesis process for producing a carbon-coated nano-Si@Graphite (n-Si@G-C) anode, in which nano-sized Si (n-Si) particles (∼50 nm in size) are anchored onto natural graphite particles by a carbothermal shock through microwave induction. During the carbothermal shock process, graphite undergoes a fast increase in temperature resulting in micron-sized Si (m-Si) particles (∼4 μm in size) to undergo stress fractures due to rapid thermal expansion. This process leads to the formation of abundant n-Si particles onto graphite particles. Subsequently, a thin carbon shell is introduced by a wet-coating process combined with a thermal decomposition of coal-tar pitch. The amorphous carbon shell offers multiple functionalities: i) preventing direct exposure of n-Si particles to the electrolyte, ii) accommodating their volume expansion, and iii) maintaining electron conduction pathways. The resulting n-Si@G-C anode allows a high reversible capacity (500.8 mAh g−1) as well as fast-charging characteristics. When utilized in a full-cell configured with a commercial-grade LiNi0.8Co0.1Mn0.1O2 cathode, it achieves a notable reduction in charging time (approximately 10.1 min@80 % state of charge). After 300 cycles, a high capacity retention (71.3 %) can be retained under 3C charging. Moreover, the distinctive structural features of the n-Si@G-C anode effectively suppress undesirable Li plating.

Effect of ultrasonic and mechanical vibration treatments on evolution of Mn-rich phases and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys

Effects of ultrasonic vibration (UV) and mechanical vibration (MV) on the Mn-rich phase modification and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys were investigated. The results show that the UV and UV+MV treatments can significantly refine and fragmentize the microstructures. In addition, UV treatment can significantly passivate the primary Mn-rich Al15Mn3Si2 intermetallics. The formation mechanisms of refinement and passivation of the grains and non-dendrite particles were discussed. Compared with the gravity die-cast alloys, the UV and UV+MV treated alloys exhibit improved tensile and creep resistance at room and elevated temperatures. These results can be attributed to the refinement of the α(Al) grains and the secondary intermetallics, the increased proportion of refined heat-resistant precipitates, and the formation of nano-sized Si particles. The ultimate tensile strength of the UV treated alloys at 350 °C exceeds that of commercial piston alloys. This indicates the high application potential of the developed piston alloys in density diesel engines.

Engineering Nano-Sized Silicon Anodes with Conductive Networks toward a High Average Coulombic Efficiency of 90.2% via Plasma-Assisted Milling.

Si-based anode is considered one of the ideal anodes for high energy density lithium-ion batteries due to its high theoretical capacity of 4200 mAh g-1. To accelerate the commercial progress of Si material, the multi-issue of extreme volume expansion and low intrinsic electronic conductivity needs to be settled. Herein, a series of nano-sized Si particles with conductive networks are synthesized via the dielectric barrier discharge plasma (DBDP) assisted milling. The p-milling method can effectively refine the particle sizes of pristine Si without destroying its crystal structure, resulting in large Brunauer-Emmett-Teller (BET) values with more active sites for Li+ ions. Due to their unique structure and flexibility, CNTs can be uniformly distributed among the Si particles and the prepared Si electrodes exhibit better structural stability during the continuous lithiation/de-lithiation process. Moreover, the CNT network accelerates the transport of ions and electrons in the Si particles. As a result, the nano-sized Si anodes with CNTs conductive network can deliver an extremely high average initial Coulombic efficiency (ICE) reach of 90.2% with enhanced cyclic property and rate capability. The C-PMSi-50:1 anode presents 615 mAh g-1 after 100 cycles and 979 mAh g-1 under the current density of 5 A g-1. Moreover, the manufactured Si||LiNi0.8Co0.1Mn0.1O2 pouch cell maintains a high ICE of >85%. This work may supply a new insight for designing the nano-sized Si and further promoting its commercial applications.

Effect of heat treatment on microstructure, mechanical and thermal properties of selective laser melted AlSi7Mg alloy

AlSi7Mg alloy manufactured by selective laser melting (SLM) was subjected to different heat treatments to satisfy the need for excellent mechanical and thermal properties. Effect of direct aging (DA), annealing (AN) and solution + aging (SA) treatment on microstructure, mechanical and thermal properties of SLMed AlSi7Mg alloy was investigated. The results showed that the molten pool boundaries which can be clearly observed in the as-built sample fade away with the increasing heat treatment temperature. The heat treatments have slight effects on the morphology and size of α-Al grains. However, significant differences can be observed in the characteristics of substructure. For the DA treatment, the Al-Si network becomes discontinuous and simultaneously promotes the precipitation of nano-sized Si particles from the supersaturated Al matrix. The original Al-Si network becomes discontinuous and coarsening in the AN sample. For the SA sample, the original cellular structure and eutectic Al-Si network completely disappeared. Coarsened and irregularly shaped Si particles, fine equiaxed Si particles as well as the needle shaped Fe-rich precipitations were observed. The room temperature tensile test showed that the strength of DA sample is the highest, followed by as-built, AN, and SA samples in a descending order. The thermal diffusivity of SA sample is the highest, followed by AN, DA and as-built sample in a descending order.

Tribological behavior of eutectic Al–12Si alloy manufactured by selective laser melting

Al–Si alloys have been extensively used to make complex-shaped components for automobile and aerospace applications. However, the Si coarse-flakes in conventionally casted alloys can initiate cracks and result in poor mechanical properties. Therefore, it is important to discover an ultra-fine grain structure that can provide desirable properties to fulfill the ever-growing application demands. The present study aims to manufacture a eutectic Al–12Si (wt.%) alloy by using an additive manufacturing process based on the selective laser melting (SLM) mechanism and compare the structure, tribological behavior, worn subsurface morphologies and mechanical properties with the conventionally casted eutectic Al–Si alloy. Structural analysis revealed that the SLMed Al–Si alloy has nanoscale spherical Si-phase in a supersaturated Al matrix, whereas that made by the traditional casting method is of microscale Si coarse-flakes. This structural refinement remarkably improves the mechanical properties to 80.8% hardness, 17.3% elastic modulus, more than twice of the tensile strength and creep behavior compared to the traditionally casted alloy. The tribological and subsurface structural evaluation confirms that the SLMed Al–Si alloy can significantly reduce the wear rate in both directions without any substantial worn subsurface damages. It is clear that the wear mechanism of the traditionally casted Al–Si alloy mainly involves the primary Si coarse-flakes crushing-delamination-pull out with severe subsurface damages. However, the nano-sized Si particles in the SLMed Al–Si alloy produce only inlays into the Al-matrix without significant subsurface damage. Thus, the refinement of the grain structure and nanoscale Si phase are the key factors for the improvement of the mechanical properties and tribological behavior of the SLMed Al–Si alloy.

The hot deformation behaviour of laser powder bed fusion deposited Al–Si–Cu alloy processed by high-pressure torsion

The tensile properties of an ultrafine-grained Al–9%Si–3%Cu alloy deposited by the laser powder bed fusion process have been investigated in this work. The additively manufactured (AM) alloy was subjected to high-pressure torsion processing at room temperature successfully at different number of turns in HPT and then inspected through hot tensile testing at 298 and 573 K using strain rates ranging from 10–1 to 10–4 s−1. The processed alloy showed extensive refinement and high dislocation density that was associated with considerable strength at ambient temperature. The as-deposited and processed samples of the alloy exhibited significantly higher tensile strength and elongation under hot deformation conditions compared with their cast counterpart alloys. The room temperature-HPT processing presented ultrafine α-Al and well-distributed nanosized eutectic Si particles which significantly improved the tensile behaviour and thermal stability of the processed microstructures. The formation of fibrous structures has enhanced the flow behaviour and cavitation resistance at the elevated testing temperature. The current work indicates the impact of room temperature-HPT processing on the mechanical performance of the controllable AM-deposited alloy to meet industrial needs without further heat treatments or alloying additions.

Graphene oxide microrolls as high- content Si carriers boosting Li-ion storage

As attractive anode materials of lithium-ion batteries, both microsized and nanosized silicon particles have been investigated widely, but each has lots of insurmountable problems to restrict their practical applications. In this work, combining the advantages of microsized and nanosized Si particles, we reported a new thought for constructing micrometer-sized Si/C particles by embedding Si nanoparticles into graphene oxide (GO)-based mirorolls. Differing to the traditional spherical shape, the resulted Si/C microrolls exhibit a unique elastic coil structure with opening ends, facilitating the stress buffer and fast charge diffusion. Besides, in order to maintain the stability of Si nanoparticles in microrolls, we chose the elastic and deformable liquid metal (LM) as the “cloth”, and sodium alginate (SA) as the “thread”, successfully tailor a novel “tight suit” for each Si nanoparticle by a facile self-assembly process. Thanks to the double protection of the conductive-elastic LM-SA coating and the microroll architecture, the resulted Si@LM-SA@GO microroll anode not only has a high Si content of 69 %, a high tap density of 0.62 g cm−3 and a high initial coulombic efficiency of 85.1 %, but also exhibits a superior volumetric capacity of 2506 mAh cm−3, and a superior cycling performance of 660 mAh cm−3 after 500 cycles at 2 A g−1. The full cell constructed using a LiNiCoMnO2 cathode can achieve a high reversible capacity of 150 mAh g−1 at 1C after 250 cycles, delivering a high-energy density of 510 Wh kg−1.

Microalloying-modulated strength-ductility trade-offs in as-cast Al–Mg–Si–Cu alloys

This work presents detailed and quantitative strengthening effects from various kinds of secondary phases in as-cast Al–Mg–Si–Cu alloys for the first time, through changing Ge and Sb content. Three typical kinds of strength-ductility trade-off relations are elaborated by deformation, embrittling and strengthening mechanisms, as reflected by solidification experiments, multi-mechanistic models and first-principles calculations. Microalloying-modulated strength-ductility trade-offs are strongly associated with their special microstructures, where the size and volume fraction of coarse primary phases increase and fine precipitates are modified. As compared to the secondary phases contributing up to 81.9% of the total strength, strengthening effects from solid-solution atoms (6.5–8.7%), grain boundaries (1.8–2.5%) and coarse primary phases are negligible. Therefore, the increased strength of modified alloys is modulated by modifying the fine precipitates, including Mg2Si (β) plates, Al4Cu2Mg8Si7 (Q) needles, Al2Cu (θ) dispersoids, (Ge, Si) rods/particles and nano-sized Si particles. On the other hand, the decreased ductility of modified alloys is determined by the secondary phases, especially the coarse primary phases like β, Q, Mg3Sb2, Mg2(Ge, Si) and (Ge, Si) structures, which also implies that the ductility cannot be predicted by the Peierls’ ductility D derived from simulating α-Al solid solutions by first-principles methods.

Electrolyte-philic and thermal-resistant polyimide separator enhances the performance of flexible silicon/carbon nanofibers for lithium-ion batteries

It is still challenging to construct a stable silicon/electrolyte interface to inhibit the mechanical fracture of Si particles and repeated formation of a solid electrolyte interface layer. The separator is a vital component in lithium-ion batteries, however, commercial polyolefin separators suffer from low thermal stability and poor electrolyte wettability. Herein, a polyimide separator is reported to achieve a stable interface of silicon anode due to its high polarity, outstanding electrolyte absorption, and reduction of side reactions. The binder-free self-standing silicon carbon (Si@C) nanofiber composite is designed by a facile electrospinning method and subsequent pyrolysis, where the nanosized Si particles are confined in polyimide-derived carbon nanofibers to form a bamboo-like morphology with good flexibility. Such flexible nanofiber film with cross-linked 3D network structure is important to increase energy density of batteries, mitigate the growth of new interfaces, and avoid the known issues of side reaction during the electrochemical operation. Encouragingly, the 40 %-Si@C composite illustrates an improved lithium storage property with high reversible capacity of 1819.7 mAh g−1 at 0.2 A g−1, excellent rate capability and cycling stability, demonstrating superiority of the film electrode and polyimide separator. This work provides new insights for stabilizing the interface electrochemistry of alloy anodes for the development of next-generation flexible energy storage devices.

Industrial Silicon-Wafer-Wastage-Derived Carbon-Enfolded Si/Si-C/C Nanocomposite Anode Material through Plasma-Assisted Discharge Process for Rechargeable Li-Ion Storage.

Silicon is a promising anode material for high-performance Li-ion batteries as a result of its high theoretical specific capacity and elemental abundance. Currently, the commercial application of the Si-based anode is still restricted by its large volume changes during the lithiation cycles and low electrical conductivity. To address these issues, we demonstrate a facile plasma-assisted discharge process to anchor nano-sized Si particles into methanol with quick quenching. After the subsequent sintering process, we obtained a Si/SiC/C composite (M-Si). The unique structure not only allowed for the electrolyte infiltration to enhance lithium ion diffusion during charge and discharge process, but also buffered the volume expansion of silicon particles to enhance the rate capability and cycle stability. The M-Si cell electrochemical results exposed good Li-ion storage performance compared to that of the bare Si used cell (B-Si). The electrode cell consisting of M-Si exhibited remarkable enhanced cyclic stability and sustained the reversible specific capacity of 563 mAhg−1 after 100 cycles, with a coulombic efficiency of 99% at a current density of 0.1C, which is higher than that of the B-Si electrode cell that was used. Hence, the as-prepared Si/SiC/C composite is an efficient anode material for Li-ion battery applications. Moreover, these results indicate that the novel plasma-assisted discharge technique will bring a potential durable methodology to produce novel high-performance electrode materials for future advanced large-scale energy-storage applications.

Crosslinked poly(acrylic acid) enhances adhesion and electrochemical performance of Si anodes in Li-ion batteries

Water-soluble binders such as poly (acrylic acid) (PAA) possess many advantages in the slurry and electrode preparation due to their low-cost and environmental friendliness. However, due to the linear nature of these binders, they are susceptible to slide under the continuous volume variation of Si-containing anodes during cycling. Therefore, a three-dimensional (3D) interconnected polymeric network is required to provide robust mechanical adhesion with the Si particles to maintain the electrode integrity for excellent cycle stability. Here, pentaerythritol (PER) is used as a crosslinking agent to connect the linear PAA binder to enhance its adhesion strength for Si anodes, which is systematically confirmed using Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric (TG) measurements. Si electrodes with crosslinked PAA-PER binder show enhanced adhesion and elasticity, exhibiting a more robust electrode integrity than purely PAA-based Si electrodes. Galvanostatic cycling shows that Si-PAA-5%PER electrodes maintain a higher discharge capacity of 514.3 mAh g-1 (after 10 cycles) for micro-sized and 1502.1 mAh g-1 (after 105 cycles) for nano-sized Si particles compared to 257.6 mAh g-1 and 1413.9 mAh g-1 for micro- and nano-sized Si in Si-PAA electrodes, respectively. XPS analyses on cycled electrodes confirmed that crosslinked PAA-PER binder has no negative effects on the SEI formation and its functionality in Si electrodes. SEM cross-sections reveal that Si-PAA-5%PER electrodes show reduced electrode thickness variation (micro-/nano-: 114.2%/182.2%) than that of Si-PAA electrodes (micro-/nano-: 134.1%/212.0%) after cycling, which indicates that crosslinked PAA-PER binder can enhance the electrode integrity due to its 3D interconnected network. This work provides meaningful insight into the exploration of novel binders and their impact on the SEI formation and functionality, especially for high-capacity alloy-type anode materials.

Advantages of using carbon fabric over Cu foil as conductive matrix for anodes of micro- and nano-sized Si

The electrochemical performances of Si anodes with carbon fabric (CF) and Cu foil as current collectors are compared. Scanning electron microscopy analysis shows that after repeated charge/discharge, the Si anode with CF is stable and does not fracture like the conventional one with Cu foil. Cyclic voltammetry analysis further reveals that the reaction of CF with Li+ is more prominent in the electrochemical reaction of anodes fabricated with micro-sized Si particles, compared to those with nano-sized Si particles. Most importantly, replacing the conventional Cu foil with CF in the Si anode results in remarkably reduced resistance and improved cell cyclability.

Evolution of microscopic strains, stresses, and dislocation density during in-situ tensile loading of additively manufactured AlSi10Mg alloy

The AlSi10Mg alloy produced by laser powder bed fusion (LPBF) possesses a novel microstructure and higher mechanical properties compared with its casting counterpart. So far, the crystallographic orientation-dependent lattice strains, average phase stresses, and dislocation density during the tensile loading of the LPBF AlSi10Mg are not well understood. This fact is impeding further optimization of microstructure and mechanical properties. High energy synchrotron X-ray diffraction providing deep penetration capability and phase-specific measurements of various bulk properties of crystal materials is applied to investigate the LPBF AlSi10Mg under loading. The crystallographic orientation-dependent lattice strains and elastoplastic properties of the Al matrix are assessed. The average phase stresses are calculated to quantify load partitioning between the Al and Si phases. The nano-sized Si particles that bear high-stress are efficient strengthening particles. The maximum value of the average phase stress of Si reaches up to ~2 GPa. Based on the modified Williamson-Hall and the modified Warren-Averbach methods, the dislocation density and its evolution during the plastic deformation are determined. A multistage strain hardening behavior is detected in the Al matrix, which is associated with the interactions between the dislocations and the cell boundary network.

Rapid homogeneous precipitation of nano-sized Si in Al–1%Si alloy by electric pulses

Rapid and homogeneous precipitation of nano-sized Si particles with high density was achieved in Al–1%Si alloy by electric pulses treatment (EPT) in a liquid nitrogen bath (∼77 K). In contrast, when processed by EPT in air or by high-temperature (527–720 K) salt bath treatment, the precipitate density decreases dramatically. The homogeneous precipitation of Si could be facilitated by both the low-temperature environment and the non-thermal effects of EPT. The low-temperature environment provides a high driving force for nucleation, and retains the quenched-in vacancies serving as potential nucleation sites. The non-thermal effects of EPT can significantly promote local migration of solutes and vacancies at such low temperatures.

Si-on-Graphite fabricated by fluidized bed process for high-capacity anodes of Li-ion batteries

Composites consisting of graphite and silicon have been considered as potential high-capacity anode materials for the next-generation Li-ion batteries (LIBs). The synthesis method is critical for determining the microstructure, which is directly related to the material performance and the cost-efficiency for making commercial electrode materials. Herein, we report the fabrication of silicon-on-graphite (Si@Gr) composites by fluidized bed granulation (FBG) for the first time. The FBG process is shown to produce composite powders comprising a uniform layer of nano-sized Si particles lodged onto the surface of micron-sized graphite particles to possess a core-shell microstructure. Adopting a suitable binder during the FBG process enables a firm adhesion of the Si nanoparticles on graphite surface during subsequent carbon-coating, where the composite particles are coated with pitch and then carbonised to form a highly electronically conductive and mechanical stabilizing layer of amorphous carbon. These carbon-coated composites exhibit a high capacity reaching over 600 mAh g−1, high rate capability and illustrates the potential of long-cycle stability in Si@Gr || Li metal cells, showing more than 70% capacity retention after 400 charge-discharge cycles even without electrolyte optimization. Furthermore, a significantly improved cycling stability is found for the carbon-coated Si@Gr materials in LiNi0.6Co0.2Mn0.2O2 (NCM-622) || Si@Gr full-cells.

Effect of HIP process and subsequent heat treatment on microstructure and mechanical properties of direct metal laser sintered AlSi10Mg alloy

PurposeThe purpose of this paper is to evaluate the effect of post process combinations, e.g. hot isostatic pressing (HIP) only, HIP + T6 heat treatments, and T6 only, with different aging time, on surface properties, microstructure and mechanical properties of stress-relieved AlSi10Mg parts produced by direct laser metal sintering.Design/methodology/approachHIP process and HIP + T6 heat treatments were applied to as stress-relieved direct laser metal sintered (DMLS) AlSi10Mg parts. Aging times of 4 and 12 h are selected to examine the optimum duration. To analyze the advantages of HIP process, a T6 heat treatment with 4 h of aging was also applied. Densities, open porosities and roughness values of as stress-relieved, HIPed, HIP + T6, and T6-only samples were measured. The samples were characterized by OM and SEM together with EDX analysis. An image analysis study was made to evaluate the inner pore structure, thereby to understand the mechanical behavior.FindingsHIP process does not cause a significant change in surface porosity; yet it has a positive influence on inner porosity. HIP process results in a microstructure of the aluminum matrix surrounded by a network of micron and nano size Si particles. Additional heat treatment results in larger particles and precipitation. After HIPing, ductility increases but strength decreases. Samples aged 4 h present improved yield and tensile strength but decreased elongation, yet samples aged for 12 h reach a combination of optimum strength and ductility. The lower level of tensile strength and ductility in T6-only condition indicates that HIP process plays a crucial role in elimination of the porosity thus improves the effectiveness of subsequent heat treatment.Originality/valueThe study investigates the effect of post-process conditions and optimizes the aging time of the T6 heat treatment after HIP process in order to obtain improved mechanical properties. The stress-relieved state was chosen as the reference to prevent distortion during HIPing or heat treatment.

Oral Administration of Si-Based Agent Attenuates Oxidative Stress and Ischemia-Reperfusion Injury in a Rat Model: A Novel Hydrogen Administration Method.

Organ ischemia-reperfusion injury (IRI), which is unavoidable in kidney transplantation, induces the formation of reactive oxygen species and causes organ damage. Although the efficacy of molecular hydrogen (H2) in IRI has been reported, oral intake of H2-rich water and inhalation of H2 gas are still not widely used in clinical settings because of the lack of efficiency and difficulty in handling. We successfully generated large quantities of H2 molecules by crushing silicon (Si) to nano-sized Si particles (nano-Si) which were allowed to react with water. The nano-Si or relatively large-sized Si particles (large-Si) were orally administered to rats with renal IRI. Animals were divided into four groups: sham, IRI, IRI + nano-Si, and IRI + large-Si. The levels of serum creatinine and urine protein were significantly decreased 72 h following IRI in rats that were administered nano-Si. The levels of oxidative stress marker, urinary 8-hydroxydeoxyguanosine were also significantly decreased with the nano-Si treatment. Transcriptome and gene ontology enrichment analyses showed that the oral nano-Si intake downregulated the biological processes related to oxidative stress, such as immune response, cytokine production, and extrinsic apoptotic signaling pathway. Alterations in the regulation of a subset of genes in the altered pathways were validated by quantitative polymerase chain reaction. Furthermore, immunohistochemical analysis demonstrated that the nano-Si treatment alleviated interstitial macrophage infiltration and tubular apoptosis, implicating the anti-inflammatory and anti-apoptotic effects of nano-Si. In conclusion, renal IRI was attenuated by the oral administration of nano-Si, which should be considered as a novel H2 administration method.

Nanosized Si particles with rich surface organic functional groups as high-performance Li-battery anodes

Nanostructured Si is a very promising anode material for lithium-ion batteries as Si possesses a theoretical specific capacity almost ten times higher than that of the conventional graphite anodes. However, difficulties associated with a low-cost and scalable production and unstable electrode/electrolyte interface of nanostructured Si limit their practical application. Herein, an improved route is developed for preparation of crystalline Si nanoparticles by directly reacting metallurgical-grade Si with ethanol catalyzed by Cu-based catalysts at 200 °C to generate alkoxysilane and Si nanostructures and the latter were ball-milled to obtain the desired Si nanoparticles. The particle size of the crystalline Si nanoparticles could be well tuned by adjusting the reaction time and the amount of ethanol. Furthermore, the surfaces of obtained Si nanoparticles were in situ modified by organic functional groups (R–CH2-OH, R–COOH, etc.), confirmed by FTIR and 1H solid-state NMR, which reacted with lithium in the 1st lithiation to form a stable artificial solid electrolyte interphase layer. As tested, the pristine Si nanoparticles exhibited both high reversible capacity and good cycle life even close to that of the carbon-coated Si nanoparticles. Ultimately, this route is cost-effective for scalable manufacture of Si nanoparticles with in situ functionalized surface that can facilitate formation of stable solid electrolyte interphase layer.

Facile synthesis of Si@void@C nanocomposites from low-cost microsized Si as anode materials for lithium-ion batteries

High-capacity anodes, such as Si, are much more attractive than graphite for next generation lithium-ion batteries (LIBs) due to their high theoretical storage capacity. However, successful practical applications of Si anodes in high energy density LIBs are hindered by the huge volume change during cycling, which causes the active material pulverization and unstable solid electrolyte interphase films. In this study, we successfully synthesized Si@void@C nanocomposites from commercial low-cost microsized Si via a combination of facile high-energy mechanical milling, resorcinol-formaldehyde resin coating and sodium hydroxide etching. The as-prepared Si@void@C consists of nanosized Si particles fully embedded into mesoporous carbon shells with abundant voids. The Si@void@C anodes exhibit a high reversible capacity of 1088 mAh g−1 over 300 cycles at a rate of 500 mA g−1. Even at a much higher current density of 8 A g−1, the Si@void@C anodes can still deliver a high reversible capacity of 714 mAh g−1. These outstanding performances are assigned to the nanosized Si that is able to alleviate mechanical strain, and the buffering effect of mesoporous carbon shells as well as abundant voids for Si volume expansion. The synthesis process is simple, scalable, and cost-effective, providing a promising alternative way to large-scale production of inexpensive high-performance silicon-based materials for next-generation LIBs.